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CRY OF EVERETT STORMWATER MANAGEMENT MANUAL <br /> 8. Kcep the center of the check dam at least 12 inches lower than the outer edges at natural gro�nd ' <br /> elevation. <br /> 9. Keep the side slopes of the check dam at 2:1 or flaner. <br /> 10. Key the stone into the ditch banks and extend it beyand the abutments a minimum oF 18 inches to <br /> avoid washouts Gom over�ow azound t6e dazn. <br /> 1 l. Usc filter fabric Coundation under a rock or sand bag check dam. If a blanket ditch lioer is used, <br /> this is not necessary. A piece of organic or synthetic blanket cut to Gt will also work for this <br /> purpose. <br /> 12. Rock check dams shall be constructed of appropriately sized rack. The rock must be plaad by <br /> hand or by mechanical mcens(no dumping of rack to form dam)to achieva complete coverage of <br /> the ditch or swale and to ensure that the center of the dam is lower than the edges. The rak used <br /> must be lerge enough to 'stay in place given 1he expected design ilow through the channel. <br /> 13. In the case of grass-lincd ditches and swales,all check dams and accumulated sediment shall be <br /> removed when the grass has matured su@'iciendy to protect the ditch or swale—unless the slope <br /> of the swale is greater than 4 penent. The area beneath the check dams shall bc seeded and <br /> mu:ched immedietely after da�n removal. <br /> 14. Ensure that channel apputtenances,such as culvert eotrances below check dams,are not subject <br /> to datnage or blockage Gom displaced stones. DCSS Drawing#206 depicts a rypicet rock c6eck <br /> dam. <br /> Matnfenance Sfandards <br /> 1. Check dams s6a11 be moniWred for perfartnance and sediment accumulation during and after cach <br /> ruuoffproducing rainfall. Sediment shall be removed when it reaches oae half the sump depth. <br /> 2. Anticipate submergence and depositiou above the check dam and erosion from high flows around • <br /> the edges of the dam. <br /> 3. If signiticant erosion occuts behveen dams,install a protectrvc riprap liner in that porlion of the <br /> channel. <br /> 3.3.9 BMP C208: Triangular Silt Dike (Geotextile-Encased Check Dam) <br /> Purpose <br /> Triangular silt dikes may be used as check dams, for perime�er protection,for temporary soil stockpile <br /> protection, for drop inlet protection,or as a temporary intercepror dikc. Sce DCSS Drawing k 207. <br /> Conditions of Use <br /> 1. May be used for temporary chcck dams in ditches oP any dimcnsion <br /> 2. May be uscd on soil or pavemcnt with adhesive or staples <br /> 3. l'riangulaz silt dikes have been used to build tcmporary: <br /> a. Sediment ponds <br /> b. Diversion ditches <br /> a Concrete wash out facilities <br /> d. Curbing <br /> e. Waterbars <br /> Volume 11—Construction Stoimwater Pollution Prevenfion <br /> 3-47 <br />