A. The city’s preferred approach to site development includes low impact development (LID) best management practices (BMPs) as an alternative to conventional stormwater management systems that rely on closed conveyance. LID is intended to manage stormwater runoff close to the source of generation and to mimic the predeveloped hydrologic condition of a site. Beginning June 30, 2018, the city will require the incorporation of low impact development best management practices, for new development and redevelopment, in accordance with the Stormwater Management Manual for Western Washington (SWMMWW) and its National Pollution Discharge Elimination System (NPDES) Western Washington Phase II Municipal Stormwater Permit as issued, and as may be amended, by the Washington State Department of Ecology.

B. LID is accomplished through minimizing the impervious surface coverage, retaining on-site natural features and vegetation, and managing runoff through dispersion, infiltration, evapotranspiration, or a combination of these approaches. Use of LID BMPs may reduce or eliminate the need for conventional detention facilities but does not remove the obligation to comply with the minimum requirements of the Stormwater Management Manual for Western Washington.

C. A variety of BMPs to minimize impervious surfaces and to manage stormwater have been developed and tested for use in Western Washington. These BMPs and the overall LID approach are described in the SWMMWW and additional guidance is provided in the latest version of the LID Technical Guidance Manual for Puget Sound.

D. The menu of LID BMPs identified in the SWMMWW are accepted by the city for use in stormwater site plans to address the minimum requirements for flow control and runoff treatment in this chapter, subject to the specifications, performance standards, and design criteria in the SWMMWW and review and approval under this chapter.