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Site Design & Landscape Planning SD-10 <br />regulations to discourage the clearing, filling, and channelization of these features. Utilize <br />them in drainage networks in preference to pipes, culverts, and engineered ditches. <br />Evaluating infiltration opportunities by referring to the stormwater management manual for <br />the jurisdiction and pay particular attention to the selection criteria for avoiding <br />groundwater contamination, poor soils, and hydrogeological conditions that cause these <br />facilities to fail. If necessary, locate developments with large amounts of impervious <br />surfaces or a potential to produce relatively contaminated runoff away from groundwater <br />recharge areas. <br />Protection of Slopes and Channels during Landscape Design <br />■ Convey runoff safely from the tops of slopes. <br />■ Avoid disturbing steep or unstable slopes. <br />■ Avoid disturbing natural channels. <br />■ Stabilize disturbed slopes as quickly as possible. <br />■ Vegetate slopes with native or drought tolerant vegetation. <br />■ Control and treat flows in landscaping and/or other controls prior to reaching existing <br />natural drainage systems. <br />■ Stabilize temporary and permanent channel crossings as quickly as possible, and ensure that <br />increases in run-off velocity and frequency caused by the project do not erode the channel. <br />■ Install energy dissipaters, such as riprap, at the outlets of new storm drains, culverts, <br />conduits, or channels that enter unlined channels in accordance with applicable <br />specifications to minimize erosion. Energy dissipaters shall be installed in such a way as to <br />minimize impacts to receiving waters. <br />■ Line on -site conveyance channels where appropriate, to reduce erosion caused by increased <br />flow velocity due to increases in tributary impervious area. The first choice for linings <br />should be grass or some other vegetative surface, since these materials not only reduce <br />runoff velocities, but also provide water quality benefits from filtration and infiltration. If <br />velocities in the channel are high enough to erode grass or other vegetative linings, riprap, <br />concrete, soil cement, or geo-grid stabilization are other alternatives. <br />■ Consider other design principles that are comparable and equally effective. <br />Redeveloping Existing Installations <br />Various jurisdictional stormwater management and mitigation plans (SUSMP, WQMP, etc.) <br />define "redevelopment" in terms of amounts of additional impervious area, increases in gross <br />floor area and/or exterior construction, and land disturbing activities with structural or <br />impervious surfaces. The definition of" redevelopment" must be consulted to determine <br />whether or not the requirements for new development apply to areas intended for <br />redevelopment. If the definition applies, the steps outlined under "designing new installations" <br />above should be followed. <br />January 2003 California Stormwater BMP Handbook 3 of 4 <br />New Development and Redevelopment <br />www.cabmphandbooks.com <br />