HomeMy WebLinkAbout028-09 - Ordinance - Amending Chapter 15.32 Stormwater ManagementIntroduced by: City Engineer
Requested by: City Engineer
Drafted by: City Engineer
Introduced: November 24, 2009
First Reading: November 24, 2009
Adopted: December 8, 2009
ORDINANCE NO. 028-o9
AN ORDINANCE OF THE CITY OF PORT ORCHARD,
WASHINGTON, AMENDING PORT ORCHARD MUNICIPAL
CODE CHAPTER 15.32 REGARDING "STORMWATER
MANAGEMENT"
WHEREAS, the City of Port Orchard has adopted regulations regarding stormwater
management as set forth in Port Orchard Municipal -Code Chapter 15:32; and --
WHEREAS, it is necessary to update and amend Chapter 15.32 in order to comply
with the current National Pollution Discharge Elimination System (NPDES) Permit for
discharges from small municipal separate storm sewers in Western Washington; now,
therefore,
THE CITY COUNCIL OF THE CITY OF PORT ORCHARD, WASHINGTON,
DO ORDAIN AS FOLLOWS:
SECTION 1: Port Orchard Municipal Code Section 15.32 is AMENDED as follows:
Chapter 15.32 STORMWATER MANAGEMENT
Sections:
15.32.010
General provisions.
15.32.020
Definitions.
15.32.030
Permits.
15.32.040
Covenants, sureties, and liability insurance.
15.32.050
Erosion and sediment control.
15.32.o6o
Grading.
15.32.o65
Minimum Site Development Requirements
15.32.070
Stormwater management.
15.32.080
Operation and maintenance.
15.32.090
Critical drainage areas.
15.32.100
Water quality.
15-32.110
Enforcement.
SECTION 2. Port Orchard Municipal Code Section 15.32.010 is AMENDED
as follows:
15.32.oio General provisions.
2.
3•
M
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Declaration of Title. This chapter shall be known as the "Stormwater
Management Ordinance."
Stormwater Management Standards and Specifications. The Port Orchard
city council recognizes that stormwater control technology is a developing
and evolving science. In order to ensure that the latest and best technology is
utilized in Port Orchard, Exhibit "A," attached to the ordinance codified in
this chapter and incorporated herein by this reference, is hereby adopted as
the "Port Orchard stormwater design manual." All references to this chapter
shall include the Port Orchard stormwater design manual. The director may
amend the Port Orchard stormwater design manual, with the approval of the
Port -Orchard -city council, as necessary to reflect changing conditions and
technology. All requirements contained in the Port Orchard stormwater
design manual, together with any amendments thereto, must be complied
with as provided in subsection (6) of this section, Applicability.
Technical Deviations. The director may grant technical deviations from
requirements contained in the Port Orchard stormwater design manual;
provided, that all of the following criteria are met:
a. The technical deviation will not otherwise result in noncompliance pith
this chapter.
b. The granting of the technical deviation will not result in noncompliance
with the development conditions imposed upon the project by the city
council.
c. The granting of the technical deviation will produce a compensating or
comparable result that is in the public interest.
d. The granting of the technical deviation will meet the objectives of safety,
function, appearance, environmental protection, and maintainability
based on sound engineering judgment.
Variances. The city council may, at a public hearing, grant a variance from the
provisions of this chapter; provided, that all of the following criteria are met:
a. The granting of the variance will produce a compensating or comparable
result that is in the public interest.
b. The granting of the variance will meet the objectives of safety, function,
appearance, environmental protection, and maintainability based on
sound engineering judgment.
Water Quality. For circumstances or conditions related to water quality which
are not specifically addressed within the scope of this chapter, the most
current edition of the Washington State Department of Ecology publication
"Stormwater Management Manual for Western Washington" is hereby
adopted as the preferred reference for the design and implementation of
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stormwater management practices.
6. Applicability. The provisions of this chapter shall apply to all site
development activities requiring land use permits and approvals as defined in
POMC 15.32.02o, both public and private, within the bounds of incorporated
Port Orchard. The provisions of POMC 15.32.o8o, Operation and
maintenance, shall also apply to existing stormwater facilities in incorporated
Port Orchard. The provisions of POMC 15.32.100, Water quality, shall apply
to all situations and circumstances throughout incorporated Port Orchard.
7. Applicability of Other Ordinances. Any land development which is required
by operation of any city of Port Orchard ordinance, state law, or federal law to
construct, install, or modify any natural or manmade drainage features
within, abutting, or serving the development shall do so in accordance with
this chapter. However, where the provisions of this chapter directly conflict
comprehensive drainage plan, the more stringent provisions shall apply to the
extent permissible by law.
8. Administration. The director shall administer this chapter. The director shall
have the authority to develop and implement procedures to administer and
enforce this chapter.
9. Appeals. An aggrieved party may appeal any administrative interpretation or
departmental ruling related to this chapter to the Port Orchard hearing
examiner.
SECTIONS. Port Orchard Municipal Code Section 15.32.020 is AMENDED as
follows:
15.32.02o Definitions.
The following definitions of terms shall apply to this chapter:
1. "Accepted performance of construction" shall mean the written
acknowledgment from the director of the satisfactory completion of all work
accepted by the city, including all work shown on the accepted plans, accepted
revisions to the plans, and accepted field changes.
2. "Applicant' shall mean the person, party, firm, corporation, or other legal
entity that proposes to engage in site development activities in incorporated
Port Orchard by submitting an application for any of the activities covered by
this chapter on a form furnished by the city and paying the required
application fees.
3. "Arterial' shall mean a road or street primarily for through traffic. A major
arterial connects an Interstate Highway to cities and counties. A minor
arterial connects major arterials to collectors. A collector connects an arterial
to a neighborhood. A collector is not an arterial. A local access road connects
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individual homes to a collector.
4. "Basin plan" shall mean a plan and all implementing regulations and
procedures including, but not limited to, land use management adopted by
ordinance for managing stormwater quality and quantity management
facilities and drainage features within individual sub -basins.
5. "Best management practices (BMPs)" shall mean the schedule of activities,
prohibitions of practices, maintenance procedures, and structural and/or
managerial practices, that when used singly or in combination, prevent or
reduce the release of pollutants and other adverse impacts to waters of
Washington and have been approved by the city as accepted BMPs.
6. "Biofiltration/biofilter facilities" shall mean vegetative BMPs that treat
stormwater by filtration through vegetation. Biofiltration facilities include,
but are not limited to, grassed or vegetated swales and filter strips.
-7. "Bond"shall mean a financial guarantee, in the form of a surety bond,
assignment of funds, or irrevocable bank letter of credit, thatshall guarantee
compliance with applicable provisions of this chapter.
8. "Certified Erosion and Sediment Control Lead (CESCL)" shall mean an
individual who has current certification through an approved erosion and
sediment control training program that meets the minimum training
standards established by the Department of Ecology (see BMP C16o in the
Stormwater Management Manual for Western Washington (2005)). A
CESCL is knowledgeable in the principals and practices of erosion and
sediment control. The CESCL must have the skills to assess site conditions
and construction activities that could impact the quality of storm water and,
the effectiveness of erosion and sediment control measures used to control
the quality of storm water discharges. Certification is obtained through an
Ecology approved erosion and sediment control course. Course listing are
provided online at Ecology's web site.
9. "City" shall mean the city of Port orchard, Washington, or as indicated by the
context, the Public Works Director, or other authorized representative of the
governmental authority of the City of Port orchard.
ro. "Civil engineer" shall mean a professional engineer currently registered in the
state of Washington to practice in the field of civil engineering.
u. "Clearing" or "land clearing" shall mean the surface removal of vegetation.
12. "Closed depressions" shall mean low-lying areas that have no surface outlet,
or such a limited surface outlet that in most storm events the area acts as a
retention basin, holding water for infiltration, evaporation, or transpiration.
13. "Comprehensive drainage plan" shall mean a detailed analysis, adoptedby the
city, for a drainage basin which assesses the capabilities and needs for runoff
accommodation due to various combinations of development, land use,
structural and nonstructural management alternatives. The plan
recommends the form, location and extent of stormwater quantity and
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quality control measures that would satisfy legal constraints, water quality
standards, and community standards, and identifies the institutional and
funding requirements for plan implementation.
14. "Contiguous land" shall mean land adjoining and touching other land
regardless of whether or not portions of the parcels have separate assessor's
tax numbers or were purchased at different times, lie in different sections, are
in different government lots, or are separated from each other by private road
or private rights -of -way.
15. "Critical drainage area" shall refer to those areas designated in POMC
15.32.090, Critical drainage areas, which have a high potential for stormwater
quantity or quality problems.
16. "Design storm event" shall mean a theoretical storm event, of a given
frequency, interval, and duration, used in the analysis and design of a
17. "Detention facilities" shall mean stormwater facilities designed to store runoff
while gradually releasing it at a predetermined controlled rate. "Detention
facilities" shall include all appurtenances associated with their designed
function, maintenance, and security.
18. "Developed site" shall mean the condition of the development site following
completion of construction of the development including all approved phases
of construction.
i9. "Director" shall mean the Public Works Director or designee(s).
20."Diversion" shall mean the routing of stormwater to other than its natural
discharge location.
21. "Drainage feature" shall mean any natural or manmade structure, facility,
conveyance, or topographic feature which has the potential to concentrate,
convey, detain, retain, infiltrate, or affect the flow rate of stormwater runoff.
22. "Drainage plan" shall mean a plan for the collection, transport, treatment,
and discharge of runoff, and may include both the plan and profile views of
the site as well as construction details and notes.
23. "Easement" shall mean an acquired privilege or right of use or enjoyment that
a person, party, firm, corporation, municipality, or other legal entity has in
the land of another.
24. "Effective Impervious Surface" shall mean impervious surfaces that are
connected via sheet flow or discrete conveyance to a drainage system.
Impervious surfaces on residential development sites are considered
ineffective if the runoff is dispersed through at least one hundred feet of
native vegetation in accordance with BMP T5.30 - "Full Dispersion," as
described in Chapter 5 of Volume V of the StornrwaterManagementManual
for Western Washington (2005).
25. "Erosion control design storm" shall mean the six-month frequency, 24-hour
duration storm event used for analysis and design of sedimentation and
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erosion control facilities.
26. `Existing stormwater facilities" shall mean those facilities constructed or
under permitted construction prior to the effective date of the ordinance
codified in this chapter.
27. "Forested land" shall mean "forested land" as defined in RCW 76.o9.02o, and
shall include all land which is capable of supporting a merchantable stand of
timber and is not being actively used in a manner incompatible with timber
growing.
28."Geotechnical engineer" shall mean a practicing professional engineer
licensed in the state of Washington who has at least four years of professional
experience in geotechnical and landslide evaluation.
29. "Geotechnical report" shall mean a study of the effects of drainage and
drainage facilities on soil characteristics, geology and ground water. The
30."Grading" shall mean any excavating, filling, or embanking of earth materials.
31. "Grubbing" shall mean the removal of vegetative matter from underground,
such as sod, stumps, roots, buried logs, or other debris, and shall include the
incidental removal of topsoil to a depth not exceeding 12 inches.
32. "Highway" shall mean a public road.
33•"Hydrograph" shall mean a graph of runoff rate, inflow rate, or discharge
rate, past a specific point over time.
34• "Hydrograph method" shall mean a method of estimating a hydrograph using
a mathematical simulation. Commonly accepted hydrograph methods include
the Soil Conservation Service TR-55 Method and the Santa Barbara Urban
Hydrograph Method.
35• Illicit connection means (1) any drain or conveyance, whether on the
surface or subsurface, which allows an illicit discharge to enter the storm
drain system including, but not limited to, any conveyances which allow any
non -storm water discharge including sewage, process wastewater, and wash
water to enter the storm drain system and any connections to the storm drain
system from indoor drains and sinks, regardless of whether said drain or
connection had been previously allowed, permitted, or approved by the City;
or (2) any drain or conveyance connected from a residential, commercial or
industrial land use to the storm drain system which has not been documented
in plans, maps, or equivalent records and approved by the City.
36. "Illicit discharge" shall mean any discharge to a municipal separate storm
sewer or to surface or ground water that is not composed entirely of storm
water, expect discharges pursuant to an NPDES permit (other than the
NPDES permit for discharges from the municipal separate storm sewer),
discharges resulting from fire fighting activities, and those discharges
expressly allowed conditionally by Port Orchard Municipal Code 15.30 Illicit
Discharge Detection and Elimination.
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37. "Impervious surface" shall mean a hard surface area that either (a) prevents
or retards the entry of water into the soil mantle as under natural conditions
prior to development or (b) causes water to run off the surface in greater
quantities or at an increased rate of flow from the flow present under natural
conditions prior to development. Common impervious surfaces include, but
are not limited to, roof tops, walkways, patios, driveways, parking lots, or
storage areas, concrete or asphalt paving, gravel roads, packed earthen
materials, and oiled, macadam or other surfaces which similarly impede the
natural infiltration of stormwater. Open, uncovered retention/detention
facilities shall not be considered as impervious surfaces for the purposes of
determining whether the thresholds for application of minimum
requirements are exceeded. Open, uncovered retention/detention facilities
shall be considered impervious surfaces for purposes of runoff modeling.
38Land distur-bingactivity"shall -mean _ any-acthdtythat results in movement of
earth, or a change in the existing soil cover (both vegetative and
nonvegetative) and/or the existing soil topography. Land disturbing activities
include, but are not limited to, demolition, construction, paving, clearing,
grading, filling, excavation and grubbing. Compaction that is associated with
stabilization of structures and road construction shall also be considered a
land disturbing activity. Vegetation maintenance practices are not considered
land -disturbing activity.
39 • "Land use permits and approvals" shall mean any use or development of land
that requires city action in legislation, administration, or approval.
40."Maintenance" shall mean any activity that is necessary to keep currently
serviceable stormwater structures, facilities, and equipment in good working
order so as to function as designed without expansion or use beyond that
previously existing and results in no significant adverse hydrologic impact.
Maintenance shall include activities taken to prevent decline, lapse or
cessation in use of the systems or structures, including complete
reconstruction of a dysfunctional stormwater facility, including cases where
environmental permits require replacing an existing structure with a different
type structure, as long as the functioning characteristics of the original
structure are not changed. Maintenance shall also include the correction of
any problem on the site property that may directly impair the functions of the
stormwater facilities.
41. "Maintenance covenant' shall mean a binding agreement between the city of
Port Orchard and the person or persons holding title to a property served by a
stormwater facility whereby the property owner promises to maintain certain
stormwater facilities, grants the city the right to enter the subject property to
inspect and to make certain repairs or perform certain maintenance
procedures on the stormwater control facilities when such repairs or
maintenance have not been performed by the properly owner, and promises
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to reimburse the city for the cost should the city perform such repairs or
maintenance.
42. "Maintenance schedule" shall mean a document detailing required
stormwater facility maintenance activities to be performed at specified
intervals.
43 • "Major development" shall mean any new development or any redevelopment
activity that (a) includes the creation or cumulative addition of 5,000 square
feet or greater of impervious surface area from the predevelopment
conditions, or (b) includes land disturbing activity of one acre or greater, or
(c) includes grading involving the movement of 5,000 cubic yards or more of
material.
44• "Manual" shall mean Exhibit "A" of the ordinance codified in this chapter
entitled the "Port Orchard stormwater design manual."
-"Minor development" shall mean any new development or redevelopment
}
activity that (a) includes the creation or addition o less than 5,0s
feet of new impervious surface area, and (b) includes land disturbing activity
of less than one acre, and (c) includes grading involving the movement of less
than 5,000 cubic yards of material.
46. "Municipal separate storm sewer system (MS4)" means a conveyance or
system of conveyances which is intended to convey only storm water
(including roads with drainage systems, municipal streets, catch basins,
curbs, gutters, ditches, man-made channels, or storm drains) and which are:
(r) owned or operated by the city of Port Orchard; (2) designed or used for
collecting or conveying stormwater; (3) are not part of a Publicly Owned
Treatment Works (any device or system used in treatment of municipal
sewage or industrial wastes of a liquid nature which is publicly owned); and
(4) are not a combined sewer (a system that collects sanitary sewage and
stormwater in a single sewer system).
47. "Native Vegetation" shall mean vegetation comprised of plant species, other
than noxious weeds, that are indigenous to the coastal region of the Pacific
Northwest and which reasonably could have been expected to naturally occur
on the site. Examples include trees such as Douglas Fir, western hemlock,
western red cedar, alder, big -leaf maple, and vine maple; shrubs such as
willow, elderberry, salmonberry, and salal; and herbaceous plants such as
sword fern, foam flower, and fireweed.
48."National Pollutant Discharge Elimination System (NPDES) Permit" shall
mean a permit issued by the Environmental Protection Agency (EPA) or by
the Washington State Department of Ecology that authorizes the discharge of
pollutants to waters of the United States from point sources, whether the
permit is applicable to an individual, group, or general area -wide basis.
49 • "New Development" shall mean land disturbing activities, including Class IV
— general forest practices that are conversions from timber land to other uses;
Ordinance No.28-09
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structural development, including construction or installation of a building or
other structure; creation of impervious surfaces; and subdivision, short
subdivision and binding site plans, as defined and applied in Chapter 58.17
RCW. Projects meeting the definition of redevelopment shall not be
considered new development.
50. "Nonforestry use" shall mean an active use of land that is incompatible with
timber growing.
51. "Off -site drainage analysis" shall mean a study of those land areas
contributing surface runoff to a development site as well as a study of the
existing and predicted impacts of surface runoff from the development site on
properties and drainage features that have the potential to receive stormwater
from the development site.
52. "Oil/water separator" shall mean a structure or device used to remove
suspended -oil -and-greasy -solids-from water.
53 • "Operation and maintenance manual" shall mean a written manual, prepared
by a qualified civil engineer, which provides a description of operation and
maintenance procedures for specific stormwater control facilities, for use by
operation and maintenance personnel.
54• "Operator" shall mean any party associated with a construction project that
meets either of the following two criteria:
a. The party has operational control over construction plans and
specifications, including the ability to make modifications to those
plans and specifications; or
b. The party has day-to-day operational control of those activities at a
project which are necessary to ensure compliance with a SWPPP for
the site or other permit conditions (e.g. they are authorized to direct
workers at a site to carry out activities required by the SWPPP or
comply with other permit conditions).
55• "Owner" shall mean any person or persons having a legal or equitable
property right or interest, whether or not said right is legal or equitable in
character, including a fee owner, contract purchaser or seller, mortgagor or
mortgagee, optionor or optionee, and beneficiary or grantor of a trust or deed
of trust.
56. "Pollution" shall mean contamination or other alteration of the physical,
chemical, or biological properties, of any waters of the City, State, or United
States, including change in temperature, taste, color, turbidity, or odor of the
waters, or such discharge of any liquid, gaseous, solid, radioactive or other
substance into any waters as will or is likely to create a nuisance or render
such waters harmful, or is otherwise detrimental or injurious to the public
health, safety, or welfare, or to domestic, commercial, industrial, agricultural,
recreational, or other legitimate beneficial uses, or to livestock, wild animals,
birds, fish, or other aquatic life.
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57. "Pollution -generating impervious surface (PGIS)" shall mean those
impervious surfaces considered to be a significant source of pollutants in
storm water runoff. Such surfaces include those which are subject to:
vehicular use; industrial activites; or storage of erodible or leachable
materials, wastes, or chemicals, and which receive direct rainfall or the run-
on or blow-in of rainfall. Erodible or leachable materials, wastes, or
chemicals are those substances which, when exposed to rainfall, measurably
alter the physical or chemical characteristics of the rainfall runoff. Examples
include erodible soils that are stockpiled, uncovered processed wastes,
manure, fertilizers, oily substances, ashes, kiln dust, and garbage dumpster
leakage. Metal roofs are also considered to be PGIS unless they are coated
with an inert, non -leachable material (i.e. baked -on enamel coating). Roofs
that are subject to venting of indoor pollutants from manufacturing,
commercia�or—otheroperation&-or-process-are—also--considered-Pf-,IS A
surface, whether paved or not, shall be considered PGIS if it is regularly used
by motor vehicles. The following are considered regularly -used surfaces:
roads, unvegetated road shoulders, bike lanes within the traveled lane of a
roadway, driveways, parking lots, unfenced fire lanes, vehicular equipment
storage yards, and airport runways. The following are not considered
regularly -used surfaces: paved bicycle pathways, separated from and not
subject to drainage form roads for motor vehicles, fenced fire lanes, and
infrequently used maintenance access roads.
58. "Pollution -generating pervious surface (PGPS)" shall mean any impervious
surface subject to use of pesticides and fertilizers or loss of soil. Typical PGPS
include lawns, landscaped areas, golf courses, parks, cemeteries, and sports
fields.
59. "Pre -development conditions" shall mean site conditions as they existed prior
to any manmade alterations. Pre -developed condition shall be assumed to be
forested land cover unless reasonable, historic information is provided that
indicates the site was prairie prior to settlement..
6o."Professional engineer" shall mean a person who, by reason of his or her
special knowledge of the mathematical and physical sciences and the
principles and methods of engineering analysis and design, acquired by
professional education and practical experience, is qualified to practice
engineering as attested by his or her legal registration as a professional
engineer in the state of Washington.
61. "Project engineer" shall mean the professional engineer responsible for the
design of the project, who will affix his/her seal on the project drainage plans
and drainage analysis. The project engineer shall be licensed in the state of
Washington and qualified by experience or examination.
62. "Receiving waters" shall mean bodies of water or surface water systems to
which surface runoff is discharged via a point source of storm water or via
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sheet flow.
63. "Redevelopment" shall mean any land disturbing activity occurring on
existing substantially developed property (i.e. has 35% or more of existing
impervious surface coverage), the creation or addition of impervious surfaces;
the expansion of a building footprint or addition or replacement of a
structure; structural development including construction, installation or
expansion of a building or other structure; replacement of impervious surface
that is not part of a routine maintenance activity; and land disturbing
activities.
64. "Retention facilities" shall mean drainage facilities designed to store runoff
for gradual release by evaporation, plant transpiration, or infiltration into the
soil. Retention facilities shall include all such drainage facilities designed so
that none of the runoff entering the facility will be discharged as surface
tide "'z�zizpp'ee&-assee'
their designed function, maintenance, and security.
65. "SEPA" shall mean the Washington State Environmental Policy Act.
66. "Shorelines of the state" shall mean the total of all "shorelines" and
"shorelines of state-wide significance" within the state, as defined in RCW
90.58.03o, also known as the Shoreline Management Act.
67. "Site" shall mean the area defined by the legal boundaries of a parcel or
parcels of land that is (are) subject to new development or redevelopment.
For road projects, the length of the project site and the right-of-way
boundaries define the site.
68."Site development activity" shall mean the alteration of topography, clearing,
paving, grading, construction, alteration of stormwater systems, site
preparation, or other activity commonly associated with site development.
69. "Soils investigation report" shall mean a study of soils on a subject property
with the primary purpose of characterizing and describing the soils. The soils
investigation report shall be prepared by a qualified soils engineer, who shall
be directly involved in the soil characterization either by performing the
investigation or by directly supervising employees.
70. "Soils engineer" shall mean a practicing civil engineer licensed as a
professional civil engineer in the state of Washington who has at least four
years of professional employment as a civil engineer dealing with soil
descriptions and characterizations.
71. "Source control BMP" shall mean a best management practice (BMP), either a
structure or operation that is intended to prevent pollutants from coming into
contact with stormwater through physical separation of areas or careful
management of activities that are sources of pollutants. Struchural Source
Control BMP's are physical, structural, or mechanical devices, or facilities
that are intended to prevent pollutants from entering storm water.
Operational BMP's are non-structural practices that prevent or reduce
ordinance No.28-o9
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pollutants from entering storm water.
72. "Stormwater" or "Storm Water" shall mean the surface flow, runoff, and
drainage consisting entirely of water from any form of natural precipitation,
including snowmelt, during and following precipitation, and resulting from
such precipitation that meets the non -pollutant requirements.
73. "Stormwater facility" shall mean a component of a manmade drainage
feature, or features, designed or constructed to perform a particular function
or multiple functions, including, but not limited to, pipes, swales, ditches,
culverts, street gutters, detention basins, retention basins, wetponds,
constructed wetlands, infiltration devices, catch basins, oil/water separators,
and sediment basins. Stormwater facilities shall not include building gutters,
downspouts, and drains serving one single-family residence.
74. "Stormwater Pollution Prevention Plan (SWPPP)" shall mean a documented
plan to implement measures to identify, prevent and control the
contamination of point source discharges of stormwater.
75. "Stormwater quality control' shall mean the control of the introduction of
pollutants into stormwater and the process of separating pollutants from
stormwater. Stormwater quality control facilities include, but are not limited
to, source controls, biofiltration/biofilter facilities, wet ponds, wetland
forebays, oil/water separators, constructed wetlands and erosion and
sedimentation control facilities.
76. "Stormwater quantity control' shall mean the control of the rate and/or
volume of stormwater released from a development site. Stormwater quantity
control facilities include, but are not limited to, detention and retention
facilities.
77. "Technical deviation" shall mean permission granted by the director to
deviate from the provisions of the ordinance.
78. "Threshold discharge area" shall mean an on -site area draining to a single
natural discharge location or multiple natural discharge locations that
combine within one -quarter mile downstream (as determined by the shortest
flowpath).
79. "Variance" shall mean permission granted by the city council to deviate from
the provisions of this chapter.
80."Waters of the State" shall include those waters as defined as "waters of the
United States" in 40CFR Subpart 122.2 within the geographic boundaries of
Washington State and "waters of the state" as defined in Chapter 90.48 RCW
which include lakes, rivers, ponds, streams, inland waters, underground
waters, salt waters and all other surface waters and watercourses within the
jurisdiction of the State of Washington.
81. "Water quality design storm event" shall mean a design storm event selected
by the director for the purpose of establishing design performance criteria for
water quality BMPs. Under most conditions, the term applies to the runoff
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rate and volume resulting from 64 percent of the precipitation of the two-year
frequency, 24-hour duration storm event.
82. "Wetland" shall mean those areas that are inundated or saturated by surface
or ground water at a frequency and duration sufficient to support, and that
under normal circumstances do support, a prevalence of vegetation typically
adapted for life in saturated soil conditions. Wetlands generally include
swamps, marshes, bogs, and similar areas. Wetlands do not include those
artificial wetlands intentionally created from non -wetland sites, including,
but not limited to, irrigation and drainage ditches, grass -lined swales, canals,
detention facilities, wastewater treatment facilities, farm ponds, and
landscape amenities, or those wetlands created after July 1, 199o, that were
unintentionally created as a result of the construction of a road, street, or
highway. Wetlands may include those artificial wetlands intentionally
---- � I e,.,, 11-.A,Prland areas to mitigate the conversion of wetlands.
SECTION 4. Port Orchard Municipal Code Section 15.32.030 is AMENDED
as follows:
15.32.030 Permits.
1. Review by Department of Public Works. Proposed site development activities
shall be reviewed by the Port Orchard department of public works to
determine the permits required.
2. Expiration of Existing Construction Plan Approval. Any construction plans
previously approved by the city prior to September 8,1998, are expired. The
director may extend the expiration date if the project is under construction
and progressing satisfactorily towards final completion.
3. Stormwater Management Permit Required. No site development activity shall
occur until a stormwater management permit has been issued, nor shall said
site development activity continue without a stormwater management permit
in force. A stormwater management permit, issued by the department of
public works, shall be required for any of the following activities:
a. Site development or redevelopment activities that meet the definition
of a major development.
b. Site development or redevelopment activities that require connection
to a public storm drainage system.
C. Grading activities that result in the movement of 150 cubic yards or
more of earth.
d. Grading activities that will result in a temporary or permanent slope
having a steepness exceeding three to one (three feet horizontal to one
foot vertical) and having a total slope height, measured vertically from
toe of slope to top of slope, exceeding five feet.
Ordinance No.28-09
Pave 14 of 40
e. Grading activities that include the construction of embankment berms
that will result in the impoundment of water to a depth exceeding 18
inches and/or with a maximum volume exceeding 2,500 cubic feet of
water.
f. Grading activities that will result in the diversion of existing drainage
courses, both natural and manmade, from their natural point of entry
or exit from the grading site.
g. Any land clearing or grading on slopes steeper than 3o percent, or
within the mandatory setback of a wetland, stream, lake, or Puget
Sound, as established by separate ordinance or by the public works
department.
4. Exemptions. The following activities are exempt from this provisions of this
section:
a. Commercial agriculture and forest practices regulated under
WAC
Title 222;
b. Development that is undertaken by the Washington State Department
of Transportation in state highway rights -of -way and is regulated by
Chapter 173-270 WAC, the Puget Sound Highway Runoff Program;
and
c. Grading activities described in POMC 15.32.o6o(9).
5. Permit Requirements. The director shall establish requirements for the
issuance of stormwater management permits, subject to the following
criteria:
a. All site development activities shall comply with the standards,
specifications, and requirements contained in the stormwater design
manual.
b. The director shall establish fees for stormwater management permits.
Stormwater management permit fees shall include fees for the review of
permit applications and documents and for inspections during
construction.
c. A stormwater management permit shall, at the time of its issuance,
specify a maximum expiration date, not to exceed three years from the
date of issuance. A stormwater management permit shall expire upon
approved completion of construction, or upon the specified maximum
expiration date, whichever comes first. In the event that a stormwater
management permit expires prior to the completion of construction, all
construction activity must cease, a new stormwater management permit
application must be submitted, and the issuance of a new stormwater
management permit shall be, at the discretion of the director, subject to
city site development standards in force at the time of the new permit
Ordinance No.28-09
Page 15 of 40
application.
d. Approved stormwater management permit placards shall be prominently
displayed on construction sites at all times until the completion of all
permitted site development activities.
6. When a Professional Engineer is Required. Unless otherwise required by
POMC 15.32.050 or 15.32.060, stormwater management permit
applications shall require the submittal of documents prepared by a
qualified professional engineer when one of the following conditions
exists:
a. Any land use or building or development on real property which meets
the definition of a major development; or
b. Any improvements within the boundaries of city rights -of -way for
which Port Orchard will ultimately assume responsibility for
�...I............ ...
c. Any site development activity that the director deems to be in the
public's best interest to require that certain stormwater management
permit application submittal documents be prepared by a professional
civil engineer.
7. Off -Site Analysis. All stormwater management permit applications which
meet any of the criteria listed in subsection (6) of this section shall include,
along with other required submittal documents, an off -site drainage analysis
as described in POMC 15.32.070(3)(f) and (8)(f) prepared by a qualified
professional engineer and based on a field investigation of the development's
off -site contributing and receiving drainage areas..
S. Geotechnical Analysis. All stormwater management permit applications for
development activities where grading or the construction of retention
facilities, detention facilities, or other stormwater facilities is proposed within
200 feet of slopes steeper than 30 percent, or where the director deems that
the proposed construction poses a potential hazard due to its proximity to a
slope, shall, when required by the director, include a geotechnical analysis,
prepared by a qualified engineer. Said geotechnical analysis shall address the
effects of ground water interception and infiltration, seepage, potential slip
planes, and changes in soil bearing strength.
9. Soils Analysis. All stormwater management permit applications which meet
any of the criteria listed in subsection (6) of this section, where the soils
underlying the proposed project have not been mapped, or where existing
soils maps of the project site are inconsistent, or where the director deems
that existing soils maps of the project site are not of sufficient resolution to
allow proper engineering analysis, shall include a soils investigation report.
io. Permit Modifications. Proposed modifications to an approved stormwater
management permit must be submitted to the department of public works
and be reviewed for compliance with this chapter. Substantial proposed
Ordinance No.28-09
Page 16 of 40
modifications, as determined by the director, shall require additional review
fees and shall require reissuance of the required permit. Minor proposed
modifications may be accepted by the director without requiring the
reissuance of the accepted permit or the payment of additional review fees.
ii. Erosion and Sedimentation Control. All final drainage, grading, clearing, or
other site development plans requiring acceptance from the department of
public works shall include a plan for the control of erosion and sedimentation
as required in POMC 15.32•o5o(i) and (3), for the period beginning with the
commencement of site development activity and continuing without
interruption until permanent site stabilization is achieved.
No clearing, grubbing, grading, or other construction activity may take place
on a project site until an erosion and sedimentation control plan has been
approved by the department of public works.
SECTION 5. Port Orchard Municipal o�c e �ectiolri5 3"'z04A is AMFNDETi
as follows:
15.32.040 Covenants, sureties, and liability insurance.
1, Site Stabilization. Prior to the issuance of a stormwater management permit
and prior to beginning any construction activity on a project site, the owner of
the project will be required to record a performance covenant or post a
performance surety for site stabilization and erosion and sedimentation
control. In addition, the owner may be required to provide a certificate tf
commercial liability insurance as outlined in subsection (5) of his section
This performance requirement for stabilization and erosion control should
not be confused with the performance bond accepted at the time of final plat
recording as a surety for construction items not yet completed. When a
performance bond is accepted for a final plat in lieu of construction
completion, the surety or covenant for stabilization and erosion control will
be released, and the new performance bond shall cover site stabilization and
erosion control along with the other incomplete construction items.
2. Performance Covenant for Site Stabilization. For project sites with less than
five acres of land disturbing activity, a performance covenant may be
recorded in lieu of performance surety for site stabilization prior to issuance
of the stormwater management permit to guarantee the city that temporary
erosion and sedimentation control and permanent site stabilization measures
will perform in accordance with this chapter. This covenant shall be recorded
with the Kitsap County auditor and shall run with the land until such a time
as the city issues final acceptance of the permitted activities, or until a
separate performance bond is posted prior to final plat approval. Upon
issuance of final project approval, the department of public works will record
Ordinance No.28-og
Page 17 of 40
a document that extinguishes the performance covenant.
3. Performance Surety for Site Stabilization. The term "bond" as defined in this
chapter shall mean a surety bond, assignment of funds, or irrevocable bank
letter of credit. For project sites with five or more acres of land disturbing
activity, a performance bond shall be posted prior to issuance of a stormwater
management permit to guarantee the city that temporary erosion and
sedimentation control and permanent site stabilization measures will
perform in accordance with this chapter. The amount of the performance
bond shall be as follows:
a. One hundred fifty percent of the estimated cost of performing minor
grading and installing temporary erosion and sedimentation control, and
permanent site stabilization measures to bring the construction site into
compliance with this chapter. A cost estimate shall be submitted by the
project -engineer subject to the approval of tho director The minimum
amount of the "bond" shall be $5,000; or
b. One thousand dollars per acre of land disturbing activity. No engineer's
estimate is required.
If the site work is determined by the director to be in violation of this chapter,
the city may use the performance bond to provide temporary and permanent
site stabilization.
All performance bonds shall run continuously until released by the city, and
shall not be subject to an expiration or cancellation date.
4. Performance Bond for Uncompleted Site Improvements. For single-family
residential developments, a performance bond shall be provided prior to the
final recording of the plat/PUD, guaranteeing completion of all site
improvements not yet completed. The amount of the performance bond shall
be 150 percent of the estimated cost of said improvements. The estimated
cost of the construction shall be determined by a civil engineer subject to the
approval of the director.
All performance bonds shall run continuously until released by the city, and
shall not be subject to an expiration or cancellation date.
5. Commercial Liability Insurance. The owner of any project must provide a
certificate of liability insurance to the department of public works prior to
issuance of a stormwater management permit. The liability insurance shall
remain in force until final project approval is issued by the city. The
commercial liability insurance shall be in the amount of not less than
$1,000,000 combined single limit bodily injury and property damage, with a
$2,000,000 aggregate. Such insurance shall include the city of Port Orchard,
its officers, and employees as additional insureds, with respect to the terms
and conditions of the policy.
6. Maintenance Bonds. A maintenance bond is required for all subdivisions and
commercial projects for which stormwater facilities and/or roads are
ordinance N0.28-og
Paee 18 of 40
required. Prior to the final approval of construction and release of any
performance sureties, a maintenance bond must be posted and maintained by
the project owner for a period of two years. The maintenance bond shall
guarantee the stormwater facilities and roads constructed under permit
against design defects and/or failures in workmanship, and shall guarantee
that the facilities constructed under the permit will be regularly and
adequately maintained throughout the maintenance period. At the end of this
time, the city will inspect the system and, when the facility is acceptable and
8o percent of the lots in that phase have been improved, the city will release
the maintenance bond. In the event that 8o percent of the lots in a residential
development have not been improved by the end of the two-year maintenance
period, the maintenance bond maybe extended, subject to the approval of the
director, for one additional year.
The amount of the maintenance bond shall be io percent of the estimated
construction cost of the stormwater facilities and roadsrequiring
maintenance, or $5,000, whichever is greater. The construction cost of the
facilities requiring maintenance shall be estimated by the project engineer,
subject to the approval of the director.
SECTION 6. Port orchard Municipal Code Section 15.32.050 is AMENDED
as follows:
15.32.050 Erosion and sediment control.
L. Minor Developments. All minor developments, as defined in this chapter,
shall be required to control erosion and sedimentation during construction,
to permanently stabilize soil exposed during construction, and to comply with
the minor development requirements described in subsection (2)(a) through
(e) of this section.
2. Minor Development Requirements.
a. Construction Access Route. Construction vehicle access shall be,
whenever possible, limited to one route. Access points shall be stabilized
with quarry spall or crushed rock to minimize the tracking of sediment
onto public roads.
b. Stabilization of Denuded Area. All exposed and unworked soils not
actively being worked shall be stabilized by suitable application of BMPs.
From September 15th through April 3oth, soils not actively being worked
shall remain unstabilized for no more than 48 hours. From May ist
through September 14th, the owner or contractor shall have the materials
readily available to stabilize denuded areas as site and weather conditions
dictate. Prior to leaving the site, stormwater runoff shall pass through a
sediment pond, sediment trap, or other appropriate BMP.
Ordinance No.28-09
Page 19 of 40
c. Protection of Adjacent Properties. Adjacent properties shall be protected
from sediment deposition by appropriate use of vegetative buffer strips,
sediment barriers or filters, dikes or mulching, or by a combination of
these measures and other appropriate BMPs.
d. Maintenance. All erosion and sediment control BMPs shall be regularly
inspected and maintained to ensure continued performance of their
intended function.
e. Other BMPs. Any adverse effects of increased runoff resulting from land
disturbing and/or land development activities shall be controlled by
appropriate BMPs.
3. Major Developments. Any new development meeting the definition of a major
development shall comply with subsection (5) of this section. For any
redevelopment project meeting the definition of a major development, those
(5) of this section.
4. Erosion and Sedimentation Control Plan Required. Compliance with the
erosion and sedimentation control requirements of subsection (5) of this
section shall be demonstrated through the implementation of an approved
erosion and sedimentation control plan.
5. Major Development Erosion and Sedimentation Control Minimum
Requirements.
a. Stabilization and Sediment Trapping. All exposed soils shall be stabilized
by suitable application of BMPs, including but not limited to sod or other
vegetation, mat covering, mulching, or application of compacted ground
base material on areas to be paved. All BMPs shall be selected, designed
and maintained in accordance with the manual. From September 15th
through April 3oth, soils not actively being worked for more than 48
hours shall be protected or stabilized. From May ist through September
14th, soils not actively being worked for more than 7 days shall be
protected and stabilized by the owner or contractor.
b. Delineate Clearing and Easement Limits. Clearing limits and/or any
easements, setbacks, sensitive/critical areas and their buffers and
drainage courses shall be clearly marked in the field, and on the
construction plans.
c. Protection of Adjacent Properties. Adjacent properties shall be protected
from sediment deposition by appropriate use of vegetative buffer strips,
sediment barriers or filters, dikes or mulching, or by a combination of
these measures and other appropriate BMPs.
d. Timing and Stabilization of Sediment Trapping Measures. Sediment
ponds and traps, perimeter dikes, sediment barriers and other BMPs
intended to trap sediment on -site shall be constructed as a first step.
These BMPs shall be functional before land disturbing activities take
Ordinance No.28-og
Page zo of ao
place. Earthen structures such as dams, dikes, and diversions shall be
stabilized according to the timing indicated in the erosion and
sedimentation control requirement in subsection (5)(a) of this section.
e. Cut and Fill Slopes. Cut and fill slopes shall be designed and constructed
in a manner that will minimize erosion. In addition, slopes shall be
stabilized in accordance with the erosion and sedimentation control
requirement in subsection (5)(a) of this section.
f. Controlling Off -Site Erosion. Properties and waterways downstream from
development sites shall be protected from erosion due to increases in the
velocity of stormwater runoff from the development site.
g. Stabilization of Temporary Conveyance Channels and Outlets. All
temporary on -site conveyance channels shall be designed, constructed,
and stabilized to prevent erosion from the expected flow velocity from a
- arf24lour durat3en stem% e—post_dpvplol)ment condition.
Stabilization adequate to prevent erosion of outlets, adjacent
streambanks, and slopes shall be provided at the outlets of all conveyance
systems.
h. Inlet Protection. All storm drain inlets made operable during construction
shall be protected so that stormwater runoff does not enter the
conveyance system without first being filtered or otherwise treated to
remove sediment. The requirement for inlet protection may be waived on
a site -specific basis when the conveyance system downstream of the inlet
discharges to an appropriate sediment containment BMP and the
conveyance system can be adequately cleaned following site stabilization.
i. Underground Utility Construction. The construction of underground
utility lines shall be subject to the following criteria:
i. For trenches on a downslope of more than five percent, no more than
500 feet of trench shall be opened at one time, unless otherwise
approved by the director.
ii. Where consistent with safety and space considerations, excavated
material shall be placed on the uphill side of trenches.
iii. Trench dewatering devices shall discharge into a sediment trap or
sediment pond.
j. Constructed Access Routes. Wherever construction vehicle access routes
intersect paved roads, provisions must be made to minimize the transport
of sediment (mud) onto the paved road by use of appropriate BMPs such
as a stabilized construction entrance. If sediment is transported onto a
road surface, the roads shall be cleaned thoroughly, as a minimum, at the
end of each day. Sediment shall be removed from roads by shoveling or
sweeping and be transported to a controlled sediment disposal area.
Street washing shall be allowed only after sediment is removed in this
manner.
k.
m.
Ordinance No.28-09
Paee 21 Of 40
Dewatering Construction Sites. Dewatering devices shall discharge into a
sediment trap or sediment pond.
Control of Pollutants Other than Sediment on Construction Sites. All
pollutants other than sediment that occur on -site during construction
shall be handled and legally disposed of in a manner that does not cause
contamination of stormwater.
Maintenance. All temporary and permanent erosion and sedimentation
control BMPs shall be maintained and repaired as needed to assure
continued performance of their intended function. All maintenance and
repair shall be conducted in accordance with the manual. The applicant
shall be responsible for assuring that any such facilities damaged during
floods, storms or other adverse weather conditions are immediately
returned to normal operating condition.
n ,..,..,..,,,i „f rro,, "nrnmT uMn... All temnorary erosion and sedimentation
control BMPs shall be removed within 3o days after final site stabilization
is achieved or after the temporary BMPs are no longer needed. Trapped
sediment shall be removed or stabilized on -site. Disturbed soil areas
resulting from removal of temporary BMPs shall be permanently
stabilized. The removal of temporary erosion and sedimentation control
BMPs may not be required for those projects, such as single-family plats,
that will be followed by additional construction under a different permit.
In these circumstances, the need for removing or retaining the measures
will be evaluated on a site -specific basis.
o. Financial Liability. A performance covenant, performance bonding, or
other appropriate financial instruments, required by POMC 15.32.040,
shall ensure compliance with the approved erosion and sedimentation
control plan.
Erosion Control Design Storm Event. Facilities designed for the control of
erosion and sedimentation shall be designed for the erosion and
sedimentation control design storm event, defined as the six-month, 24-hour
duration storm.
SECTION 7. Port Orchard Municipal Code is AMENDED by adding a new
section 15.32.o65 to read as follows:
15.32.o65 Minimum Site Development Requirements.
The following minimum site development requirements apply to new development,
redevelopment and construction site activities that result in land disturbance of
equal or greater than one acre, including projects less than one acre that are part of a
larger common plan of development or sale.
Ordinance No.28-09
Page 22 of 40
i. Plans and Reports (Minimum Requirement #r). All development and
redevelopment meeting the thresholds contained in this section shall submit
plans and reports in accordance with the criteria stipulated in the Manual.
2. Construction Stormwater Pollution Prevention Plan (SWPPP) (Minimum
Requirement #2). All new development and redevelopment is responsible for
preventing erosion and discharge of sediment and other pollutants into
receiving waters by preparing a SWPPP. The SWPPP shall include a narrative
and drawings. All BMP's shall be clearly referenced in the narrative and
marked on the drawings. The SWPPP narrative shall include documentation
to explain and justify the pollution prevention decisions made for the project
and shall be available to the Director upon request. The SWPPP shall include
each of the twelve elements below and shall be fully implemented, from initial
soil disturbance until final stabilization, unless site conditions render the
elementurmeeessary andt eexemptiop from that_ele. entisrlearlyjustified
in the SWPPP.
(a) Preservation of vegetation/marking clearing limits;
(b) Construction access;
(c) Controlling flow rates;
(d) Installing sediment controls;
(e) Stabilizing soils;
(f) Protecting slopes;
(g) Protecting drain inlets;
(h) Stabilizing channels and outlets
(i) Controlling pollutants;
6) Controlling de -Watering;
(k) Maintaining best management practices; and
(1) Management of the project.
3. Source Control of Pollution (Minimum Requirement #3). Source control best
management practices (operational and/or structural) are required for all
projects. Those practices listed in the source control chapter (Chapter 4) of
the Manual as applicable operational or structural source controls for a
particular pollutant source are required under this minimum requirement.
4. Preservation of Natural Drainage Systems and Outfalls (Minimum
Requirement #4).
(a) Natural drainage patterns shall be maintained, and discharges from
the project site shall occur at the natural location, to the maximum
extent practicable. The manner by which runoff is discharged from
the project site must not cause a significant adverse impact to
downstream receiving waters and down gradient properties. All
outfalls require energy dissipation.
5•
6
7
Ordinance No.28-09
Page 23 of 40
(b) Downstream Analysis. The following projects shall conduct an
analysis of downstream water quality impacts resulting from the
project and shall provide mitigation of these impacts:
(i) All major developments; and
(ii) Any minor developments located within critical drainage areas.
The analysis shall extend a minimum of one-fourth of a mile
downstream from the project site. The existing or potential impacts to
be evaluated and mitigated shall include excessive sedimentation,
erosion, discharges to ground water contributing to recharge zones,
violations of water quality standards, and spills and discharges of
priority pollutants.
On -site Stormwater Management (Minimum Requirement #5). All projects
shall maintain the average annual volume of water that infiltrates on a site
(ground water + interflow) at or above predevelopment levels as predicted by
develop
designed bestyma management practdrologic model. ices contained in the Manua to fulfill this
requirement.
Runoff Treatment (Minimum Requirement #6). The following require
construction of stormwater treatment facilities designed in accordance with
the Manual.
(a) Projects in which the total pollution -generating impervious surface
(PGIS) is 5,000 square feet or more; or
(b) Projects in which the total of pollution -generating aand from perviourface
(PGPS) is three-quarters (3/4) of an or
there is a surface discharge in a natural or man-made conveyance
system from the site.
The level of treatment for each project will be determined by POW
15.32.o65(7) through 15.32.o65(1o).
Oil Control Treatment Requirements.
(a) Treatment to achieve oil control applies to projects that have "high -use
sites." High -use sites area those that typically generate high
concentrations of oil due to high traffic turnover or frequent transfer
of oil. High -use sites include:
(1) An area of a expected average daily commercial
(ADT) count equal ial site subject
to orgreater than
loo vehicles per i,000 square feet of gross building area;
(ii) An area of a commercial or industrial site subject to petroleum
storage and transfer in excess of 1,500 gallons per year, not
including routinely delivered heating oil;
(iii) An area of a commercial or industrial site subject to parking,
storage or maintenance of 25 or more vehicles over 10 tons gross
weight (trucks, buses, trains, heavy equipment, etc.);
Ordinance No.28-og
Pave 24 of 40
(iv) A road intersection with a measured ADT count of 25,000
vehicles or more on the main roadway and 15,000 vehicles or more
on any intersecting roadway, excluding projects proposing
primarily pedestrian and bicycle use improvements.
(b) Oil/Water Separators. All storm water from impervious areas at high
use site shall be subject to motor vehicle traffic shall flow through a
spill -containment type oil/water separator prior to surface discharge
off site.
8. Phosphorus Treatment Requirements. Phosphorus treatment as described in
the Manual is required for the following:
er section
(a) ThoAct, ander bdies designatedreported
not supportng3benef�ial uses f the Clen at er
due to
phosphorus;
(b] ose water —bodies -listed in Washington State's Nonpoint Source
Assessment required under section 319(a) of the Clean water Ac�
to nutrients.
i. Enhancement Treatment Requirements. Enhanced treatment for reduction
in dissolved metals (primarily copper and zinc) is required for the following
project sites that discharge to fish -bearing streams, lakes, or to waters or
conveyance systems tributary to fish -bearing streams or lakes:
(a) Industrial project sites;
(b) Commercial project sites;
(c) Multi -family project sites; and
(d) High annual average daily traffic (AADT) roads as follows:
(i) Within urban growth management areas:
1. Fully controlled and partially controlled limited access
highways with AADT counts of 15,000 or more
2. All other roads with an AADT of 7,500 or greater
to. Basic Treatment Requirements. Basic treatment applies to:
(a) Project sites that discharge to the ground, unless:
(i) The soil suitability criteria for infiltration treatment are met;
(see the Manual for soil suitability criteria); or
(ii) The project uses infiltration strictly for flow control and not
treatment and the discharge is within 1/4-mile of a phosphorus
sensitive lake (use a Phosphorus Treatment facility), or within 1/4-
mile of a fish -bearing stream, or a lake (use an Enhanced
Treatment facility).
(b) Residential projects not otherwise needing designated by USEPA, the Department of Ecology, o phosphorus control by thecity of
Port Orchard;
ordinance No.28-09
Page 25 of 40
(c) Project sites discharging directly to salt waters, river segments, and
lakes listed in Appendix 1-C of the Sto•mwater ManagementManual
for Western Washington (2005);
(d) Project sites that drain to streams that are not fish bearing, or to
waters not tributary to fish -bearing streams; and
(e) Landscaped areas of industrial, commercial, and multi -family project
sites, and parking lots of industrial and commercial project sites that
do not involve pollution -generating sources (e.g. industrial activities,
customer parking, storage of erodible or leachable material, wastes or
chemicals) other than parking of employees' private vehicles. For
developments with a mix of land use types, the basic treatment
requirement shall apply when the runoff from the areas subject to the
basic treatment requirement comprise 50% or more of the total runoff.
(V;';,.,,,,,, Rennirement #7)• Except as provided in
15.32.o65(12), the following require consrrucu0n U1 .,u.,
and/or land use management BMPs that result in stormwater discharges that
match developed condition discharge durations to pre -developed condition
durations for the range of pre -developed discharge rates from 50% of the 2-
year peak flow up to the full 50-year peak flow.
(a) Projects in which the total of effective impervious surfaces is 10,000
square feet or more;
(b) Projects that convert 3/4 acres or more of native vegetation to lawn ,
landscape, or convert 2.5 acres or more of native vegetation to pasture,
and from which there is a surface discharge in a natural or man-made
conveyance system from the site; or
(c) Projects that through a combination of effective impervious surfaces
and converted pervious surfaces cause a o.1 cubic feet per second
increase in the loo-year flow frequency as estimated using the
Western Washington Hydrology Model or other approved model.
12. Flow Control Exemption. Flow control is not required for projects that
discharge directly to Puget Sound if all the following are satisfied:
(a) Direct discharge to the exempt receiving water does not result in the
diversion of drainage from any perennial stream classified as Types 1,
2, 3, or 4 in the State of Washington Interim Water Typing System, or
Types "S", "F", or "Np" in the Permanent Water Typing System, or
from any category I, Il, or III wetland;
(b) Flow runoffvolumes slittingdevices
f om the project site route
to any downstr am Type 5 stream
or category IV wetland:
(i) Design of flow splitting devices or drainage BMPs will be based
on continuous hydrologic modeling analysis. The design will
assure that flows delivered to Type 5 stream reaches will
Ordinance N0.28-09
Pal4e 26 of 40
approximate, but in not case exceed, durations ranging from 50
of the 2-year to the 50-year peak flow; and
(ii) Flow splitting devices or drainage BMP's that deliver flow to
category IV wetlands will also be designed using continuous
hydrologic modeling to preserve pre -project wetland hydrologic
conditions unless specifically waived or exempted by regulatory
agencies with permitting jurisdiction;
(c) The project site must be drained by a conveyance system
that is
comprised entirely of manmade conveyance elements (e. pipes,
ditches, outfall protection, etc.) and extends to the ordinary high water
line of the exempt receiving water;
(d)The conveyance system between the project site and the exempt
receiving water shall have sufficient hydraulic capacity to convey
a:..,a,.,, .c from fi,trrre build -out conditions (under current zoning) of
the site, and the existing condition from nonproiect areas rrom W .,�.1
runoff is or will be collected;
(e) Any erodible elements of the manmade conveyance system must be
adequately stabilized to prevent erosion; and
(f) Shoreline erosion is avoided through the use of appropriate energy
dissipation or other protective measures.
13. Wetlands Protection (Minimum Requirement #8).
(a) Discharges to wetlands shall maintain the hydrologic conditions,
hydrophytic vegetation, and substrate characteristics necessary to
support existing and designated uses. The hydrologic analysis shall
use the existing land cover condition to determine the existing
hydrologic conditions unless directed otherwise by a regulatory agency
with jurisdiction.
(b) Stormwater treatment and flow control facilities shall not be built
within a natural vegetated buffer, except for:
(i) Necessary conveyance systems as approved by the Permittee; or
(ii) As allowed in wetlands approved for hydrologic modification
and/or treatment in accordance with Guidesheet 1B in Appendix 1-
D of the Stormwater Management Manual for Western
Washington (2005).
(c) An adopted and implemented basin plan prepared in accordance with
the provisions of POMC 15.32.080(13) may be used to develop
requirements for wetlands that are tailored to a specific basin.
14. Operation and Maintenance (Minimum Requirement #9). All stormwater
facilities shall be operated and maintained in accordance with POMC
15.32.080.
Ordinance No.28-09
Palle 27 of 40
SECTION 8. Port Orchard Municipal Code Section 15.32. oho is AMENDED
as follows:
15.32.070 Stormwater management.
1. Redevelopment Activities. Where redevelopment activities meet the
definition of a major development, the requirements of this section shall
apply to that portion of the site that is being redeveloped. In addition,
where one or more of the following conditions exist, the requirements of
this section of this chapter shall apply, to the maximum extent practicable,
for the entire site, including adjoining parcels, if they are part of the
project:
a. Existing sites greater than one acre in size with 35 percent or more
b. Sites that discharge to a receiving water that has a documented water
quality problem.
c. Sites where the need for additional stormwater control measures has been
identified through a basin plan.
2. Approved Hydrological Methods for Design. Estimation of peals stormwater
runoff rates used in the design of stormwater quantity control facilities shall
utilize hydrograph methods of analysis approved by the director. The design
of storage facilities that are a part of stormwater quantity control facilities
shall be designed using methods approved by the director.
3. Stormwater Quantity Control. The following minimum requirements for
stormwater quantity control shall apply to all land developments that meet
the definition of a major development:
a. All surface water and stormwater entering the development site in its
predevelopment state shall be received at the naturally occurring or
otherwise legally existing locations. All surface water and stormwater
leaving the development site shall be discharged at all times during and
after development at the naturally occurring or otherwise legally existing
locations so as not to be diverted onto or away from adjacent downstream
properties, except, diversion which will correct an existing manmade
downstream problem may be permitted by the director. For the purposes
of this chapter, "naturally occurring location" shall mean the location of
those channels, swales, and pre-existing and established systems as
defined by the first documented topographic contours existing for the
subject property, either from maps or photographs, site inspections,
decisions of a court of law, or other means determined appropriate by the
director.
b. The post -development peals stormwater discharge rates from the
development site for the two-, io-, and ioo-year, 24-hour duration storm
Ordinance No.28-og
Pa>ze 28 of 40
events and the loo-year, seven-day duration storm event shall at no time
exceed the predevelopment peals stormwater runoff rates for the same
design storm events, except as expressly permitted by this chapter. Also,
where stormwater directly or indirectly discharges to open channels or
streams, streambank erosion protection is required; the post -development
peals stormwater discharge rate from the development site for the two-
year, 24-hour duration storm event shall not exceed 50 percent of the
predevelopment peak stormwater runoff rate for the same design storm
event. The director may require that runoff from a development site be
controlled for additional design storm events.
c. Closed depressions shall be analyzed using hydrograph routing methods.
Infiltration shall be addressed where appropriate. If a proposed project
will discharge runoff to an existing closed depression that has greater than
5,000—square—feet of —water —surface —area —at overflow —elevation, —the
following requirements must be met:
i. Case 1. The predevelopment ioo-year, seven-day and 24-hour
duration design storms from the drainage basin tributary to the closed
depression are routed into the closed depression using only infiltration
as outflow. If the design storms do not overflow the closed depression,
no runoff may leave the site for the same storm events following
development of a proposed project. This may be accomplished by
excavating additional volume in the closed depression subject to all
applicable requirements. If a portion of the depression is located off of
the project site, impacts to adjacent properties shall be evaluated.
ii. Case 2. The predevelopment ioo-year, seven-day, 24-hour duration
design storm events from the drainage basin tributary to the closed
depression are routed to the closed depression using only infiltration
as outflow, and overflow occurs. The closed depression shall then be
analyzed as a detention/infiltration pond. The required performance,
therefore, shall not exceed the predevelopment runoff rates for 50
percent of the two-year and loo percent of the to -year and loo-year,
24-hour duration and loo-year, seven-day duration design storms.
This will require that a control structure, emergency overflow spillway,
access road, and other applicable design criteria be met. If the facility
will be maintained by the city, the closed depression shall be placed in
a dedicated tract. If the facility will be privately maintained, the tract
shall be located within a drainage easement. If a portion of the
depression is located off of the project site, impacts to adjacent
properties shall be evaluated.
iii. Case 3. When a proposed project is contributory to a closed depression
located off -site, the volume of runoff discharged may not be increased
for the two-, to-, and loo-year, 24-hour duration, and the roo-year,
Ordinance No.28-09
Page 20 of ao
seven-day duration storm events. The exception to this requirement is
in the case where discharge would not result in an increase in water
surface elevation of greater than o.oi-foot for the roo-year storm
events.
d. Land developments shall provide stormwater quantity control facilities
designed to meet, as a minimum performance standard, the requirements
of this section, except in the following circumstances:
i. The development site discharges directly into Puget Sound, or directly
into the tidally influenced areas of rivers and streams discharging into
Puget Sound, where runoff quantity control is not required by other
governmental agencies.
ii. The development site discharges to a regional stormwater facility
approved by the director to receive the developed site runoff.
wetland, etc.) where it can be demonstrated by the applicant, to the
satisfaction of the director, that stormwater quantity control is not
warranted.
e. In the event that conditions downstream from a proposed development
site are determined by the director to be exceptionally sensitive to
potential stormwater discharges from the subject site, the director may
require a factor of safety be applied to the total retention/detention
storage volume and/or a reduction of allowable stormwater release rates.
f. Submittals for all proposed development projects shall include an analysis
of downstream water quantity impacts resulting from the project and
shall provide for mitigation of these impacts. The analysis shall extend a
minimum of one-fourth of a mile downstream from the project. The
existing or potential impacts to be evaluated and mitigated shall include,
but not be limited to, excessive streambank erosion, flooding, surcharging
of existing closed drainage conveyance facilities, discharge to closed
depressions, and discharge to existing off -site runoff control facilities.
g. Retention facilities and open stormwater quantity control facilities shall
not be located in dedicated public road rights -of -way.
h. Reasonable access for maintenance, as determined by the director, shall
be provided to all stormwater facilities.
i. As the first priority, streambank erosion control BMPs shall utilize
infiltration to the fullest extent practicable, only if site conditions are
appropriate and ground water quality is protected. Streambank erosion
control BMPs shall be selected, designed, and maintained according to the
manual. Streambank erosion control BMPs shall not be built within a
natural vegetated buffer, except for necessary conveyance systems as
approved by the department of public works.
4. Stormwater Quality Control. Water quality best management practices
5•
6.
Ordinance No.28-og
Page :io of 40
(BMPs) shall be used to the maximum extent practicable to control pollution
in stormwater. Water quality BMPs shall be used to comply with the
standards of this chapter, including those contained in the manual.
Construction and post -development water quality BMPs shall be utilized for
all developments. Said water quality BMPs shall provide runoff water quality
treatment for all storm events with intensities less than or equal to the water
quality design storm event, as defined in subsection (8)(b) of this section.
Illicit Discharges. Illicit discharges, as described in POMC 15.32.100(r), or
illicit connections to a stormwater drainage system, as described in POMC
15.32.100(2), are prohibited.
Experimental Best Management Practices. In those instances where
appropriate best management practices are not in the manual, experimental
BMPs should be considered. In an effort to improve stormwater quality
-
problems in a manner not addressed by the manual. Experimental BMPs
must be approved by the director. The director may require that the
performance of experimental BMPs be monitored to document their
effectiveness for future use.
7. Incorporation into Stormwater Quantity Control Facilities. Water quality
BMPs may be incorporated into the design of stormwater quantity control
facilities where appropriate.
S. Stormwater Conveyance Facilities.
a. All proposed developments must provide on -site stormwater conveyance
facilities having sufficient capacity to convey, without flooding or
otherwise damaging existing or proposed structures, the post -
development peals stormwater runoff rate resulting from a roo-year storm
event, plus any existing upstream runoff that will be conveyed through the
development site.
b. Estimation of peak stormwater runoff rates used in the design of water
conveyance facilities shall use either the rational method or a hydrograph
method of analysis accepted by the director.
c. Existing drainage ways and/or other conveyance facilities downstream
from proposed developments that are identified within the scope of the
downstream portion of the off -site drainage analysis shall have sufficient
capacity to convey, without flooding or otherwise damaging existing or
proposed structures, the post -development peak stormwater discharge for
the 25-year storm event. All newly constructed downstream drainage ways
and/or conveyance facilities shall have sufficient capacity to convey the
post -development peak stormwater discharge for the ioo-year storm
event. Downstream improvements or additional on -site stormwater
quantity control measures shall be provided to eliminate any potential
io
Ordinance No.28-09
Paee �i of 40
downstream flooding or other damage that may occur following
completion of the proposed development. The director has the authority
to waive the requirement for downstream improvements.
d. Drainage through closed conveyance structures such as pipes shall not
discharge directly onto the surface of a public road.
Easements, Tracts, and Covenants.
a. Drainage easements shall be provided in a proposed development for all
stormwater conveyance systems that are not located in public rights -of -
way or tracts. Said drainage easements shall be granted to the parties
responsible for providing on -going maintenance of the systems.
b. Stormwater facilities that are to be maintained by the city, together with
maintenance access roads to said facilities, shall be located in public right-
of-way, separate tracts dedicated to the city, or drainage easements
__--_a :_ a,...;,,„.,+oA nnan cnnce. The exception is for stormwater
conveyance pipes that may be located within easements on private
property; provided, that all catch basins can be accessed without entering
private property.
c. All runoff from impervious surfaces, roof drains, and yard drains shall be
directed so as not to adversely affect adjacent properties. Wording to this
effect shall appear on the face of all final plats/PUDs, and shall be
contained in any covenants required for a development.
Wetlands. The following requirements apply only to situations where
stormwater discharges directly or indirectly into a wetland, and must be met
in addition to meeting the requirements in Major Development Minimum
Requirement 7.35(2), Stormwater Treatment BMPs:
a. Stormwater discharges to wetlands must be controlled and treated to the
same extent as all other discharges, with the goal of meeting state water
quality and ground water quality standards.
b. Discharges to wetlands shall maintain the hydroperiod and flows of
predevelopment site conditions to the extent necessary to protect the
characteristic functions of the wetland. Prior to discharging to a wetland,
alternative discharge locations shall be evaluated, and natural water
storage and infiltration opportunities outside the wetland shall be
maximized.
c. Created wetlands that are intended to mitigate for loss of wetland acreage,
function and value shall not be designed to also treat stormwater.
d. In order for constructed wetlands to be considered treatment systems,
they must be constructed in areas which are not designated as wetland or
wetland buffer or in other areas which are in conflict with designated
critical areas and associated buffers, and they must be managed for
stormwater treatment. If these systems are not managed and maintained
in accordance with the manual for a period exceeding three years, these
Ordinance No.28-09
PnQe q2 of 40
systems may no longer be considered constructed wetlands.
in a natural vegetated buffer, except
e, or landnecessary y conveyance systems MPs shall not be built has approved by the department of
public works.
ii. Regional Facilities. When the director has determined that the public would
benefit by the establishment of a regional stormwater facility which would
serve as an alternative to the construction of separate on -site drainage
facilities, the director may recommend to the city council that a regional
stormwater facility be constructed which would serve more than one
development in providing stormwater quantity and/or quality control. In the
event that a regional stormwater facility is required by the city council, such a
regional stormwater facility shall be located outside of fish -bearing streams,
unless otherwise accepted by the Washington State Department of Fish and
:,are All f t,,,'Ptlevelonmentsconstructedonlandsdesignatedbythecity
council to be served by the regional iacinLy sua,,, a< L.-- -
stormwater management permit for a development, be required to contribute
a fair share to the cost of land purchase, design, and construction of said
regional facility. In the event that a proposed regional stormwater facility is
not yet in operation at the time of completion of construction of a
development that is to be served by said regional facility, the applicant for
said development shall be requiredto provide temporary stormwater quantity
and quality controls. Temporary quantity and quality controls may be
constructed in temporary easements, rather than in separate tracts.
12. Basin Planning. An adopted and implemented basin plan may be used to
develop requirements for source control, stormwater treatment, streambank
erosion control, wetlands and water quality sensitive areas that are tailored to
a specific basin. Adopted and implemented watershed -based basin plans may
be used to modify any or all of the minimum requirements for stormwater
quantity or quality control addressed in this chapter; provided, that the level
of protection for surface or ground water achieved by the basin plan will
equal or exceed that which would otherwise be achieved by implementation of
the provisions of this chapter in the absence of a basin plan. Basin plans shall
evaluate and include, as necessary, retrofitting of BMPs for existing
development and/or redevelopment in order to achieve watershed -wide
pollutant reduction goals. Standards developed from basin plans shall not
modify any of the above requirements until the basin plan is formally adopted
and fully implemented by the city.
13. Exemptions. Residential lots one acre or larger shall be exempt from the
provisions of this section unless otherwise determined by the director. Cases
where the exemption does not apply include, but are not limited to, sites
within or adjacent to critical areas or watersheds, steep or unstable slopes, or
where the cumulative impacts of development warrant compliance with these
Ordinance No.28-09
Pave �8 of 40
provisions. Site development activities taking place on individual lots of one
acre or larger, which meet the definition of a major development, are not
exempt from the requirements of POMC 15.32.o65. Proposed access
roadways serving residential lots larger than two and one-half acres, which
meet the definition of a major development, are not exempt from the
requirements of POMC 15.32.o65.
SECTION 9. Port Orchard Municipal Code Section 15.32.o8o is AMENDED
as follows:
15.32.080 Operation and maintenance.
i. Maintenance of Stormwater Facilities by Owners.
a. Anrperson-or- persons -holding-title _to_a nonresidential property for which
stormwater facilities and BMPs have been required by the city shall be
responsible for the continual operation, maintenance, and repair of said
stormwater facilities and BMPs in accordance with the provisions of this
chapter.
b. For privately maintained stormwater facilities, the maintenance
requirements specified in this chapter, including the manual, shall be
enforced against the owner(s) of the subject property served by the
stormwater facility.
2. Maintenance Covenant Required for Privately Maintained Drainage Facilities.
a. Prior to the beneficial use of a development constructed under a city
permit, the owner shall record a maintenance covenant that guarantees
Port Orchard that the owner shall properly operate, maintain, and inspect
the stormwater facilities, and that also gives the City the authority to enter
and inspect the facility as per POMC 15.32.120. The restrictions set forth
in such covenant shall be included in any instrument of conveyance of the
subject property and shall be recorded with the Kitsap County auditor.
b. The director may require the owners of existing stormwater facilities for
which the city has not previously accepted operation and maintenance
responsibility to record a maintenance covenant, or to request that the
city accept operation and maintenance responsibility for the stormwater
facilities subject to the requirements of this chapter.
c. Maintenance covenants shall remain in force for the life of the
development, or until the responsibility for the operation and
maintenance of the subject stormwater facilities is accepted by the city.
3. City Acceptance of New Stormwater Facilities. The city may accept for
maintenance those new residential stormwater facilities constructed under an
accepted stormwater management permit that meet the following conditions:
a. Improvements in residential plats/PUDs have been completed on at least
Ordinance No.28-09
Page 34 of 40
8o percent of the lots, unless waived by the director;
b. All drainage facilities have been inspected and accepted by the director
and said drainage facilities have been in satisfactory operation for at least
two years;
c. All drainage facilities reconstructed during the maintenance period have
been accepted by the director;
d. The stormwater facility, as designed and constructed, conforms to the
provisions of this chapter;
e. All easements required under this chapter, entitling the city to properly
operate and maintain the subject drainage facility, have been conveyed to
the city and have been recorded with the Kitsap County auditor;
f. For nonstandard drainage facilities, an operation and maintenance
manual, including a maintenance schedule, has been submitted to and
g. A complete and accurate set of reproducible mylar as -built arawings ano. a
CD containing an acceptable electronic set of as -built drawings have been
provided to the city. A professional engineer shall certify that both the
vertical and horizontal alignment meet the design objectives.
City Acceptance of Existing Stormwater Facilities. Port Orchard may
accept for maintenance those stormwater facilities for residential
developments existing prior to the effective date of the ordinance codified
in this chapter that meet the following conditions:
a. Improvements in residential plats/PUDs have been completed on at
least 8o percent of the lots; and
b. An inspection by the director has determined that the stormwater
facilities are functioning as designed; and
c. The stormwater facilities have had at least two years of satisfactory
operation and maintenance, unless otherwise waived by the director;
and
d. The person or persons holding title to the properties served by the
stormwater facilities submit a petition containing the signatures of the
title holders of more than 50 percent of the lots served by the
stormwater facilities requesting that the city maintain the stormwater
facilities; and
e. All easements required under this chapter, entitling the city to properly
operate and maintain the subject stormwater facilities, have been
conveyed the city and have been recorded with the Kitsap County
auditor; and I-
f. The person or persons holding title to the properties served by t e
stormwater facilities show proof of the correction of any defects in the
drainage facilities, as required by the director.
5. City Inspections of Privately Maintained Stormwater Facilities.
Ordinance No.28-09
Page J5 of 40
a. The director is authorized to develop an inspection program for
privately owned and maintained stormwater facilities in the city. The
purpose of this inspection program shall be to determine if said
stormwater facilities, conveyance structures and water quality facilities
are in good working order and are properly maintained, and to ensure
that stormwater quality BMPs are in place and that nonpoint source
pollution control is being implemented.
b. Whenever the provisions of the inspection program are being
implemented, or whenever there is cause to believe that a violation of
this chapter has been or is being committed, the inspector is authorized
to inspect during regular working hours and at other reasonable times
any and all stormwater drainage facilities within the city to determine
compliance with the provisions of this chapter.
follow the procedures delineated in POMC 15.32.110(3).
hispection Schedule. The director is authorized to establish a master
inspection and maintenance schedule to inspect appropriate stormwater
facilities that are not owned and operated by the city. The party (or parties)
responsible for maintenance and operation shall be identified. Critical
stormwater facilities, as so deemed by the director, may require a more
frequent inspection schedule.
SECTION io. Port Orchard Municipal Code Section 15.32.090 is AMENDED as
follows:
15.32.090 Critical drainage areas.
r. Special Drainage Improvements. In order to mitigate or eliminate
potential drainage -related impacts on critical drainage areas, the director
may require drainage improvements in excess of those required in other
sections of this chapter. For particularly sensitive drainage areas, the
Director may specify the general type of drainage improvement required.
2. Designation. The following are designated as critical drainage areas:
a. All lands having a slope of 30 percent or greater:
i. As determined by a topographic survey of the site; or
ii. As shown on a U.S.G.S. topographic quadrangle map, when other
topographic survey information is not available; or
iii. As determined by the director based on field investigation of the
site;
b. Geologic hazardous area and historically documented unstable slopes;
c. All lands within 200 feet of the ordinary high eater marls of bodies of
water possessing fish spawning and rearing habitat for anadromous and
Ordinance N0.28-09
Page 36 of 4o
resident fish species, as designated by the State Department of Fish and
Wildlife;
d. All lands designated critical areas in any comprehensive drainage plan, or
defined as critical areas by separate ordinance;
e. All lands that are classified as wetlands as defined by any separate city
ordinance or policy;
f. Any lands that have existing local requirements for the management or
protection of ground water, aquifers, or sole source aquifers;
g. Any lands that drain to a closed depression;
h. Any lands that have existing local or state requirements for the protection
of particular fish or wildlife habitats;
i. Any lands that are established by law as shellfish protection areas; and
j. Any lands determined by the director to have a high potential for drainage
_ _. .. , . .1 rr_ _. _ _ r
construction or development.
3. Conflicting Information. In the event of conflict between maps or other
available information resources, the final determination of whether or not
certain lands are critical drainage areas shall be made by the director. In
making such a final determination, the director may use detailed site surveys
and/or other topographic data that the director may require the applicant to
furnish at the applicant's expense.
SECTION 11. Port Orchard Municipal Code Section 15.32.100 is AMENDED as
follows:
15.32.100 Water quality.
r. Illicit Discharges. Illicit discharges to stormwater drainage systems are
prohibited, see Chapter 15.30 "Illicit Discharge Detection and Elimination."
2. Illicit Connections and Uses. Any MS4, natural and artificial, may only be
used to convey stormwater runoff. Violation of this section can result in
enforcement action being taken as prescribed in POMC 15.32.110.
No person shall use this system to dispose of any solid or liquid matter other
than stormwater. No person shall make or allow any connection to the
stormwater system that could result in the discharge of polluting matter.
Connections to the stormwater system from the interiors of structures are
prohibited. Connections to the stormwater system for any purpose other than
to convey stormwater or ground water are prohibited and shall be eliminated.
3. Pollution Control Device Maintenance. Owners and operators of oil/water
separators, wet ponds, biofiltration/biofilter facilities, sand filters, vaults,
sediment and erosion control systems, infiltration systems and any other
pollution control devices shall operate and maintain such control devices to
Ordinance No.28-og
Page 37 of 40
assure that performance meets the intended level of pollutant removal.
Recommended maintenance schedules for these devices are included in the
Manual.
4. Test Procedure. In the event that water quality testing is utilized in
determining whether a violation of this section has occurred, said water
quality test procedures shall be followed as described in the most recent
edition of the publication "Standard Methods for the Examination of Water
and Wastewater," published by the American Water Works Association.
5. Exemptions. The following discharges are exempt from the provisions of this
section:
a. The regulated effluent from any commercial or municipal facility holding
a valid state or federal wastewater or stormwater discharge permit;
b. Acts of nature not compounded by human negligence; and
e.—Pioperlytapplied-agricultural-irrigation-water.
SECTION 12. Port Orchard Municipal Code Section 15.32.110 is AMENDED as
follows:
15.32.iio Enforcement.
r. Violations of This Chapter. The placement, construction, or installation of any
structure, or the connection to a public storm drainage facility, or the
discharge to a public storm drainage facility, or grading, which violates the
provisions of this chapter shall be and the same hereby is declared to be
unlawful and a public nuisance and may be abated as such through the use of
civil penalties and stop work orders, as well as any other remedies which are
set forth in this chapter, including, but not limited to, revocation of any
permits. The choice of enforcement action taken and the severity of any
penalty shall be based on the nature of the violation and the damage or risk to
the public or to public resources.
2. Inspection. Whenever there is cause to believe that a violation of this chapter
has been or is being committed, the director or his assignee is authorized to
inspect during regular working hours and at other reasonable times all
development activity sites and all stormwater drainage facilities within the
city to determine compliance with the provisions of this chapter.
3. Inspection Procedures. Prior to making any inspections, the director or his
assignee shall present identification credentials, state the reason for the
inspection and request entry.
a. If the property or any building or structure on the property is unoccupied,
the director or his assignee shall first make a reasonable effort to locate
the owner or other person(s) having charge or control of the property or
portions of the property and request entry.
Ul
C.
d.
Ordinance No.28-09
Page 38 of 4o
If, after reasonable effort, the director or his assignee is unable to locate
the owner or other person(s) having charge or control of the property, and
has reason to believe the condition of the site or of the stormwater
drainage system creates an imminent hazard to persons or property, the
inspector may enter.
Unless entry is consented to, by the owner or person(s) in control of the
property or portion of the property or unless conditions are reasonably
believed to exist which create an imminent hazard, the director or his
assignee shall obtain a search warrant, prior to entry, as authorized by the
laws of the state of Washington.
The director or his assignee may inspect the development activity site
and/or the stormwater drainage system without obtaining a search
warrant, provided the inspection can be conducted while remaining on
publie-propert3--orother—property-on- which -permission -to-enter is
4. Stop Work Orders. "Stop work order" shall mean a written notice, signed by
the director and posted on the site of a construction activity, which order
states that a violation of a city ordinance has occurred and that all
construction -related activity, except for erosion and sedimentation control
activities authorized by the director, is to cease until further notice. The
director may cause a stop work order to be issued whenever the director has
reason to believe that there is a violation of the terms of this chapter. The
effect of such a stop work order shall be to require the immediate cessation of
such work or activity until authorization is given by the director to proceed.
5. Violations/Penalties. Every person who violates this chapter, or the
conditions of an accepted stormwater management plan, shall incur a civil
penalty. The penalty amount shall be set by POMC 2.64.030 for each
violation. This penalty shall be in addition to any other penalty provided by
law. Each and every such violation shall be a separate and distinct offense,
and each day of continued or repeated violation shall constitute a separate
violation.
6. Aiding or Abetting. Any person who, through an act of commission or
omission, aids or abets in any violation of this chapter has committed a civil
infraction and shall be subject to the citations, orders, sanctions, and
remedies adopted in this chapter. Additionally, any person who willfully or
knowingly causes, aids or abets a violation of this chapter by any act of
commission or omission is guilty of a misdemeanor.
7. Order to Maintain or Repair. The director shall have the authority to issue to
an owner or person an order to maintain or repair a component of a
stormwater facility or BMP to bring it in compliance with this chapter. The
order shall include:
a. A description of the specific nature, extent and time of the violation and
Ordinance No.28-og
Pace 39 of 4o
the damage or potential damage that reasonably might occur;
b. A notice that the violation or the potential violation cease and desist and,
in appropriate cases, the specific corrective actions to be taken; and
c. A reasonable time to comply, depending on the circumstances.
8. Notice of Civil Infraction — Assessment of Penalty. Whenever the director has
found that a violation of this chapter has occurred or is occurring, a notice of
civil infraction shall be issued pursuant to POMC Chapter 2.64, Code
Enforcement Officer.
g. Hazards.
a. Whenever the director determines that any existing construction site,
erosion/sedimentation problem or drainage facility poses a hazard to
public safety or substantially endangers property, or adversely affects the
condition or capacity of the drainage facilities, or adversely affects the
safetyand-operation-ofcity-right of -way, onviolates-state-water-pollution -
laws, the person to whom the permit was issued, or the person or persons
holding title to the property within which the drainage facility is located,
shall, upon receipt of notice in writing from the director, repair or
otherwise address the cause of the hazardous situation in conformance
with the requirements of this section.
b. Should the director have reasonable cause to believe that the situation is
so adverse as to preclude written notice, he may take the measures
necessary to eliminate the hazardous situation; provided, that he or she
shall first make a reasonable effort to locate the owner before acting, in
accordance with subsection (3) of this section. In such instances, the
person or persons holding title to the subject property shall be obligated
for the payment to the city of all costs incurred by the city. If costs are
incurred and a bond pursuant to this section or other city requirement has
been posted, the director shall have the authority to collect against the
bond to cover costs incurred.
SECTION 13. Severablity. If any section, sentence, clause or phrase of this
ordinance or any code section adopted or amended hereby should be held to be invalid or
unconstitutional by a court of competent jurisdiction, such invalidity or unconstitutionality
shall not affect the validity or constitutionality of any other section, sentence, clause or
phrase of this ordinance or any code section adopted or amended hereby.
SECTION 14. Effective Date. After posting and publication as required by law,
this ordinance shall be in full force and effect January 1, 2010. A summary of this
Ordinance may be published in lieu of the entire ordinance, as authorized by State Law.
ordinance Noz8-09
Paee 40 of 40
PASSED by the City Council of the City of Port Orchard, APPROVED by the Mayor
and attested by the Clerk in authentication of such passage this 8th day of December 2009.
ATTEST:
Patricia J. Ki patric , CMC, City Clerk
APPROVED AS TO FORM:
Gregory A. Jac y, ity A rn y
Lary
Sponsored by:
Robert Putaansuu, Councilmember
City of Port Orchard
Stormwater
Design Manual
Effective Date: August 24, 1999
City of Port Orchard Department of Public Works
216 Prospect Street
Port Orchard, WA 98366
(360) 876-4991
TABLE OF CONTENTS
CHAPTER 1 - INTRODUCTION
1.1 ADDITIONAL REFERENCES
1.2 PENALTIES AND ENFORCEMENT
1.3 EXISTING HAZARDS
1.4 ENGINEER'S RESPONSIBILITIES
1.4.1 PROJECT ENGINEER'S RESPONSIBILITIES
1.4.2 SOILS ENGINEER'S RESPONSIBILITIES
1.4.3 GEOTECHNICAL ENGINEER'S RESPONSIBILITIES
1.5 TRANSFER OF ENGINEERING RESPONSIBILITY
1.6 CITY STAFF ASSISTANCE
CHAPTER 2 - SUBMITTAL REQUIREMENTS
2.1 INTRODUCTION
2.2 LAND USE PERMITS - PRELIMINARY
2.2.1 PRELIMINARY DRAINAGE REVIEW
2.3 STORMWATER MANAGEMENT PERMIT
2.3.1 WHEN PERMIT REQUIRED
2.3.2 APPLICATION PROCESS
2.3.3 APPLICATION SUBMITTAL DOCUMENTS
MINIMUM REQUIREMENTS
2.4 COVENANTS, SURETIES AND LIABILITY INSURANCE
2.4.1 SITE STABILIZATION
2.4.2 PERFORMANCE COVENANT FOR SITE STABILIZATION
2.4.3 PERFORMANCE SURETY FOR SITE STABILIZATION
2.4.4 PERFORMANCE BOND FOR UNCOMPLETED
SITE IMPROVEMENTS
2.4.5 COMMERCIAL LIABILITY INSURANCE
2.4.6 MAINTENANCE BONDS
2.5 PRECONSTRUCTION MEETING
2.6 FINAL PROJECT APPROVAL
2.7 PROJECT PHASING
APPENDIX 2A: PORT ORCHARD STANDARD PLAN NOTES
CHAPTER 3 - EROSION AND SEDIMENTATION
CONTROL
3.1 OVERVIEW
3.1.1 EROSION AND SEDIMENTATION
EROSION
SEDIMENTATION
IMPACTS OF EROSION AND SEDIMENTATION
3.2 MINIMUM REQUIREMENTS
3.2.1 PERFORMANCE
3.2.2 DESIGN STORM
3.2.3 MINOR DEVELOPMENTS
3.2.4 MAJOR DEVELOPMENTS
3.2.5 EROSION AND SEDIMENTATION CONTROL PLAN
3.2.6 CLEARING AND COVERING
LEVEL 1 CONTROLS
LEVEL 2 CONTROLS
APPENDIX 3A ESC BEST MANAGEMENT PRACTICES REFERENCE GUIDE
APPENDIX 3B ESC BEST MANAGEMENT PRACTICES
CHAPTER 4 - GRADING
4.1 INTRODUCTION
4.2 APPLICABILITY
4.2.1 PERMIT EXEMPTIONS
4.2.2 ENGINEERED GRADING
4.3 SEPA REQUIREMENTS
4.4 REVIEW COORDINATION
4.5 PERMIT REQUIREMENTS
4.5.1 CONSTRUCTION LIMITS
4.5.2 CHANGED CONDITIONS, STOP WORK ORDER AND PERMIT
REVOCATION
4.5.3 ENGINEERS' NOTIFICATION OF NONCOMPLIANCE
4.5.4 PERMIT TIME LIMIT
4.5.5 INSPECTIONS
4.5.6 COMPLETION OF WORK AND FINAL APPROVAL
4.6 GRADING STANDARDS
4.6.1 SOILS ENGINEERING INVESTIGATION REPORT
4.6.2 GEOTECHNICAL ENGINEERING INVESTIGATION REPORT
4.6.3 EXCAVATIONS
GENERAL
SLOPE STEEPNESS
4.6.4 FILLS AND EMBANKMENTS
GENERAL
PREPARATION OF GROUND
FILL MATERIAL
COMPACTION
SLOPE
STRUCTURES
4.6.5 SETBACKS
GENERAL
TOP OF CUT SLOPES
TOE OF FILL SLOPES
MODIFICATION OF SLOPE LOCATION
4.6.6 DRAINAGE AND TERRACING
GENERAL
TERRACE
SUBSURFACE DRAINAGE
DISPOSAL
INTERCEPTOR DRAINS
4.6.7 IMPERVIOUS SURFACES
4.6.8 EROSION CONTROL
APPLICANT'S RESPONSIBILITY
EMERGENCY CONTACT PERSON
SEALING THE SURFACE
REVEGETATION
NOTICE OF GRADING OR FILLING
CHAPTER 5 - STORMWATER QUANTITY CONTROL
FACILITIES
5.1 GENERAL REQUIREMENTS
5.1.1 PURPOSE AND SCOPE
5.1.2 RUNOFF CONTROL
PEAK RATE CONTROL
STREAMBANK EROSION CONTROL
VOLUME CONTROL
5.1.3 CLOSED DEPRESSIONS
MINIMUM REQUIREMENTS
5.1.4 EXEMPTIONS FROM RUNOFF CONTROL REQUIREMENTS
5.2 HYDROLOGY AND DESIGN STRATEGIES
5.2.1 COMPUTATION METHODS
HYDROGRAPH ANALYSIS
LEVEL -POOL ROUTING
5.2.2 BASIC RUNOFF PARAMETERS
PRECIPITATION
CURVE NUMBERS
TIME OF CONCENTRATION
5.2.3 DESIGN STRATEGIES
DRAINAGE BASIN DELINEATION
OFF -SITE CONTRIBUTING RUNOFF
BYPASS AREAS
5.3 FACILITY DESIGN REQUIREMENTS
5.3.1 PONDS
SITE CONSTRAINTS
POND GEOMETRICS
SETBACKS
OVERFLOW
FENCING
SIGNING
BERM EMBANKMENT/SLOPE STABILIZATION
ACCESS
5.3.2 PARKING LOT PONDS
5.3.3 DETENTION TANKS AND VAULTS
GENERAL DESIGN CRITERIA
MATERIALS & STRUCTURAL STABILITY
ACCESS
5.3.4 CONTROL STRUCTURES
CONTROL STRUCTURE DESIGN CRITERIA
RECTANGULAR NOTCHED, SHARP CRESTED WEIR
V-NOTCH, SHARP CRESTED WEIR
5.3.5 RETENTION FACILITIES
SOILS IDENTIFICATION AND DETERMINATION OF
INFILTRATION RATE
DESIGN CRITERIA FOR INFILTRATION TRENCHES AND PONDS
RETENTION PONDS
INFILTRATION TRENCHES
5.3.6 INDIVIDUAL DOWNSPOUT INFILTRATION SYSTEMS
CHAPTER 6 - STORMWATER QUALITY CONTROL
FACILITIES
6.1 KNOWN POLLUTANTS IN STORMWATER
6.2 WATER QUALITY DESIGN STORM
6.3 BIOFILTRATION BMPs
6.3.1 SWALE DESIGN CRITERIA
6.3.2 FILTER STRIP DESIGN CRITERIA
6.4 WET PONDS AND WET VAULTS/TANKS
6.4.1 WET POND DESIGN
6.4.2 WET VAULT AND WET TANK DESIGN
6.5 SPILL CONTROL OIL/WATER SEPARATORS
CHAPTER 7 - COLLECTION AND CONVEYANCE
FACILITIES
7.1 PURPOSE AND SCOPE
7.2 GENERAL DESIGN CRITERIA
7.2.1 ROUTE DESIGN
7.2.2 EASEMENTS AND SETBACKS
7.2.3 MAINTENANCE ACCESS
7.2.4 DATUM
7.3 DETERMINATION OF DESIGN FLOW
7.3.1 DESIGN EVENT
7.3.2 DESIGN METHODOLOGY
7.3.3 RATIONAL METHOD
7.4 CAPACITY ANALYSIS
7.5 DESIGN CRITERIA FOR OPEN CHANNELS
7.5.1
GEOMETRY
7.5.2
FREEBOARD
7.5.3
CHANNEL LINING
7.5.4
CHECK DAMS2
7.5.5
CHANNEL LOCATION
7.5.6
BIOFILTRATION SWALES
7.6 DESIGN CRITERIA FOR CULVERTS
7.6.1 ACCEPTABLE PIPE MATERIAL
7.6.2 HEADWALLS
7.6.3 GENERAL CULVERT DESIGN CRITERIA
7.7 DESIGN CRITERIA FOR PIPE SYSTEMS
7.7.1
ACCEPTABLE PIPE MATERIAL
7.7.2
PIPE ALIGNMENT
7.7.3
CONNECTIONS TO PIPE SYSTEMS
7.7.4
VERTICAL ALIGNMENT OF PIPES AT STRUCTURES
7.7.5
DOWNSIZING OF PIPES
7.7.6
GENERAL PIPE CRITERIA
7.7.7
STEEP SLOPE INSTALLATION
7.7.8
PRIVATE SECONDARY DRAINAGE SYSTEMS
7.8 DESIGN CRITERIA FOR INLET STRUCTURES
7.9 DESIGN CRITERIA FOR OUTFALLS
7.10 STORMWATER PUMPS
7.11 BRIDGES
CHAPTER 8 - OPERATION AND MAINTENANCE
8.1 OPERATION AND MAINTENANCE MANUAL
8.2 OPERATION AND MAINTENANCE REQUIREMENTS
8.2.1 RESPONSIBIITY FOR MAINTENANCE
8.2.2 MAINTENANCE FREQUENCY
8.2.3 DISPOSAL OF WASTE FROM MAINTENANCE ACTIVITIES
8.2.4 CONTROL STRUCTURES AND CATCH BASINS
8.2.5 INFILTRATION BASINS
8.2.6 INFILTRATION TRENCHES, AND ROOF DOWNSPOUT
INFILTRATION TRENCHES
8.2.7 CONCRETE GRID AND MODULAR PAVEMENT
8.2.8 DETENTION PONDS, VAULTS AND TANKS
GENERAL
VEGETATION
SEDIMENT
ACCESS
NUISANCE CONDITIONS
8.2.9 BIOFILTRATION SWALES AND FILTER STRIPS
8.2.10 OIL/WATER SEPARATORS
APPENDIX 8A CITY OF PORT ORCHARD MAINTENANCE GUIDELINES
CHAPTER I
INTRODUCTION
CHAPTER I
INTRODUCTION
CONTENTS
1.1
ADDITIONAL REFERENCES...........................................................................1-2
1.2
PENALTIES AND ENFORCEMENT................................................................1-2
1.3
HAZARDS EXISTING.......................................................................................1-3
1.4
ENGINEER'S RESPONSIBILITIES..................................................................1-3
1.4.1 PROJECT ENGINEER'S RESPONSIBILITIES.....................................1-3
1.4.2 SOIL ENGINEER'S RESPONSIBILITIES.............................................1-4
1.4.3 GEOTECHNICAL'S ENGINEER RESPONSIBLITIES ........................1-5
1.5
TRANSFER OF ENGINEER'S RESPONSIBILITY..........................................1-5
1.6
CITY STAFF ASSISTANCE..............................................................................1-5
The Port Orchard Stormwater Design Manual is included as Exhibit "A" of the Port Orchard
Stormwater Management Ordinance.
1.1 ADDITIONAL REFERENCES
There are a number of references and standards available that address stormwater management in
the Puget Sound basin. Where conflicts exist between this manual and those other references or
standards, this manual will prevail.
However, this manual does not attempt to include all design procedures and standards related to
stormwater quantity and quality control. This is particularly true in its coverage of hydrological
analysis methods. The design engineer is expected to refer, as necessary, to the following
publications.
The Washington State Department of Ecology, Stormwater Management manual for the
Puget Sound Basin ("Technical Manual").
King County, Washington, Surface Water Design Manual.
The publication Technical Release 55: Urban Hydrology for Small Watersheds, 2°a Edition,
together with a computer program on floppy disk, available from the National Technical
Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield,
Virginia 22161 (Telephone (703) 487-4650). Request NTIS ACCESS # PB 87-101580/AS
A08. This publication can be viewed and copied at the Kitsap County Conservation District
Office in Port Orchard.
WSDOT/APWA Standard Specifications for Road, Bride, and Municipal Construction.
Address orders for all WSDOT manuals to the Engineering Publications Branch,
Transportation Building, Olympia, WA 98504-5201, or telephone (360) 753-6028.
Washington State Department of Transportation Hydraulics Manual.
1.2 PENALTIES AND ENFORCEMENT
Unless exempt from the terms of the Stormwater Management Ordinance, no person, firm,
corporation, or entity shall do any grading, filling, clearing, excavating, ditching, or create an
impervious surface, unless the work is in accordance with a valid permit issued by the City. Each
project site, which may be composed of one or more contiguous parcels of land, shall have a separate
permit.
Port Orchard is authorized to make inspections and take such actions as required to enforce the
provisions of the Stormwater Management Ordinance. The City has the authority to enter onto land
for the purpose of inspection of site development activities or to perform any duty imposed upon the,
1-2
City by ordinance, provided that the City presents proper credentials and makes a reasonable effort
to contact the property owner before entering onto that property.
The Director may require the owner of a site to remove any unpermitted or illegal facilities placed,
constructed, or installed on the site, and to implement a plan for the restoration or stabilization of
the site or correct work that has adversely impacted adjacent or downstream property owners, with
all costs borne by the owner.
Any person, firm, or corporation violating any of the provisions of the Stormwater Management
Ordinance, whether they be the property owner, the Applicant, the contractor, or any other person
acting with or without the authorization of the property owner or Applicant, shall be subject to the
penalties prescribed in Section 11 of the Stormwater Management Ordinance.
1.3 HAZARDS EXISTING
Whenever the Director determines that any excavation, embankment, erosion/sedimentation control,
or drainage facility has become a safety hazard; endangers property; or adversely affects the safety,,
use or stability of a public way, critical area, or drainage course, the owner of the subject property,
and/or the person or agent in control of the property will be required to repair or eliminate the hazard
in conformance with the requirements of the Stormwater Management Ordinance and this manual.
At the time that the Director makes the determination that a hazardous condition exists, the property
owner and/or person or agent in control of the property will be notified in writing that the hazard
exists. The Director will order the specific work to be undertaken or will order that an engineering
design be submitted for review and approval by the Director, and will specify the time period within
which the hazardous conditions be repaired or eliminated. In the event that the owner and/or the
person or agent in control of the property fails to comply with this order, that person shall be subject
to the penalties specified in the Stormwater Management Ordinance, Section 11.
1.4 ENGINEER'S RESPONSIBILITIES
Much of the information covered in this manual is addressed to professional engineers. In order to
assist the professional engineer in fulfilling his/her responsibilities related to a development project,
the following comments is included addressing the City's expectations regarding the responsibilities
of the engineer:
1.4.1 PROJECT ENGINEER'S RESPONSIBILITIES
All engineered plans submitted to the Director for review and approval shall be prepared by a
professional engineer, licensed in the State of Washington. The engineer shall be responsible for
the following:
The engineer shall prepare site development construction plans and erosion and
sedimentation control plans meeting the standards and requirements of the Stormwater
Management Ordinance, including this manual. The engineer shall remain responsible for
the accuracy, completeness and scope of all work submitted to the Director. Should errors,
omissions or inaccurate data due to the engineer's work come to the Director's attention in
1-3
the future, the engineer shall be responsible for correcting all deficiencies, when necessary,
and shall be responsible for any damages resulting from the incorrect work.
2. The engineer shall incorporate recommendations from soils engineering reports, geotechnical
engineering reports, and any other engineering recommendations into the site development
construction plans and the erosion and sedimentation control plans.
3. The engineer shall, when required by the Director, be responsible for the professional,
inspection and approval of the construction within the engineer's area of technical expertise.
This responsibility shall include, but not be limited to, inspection and approval as to the
establishment of line, grade, and drainage of the development area. In conjunction with the
carrying out of this responsibility, copies of any on -site inspection reports shall be submitted
by the engineer to the Director, when so requested.
4. The engineers shall act as the coordinating agent in the event the need arises for liaison
between the owner, other professionals, contractors, the City, and other agencies.
The engineer shall be responsible for the preparation of revised plans and the submittal of
as -built plans upon completion of work.
6. The engineer shall be responsible for verification of excavation and embankment quantities,
detention/retention pond volumes, and slope steepness.
1.4.2 SOIL ENGINEER'S RESPONSIBILITIES
When a soils investigation report is required, the minimum responsibilities of the soils engineer shall
be as follows:
The preparation of any required soils investigation report.
2. All reports, field data, test data, and recommendations shall be submitted to the Project
Engineer, and to the Director.
When required by the Project Engineer or the Director, the soils engineer shall provide
professional inspection and approval concerning the preparation of ground to receive fills,
testing for required compaction, stability of all finished slopes, and the design of
embankment fills, incorporating recommendations of the geotechnical engineer.
4. When required by the Project Engineer of the Director, the soils engineer shall prepare a final
soils report which includes locations and elevations of field density tests, summaries of field
and laboratory tests and other substantiating data and comments on any changes made during
site development.
1-4
1.4.3 GEOTECHNICAL ENGINEER'S RESPONSIBILITIES
When a geotechnical engineering report is required, the minimum responsibilities of the geotechnical
engineer shall be as follows:
1. The preparation of any required geotechnical engineering investigation report.
2. All reports, field data, test data, and geotechnical engineering recommendations shall be
submitted to the Project Engineer and to the Director.
3. When required by the Project Engineer or the Director, the geotechnical engineer shall
provide professional inspection and approval concerning the adequacy of natural ground for
receiving fills and the stability of cut or fill slopes with respect to geological matters, and the
need for subdrains or other groundwater drainage devices.
4. When required by the Project Engineer or the Director, the geotechnical engineer shall
prepare a final report following the completion of work, which includes a final description
of the geology of the site including any new information disclosed during the site grading,,
and the effect of same on recommendations incorporated into the approved site development
construction plans.
5. When required by the Director, the geotechnical engineer shall, following the completion of
site grading, provide approval as to the adequacy of the site for the intended use as affected
by geologic factors.
1.5 TRANSFER OF ENGINEERING RESPONSIBILITY
For major developments, there shall at all times during the course of work be an engineer of record
for the project performing the function of Project Engineer. If the engineer of record is changed
during the course of the work, the work shall be stopped until the replacement engineer has agreed
to accept the responsibilities of the Project Engineer.
1.6 CITY STAFF ASSISTANCE
Department of Public Works staff is available to discuss or provide clarification for any of the
matters addressed in this manual. Inquiries should be directed to:
City of Port Orchard
Department of Public Works
216 Prospect Street
Port Orchard, WA 98366
(360) 876-4991
Fax: (360) 876-4980
1-5
CHAPTER 2
SUBMITTAL REQUIREMENTS
CHAPTER 2
SUBMITTAL REQUIREMENTS
CONTENTS
2.1
INTRODUCTION............................................................................................... 2-2
2.2
LAND USE PERMITS - PRELIMINARY.........................................................
2-2
2.2.1 PRELIMINARY DRAINAGE REVIEW................................................2-2
2.3
STORMWATER MANAGEMENT PERMIT ....................................................
2-5
2.3.1 WHEN PERMIT REQUIRED.................................................................
2-5
2.3.2 APPLICATION PROCESS.....................................................................
2-5
2.3.3 APPLICATION SUBMITTAL DOCUMENTS MINIMUM
REQUIREMENTS...................................................................................
2-7
2.4
COVENANTS, SURETIES AND LIABILITY INSURANCE ........................2-20
2.4.1 SITE STABILIZATION........................................................................2-20
2.4.2 PERFORMANCE COVENANT FOR SITE STABILIZATION.........
2-20
2.4.3 PERFORMANCE SURETY FOR SITE STABILIZATION ................2-21
2.4.4 PERFORMANCE BOND FOR UNCOMPLETED SITE
IMPROVEMENTS................................................................................
2-21
2.4.5 COMMERCIAL LIABILITY INSURANCE ........................................
2-22
2.4.6 MAINTENANCE BONDS....................................................................2-22
2.5
PRECONSTRUCTION MEETING..................................................................
2-22
2.6
FINAL PROJECT APPROVAL........................................................................
2-23
2.7
PROJECT PHASING........................................................................................
2-25
APPENDIX 2A: CITY OF PORT ORCHARD STANDARD PLAN NOTES
SUBMITTAL REQUIREMENTS
2.1 INTRODUCTION
This chapter describes the requirements for submittal of plans and other documents for
review by the City of Port Orchard Department of Public Works.
The requirements of this manual cover two basic types of reviews: preliminary drainage
reviews and final review of construction plans.
1. Preliminary drainage reviews are a requirement for various land use applications and land
use policies administered by the City of Port Orchard Planning Department.
2. Final review of construction plans and related documents is part of the Stormwater
Management Permit process administered by the Department of Public Works prior to
commencement of construction activities on a project site. Often, the application for a
Stormwater Management Permit must be preceded by the preliminary approval of a land
use permit application.
2.2 LAND USE PERMITS - PRELIMINARY
The preparation and submittal of any engineering plans, reports, or supporting documents
related to an application for preliminary land use approval shall be subject to current City
land use ordinances, and must comply with current policies of the City of Port Orchard
Planning Department relating to land use permit application procedures.
2.2.1 PRELIMINARY DRAINAGE REVIEW
When, as part of a land use permit application, a preliminary drainage review is required, the
submittal requirements for such a drainage review shall be as follows:
All preliminary drainage review documents must be submitted, along with other land use
permit application documents, to the City of Port Orchard Department of Public Works. The
number of copies of documents to be submitted for the preliminary drainage review shall be
determined by the Department of Public Works.
A preliminary review fee must be paid to the City of Port Orchard upon submittal of the land
use application.
Upon satisfactory completion of the review, the Department of Public Works' recommended
conditions of Preliminary Approval will be submitted to the Planning Department for
inclusion in the Staff Report to the City Council.
2-2
PRELIMINARY DRAINAGE PLAN - CONTENTS
1. Preferred sheet size is 24" x 36". Minimum sheet size is 18" x 24" and maximum sheet
size is 36" x 48".
2. Title block, including name of proposed project/development.
3. North arrow indicator, drawing scale, Section -Township -Range.
4. The plan view of detailed drainage plans must be drawn at an engineering scale no
smaller than V = 100'.
5. Professional Engineer's seal, signed and dated.
6. Vicinity map, showing project boundaries, streets with street names, shorelines if any,
city limit boundaries if any, and distance to nearest intersection.
7. Legal description of project site.
8. Name, address, and telephone number of project developer.
9. Name, address, and telephone number of project engineer.
10. Symbol legend.
11. Property boundaries, dimensions, and area (in square feet or acres).
12. Contour lines, at maximum 5' intervals, with source to datum identified.
13. Adjoining street names and right-of-way widths.
14. Existing and proposed structures and other impervious surfaces such as parking lots,
driveways, patios, buildings, etc.
15. Existing drainage facilities, such as pipes, catch basins, channels, ponds, etc.
16. Location of on -site and adjacent off -site waste treatment systems, such as septic tanks
and distribution systems.
17. Existing and proposed utilities, with easements identified.
18. Established buffers, significant trees, and natural vegetation easements, if any.
19. Natural drainage channels, wetlands, water bodies, etc.
2-3
20. Areas where natural vegetation is to be left undisturbed.
21. The location of on -site and adjacent off -site wells and underground storage tanks.
22. Show an approximate plan for the collection and conveyance of stormwater through the
project site. As a minimum, show by flow arrows the directions of proposed stormwater
flow and indicate the method for conveyance (pipe, ditch, biofiltration swale, overland
flow, etc.).
23. Show the proposed locations and sizes of stormwater quantity and quality control
facilities.
24. Preliminary road profiles, showing existing grade and proposed finish grade.
PRELIMINARY DRAINAGE REPORT
Preliminary drainage documents shall include a Preliminary Drainage Report, prepared by
a civil engineer. This report shall include, as a minimum, the following elements:
1. Professional Engineer's seal, signed and dated.
2. Description of project location.
3. Description of pre -development site conditions.
4. Downstream drainage analysis - Level 1 Analysis (see description in this chapter).
5. Description of proposed development, including description of proposed developed site.
6. Description of proposed stormwater improvements, including conveyance, stormwater
quantity control facilities, and stormwater quality control facilities.
7. Describe design method utilized, names of any computer software routines utilized in
design process, and reference any design standards utilized.
8. Preliminary hydrological analysis, including pre -development and post -development
runoff hydrographs for the project site.
9. Preliminary sizing of storage facilities proposed for stormwater quantity and/or quality
control.
10. Preliminary report addressing potential erosion and sedimentation impacts during
construction, and general proposals for the mitigation of these impacts. This report
should include a proposal regarding the implementation of Level 1/Level 2 erosion and
sedimentation controls (See Chapter 3, Erosion and Sedimentation Control).
2-4
11. Vicinity map, noting Section, Township, and Range.
12. Pre -development and post -development basin maps, showing boundaries of project, any
off -site contributing drainage basins, on -site drainage basins, time of concentration
routes, approximate locations of all major drainage structures within the basins, and the
course of stormwater originating from the subject property and extending all the way to
Puget Sound or to the closest receiving body of water (lakes, creeks, etc.). All basin
maps must be legible and at a specified scale.
13.Other resource material such as soils maps, isopluvial maps, nomographs, charts, figures,
tables, etc.
14. Surface/subsurface soil test results and test locations (when retention/infiltration is
proposed).
2.3 STORMWATER MANAGEMENT PERMIT
2.3.1 WHEN PERMIT REQUIRED
No site development activity, including land clearing, grading or other construction activity,
shall take place on a development site prior to the issuance of a Stormwater Management
Permit. Site development activities requiring a Stormwater Management Permit are as listed
in Section 3(3) of the Stormwater Ordinance.
2.3.2 APPLICATION PROCESS
Prior to commencing site development activities on a development site, the owner of the
development must submit to the Department of Public Works a completed Stormwater
Management Permit Application.
Following submittal of a Stormwater Management Permit Application, the Director will then
make a determination of what items must be submitted for review prior to the issuance of the
permit. Among items required for review are the following:
Engineered Drainage Plan, Drainage Report, Grading Plan, and Erosion Control Plan,
required for site activities which meet the criteria listed in Section 3(6) of the
Stormwater Ordinance.
2. Abbreviated Plan (non -engineered):
Required for site activities falling below the thresholds described in Section 3(6) of
the Stormwater Ordinance.
2-5
4. Geotechnical Analysis, Soils Report, when required by Section 3 of the Stormwater
Ordinance.
Upon submittal of the required documents, the Stormwater Management Permit Application
will be scheduled for review. Applications that require only an Abbreviated Plan will be
grouped with other applications requiring only an Abbreviated Plan and will be reviewed in
the order received. All other applications will be grouped separately and will be reviewed
in the order received among that group. In the event that, during the review of an application
that included an Abbreviated Plan, it is determined that engineering will be required, the
applicant will be notified of the specific requirements.
Once review has begun on an application, it will continue without further delay. In the event
that additional information is requested or changes or revisions are requested for items
previously submitted, a time deadline will be given for the resubmittal of requested items.
As long as requested items are submitted within this deadline, the review will continue
without interruption. However, in the event that items are not submitted within the requested
time, the City may elect to suspend review. Once review has been suspended, priority will
no longer be given to that application. Upon receipt of the required items, review will again
be scheduled as if it were a new application.
Upon the satisfactory completion of the application review, the required final construction
plans will be marked "Approved for Construction by City of Port Orchard".
The Stormwater Management Permit can then be issued, subject to the submittal of the
following:
Payment of all permit fees.
2. Evidence of issuance of any permits required by other agencies.
Performance bond, or Performance Covenant for Site Stabilization, as required by
the Director.
4. Evidence of liability insurance, as required by the Director.
5. Recording of any required off -site construction -related easements.
At the time of issuance of the Stormwater Management Permit, a preconstruction meeting
must be scheduled with the Department of Public Works if, during the permit application
review, it has been determined that such a meeting is required.
Unless a preconstruction meeting is required, a permit placard will be issued at the time of
the permit issuance. This placard must be posted in clear view on the project site. Work
shall not commence until the permit placard has been properly posted on the site. The
placard must remain posted on the site throughout construction and may not be removed
until all construction is completed and accepted by the Director.
In the event that a preconstruction meeting is required, the permit placard will be issued at,
the preconstruction meeting.
2.3.3 APPLICATION SUBMITTAL DOCUMENTS: MINIMUM
REQUIREMENTS
ABBREVIATED PLAN
Abbreviated Plans need not bear the seal of a licensed professional engineer. The number
of copies of documents to be submitted for the preliminary drainage review shall be
determined by the Department of Public Works.
As a result of the review of the Stormwater Management Permit Application for which an
Abbreviated Plan has been submitted, the Department of Public Works may attach conditions
on the project as necessary to control erosion and runoff that may include but not be limited
to:
1. Drainage control measures that the Director deems appropriate for the size of the project.
2. Erosion control best management practices and other measures as appropriate to meet the
intent of this manual..
3. If the project would exacerbate existing or forecasted downstream flooding or water
quality problems, or if the project drains to a closed depression, the Director may impose
stormwater quality/quantity control measures and require an engineered Drainage and
Erosion Control Plan.
Plans shall be prepared utilizing a straight edge and features shall be drawn to scale. The
drawing shall be sufficiently clear and of a large enough scale to clearly delineate the
footprint of structures and other features described above.
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The accepted abbreviated plan, together with the conditions imposed by the Department of
Public Works following their review of the application, shall be kept on the project site
during construction and made available to the City's inspectors upon request.
The abbreviated plan shall contain the following information:
1. Name, address, and telephone of the Applicant.
2. Name, address, and telephone of the person preparing the plan.
3. Parcel number(s) and legal description of property.
4. Scale and north arrow.
5. Legend, if symbols are used that are not labeled in the plan.
6. Vicinity map of sufficient clarity to locate the property.
7. Property boundaries, dimensions, and area (in square feet or acres).
8. Contour lines from the best available source, spot elevations, or indications of direction
and steepness of slopes, with the source clearly identified.
9. Adjoining street names.
10. Existing and proposed structures and other impervious surfaces such as parking lots,
driveways, patios, buildings, etc.
11. Location of on -site and adjacent off -site waste treatment systems, such as septic tanks
and distribution systems.
12. Existing and/or proposed utilities, with easements identified.
13. Established buffers, significant trees, and natural vegetation easements, if any.
14. Natural drainage channels, wetlands, water bodies, etc.
15. Clearing limits.
16. Areas to be graded, filled, excavated, or otherwise disturbed. The location of graded
slopes should be indicated, together with the proposed steepness and height. The
location of stockpiles, haul roads and disposal sites shall also be indicated.
17. The location of on -site and adjacent off -site wells, underground storage tanks, etc.
wil
18. The location and type of erosion and sedimentation control measures proposed.
EROSION AND SEDIMENTATION CONTROL PLAN
1. All Erosion and Sedimentation Control Plans shall be prepared by and bear the stamp of
a professional civil engineer, licensed by the State of Washington.
2. The Erosion and Sedimentation Control Plan shall include at least the following
information:
a) Existing topography, as per the requirements for a drainage plan listed above.
b) Soil types, together with the location of any soil test pits or infiltration test sites.
c) Clearing and grubbing limits.
d) Finished grade.
e) Locations of all existing and proposed channels, swales, or drainage pipes which
either convey offsite stormwater through or route stormwater around the construction
area.
f) Locations of all proposed erosion and sedimentation control facilities.
g) Details of all proposed erosion and sedimentation control facilities.
h) The phasing of any erosion and sedimentation control work shall be clearly indicated
in the plan.
i) Separate plans for Level 1 and Level 2 erosion and sedimentation controls may be
necessary, when both Level 1 and Level 2 controls are required.
j) When sedimentation ponds are proposed, at least one cross section detail is required.
k) Erosion and sedimentation control plans shall include plans for mulching and
revegetation. Plans shall also include detailed planting procedures, seed/plant
specifications, and plant maintenance specifications.
1) Erosion and sedimentation control plans shall include, as a minimum, the standard
erosion and sedimentation control notes contained at the end of this chapter.
m) Erosion and sedimentation control plans shall include the name, address, and 24-hour
contact telephone number(s) of the designated emergency contact person. In
addition, plans shall include the name, address, and telephone number of the project
owner and the Project Engineer.
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n) Erosion and sedimentation control plans shall include a detailed listing of the
construction sequence.
ENGINEERED GRADING PLAN
1. All Engineered Grading Plans shall be prepared by and bear the stamp of a
professional civil engineer, licensed by the State of Washington.
2. The plan view shall be no smaller than 1" = 100'. Recommended scales are 1" = 50'
(Horizontal); 1" = 5' or 1" =10' (Vertical).
3. The first sheet, or cover sheet if one is provided, must include the following:
a) North arrow; vicinity map showing project boundaries; streets with street names;
shorelines, if any; city limit boundaries, if any; and section -township -range.
Reproductions of copyrighted materials without the permission of the owner(s) are
not acceptable.
b) Legal description of project site.
c) Name, address, and telephone number of owner of project.
d) Name, address, and telephone number of project engineer.
e) Datum for project.
0 Legend, in the event that symbols are used in plans.
g) Existing topography, as per the requirements for a topographic map for drainage
plans listed below.
4. Engineered Grading Plans shall include at least the following information:
a) Existing topography, as per the requirements for a drainage plan listed above.
b) The location of any soil test pits.
c) Clearing and grubbing limits.
d) Finished grade contours.
e) Locations of all existing channels, swales or drainage pipes that either convey offsite
stormwater through the project site, or collect and discharge site runoff from the
project site.
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0 Locations of all existing slopes steeper than 2:1.
g) Information concerning wetlands, environmentally sensitive areas, water -courses,
natural buffer areas, and similar applicable information.
h) Locations of areas to be graded, filled, excavated, or otherwise disturbed. The
location of tops and toes of graded slopes should be indicated, together with the`
proposed steepness and height of these slopes. The location of stockpiles, haul roads,
and disposal sites shall also be indicated.
i) Notations of quantities, in cubic yards, of excavation and/or fill throughout the
project site.
j) Locations of drainage structures (pipes, channels, catch basins, ponds, etc.) which are
to be constructed as a part of the grading plan.
k) Information concerning construction methods, fill material specifications, source of
fill material, compaction information, haul routes, and other construction information
when known and applicable.
1) Engineered Grading Plans shall include, as a minimum, the standard grading notes
contained at the end of this chapter.
m) Engineered Grading Plans shall include a detailed schedule for inspections by the
City.
ENGINEERED DRAINAGE PLANS
It is the responsibility of the Project Engineer to ensure that engineering plans are sufficiently
clear and concise to construct the project in proper sequence, using specified methods and
materials, with sufficient dimensions to fulfill the intent of the design guidelines contained
in this manual.
All plan reproductions submitted for review must be of sufficient quality of reproduction,
draftsmanship, line density, text size, and presentation of information to assure accurate
recognition and understanding of plan details by reviewers and construction personnel.
Plans submitted for review which contain deficiencies in legibility or presentation of
information which hinder the ability of personnel to properly evaluate proposed facilities will
be returned to the Project Engineer and review will be suspended.
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The Engineered Drainage Plan shall contain the following information:
All Drainage Plans shall be prepared by and bear the date and the stamp and signature
of a professional civil engineer, licensed by the State of Washington.
2. At least one sheet must contain a plan view of the entire project site. In the event the
project site is sufficiently large that detailed drainage plans on any given sheet do not
encompass the entire project site, then the sheet containing the plan view of the entire
site must serve as an index to subsequent detailed plan sheets.
The plan view of detailed drainage plans shall be drawn at an engineering scale no
smaller than 1" = 100'.
4. The first sheet, or cover sheet if one is provided, must include the following:
a) Vicinity map, showing project boundaries; streets with street names; shorelines, if
any; city limit boundaries, if any; and section -township -range. Reproductions of
copyrighted materials without the permission of the owner(s) are not acceptable.
b) Legal description of project site.
c) Name, address, and telephone number of project owner.
d) Name, address, and telephone number of project engineer.
e) Datum for project.
f) Legend, in the event that symbols are used in plans.
Plans shall include a topographic map showing existing conditions for the site, including:
Existing topography for the site and extending 50' beyond project boundaries.
Existing topography for adjacent rights -of -way must be included for the full
width of right-of-way. Slopes steeper than 25% shall be identified, such as
by shading or cross -hatching.
2. Contours extending 50' beyond project boundaries and including the full
width of adjacent rights -of -way. Contours shall be at a maximum 5' vertical
elevation intervals.
3. Locations and elevations of at least two benchmarks in the project vicinity.
4. Existing structures, including all structures within 100' of project boundaries.
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5. Existing access locations for the project site.
6. Existing project boundaries, rights -of -way, easements, jurisdictional bound-
aries, and sectional boundaries. All shall be clearly identified by note or
symbol and key. Project boundaries shall include bearings and dimensions.
7. Adjacent streets, including street names, centerline and right-of-way
boundaries, and centerline bearings. Widths of adjacent rights -of -way shall
be noted.
8. Existing utilities, including franchised utilities located above or below ground
and also including existing drainage facilities that transport surface water
onto, across, or from the project site. Existing drainage pipes, culverts, and
channels shall include invert or flowline elevations.
9. Existing environmentally sensitive areas (e.g. gullies, ravines, swales,
wetlands, steep slopes, estuaries, springs, wetlands, creeks, lakes, etc.). For
natural drainage features, show direction of flow and 100 year flood plain
boundary (if applicable).
10. Existing wells, sanitary sewer systems and septic tanks and drainfields within
100' of project boundaries.
11. Existing fuel storage tanks.
Plans for proposed drainage improvements shall include the following:
1. Finished grades. Show the extent of cuts and fills by existing and proposed
contours, profiles, and/or other explicit designations.
2. Existing structures to be removed.
3. Proposed structures including roads and road improvements, parking surfaces,
building footprints, walkways, landscape areas, etc. Exact lines, grades, and
gradients of proposed public roadways shall be shown.
4. Proposed lot boundaries, tracts, easements. Also, proposed changes to project
boundaries, jurisdictional boundaries, rights -of -way boundaries.
5. Proposed utilities, showing exact line and grade of all proposed utilities at
crossings with the proposed drainage system.
6. Proposed sanitary sewers, septic tanks, drainfields, and water systems.
7. Proposed fuel storage tanks.
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8. Setbacks from existing environmentally sensitive areas.
9. Proposed drainage structures, including pipes, open channels, culverts, ponds,
vaults, biofiltration swales, infiltration facilities, outfalls, rip rap treatment,
energy dissipators, etc.
10. Plan views of drainage conveyance facilities for which there is no
accompanying profile view shall include the following information: pipe
sizes, pipe types and materials, lengths of runs, gradients and exact locations
of pipes or channels, structure identifier (e.g. catch basin/manhole number),
type of structure (e.g. Type 2 CB), exact location of structures (e.g. station
and offset, or dimensioning), invert elevations in/out of structures, and top
elevations of structures. Notes should be included referencing details, cross -
sections, profiles, etc.
11. Locations of all gutter or ditch flowlines, including flow arrows indicating
direction of flow. If a cul-de-sac is proposed as part of roadway system,
show spot flowline elevations at 25' intervals along the perimeter of the cul-
de-sac. Spot elevations at flowlines may also be necessary at intersections.
12. Indicate any proposed phasing of construction.
In existing and proposed rights -of -way, drainage conveyance facilities shall be shown in
profile view. Profile views shall include:
Existing and finish grades.
2. Proposed drainage pipes, channels and structures.
3. Existing underground utilities where such utilities cross proposed drainage
facilities.
4. Profile views shall include the following information: pipe sizes, pipe types
and materials, lengths of runs, gradients and exact locations of pipes or
channels, structure identifier (e.g. catch basin/manhole number), type of
structure (e.g. Type 2 CB), exact location of structures (e.g. station and offset,
or dimensioning), invert elevations in/out of structures, and top elevations of
structures. In order to minimize duplication of information where plan and
profile views appear on the same sheet, drainage facility information
provided in the plan view can be limited to the following: structure
identifier, type of structure, pipe types and materials, and lengths of runs.
Construction notes shall appear on drainage plans. These notes must include, as a
minimum, the Drainage Notes included at the end of this chapter.
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Details must be provided for all proposed drainage structures for which there is insufficient
information in the plan view. Details are not required for structures included in the
APWA/WSDOT Standard Plans, provided that the specific APWA/WSDOT Standard Plans
are referenced in the construction notes.
Cross sections must be provided for at least the following:
1. Roadways, including access roads.
2. Detention/retention ponds (including parking lot ponds and other multi -use,
facilities), wet ponds, and sediment ponds.
Proposed ditches and swales, including biofiltration swales.
DRAINAGE REPORT
The final Drainage Report shall be on 8-1/2" x 11" paper and maps shall be folded to 8-1/2"
x 11" size unless another format is approved prior to submittal.
All reports should contain the following elements:
1. Cover Sheet, including the project name, proponent's name, address and
telephone number, project engineer, and date of submittal.
2. Table of Contents, showing the page numbers for each section of the report,
including appendices.
3. Vicinity Map.
4. Project Description: Describe the type of permit(s) for which the proponent -
is applying, the size and location of the project site, address or parcel number
and legal description of the property, property zoning, etc. Also describe
other permits required (e.g. Hydraulic Project Approval, Corps of Engineers
404 Fill Permit, etc.). Describe the project, including proposed land use,
proposed site improvements, proposed construction of impervious surfaces,
proposed landscaping, etc.
5. Existiniz Conditions: Describe existing site conditions and relevant
hydrological conditions including but not limited to: project site topography,
land cover and land use; abutting property land cover and land use; offsite
drainage to the property; creeks, lakes, ponds, wetlands, ravines, gullies,
steep slopes, springs and other environmentally sensitive areas on or adjacent
to the project site; the location of any wells both "of record" and others on the
project site and on adjacent property within 100' of the project boundaries;
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the location of any existing fuel tanks, in -use or abandoned, within the
project boundaries; general soils conditions present within the project site;
whether or not the project site is located in a groundwater sensitive area
(reference reports); existing natural and manmade drainage facilities within
and immediately adjacent to the project site; points of discharge for existing
drainage from the project site. Include references to relevant reports such as
basin plans, flood studies, groundwater studies, wetland designation,
sensitive area designation, environmental impact statements, lake restoration
plans, water quality reports, etc. Where such reports impose additional
conditions on the Proponent, those conditions shall be included in the report.
6. Developed Site Drainage Conditions: Describe the land cover resulting from
the proposed project; describe the potential stormwater quantity and quality
impacts resulting from the proposed project; describe the proposal for the
collection and conveyance of site runoff from the project site, for the control
of any increase in stormwater quantity resulting from the project, and for the
control of stormwater quality.
7. Drainage Basin Description: Describe the drainage basin(s) to which the
project site contributes runoff, and identify the receiving waters for each of
these drainage basins.
8. Description of upstream basins, identifying any sources of runoff to the
project site. This should be based on a field investigation. Any existing
drainage or erosion problems upstream which may have an impact on the
proposed development should be noted.
9. Downstream Analysis: (See detailed description below) The initial drainage
report submittal must include a Level I Downstream Drainage Analysis, for
review by the City. Any further analysis of downstream conditions required
beyond the Level 1 analysis shall become a part of the drainage report and
must be submitted as part of the final drainage report.
10. Soils Report(s), where applicable, prepared by a qualified civil engineer.
11. Geotechnical Report(s), where applicable, prepared by a qualified civil
engineer.
12. Hydrological Analysis, prepared by a qualified civil engineer.
13. Basin Map(s), showing boundaries of project, any offsite contributing
drainage basins, onsite drainage basins, approximate locations of all major
drainage structures within the basins, and depict the course of stormwater
originating from the subject property and extending all the way to Puget
Sound or to the closest receiving body of water (lakes, creeks, etc.).
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Reference the source of the topographic base map (e.g. USGS), the scale of
the map, and include a north arrow.
14. Hydraulic Design Computations, supporting the design of ALL proposed
stormwater conveyance, quantity and quality control facilities, and verifying
the capacity of existing drainage facilities. These computations may include
capacity and backwater analysis required either as part of the proposed
drainage design or as a part of the downstream drainage investigation, and
flood routing computations required for the design of detention/retention
storage facilities, for wetland impact analysis, or for flood plain analysis.
15. Erosion and Sedimentation Control Design Report and Computations,
including the following: a description of proposed Level 1 and Level 2
erosion control objectives and strategies; a description of erosion control
facilities and other temporary water quality facilities proposed; a description
of the revegetation plan for the project site; identification of areas of concern
regarding soil stability and/or water quality impacts; computations for the
sizing of temporary stormwater conveyance and quantity control facilities;
computations for the design and sizing of proposed sediment containment
facilities, etc.
16. Maintenance and Operation Manual: (See detailed description below).
17. Appendices: Include the following: Technical Information Report (See
sample at end of this chapter); copies of any additional relevant reports,
prepared by others, which support or corroborate the findings, conclusions,
or assumptions contained in the drainage report; copies of any additional
permits (or completed permit applications) required for the project.
DOWNSTREAM ANALYSIS
The initial drainage report submittal should include a Level 1 downstream drainage analysis,
for review by the City. This Level 1 analysis, as well as the location of the project in a -
drainage basin, will be used as a basis for determining whether a Level 2 and/or Level 3
downstream analysis will be required. Any further analysis of downstream conditions
required beyond the Level 1 analysis shall become a part of the drainage report and must be
submitted as part of the final drainage report.
o Level 1 Anal All proposed projects requiring a Stormwater Management Permit
shall include at least this level of analysis with the initial permit application. The
following steps should be completed for this level of analysis:
Define and physically verify the study area. The upstream portion of the
study area shall encompass the entire tributary drainage area (the area that
drains to the proposed project site). The remaining portion of the study area
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shall extend downstream of the proposed project discharge location to a point
on the drainage system where the proposed project site constitutes 15 percent
or less of the total tributary area, but in no event less than 1/4 mile.
2. Review all available resource information regarding existing and potential
water quality, runoff volumes and rates, flooding and streambank erosion
problems within the study area.
3. Physically inspect the existing on -site and off -site drainage system problems
reported in the resources.
4. On a map (minimum USGS 1:24000 Quadrangle Topographic Map) delineate
the study area, together with the drainage system onto and from the proposed
site.
5. Describe in a narrative form, observations regarding the makeup and general
condition of the drainage system.
6. Include such information as pipe sizes, channel characteristics, and
stormwater facilities.
7. Identify on the map and describe any evidence of the types of existing or
predicted problems listed below in Table 2-1. Following the review of the
Level 1 analysis, the City will determine whether a Level 2 analysis is
required, based on the evidence of existing or predicted problems.
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TABLE 2-1 EVIDENCE OF EXISTING OR PREDICTED PROBLEMS
Evidence of potential for contamination of surface waters.
2. Overtopping, scouring, bank sloughing or sedimentation.
3. Significant destruction of aquatic habitat or organisms (for example,
severe siltation or incision in a stream).
4. Evidence of potential for contamination of ground water.
o Level 2 Analysis: At the location of each existing or predicted water quality
and quantity problem identified in the Level 1 analysis, provide a rough
quantitative analysis to define and evaluate proposed mitigation for the
problem. This analysis should include the total composite drainage area
tributary to that location for pre -development and post -development runoff
conditions. For this level of analysis, it will be permissible to use non -survey
field data (collected with hand tapes, hand level and rods, etc.) and
approximate hydraulic computations using methods described in Chapter 7.
o Level 3 Analysis: A Level 3 analysis shall be performed for those existing
or predicted drainage problem locations where the Director determines that
the analysis results must be as accurate as possible. Examples of conditions
that might require a Level 3 analysis are: if the site is flat; if the system is
affected by downstream controls; if minor changes in the drainage system
could flood roads, buildings or septic systems; or if the proposed project will
contribute more than 15 percent of the total peak flow to the drainage
problem location. The Level 3 analysis is similar to the Level 2 analysis but
is a more precise quantitative analysis, utilizing field survey profile and
cross-section topographic data prepared by a licensed surveyor or
engineer.
o Solutions to Drainage Problems Identified by the Analysis: For any existing
or predicted off -site drainage problem, the design engineer must demonstrate
that the proposed project engineering plan has been designed so that it neither
aggravates the existing problem nor creates a new problem. As an
alternative, the applicant may arrange with the owners of the affected off -site
properties to install measures that will correct the existing or predicted
problem, subject to all applicable permit requirements.
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Any proposed drainage easements must be endorsed by the affected property owners
and be recorded prior to approval of the proposed project engineering plan. In some
cases, an existing drainage problem identified by the local government may be
scheduled for solution. In these cases, the applicant should contact the City to check
for potential cost sharing to solve the existing problem.
For any predicted off -site problem, the design engineer must demonstrate that the
proposed engineering plan has been designed to mitigate the predicted problem. As
an alternative, the applicant may arrange with the owners of off -site properties to
install measures that will mitigate the predicted problem. Any proposed drainage
easements must be endorsed by the affected property owners and be recorded prior
to approval of the proposed project engineering plan.
2.4 COVENANTS, SURETIES, AND LIABILITY INSURANCE
2.4.1 SITE STABILIZATION
Prior to the issuance of a Stormwater Management Permit and prior to beginning any
construction activity on a project site, the owner of the project will be required to record a
performance covenant or post a performance surety for site stabilization and erosion and
sedimentation control. In addition, the owner may be required to provide a Certificate of
Commercial Liability Insurance as outlined in Section 2.4.5 below.
This performance requirement for stabilization and erosion control should not be confused
with the performance bond accepted at the time of final plat recording as a surety for
construction items not yet completed. When a performance bond is accepted for a final plat
in lieu of construction completion, the surety or covenant for stabilization and erosion control
will be released, and the new performance bond shall cover site stabilization and erosion
control along with the other incomplete construction items.
2.4.2 PERFORMANCE COVENANT FOR SITE STABILIZATION
For project sites with less than 5 acres of land disturbing activity, a Performance Covenant
may be recorded in lieu of performance surety for site stabilization prior to issuance of the
Stormwater Management Permit to guarantee Port Orchard that temporary erosion and
sedimentation control and permanent site stabilization measures will perform in accordance
with the Stormwater Management Ordinance. This Covenant shall be recorded with the
Kitsap County Auditor and shall run with the land until such a time as Port Orchard issues
final acceptance of the permitted activities, or until a separate performance bond is posted
prior to final plat approval. Upon issuance of final project approval, the Department of
Public Works will record a document that extinguishes the Performance Covenant.
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2.4.3 PERFORMANCE SURETY FOR SITE STABILIZATION
The term "Bond" as defined in the ordinance shall mean a surety bond, assignment of funds,
or irrevocable bank letter of credit. For project sites with 5 or more acres of land disturbing
activity, a Performance Bond shall be posted prior to issuance of a Stormwater Management
Permit to guarantee the City that temporary erosion and sedimentation control and permanent
site stabilization measures will perform in accordance with the ordinance. The amount of
the Performance Bond shall be as follows:
o One hundred fifty percent (150%) of the estimated cost of performing minor grading
and installing temporary erosion and sedimentation control, and permanent site
stabilization measures to bring the construction site into compliance with the
ordinance. A cost estimate shall be submitted by the project engineer subject to the.
approval of the Director. The minimum amount of the "Bond" shall be five thousand
dollars ($5,000.00).
(OR)
o One thousand dollars ($1,000.00) per acre of land disturbing activity. No engineer's
estimate is required.
If the site work is determined by the Director to be in violation of the Stormwater
Management ordinance, the City may use the Performance Bond to provide temporary and
permanent site stabilization.
All Performance Bonds shall run continuously until released by the City, and shall not be
subject to an expiration or cancellation date.
2.4.4 PERFORMANCE BOND FOR UNCOMPLETED SITE IMPROVEMENTS
For single family residential developments, a Performance Bond shall be provided prior to
the final recording of the plat/PUD, guaranteeing completion of all site improvements not
yet completed. The amount of the Performance Bond shall be one -hundred fifty percent
(150%) of the estimated cost of said improvements. The estimated cost of the construction
shall be determined by a civil engineer subject to the approval of the Director.
All Performance Bonds shall run continuously until released by the City, and shall not be
subject to an expiration or cancellation date.
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2.4.5 COMMERCIAL LIABILITY INSURANCE
The owner of any project must provide a Certificate of Liability Insurance to the Department
of Public Works prior to issuance of a Stormwater Management Permit. The liability
insurance shall remain in force until final project approval is issued by the City. The
commercial liability insurance shall be in the amount of not less than one million dollars
($1,000,000.00) combined single limit bodily injury and property damage, with a two million
dollar ($2,000,000.00) aggregate. Such insurance shall include the City of Port Orchard, its
officers and employees as additional insureds, with respect to the terms and conditions of the
policy.
2.4.6 MAINTENANCE BONDS
A maintenance bond is required for residential plats/PUD's and other projects for which
maintenance of the stormwater facilities and/or roads is to ultimately be taken over by the
City.
Prior to the final approval of construction and release of any performance sureties, a
Maintenance Bond must be posted and maintained by the project owner for a period of two
(2) years. The Maintenance Bond shall guarantee the stormwater facilities and roads
constructed under permit against design defects and/or failures in workmanship, and shall
guarantee that the facilities constructed under the permit will be regularly and adequately
maintained throughout the maintenance period. At the end of this time, the City will inspect
the system and, when the facility is acceptable and eighty percent (80%) of the lots in that
phase have been improved, the City will take over the maintenance and operations of the
system. In the event that eighty percent (80%) of the lots in a residential development have
not been improved by the end of the two year maintenance period, the maintenance bond
may be extended, subject to the approval of the Director, for one (1) additional year.
The amount of the Maintenance Bond shall be ten percent (10%) of the estimated
construction cost of the stormwater facilities and roads requiring maintenance, or five
thousand dollars ($5,000.00), whichever is greater. The construction cost of the facilities
requiring maintenance shall be estimated by the Project Engineer, subject to the approval of
the Director.
2.5 PRECONSTRUCTION MEETING
When a preconstruction meeting is required prior to construction, such a meeting should be
attended by:
o A representative of the owner.
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o The designated emergency contact person.
o A representative of the general contractor.
o A representative of City Public Works.
o Representatives from all affected utilities.
The agenda for the preconstruction meeting will include at least the following:
o Verification that all required permits have been issued.
o Issuance of the Stormwater Management Permit placard, to be posted on the project
site.
o Verification that the contractor is in possession of current final approved plans.
o Discussion of the duties of the designated emergency contact person.
o Discussion of coordination of work by affected utilities.
o Discussion of City requirements concerning erosion control and construction
sequence, inspection requirements, plan changes, and protection of critical drainage
areas.
For projects where the City Public Works Department has required a preconstruction
meeting, no work shall take place on a project site prior to the preconstruction meeting.
In the event that work takes place on the project site prior to the preconstruction meeting, the
owner and/or contractor shall be in violation of the Port Orchard Stormwater Management
Ordinance and shall be subject to a monetary penalty as described in Section 11 of the
Stormwater Management Ordinance. In addition, the issuance of the Stormwater
Management Permit may be delayed and restoration work may be required for those areas
of the site disturbed prematurely.
2.6 FINAL PROJECT APPROVAL
Public Works will not recommend the approval of final plats or the granting of certificates
of occupancy, and will not release financial securities until the following applicable items
have been completed: [It should be noted that performance bonds may be accepted in lieu
of the items listed below, for final plats, in the event that the plat will be recorded prior to
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construction completion. However, in no event shall a performance bond be accepted for
safety items such as guard rails or pond fencing.]
For permits requiring an Abbreviated Plan only:
o Conditions of the Abbreviated Plan must be met, except that final landscape planting
may be delayed to the appropriate season for said planting.
For permits requiring engineered Drainage Plans, Erosion and Sedimentation Control Plans,
or Grading Plans:
o Completion, to the satisfaction of the Director, of all work indicated on the
engineered plans.
o Certification, by the project engineer, of the as -built live and dead storage pond
volumes.
o Certification, by the project engineer, that all pond side slopes are 2H:1V or flatter
for fenced ponds, and 4H:1 V or flatter for unfenced ponds.
o Submittal of one set of reproducible mylar as -built plans along with two sets of
blueprint copies. All sheets containing road and drainage plans, profiles and
associated details shall be included in the as -built set. It is not necessary to include
grading and erosion control plans and details. The as -built plan set shall be stamped
"RECORD DRAWING" and shall be signed and sealed by a professional engineer
or land surveyor.
o Submittal of a recorded (with the Kitsap County Auditor) Maintenance Covenant for
maintenance of private storm drainage facilities which gives the City the right to
inspect the facilities and guarantees the City that the facilities will be properly
maintained. A standard Maintenance Covenant form is available from the
Department of Public Works.
o Review and approval by the Department of Public Works of the final plat map and
associated documentation.
o Recording (with the Kitsap County Auditor) covenants, conditions and restrictions,
maintenance easements, agreements with adjacent property owners, conservation
easements, and similar documents as required in the approved plans, SEPA
Conditions, or Conditions of Preliminary Approval.
o Fulfillment of all conditions of approval.
2-24
o Permanent stabilization and restoration of the project site. Final replanting may be
delayed to the appropriate season, provided that temporary soil stabilization measures
are in place and financial security is provided to assure the completion of work.
o Submittal, by the project engineer, of the Operation and Maintenance Manual for
privately maintained and/or non-standard stormwater facilities.
o Payment of all outstanding fees.
o Submittal of any required maintenance bonds.
2.7 PROJECT PHASING
The phasing of construction is permitted when in accordance with current land use policies,
conditions of Preliminary Approval, and SEPA conditions.
The Drainage Plan and the Erosion and Sedimentation Control Plan for the initial phase of
a project shall incorporate all detention/retention facilities, water quality facilities, and
erosion control facilities necessary to serve the initial phase as if no further construction were -
to take place (a "stand alone" project).
It is of particular importance that runoff control facilities be designed so that stormwater
release rates for each phase do not exceed allowable release rates for a given stage of "build -
out". It will sometimes be necessary that the control structure be modified with each
additional construction phase. With the addition of each phase of development, the project
must maintain its ability to "stand alone" without dependence on future phases of
development.
In the event that the scope of the Drainage Plan and Erosion and Sedimentation Control Plan
includes the entire project with all of its phases, plans must indicate the phasing limits for
land clearing, erosion control, grading, construction of drainage facilities, and construction
of impervious surfaces.
2-25
APPENDIX 2A:
PORT ORCHARD STANDARD PLAN NOTES
GENERAL NOTES
1. All workmanship and materials shall conform to the MOST CURRENT
Standard Specifications for Road, Bridge and Municipal Construction
prepared by WSDOT and APWA as adopted by the Port Orchard Department
of Public Works.
2. Any revisions to the approved construction plans shall be reviewed and
approved by Public Works prior to implementation in the field.
3. The contractor shall maintain a set of the approved construction drawings on -
site at all times while construction is in progress.
4. It shall be the responsibility of the contractor to obtain all necessary permits
from the Public Works Department prior to commencing any work within
City right-of-way.
5. The contractor shall be responsible for providing adequate traffic control at
all times during construction alongside or within all public roadways. Traffic
flow on existing public roadways shall be maintained at all times, unless
permission is obtained from the Public Works Department for road closure
and/or detours.
6. The locations of existing utilities on this plan is approximate only. The
contractor shall contract the "Underground Locate" center at 1-800-424-5555,
and non -subscribing individual utility companies 48 hours in advance of the
commencement of any construction activity. The contractor shall provide for
protection of existing utilities from damage caused by the contractor's
operations.
7. Rockeries or other retaining facilities exceeding 4 ft. in height require a
separate permit from the Public Works Department.
8. A "Forestry Practices" permit may be required prior to logging of the site.
Contact the City of Port Orchard Planning Department for further
information.
DRAINAGE NOTES
l . The contractor shall ensure that the drainage is installed and operational prior
to commencement of paving work.
2A-2
2. All steel pipe and parts shall be galvanized. All submerged steel pipes and
parts shall be galvanized and have asphalt treatment #1 or better.
Drainage stubouts on individual lots shall be located with a five foot high 2" x 4"
stake marked "STORM". The stubout shall extend above surface level and be
secured to the stake.
GRADING NOTES
The contractor shall notify the engineer in the event or discovery of poor soils,
groundwater or discrepancies in the existing conditions as noted on the plans.
2. Maximum slope steepness shall be 2:1 Horizontal:Vertical for cut and fill slopes.
3. Unless otherwise specified, all embankments in the Plan Set shall be constructed in
accordance with Section 2-03.3(14)B of the WSDOT Standard Specifications.
Embankment compactions shall conform to Section 2-03.3(14)C, Method B of said
Standard Specifications.
4. Embankments designed to impound water shall be compacted to 95% maximum
density per section 2-03.3(14)C, Method C of WSDOT Standard Specifications.
5. All areas receiving fill material shall be prepared by removing vegetation,
noncomplying fill, topsoil, and other unsuitable material, by scarifying the surface
to provide a bond with the new fill, and where slopes are steeper than 3 horizontal
to 1 vertical and the height is greater than 5 ft., by benching into sound competent
material as determined by a soils engineer.
GENERAL EROSION AND SEDIMENTATION CONTROL NOTES
The following erosion and sedimentation control notes apply to all construction site activities
at all times, unless otherwise specified on these plans:
Approval of this erosion and sedimentation control plan does not constitute an
acceptance of the permanent road or drainage design.
2. The owner and his/her contractor shall be responsible at all times for preventing silt -
laden runoff from discharging from the project site. Failure by the owner and/or
contractor can result in a fine. The designated temporary contact person noted on this
plan must be available for contact by telephone on a 24 hour basis throughout
construction and until the project has been completed and accepted by the city.
The implementation of these ESC plans and the construction, maintenance,
replacement and upgrading of these facilities is the responsibility of the owner and/or
2A-3
contractor from the beginning of construction until all construction is completed and
accepted by the city and the site is stabilized.
4. Prior to beginning any work on the project site, a preconstruction conference must
be held, and shall be attended by the general contractor, the project engineer,
representatives from affected utilities, and a representative of the City.
5. The boundaries of the clearing limits shown on this plan shall be clearly flagged and
inspected by the City prior to any clearing or construction taking place. During
construction, no disturbance beyond the flagged clearing limits shall be permitted.
The flagging shall be maintained by the owner and/or contractor until all construction
is approved.
6. All rocked construction entrances shown on this plan shall be installed prior to
beginning construction. In addition, equipment for the cleaning of public roadways
shall be available at all times during construction.
7. The erosion and sedimentation control facilities shown on this plan are to be
considered adequate basic requirements for the anticipated site conditions. During
construction, deviations from this plan may be necessary in order to maintain water
quality. Minor departures from this plan are permitted subject to the approval of the
city inspector. However, except for emergency situations, all other deviations from
this plan must be designed by the project engineer and approved by the City prior to
installation.
8. All erosion and sedimentation control measures shall be inspected by the owner'
and/or contractor on a frequent basis and immediately after each rainfall, and
maintained as necessary to insure their continued functioning. All sediment must be
removed from silt fences, straw bales, sediment ponds, etc. prior to the sediment
reaching %2 its maximum potential depth.
9. At no time shall concrete, concrete by-products, vehicle fluids, paint, chemicals, or
other polluting matter be permitted to discharge to the temporary or permanent
drainage system, or to discharge from the project site.
10. Permanent detention/retention ponds, pipes, tanks or vaults may only be used for
sediment containment when specifically indicated on these plans.
LEVEL 1 EROSION AND SEDIMENTATION CONTROL NOTES
The following notes apply to all site activities within the time period specified on this plan
for Level 1 controls.
2A-4
I . The clearing of land, including the removal of existing vegetation or other ground
cover, must be limited to only as much land area as can receive appropriate protective
cover or be otherwise stabilized, after having been cleared or otherwise disturbed, by
no later than September 30 of a given year. Unless immediate stabilization is
specified in the Level 1 erosion and sedimentation control plan, all areas cleared or
otherwise disturbed must be appropriately stabilized. Unless otherwise approved by
the Director, seeding, fertilizing, and mulching of cleared or otherwise disturbed
areas shall be performed during the following periods: March 1 to May 15 and
August 15 to October 1. Permission to seed after October 1 will only be given when
physical completion of the project is imminent and the environmental conditions are
conducive to satisfactory growth. In the event that permanent stabilization is not
possible, an alternative method of ground cover (such as mulching, netting, plastic
sheeting, erosion blankets, etc.) must be installed by no later than October 1.
2. In the event that construction activities or other site development activities are
discontinued for 15 consecutive days or more, the property owner shall be
responsible for the inspection of all erosion and sedimentation control facilities
immediately after significant storm events, and at least once every 15 days. The
property owner shall be responsible for the maintenance and repair of all erosion and
sedimentation control facilities.
During periods of inclement weather, the owner or contractor shall have the materials
readily available to stabilize denuded areas.
LEVEL 2 EROSION AND SEDIMENTATION CONTROL NOTES
The following notes apply to all site activities within the time period specified on this plan
for Level 2 controls.
On sites where uninterrupted construction activity is in progress, the clearing of land,
including the removal of existing vegetation or other ground cover, shall be limited
to only as much land area as can receive appropriate protective cover or be otherwise
stabilized within 15 days after having been cleared or otherwise disturbed. In the
event that any land area remains unprotected or has not been appropriately stabilized
15 days after having been cleared, all construction activity on the site, except for
approved erosion and sedimentation control activity, shall immediately cease until
such a time as said land area has been appropriately protected or stabilized.
2. In site areas where no further work is anticipated within 48 hours, all areas stripped
of vegetation or otherwise exposed, including roadway embankments, shall be
immediately protected or stabilized by a method approved by the City.
2A-5
The contractor shall at all times have available for the project sufficient quantities of
protective covering materials to immediately stabilize all disturbed areas, if directed
to do so by the project engineer or the Director.
4. The Project Engineer shall visit the development site a minimum of once per week,
while Level 2 controls are required, for the purpose of inspecting the erosion and,
sedimentation control facilities, reviewing the progress of construction, and verifying
the effectiveness of the erosion control measures being undertaken. The Project
Engineer shall immediately inform the Director of any problems or potential
problems observed during said site visits, as well as any recommended changes in
the erosion control measures to be undertaken. When requested by the Director, the
Project Engineer shall provide the Director with written records of said weekly site
visits, including dates of visits and noted site observations.
5. When Level 2 Controls have been recommended by the project engineer and/or
required by the City during the period from October 1 through April 30 only, and
construction on a site has not been completed and approved by the City by October
1 of a given year or exposed ground surfaces are not permanently stabilized by that
date, no work shall be permitted on the project site other than for the installation or
maintenance of approved erosion and sedimentation control facilities until such a
time as a Level 2 erosion and sedimentation control plan has been approved by the
City and Level 2 Controls have been implemented on the project site.
2A-6
CHAPTER 3
EROSION AND SEDIMENTATION CONTROL
CHAPTER 3
EROSION AND SEDIMENTATION CONTROL
CONTENTS
3.1 OVERVIEW....................................................................................................... 3-3
3.1.1 EROSION AND SEDIMENTATION....................................................3-3
3.2 MINIMUM REQUIREMENTS.......................................................................... 3-6
3.2.1 PERFORMANCE...................................................................................3-6
3.2.2 DESIGN STORM................................................................................... 3-6
3.2.3 MINOR DEVELOPMENTS.................................................................. 3-6
3.2.4 MAJOR DEVELOPMENTS.................................................................. 3-7
3.2.5 EROSION AND SEDIMENTATION CONTROL PLAN ................... 3-10
3.2.6 CLEARING AND COVERING........................................................... 3-11
LEVEL 1 CONTROLS..........................................................................3-11
LEVEL 2 CONTROLS..........................................................................3-12
APPENDIX 3A ESC BEST MANAGEMENT PRACTICES REFERENCE GUIDE. 3-14
ESC BEST MANAGEMENT PRACTICES REFERENCE GUIDE ............................ 3-15
APPENDIX 3B ESC BEST MANAGEMENT PRACTICES ............................. 3-21
FIGURES & TABLES
INDEX
Figure Title
FIGURE 3-1
STABILIZED CONSTRUCTION ENTRANCE
FIGURE 3-2
ORIENTATION OF NETTING AND MATTING
FIGURE 3-3
SURFACE ROUGHENING TECHNIQUES
FIGURE 3-4
STAIR -STEPPING CUT SLOPES AND GROOVING SLOPES
FIGURE 3-5
SEDIMENT TRAP
FIGURE 3-6
ESC STRUCTURAL PRACTICES
FIGURE 3-7
SEDIMENTATION POND
FIGURE 3-8
SEDIMENTATION POND BAFFLES
FIGURE 3-9
FILTER FABRIC FENCE
FIGURE 3-10
BRUSH BARRIER
FIGURE 3-11
GRAVEL FILTER BERM
FIGURE 3-12
SANDBAG BERM/CHECK DAM
FIGURE 3-13
STRAW/HAY BALE BARRIER
FIGURE 3-14
FILTER FABRIC FENCE INLET BARRIER
FIGURE 3-15
BLOCK AND GRAVEL FILTER INLET BARRIER
FIGURE 3-16
GRAVEL AND WIRE MESH FILTER INLET BARRIER
FIGURE 3-17
PIPE SLOPE DRAIN
FIGURE 3-18
INTERCEPTOR DIKE/BERM
FIGURE 3-19
SUBSURFACE DRAIN
FIGURE 3-20
LEVEL SPREADER
FIGURE 3-21
CHECK DAM
TABLES TITLE
TABLE 3-1 MULCH MATERIAL, APPLICATION RATES AND SPECIFICATIONS
TABLE 3-2 TEMPORARY EROSION CONTROL SEED MIXTURE
TABLE 3-3 PERMANENT EROSION CONTROL SEEDING MIXTURE
TABLE 3-4 FILTER FABRIC FENCE EQUIVALENT OPENING SIZE (EOS)
3-2
EROSION AND SEDIMENTATION CONTROL
3.1 OVERVIEW
Each year large amounts of sediment are washed from construction sites into lakes, streams,
watercourses, and Puget Sound. Sedimentation is a major source of pollution of the surface
water draining from watersheds in which development is occurring. This needless damage
to our water resources and the consequent cost to the taxpayers of the City of Port Orchard
for cleanup could be largely avoided through the implementation of adequate erosion and
sediment control practices.
This chapter contains requirements and standards for erosion and sedimentation control
(ESC) recommended by the City of Port Orchard. Also, this chapter contains information
on the purpose for various erosion and sedimentation control practices, the site conditions
where these practices are appropriate, and the recommended design criteria for their
construction and maintenance.
3.1.1 EROSION AND SEDIMENTATION
EROSION
The likelihood that a given construction area has the potential for serious erosion is largely
dependent on three things: the characteristics of the soils, the extent and type of vegetative
cover, and the topography of the site.
Soils containing high percentages of fine sands and silts are usually more erodible than soils
that have a higher content of clay or organic material. Although clays are more resistant to
erosion, they absorb less rainfall and tend to produce more surface runoff, which acts to
erode the soil. Once clays have eroded, they are more likely to be carried along in the runoff
and are difficult to remove from the surface water. Soils with high organic content tend to
be more resistant to erosion. However, they are resistant to infiltration and are often found
in areas likely to impound water. Well -drained and well -graded gravel and gravel -sand
mixtures are usually the least erodible soils.
Vegetative cover is very important in controlling erosion by 1) shielding the soil surface
from the impact of falling rain, 2) by holding the soil particles in place, 3) by maintaining,
the soil's capacity to absorb water, and 4) by slowing the flow of runoff over the ground. By
minimizing the size of the areas to be cleared, and by staging the removal of vegetation, the
extent of erosion and the time during which erosion can take place is also kept to a minimum.
By establishing temporary and permanent vegetative cover for those areas that are disturbed,
soil erosion and the resulting sedimentation downstream can be significantly reduced.
3-3
The size, shape, and slope of the watershed that the construction site is a part of, influences
the amount and rate of runoff through the site. If the site is downstream of a large watershed,
or if the site itself is sizable, there is the potential for a considerable amount of runoff to be
flowing through the site during a storm. If the site has steep slopes, the velocity of the runoff
will be greater, resulting in a higher potential for erosion.
The site's orientation can also be a factor. If the site faces to the north away from the sun (or
if the site has poor soils for growing plants), it may be very difficult to establish a permanent
vegetative cover following construction. For this reason, it is important to take into
consideration the natural development of existing vegetation on a site prior to clearing.
Hydroseeding a site is no guarantee that plant life will become re-established to the extent
that erosion protection can take place without costly maintenance and periodic replanting.
SEDIMENTATION
Sediments are the fine particles of soil which are carried in surface runoff and which are
eventually deposited after the water has slowed down enough for the soil particles to settle
out. Excessive amounts of sediment are generated by erosion during major storm events.
Some erosion and sedimentation occurs during all storm events. Sediment is often carried
farther downstream with each peak storm event, being picked up from where it was deposited
during the previous peak storm. For this reason, it is important to bear in mind that the
facilities that are placed on a site to collect sediment (silt fencing, ponds, etc.) are going to
be primary sources of sediment in later storms.
Most soils in Kitsap County contain fine silt which, when suspended in water, remains
suspended for long periods of time and does not immediately settle out once the flow of
water slows down. Suspended silt usually gives water an opaque, light brown appearance,
a condition called "turbidity". This condition is harmful to plants in that it inhibits
photosynthesis, which in turn reduces food supply and habitat to fish. Turbid stream water
can also directly affect some species of fish that rely on their vision for feeding. Silt
suspended in stormwater so as to cause turbidity is a violation of Chapter 10 of the
Stormwater Management Ordinance, and also of the Clean Water Act.
IMPACTS OF EROSION AND SEDIMENTATION
Erosion and sedimentation can cause both economic and environmental impacts:
Economic Impacts:
a. Sediment fills channels and ponds, resulting in the need for more frequent
sediment removal, and also resulting in the increased likelihood of damage
to property from flooding.
b. Cost of restoration of topsoil to promote plant growth.
C. Cost of restoration of eroded slopes, channels, and roads.
3-4
d. Cost to clean storm sewers, catch basins, and other drainage facilities.
e. Cost to clean up downstream channels, lakes, streams, and wetlands.
2. Environmental Impacts
a. Eroded soil contains nutrients that could trigger the growth of algae, which
then reduces water clarity, depletes oxygen, and leads to fish kills.
b. Erosion of stream banks and adjacent areas destroys vegetation that provides
aquatic and wildlife habitat.
C. Excessive deposits of sediment in streams blanket the bottom, destroying fish
spawning areas.
d. Turbidity of the water, resulting from sedimentation, reduces in -stream
photosynthesis, which leads to reduced food supply and habitat.
e. Erosion removes the fines from topsoil, reducing its ability to support plant
growth.
f. Sediment physically damages fish by abrasion and clogging of their gills.
3-5
3.2 MINIMUM REQUIREMENTS
Section 5(3) of the Port Orchard Stormwater Management Ordinance requires that all new
major developments and redevelopments comply with the erosion and sedimentation control
requirements specified. Section 10(2) of the Ordinance states that it is a violation for any
person to cause the pollution of any waters of Port Orchard. Section 10(4) of the Ordinance
states that the owners of erosion control devices must operate and maintain such control
devices in a manner which will prevent discharge of pollutants to waters of Port Orchard.
Finally, Section 11(5) of the Ordinance states that a violation of the water quality provisions
of the Ordinance will result in a penalty to the violator (whether owner or contractor) of up
to $1,000 per offense per day.
3.2.1 PERFORMANCE
The erosion and sedimentation control measures shall perform so that no sediment larger
than a #200 sieve, (0.075 min) leaves the site or enters on -site wetlands, streams, or lakes.
3.2.2 DESIGN STORM
Unless otherwise specified, the design storm event for erosion and sedimentation control
BMPs shall be the 2-year, 24-hour storm event.
3.2.3 MINOR DEVELOPMENTS
Developments are considered by Port Orchard to be "minor developments" when they (a)
result in the creation or addition of less than 5,000 square feet of impervious surface area,
(b) are site disturbing activities of less than 1 acre, and (c) result in the grading of less than
5,000 cubic yards of material.
Minor Developments are required to control erosion and sedimentation during construction,
to permanently stabilize soil exposed during construction, and to comply with the following
Minor Development Requirements:
Construction access route. Construction vehicle access shall be, whenever possible,
limited to one route. Access points shall be stabilized with quarry spalls or crushed rock
to minimize the tracking of soils and debris onto public roads.
2. Stabilization of denuded area. All exposed soils shall be stabilized by suitable
application of BMPs, including but not limited to, sod or other vegetation, mat covering,
mulching, or application of compacted ground base material on areas to be paved. All
BMPs shall be selected, designed and maintained in accordance with this Manual. From
October 1 through April 30, soils not actively being worked for more than 48 hours shall
be protected or stabilized. From May 1 through September 30, the owner or contractor
shall have the materials readily available to stabilize denuded areas as site and weather
conditions dictate.
3-6
3. Protection of adjacent properties. Adjacent properties shall be protected from sediment
deposition by appropriate use of vegetative buffer strips, sediment barriers or filters,
dikes or mulching, or by a combination of these measures and other appropriate BMPs.
4. Maintenance. All erosion and sediment control BMPs shall be regularly inspected and
maintained to ensure continued performance of their intended function.
5. Other BMPs. Other appropriate BMPs to mitigate the effects of increased runoff shall
be applied.
Minor Developments may require an erosion and sedimentation control plan when a
Stormwater Management Permit is required pursuant to Section 3.20 of the Ordinance.
3.2.4 MAJOR DEVELOPMENTS
Developments and redevelopment activities are considered by Port Orchard to be "major
developments" which include the creation or addition of 5,000 square feet or greater of new
impervious surface area, result in the displacement of 5,000 cubic yards or more of material,
or involve land disturbing activities on greater than 1 acre.
Major Developments will be required to control erosion and sediment during construction,
to permanently stabilize soil exposed during construction, and to comply with the following.
Major Development Requirements:
1. Stabilization of denuded area. All exposed soils shall be stabilized by suitable
application of BMPs, including but not limited to, sod or other vegetation, mat covering,
mulching, or application of compacted ground base material on areas to be paved. All
BMPs shall be selected, designed and maintained in accordance with this Manual. From
October 1 through April 30, soils not actively being worked for more than 48 hours shall
be protected or stabilized. From May 1 through September 30, the owner or contractor
shall have the materials readily available to stabilize denuded areas as site and weather
conditions dictate.
2. Delineate clearing and easement limits. Clearing limits, any sensitive/critical areas and
their buffers, and drainage courses shall be clearly marked in the field.
3. Protection of adjacent properties. Adjacent properties shall be protected from sediment
deposition by appropriate use of vegetative buffer strips, sediment barriers or filters,
dikes or mulching, or by a combination of these measures and other appropriate BMPs.
4. Timing and stabilization of sediment trapping measures. Sediment ponds and traps,
perimeter dikes, sediment barriers and other BMPs intended to trap sediment on -site shall'
be constructed as a first step in grading. These BMPs shall be functional before land
3-7
disturbing activities take place. Earthen structures such as dams, dikes, and diversions
shall be seeded and mulched according to the timing indicated in item (1) above.
Cut and fill slopes. Cut and fill slopes shall be designed, constructed and stabilized in
a manner that will minimize erosion. Slopes shall be stabilized in accordance with the
section titled "Clearing and Covering" found elsewhere in this chapter.
6. Controlling off -site erosion. Properties and waterways downstream from development
sites shall be protected from erosion due to increases in the volume, velocity, and peak
flow rate of stormwater runoff from the development site by the implementation of
appropriate BMPs to minimize adverse downstream impacts.
7. Stabilization of temporary conveyance channels and outlets. All temporary on -site
conveyance channels shall be designed, constructed, and stabilized to prevent erosion
from the expected flow velocity from a 2-year, 24-hour storm event for post -development
conditions. Stabilization adequate to prevent erosion of outlets, adjacent stream banks,
slopes, and downstream reaches shall be provided at the outlets of all conveyance
systems.
Storm drain inlet protection. All storm drain inlets made operable during construction
shall be protected so that stormwater runoff shall not enter the conveyance system
without first being filtered or otherwise treated to remove sediment. The requirement for
inlet protection may be waived on a site specific basis when the conveyance system
downstream of the inlet discharges to an appropriate sediment containment BMP and the
conveyance system can be adequately cleaned following site stabilization.
9. Underground utility construction. The construction of underground utility lines shall be
subject to the following criteria:
For trenches on a downslope of more than 5%, no more than 500 feet of trench shall be
opened at one time, unless otherwise approved by the Director.
Where consistent with safety and space considerations, excavated material shall be
placed on the uphill side of trenches.
Trench dewatering devices shall discharge into a sediment trap or sediment pond.
10. Constructed access routes. Wherever construction vehicle access routes intersect paved
roads, provisions must be made to minimize the transport of sediment (mud) onto the
paved road. If sediment is transported onto a road surface, the roads shall be cleaned
thoroughly, as a minimum, at the end of each day. Sediment shall be removed from
roads by shoveling or sweeping and be transported to a controlled sediment disposal area.
Street washing shall be allowed only after sediment is removed in this manner.
11. Removal of temporary BMPs. All temporary erosion and sedimentation control BMPs
shall be removed within 30 days after final site stabilization is achieved or after the
temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized
on -site. Disturbed soil areas resulting from removal of temporary BMPs shall be
permanently stabilized. The removal of temporary erosion and sedimentation control
BMPs may not be required for those projects, such as single family plats, that will be
followed by additional construction under a different permit. In these circumstances, the
need for removing or retaining the measures will be evaluated on a site specific basis.
12. Dewatering construction sites. Dewatering devices shall discharge into a sediment trap
or sediment pond.
13. Control of pollutants other than sediment on construction sites. All pollutants other than
sediment that occur on -site during construction shall be handled and legally disposed of
in a manner that does not cause contamination of surface waters.
14. Maintenance. All temporary and permanent erosion and sedimentation control BMPs
shall be maintained and repaired as needed to assure continued performance of their
intended function. All maintenance and repair shall be conducted in accordance with this
Manual. The Applicant shall be responsible for assuring that any such facilities damaged
during floods, storms, or other adverse weather conditions are immediately returned to
normal operating condition.
15. Financial liability. Performance bonding or other appropriate guarantees shall be
required for all projects to ensure compliance with the approved erosion and
sedimentation control plan.
3-9
3.2.5 EROSION AND SEDIMENTATION CONTROL PLAN
The Ordinance requires that an Erosion and Sedimentation Control (ESC) plan be submitted
for review and approval prior to beginning site development activities.
Public Works staff will review the ESC plan to verify that a reasonable plan is being
proposed to control erosion and sedimentation, and ultimately, to preserve the quality of the
stormwater leaving the construction site.
A Stormwater Management Permit will not be issued until an ESC plan is approved which
complies with the minimum requirements for erosion and sedimentation control and which
represents a reasonable plan for the specific project site. Port Orchard will require that the
plan be strictly adhered to as minimum requirements for erosion and sedimentation control.
Erosion and sedimentation controls shall be maintained until the project site is permanently
stabilized.
An Erosion and Sedimentation Control plan must address the control of erosion and
sedimentation continuously throughout construction and also following construction. The
ESC plan may be a separate plan specifically addressing erosion and sedimentation control,
or it can be a part of another construction plan. For all major developments, the ESC plan
must also be prepared by and bear the seal of a Civil Engineer.
At times it will be found that the approved erosion and sedimentation control facilities are
not adequate. This may be because of unanticipated conditions that have arisen on the
construction site, or because of damage resulting from storms, construction equipment, soil
failures, etc. In order to maintain the quality of water leaving the project site under these
circumstances, it may be necessary that the erosion and sedimentation control facilities be
modified. In circumstances where the erosion and sedimentation control facilities are to be
modified, the following rule must be followed:
Except for emergency conditions or when changes are deemed by the Director to be
of a minor nature, the Project Engineer must revise the ESC plan and submit it for
approval to the City prior to any modifications being made on the project site.
It should be emphasized that, except for emergency conditions, the contractor may not
deviate from the ESC plan and that only the Project Engineer (not the owner or contractor)
is authorized to direct changes in the erosion and sedimentation control facilities.
For an ESC plan to be effective, it is essential that provisions for erosion and sedimentation
control measures be made in the early planning stage of the project. The following basic
planning principles should be applied to the maximum extent possible in order to control
erosion/sedimentation during and after construction:
1. Fit the project to the terrain to minimize the amount of clearing and grading.
3-10
2. Time grading and construction to minimize soil exposure, particularly for highly erodible
soils.
3. Retain existing vegetation whenever feasible.
4. Vegetate and mulch denuded areas.
5. Direct runoff away from denuded areas in a timely manner.
6. Minimize length and steepness of slopes.
7. Keep runoff velocities low.
8. Prepare drainage ways and outlets to handle concentrated or increased runoff.
9. Trap sediment on site.
10. Inspect and maintain control measures frequently.
3.2.6 CLEARING AND COVERING
Because the needs for erosion and sedimentation control on a project site can be much
different in wet seasons of the year than in dry seasons, and because the sensitivity to
pollution of the downstream drainage course can result in differing levels of precaution in
the control of water quality, the City has established a two -level criteria concerning the
clearing of vegetation from a site and the covering of exposed areas.
LEVEL 1 CONTROLS
The following erosion and sedimentation control measures, herein called Level 1 Controls,
must be implemented on any sites where vegetation or other existing ground cover is
removed or has been removed, except when Level 2 Controls are recommended by the
Project Engineer and/or are required by the Director:
(1) The clearing of land, including the removal of existing vegetation or other ground -
cover, must be limited to only as much land area as can receive appropriate protective
cover or be otherwise stabilized, after having been cleared or otherwise disturbed, by
no later than September 30 of a given year. Unless immediate stabilization is
specified in the Level 1 erosion and sedimentation control plan, all areas cleared or
otherwise disturbed must be appropriately stabilized. Unless otherwise approved by
the Director, seeding, fertilizing, and mulching of cleared or otherwise disturbed
areas shall be performed during the following periods: March 1 to May 15 and
August 15 to October 1. Permission to seed after October 1 will only be given when
physical completion of the project is imminent and the environmental conditions are
conducive to satisfactory growth. In the event that permanent stabilization is not
possible, an alternative method of ground cover (such as mulching, netting, plastic
sheeting, erosion blankets, etc.) must be installed by no later than September 30.
(2) In the event that construction activities or other site development activities are
discontinued for 15 consecutive days or more, the owner shall be responsible for the
inspection of all erosion and sedimentation control facilities immediately after
significant storm events, and at least once every 15 days. The property owner shall
3-11
be responsible for the maintenance and repair of all erosion and sedimentation
control facilities.
(3) The owner or contractor shall have the materials readily available to stabilize
denuded areas as site and weather conditions dictate. Prior to leaving the site,
stormwater runoff shall pass through a sediment pond, sediment trap, or other
appropriate BMP.
LEVEL 2 CONTROLS
Level 2 Erosion Controls will be required under the following circumstances:
(1) Beginning October 1 of any given year and continuing through April 30 of the
following year: when recommended by the Project Engineer, or when the Director
has determined that Level 1 Controls alone will not adequately protect downstream
receiving waters or adjacent properties from erosion and sedimentation during the
rainy winter months.
(2) Year round implementation: when recommended by the Project Engineer, or when
the Director has determined that more stringent erosion control measures than those
provided by Level 1 Controls are necessary during dry as well as wet seasons of the
year, due to the proximity of the site activities to critical drainage areas, steep slopes,
or unstable soils.
When the scope of a project is large enough, or work is scheduled late enough in the year that
the City cannot be reasonably assured of work completion before October 1, the ESC plan
should be a minimum two phase plan, showing Level 1 Controls and also Level 2 Controls.
The requirements for Level 2 Controls are as follows (see also Level 2 Erosion and
Sedimentation Control Notes, pg. 2A-4):
(1) On sites where uninterrupted construction activity is in progress, the clearing of land,
including the removal of existing vegetation or other ground cover, shall be limited
to only as much land area as can receive appropriate protective cover or be otherwise
stabilized within 15 days after having been cleared or otherwise disturbed. In the
event that any land area remains unprotected or has not been appropriately stabilized
15 days after having been cleared, all construction activity on the site, except for
approved erosion and sedimentation control activity, shall immediately cease until
such a time as said land area has been appropriately protected or stabilized.
(2) In site areas where no further work is anticipated within 48 hours, all areas stripped
of vegetation or otherwise exposed, including roadway embankments, shall be
immediately protected or stabilized by a method approved by the City.
3-12
(3) The contractor shall at all times have available for the project sufficient quantities of
protective covering materials to immediately stabilize all disturbed areas, if directed
to do so by the Project engineer or the Director.
(4) The Project Engineer shall visit the development site a minimum of once per week
while Level 2 controls are required for the purpose of inspecting the erosion and
sedimentation control facilities, reviewing the progress of construction, and verifying
the effectiveness of the erosion control measures being undertaken. The Project
Engineer shall immediately inform the Director of any problems or potential
problems observed during said site visits, as well as of any recommended changes
in the erosion control measures to be undertaken. When requested by the Director,
the Project Engineer shall provide the Director with written records of said weekly
site visits, including dates of visits and noted site observations.
(5) When Level 2 Controls have been recommended by the project engineer and/or
required by the City during the period from October 1 through April 30 only, and
construction on a site has not been completed and approved by the City by October
1 of a given year or exposed ground surfaces are not permanently stabilized by that
date, no work shall be permitted on the project site other than for the installation or
maintenance of approved erosion and sedimentation control facilities until such a
time as a Level 2 erosion and sedimentation control plan has been approved by the
City and Level 2 Controls have been implemented on the project site.
In the event that ground on a project site is left bare after October 1, and Level 2 Controls
are not followed, the City may issue a Stop Work Order for the entire project until
satisfactory Level 2 Controls are provided. In addition, the Owner will be subject to the
penalties provided in Section 10 and Section 11 of the Ordinance.
In the event that ground on a project site is left bare after October 1, Level 2 Controls are not
followed, and the City is unsuccessful in contacting the Owner or his/her designated,
emergency contact person, the City may enter the project site and install temporary ground
cover measures and bill the Owner for all expenses incurred by the City. These costs will
be in addition to any monetary penalties levied against the Owner.
3-13
APPENDIX 3A
ESC BEST MANAGEMENT PRACTICES REFERENCE
GUIDE
ESC BEST MANAGEMENT PRACTICES REFERENCE GUIDE
Impact: Control Measure:
CONSTRUCTION VEHICLE TRAFFIC
Mud, dirt, rock transported
onto roads from site having
bare ground
Erosion of constructed roads
following rough grading,
caused by construction
equipment.
Surface and air movement of
dust from exposed soil sur-
faces subjected to vehicle
traffic.
BARE GROUND
Surface runoff over bare
ground results in silt sus-
pended in stormwater, caus-
ing turbidity.
Water velocity and turbu-
lance caused erosion.
Sheetflow velocity causes
erosion on small slope areas
no steeper than 2:1.
During extended rainy peri-
ods, bare ground is subject
to erosion.
Stabilized Construction
Entrance (may be used with
Filter Fabric Fence).
Construction Road Stabil-
ization.
Dust Control (may be used
with Stabilized Construction
Entrance).
Limit Clearing of Site.
Rip Rap.
Straw/Hay Bale Barrier.
Cover areas left unworked
for more than 48 hours (may
use Mulching, Sodding or
Plastic Sheeting).
REV 10/21/96 3A-1
Page
3B-2
3B-4
3B-7
3B-37
3B-8
Bare ground, seed beds, or Plastic Sheeting. 313-22
other areas are subject to
erosion unless immediate
erosion protection is pro-
vided, particularly during
winter when seeding is not
recommended, or when areas
cannot be covered by mulch-
ing.
SEDIMENT IN STORMWATER
Sediment -laden runoff from a Sediment Trap. 3B-23
small site having a tributary
drainage area of less then 3 acres
and where permanent stabilization
is expected within 6 months.
Sediment -laden runoff from a site Sediment Pond. 313-25
having a tributary drainage area of
less then 10 acres and where
permanent stabilization is not
expected within 6 months.
Sediment -laden runoff dis-
Filter Fabric Fence (may 3B-29
charges from site by sheet
also be used with Sediment
flow or from minor swale or
Trap, Sediment Pond, Brush
ditch with maximum flow of
Barrier, or Inlet Barrier).
0.5 cfs.
Sediment -laden runoff sheet- Brush Barrier (may be used 3B-33
flows from < 1 A acre tribu- with Filter Fabric Fence).
tary area of site, and resi-
due brush is available.
Sediment -laden runoff in Gravel Filter Berm. 313-35
cleared rights -of -way or
other traffic areas.
Small amounts of sediment Straw/Hay Bale Barrier. 3B-37
migrate from bare disturbed
slopes no steeper than 2:1.
REV 10/21/96 3A- 3
STOCKPILES
- Exposed, uncompacted earth Cover and properly locate 313-53
stockpiles are constructed stockpiles (may be used in
during winter months, or are conjunction with Topsoiling
otherwise prone to excessive Plastic Sheeting, Mulching,
erosion caused by surface runoff Nets and Mats).
SHORELINES
Graded slopes, or the place- Restrict placement of 313-54
ment of earth at or near constructed slopes or
shorelines, may slough, earthworks (may be used
slide or erode. with Plastic Sheeting, or
Nets and Mats).
STREAMS
Increased stream flow or Structural Streambank 3B-55
disturbance during construc- Stabilization (may be
tion results in eroding used with Rip Rap).
section of stream bank.
Increased stream flows or Vegetative Streambank 3B-56
disturbance during construc- Stabilization.
tion resulting in a poten-
tial for excessive erosion
of stream banks.
OUTFALLS
Flow velocity at outlet of a Outlet Protection (may be 313-57
channel or pipe could result used with Rip Rap).
in erosion of downstream or
flooding at outlet.
NO DEFINED DOWNSTREAM
Runoff flow, which is rela- Level Spreader. 3B-58
tively free of sediment, is
concentrated on -site and can
cause damage to downstream
property if not converted to sheetflow.
REV 10/21/96 3A-5
APPENDIX 3B
ESC BEST MANAGEMENT PRACTICES
REV 10/21/96
CONTROL MEASURE: STABILIZED CONSTRUCTION ENTRANCE.
Purpose: Reduces the amount of debris transported onto public roads from construction
equipment by action of vehicle tires traveling over gravel pad removing most mud and debris
from tires.
Design Criteria/Specifications:
Design: (1) See Figure 3-1 for detail, (2) Stabilized Construction Entrances should be
located wherever vehicle access routes intersect paved roads; (3) Material should be quarry
spalls, 4" - 8" size; (4) The rock pad should be at least 12-inches thick and 100-feet in
length. Length may be reduced to 50-feet for sites with minor grading (less than 1 acre of
exposed soil); (5) Width should be the full width of the vehicle ingress and egress area.
Minimum width should be 20-feet. Additional subgrade stabilization such as a geotextile
mat may be required.
Procedures: (1) A filter fabric fence should be installed downhill from the construction
entrance to intercept and contain any sediment -laden runoff from the entrance or from tire
washing; (2) If the- rock pad does not adequately remove the mud from vehicle wheels, the
wheels should be hosed off before the vehicle enters a paved street. The washing should be
done on an area covered with crushed rock and wash water should drain to a sediment
retention facility; (3) Street cleaning equipment should be available as required.
Maintenance: (1) Entrances may require periodic top dressing with 2-inch stone, as
necessary to prevent tracking or flow of mud onto public roadways; (2) If sediment is
transported onto a road surface, the roads shall be cleaned thoroughly as a minimum at the
end of each day. Sediment should be removed from roads by shoveling or sweeping. Street
washing should take place only after sediment has been removed as described above; (3)
Any rock spalls that are loosened from the pad and end up on the roadway shall be removed
immediately.
REV 10/21/96 3B-1
Qsr,
p7
��n oay�00
'64e We ,� 44� to
i0es�, ss
R = 25' min.
12" min.
4" to 8" quarry spalls
provide full width of
ingress/egress area
REV 10/21 /96 3 B - 2
CONTROL MEASURE: CONSTRUCTION ROAD STABILIZATION.
Purpose: Temporarily stabilizes roads, parking areas, and on -site transportation routes with
stone immediately after grading, reduces erosion caused by construction traffic or runoff.
Design Criteria/Specifications:
Design: (1) Provide rock stabilization wherever there is the potential for erosion of
temporary construction routes by construction traffic during wet weather; (2) Rock
stabilization maybe unnecessary where soils on site are gravelly; (3) A 6-inch depthof
2"-4" crushed rock, gravel base, or crushed surfacing base course shall be applied
immediately after grading or the completion of utility installation within the right-of-way.
A 4-inch course of asphalt treated base (ATB) may be used instead of the crushed rock.
Procedures: (1) Where feasible, alternative routes should be made for construction traffic;
one for use in dry condition, the other for wet conditions which incorporates the measures
listed below; (2) Temporary roads should follow the contour of the natural terrain to the
extent possible. Slope should not exceed 15 percent. Roadways should be carefully graded
to drain transversely. Provide drainage swales on each side of the roadway in the case of a
crowned section, or one side in the case of a super elevated section. (3) Installed inlets shall
be protected to prevent sediment laden runoff from entering the storm system. (See BMPs
on Filter Inlet Barriers).
Maintenance: Inspect stabilized areas regularly, especially after large storm events. Add
crushed rock if necessary and restabilize any areas found to be eroding.
REV 10/21/96 3B-3
CONTROL MEASURE: DUST CONTROL.
Purpose: Prevents surface and air movement of dust from exposed soil surfaces.
Design Criteria/Specifications: (1) Minimize the period of soil exposure through use
of temporary ground cover and other temporary stabilization practices. (See Bare Ground
BMPs). (2) Site should be sprinkled with water until surface is wet. Repeat as needed.
To prevent carryout of mud onto street, refer to Stabilized Construction Entrance BUT in
this section. (3) Spray exposed soil areas with an appropriate dust palliative. Note: oil is
prohibited for use as a palliative.
REV 10/21/96 3B-4
CONTROL MEASURE: LIMIT CLEARING OF SITE.
Purpose: Reduces likelihood of, or extent of, turbidity in downstream stormwater by
minimizing the source of silt picked up on surface runoff.
Design Criteria/Specifications: Clearing should be limited to the minimum area necessary
to perform work and immediately revegetate cleared areas. When possible, construction
should be planned in stages, and only the stage being worked on should be cleared. Once
work is completed, a given stage of construction should be immediately revegetated or
otherwise stabilized.
REV 10/21 /96 3 B - 5
CONTROL MEASURE: RIP RAP.
Purpose: Slows the velocity of concentrated runoff. Also stabilizes slopes with seepage
problems and/or non -cohesive soils by placement of large, loose, angular stone.
Design Criteria/Specifications: (1) See Table 7-4 in Chapter 7 for recommended stone
sizes for a given flow velocity; (2) For durability, stability. and economy, it is
recommended that graded rather than uniform rip rap be utilized; (3) Since rip rap is used
where erosion potential is high, construction should be sequenced so that the rip rap is put
in place with the minimum possible delay. Disturbance of areas where rip rap is to be placed
should be undertaken only when final preparation and placement of the rip rap can follow
immediately behind the initial disturbance. Where rip rap is used for outlet protection, the
rip rap should be placed before or in conjunction with the construction of the pipe or channel
so that it is in place when the pipe or channel begins to operate.
Maintenance: Rip rap coverings should be inspected on a regular basis and after every large
storm event.
REV 10/21/96 3 B - 6
CONTROL MEASURE: COVER AREAS LEFT UNWORKED FOR MORE
THAN 48 HOURS. (See also Mulching, Sodding, Plastic
Sheeting BMPs).
Purpose: Minimize the area exposed to rainfall and surface runoff, thereby reducing the
amount of erosion of bare ground and the amount of sediment that might collect in
sedimentation control structures, such as sediment ponds or silt fences.
Design Criteria/Specifications: During the time period of October 1 through April 30, and
at other times of the year when there are extended periods of inclement weather, all project -
disturbed soil areas that are to be left unworked for more than 48 hours should be covered
by mulch, sodding, or plastic covering. This procedure is based on the increased potential
for, and consequences of, failure of erosion.and sedimentation control structures during this
period of high precipitation and the assumption that areas not being worked are likely to be
left unattended.
REV 10/21/96 3B-7
CONTROL MEASURE: MULCHING. (See also Nets and Mats).
Purpose: Mulching provides immediate temporary protection to exposed areas and allows
germination and protection of seeded areas by conserving moisture, moderating soil
temperatures, and holding fertilizer, seed and topsoil in place.
Design Criteria/Specifications:
Design: (1) Prepare soil as for seeding; (2) For application rates and specifications, see
Table 3-1; (3) Nets and Mats used in conjunction with mulch should be used on slopes
steeper than 2: 1; (4) Wood fiber cellulose blankets are considered protective mulches and
can be used alone on erodible soils and during all times of the year.
Materials: (1) Hay or Straw: Use straw where mulch effect is to be maintained for more
than 3 months. Hay and straw are subject to wind blowing unless kept moist or tied down.
They are the most common and widely used mulching material; good for erosion control in
critical areas. Anchor by crimping, discing, rolling or punching into soil, covering with
netting, spraying with a chemical or fiber binder or by keeping moist; (2) Wood fiber
cellulose (partly -digested wood fibers): When used for erosion control on critical areas, the
application rate should be doubled. Apply with hydromulcher. No tie down is required.
Packaged in 100-lb. bags. Not recommended for highly erodible soils in hot weather; (3)
Gravel, Crushed Stone or Slag: Excellent mulch for short slope and around woody plants and
ornamentals. Use where subject to foot traffic; (4) Corn Stalks: shredded into 4 - 6"
lengths, decomposes slowly and resists windblow; (5) Wood Chips: Cannot be closely
mowed. Decompose slowly and do not require tacking. Does not provide nitrogen to seeds
unless treated. Tends to wash down slopes steeper than 6%; (6) Bark Chips/Shredded
Bark: Cannot be closely mowed. Additional nitrogen for seeds not required. Tends to wash
down slopes steeper than 6%. Avoid tilling bark or sawdust into soil, as it tends to remove
nitrogen from soil, releasing it only when it decays.
Procedures: (1) Mulches should be used following temporary or permanent seeding;
(2) Mulching should immediately follow seeding in areas with slopes steeper than 2: 1; (3)
Mulches should be used in cleared areas that cannot be seeded because of the season; (4)
Mulches should be used on exposed soils (including Stockpiles which are not final graded
within 15 days) unless covered with Plastic Sheeting.
Maintenance: Mulched areas should be checked periodically, especially following severe
storms, when damaged areas of mulch or tie -down material should be repaired.
REV 10/21/96 3B-8
Mulch
Quality
Application Rates
AWlication Rates
Depth of
M�
nos
per 1000 sq ft
per Acre
A nliR, cation
Gravel,
Washed: 3/4" -
9 cu. yds.
400 cu. yds.
3"
Crushed Stone
1-1/2" size
or Slag
Hay or Straw
Air-dried; free
75-100 lbs., 2-3
1.5-2.5 tons (90-
Lightly cover
from undesire-
bales
120 bales)
entire surface
able seed &
(min. 2")
coarse material
Wood Fiber
Dyed green.
25-30 lbs.
1000-1500 lbs.
2"
Cellulose
No growth
organism
inhibiting
factors
REV 10/21 /96 3 B - 9
CONTROL MEASURE: NETS AND MATS. (See also Mulching).
Purpose: To provide immediate temporary protection of exposed steep slopes and highly
erodible soils. Also to provide temporary protection of waterway slopes.
Design Criteria/Specifications: (1) See Figure 3-2 for design features; (2) Nets and
mats used alone, without mulch, do not retain soil moisture or modify soil temperature;
(3) It is critical during installation to obtain firm, continuous contact between the net/mat
material and the soil. Without such contact, the material is useless and erosion occurs; (4)
When anchoring material, it is important to use an adequate number of staples and to roll
the material after laying it to ensure that the soil is protected. Netting should be securely
anchored to the soil with No. 11 gauge wire staples at least 6-inches long, with an overlap
of 3- inches; (5) Site preparation is the same as for temporary seeding; (6) Where soil
is highly erodible, nets should only be used in conjunction with organic mulch; (7) Jute
nets should be heavy, uniform cloth woven of single jute yarn, which, if 36- to 48-inches
wide, shall weigh an average of 1.21bs. per linear yard. Jute matting must be applied so that
it is in complete contact with the soil, otherwise erosion will occur beneath it;
(8) Wood fiber cellulose blankets are considered protective mulches and may be used alone
on erodible soils and during all times of the year.
REV 10/21/96 3B-10
Orientation of Netting and Matting
On shallow slopes, strips of netting may be applied
across the slope. (Slopes up to 1:1)
Where there is a berm at the top of the
slope, bring the netting over the berm and
anchor it behind the berm.
I Berm
q iC ► ir�_
•—III �;�..
On steep slopes, apply strips of netting parallel to
the direction of flow and anchor securely.
(Slopes greater than 1:1)
Bring netting down to a level area before
terminating the installation. Tum the end
under 6" and staple at 12" intervals.
In ditches, apply netting parallel to the direction of
flow. Use check slots every 15 feet Do not join
strips in the center of the ditch.
REV 10/21 /96 3 B -11
CONTROL MEASURE: TOPSOILING (See also Temporary Erosion Control
Seeding and Permanent Seeding).
Purpose: Provides a suitable growth medium for final site stabilization with vegetation.
Design Criteria/Specifications: (1) Stripping of existing topsoil should be confined to
the immediate construction area, and all surface runoff control structures should be in place
prior to stripping; (2) Topsoil should not be placed while in a frozen or muddy condition,
or when the subgrade is excessively wet; (3) Topsoil should be spread at a compacted
depth of 2 - 6-inches. More topsoil is needed if the subsoil is rocky; (4) Sufficient time
should be allowed in scheduling for topsoil to be spread and bonded to subsoil prior to
seeding, sodding or planting; (5) Care must be taken not to apply topsoil to subsoil if the
two soils have contrasting textures. Sandy topsoil over clayey subsoil is a particularly poor
combination, as water creeps along the junction between the soil layers and causes the topsoil
to slough.
REV 10/21/96 3 B -12
CONTROL MEASURE: TEMPORARY EROSION CONTROL SEEDING. (See
also Topsoiling, Surface Roughening, Mulching, Plastic
Sheeting and Nets and Mats).
Purpose: Reduces erosion and sedimentation by temporarily stabilizing exposed soils for
up to 1 year.
Design Criteria/Specifications: (1) Seeding can be done during the period of March 1
through September 30 (if planted between May 15 and August 15 irrigation may be
required). Seeding can sometimes also be done successfully during the remainder of the
year, October 1 through February 29, provided that the seed bed is immediately stabilized
by mulching, nets/mats or plastic sheeting; (2) Site preparation, including the installation
of surface runoff control measures, should be completed prior to seeding. The seed bed
should be firm but not compact, with a fairly fine surface. Surface roughening should be
done at right angles to the slope and preferably "track walked" up slope. "Track -walking"
is driving a crawler tractor up and down the slope, leaving a pattern of cleat imprints parallel
to slope contours; (3) "Hydroseeding" applications with approved seed -mulch -fertilizer
mixtures may also be used; (4) Soil amendments/fertilizers should be applied as
recommended by suppliers. When seeding over subsoil (without topsoil), avoid over -
fertilizing, especially near aquatic features. Instead, use mulch to assist in nourishing soil.
Project sites adjacent to bodies of water must use nonphosphorus fertilizer; (5) Apply an
appropriate seed mixture to the prepared seedbed at a rate of 1201bs. per acre. Table 3-2
gives recommended temporary erosion control seed mixture.
Maintenance: (1) Inspect seeded areas for failure and make necessary repairs and reseed
immediately; (2) Seed should be supplied with adequate moisture. Supply water as
needed, especially in abnormally hot or dry weather, or on adverse sites. Water application
rates should be controlled to prevent runoff. Insufficient amounts of water may be more
harmful than no water.
REV 10/21/96 3 B -13
Name
Proportions By
Weight
Percent Purity
Percent
Germination
Redtop (Aerostis albe)
10%
92%
90%
Annual Rye (Lolium muliflorum)
40%
98%
90%
Chewings Fescue (Festuca rebra
commutate) (Jamestown, Banner,
Shaddow or Koket)
40%
97%
80%
White Dutch Clover
I 10%
96%
90%
* Apply at a rate of 120 lbs./acre.
REV 10/21/96 3B-14
CONTROL MEASURE: PERMANENT EROSION CONTROL SEEDING. (See
also Topsoiling, Surface Roughening, Mulching, Plastic
Sheeting, Nets and Mats).
Purpose: Establishes a permanent protective layer of vegetation as fast as possible to
prevent soil erosion by wind or water, and to improve wildlife habitat and site aesthetics.
Design Criteria/Specifications: (1) Seeding should be done immediately after final
shaping if completed during the period of March 1 through September 30 (if planted between
May 15 and August 15, irrigation may be required). Sites which cannot be seeded during this
time period should be protected until the next seeding period with Mulching; (2) Site
preparation should include Topsoiling and the installation of surface runoff control mea-
sures. The seedbed should be firm with a fairly fine surface; (3) If construction fills have
left proposed seedbed with a loose, rough, or irregular surface, surface should be "track
walked" up the slope or smoothed with a blade and rolled prior to planting. "Track -walking"
is driving a crawler tractor up and down the slope, leaving a pattern of cleat imprints parallel
to slope contours; (4) If proposed seedbed has tightly compacted surface, break with chisel
plow or other suitable implement; (5) Soil amendments/fertilizers should be applied as
recommended by suppliers. Project sites adjacent to bodies of water must use nonphosphorus
fertilizer; (6) Apply an appropriate seed mixture to the prepared seed bed at a rate of 120
lbs. per acre. Table 3-3 gives recommended seed applications.
Maintenance: (1) Inspect seeded areas for failure and make necessary repairs and reseed
immediately. Conduct a follow-up survey after one year and replace failed plantings where
necessary; (2) If a stand has less than 40% cover, re-evaluate choice of plant materials and
quantities of lime and fertilizer. Re-establish the stand following seedbed preparation and
seeding recommendations, omitting lime and fertilizer in the absence of soil test results. If
the season prevents re -sowing of seed, Mulch, Nets/Mats or Plastic Sheeting is an effective
temporary cover.
REV 10/21/96 3 B -15
Name
Proportions By
Percent Purity
Percent
Weight
Germination
Urban Wlication:
30%
85%
80%
Kentucky Bluegrass (Adelphi,
Baron or Fylking)
Creeping Red Fescue (Pennant)
40%
98%
90%
Perennial Rye (Derby, Pennant
30%
95%
90%
Rural AWlication:
15%
85%
80%
Kentucky Bluegrass (pm
ratty msis) (Birka, Majestic or
Sydsport)
Tall Fescue (Festuca arundincea)
40%
95%
90%
(Arid, Jaguar or Rebel)
Perennial Rye olium Ferenne)
30%
95%
90%
(Derby or Pennant)
Chewin s Fescue(Banner)
15%
95%
90%
* Apply at a rate of 120 lbs/acre. Cover seed with topsoil or mulch no deeper than 1/2-inch.
REV 10/21/96 3B-16
CONTROL MEASURE: SURFACE ROUGHENING. (See also Erosion Control
Seeding, Mulching, Topsoiling, Permanent Seeding, Sodding).
Purpose: Aids in the establishment of vegetative cover and increases infiltration.
Design Criteria/Specifications: (1) Surface Roughening is intended to aid in the
establishment of vegetative cover, which in turn is intended to protect the face of the slope
from rainfall impact and sheetflow, bind the surface of the slope to retard erosion, and reduce
the velocity of surface runoff. Surface roughening is not intended to accomplish any of the
above by itself, and definitely should not be used to directly reduce the velocity of surface
runoff; (2) Graded slopes steeper than 3:1 but less than 2:1 should be roughened before
seeding. This can be accomplished in a variety of ways, including "track -walking", or
driving a crawler tractor up and down the slope, leaving a pattern of cleat imprints parallel
to slope contours. The tread imprints are ideal places to trap seeds and encourage plants to
become established; (3) Graded areas steeper than 2:1 should be stair -stepped with
benches. The stair -stepping will help vegetation become established and also trap soil
eroded from the slopes above; (4) See Figure 3-3 and Figure 34 for detail.
REV 10/21/96 3B-17
i�-5%00.0--O
undisturbed area
tread grooves
perpendicular to slope direction
undisturbed vegetation
diversion
dozer treads create grooves
perpendicular to slope direction
1P
5
.�alp
REV 10/21/96 3B-18
Debris from slope above
is caught by steps\ '..M;•i••�•
_ &
v
Graf _ jN t
I:.11l� I
::.UP
- :;;;:: ;.. ,•,ram
=.:.. 40w L"All
Water, soil, and fertilizer are held
by steps - plants can become
established on the steps.
Stair Stepping Cut Slopes
1
i
Grooving is cutting funuws along
the contour of a slope. In•egularities
in the soil surface catch rainwater
and provide some coverage of
lime, fertilizer and seed.
�:4•�,�f :, I I 1 I
1 1
L
Grooving Slopes
I1=1_!1!G:!IIG_=:1
REV 10/21/96 3B-19
CONTROL MEASURE: SODDING. (See also Topsoiling BW).
Purpose: Establishes permanent turf for immediate erosion protection. Also stabilizes
drainage ways where concentrated overland flow will occur.
Design Criteria/Specifications: (1) Shape and smooth the surface to final grade; (2)
Apply topsoil as per this section; (3) Lime should be added to reach a soil Ph value of
6.5 (based on soil tests); (4) Soil amendments/fertilizers should be applied as
recommended by suppliers. Project sites adjacent to bodies of water must use non -
phosphorus fertilizer. It is recommended that fertilizers used not be highly soluble; (5)
Lime and fertilizer should be worked into the soil 1 to 2-inches deep and the surface
smoothed; (6) Sod should be harvested, delivered and installed within a period of 36
hours. It should not be harvested or trawRlanted when moisture content (excessively dry or
wet) may adversely affect its survival; (7) Lay strips of sod beginning at the lowest area
to be sodded and perpendicular to the direction of water flow. Wedge strips securely in
place. Square the ends of each strip to provide for a close, tight fit. Stagger joints at least
12-inches. Staple if on steep slopes. Roll the sodded area and irrigate; (8) When sodding
is carried out in alternating strips, or other patterns, seed the areas between the sod immedi-
ately after sodding; (9) Sod should be free of weeds and be of uniform thickness (approx.
1-inch) and should have a dense root mat for mechanical strength.
Maintenance: Sodded areas should be inspected regularly, especially after large storm
events. Re -tack, re -sod, or re -seed as necessary.
REV 10/21/96 3B-20
CONTROL MEASURE: PLASTIC SHEETING.
Purpose: Provides immediate temporary erosion protection to slopes and disturbed areas
that cannot be covered by Mulching. Also, protects disturbed areas which require covering
during periods of inactivity in winter months. Plastic sheeting is the preferred covering for
seedbeds planted during winter months, in that it not only protects against heavy rains but
also provides warmth and light to promote germination and growth of seeds.
Design Criteria/Specifications: (1) Plastic sheeting should have a minimum thickness
of 6 mil and meet the requirements of WSDOT/APWA Section 9-14.5; (2) Covering
should be installed and maintained tightly in place by using sandbags or tires on ropes with
a maximum 10 foot grid spacing in all directions. All seams shall be taped or weighted down
full length and there should be at least a 12 - 24-inch overlap of all seams. Seams should
then be rolled and staked or tied; (3) Covering should be installed immediately on areas
seeded during winter months, and removed as soon as possible once vegetation is well grown
to prevent burning the vegetation through the plastic sheeting, which acts as a greenhouse;
(4) When covering is used on unseeded slopes, it should be left in place until the next
seeding period; (5) Plastic covering sheets should be buried two feet at the top of slopes
in order to prevent surface water flow beneath sheets
Maintenance: Plastic covering must be checked often for rips and places where the plastic
may be dislodged. Contact between the plastic and the ground should always be maintained.
Any air bubbles found should be removed immediately or the plastic may rip during the next
windy period. Re -anchor or replace as necessary.
REV 10/21/96 3B-21
CONTROL MEASURE: SEDIMENT TRAP.
Purpose: Collects and stores sediment from a site cleared and/or graded during
construction. It is intended for use on relatively small building areas with no unusual
drainage features, and for projects with anticipated short "build -out" time (approximately 6
months or less). It is a temporary measure with a design life of less than 1 year. Sediment
traps do not remove fine silt and clay suspended in stormwater.
Design Criteria/Specifications: (1) Sediment traps are recommended on relatively
small building sites where the tributary drainage area is less than 3 acres; (2) See Figure
3-5 and 3-6 for design features; (3) Sediment traps may be formed completely by excava-
tion or by construction of a compacted embankment. It should have a 1.5 foot deep sump
for sediment storage. The outlet should be a weir/spillway section, with the lower 2 feet
acting as a filter for sediment and the upper foot as the overflow spillway depth. A filter
fabric fence should be provided to filter the runoff from the trap prior to discharge from the
site; (4) The trap bottom should be level, with 3:1 side slopes. A 3:1 ratio between the
trap length and width is desirable. Length is defined as the average distance from the inlet
to the outlet of the trap; (5) The sediment trap should be sized to provide sufficient
volume for sediment storage (assuming a storage depth of 1.5 feet) PLUS an additional 2 feet
of storage depth for settling. The sediment volume shall be calculated by the engineer, based
on currently established practices, such as contained in the D.O.E. Stormwater Management
Manual for the Puget Sound Basin; (6) Retention ponds shall not be used for temporary
sediment and erosion control, unless approved by the Director. In the event that a retention
pond is approved for use as a sediment trap, the trap must be left at least 2 feet above the
future finished grade for the retention pond and the trap must be completely lined with filter
fabric or other device to prevent the migration of sediment to the plane of infiltration.
Maintenance: Sediment traps must be maintained until the site area is permanently
protected against erosion by vegetation and runoff from impervious surfaces is directed to
permanent drainage facilities. The key to having a functional sediment trap is continual
monitoring and regulmaintenance. The size of the trap is less important to its
effectiveness than is regular sediment removal. Sediment should be removed from the trap
when it reaches one half (%2) of the designed maximum sediment storage depth. Regular
inspections should be done and additional inspections made after each large runoff -producing
storm event.
REV 10/21/96 3B-22
1' depth of 2" - 4" rock
2' settling
1.5' sediment sl
Outflow channel is
constructed by
excavation —�
4'
1' depth
11/4" -1IN washed gravel
1' overflow depth
rnr—r T
x
filter fabric fencing
Note: May be constructed by
excavation or by building a berm. -
Cross Section — No Scale
_ overflow spillway
/ 6' minimum width
1.5' sediment storage
2' settling depth &
1' depth of 2" - 4" rock
1' depth o2/4"- 1W washed gravel
Sediment Trap Outlet — No Scale
REV 10/21/96 3B-23
CONTROL MEASURE: SEDIMENT POND.
Purpose: Collects and stores sediment from sites cleared and/or graded during
construction prior to establishment of permanent vegetation and/or construction of permanent
drainage facilities. A sediment pond is usually a temporary structure having a design life of
less than 1 year. However, it may be a more permanent facility, especially if required to
provide runoff quality control until the site area is permanently stabilized.
Design Criteria/Specifications: (1) Sediment ponds are recommended on building
sites where the tributary drainage area is less than 10 acres; (2) See Figure 3-6, 3-7, and
3-8 for design features; (3) Sediment ponds may be formed by excavation or by
construction of a compacted embankment. It may have one or more inflow points carrying
sediment -laden runoff. Baffles to spread the flow throughout the basin should be included.
A securely anchored riser pipe is the principal discharge mechanism along with an
emergency overflow spillway. The riser pipe should be solid with two 1-inch diameter
dewatering holes located at the top of the sediment storage volume on opposite sides of the
riser pipe. Outlet protection is provided to reduce erosion at the pipe outlet. A filter fabric
fence should be provided to filter the runoff from the pond prior to discharge from the site;
(4) Sediment ponds should have a maximum 3 foot deep sump for sediment storage; (5)
The pond bottom should be level, with 3:1 side slopes; (6) The sediment pond should
be sized to provide sufficient volume for sediment storage PLUS an additional 2 feet of
depth for settling. Settling depth and sediment volume storage depth shall be calculated by
an engineer (see the D.O.E. Stormwater Management Manual for the Puget Sound Basin).
(7) Retention ponds shall not be used for temporary sediment and erosion control, unless
approved by the Director, in that the collection of sediment in such a pond may later reduce
its effectiveness as a retention device. In the event that a retention pond is approved for use
as a sediment pond, the pond must be left at least 2 feet above the future finished grade for
the retention pond and the pond must be completely lined with filter fabric or other device
to prevent the migration of sediment to the plane of infiltration.
Maintenance: Sediment ponds must be maintained until the site area is permanently
protected against erosion by vegetation, and until runoff from impervious surfaces is directed
to permanent drainage facilities. The key to having a functional sediment pond is continual
monitoring and regrular maintenance. The size of the pond is less important to its
effectiveness than is regular sediment removal. Sediment should be removed from the pond
when it reaches approximately '/2 of the total designed sediment storage depth. Regular
inspections should be done and additional inspections made after each large runoff -producing
storm event.
REV 10/21/96 3B-24
Y_I • �
` OI
REV 10/21/96 3B-25
pond length z 3x pond width
filter fabric fence
P•.s emergency '
inflow, ravernow
\sPRMY
tA level botloom
r�
r
perforated drain pipe• in outlet pipe
gravel -filled trench
riser pipe w/weighted base
'Note: Sediment dawatering may be accomplished with perforated pipe in trench as shown or with a perforated
riser pipe covered with filter fabric and a gravel "cone". A control structure may also be required; see
Conditions Where Prec lice Applies.
1' spillway depth
1' freeboard
riser pipe, open at top
(principal spillway)-��
dewatering outlets
7 max.4"
! min. 2' settling depth
sediment storage
s . v 3' maximum depth '
PW
level grade
perforated drain pipe in
gravel -filled trench for sift
dewatering; trench
wrapped w/fiiter fabric full
length
provide a rebar trash rack on
riser pipes Z 18"
6' min.
emergency overflow
spillway crest
�-rse
filter fabric
outlet pipe
anti -seep collars
weighted base to
prevent floatation
Section A -A
energy dissipating rock
REV 10/21/96 3B - 2 6
Riser (outlet)
1
Inflow
Normal Pool
W� = A
L1+L2
W. = effective width of basin
A = surface area of basin when filled
to crest
L = shortest travel distances around
the baffle from inlet to outlet
Riser here Is In very
If riser is placed here no poor location; baffle
baffle Is required is required
------- 4 ---_.O
` � e'4FFLE t
Lt I W.
Normal Pool
1
Inflow i
Riser
Kill
• L, L, W
.
Baffle
Normal Pool
In this case it is t
important to place Inflow
baffle so that L, = L,
Sheets of plywood 4 ft. x 8 ft. x % in. Elevation of
exterior plywood or equivalent / riser crest
Depth of water in i
f
basin when full 1 _
3' Max. I 1 t r
U U L
Elevation of 1
basin bottom 6 ft. centers I
Posts 4 in. square
or 5 in. round
minimum set at
least 3 ft. into
ground
REV 10/21/96 3 B - 2 7
CONTROL MEASURE: FILTER FABRIC FENCE. (See also Sediment Trap,
Sediment Pond, Brush Barrier, and Inlet Barrier BMPs).
Purpose:-- __ Intercepts and detains small amounts of sediment from disturbed areas during
construction operations in order to prevent the sediment from leaving the site. Filter fabric
fences also decrease the velocity of sheet flows and low to moderate channel flows. A filter
fabric fence is a temporary structure of wood or steel fence posts, wire mesh fencing, and a
suitable permeable filter fabric. Note: filter fences are applicable for sheet or overland
flows, and cannot effectively filter large amounts of concentrated flow due to clogging.
Therefore, they should be used in conjunction with a sediment trap or pond when the flow
path length across the tributary basin exceeds 100 feet. Filter fences shall not be constructed
across streams.
Design Criteria/Specifications: (1) Filter fences should be located a) immediately
upstream of the runoff discharge point from a site, b) downslope of disturbed areas where
runoff may occur in the form of sheet runoff, and c) in minor swales/ditches, prior to or
following a sediment trap/pond, where concentrated flows do not exceed 0.5 cfs.; (2)
See Figure 3-9 for design features; (3) The geotextile used must meet the standards listed
below. A copy of the manufacturer's fabric specifications must be available on -site.
AOS (ASTM D4751)
Water Permittivity (ASTM D4491)
Grab Tensile Strength (ASTM D4632)
Grab Tensile Elongation (ASTM D4632)
Ultraviolet resistance (ASTM D-4355)
= 30-100 sieve size (0.60-0.15 min) for silt film
= 0.02 sec' min.
= 180 lbs. Min. For extra strength fabric
100 lbs. Min. For standard strength fabric
= 30% max.
= 70% min.
Standard strength fabric requires wire backing to increase the strength of the fence. Wire
backing or closer post spacing may be required to extra strength fabric if field performance
warrants a stronger fence. Where the fence is installed, the slope shall be no steeper than
2H:1V.
The following standard notes should appear with the Filter Fabric Fence Detail, in addition
to any other standard notes:
Standard Notes:
a. The filter fabric shall be purchased in a continuous roll cut to the length of
the barrier to avoid use of joints. When joints are necessary, filter fabric shall
be spliced together only at a support post, with a minimum 6-inch overlap,
and both ends securely fastened to the post.
REV 10/21 /96 3 B - 2 8
b. The filter fabric fence shall be installed to follow the contours (where
feasible).
C. When standard strength filter fabric is used, a wire support fence shall be
fastened securely to the upslope side -of the posts using heavy-duty wire
staples at least 1-inch long, tie wires or hog rings. The wire shall extend into
the trench a minimum of 4-inches. At least 24-inches or more above ground.
d. Filter fabric shall not be stapled to existing trees.
e. The trench shall be backfilled with 3/4-inch minimum diameter washed
gravel.
f. Filter fabric fences shall be inspected immediately after each rainfall and at
least daily during prolonged rainfall. Any required repairs shall be made
immediately.
g. Filter fabric fences shall be removed when they have served their useful
purpose, but not before the upslope area has been permanently stabilized.
Maintenance: (1) Filter fabric fences should be inspected immediately after each runoff -
producing rainfall and at least daily during prolonged rainfall. Any required repairs should
be made immediately; (2) Sediment should be removed when it reaches approximately one
third the height of the fence (8-inch maximum), especially if heavy rains are expected; (3)
Any sediment deposits remaining in place after the filter fence is no longer required should
be dressed to conform with the existing grade, prepared, and seeded.
REV 10/21/96 3 B - 2 9
4
N
Filter fabric material in continuous
rolls; Use staples or wire rings to
attach fabric to wine
Wire mesh support fence for slit
% film fabrics
�'u1ta�wth�►�inwvioramim
i IBn 8 by 12" bottomtrencr material
i!
I I 6' Max.
2" by 2" wood posts, standard or
better or equivalent
Wire mesh support fence
for slit film fabrics %-�
Filter fabric
material
to
Provide washed gravel backfill •i ,
or compacted native soil as —+— 1 I
directed by local government
Bury bottom of filter material in 8
8 by 12 trench
2" by 2" wood posts, s
or better or equivalent
N
T
4
rn
REV 10/21 /96 3 B - 3 0
CONTROL MEASURE: BRUSH BARRIER (See also Filter Fabric Fence BMP).
Purpose: Retains sediment from very small disturbed areas by construction of a temporary
barrier made from residue materials available from clearing and grubbing the site.
Design Criteria/Specifications: (1) Locate below disturbed areas subject to sheet or
rill erosion, where enough residue material is available for the construction of such a barrier,
and where the disturbed area is less than 1/4 acre; (2) A brush barrier should not be
considered a replacement for a sediment trap or sediment pond; (3) See Figure 3-10 for
design features; (4) Minimum height = 3-feet, maximum height = 5-feet; (4) Minimum
width, front to back, = 5-feet at base, maximum width = 15-feet; (5) To enhance the
brush barrier's filtration capacity, the designer should consider specifying filter fabric
anchored over the brush berm. The fabric shall be secured on the uphill side in the trench
with compacted backfill, and staked on the downhill side.
Maintenance: (1) Brush barriers generally require little maintenance, unless there
are very heavy deposits of sediment. Occasionally, tearing of the fabric may occur; (2)
When the barrier is no longer needed the fabric can be removed to allow natural
establishment of vegetation. Over time, the barrier will decompose.
REV 10/21/96 3B-31
min. Thigh
finer fabric draped over
brush pile and secured in —�
trench w/compacted ba;w, 1
6" x 6" (min.). trench along
uphill edge of brush barrier
L
7
`��— anchor downhill edge
r, of brush barrier w/
- twine fastened to
r-- . fabric & stakes
vegetative debris/brush piled
uniformly in row to form barrier
REV 10/21/96 3B - 3 2
CONTROL MEASURE: GRAVEL FILTER BERM.
Purpose: Intercepts and temporarily retains sediment from rights -of -way or in traffic areas
on construction sites where durability and large sediment capacity is required. This is a very
efficient method of sediment removal.
Design Criteria/Specifications: (1) See Figure 3-11 for design features; (2) Berm
material should be 3/4-inch to 3-inch well -graded gravel or crushed rock with less than 5%
fines; (3) Berm dimensions should be 1-foot high with 3:1 side slopes; (4) Berms
should be spaced as follows:
Distance Between Berms Maximum Slope
(Feet) (%)
300
5
200
10
100
>10
Maintenance: Gravel Filter Berms should be inspected regularly, and immediately
after each rainfall and at least daily during prolonged rainfall. Sediment should be removed
and filter material replaced as needed.
REV 10/21 /96 3 B - 3 3
REV 10/21/96 3B-34
CONTROL MEASURE: STRAW/HAY BALE BARRIER.
Purpose: Intercepts and detains small amounts of sediment from disturbed areas of
limited extent, preventing sediment from leaving the project site, and also decreases the
velocity of sheet flow from the face of steep slopes.
Design Criteria/Specifications: (1) See Figure 3-12 and 3-13 for design features;
(2) Locate below disturbed areas subject to sheet and rill erosion, where the size of the
drainage area is no greater than 1/4 acre per 100 feet of barrier length, where the maximum
slope length behind the barrier is 100 feet (50 feet if the slope is steeper than 10%), and
where the maximum slope gradient behind the barrier is 50% (2: 1); (3) Locate in minor
swale or ditch lines where the maximum contributing drainage area is no greater than 2 acres;
(4) Straw/hay bale barriers should not be used where their effectiveness is required for
more than 3 months; (5) For sheetflow applications: a) Bales should be placed in a
single row, lengthwise on the contour, with ends of adjacent bales tigWIX abutting one
another; b) All bales should be either wire -bound or string -tied. Straw bales should be
installed so that bindings are oriented around the sides rather than along the tops and bottoms
of the bales in order to prevent deterioration of the bindings; c) The barrier should be
entrenched and backfilled. A trench should be excavated the width of the bale and the length
of the proposed barrier to a minimum depth of 4-inches. The trench should be deep enough
to remove all grass and other material which might allow underflow. After the bales are
staked and chinked (filled by wedging), the excavated soil should be backfilled against the
barrier. Backfill soil should conform to the ground level on the downhill side and should be
built up to 4-inches against the uphill side of the barrier; d) Each bale should be securely
anchored by at least 2 stakes or rebars driven through the bale. The first stake in each bale
should be driven toward the previously laid bale to force the bales together. Stakes or rebars
should be driven deep enough into the ground to securely anchor the bales. Stakes should
not extend above the bales but instead should be driven flush with the top of the bale for
safety reasons; e) The gaps between the bales should be chinked (filled by wedging) with
straw to prevent water from escaping between the bales. Loose straw scattered over the area
immediately uphill from a straw bale barrier tends to increase barrier efficiency. Wedging
should be done carefully in order not to separate the bales; (6) In channel flow applica-
tions: a) The bales should be placed in a single row, lengthwise, orientedyemendicular
to the direction of flow, with ends of adjacent bales tightly abutting one another; b) The
remaining steps for installing a straw bale barrier for sheetflow applications apply here,
except that the barrier should be extended to such a length that the bottoms of the end bales
are higher in elevation than the top of the lowest middle bale to assure that sediment -laden
runoff will flow either through or over the barrier but not around it.
Maintenance: (1) Straw/Hay bale barriers should be inspected immediately after
each runoff -producing rainfall and at least daily during prolonged rainfall; (2) Close
attention should be paid to the repair of damaged bales, end runs, and undercutting beneath
bales; (3) Necessary repairs to barriers or replacement of bales should be accomplished
REV 10/21/96 3 B - 3 5
promptly; (4) Sediment deposits should be removed after each runoff -producing rainfall.
They should be removed when the level of deposition reaches approximately 1/3 the height
of the barrier; (5) Any sediment deposits remaining in place after the straw bale barrier
is no longer required should be dressed to conform to the existing grade, prepared and
seeded; (6)-- Straw/liay -bale banners are temporary and -Have a life expectancy of 3-months
or less. They should be removed and replaced with new bales until upslope areas have been
stabilized.
REV 10/21/96 3B- 3 6
1. Excavate the trench.
�-�- �.. ,i• 4"
Flow �
Me
width
8. Wedge loose straw between bales.
2. Place and stake straw bales.
1.
4. BackEM and compact the excavated
soil.
I
Construction of A Straw Bale Barrier
LUPoints A should be higher than .c�A _,�:5b ••+t
point
Proper Placement of Straw Sale Barrier In Drainage Way
REV 10/21/96 3B-37
Binding Wire
or Twine .,
Filtered Runoff
Staked and Entrenched Stray"
Bate
Compacted Soffto
Prevent Piping
/ Sediment Laden
Runoff
REV 1021/96 3B- 3 8
CONTROL MEASURE: FILTER FABRIC FENCE INLET BARRIER.
Purpose: Prevents sediment from entering storm drainage system prior to permanent
stabilization of the disturbed area.
Design Criteria/Specifications: (1) This device is applicable where the inlet drains a
relatively small (less than 1 acre) flat area (less than 5% slope); (2) See Figure 3-14 for
design features; (3) Place 2" x 2" wooden stakes around the perimeter of the inlet a
maximum of 3-feet apart and drive them at least 18- inches into the ground. The stakes must
be at least 3-feet long; (4) Excavate a trench approximately 8- inches wide and 12-inches
deep around the outside perimeter of the stakes; (5) Staple the filter fabric (material
specifications: see the section on Filter Fabric Fence) to the wooden stakes so that 32-
inches of the fabric extends and can be formed into the trench. Use heavy-duty wire staples
at least 1/2-inch long; (6) Backfill the trench with 3/4-inch minus washed gravel all the way
around; (7) Do not place fabric under the grate, as the collected sediment may fall into the
drain when the fabric is retrieved.
Maintenance: Inspections should be made on a regular basis, especially after large
storm events. If the fabric becomes clogged, it should be replaced. Sediment should be
removed when it reaches approximately 1/3 the height of the fence. If a sump is used,
sediment should be removed when it fills approximately 1/3 the depth of the hole.
REV 10/21/96 3B-39
Drop Inlet
Filterwith Grate
Stakes
Stakes T
Titer Fabric
--_7
Runoff Water
with Sediment Washed Gravel
� Filtered Water
'r I 12" '1$ ~
I
Buried Fitter
Fabric (�
8"
REV 10/21/96 3 B - 4 0
CONTROL MEASURE: BLOCK AND GRAVEL FILTER INLET BARRIER.
Purpose: Prevents sediment borne in heavy runoff flows from entering a storm drainage
system prior to permanent stabilization of the disturbed area.
Design Criteria/Specifications: (1) This device is applicable where flows greater than
0.5 cfs are expected, but inlet will not be exposed to traffic; (2) See Figure 3-15 for design
features; (3) Place concrete blocks lengthwise on their sides in a single row around the
perimeter of the inlet, so that the open ends face outward, not upward. The ends of adjacent
blocks should abut. The height of the barrier can be varied, depending on design needs, by
stacking combinations of blocks that are 4-inches, 8-inches and 12-inches wide. The row of
blocks should be at least 12-inches but not greater than 24-inches high; (4) Place wire
mesh over the outside vertical face (open end) of the concrete blocks to prevent stone from
being washed through the blocks. Use hardware cloth or comparable wire mesh with Y2-inch
openings; (5) Pile stone against the wire mesh to top of the blocks. Use 3/4- to 3-inch
washed gravel.
Maintenance: (1) Inspections should be made on a regular basis, especially after
large storm events. Sediment should be removed when it reaches approximately 1/3 the
height of the barrier. If a sump is used, sediment should be removed when it fills approxi-
mately 1/3 the depth of the hole; (2) If the stone filter becomes clogged with sediment, the
stones must be pulled away from inlet and cleaned or replaced. Since cleaning of gravel at
a construction site may be difficult, an alternative approach would be to use the clogged
stone as fill and put fresh stone around the inlet.
REV l 0/21 /96 3 B - 41
I.igurc 3-15 BLOCK AND GRAVET FILTF;R INLET BARRIER
CONTROL MEASURE: GRAVEL AND WIRE MESH FILTER INLET BARRIER
Purpose: Prevents sediment from entering a storm drainage system prior to permanent
stabilization of the disturbed area, while protecting the temporary inlet barrier from
construction traffic.
Design Criteria/Specifications: (1) This device is applicable where flows greater than
0.5 cfs are expected and construction traffic may occur over the inlet; (2) See Figure 3-16
for design features; (3) Place wire mesh over the drop inlet so that the wire extends a
minimum of 1 foot beyond each side of the inlet structure. Use hardware cloth or
comparable wire mesh with Y2-inch openings. If more than one strip of mesh is necessary,
overlap the strips. Place filter fabric (material specifications: see the section on Filter
Fabric Fence) over wire mesh; (4) Extend the filter fabric beyond the inlet opening at
least 18-inches on all sides. Place 3/4- to 3-inch washed gravel over the filter fabric/wire
mesh. The depth of the gravel should be at least 12-inches over the entire inlet opening.
Maintenance: (1) Inspections should be made on a regular basis, especially after
large storm events. Sediment should be removed when it reaches approximately 1/3 the
height of the gravel. If a sump is used, sediment should be removed when it fills approxi-
mately 1/3 the depth of the hole; (2) If the stone filter becomes clogged with sediment,
the stones must be pulled away from the inlet and cleaned or replaced. Since cleaning of
gravel at a construction site may be difficult, an alternative approach would be to use the
clogged stone as fill and put fresh stone around the inlet; (3) If the filter fabric becomes
clogged, it should be replaced.
REV 10/21/96 3B-43
18" Min. Gravel (12" Min. depth)
Runoff
Waterwith
Sediment
MR" lu
Sediment
�-- Filtered Water \- Wire Mesh
with Filter
Fabric on top
REV 10/21/96
3B-44
CONTROL MEASURE: PIPE SLOPE DRAINS. (See also Interceptor Dike/Berm
and Swale 13W).
Purpose:. Carries concentrated runoff down steep slopes without gullies, channel
erosion, or saturation of slide -prone soils. Temporary pipe slope drains can provide valuable
protection of exposed slopes until permanent drainage structures can be installed.
Design Criteria/Specifications: (1) When used in conjunction with interceptor
dikes/berms and swales, temporary pipe slope drains can be used to convey stormwater
from the entire drainage area above a slope to the base of the slope without erosion. It is very
important that these temporary structures be installed properly since their failure will often
result in severe gully erosion. The entrance section should be securely entrenched, all
connections should be watertight, and the conduit should be anchored securely; (2) See
Figure 3-17 for design features; (3) The capacity for temporary drains should be sufficient
to handle the peak flow from a 10-year, 24-hour design storm (may be computed using the
Rational Method); (4) The maximum drainage area per pipe should be 10 acres. For larger
areas, a rocklined channel should be installed (see Rip Rap BMP), or more than one pipe
should be installed; (5) The entrance should consist of a standard flared end section for
drain pipes 12-inches and larger with a minimum 6-inch toe plate to prevent runoff from
undercutting the pipe inlet. The slope of the entrance should be at least 3 percent; (6) The
soil around and under the pipe and entrance section should be thoroughly compacted; (7)
The flared inlet section should be securely connected to the slope drain and have gasketed,
watertight connecting bands; (8) Slope drain sections should be securely fastened together
and have gasketed watertight fittings, and be securely anchored into the soil; (9)
Interceptor dikes should be used to direct runoff into a slope drain. The height of the dike
should be at least 1-foot higher at all points than the top of the inlet pipe; (10) The area
below the outlet should be stabilized with a rip rap apron (see Rip Rap BMP). If the pipe
slope drain may convey sediment -laden runoff, it should be directed to a sediment
trap/pond.
Maintenance: Inlet and outlet points should be checked regularly, and especially after
heavy storms. The inlet should be free of undercutting, and no water should be going around
the point of entry. If there are problems, the headwall should be reinforced with compacted
earth or sand bags. The outlet point should be free of erosion and installed with appropriate
outlet protection.
REV 10/21 /96 3 B - 4 5
Discharge into a stabilized Earth Dike
watercourse or a sediment
trapping device or onto a
stabilized area I _ 1�
Corrugated metal or
CPEP pipe
Slope = 2:1 � H= D + 12«
elbows
Slope 3% or
steeper
6" min.
cutoff Waii
Standard flared
Corrugated metal entrance section
or CPEP pipe ` \\\� Diameter D (for pipe 212")
J
4' min. at less
than 1 % slope
.. ����
1�
Riprap per Table 7-4
Niepprth of apron shall be
qual to pipe diameter
REV 10/21/96 3B-46
CONTROL MEASURE: INTERCEPTOR DIKE/BERM AND SWALE. (See also
Pipe Slope Drains).
Purpose: Intercepts storm runoff from drainage areas above unprotected slopes and
directs it to a stabilized outlet. When placed above a slope, it reduces the volume of water
reaching the disturbed area by intercepting runoff from above. When placed horizontally
across a slope following the contours, it reduces the velocity of runoff flowing down the
slope by reducing the distance that the runoff can flow directly downhill.
Design Criteria/Specifications: (1) See Figure 3-18 for design features; (2) Minimize
construction traffic over temporary dikes; (3) Dikes/Berms should meet the following
design criteria:
Top Width: 2 feet minimum.
Height: 18-inches minimum. Measured from upslope toe and at a
compaction of 90% Modified Proctor.
Side Slopes: 2:1 or flatter.
Grade (along Topography dependent, except that dikes should
toe of dike be limited to grades not exceeding 5%, with
or berm): positive drainage to a suitable outlet.
Stabilization: Use appropriate BMPs for sheet flow based on runoff
velocities and dike materials.
Outlet: The upslope side of the dike should provide positive drainage
to the dike outlet. No erosion should occur at the outlet.
Provide energy dissipation measures as necessary. Sediment -
laden runoff should be released through a sediment trap
and/or sediment pond.
(4) Interceptor swales should meet the following design criteria:
Bottom Width: 2 feet minimum; the bottom width should be level.
Depth: 1 foot minimum.
Side Slopes: 2:1 or flatter.
Grade of Maximum 5%, with positive drainage to a suitable outlet (such
swale: as a sediment trap and/or sediment pond).
REV 10/21/96 3B-47
Stabilization: Apply erosion control seed or rock. Rock should be 12-
inches thick, pressed into the bank and extending at least fl-
inches vertical from the bottom.
Outlet: Level spreader or rip rap to stabilized outlet sediment trap
and/or sediment pond.
(5) Dike/berm and swale spacing should meet the following criteria:
< 5% 300 feet
5% - 10% 200 feet
10% - 25% 100 feet
25% - 50% 50 feet
Maintenance: The dike/berm or swale should be inspected after every major storm
and repairs made as necessary. Damage caused by construction traffic or other activity
should be repaired before the end of each working day.
REV 10/21 /96 3 B - 4 8
REV 10/21/96 3B-49
CONTROL MEASURE: SUBSURFACE DRAINS. (See also Filter Fabric Fence,
Sediment Trap or Sediment Pond BNIPs).
Purpose: Provides a dewatering mechanism for draining excessively wet, sloping soils;
usually consists of an underground perforated pipe that will intercept and convey
groundwater.
Design Criteria/Specifications: (1) See Figure 3-19 for design features; (2) Subsurface
drains may be relief drains or interceptor drains. Relief drains are used either to lower the
water table or to remove surface water. They are installed along a slope and drain in the
direction of the slope. They can be installed in a parallel pattern, a herringbone pattern, or
a random pattern. Interceptor drains are used to remove water as it seeps down a slope to
prevent the soil from becoming saturated and.subject to slippage. They are installed across
a slope and drain to the side of the slope. They usually consist of a single or a series of single
pipes instead of a patterned layout; (3) Subsurface drains should be sized for the required
capacity; (4) The minimum effective diameter for a subsurface drain should be 4-inches;
(5) The minimum velocity recommended to prevent silting is 1.4 ft/sec. The line should
be laid to achieve at least this velocity; (6) Gravel and filter fabric should be used around
all drains for proper bedding and filtration of fine materials; (7) The outlet of the subsurface
drain should empty into a sediment trap or sediment pond. If free of sediment, it should
empty into a receiving channel, swale or stable vegetated area. The outlet should be
adequately protected from erosion and undermining; (8) The strength and durability of the
pipe should be adequate for site conditions in accordance with the manufacturer's
specifications; (9) The trench should be constructed on a continuous grade with no reverse
grades or low spots; (10) Soft or yielding soils under the drain should be stabilized with
gravel or other suitable material; (11) Deformed, warped or otherwise unsuitable pipe
should not be used; (12) Backfilling should be done immediately after placement of pipe.
No sections of pipe should remain uncovered overnight. Backfill material should be placed
in the trench in such a manner that the drain pipe is not displaced or damaged.
Maintenance: (1) Subsurface drains should be checked periodically to insure that they are
free -flowing and not clogged with sediment; (2) The outlet should be kept clean and free
of debris; (3) Surface inlets should be kept open and free of sediment and other debris;
(4) Trees located too close to a subsurface drain often clog the system with their roots. If
a drain becomes clogged, relocate the drain or remove the trees (if tree removal is permitted);
(5) Where drains are crossed by heavy vehicles, the line should be checked to insure that
it is not crushed.
REV 10/21 /96 3 B - 5 0
� A
Lateral
Main
Outlet
Parallel
11
Filter Fabric
8/•" minus Gravel
a/tisu�.��w�ii ebf
Typical Section
•—Water Table Before Drainage
Water Table After Drainage
Interceptor Drain
Seepage Area
Groundwater Flow Impermeable Layer
REV 10/21/96 3 B - 51
CONTROL MEASURE: COVER AND PROPERLY LOCATE STOCKPILES.
(See also Filter Fabric Fence, Interceptor Dike/Berm and
Swale, Plastic Sheeting, Mulching, Nets and Mats).
Purpose: Covering and properly locating earth stockpiles can reduce or prevent
excessive erosion of the stockpiled material.
Design Criteria/Specifications: (1) Earth stockpiles should be set back at least 50 feet
from downslope drainage features (e.g. channels, catch basins, detention ponds, pavement,
stream banks, critical drainage areas); (2) Stockpiles should be located on the uphill side
of the excavated area wherever possible so that they can act as diversions; (3) Earth
stockpiles should not be placed on pavement without implementation of a procedure to
prevent sediment transport; (4) Earth stockpiles should be completely covered or
otherwise stabilized with an appropriate BUT on a daily basis during winter months and
within 30 days during dry seasons. (5) The bottom of a stockpile should be circled with
an interceptor swale and/or filter fabric fence to catch sediment -laden runoff from the
stockpile.
REV 10/21/96 3B-52
CONTROL MEASURE: RESTRICT PLACEMENT OF CONSTRUCTED
SLOPES OR EARTHWORKS. (See also Plastic
Sheeting, Nets and Mats BUTs). .
Purpose: Prevent the likelihood of earth material sloughing, sliding or eroding into
natural water bodies.
Design Criteria/Specifications: (1) Do not locate cut or fill slopes near natural bodies
of water; (2) Do not dump or otherwise place earth into, or in the proximity of, natural
bodies of water; (3) Exposed soil at stream crossings or near other natural bodies of water
which could slough into the water should not be left at an angle steeper than 2:1 unless
engineered and reinforced to withstand sloughing and erosion; (4) A filter fabric fence (or
other sediment trapping device) should be placed at the toe of slopes located near natural
bodies of water or streams; (5) exposed soil located in the immediate tributary area of a
natural body of water should be stabilized on a daily basis using slope covering such as
plastic sheeting, nets and mats, or other means which will positively prevent erosion; (6)
Roads and approaches over culverts should be stabilized with crushed rock or other
appropriate means within 24 hours of reaching grade.
Note that Hydraulic Project Approval permits (State of Washington Department of Fish and
Wildlife) are required for work at stream crossings. Also note that work near or in streams
or other natural bodies of water may be subject to additional requirements of other
ordinances regarding critical areas and wetlands.
REV 10/21/96 3B-53
CONTROL MEASURE: STRUCTURAL STREAMBANK STABILIZATION.
(See also Rip Rap BMP).
Purpose: Protects stream banks from the erosive forces of moving water by
construction of permanent structural measures.
Design Criteria/Specification: (1) Design should be based on criteria and input/review
from a qualified fisheries biologist; (2) Since each reach of a channel requiring protection
is unique, measures for streambank protection should be installed according to a plan and
adapted to the specific site; (3) See Chapter 7, Collection and Conveyance Facilities,
concerning open channels and bank stabilization; (4) Structural streambank stabilization
measures should conform to Department of Fish and Wildlife permit requirements.
Note that Hydraulic Project Approval permits (State of Washington Department of Fish and
Wildlife) are required for work at stream crossings. Also note that work near or in streams
or other natural bodies of water may be subject to additional requirements of other
ordinances regarding critical areas and wetlands.
REV 10/21/96 3B- 54
CONTROL MEASURE: VEGETATIVE STREAMBANK STABILIZATION.
Purpose: Protects stream banks from erosive forces of moving water through the use
of vegetation.
Design Criteria/Specifications: Streambank stabilization design should be based on
criteria and input/review from a qualified fisheries biologist. See also Chapter 7, Collection
and Conveyance Facilities, concerning open channels and streambank stabilization.
Note that Hydraulic Project Approval permits (State of Washington Department of Fish and
Wildlife) are required for work at stream crossings. Also note that work near or in streams
or other natural bodies of water may be subject to additional requirements of other
ordinances regarding critical areas and wetlands.
REV 10/21/96 3B-55
CONTROL MEASURE: OUTLET PROTECTION. (See also Rip Rap BMP).
Purpose: Prevents scour at channel or pipe outlets, minimizes potential for downstream
erosion or flooding by reducing the velocity of concentrated stormwater flows.
Design Criteria/Specifications: (1) All outfalls should be provided with a rock splash
pad; (2) Mechanisms which reduce velocity prior to discharge from an outfall are
encouraged (e.g. drop manholes or rapid expansion into pipes of larger diameter); (3) See
Table 7-4 in Chapter 7, for recommended rock sizes for rock protection at outfalls; (4)
Engineered energy dissipators must be used for outfalls with velocity at design flow greater
than 20 fps.
Maintenance: Inspect regularly and following heavy rainfall events and restore or replace
damaged facilities. The outlet should remain free of undercutting.
REV 10/21/96 3B-56
CONTROL MEASURE: LEVEL SPREADER
Purpose: Reduces the velocity of concentrated runoff and converts concentrated runoff
to sheetflow for release onto areas stabilized by existing vegetation.
Design Criteria/Specifications: (1) See Figure 3-20 for design features; (2) The grade
of the channel for the last 20 feet before entering the level spreader should be less than or
equal to 1 percent. The grade of the level spreader should be 0 percent to insure uniform
spreading of storm runoff; (3) A 6-inch high gravel berm spreader should be placed across
the level lip and should consist of washed crushed rock, 2 to 4-inch or 3/4-inch to 1 '/z-inch
size; (4) The spreader length should be determined by estimating the flow expected from
the 10-year, 24-hour storm, and selecting the appropriate length from the following table:
0 - 0.10
15
0.10 - 0.20
20
0.20 - 0.30
30
0.30 - 0.40
40
(5) the depth of the spreader as measured from the lip should be at least 6-inches and it
should be uniform across the entire length; (6) The slope of the undisturbed outlet should
not exceed 20 percent.
Maintenance: The spreader should be inspected after every runoff event to insure
that it is functioning correctly. The contractor should avoid the placement of any material
on or prevent construction traffic across the structure. If the spreader is damaged by
construction traffic, it should be immediately repaired.
REV 10/21/96 3B-57
00*
Interceptor Berm
Last 20' of Interceptor e
not to exceed 1 % Grade
Channel Grade 0%
Stabilized Slope
6" Gravel Berm Spreader
Undisturbed Outlet
REV 10/21/96 3 B - 5 8
S
CONTROL MEASURE: DIVERSION CHANNELS AND DITCHES.
Purpose: Collects and conveys upslope contributing runoff prior to entering exposed
soil areas and routes it around the construction site.
Design Criteria/Specifications: (1) Concentrated drainage flow entering the construction
site should, whenever possible, either be conveyed around the areas of the site that are to be
distudrA or the existing drainage channel through the site should be left undisturbed. Off -
site drainage flowing through a construction site must be discharged at its natural discharge
location; (2) See Chapter 7, Collection and Conveyance Facilities, concerning open
channel design. See also Outlet Protection BMPs; (3) Temporary on -site conveyance
channels and ditches should be designed and constructed to accommodate the peak flow from
a 10-year, 24-hour design storm event. for the post -development condition without erosion,
with 0.5 feet of freeboard; (4) Stabilization measures to prevent erosion of outlets,
adjacent stream banks, slopes, and downstream reaches should be provided at the outlets
of all pipes and channels.
REV 10/21 /96 3 B - 5 9
CONTROL MEASURE: CHECK DAMS.
Purpose: Reduces the velocity of concentrated flows, reducing erosion of the swale or
ditch and slows water velocity to allow retention of sediments. Check dams are not
permitted in streams unless approved by the Department of Fish and Wildlife.
Design Criteria/Specifications: (1) See Figure 3-21 for design features; (2) Check
dams in association with sumps work more effectively at slowing flow and retaining
sediment; (3) Check dams can be constructed of rock, logs or pea -gravel filled sandbags.
A 1-foot deep sump should be provided immediately upstream of each check dam; (4)
The maximum spacing between the dams should be such that the toe of the upstream dam
is at the same elevation as the top of the downstream dam; (5) Rock check dams should
be constructed of appropriately sized rock, such as rock spalls, 4-inch minus. The rock
should be hand or machine placed (no dumping allowed) to achieve complete coverage of
the ditch or swale and to ensure that the center of the dam crest is lower than the crest ends.
The rock used should be large enough to stay in place given the expected design flow
through the channel; (6) Log check dams should be constructed of 4 to 6-inch diameter
logs. The logs should be embedded into the soil at least 18-inches. Removal of log check
dams will result in more disturbance of the soil than will the removal of rock check dams.
Consequently, extra care should be taken to stabilize the area when log dams are used in
permanent ditches or swales; (7) In the case of grass -lined ditches and swales, check dams
should be removed when the grass has matured sufficiently to protect the ditch or swale
unless the slope of the Swale is greater than 4%. The area beneath. the check dams should be
seeded and mulched immediately after dam removal.
Maintenance: Check dams should be monitored for performance and sediment
accumulation during and after each runoff -producing storm event. Sediment should be
removed when it reaches 1 /3 the sump depth.
REV 10/21/96 3 B - 6 0
4"-6" Logs
• i�•1 • ♦ ♦ w • I 1 � M I
Aj.:
a. Log Check Dam
NO SCALE
rock.._=,.:
Flow
b. Rack Check Dom
NO SCALE
c. Spacing Between Check Dams
L = the distance such that
points A & B are of equal
REV 10/21/96 3 B - 61
CONTROL MEASURE: RESTRICT THE LENGTH OF TRENCH OPENED AT
ANY ONE TIME.
Purpose: Control the erosion of open trench bottoms by limiting the length of run, thus
limiting the velocity of water flowing through the trench.
Design Criteria/Specifications: For trenches on a downslope of more than 5%, no more
than 500-feet of trench should be opened at one time.
REV 10/21/96 3 B - 6 2
CONTROL MEASURE: DIVERT SURFACE RUNOFF FROM ENTERING
TRENCHES. (See also Interceptor Dike/Berm and Swale
BMP).
Purpose: Diverting surface runoff from entering open trenches will reduce the flow of
water into the trenches and reduce the degree of erosion of trench bottoms.
Design Criteria/Specifications: Place excavated material from trenches on the uphill
side of the trench when safety and space constraints allow. A note to this effect should be
included on the ESC plan.
REV 10/21/96 3B-63
CONTROL MEASURE: DISCHARGE DEWATERING DEVICES PROPERLY.
(See also Sediment Trap and Sediment Pond BMP).
Design Criteria/Specifications: Direct the discharge of dewatering devices from
trenches or other areas so as not to adversely impact flowing streams, drainage systems or
off -site property. Dewatering devices shall not discharge to sanitary sewers.
REV 10/21/96 3 B - 64
CHAPTER 4
GRADING
CHAPTER 4
GRADING
CONTENTS
4.1
INTRODUCTION
4-2
4.2
APPLICABILITY
4-2
4.2.1
PERMIT EXEMPTIONS
4-3
4.2.2
ENGINEERED GRADING
4-4
4.3
SEPA REQUIREMENTS
4-4
4.4
REVIEW COORDINATION
4-5
4.6
PERMIT REQUIREMENTS
4-6
4.6.1
CONSTRUCTION LIMITS
4-6
4.6.2
CHANGED CONDITIONS, STOP WORK ORDER AND PERMIT
REVOCATION
4-6
4.6.3
ENGINEERS' NOTIFICATION OF NONCOMPLIANCE
4-6
4.6.4
PERMIT TIME LIMIT
4-7
4.6.5
INSPECTIONS
4-7
4.6.6
COMPLETION OF WORK AND FINAL APPROVAL
4-7
4.7
GRADING STANDARDS
4-8
4.7.1
SOILS ENGINEERING INVESTIGATION REPORT
4-8
4.7.2
GEOTECHNICAL ENGINEERING INVESTIGATION REPORT
4-8
4.7.3
EXCAVATIONS
4-8
4.7.4
FILLS AND EMBANKMENTS
4-9
4.7.5
SETBACKS
4-10
4.7.6
DRAINAGE AND TERRACING
4-11
4.7.7
IMPERVIOUS SURFACES
4-12
4.7.8
EROSION CONTROL
4-13
GRADING
4.1 INTRODUCTION
These regulations establish minimum requirements for grading and earthwork construction
including excavating and filling. They are intended to promote the general health, safety,
and welfare of the public and require the Applicant to follow sound land use and
development procedures.
The purpose of this chapter is to mitigate, minimize, or eliminate the impacts caused by
grading activities on public or private property.
It is not the intent of these policies to make Port Orchard a guarantor or protector of public
or private property in regard to land development activity.
4.2 APPLICABILITY
A Stormwater Management Permit shall be required prior to the commencement of the
following grading activities:
1. When grading activities exceed 150 cubic yards of earth, OR;
2. When grading activities will result in a temporary or permanent slope having a steepness
exceeding 3 to 1 (3 feet horizontal to 1 foot vertical) and having a total slope height,
measured vertically from toe of slope to top of slope, exceeding 5 feet, OR;
3. When grading activities include the construction of embankment berms which have the
potential to impound water to a depth exceeding 2 feet and/or have a maximum volume
exceeding 2,500 cubic feet at maximum water surface depth, OR;
4. When grading activities will result in the diversion of existing drainage courses, both
natural and man-made, from their natural point of entry or exit from the grading site, OR;
5. When grading activities will result in the creation of impervious or nearly impervious
surfaces that are 5,000 square feet or more in area, OR;
6. When grading activities involve the clearing or disturbance of 1 acre or more of land.
4-2
4.2.1 PERMIT EXEMPTIONS
The following grading activities shall not require the issuance of a Stormwater Management
Permit:
1. Excavation for utilities, wells, or tunnels under separate permit.
2. An excavation below finished grade for basements and footings of a building, retaining
wall or other structure authorized by a valid building permit. This shall not exempt the
placement of any fill material removed from such an excavation, and shall not exempt
any excavation beyond the limits of the basement or footing excavations having an
unsupported height greater than 5 feet after the completion of such a structure.
3. Agricultural crop management outside of critical drainage areas, limited to the
preparation of soil by turning, discing, or other means endorsed by the Kitsap
Conservation District.
4. Excavation for cemetery graves.
5. Disturbance of topsoil to a maximum depth of 12" confined to less than 1 acre of land
clearing activity.
6. Solid waste disposal sites, wood waste fills, problem waste and demolition waste sites
authorized pursuant to R.C.W. 70.95, and regulations presently enacted or as may be
amended or as specifically approved by the Bremerton Kitsap County Health
Department. Grading activities associated with said disposal activities will not be
exempt from the provisions of the Stormwater Management Ordinance.
7. Mining, quarrying, excavating, processing, and/or stockpiling of rock, sand, gravel,
aggregate or clay where established and provided by law, provided such operations do
not affect the lateral support of, or increase the stresses in, or pressure upon, any adjacent
or contiguous land.
8. Exploratory excavations under the direction of a qualified civil engineer.
9. Grading activities already approved by separate permits granted by any governing
authority.
10. Emergency sandbagging, diking, ditching, filling, or similar work during or after periods
of extreme weather conditions when done to protect life or property.
11. Maintenance work on public roads performed under the direction of Port Orchard
Department of Public Works or Washington State Department of Transportation
personnel.
4-3
4.2.2 ENGINEERED GRADING
Grading activities, as well as all other site development -related activities, must comply with
the requirements of this Manual regarding land clearing, the conveyance of surface runoff,
and the quantity and quality control of surface runoff.
A grading plan and an erosion and sedimentation control plan, prepared by a civil engineer,
shall be submitted to the Department of Public Works for review and approval of the
following grading activities:
o The displacement of 5,000 or more cubic yards of material within the project site, OR;
o The creation and/or displacement of less than 5,000 cubic yards of material when the
Director deems that engineering is appropriate.
In addition, a soils report and/or a geotechnical report may be required for certain site
conditions or grading activities as described in this chapter.
A Performance Covenant or a performance bond and commercial liability insurance shall be
provided as a minimum requirement prior to the issuance of a Stormwater Management
Permit for engineered grading activities.
4.3 SEPA REQUIREMENTS
Unless the proposed grading has already been addressed in a SEPA (State Environmental
Protection Act) Environmental Checklist submitted as part of a land use application, a SEPA
Environmental Checklist must be submitted at the time of application for a Stormwater
Management Permit for grading, for the following proposed activities:
o The displacement of 500 or more cubic yards of material.
o Clearing or grading within or near streams, bodies of water, or other critical areas, as
determined by the City.
A SEPA Environmental Checklist will not be required when other ordinances specifically
exempt the proposed activity from meeting SEPA requirements.
A final determination of whether or not a SEPA Environmental Checklist is required for a
project will be made by the Director.
4-4
A Determination of Non -Significance (D.N.S.) or a final Environmental Impact Statement
(F.E.I.S.) must be issued before the Stormwater Management Permit is issued. Provisions
contained in the Determination of Non -Significance or the final Environmental Impact
Statement shall be considered when approving the Stormwater Management Permit for
grading, and the conditions of issuance of the permit shall not be less restrictive than the
D.N.S. or the F.E.I.S.
The SEPA Environmental Checklist review may run concurrently with the application for
the Stormwater Management Permit. Any questions or comments concerning the SEPA
Environmental Checklist review should be addressed to the City Department of Public
Works.
4.4 REVIEW COORDINATION
When grading activities are proposed for a site and such activities are related to a project
requiring land use approval from the City, a Stormwater Management Permit for the
proposed grading activity will not be issued by the City until all land use permits and/or
approvals are granted.
Conditions imposed by the City affecting the Stormwater Management Permit for grading
must be incorporated into the project's design and must be implemented prior to final
approval of the project.
When development is intended or proposed on a site affected by issuance of a Stormwater
Management Permit for grading, work allowed by issuance of that permit shall be
subordinate to future site development conditions or requirements.
When grading on a parcel of land is proposed which is intended to facilitate the future
development of a site, or which may limit the future use of the site, the City may at its own
discretion require that a notice be recorded as a public record containing provisions which
will include the nature and extent of the grading which has occurred on the parcel. The latest
version of the form entitled "Notice of Grading or Filling" shall be used.
4-5
4.5 PERMIT REQUIREMENTS
4.5.1 CONSTRUCTION LIMITS
Prior to the commencement of permitted clearing and grading activities, clearing and grading
limits must be clearly and visibly identified using staking and/or flagging. Under no
circumstances may areas beyond the property boundaries be disturbed without the prior
approval of the owners of those properties and without the issuance by the City of all
necessary permits to work within these areas. Clearing limits may require inspection by the
Department of Public Works prior to commencement of site work activities.
4.5.2 CHANGED CONDITIONS, STOP WORK ORDER, AND PERMIT
REVOCATION
Should the City become aware of conditions that invalidate the original design data used to
obtain the Stormwater Management Permit or determine that the Applicant is not complying
with the conditions of the Permit or approved plans, the City may revoke the original permit
and/or order work stopped on the project. The City may require the Applicant to resubmit
information or plans for review and approval and apply for a new Stormwater Management
Permit.
The City may order all or part of a permitted work stopped for any period of time for any of
the following reasons:
1. The Applicant fails to comply with the conditions of the permit.
2. The permit was granted on the basis of erroneous information submitted to the City by
the Engineer or Applicant.
3. The weather or weather -created conditions cause off -site or downstream drainage, water
quantity, or water quality problems.
4. The work has become a hazard to life, endangers property or adversely affects the use
or stability of a public way or drainage course.
4.5.3 ENGINEERS' NOTIFICATION OF NONCOMPLIANCE
If, in the course of fulfilling his/her responsibility under this chapter, the project civil
engineer or any associated engineer finds the work is not being done in conformance with
this chapter or with the conditions of permit approval or the approved Grading Plan, the
discrepancies shall be reported immediately in writing to the person in charge of the grading
4-6
work and to the Director. Recommendations for corrective measures, if necessary, shall be
submitted.
4.5.4 PERMIT TIME LIMIT
A Stormwater Management Permit, for grading only, shall expire upon approved completion
of all work, or 6 months from the date the permit was issued, whichever comes first. If the
Applicant requests a time extension for the Stormwater Management Permit, the Director has
the authority to grant or to deny such an extension request. In the event that work is not
completed at the time of expiration of the permit, and the permit expiration date has not been
extended by the Director, all work must cease and a new Stormwater Management Permit
application must be submitted and approved prior to the resumption of work. Work not
completed pursuant to the earlier permit will be reviewed in accordance with the most recent
version of this Manual.
4.5.5 INSPECTIONS
The Department of Public Works shall be called for inspection as follows:
o After erosion and sedimentation control facilities are in place and prior to the
commencement of grading operations.
o After rough grading is completed.
o For final inspection, following site stabilization.
4.5.6 COMPLETION OF WORK AND FINAL APPROVAL
Final approval of work and the release of performance bonds shall not take place until the
following has been completed:
o All work, including installation of all drainage facilities and their protective devices, and
all erosion control measures, including permanent stabilization, have been completed in
accordance with the final approved Grading Plan and the approved Erosion and
Sedimentation Control Plan.
o Final inspection and approval of work by the City.
o Any required final reports and statements of approval from the project engineer have
been submitted to and approved by the City.
o Any required easements related to operation and maintenance of drainage facilities have
been recorded.
4-7
4.6 GRADING STANDARDS
The following grading standards are intended as MINIMUM requirements for grading in the
City. If circumstances create a hazard to life, endanger or adversely affect the use or stability
of a public way, adjacent property, critical area, or drainage course, the City may impose
additional or more stringent requirements to fulfill the intent of the Stormwater Management
Ordinance.
4.6.1 SOILS ENGINEERING INVESTIGATION REPORT
When the proposed work involves soils which may be excessively erodible or which may
have limited compaction capability due to the moisture content or the potential unsuitable
nature of the material itself, or the Director requires a soils investigation report prepared by
a qualified professional engineer for a proposed structure to be placed on fill material, the
City shall require a soils engineering investigation report prepared by a soils engineer. This
report shall include, as a minimum, 1) data regarding the nature, distribution and strength of
existing soils, 2) conclusions and recommendations for grading procedures and/or erosion
control measures, 3) design criteria for corrective measures when necessary, 4) opinions and
recommendations covering a site's adequacy for further development, and 5) allowable
bearing pressure, if applicable. Recommendations in the report shall be incorporated in the
proposed plans or specifications.
4.6.2 GEOTECHNICAL ENGINEERING INVESTIGATION REPORT
When on -site conditions or the proposed work involves slide prone or unstable soils, or when
proposed slopes do not meet the minimum design standards described in this Manual, or
when existing slopes steeper than 25% are to be cleared, graded or otherwise disturbed, the
City shall require a geotechnical engineering investigation report prepared by a qualified
professional engineer. This report shall include, as a minimum, 1) data regarding the effects
of groundwater interception and infiltration, seepage, potential slip planes, and changes in
soil bearing strength of existing soils, 2) conclusions and recommendations for grading
procedures and design criteria for corrective measures when necessary, 3) recommendations
regarding erosion control procedures, and 4) opinions and recommendations covering a site's
adequacy for further development, and 5) allowable bearing pressure, if applicable.
Recommendations in the report shall be incorporated in the proposed plans or specifications.
4.6.3 EXCAVATIONS
GENERAL
Unless otherwise recommended in an approved soils engineering investigation report and/or
geotechnical engineering investigation report, all excavations must comply with the
following minimum requirements.
SLOPE STEEPNESS
Excavated slope faces shall be no steeper than is safe for the intended use and shall not be
steeper than 2 horizontal to 1 vertical (2:1).
4.6.4 FILLS AND EMBANKMENTS
GENERAL
Unless otherwise recommended in an approved soils engineering investigation report or
geotechnical engineering investigation report, all fills and embankments must comply with
the following minimum requirements.
PREPARATION OF GROUND
Fill slopes shall not be constructed on natural slopes steeper than 2 horizontal to 1 vertical
(2:1). The ground surface shall be prepared to receive fill by removing vegetation,
noncomplying fill, topsoil and other unsuitable materials, scarifying the surface to provide
a bond with the new fill and, where natural slopes are steeper than 3 horizontal to 1 vertical
(3:1) and the height is greater than 5 feet, by benching into sound bedrock, glacial till or
other competent material as determined by a soils engineer. The bench under the toe of fill
on a slope steeper than 3 horizontal to 1 vertical (3:1) shall be at least 10 feet wide. The area
beyond the toe of fill shall be sloped for sheet overflow or a paved drain shall be provided.
When fill steeper than 3:1 and higher than 5' is to be placed over an excavation, the soils
engineer and/or geotechnical engineer shall certify that the foundation is suitable for the fill.
FILL MATERIAL
Detrimental amounts of organic material shall not be permitted in fills. Except as permitted
by the Director, no rock or similar irreducible material with a maximum dimension greater
than 12 inches shall be buried or placed in fills.
EXCEPTION: The Director may permit placement of larger rock or similar irreducible
material i.e. concrete, etc. when a soils engineer properly devises a method of placement
and continuously inspects its placement and approves the fill stability. The following'
conditions shall also apply:
A. Prior to issuance of a Stormwater Management Permit for grading, potential rock
disposal areas shall be delineated on the grading plan.
4-9
B. Rock sizes greater than 12 inches in maximum dimension shall be 10 feet or more
below grade, measured vertically.
C. Rocks shall be placed so as to assure filling of all voids with well -graded soil.
COMPACTION
All fills and embankments shall be compacted to a minimum of 90 percent of maximum dry
density, as determined by the tests described in the WSDOT/APWA Standard Specifications
for Road, Bridge, and Municipal Construction. Embankments constructed as berms for the
holding back of water shall be compacted to a minimum of 95 percent of maximum dry
density. Soil density shall be determined utilizing the Modified Proctor method. Fills on
sites of proposed structures shall be compacted as directed by the City Building Official in
accordance with the Uniform Building Code. Where the Director requires testing of the
compaction of soils outside public right-of-way, compaction shall be tested by an
independent soils testing lab at the owner's expense.
SLOPE
The slope of fill surfaces shall be no steeper than is safe for the intended use and shall be no
steeper than 2 horizontal to 1 vertical (2:1).
STRUCTURES
Fills which are intended to support structures shall be constructed in conformance with the
requirements of the latest edition of the Uniform Building Code, as adopted by Port Orchard,
and an assignment of allowable soil -bearing pressures will be under the jurisdiction of the
City Building Official in accordance with the U.B.C. When fill is proposed over an area that
the City deems to be a potential building site, and the Applicant does not state an intent to
construct buildings on the fill area, the City may at its own discretion require that a notice
be recorded as a public record containing provisions which will include the nature and extent
of the grading which has occurred on the parcel. The latest version of the form entitled
"Notice of Grading or Filling" shall be used.
4.6.5 SETBACKS
GENERAL
Excavation and fill slopes shall be set back from site boundaries in accordance with this
section. Setback dimensions shall be horizontal distances measured perpendicular to the site
boundary.
TOP OF CUT SLOPES
4-10
The top of cut slopes shall not be made nearer to a site boundary line than one fifth (1/5) of
the vertical height of cut with a minimum of 2 feet and a maximum of 10 feet. The setback
may need to be increased for any required interceptor drains.
TOE OF FILL SLOPES
The toe of fill slopes shall be made not nearer to the site boundary line than one half (1/2)
the height of the slope with a minimum of 5 feet and a maximum of 20 feet. Where a fill
slope is to be located near the site boundary and the adjacent off -site property is developed,
special precautions shall be incorporated in the work as the Director deems necessary to
protect the adjoining property from damage as a result of such grading. These precautions
may include but are not limited to:
1. Additional setbacks.
2. Provision for retaining or slough walls.
3. Mechanical or chemical treatment of the fill slope surface to minimize erosion.
4. Provisions for the control of surface waters.
MODIFICATION OF SLOPE LOCATION
The Director may approve or require alternate setbacks and may require an investigation and
recommendation by a qualified engineer to demonstrate that the intent of this section has
been satisfied.
4.6.6 DRAINAGE AND TERRACING
GENERAL
Unless otherwise indicated on the approved grading plan, drainage facilities and terracing
shall conform to the provisions of this chapter for cut or fill slopes steeper than 3 horizontal
to 1 vertical (3:1).
TERRACE
Terraces at least 6 feet in width shall be established at not more than 30-foot vertical
intervals on all cut or fill slopes to control surface drainage and sloughing except that where,
only one terrace is required, it shall be at mid -height. For 3:1 or steeper cut or fill slopes
greater than 60 feet and up to 120 feet in vertical height, one terrace approximately mid -
height shall be 12 feet in width. Terrace widths and spacing for cut and fill slopes greater
than 120 feet in height shall be designed by a geotechnical civil engineer and approved by
4-11
the Director. Suitable access shall be provided to permit proper cleaning and maintenance
of the terraces.
A single run of swale or ditch shall not collect runoff from a tributary area exceeding 13,500
square feet (projected) without discharging into a down drain.
SUBSURFACE DRAINAGE
Cut and fill slopes shall be provided with subsurface drainage as necessary for stability.
DISPOSAL
All drainage facilities shall be designed to carry waters to the nearest practicable drainage
way approved by the Director or other appropriate jurisdiction as a safe place to deposit such
waters. Erosion of ground in the area of discharge shall be prevented by installation of non -
erosive downdrains or other devices.
Building pads shall have a drainage gradient of 2 percent (2%) toward approved drainage
facilities, unless waived by the Director.
INTERCEPTOR DRAINS
Paved interceptor drains shall be installed along the top of all graded slopes where the
contributing drainage area uphill from the slope has a drainage path greater than 40 feet
measured horizontally. Interceptor drains shall be paved with a minimum of 3 inches of
concrete or gunite and reinforced. They shall have a minimum depth of 12 inches and a
minimum paved with of 30 inches measured horizontally across the drain. The slope of drain
shall be approved by the Director.
4.6.7 IMPERVIOUS SURFACES
In the event that impervious or nearly impervious surfaces are proposed that equal 5,000
square feet or more, or 1 acre or more of land area is to be disturbed, the Stormwater
Management Permit application shall include an engineered drainage plan and drainage
report, as described in Chapter 2, Submittal Requirements, and shall comply with the
quantity control requirements of Chapter 5, Stormwater Quantity Control Facilities, as well
as the runoff quality control requirements of Chapter 6, Stormwater Quality Control
Facilities. Compacted gravel, such as crushed rock compacted to 95 percent maximum dry
density, shall be considered a nearly impervious surface.
4-12
4.6.8 EROSION CONTROL
An application for a Stormwater Management Permit for grading shall include an Erosion
and Sedimentation Control Plan. This plan shall meet the requirements of Chapter 2,
Submittal Requirements, and shall conform to the standards for erosion and sedimentation
control included in Chapter 3, Erosion and Sedimentation Control.
APPLICANT'S RESPONSIBILITY
Temporary erosion and sedimentation control facilities shall be installed prior to any clearing
and/or grading taking place. The Applicant is responsible at all times for the installation and
maintenance of erosion and sedimentation control facilities.
EMERGENCY CONTACT PERSON
An emergency contact person having the means and the authority to institute emergency
erosion and sedimentation control measures shall be available at all times until construction
is completed, on a 24 hour per day basis. The name, address and 24 hour telephone
number(s) for the emergency contact person shall be listed with the City Department of
Public Works. In the event that the City becomes aware of an emergency condition on the
project site and is unable to contact the designated emergency contact person, or deems that
the response to the emergency situation is inadequate, the City may enter the project site and
perform any emergency work deemed necessary to protect life and limb, property, or
adjacent public ways, critical areas or drainage courses. The project owner will be required
to reimburse the City for all related costs incurred by the City for such emergency work.
SEALING THE SURFACE
At the end of each day's work, the contractor must grade all areas to drain, and seal the
surface using an acceptable means of compaction.
REVEGETATION
Unless the approved plan provides otherwise, all cleared areas shall be seeded as soon as
possible, or receive some other acceptable surface stabilization treatment in accordance with
Chapter 3, Erosion and Sedimentation Control.
4-13
NOTICE OF GRADING OR FILLING
THIS NOTICE made this day of , 19_, by the City of Port Orchard, by
and through the City of Port Orchard Department of Public Works;
WHEREAS, , is the owner or contract purchaser of certain
piece of property located in the City of Port Orchard, State of Washington, and described as
follows:
AND,
WHEREAS, The CITY OF PORT ORCHARD, by and through the Department of Public Works,
has issued a Stormwater Management Permit for grading or filling for a project on the above -
noted parcel of property; and whereas the approved plans are on file in the office of the
Department of Public Works, at 216 Prospect Street, Port Orchard, Washington;
NOW, THEREFORE, the public is hereby notified that grading or filling may occur on the
above -described property and said activity may limit the use of the property for development
purposes. Prospective purchasers may wish to consult City records and requirements before
purchasing said property.
OWNER OR OWNER'S AGENT Address
City, State, Zip
STATE OF WASHINGTON
) ss
County of Kitsap
On this day personally appeared before me
to me known to be the individual or individuals, described in and who executed the within and
foregoing instrument and acknowledged that he (she or they) signed the same in a free and
voluntary act, for the uses and purposes therein mentioned.
GIVEN under my hand an official seal this _ day of , 19
NOTARY PUBLIC in and for the State
of Washington, residing at
Note: This notice may be recorded as a courtesy only; no guarantee of recording is made or
implied nor is this notice intended to substitute for actual physical inspection of any real
property.
4-14
CHAPTER 5
STORMWATER QUANTITY CONTROL
FACILITIES
CHAPTER 5
STORMWATER QUANTITY CONTROL
FACILITIES
CONTENTS
5.1 GENERAL REQUIREMENTS
5-3
5.1.1
PURPOSE AND SCOPE
5-3
5.1.2
RUNOFF CONTROL
5-3
5.1.3
CLOSED DEPRESSIONS
5-4
5.1.4
EXEMPTIONS FROM RUNOFF CONTROL REQUIREMENTS 5-5
5.2 HYDROLOGY AND DESIGN STRATEGIES
5-6
5.2.1
COMPUTATION METHODS
5-6
5.2.2
BASIC RUNOFF PARAMETERS
5-7
5.2.3
DESIGN STRATEGIES
5-20
5.3 FACILITY
DESIGN REQUIREMENTS
5-22
5.3.1
PONDS
5-22
5.3.2
PARKING LOT PONDS
5-34
5.3.3
DETENTION TANKS AND VAULTS
5-37
5.3.4
CONTROL STRUCTURES
5-44
5.3.5
RETENTION FACILITIES
5-48
5.3.6
INDIVIDUAL DOWNSPOUT INFILTRATION SYSTEMS
5-52
FIGURES & TABLES
FIGURE TITLE
FIGURE 5-1
ISOPLUVIAL MAP - 2 YR., 24 HR............................................................. 5-8
FIGURE 5-2
it it - 5 YR., 24 HR.....................................................................
5-9
FIGURE 5-3
it - 10 YR., 24 HR...................................................................
5-10
FIGURE 5-4
it - 25 YR., 24 HR...................................................................
5-11
FIGURE 5-5
it - 50 YR., 24 HR..................................................................
5-12
FIGURE 5-6
�� �� - 100 YR., 24 HR.................................................................
5-13
FIGURE 5-7
�� �� - 100 YR., 7 DAY................................................................
5-14
FIGURE 5-8
VOLUME CORRECTION FACTOR..........................................................
5-26
FIGURE 5-9
DEBRIS BARRIER DETAIL.......................................................................
5-27
FIGURE 5-10
GRAVEL FILTER WINDOW DETAIL ......................................................
5-28
FIGURE 5-11
SECONDARY RISER STACK....................................................................
5-29
FIGURE 5-12
EMERGENCY OVERFLOW SPILLWAY WEIR SECTION ....................
5-30
FIGURE5-13
POND SIGN DETAIL..................................................................................5-31
FIGURE 5-14
TEXTURAL TRIANGLE (USDA)..............................................................
5-33
FIGURE 5-15
BOLLARDS DETAIL..................................................................................
5-36.
FIGURE 5-16
DETENTION TANK DETAIL.....................................................................
5-40
FIGURE 5-17
DETENTION VAULT DETAIL..................................................................
5-41
FIGURE 5-18
DETENTION TANK ACCESS RISER ........................................................
5-42
FIGURE 5-19
SOLID LOCKING LID................................................................................
5-43
FIGURE 5-20
ORIFICE LOCATION - TEE RISER...........................................................
5-45
FIGURE 5-21
ORIFICE LOCATION - BAFFLE RISER ...................................................
5-46
FIGURE 5-22
TEE SECTION WITH NOTCH WEIR & BAFFLE ....................................
5-47
FIGURE 5-23
CATCH BASIN SUMP - INFILTRATION SYSTEM ................................
5-53
FIGURE 5-24
OBSERVATION WELL..............................................................................
5-56
FIGURE 5-25
OVERFLOW DEVICES...............................................................................
5-57
FIGURE 5-26
INDIVIDUAL DOWNSPOUT INFILTRATION SYSTEM
- STANDARD DESIGN...............................................................................
5-58
TABLE TITLE
TABLE 5-1 HYDROLOGIC SOILS GROUPS............................................................... 5-16
TABLE 5-2 MODIFIED CURVE NUMBERS................................................................ 5-17
TABLE 5-3 MANNING'S COEFFICIENTS/"K" FACTORS ......................................... 5-19
TABLE 5-4 SOIL INFILTRATION RATES (BASED ON TEXTURAL
ANALYSIS).................................................................................................. 5 - 51
TABLE 5-5 INDIVIDUAL DOWNSPOUT INFILTRATION - SIZING CHART ......... 5-59
5-2
STORMWATER QUANTITY CONTROL FACILITIES
5.1 GENERAL REQUIREMENTS
5.1.1 PURPOSE AND SCOPE
This chapter presents City of Port Orchard policy concerning the control of runoff from
development sites. The scope of this chapter includes the following:
Methods for estimating the peak flow rates and volumes of surface water runoff and
input data required.
2. Strategies to follow in completing a hydrologic analysis and the design of runoff
quantity control facilities.
Design criteria and specifications for the construction of runoff quantity control
facilities.
5.1.2 RUNOFF CONTROL
When land development activity takes place in Port Orchard; any increases in surface runoff
resulting from development activity must be controlled so that the peak rates and volumes
of runoff leaving the post -development site do not exceed the capacity of receiving drainage
conveyance facilities; do not increase the potential for streambank erosion; and do not add
significant volume to an off -site closed depression. On -site runoff quantity control facilities
must be provided to limit such peak runoff rates and volumes as outlined below.
PEAK RATE CONTROL
The post -development peak stormwater discharge rates from the development site for the 2,,
10, and 100-year, 24-hour duration storm events and the 100-year, 7-day duration storm
event, shall at no time exceed the pre -development peak stormwater runoff rates for the same
design storm event, except as expressly permitted by the Stormwater Management
Ordinance. Additionally, the Director may require that runoff from a development site be
controlled for additional design storm events.
STREAMBANK EROSION CONTROL
One primary objective in controlling the peak rate of runoff from a project site is to assure
that, for a specific storm event, stormwater flowing downstream does not exceed the capacity
of existing drainage conveyance structures. However, runoff quantity control is also
necessary in order to prevent erosion of channels and adverse impact to habitats downstream.
Downstream open channels tend to be most impacted by an increase in the frequency and
duration of "bank full" flow conditions during less intense but more frequent storm events.
Stormwater detention facilities have the potential to create just such a condition. These
facilities increase the frequency that flows will be discharged at design peak flow rates
during lesser storm events and prolong the period during which flows are being released at
the peak rate (due to the increased volume of runoff). As a result, downstream channels will
5-3
experience "bank full" conditions more frequently and for significantly longer periods of
time than before development. Since nothing can be done (aside from on -site stormwater
retention) to reduce the volume of runoff and the resulting increase in the duration of peak
downstream flow, detention systems must be designed so that, during lesser storm events,
the release rate is lowered to less than "bank full" flow rates. Current available research
indicates that the pre -development peak runoff rate from a 2-year, 24-hour storm represents
"bank full" downstream conditions.
Where stormwater directly or indirectly discharges to open channels or streams, streambank
erosion protection is required. The post -development peak stormwater discharge rate from
a development site for the 2-year, 24-hour duration storm event shall not exceed fifty percent
(50%) of the pre -development peak runoff rate for the same design storm event. The
Director may require that runoff from a development site be controlled for additional design
storm events.
VOLUME CONTROL
In some cases, the project engineer and/or the Director may determine that rate control from
the developed site will not adequately protect downstream properties due to inadequate
capacity in the receiving drainage course or due to the existence of a receiving closed
depression. In such cases, developed runoff may be retained on -site in an infiltration facility
so as to avoid discharge to downstream properties. Where retention facilities are required,
the design storms shall be the 100-year, 24-hour duration and the 100-year, 7-day duration
storm events. Specific design criteria for retention facilities are given in this chapter.
5.1.3 CLOSED DEPRESSIONS
Closed depressions are low lying areas which have no, or such a limited surface outlet, that
in most storm events the area acts as a retention basin, holding water for infiltration into the
ground or evaporation into the air. By their nature, closed depressions may contain wetlands
that will require projects to meet the requirements of applicable sensitive areas rules and
ordinances.
MINIMUM REQUIREMENTS
Closed depressions shall be analyzed using hydrograph routing methods. Infiltration shall
be addressed where appropriate. If a proposed project will discharge runoff to an existing
closed depression that has greater than 5,000 square feet of water surface area at overflow
elevation, the following requirements must be met:
CASE l:
The pre -development 100-year, 7-day and 24-hour duration design storms from the
drainage basin tributary to the closed depression are routed into the closed depression
using only infiltration as outflow. If the design storms do not overflow the closed
depression, no runoff may leave the site for the same storm events following
development of a proposed project. This may be accomplished by excavating
additional volume in the closed depression subject to all applicable requirements. If
a portion of the depression is located off of the project site, impacts to adjacent
properties shall be evaluated.
5-4
CASE 2:
The pre -development 100-year, 7-day 24-hour duration design storm events from the
drainage basin tributary to the closed depression are routed to the closed depression
using only infiltration as outflow, and overflow occurs. The closed depression shall
then be analyzed as a detention/infiltration pond. The required performance, therefore,
shall not exceed the pre -development runoff rates for 50% of the 2-year and 100% of
the 10-year; 100-year, 24-hour duration; and 100-year, 7-day duration design storms.
This will require that a control structure, emergency overflow spillway, access road,
and other applicable design criteria be met. If the facility will be maintained by the
City, the closed depression shall be placed in a dedicated tract. If the facility will be
privately maintained, the tract shall be located within a drainage easement. If a portion
of the depression is located off of the project site, impacts to adjacent properties shall
be evaluated.
CASE 3:
When a proposed project is contributory to a closed depression located off -site, the
volume of runoff discharged may not be increased for the 2, 10, and 100-year, 24-hour
duration, and the 100-year, 7-day duration storm events. The exception to this
requirement is in the case where discharge would not result in an increase in water
surface elevation of greater than 0.01-foot for the 100-year storm events.
5.1.4 EXEMPTIONS FROM RUNOFF CONTROL REQUIREMENTS
1. Residential lots 2.5 acres or larger are exempt from provisions of this chapter unless
otherwise determined by the Director. Cases where the exemption does not apply
includes, but is not limited to, sites within or adjacent to critical areas or watersheds,
steep or unstable slopes, or where the cumulative impacts of development warrant.
Site development activities taking place of individual lots of 2.5 acres or larger, which
meet the definition of a Major Development, are not exempt from the requirements of
this chapter. Proposed access roadways serving residential lots larger than 2.5 acres
which meet the definition of a Major Development are not exempt form the
requirements of this chapter.
2. On -site peak rate runoff control will generally NOT be required for projects that
propose to construct less than 5,000 square feet of new impervious surface on an
individual parcel. However, proposed projects located in proximity to critical drainage
areas shall not qualify for this exemption if it is determined by the Director that more
strict peak runoff rate or runoff volume controls are warranted. Also, if there is a
recorded condition of a plat, short plat, or large lot subdivision approval that requires
peak rate runoff control for an individual lot, such as an individual downspout
infiltration system, that parcel will not qualify for this exemption.
3. Land developments shall provide stormwater quantity control facilities designed to
meet, as a minimum performance standard, the requirements of this Section, except in
the following circumstances:
(a) The development site discharges directly into Puget Sound, or directly into the
tidally influenced areas of rivers and streams discharging into Puget Sound,
where runoff quantity control is not required by other governmental agencies.
5-5
(b) The development site discharges to a regional stormwater facility approved by
the Director to receive the developed site runoff.
(c) The development site discharges to a receiving body of water (lake, wetland,
etc.) where it can be demonstrated by the Applicant, to the satisfaction of the
Director, that stormwater quantity control is not warranted.
Projects qualifying for direct discharge will be required to provide water quality facilities,
as described in Chapter 6.
5.2 HYDROLOGY AND DESIGN STRATEGIES
5.2.1 COMPUTATION METHODS
HYDROGRAPH ANALYSIS
All runoff quantity control facilities must be designed using hydrograph analysis methods
for estimating storm runoff rates. Runoff control storage facilities must be designed using
appropriate storage routing methods.
In the Puget Sound area, the two most commonly accepted hydrograph methods for
estimating storm runoff are the Soil Conservation Service (SCS) TR-55 Hydrograph Method
and the Santa Barbara Urban Hydrograph Method.
The SCS TR-20 Hydrograph Method has been in common use in this region for a number
of years and is familiar to most engineers. However, it is limited to larger basins and is not
permitted for the design of runoff control facilities in the City for basins smaller than 100
acres.
The Santa Barbara Urban Hydrograph Method is permitted for the design of runoff control
facilities in the City for any size basin. A detailed explanation of this method is covered in
the D.O.E. Stormwater Manual or King County Surface Water Design Manual.
Commercial software is presently available for use by engineers for using either of these
methods. However, it should be understood that when a computer program is used in a
design, the City is limited to only reviewing the appropriateness of the computation
procedure and the input parameters used. When submitting computations, the engineer must
thoroughly document all data input. It will be expected that the design engineer have a
complete understanding of the processes being performed by any software routine.
LEVEL -POOL ROUTING
The storage capacity of detention, retention, and infiltration systems must be designed using
a level pool routing technique.
SCS Technical Release 55 is appropriate for generating stormwater runoff hydrographs.
However, the methods followed in Release 55 for estimating detention storage volumes are
NOT acceptable to the City in the design of detention facilities.
5-6
The Washington State Department of Ecology's Stormwater Management Manual for the
Puget Sound Basin ("Technical Manual") includes a description of a level pool routing
technique which is widely accepted by various municipalities in the Puget Sound area.
Although it tends to be more difficult to compute manually than the SCS storage volume
method, it tends to result in a much more accurate estimation of storage requirements.
5.2.2 BASIC RUNOFF PARAMETERS
This manual does not attempt to provide a detailed description of the SCS TR-20
Hydrograph Method, Santa Barbara Urban Hydrograph Method or Level Pool Routing
Methods, as detailed descriptions of these methods are readily available to the design
engineer from the Department of Ecology or the Soil Conservation Service. Instead, the
following comments are offered to assist the design engineer in implementing these methods.
PRECIPITATION
The isopluvial maps for Kitsap County for the 2, 5, 10, 25, 50, and 100-year recurrence
interval, 24-hour duration storm events are shown in Figures 5-1 to 5-6. They were taken
from NOAA Atlas 2, "Precipitation - Frequency Atlas of the Western United States, Volume
IX -Washington". The 100-year, 7-day isopluvial map shown on Figure 5-7 was taken from
the U.S. Weather Bureau Technical Paper No. 49, "Two -to -Ten Day Precipitation for Return
Periods 2 to 100 years in the Contiguous United States".
5-7
3W 2W 1 W
28 Kitsap
County
2-YEAR 24-HOUR PRECIPITATION
27 ,o �`��o ISOPLUVIALS OF 2—YEAR 24—HOUR
PRECIPITATION IN TENTHS OF AN INCH
126
125
124
DATA SOURCE:
U.S. DEPARTMENT OF COMMERCE
23 DnvKnona sw ct sum= AGIMsm7mm
VZOAL SWM OWCH. 0"= OF MVMaACY. WATQ 2LOM !
br
U.S. DEPARTMENT OF AGRICULTURE
20"VA 7IM
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3W 2W 1W
1E
lE
FL
2E 3E
28
,o
27
261
251
24
23
l.r.®
22
2E 3E
6
5-8
3W 2W 1W
28 Kitsap
County
I5-YEAR 24-HOUR PRECIPITATION
27 �'���o ISOPLUVIALS OF 5-YEAR 24-HOUR
PRECIPITATION IN TENTHS OF AN INCH
so
126
1 E 2E 3E
28
0
IN
271
261
I�' � � ria '9215
J
24 6 24
6
DATA SOURCE:
r,
U.S. DEPARTMENT OF COMMERCE
23 f"V0004^.L .00= SUIVA= "°emsm"m i 23
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U.S. DEPARTMENT OF AGRICULTURE
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3W 2W 1 W tE 2E 3E
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3W 2W 1 W
28 Kitsap
County
10—YEAR 24—HOUR PRECIPITATION
27 �o r`�ro ISOPLUVIALS OF 10—YEAR 24—HOUR
PRECIPITATION IN TENTHS OF AN INCH
126
lE 2E 3E
28
a
0
271
261
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d
25
®
25
24
r
3
24
�
e
DATA SOURCE:
'
U.S. DEPARTMENT OF COMMERCE
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23
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22
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2W 1 W
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3W
2W 1 W 1E 2E
28 Kitsap
County
25-YEAR 24-HOUR PRECIPITATION
27 t@0_@ ISOPLUVIALS OF 25-YEAR 24-HOUR
PRECIPITATION IN TENTHS OF AN INCH
126
125
124
DATA SOURCE:
U.S. DEPARTMENT OF COMMERCE
23 aVAK"o'TAL Bowe[ ADnA= A01Nf1RA"
v[cAL sTjM g1/AIOI _,WE Cr MVDVJM=Y. WArAM BUNS u
A.
U.S. DEPARTMENT OF AGRICULTURE
0001ME004 DrAMM UL CONSOWATIOM 10V=
WIDOW IVM
C
22
3W 2W
1
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L
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28
271
11
251
24
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1
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23
22
2E 3E
3W 2W 1W
28 Kitsap
County
50-YEAR 24-HOUR PRECIPITATION
27 ro'"��'ro ISOPLUVIALS OF 50—YEAR 24—HOUR
PRECIPITATION IN TENTHS OF AN INCH
126
125
124
DATA SOURCE:
U.S. DEPARTMENT OF COMMERCE
IpW^L MirA= NRAICK mna Or N,INawv..uvoe SUMM
I.
U.S. DEPARTMENT OF AGRICULTURE
M�1D�t Ino
22
3W 2W 1 N
1E
1E
ZE 3E
28
271
26
251
® 24
U
23
.. m
22
2E 3E
5-12
i
3W 2W 1 kv
28 Kitsap
County
100-YEAR 24-HOUR PRECIPITATION
27 ISOPLUVIALS OF 100—YEAR 24—HOUR C
PRECIPITATION IN TENTHS OF AN INCH
125
2
I 2E 3E
28
1�
•
I
7 � • J
24
If24
l
DATA SOURCE:
Q
U.S. DEPARTMENT OF COMMERCE
23 a"""'"k'°DOM WVM AOMMIR„ MM
i
?
23
s.coK Srj= wunrx O.IQ OF N.OROIOCY. WARIM WJW-W
,
S
U.S. DEPARTMENT OF AGRICULTURE
DOO IXAM OIMSM IM ODrIVVAT*N SORVI E
I
SUITEmp I ISM
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®
® ®
®
2
2
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2E
3E
3W 2W 1 W f E
28 Kitsap
County
100-YEAR 7-DAY PRECIPITATION
27 to 0*'@ ISOPLUVIALS OF 100—YEAR 7—DAY
PRECIPITATION IN INCHES
126
it
125
� 4
24
1
O
0
DATA SOURCE: • '
23
t
U.S. Wencher Bureau Technical
Paper No. 49, "Two -to -Ten -Day
Precipitation for Return Periods a
2 to 100 Years in the Contiguous p �y
United States"
22
3W 2W 1 W 1 E
2E 3E
28
O
27
261
251
24
V
J
2.3
t.rms
22
2E 3E
5-14
CURVE NUMBERS
SCS has post -development "curve number" (CN) values based on soil type and land use.,
These curve numbers have been assigned to one of four hydrologic soil groups according to
their runoff characteristics. Table 5-1 identifies the hydrologic soil groups for the most
common soils in Kitsap County. This list is derived from the soils listed in the SCS Soil
Survey for Kitsap County together with the comprehensive hydrologic soil group listing
found in the SCS TR-55 literature.
The curve numbers included in the D.O.E. Technical Manual have been modified by SCS
to more accurately reflect conditions common to the Puget Sound area. Generally, the curve
numbers appearing in the D.O.E. Technical Manual tend to be higher than those found in the
SCS TR-55 literature. Port Orchard requires that these modified curve numbers, as listed
in Table 5-2, be used in any hydrological analysis. More conservative curve number values
are acceptable.
For storm durations other than 24 hours, an adjustment must be made to the CN values given
in Table 5-2. Based on information obtained from SCS, the following equation shall be used
for adjusting these CN's for the 7-day design storm:
CN,_aay = 0. 15 49 CN + 0.8451 ((CNz.1"/631.8) + 15)
Note that some commercially available software performs this adjustment automatically.
Individual curve numbers for a basin must be merged into a "composite" curve number for
use as input in either the SCS method or the SBUH method. The SBUH method further
requires that a separate composite curve number be computed for the pervious portion and
the impervious portion of the site.
To compute composite curve numbers, the following steps should be followed:
1. Break a basin down into areas of differing ground cover or land use.
2. Break down each of these areas based on the homogeneous characteristics on an area
(soil groups, pervious versus impervious, etc.).
3. Determine the land area, in acres, for each of these sub -areas and note the curve
number for that sub -area.
4. Compute the total acreage and the composite pervious curve number. The composite
curve number should be derived by taking the area times the curve number of each of
the pervious sub -areas and then dividing this sum by the total area:
CompositeQV
(CNxA), +(CNXA)Z ... (CNXA)N
=
Moral
5-15
Table 5-1 HYDROLOGIC SOIL GROUP OF THE SOILS OF KITSAP
SOIL GROUP
HYDROLOGIC
GROUP`
SOIL GROUP
HYDROLOGIC
GROUP*
Alderwood
C
Mukilteo
C/D
Beaches
Variable
Neilton
A
Belfast
B
Norma
C/D
Bellingham
C/D
Pits
Variable
Cathcart
B
Poulsbo
D
Dystric Xerorthents
Variable
Ragnar
B
Grove
A
Schneider
B
Harstine
C
Semiahmoo
C/D
Indianola
A
Shalcar
C/D
Kapowsin
D
Shelton
C
Kilchis
D
Sinclair
C
Kitsap
C
Tacoma
D
McKenna
C/D
Urban
Variable
HYDROLOGIC SOIL GROUP CLASSIFICATIONS
A. (Low runoff potential). Soils having high infiltration rates, even when
thoroughly wetted, and consisting chiefly of deep, well -to -excessively drained sands
or gravels. These soils have a high rate of water transmission.
B. (Moderately low runoff potential). Soils having moderate infiltration rates
when thoroughly wetted, and consisting chiefly of moderately fine to moderately
coarse textures. These soils have a moderate rate of water transmission.
C. (Moderately high runoff potential). Soils having slow infiltration rates when
thoroughly wetted, and consisting chiefly of soils with a layer that impedes
downward movement of water, or soils with moderately fine to fine textures. These
soils have a low rate of water transmission.
D. (High runoff potential). Soils having very slow infiltration rates when
thoroughly wetted and consisting chiefly of clay soils with a high swelling potential,
soils with a permanent high water table, soils with a hardpan or clay layer at or near
the surface, and shallow soils over nearly impervious material. These soils have a
very slow rate of water transmission.
Note: Two Hydrologic soil groups such as C/D indicates the Drained/Undrained
situation.
* From SCS, TR-55, Second Edition, June 1986, Exhibit A-1.
5-16
Table 5-2 MODIFIED CURVE NUMBERS
Runoff curve numbers for selected agricultural, suburban, and urban land use for Type IA
rainfall distribution, 24-hour storm duration. (Published by SCS in 1982)
LAND USE DESCRIPTION
CURVE NUMBERS BY
HYDROLOGIC
SOIL GROUP
A
B
C
D
Cultivated land': Winter condition
86
91
94
95
Mountain open areas: Low growing brush & grassland
74
82
89
92
Meadow or pasture:
65
78
85
89
Wood or forest land: Undisturbed
42
64
76
81
Established second growth 4
48
68
78
83
Young second growth or brush
55
72
81
86
Orchard: With cover crop
81
88
92
94
Open spaces, lawns, parks, golf courses, cemeteries, landscaping
Good condition: Grass cover on >= 75% of area
68
80
86
90
Fair condition: Grass cover on 50-75% of area
77
85
90
92
Gravel roads & parking lots:
76
85
89
91
Dirt roads & parking lots:
72
82
87
89
Impervious surfaces, pavement, roofs, etc.
98
98
98
98
Open water bodies: Lakes, wetlands, ponds, etc.
100
100
100
100
Single family residential Z:
Dwelling unit/gross acre % Impervious'
Separate curve number shall be selected
1.0 DU/GA 15
for pervious
and impervious portions of
1.5 DU/GA 20
the site or basin.
2.0 DU/GA 25
2.5 DU/GA 30
3.0 DU/GA 34
3.5 DU/GA 38
4.0 DU/GA 42
4.5 DU/GA 46
5.0 DU/GA 48
5.5 DU/GA 50
6.0 DU/GA 52
6.5 DU/GA 54
7.0 DU/GA 56
PUDs, condos, apartments, % impervious
Commercial businesses & must be computed
Industrial areas
' For a more detailed description of agricultural land use curve numbers, refer to National
Engineering Handbook, Sec. 4, Hydrology, Chapter 9, August 1972.
2 Assumes roof and driveway runoff is directed into street/storm system.
3 The remaining pervious areas (lawn) are considered to be in good condition for these
curve numbers.
4 Modified by KCPW, 1995.
5-17
TIME OF CONCENTRATION
The time of concentration (Tc) is the length of time for runoff to travel from the
hydraulically most distant point of a watershed to the point of discharge from the watershed.
For computation purposes, it is assumed that water moves through the watershed as
sheetflow (having a maximum depth of 0.1-foot), as shallow concentrated flow (having a
maximum depth exceeding 0.1-foot), and as open channel flow.
It is assumed that runoff in a watershed begins as sheetflow. It is also assumed that
regardless of site conditions, the maximum distance that runoff will travel in the form of
sheetflow will not exceed 300-feet. Where there are no topographic features suggesting
channel flow within the first 300-feet of flow, it may be assumed that the first 300-feet of
flow is sheetflow and the remaining flow distance until water reaches a channel is shallow
concentrated flow.
For further discussion of methods of computing time of concentration, the designer is
T = 0.42(n, L )0.s
(Pz )0.5(S, )0.4
referred to the Washington State Department of Ecology "Stormwater Manual".
For computing the travel time of sheetflow, the following formula should be used:
where T = travel time, in minutes
n, = Manning's roughness coeff.-sheetflow (Table 5-3)
L = flow length, in feet
P2 = 2-year, 24-hour rainfall, in inches (Figure 5-1)
s" = slope of land, in feet per foot
Note that when the SCS TR-55 Hydrograph Method is used, the travel time, "T", must be
converted from minutes to hours.
Travel time for shallow concentrated flow and open channel flow is computed using the
T= L
Vx60
following formula:
where T = travel time, in minutes
L = flow length, in feet
V = average velocity, in feet per second
60 = conversion factor from seconds to minutes
5-18
"n" AND "k" Values Used in Time Calculations for Hydrographs
"ns" Sheet Flow Equation Manning's Values (for the initial 300 ft. of travel)
ns
Smooth surfaces (concrete, asphalt, gravel, or bare hand packed soil)
0.011
Fallow fields or loose soil surface (no residue)
0.05
Cultivated soil with residue cover (s _< 0.20 ft/ft)
0.06
Cultivated soil with residue cover (s > 0.20 ft/ft)
0.17
Short prairie grass and lawns
0.15
Dense grasses
0.24
Bermuda grass
0.41
Range (natural)
0.13
Woods or forest with light underbrush
0.40
Woods or forest with dense underbrush
0.80
*Manning values for sheet flow only, from Overton and Meadows 1976 (See TR-55,
1986)
"k" Values Used in Travel Time/Time of Concentration Calculations
Shallow Concentrated Flow (After the initial 300 ft. of sheet flow, R = 0.1)
ks
1. Forest with heavy ground litter and meadows (n = 0.10) 3
2. Brushy ground with some trees (n = 0.060) 5
3. Fallow or minimum tillage cultivation (n = 0.040) 8
4. High grass (n = 0.035) 9
5. Short grass, pasture, and lawns (n = 0.030) 11
6. Nearly bare ground (n = 0.025) 13
7. Paved and gravel areas (n = 0.012) 27
* *Channel flow (intermittent) (At beginning of visible channels R = 0.2)
kc
1.
Forested swale with heavy ground litter (n = 0.10)
5
2.
Forested drainage course/ravine with defined channel bed (n = 0.050)
10
3.
Rock -lined waterway (n = 0.035)
15
4.
Grassed waterway (n = 0.030)
17
5.
Earth -lined waterway (n = 0.025)
20
6.
CMP pipe (n = 0.024)
21
7.
Concrete pipe (0.012)
42
8.
Other waterways and pipe 0.508/n
Channel Flow (Continuous stream, R = 0.4) kc
9. Meandering stream with some pools (n = 0.040)
10. Rock -lined stream (n = 0.035)
11. Grass -lined stream (n = 0.030)
12. Other streams, man-made channels and pipe 0.807/n**
**See Table 7-3 for additional Mannings "n" values for open channels.
20
23
27
5-19
Average velocity is computed using the following formula:
V = k ,-
where: V = velocity, in feet per second
k = velocity factor, in feet per second (Table 5-3)
S. = slope of flow path, in feet per foot
Table 5-3 lists Manning's roughness coefficient, "n,", for sheetflow and also velocity factor
"k" for shallow concentrated flow and open channel flow. The factors in Table 5-3 should
be used for both the SCS and SBLTH methods. Note that the "n," values given in Table 5-3
are only appropriate for sheetflow conditions.
Time of concentration, for input in either the SCS method or the SBUH method, is the sum
of the travel times for sheetflow, shallow concentrated flow, and channel (intermittent) flow.
In computing the time of concentration, it is important to note that, except for very large
basins, the largest and most significant component in the total time of concentration is that
portion of the time devoted to sheetflow. For this reason, extreme care should be given to
realistically determining the true travel time for the sheetflow component of the time of
concentration. In reviewing the hydrological analysis, City staff will pay close attention to
this factor.
In calculating total time of concentration, the following limitations will apply:
1. The flow segment used for the sheetflow component of the total time of concentration
should not extend for more than 300'.
2. For segments of the Tc route flowing through closed conveyance facilities, such as pipes
and culverts, standard hydraulics formulas should be used for establishing velocity and travel
time.
3. For segments of the Tc route flowing through lakes or submerged wetlands, travel time
is normally very short. The travel time can be determined using an appropriate storage routing
technique, or it can be assumed to be "zero".
5.2.3 DESIGN STRATEGIES
In order to aid the engineer in designing a runoff quantity control facility, the following
comments are offered. City encourages innovative design to stormwater management;
therefore, consideration will be given to other reasonable design strategies.
5-20
DRAINAGE BASIN DELINEATION
- - Within an overall drainage basin that is contributing stormwater to a runoff control facility,
it may be necessary to delineate separate sub -basins and to then generate separate
hydrographs for each sub -basin. Sub -basins must be delineated when there are areas within
a larger basin that are hydraulically self-contained, or that have similar land use and/or runoff
characteristics. When several sub -basins are contributing runoff to a single runoff control
facility, the individual hydrographs from each sub -basin should be added together to produce
a single hydrograph representing runoff flows to the facility. When adding hydrographs, it
is important that the travel time be taken into consideration, from the discharge point of a
given sub -basin to the runoff control facility.
OFF -SITE CONTRIBUTING RUNOFF
In general, off -site contributing runoff may only be routed through the runoff control facility
if the pre -development peak 2-year and 100-year flow rates from the off -site contributing
area do not exceed the pre -development on -site peak flow rates for the same storm events.
Otherwise, off -site flows should be routed through the project site separate from the on -site
flows.
If off -site flows are to be routed through the runoff control facility, orifice sizes should
generally not be increased to accommodate off -site flows. Instead, additional freeboard
should be provided so that offsite flows can be discharged through the control structure
without overtopping the emergency overflow spillway.
BYPASS AREAS
Runoff from small portions of a development site may be permitted to be released at post -
development rates (uncontrolled) provided that: (1) the "bypass" area rejoins the pre -
development downstream drainage course within a relatively short distance downstream of
the runoff control facility; (2) the design engineer has demonstrated in the downstream
analysis and in capacity calculations that the downstream drainage course conveying the
uncontrolled flows from the "bypass" area will not be adversely impacted by the increased
runoff rate; (3) easements are obtained from all downstream property owners through whose
property the undetained runoff flows prior to rejoining the detained runoff from the site; and
(4) the total release rate from the project site, including the "bypass" area, shall not exceed
the total allowable release rates from the project site. In the event that the downstream
drainage course will be adversely impacted by increased runoff from the "bypass" area,
downstream improvements will be required, along with an easement from the affected
downstream property owner(s).
CORRECTION FACTORS
When designing streambank erosion control BMPs by the SBUH Method, it will be
necessary to increase the facility size by applying a correction factor to the calculated storage
volume. The correction factor, which is based on the site impervious cover, is shown on
Figure 5-8. Note that the factor does not apply to infiltration facilities or those designed by
a continuous simulation model such as HSPF.
5-21
5.3 FACILITY DESIGN REQUIREMENTS
The term "detention facility" commonly refers to the temporary storage of water for eventual
gradual release to a downstream surface drainage course. "Retention", on the other hand,
commonly refers to the permanent storage of stormwater. Actually, a retention facility also
temporarily stores water for eventual gradual release through evaporation as well as
infiltration to the groundwater system.
Detention facilities usually take the form of open ponds, underground tanks, and vaults.
Retention facilities are most often open ponds or other open depressions, or they are
underground infiltration systems. The Director may allow a retention system to be designed
with some controlled release where it has been demonstrated that downstream conditions will
not be adversely impacted by such a controlled release of stormwater.
All runoff quantity control facility designs must address overflow caused both as a result of
plugging of the normal outlet and also as a result of stormwater conditions that exceed the
design capacity of the facility. The engineering design of all runoff quantity control facilities
must identify the route of overflow from a storage facility, following the corridor of least
resistance, to the point where this overflow enters the existing downstream drainage system.
5.3.1 PONDS
Open ponds for runoff quantity control are encouraged by the City when site constraints
allow.
Also, the City encourages the design of runoff quantity control ponds to function as multi-
purpose facilities (such as parks, recreation or sports facilities, or parking lots), provided that
any alternative uses are compatible with their primary stormwater functions and with
maintenance standards. Every effort will be made by Department of Public Works staff to
cooperate in the development of such a facility.
Finally, the City encourages the use of regional ponds serving more than one development.
Regional facilities can be more effective in improving water quality, can be more cost
effective not only to construct but also to maintain, and can be more easily designed to serve
as a multi -purpose facility.
The following design criteria apply to open ponds:
SITE CONSTRAINTS
1. All open ponds to be maintained by the City shall be located in a separate tract dedicated
to the City. Open ponds shall not be located in dedicated public road right-of-way areas.
2. Open ponds that are designed to function as multi -use recreational facilities shall be
located in a separate tract or in designated open space and shall be privately maintained.
POND GEOMETRICS
5-22
1. Open ponds shall be designed to have a minimum of 1-foot of freeboard above the
maximum design water surface elevation.
2. Ponds shall have a minimum length to width ratio, at the maximum water surface, of 2:1
in order to enhance water quality benefits. Higher length to width ratios may be required
(for example, see Chapter 6, Stormwater Quality Control Facilities, for wetpond design
criteria).
3. All pond outlet pipes shall be provided with a Debris Barrier (see Figure 5-9).
4. Ponds shall be designed as "flow -through" facilities with two or more sequential "cells"
divided by a gravel filter window. The top of the gravel filter window should be set 1-
foot below the maximum design water surface elevation.
For multi -cell detention ponds, the upstream cell ("forebay") shall be designed for the
entrapment and containment of sediment. The bottom of this "forebay" shall be flat and
designed to provide a minimum of 0.5-feet of dead storage for sediment. This dead
storage may not be included in the calculation of total available detention storage for the
pond. The 0.5 feet of available sediment storage assumes that both cells of the pond are
approximately equal in size. In the event that the "forebay" is less than one half of the
total pond volume, the depth of available sediment storage shall be proportionately
increased to provide the equivalent volume of sediment storage. See Chapter 6,
Stormwater Quality Control Facilities, for additional forebay sizing criteria that may be
required on some ponds for water quality purposes.
6. All ponds with a permanent pool depth exceeding 18-inches, or side slopes steeper than
4H:1V, shall be fenced. Interior side slopes above the freeboard elevation of unfenced
ponds may be as steep as 2H:1 V provided that a 10' wide safety bench is provided at the
point of slope transition. For safety reasons, all ponds with a permanent pool depth`
exceeding 18-inches shall have maximum slopes of 3H:1 V in addition to perimeter
fencing. Exterior pond side slopes shall be not steeper than 2H:IV.
7. Pond walls may be designed as retaining walls, provided that: (1) the design is prepared
and stamped by a qualified engineer registered in the State of Washington, (2) at least
25% of the pond perimeter will be a vegetated soil slope of not greater than 4H:1V, (3)
maintenance access is provided to the bottom of the pond, and (4) a fence is provided
around the entire perimeter of the pond.
SETBACKS
1. Ponds shall maintain minimum setback distances as follows:
- 10 feet - maximum water surface to property lines and structures
- 1/2 berm height, 5 feet minimum, 20 feet maximum - from toe of pond berm
embankment to nearest tract property boundary lines
- 10 feet - maximum water surface to septic tank or distribution box`
- 30 feet - maximum water surface to septic drainfields*
- 200 feet - maximum water surface to top of slopes steeper than 30%`*
- 100 feet - wells
5-23
"The Bremerton Kitsap County Health District (BKCHD) may require greater setbacks
"A deviation from these setbacks may be granted by the Director with recommendations
from a qualified geotechnical engineer.
Where pond setbacks cross property lines, siting of such facilities will not be allowed
without written authorization from the affected property owner.
2. Manholes and catch basins shall maintain a minimum separation of 5 feet from the face
of the structure to any adjacent tract or property boundary.
OVERFLOW
1. The detention pond outlet pipe shall be fitted with a secondary riser stack to convey
runoff to the control structure in the event that the entrance to the outlet pipe becomes
plugged. Figure 5-11 is a standard detail for the secondary riser stack.
2. All ponds shall be provided with an emergency overflow spillway designed to safely pass
the 100-year, 24-hour design storm event for post -development site conditions assuming
the pond is full to the crest of the spillway. The emergency overflow spillway is intended
to provide safe overflow over the pond embankment in the event of control structure
failure or for storm/runoff events exceeding design. The subgrade of the spillway should
be set at or above the 100-year, 24-hour overflow elevation of the control structure. The
spillway shall be located to direct overflows safely towards the downstream conveyance
system and shall be located in existing soil wherever feasible. The emergency overflow
spillway shall be armored with 6" median diameter rip rap in conformance with Section
9-13 of the WSDOT/APWA Standard Specifications and shall extend to the toe of each
face of the berm embankment.
5-24
The emergency overflow spillway weir section (see Figure 5-12) shall be designed for the
maximum design storm event for post -development conditions, using the following formula:
L = Qroo 3 -2.4 H2
3.21 H2
where L = Length of bottom of weir, in feet (6-feet min.)
Q]oo = 100-year, 24-hour post -development flow rate, in cfs
H = Height of emergency overflow water surface, in feet
(0.2-feet minimum)
FENCING
Fencing, where required around a pond, shall consist of a minimum 6' high chain link
fence. A minimum of one locking access road gate shall be provided that is 16' wide
consisting of two swinging sections 8' in width. Any proposed pedestrian -only access
gates shall be a minimum of 4' in width. Fence material shall be No. 11 gauge
galvanized steel fabric with bonded vinyl coating. Vinyl coating shall be green in open
areas and black in wooded areas. Fence posts shall be galvanized steel, with top caps,
and set a minimum of 3-feet deep in concrete. Cross bars shall connect adjacent fence
posts, with diagonal braces at corners and ends. All posts, cross bars and gates shall be
painted or coated the same color as the vinyl clad fence.
SIGNING
All ponds shall have signs placed so that at least one is clearly visible and legible from
all adjacent streets, sidewalks or paths. Signs shall meet the design and installation
requirements illustrated in Figure 5- 13.
5-25
5-26
14 VW. DII IWMI I
bars with ends
welded to
bar -frame
I'min.
I t
I �
Beveled pipe end section
Pipe coupling 2" x 5" anchor strips welded
to 3/4" dia. bar -frame at 4
places spaced uniformly.
Fasten with'/:" non-
corrosive bolts and nuts
Note:
1. CMP end -section shown.
lay be removed
3/4" dia. bai
frame
3"-5" for 18" dia.
5"-8" for 24" dia.
r-9" for 30" dia. & greater
4" O.C.
max. bar
spacing
5-27
Top of Berm
dividing pond
into two cells
Top
Lr-
GA
�x
Note: "Key" not required
Elevation is one foot
below 100 year, 24 hour
design water surface
Pond
5-28
v
5-29
Figure 5-12 EMERGENCY OVERFLOW
SPILLWAY
NVEIR SECTION
A
i
No,
U
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Q
ce
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LAJ
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W
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5-30
Figure 5-13 Publicly Owned Pond Sign Design
CITY OF PORT ORCHARD
DEPARTMENT OF PUBLIC WORKS
STORMWATER MANAGEMENT FACILITY
DO NOT
ENTER
For more information call 876-4991
Specifications
Size: 1' X 2'
Material: Aluminum with white reflective sheeting
Silk screen lettering
Installation: Secured to chain link fence if available
otherwise installed on 8' X 4" X 4" post
buried 30" into ground
5-31
BERM EMBANKMENT/SLOPE STABILIZATION
Pond berm embankments shall be constructed on native consolidated soil (or adequately
compacted and stable fill soils), which is free of loose surface soil materials, roots, and
other organic debris.
2. Pond berm embankments shall be constructed by excavating a "key" equal to 50% of the
berm embankment cross -sectional height and width measured through the center of the
berm (except on till soils where the "key" minimum depth can be reduced to 1-foot of
excavation into the till).
3. The berm embankment shall be constructed of compacted soil (95% maximum dry
density, Modified Proctor method per ASTM D1557) placed in 6 to 8 inch lifts with hand
held equipment and 10 to 12 inch lifts with heavy equipment, with the following soil
characteristics per the United States Department of Agriculture's Textural Triangle: a
minimum of 30% clay, a maximum of 60% sand, a maximum of 60% silt, with nominal
gravel and cobble content (Note: in general, excavated glacial till will be well -suited for
berm embankment material). See Figure 5-14 for USDA's Textural Triangle.
4. Anti -seepage collars shall be placed on outflow pipes in berm embankments impounding
water greater than 8-feet in depth.
5. Exposed earth on the pond side slopes shall be sodded or seeded with appropriate seed
mixture (see Chapter 3, Erosion and Sedimentation Control). Establishment of protective
vegetative cover shall be ensured with appropriate surface protection BMPs and reseeded
as necessary.
6. Pond berm embankments 6-feet or less in height including freeboard, measured through
the center of the berm, shall have a minimum top width of 6-feet, unless otherwise
recommended by a qualified engineer.
7. Where maintenance access is provided along the top of berm, the minimum width of the
top of berm shall be 15 feet.
8. Pond berm embankments greater than 6-feet in height, as measured through the center
of the berm, shall require design by a qualified geotechnical engineer licensed in the
State of Washington. Berm embankment width shall otherwise vary as recommended
by the engineer.
5-32
100X sand
Textural Triangle U.S.D.A.
100% clay
90 ____ 10
80 __ -Y ___ 20
70 --- —N \ --- "---- 30 ON
60 ` '40
50 �Y —___\ 50
---- _ \Silty / \
SO)AY! \\ ! \\\
40 i \`� Clay/ \\\
�60
�V 9 It
?j \ \ ! \ / ! \\\ ! Cori
--- `! \ ! \' Loam` / / ---
Q 30 (-Y-----�— —r ---- r----—LGDl�y 70
Son
\\\ LOOM �' \
.. .......x:._t:::::. Silt\
10
90
:.......... ::1':::: , ! \ / \ \Silt !
............
90 80 70 60 50 40 30 20 10
Percent SAND
10oX silt
5-33
ACCESS
1. Pond access roads shall provide access to the control structure(s) and alongside the pond
as necessary for vehicular maintenance access to the pond forebay. For ponds with
forebay bottoms which cannot be accessed from the top edge of the forebay by a backhoe
with a maximum reach of 20 feet, an access road shall be constructed extending to the
bottom of the first cell, having a minimum width of 15-feet and a maximum steepness
of 20%.
2. Access roads to control structures shall have a maximum slope of 12%. A means shall
be provided for vehicle turn around, allowing for a 40-feet minimum outside turning
radius. Access roads to the pond bottom shall allow for a vehicle to approach the pond,
turn, and back down the access ramp into the pond.
3. Vehicle access shall be limited by bollards if the pond is not fenced. Bollards (see Figure
5-15) shall consist of two fixed bollards on each side of the access road and two
removable bollards equally located between the fixed bollards.
4. Pond access roads shall be constructed by utilizing one of the following techniques:
Construct an asphalt surface meeting City standards; OR
Construct a gravel surface road by removing all unsuitable material, providing a
minimum 6" of suitable subgrade material compacted to 95%, and providing a
minimum 2" thick crushed rock surface; OR
Construct a landscape block surface by removing all unsuitable material, laying a
geotextile fabric over the native soil, placing landscape blocks, filling the
honeycombs with soil particles, and planting grass.
When the length of a pond access road exceeds 40-feet, a vehicle turn -around must be
provided, designed to accommodate vehicles having a maximum length of 31-feet and
having an outside wheelpath radius of 40-feet. The Director may allow an exception
from the turn -around requirement if the access road slope is 8-percent, or less, and the
road has a straight alignment.
5.3.2 PARKING LOT PONDS
Parking lot ponds, as well as any pond having a paved bottom (tennis courts, etc.), are a
variation on the concept of multi -purpose runoff quantity control facilities. However,
because a parking lot is usually a land use permit requirement, it is essential that any
secondary design of a parking lot as a runoff quantity control pond be compatible with the
parking lot use.
5-34
Any parking lot ponds shall be designed to have a maximum depth shallow enough so as not
to damage passenger vehicles parked in the pond during flooding. In addition, the bounds
of the ponding area shall be limited so as to maintain pedestrian access and to not encroach
into established fire access lanes. Paved ponds provide less water quality benefit
(biofiltration, biologic activity) than vegetated ponds. Therefore, more stringent water
quality measures may be required prior to discharge of stormwater from the project site.
5-35
PAMIT TC
e•xs•sm
FIXED BOLLARD
y«-
rji• MINII+BMI TNIC1cNEs5
GALAwasp MEL. at
AL.UmMm". sum9m <
sloe mmonlow I
GamrwLTBAN POST
DIMiIAlOMS.
CLASS C '�:'''�%
Y w11J
Am]
MI
C1sIWs*ER 4 Si0l3
r�
i
L
—6•xc•54s x 4""
•&ALVMlXKb BYE SOLT
w/w4kom &wv mm.
RECESS bw "D KGN
OOLT THLRAOS.
ypD" MINOSATIMT GALVAUIZED
cjwN "Ac" BD 1N CONCIETE.
.,y : ,
hill c �
VEI. 00.
. t�• i
REMOVABLE BOLLARD
NOTES:
1. TIMBER SHALL BE DOUGLAS FIR, DENSE CONSTRUCTION GRADE, AND
SHALL BE PENTACHLOROPHENOL PRESSURE TREATED BY EMPTY CELL
PROCESS WITH MINIMUM NET RETENTION OF 0.05 LBS./CU. FOOT OF
THE DRY SALT. (USE LIGHT PETROLEUM SOLVENT.)
2. STEEL TUBE SHALL CONFORM TO ASTM A53 OR ASTM A53 GRADE A
3. NUTS, BOLTS, & WASHERS SHALL CONFORM TO ASTM A307.
4. ALL STEEL PARTS SHALL BE GALVANIZED.
5. CONCRETE SHALL BE CLASS C.
5-36
The following are criteria specific to parking lot pond design:
1. The maximum depth of water shall not exceed 0.5-feet at any location in the parking lot.
2. The limits of ponded water at maximum water depth shall not encroach into any
established fire lanes or principal ingress/egress lanes.
3. Signs shall be erected adjacent to the parking lot pond area identifying the area as a
stormwater detention control area subject to ponding, and identifying the specific parking
spaces subject to flooding.
4. The parking lot pond shall be designed so that it will completely drain, leaving no areas
of entrapped water in puddles or behind curbs.
5. Overflow control shall be provided on the perimeter of the parking lot pond area, with
the flow elevation equal to the design maximum water surface elevation.
5.3.3 DETENTION TANKS AND VAULTS
Tanks are typically constructed of corrugated pipe, whereas vaults are usually constructed
of reinforced concrete. Both function to provide underground storage of stormwater as part
of a runoff quantity control system.
As with any underground structure, it is important not only that tanks and vaults be designed
for their function as runoff quantity control facilities, but also that they be constructed to
withstand an environment of periodic inundation, potentially corrosive chemical or electro-
chemical soil conditions, and heavy ground surface loadings. Also, they shall be reasonably
accessible for maintenance.
Tanks and vaults provide less water quality benefit (biofiltration, biologic activity) than open
ponds. Therefore, more stringent water quality measures may be required prior to discharge
of stormwater from the project site.
Tanks and vaults typically do not have a built-in design feature for the containment of
sediment, as does the multi -cell pond. For this reason, it will be required that when tanks or
vaults are used for detention storage, there either shall be a surface sediment containment
pond upstream of the tank or vault, or the tank/vault shall be oversized to allow for the
temporary accumulation of sediment in the tank. Where the tank or vault is designed to
provide sediment containment, a minimum of 0.5' of dead storage shall be provided and the
tank/vault shall be laid flat.
Tanks and vaults can be used in conjunction with other detention storage facilities, such as'
ponds or parking lot ponds, to provide initial or supplemental storage.
The following are criteria specific to detention tank and vault design:
GENERAL DESIGN CRITERIA
5-37
1. Detention tanks and vaults are permitted within public road rights -of -way. For single-
family plats and PUD's, detention tanks and vaults not located in public rights -of -way
shall be located in separate tracts dedicated to the City.
2. All tanks and vaults shall be designed as flow through systems unless separate sediment
containment is provided.
3. The minimum pipe size for a detention tank is 36". If the collection pipe is designed to
also provide storage, the resulting maximum water surface elevation shall maintain a
minimum 1 foot of freeboard in any catch basin below the catch basin grate. Pipe
capacity shall be verified utilizing backwater analysis as per Chapter 7. Also, pipe
material and surface treatment shall conform to the standards for detention tanks.
4. Detention tanks and vaults shall have a minimum of 0.5-feet of dead storage. The bottom
of the tank or vault shall be flat.
5. The minimum internal height of a vault or tank shall be 3 feet and the minimum width
shall be 3 feet. The maximum depth to the vault invert shall be 20 feet.
MATERIALS & STRUCTURAL STABILITY
1. Pipe material, joints, and protective treatment for tanks and vaults shall be in accordance
with WSDOT/APWA Standard Specifications Section 9.05. All galvanized steel or iron
pipe or pipe arch shall have a protective coating of Treatment 1 or greater.
2. All tanks and vaults shall meet structural requirements for overburden support and traffic
loading, if appropriate. HS-20 live loads shall be accommodated for tanks and vaults
lying under roadway or parking areas. Metal tank end plates shall be designed for
structural stability at maximum hydrostatic loading conditions. Flat end plates generally
require thicker gage material than the pipe and/or require reinforcing ribs. Tanks and
vaults shall be placed on stable, well consolidated native material with a suitable
bedding. Tanks and vaults shall not be allowed in fill slopes, unless analyzed in a
geotechnical report for stability and construction practices.
3. Detention Vaults shall be constructed of minimum 3,000 psi structural reinforced
concrete. All construction joints shall be provided with water stops. All vaults shall be
designed by a qualified structural engineer. Structural designs for cast -in -place vaults
require a separate commercial building permit issued by the City. Vaults shall be placed
on stable, well consolidated native material with suitable bedding. Vaults shall not be
allowed in fill slopes, unless analyzed in a geotechnical report for stability and
construction practices.
4. In moderately pervious soils where seasonal groundwater may induce flotation, buoyancy
tendencies shall be balanced by ballasting with earth backfill or concrete backfill, by
providing concrete anchors, by increasing the total weight, or by providing subsurface
drains to permanently lower the groundwater table. Calculations may be required which
demonstrate stability.
5-38
ACCESS
1. All areas of the vault shall be within 50-feet of a minimum 36-inch diameter access
cover. A ladder to the bottom of the vault may be required.
2. CMP access risers: Outside of any areas subject to vehicular loads, 36-inch minimum
diameter CMP access risers of the same gage as the tank material may be used for access
along the length of the tank and at the upstream terminus of the tank if the tank is
designed with a common inlet/outlet so that it is a backup system rather than flow
through system. The Director may allow risers in traffic areas with an appropriate traffic
bearing design. See Figure 5-18 for details.
3. All risers are required to have solid lids.
4. All tank and vault access openings shall have round, solid, locking lids using 1/2"
diameter allen head screw locks (See Figure 5-19).
5. Conveyance pipes shall not be permitted to connect directly to detention tanks.
6. Access roads are required to all detention tank and vault access openings and control
structures not located in improved public rights -of -way. The access roads shall meet the
requirements for access roads for ponds described previously.
5-39
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NOTE: AN slats pain e+er►-& aersatant. Stets awn ""'
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5-40
Second manhole required only If length of detention chamber Is > 50'or one per
call for multi -called vaults. Provide partitions as required with adequate
flow -through at bottom (leaving 0.5' dead storage) & air vent at top.
i I I i Flow
A ( Standard J Outlet Pipe
t Ladder or steps � A
i1--6Flow I I
II I
Wall
flange (t1rp.)
Inlet �,
Pipe
Water quality,
storm for
water quality
wet vault
Frames. grates and round solid covers
/marked "drain" with locking baits
_ 1
p wa. •.wb. ..�.
1. • psbddaK wld�
T Pod Iwel Iwet
vokww T O 50% (dryly
0.6' dead
Plan View
nts
Overflow depth
(6" min.)
Flow restrictor
S, (FROP•T shown)
12" level storage Flow
2" bottom
Capacity of outlet pipe
Standard steps or ladder s not less than developed
design flow.
0"M pi" to a'.
Hry Brit OM 4*M��j Floor grate with 2'a 2' hinged
access door
SECTION A,A
Notes:
1. Plans snust be designed & stamped by a registered professional structural engineer.
2. All metal parts shall be corrosion resistant.
3. Provide water stop' at all cast -in -place construction joints. Precast vaults shall have
approved rubber gasket system.
I
5-41
Restrictions for application: use only for access to detention tanks. Not allowed
for use in roadways, driveways, parking stalls or where vehicular loads would occur.
Protective bollard
required between
an adjacent _
vehicular load
area and lid
0 4 min.)
36" CMP riser
Standard locking
M.H. Frame & cover
Compacted
pipe bedding
M.H. Steps 12" O.C.
Weld or bolt 10
standard M.H. steps
Frame locking lid
(marked "drain")
mounted over 24" dia.
Eccentric opening
• 5v — Detention tank
Standard Type 2 CB
concrete top slab
36" Riser, 36" din. Min., same
material & gage as tank
welded or fused to tank
Detention tank
Notes:
1. Use adjusting blocks as required to bring frame to grade.
2. All materials must be corrosion resistant.
3. Must be conveniently located for maintenance vehicle access.
5-42
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5-43
5.3.4 CONTROL STRUCTURES
Detention control structures may be either weir structures or orifice structures. Weir
structures may be either enclosed in a catch basin or vault, or they may be installed in the
open, provided that they are accessible for maintenance and are not exposed to damage.
All detention control facilities shall provide oil/water separation prior to discharge. This can
be accomplished by incorporating oil/water separation into the design of the control structure
(e.g. utilizing a FROP-T device in a Type 2 catch basin) or by installing a separate spill
containment (SC) oil/water separator vault. Oil/water separation measures are required for
control of storms up to the 100-year/24-hour design storm.
CONTROL STRUCTURE DESIGN CRITERIA
1. Flow control manholes shall have solid locking covers. Open grates shall not be
permitted in control manholes.
2. Multiple orifices are usually necessary in order to meet the 2-year, 10-year, and 100-year
performance requirements for a detention system. Usually, no more than 2 orifices will
be necessary in order to achieve the required performance. However, high flow rates
may result in excessively large orifice sizes that are impractical to construct. In such
cases, several orifices may be located at the same elevation to reduce the size of each
individual orifice.
3. Orifices may be constructed on a "Tee" riser section as shown in Figure 5-20 or on a
baffle as shown in Figure 5-21.
4. When it is required that the release rate from a 2 year, 24-hour storm event be limited to
50% of the pre -development 2-year release rate, there may be instances where the 2-year
water surface elevation is too high to physically construct an upper orifice above the 2-
year storage elevation. In such an instance, a notch weir in the riser pipe may be used
to meet performance. See Figure 5- 22 for design and sizing criteria.
5. Where flow control is provided using weir control rather than orifice control, an
alternative method shall be used for providing oil/water separation. Either an oil/water
separation baffle shall be installed (see Figure 5- 22), or a separate oil/water separation
tructure shall be provided.
5-44
PC
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5-45
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5- 46
Bolt and Seal Baffle
to Riser us Rpmdred
tch Weir Width
A
Notch Weir
Cut In Riser
Baffle for
Oil / Water
Separation
Size as Req'd
-w--
Q release
Side View
0 . C(L - 0.2H)H'nds
Notch Weir Depth
as Required
Overtopping Allowed
Above 10 Year
Design Flow if
Q-release
Within Performance
Requirements
:ad
i Meet
ante
0
Top View
Oil / Water
Separation
Required up
to 10 Year
Design Flow
Baffle
Riser
,,.. Between Baffle
and Riser Must be
Sufficient to Pass
Design Q
where C 327 + 0.40 H/P (in tees).
L Length of the ponlon of the riser circumterence as necessary (in feet), not to
exceed 50% of the clrcumterence.
H&P as shown above
D . Inside riser diameter.
Note that to account for side contractions. subtract 0.1 H imm L for each side of the notch weu.
Notch Weir
5-47
6. Properly designed weirs, such as rectangular notched weirs, v-notched weirs, or sutro
weirs, may be used as flow restrictors located either in catch basin structures, or mounted
on a concrete retaining structure in the open. Formulas for sizing rectangular notched
weirs and v-notched weirs are as follows:
RECTANGULAR NOTCHED, SHARP CRESTED WEIR
3
Q=C(L-0.2H)H
where: Q = Weir discharge, in cubic feet per second
C = 3.27 + 0.40 H/P, in feet
P = Height of weir bottom above downstream water surface in feet
H = Height from weir bottom to crest, in feet
L = Length of weir, in feet*
For weirs notched out of circular risers, Length is the portion of the riser circumference,
not to exceed 50% of the circumference.
V-NOTCH, SHARP CRESTED WEIR
Q = Cd(Tan 0/2)H"
where: Q = Weir discharge, in cubic feet per second
Cd = Contraction coefficient, in feet'
0 = Internal angle of notch, in degrees
H = Height from weir bottom to crest, in feet
0 Cd values may be taken from the following chart:
7. The control structure shall be designed to pass the 100-year, 24-hour duration storm event
as overflow without causing flooding of the contributing drainage area and without
allowing runoff to discharge through the emergency overflow spillway.
5.3.5 RETENTION FACILITIES
Underground infiltration trench systems are highly susceptible to failure by the reduction in
infiltration capacity caused by the plugging of the infiltration surface with sediment and/or
oily substances, as well as plugging resulting from improper construction practices.
Ordinary maintenance usually cannot restore the infiltration function, and when failure
occurs the entire system usually requires replacement. Because of the risk involved, these
systems shall remain private and it will be the responsibility of the property owner to provide
maintenance and to bear the cost of repair or replacement of the system. Infiltration trenches
5-48
will not be allowed for use in residential developments unless a deviation from this
requirement is granted by the Director.
Infiltration ponds are allowed for use in all types of developments. The basic requirements
for infiltration ponds are the same as for detention ponds, with other specific criteria noted
below.
In general, the setback, overflow and safety requirements for detention facilities also apply
to infiltration ponds and trenches.
SOILS IDENTIFICATION AND DETERMINATION OF INFILTRATION RATE
Projects considered for on -site stormwater retention systems are required to provide soil
classification information verifying the infiltration capability of site soils. A Soils Report.
is required for the location of each infiltration system proposed. The report shall include a
Particle -Size Analysis performed by ASTM Test Method D-422-63. One sample for every
5,000-sf of infiltrating surface area is required to be obtained from the location of the
proposed system, at a point 36-inches below the infiltration surface. Test results, including
certification of the sample location and the depth to seasonal high groundwater table, shall
bear the seal of a licensed professional engineer who has recognized expertise in the
classification and mechanics of soils. The analysis will be used as the basis for determining
the USDA Textural Classification.
The soil infiltration rate used for final design shall conform to Table 5-4 utilizing a factor of
safety of 2.0.
Soils with an infiltration rate of less than 0.5-inches per hour are generally considered
unsuitable for streambank erosion control. Infiltration systems shall not utilize fill material,
nor be placed over fill soils.
5-49
DESIGN CRITERIA FOR INFILTRATION TRENCHES AND PONDS
The following design criteria apply specifically to ponds and trenches designed to infiltrate
all or a portion of runoff (retention):
1. All ponds and trenches utilizing infiltration shall be designed using an appropriate
storage routing method.
2. Facilities utilizing infiltration shall have bottoms a minimum of 18-inches above seasonal
high ground water.
3. All retention facilities shall be a minimum of 200-feet from any slope steeper than 30%.
This distance may be reduced based on a geotechnical engineering report.
4. All stormwater, prior to discharge to a facility designed to utilize infiltration, shall pass
through a designed biofiltration swale system and through a presettling basin. In
addition, all stormwater from paved areas subject to motor vehicle traffic shall now
through a spill -containment type oil/water separator.
For runoff quantity control facilities utilizing infiltration, those facilities shall be
designed for a 100-year, 7-day storm event and also for a 100-year, 24-hour storm event,
and shall have a maximum draw down time of 48-hours.
6. Until all project improvements which produce surface runoff are completed and all
exposed ground surfaces are stabilized by revegetation or landscaping, facilities utilizing
infiltration may not be operated, and no surface runoff may be permitted to enter the
system.
7. The soil infiltration rate used for the design of infiltration systems shall be based on a
textural analysis, according to Table 5-4. A safety factor of 2 shall be applied to the
infiltration rate.
5-50
Table 5-4 SOIL INFILTRATION RATES BASED ON TEXTURAL ANALYSIS
SOIL TEXTURE CLASS
INFILTRATION RATE (MIN/IN)
1. Gravel
coarse sand
1
2. Sand
5
3. Loamy
sand
15
4. Sandy
oam
30
5. Loam
Unsuitable
RETENTION PONDS
Infiltration ponds can be open or be lined with a 6 to 12-inch layer of filter material such
as coarse sand or a suitable filter fabric to help prevent the buildup of impervious
deposits on the soil surface. The filter layer can be replaced or cleaned when/if it
becomes clogged.
2. Establishing a healthy stand of vegetation on the pond side slopes and floor is
recommended. This vegetation will not only prevent erosion and sloughing, but will also
provide a natural means of maintaining relatively high infiltration rates. Erosion
protection of inflow points to the basin shall also be provided. Removal of accumulated
sediment is a problem only at the basin floor. Little maintenance is normally required
to maintain the infiltration capacity of side slope areas.
INFILTRATION TRENCHES
Trenches shall be designed to utilize infiltration through the bottom only, without taking
into account sidewall infiltration. Storage volume shall be based on a maximum 30%
void ratio for drainrock.
2. There is no minimum spacing between trench centerlines and no maximum trench width.
However, flow distribution lines shall be installed at a spacing of 10-feet or less between
pipes.
3. A Type 2 catch basin with sump (see Figure 5-23) shall be located on the upstream end
of the trench, which provides a minimum of 36-inches of depth below the invert of the
outlet pipe. A FROP-T device shall be provided on the outlet to the trench as shown on
the detail. Additional Type 2 catch basins shall be placed along the trench to provide
cleanout access such that all portions of the trench are within 150 feet of a catch basin.
4. An observation well (see Figure 5-24) shall be installed adjacent to the infiltration trench
and within 25-feet of the facility for the purpose of monitoring ground water conditions.
5-51
The observation well should consist of perforated PVC pipe, 6-inches in diameter,
backfilled with the same clean gravel material used in the infiltration trench. It should
be located in the center of the structure and be constructed flush with the ground
elevation of the trench. The top of the well should be capped to discourage vandalism
and tampering.
5. The aggregate material for the infiltration trench shall consist of a washed aggregate free
of fines with a maximum diameter of 1-1/2-inches and a minimum diameter of 3/4-
inches.
6. A geotextile material shall be placed over the top of the trench to prevent backfill
material from contaminating the washed rock.
5.3.6 INDIVIDUAL DOWNSPOUT INFILTRATION SYSTEMS
Individual downspout infiltration systems are trench infiltration systems designed to receive
only stormwater from roof downspout drains. They shall be designed so as not to receive
surface water from paved areas. Also, a single individual downspout infiltration system can
only serve a maximum of 5,000 square feet of roof area.
The following standardized design criteria is intended to guide the homeowner in providing
an acceptable design for an individual downspout infiltration system. Deviation in design
or construction from the standardized design criteria detailed below may require design by
a qualified engineer. This will be left to the discretion of the Director.
5-52
STORM DRAIN
NOTES:
1. METAL PAR15 OmW10S10N RESISTANT
w"NaZm ►K ►ARTS lO WE ►
ASPHALT 1RWMENr 1
2. nUME t LADOM OR SUPS O"SET W.
A CLfJ1N041T CATS a V4 mz PROP TOP
& C M-000 SPACE a CLW Or MW PLAN
h CTFANOLIT GALE
3. If WUL OMM PM COWUMTS TO CEMENT CONCIIETE
PIPE: OUTLET PIPE TO WWE SMOOTH O.O. ED" TO
CONCRM PPE LD. LESS 1/4'
MMAAIMED .LID Nc LIDDRAW
Infiltration Catch Basin
Type II - 48'
NTS
Perforated Pipe
Infiltration Trench
5-53
1. Individual downspout infiltration systems will not normally require design by a civil
engineer provided that: 1) the proposed site development does not result in a net increase
in impervious surfaces of more than 5,000 square feet; 2) the system is sized according
to the sizing chart shown in Table 5-5; and 3) the system is constructed according to the
standard design shown in Figure 5-25.
2. Prior to approval of an individual downspout infiltration system, a site plan shall be
submitted showing the location of the proposed infiltration system together with adjacent
building structures, wells, septic drainfields and tanks, curtain drains, and property lines.
All trenches shall be a minimum of 5 feet from any property line, 10 feet from any
structure, 30 feet downslope or 100 feet upslope from any septic drainfield, 15 feet
downslope or 50 feet upslope from any septic tank, 10 feet downslope or 30 feet upslope
of any curtain drain, 50 feet from private wells and 100 feet from public wells. Greater
setbacks may be required by the Bremerton Kitsap County Health District (BKCHD) or
the Director.
4. All trenches shall be a minimum of 50 feet from any slope steeper than 45%. This
distance may be reduced based on a geotechnical engineering report.
There is no minimum spacing between trench centerlines and no maximum trench width.
However, flow distribution lines shall be installed at a maximum spacing of 10 feet or
less between pipes.
6. Trench length shall not exceed 100 feet from the inlet sump.
7. A minimum of one soil log shall be obtained for each proposed individual downspout
infiltration system. The soil log shall extend a minimum of 18" below the bottom of the
trench, describe the USDA textural class of the soil horizon through the depth of the log,
and note any evidence of high groundwater level, such as mottling.
8. Trench bottoms shall be a minimum of 12 inches above seasonal high ground water or
relatively impervious layer.
9. Geotextile filter fabric shall be placed on top of the drain rock prior to backfilling.
10. A catch basin inlet sump (See Figure 5-25) shall be located upstream of the trench, which
provides a minimum of 24" of depth below the invert of the outlet pipe. The outlet tee
shall be designed so as to be submerged at all times, and a screening material shall be
installed on the pipe outlet.
11. An overflow device is required for all downspout infiltration systems. Examples are
given in Figure 5-26. In situations where the elevation difference between the bottom
of the downspouts and the top of the infiltration bed is less than 3 feet, the overflow
device may be as simple as an elbow on the downspout pipe. Where elevation
differences exceed 3 feet, the overflow must be placed at the observation well or catch
basin near the bed itself. Alternatively, the overflow device may be deleted if the washed
gravel is extended to the ground surface, allowing runoff to flow out the top in the event
of overflow.
5-54
12. An observation well (see Figure 5-24) is recommended, but not required. The
observation well allows the homeowner to monitor the performance of the facility.
13. Following completion of construction of a downspout infiltration system, an "as -built"
drawing of the infiltration system shall be submitted to the City.
5-55
Geote
Coves
4"
P%
NTS
Pvr C2e
;oil or
negate
I'isturbed
terial
5-56
Roof v v
-/_Truich CB
_ Roof Drain
t _ _ CB Trench
Not to Scale
Roof
Observatkxul Wolf
r — — (Optimal) 4- Perivrated Pipe
G _
Sump W/
Sold Lid
Roof Drain
PROFLE MEW
nts
GeotextileSheet Overflow
Cover �\ ... %� Splash Blodc
,w w
�ra.ow.r
ar.
SECTION A A �� M
OwrrdMT�
Not to Scale
V*ft PWL WMMA w
MniMirTrM
al Ili*
Y��IYrd
5-57
Splash Block Overflow
Overflow
Wash Block
Elevation change
Less Than 3'_
— — — — CB
Stand Pipe Overflow t
Elevatlon Change
Solid 4" Pipe —� More Than 3'
Perforated 4" Pipe
ppoppIp-
L" — — awl CS
Bubble -up Overflow
Elevation change
More Than 3'
�.1Water Flow`
Varies e.
5-58
COARSE - MEDIUM SAND (5 MIN/IN)
GRAVEL
DEPTH
ROOF AREA
3000 SF
4000 SF
5000 SF
1'
247
330
412
1.5'
203
271
339
2'
175
233
291
2.5'
154
206
257
3'
139
185
231
FINE - LOAMY SAND (15 fvffNW
GRAVEL
DEPTH
ROOF AREA
3000 SF
4000 SF
5000 SF
1'
416
554
692
1.5'
323
431
539
2'
268
357
446
2.5'
230
306
383
3'
202
269
336
SANDY LOAM, LOAM (30 MIN/IN)
GRAVEL
DEPTH
ROOF AREA
3000 SF
4000 SF
5000 SF
1'
535
713
891
1.5'
403
538
672
2'
327
436
544
2.5'
276
368
460
31
240
1320
399
*Roof areas less than 3000 sf shall be designed for 3000 sr uruess
otherwise approved by the Director.
5-59
CHAPTER 6
STORMWATER QUALITY CONTROL
FACILITIES
CHAPTER 6
STORMWATER QUALITY CONTROL FACILITIES
. llw"- mm
6.1
KNOWN POLLUTANTS IN STORMWATER
6-2
6.2
WATER QUALITY DESIGN STORM
6-3
6.3
BIOFILTRATION BMPs
6-3
6.3.1 SWALE DESIGN CRITERIA
6-4
6.3.2 FILTER STRIP DESIGN CRITERIA
6-5
6.4
WET PONDS AND WET VAULTS/TANKS
6-6
6.4.1 WET POND DESIGN
6-6
6.4.2 WET VAULT AND WET TANK DESIGN
6-8
6.5
SPILL CONTROL OIL/WATER SEPARATORS
6-9
STORMWATER QUALITY CONTROL FACILITIES
Port Orchard requires that land development activities address the development's impact on
stormwater quality as well as quantity.
This chapter describes facilities that can significantly improve the removal of finer sediment
and metals. One of these facilities, or other treatment BMP approved by the Director, will
be required prior to stormwater discharges from all major development sites.
This chapter provides detail for a spill control (SC) type oil/water separator that is required
for all areas subject to vehicular traffic. Other types of oil/water separators may be required
for development sites with certain industrial uses. Design information can be found for these
other types of separators in the D.O.E. stormwater manual as well as from the product
manufacturers.
6.1 KNOWN POLLUTANTS IN STORMWATER
Pollutants typically found in stormwater runoff in developing areas include the following:
o Sediment
o Metals (e.g. copper, lead, zinc)
o Oil, grease and other petroleum hydrocarbon
o Nutrients (e.g. phosphorus, nitrogen)
o Fecal Coliform ( a non-pathogenic indicator of possible pathogenic bacteria)
Sediment: Policies contained elsewhere in this Manual address not only the source control
of sediment pollution but also the treatment of sediment -laden runoff. The policies
concerning erosion and sedimentation control primarily address the control of erosion and
the entrapment and on -site removal of sediment resulting from land -disturbing activities.
The design requirements of runoff quantity control facilities include features that serve to
allow settling out of suspended sediments in runoff. In addition, the requirement to limit the
runoff release rate from a developed site to 50% of the 2-year pre -development rate can be
expected to significantly limit stream bank erosion and its resulting sedimentation.
Metals: Sumps in drainage structures and in the bottom of detention storage facilities tend
to collect a significant proportion of metals contained in storm runoff. In addition, metals
often become attached to suspended sediment particles and are then removed as part of the
process of treating sediment -laden runoff. However, the smallest particles of sediment are
often very difficult to remove and do not readily settle out of stormwater.
Oil and Grease: Spill -control (SC) type or the larger chambered vault (API) type oil/water
separators, are ineffective in removing suspended oil droplets from stormwater
concentrations typically reported in urban areas. For certain industrial sites where a high
concentration of oil is expected, the coalescing plate (CPS) type oil/water separator is the
most effective at removing suspended oil droplets. Biofiltration BMP's are generally more
RM
effective than oil/water separators in removing suspended oil droplets from urban
stormwater.
In addition to oils, oil/water separators and biofiltration swales can remove grease and other
heavier petroleum hydrocarbons. Lighter petroleum hydrocarbons, including those present,
in gasoline and other fuels, are generally less miscible in water and are not removed
effectively.
Nutrients: Nutrients such as phosphorus and nitrogen are occasionally present in stormwater
at levels which can accelerate the eutrophication, or enrichment, process in certain water
bodies. Water bodies in which the growth of nuisance algae species is limited by levels of
a nutrient are particularly susceptible to negative ecological impacts. In general, freshwater
bodies tend to be phosphorus -limited, whereas marine waters tend to be nitrogen -limited.
Nutrients are among the most difficult pollutants to remove from stormwater. Sources of
phosphorus and nitrogen loading include overuse and improper application of detergents and
fertilizers, practices which can be corrected through education and enforcement. It is
recommended that the focus of the control of nutrients be public education and restrictions
included in residential plat covenants and issuance of land use permits.
The construction of stormwater facilities to treat nutrients in runoff will usually not be
required, unless it is determined during the development review process that nutrients in the
project storm runoff could accelerate eutrophication of downstream waters, or could pose the
risk of nitrate contamination of groundwater. Should nutrient control be required, both
source control and runoff treatment BMP's shall be required.
For design criteria for nutrient control facilities, the designer is referred to Washington State
Department of Ecology Stormwater Management Manual for the Puget Sound Basin.
Fecal Coliform: Fecal coliform bacteria level is an indicator of possible pathogenic bacterial
contamination. This Manual addresses bacterial contamination of stormwater only in its
setback requirements for infiltration facilities from septic drainfields. The intent of these
setback requirements is to avoid adverse impacts of infiltration facilities on septic system
performance.
6.2 WATER QUALITY DESIGN STORM
The water quality design storm, used for the design of water quality treatment facilities, shall
be the 6-month, 24-hour storm event. In that the precipitation data from isopluvial maps is
not available for the 6-month, 24-hour storm event, the design engineer can use 64% of the
2-year, 24-hour precipitation as equivalent to the 6-month, 24-hour precipitation.
6.3 BIOFILTRATION BMPs
There are two types of biofiltration-type BMPs: the biofiltration swale and the vegetated
filter strip. A biofiltration swale is a vegetated channel that is sloped like a standard storm
6-3
drain channel; stormwater enters at one end and exits at the other with treatment provided
as the runoff passes through the channel. With vegetated filter strips the flow is distributed
broadly along the width of the vegetated area; treatment is provided as runoff travels as sheet
flow through the vegetation.
Which method to use depends upon the drainage patterns of the site. A vegetated strip would
function well where the water can be spread along the length of a parking lot. Gaps in the
lot curb provide the entry points. The grade of the parking lot should be flat immediately
parallel to the strip.
6.3.1 SWALE DESIGN CRITERIA
Biofiltration swales shall be designed using the Manning Equation for uniform open channel
flow as discussed in Chapter 7 Collection and Conveyance Facilities. The swale shall be
sized to provide treatment of the developed peak flow rate from the water quality design
storm, and shall have adequate capacity to pass the developed peak flow from a 100 year
event without excessive velocity that may cause scouring of the channel. The specific
parameters for biofiltration swale design are as follows:
Geometry:
The Swale shall have a trapezoidal cross section, minimum bottom width of 2 feet, maximum
bottom width of 8 feet, minimum freeboard of 1 foot, and maximum side slope steepness of
3H:IV. The longitudinal slope of the swale shall be from 1 % to 6%, and the length shall be
as required to achieve the minimum residence time listed below.
Water QuajjW
The performance of the swale shall be evaluated for treatment of the water quality design
storm with a maximum flow depth of 3 inches, a Manning "n" value of 0.20, a maximum
flow velocity of 1.0 feet per second, and a minimum residence time of 5.0 minutes (300
seconds). The minimum required length of the swale will be calculated by multiplying the
actual flow velocity by the minimum residence time in seconds.
Stability Check:
The stability of the swale shall be evaluated using the developed peak flow rate from the 100
year storm event with a Manning "n" value of 0.035, which assumes that the grass has been
knocked over by the flow. If the velocity exceeds 3.5 feet per second, the swale should be
enlarged or the contributing flow should be decreased as necessary.
Other Design Considerations:
The biofiltration swale shall be lined with a minimum of 4 inches of Type "A" topsoil
according to W.S.D.O.T. Standard Specifications.
The swale should be seeded, fertilized, and mulched according to the recommendations of
the local Soil Conservation District as follows:
Seed Mixture:
70% Tall Fescue (Alta, Boyager, Orfawn)
20% Perrenial Rye
10% White Clover
Application Rate (per 1000 S.F.):
5 lbs. Seed
7 lbs. Fertilizer (10-20-20)
50 lbs. Wood Fiber Mulch
The contractor may be required to provide the City with documentation for the seed mixture
used.
Seeding of the swale should be performed only from March 1 - May 15 or August 15 -
October 1 according to W.S.D.O.T. Standard Specifications, with the exception that seeding
may be performed from May 16 - September 30 if irrigation is provided.
Sodding of the swale will be allowed provided that the sod meets the seed mixture
specifications listed above, or if the sod is overseeded with the appropriate seed mixture at
the next available planting time.
For swales with longitudinal slopes exceeding 4% and/or swales with bottom widths wider
than 4 feet, the use of flow spreaders and check dams should be considered to promote broad
shallow flow.
Slope transitions from the required 3:1 side slope of a swale to a steeper slope or wall are
generally discouraged due to problems with the steeper slope sloughing into the swale
bottom and with the amount of shading that is caused by the wall or slope. Slope transitions
should always take place above the 1 foot minimum swale depth, and should normally be
separated from the swale by a flat bench. The Director will only allow these slope transitions
on a case by case basis.
6.3.2 FILTER STRIP DESIGN CRITERIA
1. Filter strips shall be designed so that each lineal foot of length will receive runoff
from a maximum of 140 square feet of impervious surface.
2. Filter strips shall be sized by providing 0.25 square feet of strip area per square
foot of tributary impervious surface.
AN
3. Curbing for impervious areas contributing to filter strips shall provide a 1 foot gap
for every 5 feet of curbing.
4. The transverse slope of impervious areas contributing to filter strips shall be level,
and the impervious cross slope shall not exceed 10 percent.
5. Filter strips shall have a minimum cross slope of 2 percent and a maximum cross
slope of 15 percent.
6. Runoff from filter strips shall be intercepted at the bottom of the strip by a swale
sized to convey the peak rate of runoff for the 100-year storm event.
6.4 WET PONDS AND WET VAULTS/TANKS
Wet ponds and wet vaults/tanks utilize permanent pools of water to treat stormwater runoff.
The primary treatment mechanism is settling of sediments which results in a reduction in
total suspended solids, including soil particles as well as insoluble metals, which attach to
the particles. In wet ponds, especially those containing shallow vegetated areas, additional
treatment is achieved through microbial decomposition and plant uptake of certain nutrients
and other pollutants.
6.4.1 WET POND DESIGN
Sizing Wet Ponds:
The permanent pool volume shall be equal to the runoff volume generated by the post
development 6-month, 24-hour design storm from the entire contributing basin including any
off -site contributing areas. It is not necessary to vegetate the permanent pool, but
establishment of a shallow marsh system can provide additional pollutant removal
capabilities.
A minimum permanent pool depth of 3 feet is recommended so that re -suspension of trapped
pollutants is inhibited. A maximum depth of 6 feet is recommended. Permanent pools
deeper than 6 feet could potentially contaminate ground water. Also, deeper ponds can
stratify and create anaerobic conditions that cause pollutants that are normally bound in the
sediment (e.g., metals and phosphorus) to re-solubilize; their release back to the water
column can seriously affect the effectiveness of the BMP and also create nuisance
conditions.
Ponds designed to provide stream bank erosion control may be deeper than 6 feet as long as
the permanent pool volume provided for runoff treatment does not exceed 6 feet.
MW
Pond Configuration and Geometry
Wet ponds shall be multi -celled, with at least two cells, and preferably three. The cells
should be approximately equal in size. The first cell should be easily accessible for
maintenance purposes.
Long, narrow, and irregularly shaped ponds are preferred, as these configurations are less,
prone to short-circuiting and tend to maximize available treatment area. The length -to -width
ratio should be at least 3:1 and preferably 5:1. Irregularly shaped ponds may perform more
effectively and will have a more natural appearance.
The inlet and outlet should be at opposite ends of the pond where feasible. If this is not
possible, then baffles can be installed to increase the flow path and water residence time.
The pond bottom shall be level to facilitate sedimentation.
Pond walls may be retaining walls, provided that 1) the design is prepared and stamped by
a structural engineer registered in the State of Washington, 2) that they are constructed of
reinforced concrete, 3) that at least 25 percent of the pond perimeter will be a vegetated soil
slope of not greater than 3H:1V, 4) that maintenance access is provided to the bottom of the
pond, and 5) that a fence is provided around the entire perimeter of the pond.
Access:
Pond access requirements shall be the same as for any pond (see Chapter 5, Stonnwater
Quantity Control Facilities).
Site Constraints:
Site constraints are any restrictions such as property lines, easements, structures, etc. that
impose constraints on development. Use of a site may also be constrained by governmental
ordinances or policies concerning sensitive areas. These should also be reviewed for specific
application to the proposed development.
The minimum setbacks for wet ponds, as measured from the maximum permanent pool water
surface, are the same as those listed in Chapter 5 for detention ponds with the following
exceptions:
• 200 feet from any slope steeper than 30%; this distance may be reduced based on a
geotechnical engineering report.
100 feet from existing or proposed septic drainfields
Locating a wet pond within 100 feet of a neighboring property line may require the
developer to secure easements from adjacent owners due to the fact that the location
3M
of the wet pond may be an encumbrance on adjacent properties with regard to future
septic drainfield locations.
Dam Safety:
Failure of an impoundment structure can cause significant property damage and even loss
of life. Such structures should be designed only by professional engineers registered in the
State of Washington who are qualified and experienced in impoundment design. For ponds
impounding more than 10 acre feet of water, the design will require review and approval by
the Washington State Department of Ecology.
6.4.2 WET VAULT AND WET TANK DESIGN
Limitation:
Wet vaults and wet tanks are only recommended for small areas due to lack of biological
treatment and maintenance difficulties. These facilities should only be used as a last resort
for water quality.
Purpose and Definition:
Wet vaults and tanks are underground facilities used for the storage of surface water, and are
typically constructed from reinforced concrete (vaults) or corrugated pipe (tanks). Wet
vaults and tanks are designed to provide runoff treatment through the use of a permanent
pool of water. Streambank erosion control can also be provided by adding a "live storage"
volume above the permanent pool. Figure 5-16, Detention Tank Detail, and Figure 5-17,
Detention Vault Detail, illustrate tank/vault systems.
If a wet vault/tank is designed to provide runoff treatment but not streambank erosion control
it should be located "off-line" from the primary conveyance/detention system. Flows above
the peak water quality design storm (6-month, 24-hour event) should bypass the facility in
a separate conveyance to the point of discharge. A mechanism should be provided at the
bypass point to take the facility "off-line" for maintenance.
Sizing Criteria:
The sizing criteria for a wet vault/tank shall be the same as for a wet pond.
Geometrics:
The vault shall be divided into a minimum of 2 cells using baffles, with the first cell
occupying about one third of the area. The top of the baffle walls should be coincident with
the depth of the permanent pool.
The length -to -width ratio at the design surface elevation shall be no less than 3:1, and
preferably 5:1.
Materials and Structural Stability:
The material and structural stability design for wet vaults/tanks shall follow the
recommendations for detention tanks and vaults contained in Chapter 5.
Access:
Access requirements for wet vaults/tanks are the same as those for detention tanks and vaults
as listed in Chapter 5.
6.5 OIL/WATER SEPARATORS
Three common types of oil/water separators are described below:
1) Spill Control (SC -type)
2) American Petroleum Institute (API -type)
3) Coalescing Plate Separator (CPS -type)
The use of other types of oil/water separators is permitted when documented performance
data is provided demonstrating the ability to conform with discharge requirements. Because
most oil/water separators are manufactured units, only limited design information is provided
in this chapter. In those cases where an oil/water separator is considered, the engineer is
encourage to contact the appropriate manufacturer or supplier. The reader is also encourage
to refer to the Department of Ecology's "Stormwater Management Manual for the Puget
Sound Basin" for specific design information. Department of Ecology (WSDOE) guidelines
require that stormwater have no visible sheen, average less than 10 mg/1 of oil and grease
daily, and at no time exceed a daily maximum of 15 mg/l. Regardless of the separator type„
the following design criteria should be considered:
1. Under no circumstances should any portion of the contributing drainage area contain
disturbed pervious areas which can be source of sediment.
2. If required, separators should precede all other treatment and streambank erosion control
BMPs.
3. Appropriate access must be provided for efficient inspection and maintenance.
4. Stormwater from rooftops, and other impervious surfaces not likely to be contaminated
by oil shall not discharge to an oil/water separator.
Any stormwater pump mechanism required shall be installed downstream of the
separator to prevent oil emulsification.
6. Oil/water separators shall have an appropriate forebay to collect floatable and large
settleable solids. The forebay surface area shall not be less than 20 sq. ft per 10,000 sq.
ft. of area contributing to the separator.
7. Separators shall be sized for the 6-month, 24-hour design storm. Larger storms shall be
diverted around the separator by use of an appropriate diversion/bypass structure.
6.5.1 SPILL CONTROL OIL/WATER SEPARATORS
Spill control (SC) oil/water separators are required for development sites that include areas
subject to vehicular traffic.
An SC -type oil/water separator is a simple underground vault or manhole with a tee or down
turned elbow outlet. The SC -type oil/water separator is effective at retaining only small
spills. It will not remove diluted oil droplets dispersed into the stormwater from oil -
contaminated pavement.
For small projects where 8" diameter pipe is used, the SC oil/water separator may consist of
a removable, down turned 8" elbow located in a Type 1 catch basin. For larger sites where
12" or larger diameter pipe is used, the SC oil/water separator shall consist of a tee as shown
in Chapter 5, Figure 5-21.
6.5.2 API -TYPE OIL/WATER SEPARATORS
The API -type oil/water separator is a chamber designed to provide flow conditions that re
sufficiently quiescent to allow globules of free oil to rise to the water surface and coalesce
into a separate oil phase. This general type of unit is typically assumed to have no short
circuiting, turbulence, or eddies. Sizing of an API -Type oil/water separator is based upon
the vertical rise rate of oil globules, and its relationship to the vault surface loading rate.
The reader is referred to the WSDOE "Stormwater Manual for the Puget Sound Basin"
and American Petroleum Institute Publication 421 (1990) for specific design information.
6.5.3 CPS -TYPE OIL/WATER SEPARATORS
The coalescing plate oil/water separator (CPS) has a series of parallel inclined plates that
act to increase surface area by the sum of the horizontal projections of the plates added.
Oil collected from CPS systems typically have a lower water content that conventional
separators, and an overall higher removal rate. The extra surface area provided by a CPS
oil/water separator may also be attractive where space is limited.
Manufacturers of CPS oil/water separators provide standard plate packages which are
rated at a particular flow. Because the manufacturer's flow rating is different than
conditions found on individual sites, the engineer must compare the plate surface area
requirements with the following:
An = Q
RiseRate
6-10
Where A, = projected surface are of the plate in sq. ft.; note that the actual surface area,
A�, = An/cosine H.
H = angle of the plates with the horizontal in degrees, usually varies from 45-60 degrees.
Q = design flow in cubic feet per min (cfm).
RiseRate — recommend using 0.033 ft/min.
The determination of late surface area requirements and number of plates required is
theoretically based and is standard for most parallel plate configurations.
The width, depth, and length of the plate pack and the chamber in which the plate pack is
placed is completely flexible and is a function of the plate sizes provided by the particular
pack manufacturer and standard size vaults that are available for small sites.
6-11
CHAPTER 7
COLLECTION AND CONVEYANCE
FACILITIES
CHAPTER 7
COLLECTION AND CONVEYANCE FACILITIES
CONTENTS
7.1
PURPOSE AND SCOPE..................................................................................... 7-2
7.2
GENERAL DESIGN CRITERIA........................................................................ 7-2
7.2.1
ROUTE DESIGN..................................................................................... 7-2
7.2.2
EASEMENTS AND SETBACKS........................................................... 7-2
7.2.3
MAINTENANCE ACCESS.................................................................... 7-3
7.2.4
DATUM................................................................................................... 7-3
7.3
DETERMINATION OF DESIGN FLOW.......................................................... 7-3
7.3.1
DESIGN EVENT..................................................................................... 7-3
7.3.2
DESIGN METHODOLOGY................................................................... 7-4
7.3.3
RATIONAL METHOD........................................................................... 74
7.4
CAPACITY ANALYSIS..................................................................................... 7-9
7.5
DESIGN CRITERIA FOR OPEN CHANNELS ...............................................
7-10
7.5.1
GEOMETRY.........................................................................................
7-10
7.5.2
FREEBOARD........................................................................................7-10
7.5.3
CHANNEL LINING..............................................................................
7-10
7.5.4
CHECK DAMS.....................................................................................
7-10
7.5.5
CHANNEL LOCATION.......................................................................7-11
7.5.6
BIOFILTRATION SWALES................................................................
7-11
7.6
DESIGN CRITERIA FOR CULVERTS...........................................................
7-14
7.6.1
ACCEPTABLE PIPE MATERIAL.......................................................
7-14
7.6.2
HEADWALLS.......................................................................................7-16
7.6.3
GENERAL CULVERT DESIGN CRITERIA ......................................
7-16
7.7
DESIGN CRITERIA FOR PIPE SYSTEMS ....................................................
7-18
7.7.1
ACCEPTABLE PIPE MATERIAL.......................................................
7-18
7.7.2
PIPE ALIGNMENT...............................................................................
7-18
7.7.3
CONNECTIONS TO PIPE SYSTEMS .................................................
7-18
7.7.4
VERTICAL ALIGNMENT OF PIPES AT STRUCTURES .................
7-18
7.7.5
DOWNSIZING OF PIPES....................................................................
7-19
7.7.6
GENERAL PIPE CRITERIA................................................................
7-19,
7.7.7
STEEP SLOPE INSTALLATION........................................................
7-20
7.7.8
PRIVATE SECONDARY DRAINAGE SYSTEMS ............................
7-20
7.8
DESIGN CRITERIA FOR INLET STRUCTURES ..........................................
7-20
7.9
DESIGN CRITERIA FOR OUTFALLS...........................................................
7-23
7.10
STORMWATER PUMPS.................................................................................
7-23
7.11
BRIDGES
..........................................................................................................
7-23
COLLECTION AND CONVEYANCE FACILITIES
7.1 PURPOSE AND SCOPE
This chapter presents City policy concerning the selection, design, sizing, and construction
of stormwater collection and conveyance facilities, including open channels and ditches,
culverts, piped storm sewers, inlet and junction structures, and outfalls. Some conveyance
facilities function both as water quality facilities and as conveyance facilities (e.g.
biofiltration swales and oil/water separators). Design criteria for these facilities are found
in Chapter 6, Stormwater Quality Control Facilities. Some outfall structures also function
as part of runoff control facilities (e.g. control manholes, emergency overflow spillways,
infiltration trenches and flow dispersal trenches). Design criteria for these facilities are
found in Chapter 5, Stormwater Quantity Control Facilities.
Vegetated open channels significantly improve water quality, and are also easier to inspect
and maintain than piped systems. It is recognized, however, that with the urbanization of the
City comes the need for sidewalks and curbing which often results in the necessity to install
piped storm sewers.
This manual provides established standards for engineering design, suitability of purpose and
method of analysis. In addition, the Washington State Department of Transportation,
Standard Specifications for Road, Bridge, and Municipal Construction, most recent edition,
and the Washington State Department of Ecology Stormwater Management Manual for the
Puget Sound Basin (Technical Manual) can be considered approved standards for design and
construction unless differing standards are specifically required in this manual. The King
County Surface Water Design Manual is an excellent reference containing in-depth
discussion on most of the contents of this chapter.
7.2 GENERAL DESIGN CRITERIA
7.2.1 ROUTE DESIGN
New conveyance system alignments on private property must be located in drainage
easements that are adjacent and parallel to property lines, located entirely on one property
and not split between adjacent properties.
7.2.2 EASEMENTS AND SETBACKS
Drainage easements shall be provided in a proposed development for all stormwater facilities
that are not located in public rights -of -way or tracts. Said drainage easements shall be
granted to the parties responsible for providing on -going maintenance of the stormwater
facilities.
7-2
Stormwater facilities that are to be maintained by the City, together with maintenance access
roads to said facilities, shall be located in public right-of-way, separate tracts dedicated to
the City, or drainage easements located in designated Open Space. The exception is for
stormwater conveyance pipes that may be located within easements on private property,
provided that all catch basins can be accessed without entering private property
All drainage easements, public and private, must have a minimum width of 15', with the
exception that private secondary roof and yard drain systems may be located within 10'
easements. All pipes must be located within the easement so that each pipe face or top edge
of channel is no closer than 5' from its adjacent easement boundary (secondary roof and yard
drain pipes shall be centered in the easement). Open channels shall be located within the
easement so that the water surface elevation at the top of freeboard is no closer than 5' from
each easement boundary. For pipes larger than 5' in diameter and for channels having a top
width at freeboard wider than 5', the easement width must be accordingly larger than the
minimum 15' in order to meet the required setbacks from the easement boundaries.
The minimum required building setback from all drainage easements is 5' from the easement
line and 10' from the drainage structure, whichever is greater.
7.2.3 MAINTENANCE ACCESS
Maintenance access must be provided for all manholes, catch basins, vaults, or other
drainage facilities that are to be maintained by the City. It is not generally necessary to
provide vehicular access along the entire length of a drainage pipe or swale as long as access
is provided at each end. Maintenance access shall consist of an access easement and a
constructed access road, with turn -around if necessary. Access roads shall be constructed
as specified in Chapter 5, Stormwater Quantity Control Facilities.
7.2.4 DATUM
A datum tied to a section corner shall be used in the design of drainage systems. All datum
shall be either NGVD29 or NAD83.
7.3 DETERMINATION OF DESIGN FLOW
7.3.1 DESIGN EVENT
All conveyance systems must be designed, at a minimum, to convey a peak stormwater rate
resulting from a 100-year frequency storm event, EXCEPT:
o Other governing authorities may require that the design of some structures be based on
a larger storm event.
7-3
o Some water quality facilities are designed to function primarily under low flow
conditions. However, unless higher flows are diverted from these water quality
facilities, they must also be designed to have sufficient conveyance capacity for 100-
year storm flow rates.
7.3.2 DESIGN METHODOLOGY
For all existing and proposed conveyance systems receiving drainage from a contributing
area of 25 acres or less and having a time of concentration of 100 minutes or less, the
Rational Method may be used as described in this Chapter. For all other conditions an
approved hydrograph method as described in Chapter 5, Stormwater Quantity Control
Facilities, must be used.
7.3.3 RATIONAL METHOD
The traditional Rational Method, as described in most engineering manuals, is preferred by
the City for designing systems serving smaller contributing basins primarily because it tends
to provide higher runoff rates than hydrograph methods do, resulting in a more conservative
design with a built-in factor of safety.
With the traditional Rational Method, peak runoff rates can be determined using the
following formula:
Q=CIA
where Q = Runoff in cubic feet per second
C = Runoff coefficient
I = Rainfall intensity in inches per hour
A = Contributing area in acres
The runoff coefficient (C) should be based on Table 7-1, Runoff Coefficients -'C' Values for
the Rational Method.
The rainfall intensity (I) should be based on Figure 7-1, Rainfall Intensity -Duration Curves,
prepared by the U.S. Weather Bureau for the Mayfield - Bremerton - Port Orchard - Sumner
areas.
7-4
The rainfall intensity is based on the time of concentration, in minutes. The time of
concentration should be computed from the most hydraulically distant point in the
contributing basin to the structure being designed, using the formula
T= L
60V
where T = Time of concentration, in minutes
L = Length of run, in feet
V = Velocity, in feet per second
Velocity can be estimated using Figure 7-2, Average Velocities For Estimating Travel Time
For Overland Flow.
An initial collecting time of 10 minutes for unpaved areas and 5 minutes for paved areas may
be taken at the most hydraulically distant point of flow. From this point, the overland flow
time for each significantly different slope and overland flow condition must be calculated.
Once the runoff has reached the drainage facility being sized, the total time of concentration;
Tc, is calculated by summing the concentration time of each individual run plus the initial
collecting time:
Tc = T, + Tz ... TN + Initial Collecting Time
7-5
Table 7-1
RUNOFF COEFFICIENTS - "C" VALUES FOR THE RATIONAL METHOD
UNDEVELOPED LAND
licit
FLAT
0-5%
licit
ROLLING
>5%
Wood & Forest
0.05
0.10
Sparse Trees & Ground Cover
0.10
0.15
Light Grass to Bare Ground
0.15
0.20
DEVELOPED AREA
Pavement & Roofs
0.90
0.90
Gravel Roads & Parking Lots
0.75
0.80
City Business
0.85
0.90
Apartment Dwelling Areas
0.80
0.85
Industrial Areas(Heavy)
0.70
0.80
Industrial Areas (Light)
0.60
0.70
Earth Shoulder
0.50
0.50
Playground
0.25
0.30
Lawns, Meadows & Pastures
0.20
0.25
Parks & Cemetery
0.15
0.20
SINGLE FAMILY RESIDENTIAL AREAS
licit
(Density is in dwelling units per gross acre (DU/GA)
1.0 DU/GA
0.30
2.0 DU/GA
0.36
3.0 DU/GA
0.42
4.0 DU/GA
0.48
6.0 DU/GA
0.60
9.0 - 15.0 DU/GA
0.7
7-6
Figure 7-I RAINFALL INTENSITY -DURATION CURVES
Fiture 7-2 AVERAGE VELOCITIES
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7.4 CAPACITY ANALYSIS
The capacity of pipe systems and open channels can often be estimated using the Manning
equation for steady uniform flow as follows:
1.486 2
Q= AR3S2
n
1.486 2 1
V =
R3 S2
n
where Q = Capacity, in cubic feet per second
V = Velocity, in feet per second
n = Roughness coefficient
A = Area of cross section, in square feet
R = Hydraulic radius
S = Slope, in feet per foot
R_A
P
The hydraulic radius (R) is
where R = Hydraulic radius
A = Area of cross section, in square feet
P = Wetted perimeter, in feet
Typical values for the Manning roughness coefficient "n" are given in Tables 7-2 and 7-3.
This capacity estimate using the Manning equation may be acceptable for final design
purposes provided that the conveyance system contains no flow restrictions such as tailwater
or abrupt changes in channel cross section or slope that might cause non -uniform flow. It
should also be noted that the Manning equation does not take into account entrance, exit,
bend and junction losses within catch basins or manholes.
To estimate the capacity of a conveyance system where uniform flow is not expected or
where losses within the system may cause surcharging of water, it is recommended that a
Backwater Analysis be performed on the system. Furthermore, when estimating the capacity
of a culvert, it is often necessary to use alternate methods of analysis to account for various'
submerged and unsubmerged flow conditions.
7-9
It is the responsibility of the design engineer to determine the appropriate method of analysis
in determining the capacity of the proposed conveyance system. Many engineering manuals,
handbooks and computer software are available to assist the design engineer.
7.5 DESIGN CRITERIA FOR OPEN CHANNELS
It is important to recognize that water quality is also degraded by sedimentation resulting
from the erosion of channels. For this reason, the City will strictly adhere to the design
criteria contained in this chapter concerning the rock armoring of channels subject to high
velocities of flow.
7.5.1 GEOMETRY
Channel side slopes shall be no steeper than 2:1 for undisturbed ground (cuts), as well as for
disturbed ground (embankments). All constructed channel slopes shall be compacted to a
minimum 95% compaction.
7.5.2 FREEBOARD
Channels shall be designed to provide sufficient freeboard so as not to saturate any adjacent
public road base with 100-year peak flows. A minimum of 1 foot of freeboard is
recommended, but in no case should channel freeboard be less than 0.5 feet.
7.5.3 CHANNEL LINING
Channels having a flowline slope of 6% or greater OR having a peak design velocity
exceeding 5 feet per second shall be rock -lined with rip rap or shall incorporate energy
dissipation devices designed by a qualified civil engineer. As an alternative, the engineer
may submit computations for the design of rip rap to resist the overturning influence of
flowing water.
7.5.4 CHECK DAMS
Check dams are not generally recommended for use in open channels due to the problems
they pose for routine maintenance operations. However, check dams are recommended for
use in temporary channels as an erosion and sedimentation control device (see Chapter 3,
Erosion and Sedimentation Control) and for stepping down channels being used for
biofiltration (see Chapter 6, Stormwater Quality Control Facilities). Where check dams are
proposed, they shall be spaced at maximum 2' elevation intervals.
7-10
7.5.5 CHANNEL LOCATION
Open channels are not recommended through residential lots, particularly at the rear of lots
away from the street. Channels in these locations are very difficult to access for maintenance
and tend to be misused or altered by property owners. The City prefers that open channels
be located in rights -of -way and open spaces where possible. If stormwater must be conveyed,
through an individual residential lot, it should be piped.
7.5.6 BIOFILTRATION SWALES
It is encouraged that every opportunity be taken to design open channels to provide
biofiltration throughout an entire drainage system and not just at the downstream end of the
system. Engineers are also encouraged to consider innovative means of collecting and
conveying runoff so as to incorporate biofiltration into the drainage system design. See
Chapter 6, Stormwater Quality Control Facilities, for more information concerning
biofiltration.
7-11
Table 7-2
VALUES OF THE ROUGHNESS COEFFICIENT, "n", FOR PIPES
TYPE OF PIPE MATERIAL
"n"
Concrete
0.012
Ductile Iron
0.012
Corrugated Metal (CMP) - Annular - 2-2/3" x %"
0.024
Corrugated Metal (CMP) - Annular - 3" x 1"
0.027
Corrugated Metal (CMP) - Annular - 6" x 2"
0.030
Corrugated Metal (CMP) - Helical - 2-2/3" x %2"
12 inch diameter
0.011
18 inch diameter
0.013
24 inch diameter
0.015
36 inch diameter
0.018
48 inch diameter
0.020
60 inch diameter and larger
0.021
Corrugated High Density Polyethylene (CPEP) - single wall
0.024
Corrugated High Density Polyethylene (CPEP) - smooth wall
0.012
Spiral Rib Metal (SRP)
0.011
Polyvinyl Chloride PVC
0.011
High Density Polyethylene (HDPP) - butt fused
0.009
7-12
Type and Channel and Description
Manning's
«n" (Normal)
Type and Channel and Description
Manning's
"n" (Normal)
A. Constructed Channels
6. Sluggish reaches, weedy
a. Earth, straight & uniform
deep pools
0.070
1. Clean, recently completed
0.018
7. Very weedy reaches, deep
0.100
2. Gravel, uniform section, clean
0.025
pools, or floodways with
3. With short grass, few weeds
0.027
heavy stand of timber and
b. Earth, winding and sluggish
0.025
underbrush
1. No vegetation
0.025
b. Mountain streams, no
2. Grass, some weeds
0.030
vegetation in channel, banks
3. Dense weeds or aquatic plants
0.035
usually steep, trees and brush
in deep channels
along banks submerged at high
4. Earth bottom and weedy
0.030
stages
banks
0.035
1. Bottom; gravel, cobbles, and
0.040
5. Stony bottom and weedy
0.040
few boulders
banks
2. Bottom; cobbles with large
0.050
6. Cobble bottom and clean
0.035
boulders
sides
0.040
B-2. Flood Plains
c. Rock lined
a. Pasture, no brush
1. Smooth and uniform
1. Short grass
0.030
2. Jagged and irregular
0.080
2. High grass
0.035
d. Channels not maintained, weeds
0.050
b. Cultivated areas
and brush uncut
0.070
1. No crop
0.030
1. Dense weeds, high as flow
2. Mature row crops
0.035
depth
0.100
3. Mature field crops
0.040
2. Clean bottom, brush on sides
c. Brush
3. Same, highest stage of flow
1. Scattered brush, heavy weeds
0.050
4. Dense brush, high stage
2. Light brush and trees
B. Natural Streams
0.030
3. Medium to dense brush
0.060
B l . Minor streams (top width at flood
4. Heavy, dense brush
0.070
stage < 100 ft.)
0.035
d. Trees
0.100
a. Streams on plain
1. Dense willows, straight
1. Clean, straight, full stage no
0.040
2. Cleared land with tree
0.150
rifts or deep pools
stumps, no sprouts
0.040
2. Same as above, but more
0.040
3. Same as above, but with
stones and weeds
0.050
heavy growth of sprouts
0.060
3. Clean, winding, some pools
4. Heavy stand of timber; a few
and shoals
down trees, little
0.100
4. Same as above, but some
undergrowth, flood stage
weeds
below branches
5. Same as 4, but more stones
5. Same as above, but with
flood stage reaching
0.120
branches
Note: These "n" values are "normal" for use in analysis of channels. For conservative design for channel capacity the
"maximum" values listed in other references should be considered. For cahnnel bank stability the minimum values should
be considered.
7-13
7.6 DESIGN CRITERIA FOR CULVERTS
Culverts, for the purposes of this manual, are single runs of pipe that are open at each end
and that do not have structures such as catch basins or manholes. It should be noted that
culverts designed for fish passage, as governed by the Department of Fish and Wildlife, often
require additional design considerations such as depth of flow and velocity that may differ
considerably from the design requirements included in this chapter.
7.6.1 ACCEPTABLE PIPE MATERIAL
The pipe materials contained in Table 7-5 are approved for use for culverts, subject to the
limitations indicated. Pipe material specifications, joints and protective treatments shall
be in accordance with WSDOT/APWA Standard Specifications.
7-14
Materials allowed for storm drainage conveyance systems:
- Plain concrete (12" diameter only, and only for driveway culverts).
- Ductile Iron, Class 50 or 52.
- Reinforced concrete pipe.
- Galvanized corrugated iron or steel pipe (with Treatment 1 through 6).
- Galvanized steel spiral rib pipe (with Treatment 1 through 6).
- Corrugated aluminum pipe.
- Aluminum spiral rib pipe.
- Aluminized Type 2 corrugated steel (meeting AASHTO treatment M274 and M56).
- Corrugated high density polyethylene pipe (CPEP) - smooth interior (maximum 24" diameter)
meeting AASHTO standard M-294.
- Corrugated high density polyethylene pipe (CPEP) - single wall, fully corrugated meeting
AASHTO standard M-252 (permitted only outside public right-of-way, for use in temporary
storm sewer systems, and as downspout/footing/yard drain collectors on private property).
- Polyvinyl chloride (PVC) sewer pipe (SDR 35, meeting requirements of ASTM D3034)
(permitted only outside public right-of-way and only in privately maintained drainage systems,
and with a minimum 3' of cover).
- High density polyethylene pipe (HDPP) (only 12" to 24" diameter permitted in right-of-way).
Pipe must comply with requirements of Type III C5P34 per ASTM D 1248 and have the PPI
recommended designation of PE3408 and have an ASTM D3350 cell classification of 345434C
or 345534C. Pipe shall have a manufacturer's recommended hydrostatic design stress rating of
800 psi based on a material with a 1600 psi design basis determined in accordance with ASTM
D2837-69. Pipe shall have a suggested design working pressure of 50 psi at 73.4 degrees F and
SDR of 32.5.
7-15
7.6.2 HEADWALLS
Concrete headwalls are required for all CPEP, HDPP and PVC culverts and pipe systems
having exposed pipe ends. For detail, see Figure 7-3, Concrete End Protection.
7.6.3 GENERAL CULVERT DESIGN CRITERIA
1. Maximum design headwater depth shall be 1.5 times the diameter of the culvert, with
no saturation of roadbeds.
2. Minimum culvert diameters are as follows:
a) For cross culverts under public and private roadways - min. 18".
b) For all other roadway culverts, including driveway culverts - min. 12".
3. No bends shall be permitted in culvert pipes.
4. Minimum cover over culverts: 2' under primary roads, F under secondary roads and
in all roadside applications and on private property.
5. Maximum culvert length: 300'.
6. Minimum separation from other utility pipes and conduits: 6" vertical (with
bedding), 3' horizontal, unless otherwise specified by Department of Ecology
(sanitary sewer crossings) or by the purveyor of the utility in question.
7. Pipe bedding and backfill shall conform to WSDOT specifications.
8. The entrances and outlets to all culverts 18" in diameter and larger shall be stabilized
with quarry rock or other energy dissipation in order to minimize scouring of the
channel. The recommendations within Table 7-4 should be followed with the
exception that the inlet protection should extend upstream a minimum of 5' and
should have a minimum height matching the design headwater elevation, and the
outlet protection should have a minimum height of 1' above the design tailwater
elevation, or V above the crown of the pipe, whichever is greater.
7-16
PIPE MATERIAL
D/4 (60 Min.)
MINIMUM t'; f r
3:1 SLOPE : •%,'
D/4 (6" Min.)
. +•
� � r
r- r�ON
•r'^ter of i
1 #4
CONTINUOUS 1 r
(SPLICE CK) ---�
I
I
•
NO
WWORCNG SM SHALL HAVE 1 1/2 kWh CLEAR
COVER TO ALL COMMM SURFACES AND St" BE
GRADE 40 OR GRADE G&
Concrete End Protection
N.T.S.
7-17
7.7 DESIGN CRITERIA FOR PIPE SYSTEMS
Pipe systems, for the purposes of this manual, are systems comprising more than one run of
pipe and including at least one junction type of structure such as a catch basin or manhole.
7.7.1 ACCEPTABLE PIPE MATERIAL
The pipe materials listed in Table 7-5 are approved for use in pipe systems, subject to the
limitations indicated. Pipe material specifications, joints and protective treatments shall be
in accordance with WSDOT/APWA Standard Specifications.
7.7.2 PIPE ALIGNMENT
Bends are not permitted in storm drainage pipes, except for the following applications:
1. Bends may be permitted with HDPP pipe in steep slope installations.
2. On private property, pipes smaller than 8" that are to be privately maintained may have
bends.
For pipes 8" or larger in diameter, changes in direction must take place in a catch basin or
manhole only. For pipes smaller than 8" in diameter, changes in direction may also take
place in a cleanout.
7.7.3 CONNECTIONS TO PIPE SYSTEMS
For all piped drainage systems, connections may only be made at a structure, such as a catch
basin or manhole. Tees, wyes, saddles, or other types of connections to storm drainage pipes
will not be permitted, EXCEPT that on private property, pipes smaller than 8" that are to be
privately maintained may have tee and wye connections.
7.7.4 VERTICAL ALIGNMENT OF PIPES AT STRUCTURES
Where minimum fall is proposed between inlet and outlet pipes in a catch basin or manhole,
pipes must be aligned vertically by one of the following criteria, in order of preference:
Match pipe crowns.
2. Match 80% diameters of pipes.
Perform backwater analysis.
For catch basins having a sump with dead storage, drop manhole connections will not be
required.
7.7.5 DOWNSIZING OF PIPES
Pipes discharging from drainage structures may be of a smaller size than pipes entering that
structure, provided that the smaller receiving pipe has sufficient flow capacity. The
downsizing of pipes in such a manner is to be considered an obstruction having potential
backwater effects. Such downsizing of pipes will only be permitted when the engineer has
demonstrated, using backwater calculations, that a minimum 1.0' of freeboard will be
maintained in all upstream structures and/or upstream channels.
7.7.6 GENERAL PIPE CRITERIA
1. Minimum pipe cover: 2' under primary roads, F under secondary roads and on private,
property.
2. Minimum velocity: 3 fps unless otherwise approved by the Director as a Technical
Deviation.
3. Maximum velocity: 30 fps, except that there is no maximum velocity requirement for
ductile iron pipe or butt welded HDPP.
4. Minimum pipe diameter: 12" in right-of-way (8" may be permitted for street crossings
if shallow gradients or utility conflicts exist); 8" is permitted for privately maintained
primary conveyance lines; no minimum diameter is specified for privately maintained
secondary roof and yard drain systems.
5. Maximum pipe length between structures: 300'.
6. Minimum separation from other utility pipes and conduits: 6" vertical (with bedding),
3' horizontal, unless otherwise specified by Department of Ecology (sanitary sewer
crossings) or by the purveyor of the utility in question.
7. Debris barriers as shown in Figure 5-9 shall be installed at all inlets where an open
channel discharges to a piped drainage system. Additionally, debris barriers are required
at all outlets of piped systems where the pipe is 18" in diameter or larger and catch basins
with sumps are located upstream of the outlet. This additional requirement is to deter
small children from crawling up the pipe where they might fall into a catch basin full of
water.
8. All pipe lengths and slopes shown on construction plans shall be based on measurements
from center of structure to center of structure.
9. Pipe trench backfill: Bedding and backfill shall conform to WSDOT specifications.
7-19
7.7.7 STEEP SLOPE INSTALLATION
Pipe systems located on slopes of 10% or greater declivity may require special design
consideration for pipe anchoring and alternate pipe materials. The King County Surface
Water Design Manual contains specific recommendations on maximum pipe slopes,
maximum velocities and pipe anchoring. It is the responsibility of the project engineer to
incorporate any necessary design measures required to locate pipe systems on slopes.
7.7.8 PRIVATE SECONDARY DRAINAGE SYSTEMS
Stormwater will not be permitted to discharge directly onto the surface of any City road. For
example, drainage from downspouts, roofs or subsurface drains will not be permitted to
discharge into roadside gutters through openings in curbs. Also, concentrated drainage will
not be permitted to discharge so as to flow across sidewalks or over curbs.
For single family residential lots, roof and downspout drainage must be directed to a lot
drainage stubout or to an individual downspout infiltration system, with the following
exception: splash blocks will be permitted, provided that drainage from downspouts has been
designed to sheet flow through a minimum 50' of vegetation prior to discharge to adjacent
properties. This exception does not waive the requirement of the design engineer to account
for the developed runoff from the residential lot during the design of the stormwater facilities
for the development.
7.8 DESIGN CRITERIA FOR INLET STRUCTURES
1. In public right-of-way, structures for introducing stormwater into piped drainage systems
must conform to the latest edition of WSDOT/APWA standards. Inlets without sumps
for sediment containment are not permitted in public right-of-way.
2. The maximum depth of Type 1 and 1L catch basins is 5', measured from top of grate to
invert of lowest pipe. Ladders must be provided in all Type 2 catch basins and manholes
having a depth greater than 5'.
3. Thru-curb inlets are required on all catch basins located at roadway sags and in low
points of cul-de-sacs. See Figure 7-4 for specifications regarding installation of thru-curb
inlets in asphalt -thickened edge pavement.
4. Vaned grates are required for all catch basin inlets located on roadway grades steeper
than 6%.
7-20
5. The following maximum inlet spacings are recommended: (1) for roadway slopes less
than 1%, maximum gutter flow distance should not exceed 150; (2) roadway slopes from
1 % to 3%, maximum gutter flow not to exceed 200'; (3) roadway slopes greater than 3%,
maximum gutter flow length of 300'.
6. The maximum design water surface elevation in inlet structures shall be 1 foot below the
top of the structure.
7-21
1/8' x r DUMMY JOOM
4' TRMISMON i 1'
tHC1sm EDGE to
ASPHALT CURB
ASPHALT SIDEWAW
(MMERE SPECJFlED)
BACK OF
THICKENED
1' 4' TRANSMON EDGE
\ THICKENED EDGE to .
ASPHALT CURB
IInUn1W=
--Ili-ll��l�� : � --
B.�
TOP OF THICKENED EDGE
EXTRUDED OR HAND FORMED
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EXTRUDED OR HAND FORMED
SECTION A —A
Through -Curb Inlet with Thickened Edge
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7-22
7.9 DESIGN CRITERIA FOR OUTFALLS
Outfalls are points where collected and concentrated stormwater runoff is discharged into an
open drainage feature such as a ditch, channel, swale, stream, river, pond, lake or other open
body of water.
7.10 STORMWATER PUMPS
Stormwater pumps will only be permitted as a Technical Deviation approved by the Director.
Any stormwater pumps so permitted must, at a minimum, meet the following criteria:
The proposed pump system is not intended to circumvent other drainage requirements.
2. The proposed pump system is the only feasible alternative to flooding.
3. The pump system must provide storage for a minimum of 25% of the runoff volume
from a 2-year, 24-hour storm event. An emergency backup power source may be
required, at the discretion of the Director.
4. The pump system must include dual pumps with an external alarm system.
5. Pump systems serving commercial and/or multi -family developments and individual
single-family building sites must be privately operated and maintained. Prior to final
approval of the project served by such a pump system, an agreement establishing
responsibility for payment of costs resulting from the operation and maintenance of the
pump system must be approved by the City and must be legally recorded.
7.11 BRIDGES
The design of all bridges shall conform to WSDOT standards and specifications and
AASHTO standards. The hydraulic design of bridges shall conform to Department of Fish
and Wildlife standards as well as with this Manual.
7-23
CHAPTER 8
OPERATION AND MAINTENANCE
CHAPTER 8
OPERATION AND MAINTENANCE
CONTENTS
8.1 OPERATION AND MAINTENANCE MANUAL
8-2
8.2 OPERATION AND MAINTENANCE REQUIREMENTS
8-4
8.2.1
RESPONSIBIITY FOR MAINTENANCE
8-4
8.2.2
MAINTENANCE FREQUENCY
8-4
8.2.3
DISPOSAL OF WASTE FROM MAINTENANCE ACTIVITIES
8-4
8.2.4
CONTROL STRUCTURES AND CATCH BASINS
8-4
8.2.5
INFILTRATION BASINS
8-5
8.2.6
INFILTRATION TRENCHES, AND ROOF DOWNSPOUT
INFILTRATION TRENCHES
8-5
8.2.7
CONCRETE GRID AND MODULAR PAVEMENT
8-5
8.2.8
DETENTION PONDS, VAULTS AND TANKS
8-6
8.2.9
BIOFILTRATION SWALES AND FILTER STRIPS
8-7
8.2.10
OIL/WATER SEPARATORS
8-8
APPENDIX 8A CITY OF PORT ORCHARD MAINTENANCE GUIDELINES
OPERATION AND MAINTENANCE
For stormwater quantity and quality control facilities to achieve their intended results, proper
operation and timely maintenance are essential.
For most developments other than single-family residential, the permanent responsibility for
operation and maintenance of stormwater facilities rests with the property owner. In addition, for
single-family developments, the property owner/developer must temporarily bear this responsibility
for a period of time following the completion of construction.
8.1 OPERATION AND MAINTENANCE MANUAL
Upon completion of construction, and when "as -built" construction plans are submitted to the City,
an Operation and Maintenance (O & M) Manual shall be submitted to the City for all proposed
stormwater quantity and quality control facilities that are to be privately maintained or that have
special non-standard features. The O & M Manual shall be prepared by a civil engineer. This
manual should be brief and simply written so it can be effectively followed by those persons who
will be responsible for operating and maintaining the facilities.
The following basic outline should be followed in the preparation of the Operation and Maintenance
Manual:
General Information:
a. Purpose of O & M Manual (briefly provide an introduction to the O & M Manual and a
general statement on the overall purpose of operation and maintenance of the facility).
b. Location and Access to Facility (name of stream/tributary/lake, etc., that facility
discharges to, nearest cross streets; traveling directions to facility, including location of
maintenance access roads). Include a vicinity map.
C. Purpose of Facility (e.g. peak rate runoff control, water quality, etc.).
d. General Description of Facility (e.g. detention pond, biofiltration swale, etc.).
e. Ownership (name, address, and telephone number of owner of facility).
f. Project History (development for which facility was constructed, date of construction,
original project engineer and contractor, any significant modifications that have taken
place during the life of the facility).
g. Project Data Sheet (lists all major features of the facility in an easy -to -follow tabular
format, including catchment area, impervious area, off -site contribution of runoff, storage
volume, orifice sizes, and designed release rates).
Aw
2. Facility Operation (this section provides detailed procedures for normal "day-to-day" operation
as well as emergency situations).
a. Operating Instructions for Normal Operation.
b. Emergency Action Plan (special operating procedures to be followed during emergency
conditions resulting from extreme weather conditions or from structural failure of the
facility). 24-hour emergency contact telephone numbers must be included.
3. Facility Maintenance (detailed information and instructions on performing periodic
maintenance of the facility).
a. Regularly Scheduled Maintenance (maintenance tasks performed on a regularly scheduled
basis).
b. Monitored Maintenance (involves periodic surveillance of facility and making repairs and
modification as needed).
Maintenance Plan (instructions for performing periodic maintenance should be given in
detail, so that new personnel can understand the tasks and experienced personnel can
verify that the work has been performed properly. All regularly scheduled and monitored
maintenance should be identified and listed in a maintenance plan section of the O & M
Manual).
d. Unscheduled Maintenance (despite having a proper maintenance program, unexpected
deficiencies can occur at any time, prompting the need for repairs and maintenance, e.g.
repairing and reseeding eroded areas on embankments. Although unscheduled
maintenance cannot be planned for in a maintenance plan, an owner should anticipate the,
need for repair or rehabilitation of unexpected deficiencies. To this end, a section should
be provided in the maintenance plan that gives instructions for dealing with unscheduled
maintenance).
4. Facility Inspection (this section specifies required frequency intervals for inspections and
includes an inspection checklist and an inspection report form).
a. Routine Inspections (a brief, visual inspection of the major features of the facility,
performed on a frequent, informal basis, e.g. weekly, monthly).
b. Periodic Inspection (a periodic inspection is a more detailed inspection, during which all
features and equipment at the facility are evaluated at regularly scheduled intervals.). A
checklist should be provided to ensure that all critical features are examined.
Inspection Report Form (a simple form, to be completed by the persons performing the
periodic inspection, reporting the date of inspection, person performing inspection,
findings, inspection checklist).
8.2 OPERATION AND MAINTENANCE REQUIREMENTS
The following minimum requirements for operation and maintenance of stormwater facilities shall
be incorporated into the Operation and Maintenance Manual:
8.2.1 RESPONSIBIITY FOR MAINTENANCE
Property owners are responsible for the maintenance, operation, or repair of stormwater drainage
systems and BMPs. Property owners shall maintain, operate, and repair these facilities in
compliance with the requirements of the Stormwater Management Ordinance and with the
requirements of this Manual.
8.2.2 MAINTENANCE FREQUENCY
Stormwater facilities shall be inspected and maintained routinely and cleared of debris, sediment,
and vegetation when the functioning and/or design capacity of the facility is affected. Where lack
of maintenance is causing or contributing to a water quality problem, immediate action shall be taken
to correct the problem.
8.2.3 DISPOSAL OF WASTE FROM MAINTENANCE ACTIVITIES
Disposal of waste from maintenance activities shall be conducted in accordance with the minimum
Functional Standards for Solid Waste Handling, Chapter 173-304 WAC, guidelines for disposal of
waste materials from stormwater maintenance activities, and where appropriate, the Dangerous
Waste Regulations, Chapter 173-303 WAC. In addition, the D.O.E. "Technical Manual' addresses
disposal procedures.
8.2.4 CONTROL STRUCTURES AND CATCH BASINS
Control structures and catch basins have a history of maintenance -related problems and it is
imperative that a good maintenance program be established for their proper functioning. A typical'
problem is that sediment builds up inside the structure, blocking or restricting flow to the outlet. To
prevent this problem, these structures should be routinely cleaned out. Regular inspections of
control structures should be conducted to detect the need for non -routine cleanout, especially if
construction or land -disturbing activities are occurring in the contributing drainage area.
Maintenance standards for control structures are contained in Appendix 8A.
58.2.5 INFILTRATION BASINS
Inspection Schedule: When infiltration basins are first placed into use, they should be inspected on
a monthly basis, and more frequently if a large storm occurs in between scheduled inspections.
During the period of October 1 through March 31, inspections shall be conducted monthly.
Thereafter, once it is determined that the basin is functioning in a satisfactory manner and that there
are no potential sediment problems, inspection can be reduced to a semi-annual basis with additional
inspections following the occurrence of a large storm. This inspection shall include investigation
for potential sources of contamination.
Sediment Control: Grass bottoms in infiltration basins seldom need replacement since grass serves,
as a good filter material. If silt laden water is allowed to trickle through the turf, most of the
suspended material is strained out within a few yards of surface travel. Well established turf on a
basin floor will grow through sediment deposits forming a porous surface and preventing the
formation of an impenetrable layer. Grass planted on basin side slopes will also prevent erosion.
Vegetation Maintenance: Maintenance of vegetation established on the basin floor and side slopes
is necessary in order to promote dense vegetation with extensive root growth. This enhances
infiltration, prevents erosion and consequent sedimentation, and prevents invasive weed growth.
Bare spots are to be immediately stabilized and revegetated.
The use of low -growing, stoloniferous grasses will permit long intervals between mowings. Mowing
twice a year is generally satisfactory. Fertilizers should be applied only as necessary and in limited
amounts to avoid contributing to pollution problems, including ground water pollution. Consult the
local Conservation District for appropriate fertilizer types and application rates.
8.2.6 INFILTRATION TRENCHES AND ROOF DOWNSPOUT INFILTRATION
TRENCHES
Inspection Schedule: The observation well should be monitored periodically. For the first year after
completion of construction, the well should be monitored after every large storm (>I inch in 24
hours), and during the period from October 1 through March 31, inspections should be conducted
monthly. From April 1 through September 30, the facility should be monitored on a quarterly basis.
Once the performance characteristics of the structure have been verified, the monitoring schedule
can be reduced to an annual basis unless the performance data indicate that a more frequent schedule
is required.
8.2.7 CONCRETE GRID AND MODULAR PAVEMENT
Where turf is incorporated into concrete grid and modular pavement installations, normal turf
maintenance such as watering, fertilizing and mowing, will be necessary. Mowing is seldom
E:�
required in areas of frequent traffic. It is documented that the hard surfaces in these installations
require very little maintenance. However, fertilizers, pesticides and other chemicals may have
adverse effects on concrete products. The use of such chemicals should be restricted as much as
possible.
8.2.8 DETENTION PONDS, VAULTS, AND TANKS
GENERAL
Maintenance is of primary importance if detention ponds are to continue to function as originally
designed. See Appendix 8A for specific maintenance requirements.
Debris removal in detention basins can be achieved through the use of trash racks or other screen
devices.
VEGETATION
In wet ponds, periodic removal of dead vegetation will be necessary. The frequency of removal has
not been established. Since decomposing vegetation can release pollutants captured in the pond,
especially nutrients, it may be necessary to harvest dead vegetation annually prior to the winter wet
season. Otherwise, the decaying vegetation can export pollutants out of the pond and also can cause
nuisance conditions to occur. If harvesting is to be done in the shallow marsh area, a written
harvesting procedure shall be prepared by a qualified wetland specialist and will be submitted with
the drainage design to the City.
It is permissible to temporarily drain wet ponds during late Spring (MAY) and Summer if there is
sufficient concern regarding insect breeding. However, it is imperative that vegetation in shallow
marsh areas not die off during drawdown periods. Otherwise, the pollutant removal
effectiveness of the wetpond can be severely impacted. In addition, the decaying vegetation
can create nuisance conditions. Unless the owner provides test results demonstrating the absence
of pollution from the standing water, any standing water removed during the maintenance operation
must be disposed of to a sanitary sewer at an approved discharge location. Residuals must be
disposed of in accordance with current Bremerton-Kitsap County Heath District requirements.
SEDIMENT
Maintenance of sediment forebays and attention to sediment accumulation within the ponds, vaults
and tanks is extremely important. Sediment deposition should be continually monitored in the basin.
Owners, operators, and maintenance authorities should be aware that significant concentrations of
metals (e.g., lead, zinc, copper and cadmium) as well as some organics such as pesticides, may be
expected to accumulate at the bottom of these treatment facilities. Testing of sediment, especially,
near points of inflow, should be conducted regularly to determine the leaching potential and level
of accumulation of problem material before disposal. Any problem materials encountered in
sediment material shall be disposed of in accordance with Bremerton-Kitsap County Health District
requirements.
E:.
ACCESS
Maintenance access must be provided at all times to detention storage facilities, infiltration basins,
control structures, etc. Access roads must be maintained to provide access by heavy vehicles.
Gravel surfaces must be maintained and repaired and vegetation removed which would otherwise
restrict the 15' width of the road, the 40' minimum outside turning radius, or the turnaround areas.
Fences and gates must be repaired as necessary to maintain security. Where no fence is provided,
bollards must be installed at all times to restrict vehicle access. All signs shall be in place and
readable. Any damage resulting from vandalism shall be repaired. All manhole and catch basin lids
shall be in place and locked (where locks are provided). Refer to Chapter 5, Stormwater Quantity
Control Facilities, for design requirements for access facilities.
NUISANCE CONDITIONS
The presence of wet ponds in established urban areas is perceived by many people to be undesirable.
They are often thought of as mud holes where mosquitoes and other insects breed.
If the wet pond has a shallow marsh established, the pond can become a welcomed addition to an
urban community. Constructed fresh water marshes can provide miniature wildlife refuges, and
while insect populations are increased, insect predators also increase, often reducing the problem to
a tolerable level.
8.2.9 BIOFILTRATION SWALES AND FILTER STRIPS
Groomed biofilters planted in grasses must be mowed regularly during the summer to promote
growth and pollutant uptake. Fertilizing and watering of biofilters may also be required. Be sure
not to cut below the design flow depth (maintenance personnel must be made aware of this
requirement). In addition:
1. Remove and dispose of cuttings promptly, so that no pollutants can enter receiving waters.
2. If the objective is prevention of nutrient transport, mow grasses or cut emergent wetland -type
plants to a low height at the end of the growing season. For other pollution control objectives,
let the plants stand at a height exceeding the design water depth by at least two inches at the end
of the growing season.
3. Remove sediments during summer months when they 1) build up to 6 inches at any spot, 2)
cover biofilter vegetation, or 3) interfere with biofilter operation. If the equipment leaves bare
spots, re -seed them immediately.
4. Inspect biofilters at least monthly, especially after periods of heavy runoff. Remove sediments,
fertilize, and re -seed as necessary. Be careful to avoid introducing fertilizer to receiving waters
or ground water.
5. Clean curb cuts when soil and vegetation buildup interferes with flow introduction.
HIM
6. Provide educational information for residents near biofilters concerning the purpose and
importance of keeping them free of lawn debris and litter.
7. Remove litter in order to keep biofilters attractive in appearance.
8. Roadside ditch cleaning should be based on an analysis of hydraulic necessity. Remove only
the amount of sediment necessary to restore needed hydraulic capacity, leaving vegetative plant
parts in place to the maximum extent possible.
8.2.10 OIL/WATER SEPARATORS
Oil/water separators must be cleaned frequently to keep accumulated oil from escaping during
storms. They must be cleaned by October 1 of each year to remove material that has accumulated
during the dry season, and again after each significant storm. In addition:
1. The facility shall be inspected weekly by the owner.
2. Any oil absorbent pads shall be replaced by October 1 of each year and additionally as needed
throughout the year.
3. The effluent shutoff valve is to be closed during cleaning operations.
4. Waste oil and residuals shall be disposed of in accordance with current Bremerton-Kitsap County
Heath District requirements, as well as with State and Federal law.
5. Any standing water removed during the maintenance operation must be disposed of to a sanitary
sewer at a discharge location approved by the City or the local Sewer District.
6. Any standing water removed shall be replaced with clean water to prevent oil from passing
through the outlet weir or orifice.
7. Coalescing plates are to be removed and cleaned in a location that allows for collection and
proper disposal of wash water. Cleaning of coalescing plates shall be in accordance with
manufacturer's recommended procedures.
MW
APPENDIX 8A
PORT ORCHARD MAINTENANCE GUIDELINES
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