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CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br />11 <br />o Slopes 5 to 40 percent: Dependent on runoff velocities and dike materials. <br />Stabilization should be done immediately using either sod or riprap or other <br />measures to avoid erosion. <br />h. The upslope side of the dike shall provide positive drainage to the dike outlet. No <br />erosion shall occur at the outlet. Provide energy dissipation measures as necessary. <br />Sediment -laden runoff must be released through a sediment trapping facility. <br />i. Minimize construction traffic over temporary dikes. Use temporary cross culverts for <br />channel crossing. <br />9. Interceptor swales shall meet the following criteria: <br />a. Bottom Width = 2 feet minimum; the bottom shall be level <br />b. Depth = 1-foot minimum <br />c. Side Slope = 2:1 or flatter <br />d. Grade = Maximum 5 percent, with positive drainage to a suitable outlet (such as a <br />sediment pond) <br />e. Stabilization = Seed as per BMP C120, Temporary and Permanent Seeding, or BMP <br />C202, Channel Lining, 12 inches thick of riprap pressed into the bank and extending at <br />least 8 inches vertical from the bottom. <br />10. Inspect diversion dikes and interceptor swales once a week and after every rainfall. Immediately <br />remove sediment from the flow area. <br />11. Damage caused by construction traffic or other activity must be repaired before the end of each <br />working day. <br />12. Check outlets and make timely repairs as needed to avoid gully formation. When the area below <br />the temporary diversion dike is permanently stabilized, remove the dike and fill and stabilize the <br />channel to blend with the natural surface. <br />3.3.2 BMP C201: Grass -Lined Channels <br />Purpose <br />Purpose is to provide a channel with a vegetative lining for conveyance of runoff. <br />Conditions of Use <br />This practice applies to construction sites where concentrated runoff needs to be contained to prevent <br />erosion or flooding. <br />• When a vegetative lining can provide sufficient stability for the channel cross-section and at <br />lower velocities of water (normally dependent on grade). This means that the channel slopes are <br />generally less than 5 percent and space is available for a relatively large cross-section. <br />• Typical uses include roadside ditches, channels at property boundaries, outlets for diversions, and <br />other channels and drainage ditches in low areas. <br />Channels that will be vegetated should be installed before major earthwork and hydroseeded with <br />a BFM. The vegetation should be well established (i.e., 75 percent cover) before water is allowed <br />to flow in the ditch. With channels that will have high flows, erosion control blankets should be <br />installed 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 hydromulch and <br />blankets. <br />Volume 11 — Construction Stormwater Pollution Prevention <br />3-37 <br />