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9 • <br />chapter 4-Site-Specific industrial Storm Water BMPs <br />before sediment is removed. For short slopes, a dike or swale at the top of the slope reduces the <br />amount of runoff reaching the disturbed area. For longer slopes, several dikes or swales are placed <br />across the slope at intervals. This practice reduces the amount of runoff that accumulates on the <br />face of the slope and carries the runoff safely down the slope. In all cases, runoff is guided to a <br />sediment trapping area or a stabilized outfall before release. <br />What to Consider <br />0 <br />Temporary dikes and swales are used in areas of overland flow; if they remain in place longer than <br />15 days, they should be stabilized. Runoff channeled by a dike or swale should be directed to an <br />adequate sediment trapping area or stabilized outfall. Care should be taken to provide enough <br />slope for drainage but not too much slope to cause erosion due to high runoff flow speed. <br />Temporary interceptor dikes and swales may remain in place as long as 12 to 18 months (with <br />proper stabilization) or be rebuilt at the end of each day's activities. Dikes or swales should remain <br />in place until the area they were built to protect is permanently stabilized. Interceptor dikes and <br />swales can be permanent controls. However, permanent controls:. should be designed to handle <br />runoff after construction is complete; should be permanently stabilized; and should be inspected <br />and maintained on a regular basis. Temporary and permanent control measures should be <br />inspected once each week on a regular schedule and after every storm. Repairs necessary to the <br />dike and flow channel should be made promptly. <br />Advantages of Interceptor Dikes and Swales <br />• Are simple and effective for channeling runoff away from areas subject to erosion <br />• Can handle flows from large drainage areas <br />• Are inexpensive because they use materials and equipment normally found onsite <br />Disadvantages of Interceptor Dikes and Swales <br />• If constructed improperly, can cause erosion and sediment transport since flows are <br />concentrated <br />• May cause problems to vegetation growth if water flow is too fast <br />• Require additional maintenance, inspections, and repairs <br />4-7Z