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i <br /> . Side Slope: 2H:1V or flatter. <br /> . Grade: Maximum 5 percent,with positive drainage to a suitable outlet (such as a <br /> sediment pond). 1 <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 I <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 I <br /> fill and stabilize the channel to blend with the natural surface. <br /> BMP C201: Grass-Lined Channels t <br /> Purpose <br /> To provide a channel with a vegetative liningforonvey conveyance of runoff. See Figure II- <br /> Y g <br /> 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- I <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. 1 <br /> . Typical uses include roadside ditches, channels at property boundaries, outlets for <br /> diversions, and other channels and drainage ditches in low areas. 1 <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 /> 2014 Stormwater Management Manual for Western Washington <br /> Volume II- Chapter 4 -Page 333 1 <br />