1710 W MARINE VIEW DR 2024-01-03

and staples. o In the case of grass -lined ditches and swales, 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. Maintenance Standards . Inspect TSDs for performance and sediment accumulation during and after each rainfall that produces runoff. Remove sediment when it reaches one half the height of the TSD. . Anticipate submergence and deposition above the TSD and erosion from high flows around the edges of the TSD. Immediately repair any damage or any undercutting of the TSD. BMP C209: Outlet Protection Purpose Outlet protection prevents scour at conveyance outlets and minimizes the potential for downstream erosion by reducing the velocity of concentrated stormwater flows. Conditions of Use Use outlet protection at the outlets of all ponds, pipes, ditches, or other conveyances that discharge to a natural or manmade drainage feature such as a stream, wetland, lake, or ditch. Design and Installation Specifications . The receiving channel at the outlet of a pipe shall be protected from erosion by lining a min- imum of 6 feet downstream and extending up the channel sides a minimum of 1—foot above the maximum tailwater elevation, or 1-foot above the crown, whichever is higher. For pipes lar- ger than 18 inches in diameter, the outlet protection lining of the channel shall be four times the diameter of the outlet pipe. • Standard wingwalls, tapered outlets, and paved channels should also be considered when appropriate for permanent culvert outlet protection (WSDOT, 2015). BMP C122: Nets and Blankets or BMP C202: Riprap Channel Lining provide suitable options for lining materials. . With low flows, BMP C201: Grass -Lined Channels can be an effective alternative for lining material. . The following guidelines shall be used for outlet protection with riprap: • If the discharge velocity at the outlet is less than 5 fps, use 2-inch to 8-inch riprap. Min- imum thickness is 1-foot. • For 5 to 10 fps discharge velocity at the outlet, use 24-inch to 48-inch riprap. Minimum 2019 Stormwater Management Manual for Western Washington Volume ll - Chapter 3 - Page 355