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1 <br />1 <br />• Side Slope: 2H:1 V or flatter. <br />• Grade: Maximum 5 percent, with positive drainage to a suitable outlet (such as a <br />sediment pond). <br />Stabilization: Seed as per BMP C120: Temporary and Permanent Seeding (p.278), <br />or BMP C202: Channel Lining (p.338), 12 inches thick riprap pressed into the bank <br />and extending at least 8 inches vertical from the bottom. <br />Inspect diversion dikes and interceptor swales once a week and after every rainfall. <br />Immediately remove sediment from the flow area. <br />Damage caused by construction traffic or other activity must be repaired before the end <br />of each working day. <br />Check outlets and make timely repairs as needed to avoid gully formation. When the <br />area below the temporary diversion dike is permanently stabilized, remove the dike and <br />fill and stabilize the channel to blend with the natural surface. <br />BMP C201: Grass -Lined Channels <br />Purpose <br />To provide a channel with a vegetative lining for conveyance of runoff. See Figure II- <br />4.2.1 Typical Grass -Lined Channels (p.336) for typical grass -lined channels. <br />Conditions of Use <br />This practice applies to construction sites where concentrated runoff needs to be con- <br />tained to prevent erosion or flooding. <br />. When a vegetative lining can provide sufficient stability for the channel cross sec- <br />tion and at lower velocities of water (normally dependent on grade). This means <br />that the channel slopes are generally less than 5 percent and space is available for <br />a relatively large cross section. <br />. Typical uses include roadside ditches, channels at property boundaries, outlets for <br />diversions, and other channels and drainage ditches in low areas. <br />• Channels that will be vegetated should be installed before major earthwork and <br />hydroseeded with a bonded fiber matrix (BFM). The vegetation should be well <br />established (i.e., 75 percent cover) before water is allowed to flow in the ditch. With <br />channels that will have high flows, erosion control blankets should be installed <br />over the hydroseed. If vegetation cannot be established from seed before water is <br />allowed in the ditch, sod should be installed in the bottom of the ditch in lieu of <br />hydromulch and blankets. <br />2414 Stormwater Management Manual for Western Washington <br />Volume 11 - Chapter 4 - Page 333 <br />