Chapter 12.20
STORM WATER MANAGEMENT
Sections:
12.20.010 Redevelopment activities.
12.20.020 Approved hydrological methods for design.
12.20.030 (Repealed)
12.20.035 (Repealed)
12.20.040 Storm water quality control.
12.20.050 Illicit discharges.
12.20.060 Experimental best management practices.
12.20.070 Incorporation into storm water quantity control facilities.
12.20.080 Minimum requirements – Major developments.
12.20.085 Minimum requirements – Minor developments.
12.20.090 Storm water conveyance facilities.
12.20.100 Easements, tracts and covenants.
12.20.110 (Repealed)
12.20.120 Regional facilities.
12.20.130 Basin planning.
12.20.010 Redevelopment activities.
(1) For road-related projects, runoff from the replaced and new impervious surfaces (including pavement, shoulders, curbs, and sidewalks) shall meet all the minimum requirements listed in Chapter 12.18 if the new impervious surfaces total five thousand square feet or more and total fifty percent or more of the existing impervious surfaces within the project limits. The project limits shall be defined by the length of the project and the width of the right-of-way or easement.
(2) Other types of redevelopment projects shall comply with all the minimum requirements listed in Chapter 12.18 for the new and replaced impervious surfaces if the total of new plus replaced impervious surfaces is five thousand square feet or more, and the valuation of proposed improvements – including interior improvements – exceeds fifty percent of the assessed value of the existing site improvements.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 34, 2009: Ord. 199 (1996) § 7.05, 1996)
12.20.020 Approved hydrological methods for design.
Estimation of peak storm water runoff rates used in the design of storm water quantity control facilities shall utilize the latest version of the Western Washington hydrology model. The design of storage facilities that are a part of storm water quantity control facilities shall be designed using methods contained in the manual.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 35, 2009: Ord. 199 (1996) § 7.10, 1996)
12.20.030 (Repealed)*
* Editor’s Note: Former Section 12.20.030, “Storm water quantity control – Engineered flow control,” was repealed by Ordinance 433 (2009). Section 2 of Ordinance 375 (2007) and Section 7.20 of Ordinance 199 (1996) were formerly codified in this section.
12.20.035 (Repealed)*
* Editor’s Note: Former Section 12.20.035, “Storm water quantity control – Prescriptive flow control,” was repealed by Ordinance 433 (2009). Section 4 of Ordinance 375 (2007) was formerly codified in this section.
12.20.040 Storm water quality control.
Water quality best management practices (BMPs) shall be used on either a volume or flow rate basis.
(1) Water Quality Design for Volume Based Treatments.
A. The ninety-first percentile, twenty-four-hour runoff volume indicated by the latest version of the Western Washington hydrology model shall be used; or
B. Ninety-one percent of the volume of runoff volume of the time series estimated by the latest version of the Western Washington hydrology model is treated.
(2) Water Quality Design for Flow Rate Based Treatments.
A. Preceding Detention Facilities or When Detention Facilities Are Not Required. The flow rate at or below which ninety-one percent of the runoff volume, as estimated by the latest version of the Western Washington hydrology model, is treated.
B. Downstream of Detention Facilities. The water quality design flow rate must be the full two-year release rate from the detention facility.
(3) Water Quality Design for Infiltration Based Treatments. Ninety-one percent of the volume of runoff volume of the time series as estimated by the latest version of the Western Washington hydrology model is infiltrated through the treatment media.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 36, 2009: Ord. 199 (1996) § 7.30, 1996)
12.20.050 Illicit discharges.
Illicit discharges, as described in Section 12.30.020, or illicit connections to a storm water drainage system, as described in Section 12.30.030, are prohibited.
(Ord. 199 (1996) § 7.32, 1996)
12.20.060 Experimental best management practices.
In those instances where appropriate best management practices are not in the manual, experimental BMPs may be considered. In an effort to improve storm water quality technology, experimental BMPs are encouraged as a means of solving 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.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 37, 2009: Ord. 199 (1996) § 7.33, 1996)
12.20.070 Incorporation into storm water quantity control facilities.
Water quality BMPs may be incorporated into the design of storm water quantity control facilities where appropriate.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 38, 2009: Ord. 199 (1996) § 7.34, 1996)
12.20.080 Minimum requirements – Major developments.
1. Major developments shall comply with all the minimum requirements listed in Chapter 12.18, Minimum Site Development Requirements.
2. Major developments may meet these minimum requirements for an equivalent (flow and pollution characteristics) area within the same site. For public roads projects, the equivalent area does not have to be within the project limits, but must drain to the same receiving water.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 39, 2009: Ord. 375 (2007) § 3, 2007: Ord. 199 (1996) § 7.35, 1996)
12.20.085 Minimum requirements – Minor developments.
1. Minor developments that:
(a) Create or add two thousand square feet, or greater, of new, replaced, or new plus replaced impervious surface area; or
(b) Have land disturbing activity of seven thousand square feet or greater;
shall comply with minimum requirements contained in Sections 12.18.010, 12.18.020, 12.18.030, 12.18.040, and 12.18.050 (minimum requirements Nos. 1 through 5).
2. Minor developments that fall under these thresholds shall comply with the following minimum erosion control criteria:
(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 soils and debris onto public roads.
(b) 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 the manual. From October 1st to April 30th, no soils shall remain unstabilized for more than two days. From May 1st to September 30th, no soils shall remain unstabilized for more than seven days.
At all times of the year, the contractor shall have sufficient materials, equipment and labor on site to stabilize and prevent erosion from all denuded areas within twelve hours as site and weather conditions dictate.
(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.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 40, 2009)
12.20.090 Storm water conveyance facilities.
(a) All proposed developments must provide on-site storm water conveyance facilities having sufficient capacity to convey, without flooding or otherwise damaging existing or proposed structures, the post-development peak storm water runoff rate resulting from a one-hundred-year storm event, plus any existing upstream runoff that will be conveyed through the development site.
(b) Estimation of peak storm water runoff rates used in the design of water conveyance facilities shall use one of the following methods:
(1) The rational method as shown in the manual; or
(2) The Santa Barbara urban hydrology (SBUH) event model method. The SBUH method is defined in the Stormwater Management Manual for Western Washington (2005); or
(3) The latest version of the Western Washington hydrology model (WWHM).
(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 storm water discharge for the one-hundred-year storm event. All newly constructed downstream drainage ways and/or conveyance facilities shall have sufficient capacity to convey the post-development peak storm water discharge for the one-hundred-year storm event. Downstream improvements or additional on-site storm water quantity control measures shall be provided to eliminate any potential 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.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 41, 2009: Ord. 199 (1996) § 7.40, 1996)
12.20.100 Easements, tracts and covenants.
(a) Drainage easements shall be provided in a proposed development for all storm water conveyance systems that are not located in public rights-of-way. The drainage easements shall be granted to the parties responsible for providing ongoing maintenance of the systems. Drainage easements through structures are not permitted.
(b) Storm water facilities that are to be maintained by Kitsap County, together with maintenance access roads to the facilities, shall be located in the public right-of-way, in separate tracts dedicated to Kitsap County, or in drainage easements granted to Kitsap County.
(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, and shall be contained in any covenants required for a development.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 42, 2009: Ord. 199 (1996) § 7.50, 1996)
12.20.110 (Repealed)*
* Editor’s Note: Former Section 12.20.110, “Wetlands,” was repealed by Ordinance 433 (2009). Section 7.60 of Ordinance 199 (1996) was formerly codified in this section.
12.20.120 Regional facilities.
When the director has determined that the public would benefit by the establishment of a regional storm water facility which would serve as an alternative to the construction of separate on-site drainage facilities, the director may recommend to the board that a regional storm water facility be constructed which would serve more than one development in providing storm water quantity and/or quality control. In the event that a regional storm water facility is required by the board, such a regional storm water facility shall be located outside of fish-bearing streams, unless otherwise accepted by the Washington State Department of Fish and Wildlife. All future developments constructed on lands designated by the board to be served by the regional facility shall, at the time of issuance of a site development activity permit for a development, be required to contribute a fair share to the cost of land purchase, design and construction of the regional facility. In the event that a proposed regional storm water facility is not yet in operation at the time of completion of construction of a development that is to be served by the regional facility, the applicant for the development shall be required to provide temporary storm water quantity and quality controls. Temporary quantity and quality controls may be constructed in temporary easements, rather than in separate tracts.
(Ord. 199 (1996) § 7.70, 1996)
12.20.130 Basin planning.
An adopted and implemented basin plan tailored to a specific basin may be used to develop requirements for source control, storm water treatment, flow control, wetlands and water quality sensitive areas. Adopted and implemented watershed-based basin plans may be used to modify any or all of the minimum requirements for storm water quantity or quality control addressed in this title; 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 title 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 by the State Department of Ecology and Kitsap County and fully implemented by Kitsap County.
(Ord. 441 (2009) § 2 (part), 2009; Ord. 433 (2009) § 43, 2009: Ord. 199 (1996) § 7.80, 1996)