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CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br />r <br />r <br />u <br />Conditions of Use <br />Where the runoff from an exposed site or disturbed slope must be conveyed to an erosion control facility <br />which can safely contain the stormwater: <br />1. Locate upslope of a construction site to prevent runoff from entering disturbed area <br />2. When placed horizontally across a disturbed slope, it reduces the amount and velocity of runoff <br />flowing down the slope <br />3. Locate downslope to collect runoff from a disturbed area and direct it to a sediment basin. <br />Design and Installation Specifications <br />1. Dike and/or Swale and channel must be stabilized with temporary or permanent vegetation or <br />other channel protection during construction. <br />2. Channel requires a positive grade for drainage; steeper grades require channel protection and <br />check dams <br />3. Review construction for areas where overtopping may occur <br />4. Can be used at top of new fill before vegetation is established <br />5. May be used as a permanent diversion channel to carry the runoff <br />6. Subbasin tributary area should be 1 acre or less <br />7. Design capacity for the peak flow from a 10-year, 24-hour storm, assuming a Type lA rainfall <br />distribution, for temporary facilities. Alternatively, use 1.6 times the 10-year, 1-hour time step <br />flow indicated by an approved continuous runoff model. If a 15-minute (or less) time step is <br />used, no correction factor is required. <br />8. Interceptor dikes shall meet the following criteria: <br />a. Top Width = 2 feet minimum <br />b. Height = 1.5 feet minimum on berm <br />c. Side Slope = 2:1 or flatter <br />d. Grade = Depends on topography, however, dike system minimum is 0.5 percent, <br />maximum is 1 percent <br />e. Compaction = Minimum of 90 percent ASTM D698 standard proctor <br />f. Horizontal Spacing of Interceptor Dikes: <br />Average Slope <br />Slope % <br />Flowpath Length <br />201-1:1 V or less <br />3-5% <br />300 feet <br />(10 to 20)H:1V <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 />g. Stabilization depends on velocity and reach: <br />o Slopes less than 5 percent: Seed and mulch applied within 5 days of dike <br />construction (see BMP C121, Mulching). <br />Volume ll — Construction Stormwater Pollution Prevention <br />3-36 <br />