Laserfiche WebLink
1 <br />. May be used as a permanent diversion channel to carry the runoff. <br />Sub -basin tributary area should be one acre or less. <br />. Design capacity for the peak volumetric flow rate calculated using a 10-minute time <br />step from a 10-year, 24-hour storm, assuming a Type 1 A rainfall distribution, for <br />temporary facilities. Alternatively, use 1.6 times the 10-year, 1-hour flow indicated <br />by an approved continuous runoff model. For facilities that will also serve on a per- <br />manent basis, consult the local government's drainage requirements. <br />Interceptor dikes shall meet the following criteria: <br />. Top Width: 2 feet minimum. <br />Height: 1.5 feet minimum on berm. <br />. Side Slope: 2H :1 V or flatter. <br />• Grade: Depends on topography, however, dike system minimum is 0.5%, and max- <br />imum is 1 %. <br />Compaction: Minimum of 90 percent ASTM D698 standard proctor. <br />. Horizontal Spacing of Interceptor Dikes: <br />Average Slope <br />Slope Percent <br />Flowpath Length <br />20H:1 V or less <br />3-5% <br />300 feet <br />(10 to 20)H:lV <br />5-10% <br />200 feet <br />(4 to 10)H :1 V <br />10-25% <br />100 feet <br />(2 to 4)H :1 V <br />25-50% <br />50 feet <br />Stabilization: depends on velocity and reach <br />• Slopes <5%: Seed and mulch applied within 5 days of dike construction (see BMP <br />C121: Mulching (p.284)). <br />• Slopes 5 - 40%: Dependent on runoff velocities and dike materials. Stabilization <br />should be done immediately using either sod or riprap or other measures to avoid <br />erosion. <br />. 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 neces- <br />sary. Sediment -laden runoff must be released through a sediment trapping facility <br />. Minimize construction traffic over temporary dikes. Use temporary cross culverts for <br />channel crossing. <br />Interceptor swales shall meet the following criteria: <br />Bottom Width: 2 feet minimum; the cross-section bottom shall be level. <br />. Depth: 1-foot minimum. <br />2014 Stormwater Management Manual for Western Washington <br />I <br />1 <br />1 <br />1 <br />1 <br />�1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />d <br />1 <br />1 <br />1 <br />1 <br />Volume 11 - Chapter 4 - Page 332 <br />1 <br />