1710 W MARINE VIEW DR 2024-01-03

upstream dam is at the same elevation as the top of the downstream dam. . Keep the maximum height at 2 feet at the center of the check dam. . Keep the center of the check dam at least 12 inches lower than the outer edges at natural ground elevation. . Keep the side slopes of the check dam at 2H:1 V or flatter. . Key the stone into the ditch banks and extend it beyond the abutments a minimum of 18 inches to avoid washouts from overflow around the dam. . Use filter fabric foundation under a rock or sand bag check dam. If a blanket ditch liner is used, filter fabric is not necessary. A piece of organic or synthetic blanket cut to fit will also work for this purpose. . In the case of grass -lined ditches and swales, all check dams and accumulated sediment shall be removed when the grass has matured sufficiently to protect the ditch or swale - unless the slope of the swale is greater than 4 percent. The area beneath the check dams shall be seeded and mulched immediately after dam removal. • Ensure that channel appurtenances, such as culvert entrances below check dams, are not subject to damage or blockage from displaced stones. . See Figure II-3.16: Rock Check Dam. Maintenance Standards Check dams shall be monitored for performance and sediment accumulation during and after each rainfall that produces runoff. Sediment shall be removed when it reaches one half the sump depth. . Anticipate submergence and deposition above the check dam and erosion from high flows around the edges of the dam. . If significant erosion occurs between dams, install a protective riprap liner in that portion of the channel. See BMP C202: Riprap Channel Lining. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/E merging-stormwater-treatment-technologies 2019 Stormwater Management Manual for Western Washington Volume /I - Chapter 3 - Page 352