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BMP C232: Gravel Filter Berm <br />Purpose <br />A gravel filter berm retains sediment by filtering runoff through a berm of gravel or crushed rock. <br />Conditions of Use <br />Use a gravel filter berm where a temporary measure is needed to retain sediment from construction <br />sites. <br />Do not place gravel filter berms in traffic areas; gravel filter berms are not intended to be driven over. <br />Place gravel filter berms perpendicular to the flow of runoff, such that the runoff will filter through the <br />berm prior to leaving the site. <br />Design and Installation Specifications <br />. Berm material shall be % to 3 inches in size, washed well -grade gravel or crushed rock with <br />less than 5 percent fines. Do not use crushed concrete. <br />. Spacing of berms: <br />o Every 300 feet on slopes less than 5 percent <br />o Every 200 feet on slopes between 5 percent and 10 percent <br />o Every 100 feet on slopes greater than 10 percent <br />. Berm dimensions: <br />o 1 foot high with 3H :1 V side slopes <br />o 8 linear feet per 1 cls runoff based on the 10-year, 24-hour design storm <br />See Figure 11-3.21: Gravel Filter Berm for a photo of a gravel filter berm application. <br />Maintenance Standards <br />Regular inspection is required. Sediment shall be removed and filter material replaced as needed. <br />2019 Stormwater Management Manual for Western Washington <br />Volume ll - Chapter 3 - Page 368 <br />