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BMP T5.14: Rain Gardens <br /> Rain gardens shall be designed in accordance with the SWMMWW and include capacity for the total <br /> hard surface area (at least 5%) and any contributing area from lawn/landscaped areas (at least 2%). <br /> Top of Ponding Area (ft2) = 0.05 * Total hard surface area (ft2) +0.02 * Lawn/landscape area (ft2) <br /> ■ Total hard surface area(ft2): <br /> ■ Lawn/landscape area (ft2): <br /> ■ Total contributing area(ft2): <br /> ■ Top of ponding area (ft2): <br /> The following table provides minimum rain garden footprints based upon total contributing area. <br /> M1Total Contributing op of Minimum Bottomof Minimum Top . <br /> Area(ft2) Ponding Area(ft2) Ponding Area(ft2) Berm Area(ft2) <br /> 2:1 <_800 40 0.11 50 <br /> 2:1 5 1,400 70 0.13 110 <br /> 3:1 53,000 150 0.06 235 <br /> BMP T5.10B: Downspout Dispersion Systems <br /> Downspout dispersion systems are splash blocks ortrencheswhich spread roof runoff over vegetated <br /> perviousareas. You should select the dispersion system based on the amount of roof area draining <br /> to the dispersion system. Downspout dispersion shall be designed in accordance with the <br /> SWMMWW. <br /> Downspout Dispersion Trench <br /> Roof downspout dispersion trenches serving up to 700 ft' roof area may use a simple <br /> dispersion trench (2 ft wide X 10 ft long). Multiple simple dispersion trenches may be used <br /> as long as none of their tributary areas exceed 700 ft2 and the flow paths from the trenches <br /> do not overlap. <br /> ■ Roof area requiring mitigation (ft2): <br /> ■ Number of simple dispersion trenches proposed: <br /> ❑ Include the following on the Stormwater Site Plan:dispersion trench location and <br /> dimensions; roof area(includingftzdrainingto each dispersion trench) <br /> City of Everett Public Works <br /> Small Project Stormwater Site Plan/Report—Sept.2023 Page 35 of 40 <br />