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Chapter 4-Site-SpeciFc /ndustrialstorm water BMPs <br />in. terceptor Dikes and Svvales <br />What Are They <br />Interceptor dikes (ridges of compacted soil) and swales (excavated depressions) are used to keep <br />upslope runoff from crossing areas where therel lied outfalf (point of discharge) )see section on Outlet <br />and speed of flow and then guide it to a stab <br />Protection) or sediment trapping area (see sections on Level Spreaders, Vegetated Filter Strips, <br />Sediment Traps, and Temporary Sediment Basins). Interceptor dikes and swales divert runoff using <br />a combination of earth dike and vegetated swale. Runoff is channeled away from locations where <br />there is a high risk of erosion by placing a diversion dike or swale at the top of a sloping disturbed <br />flows <br />area. Dikes and e collect <br />dik s and swales can be either temporary concentrated flows <br />ent1 storm <br />that are combined). Int Intercptor <br />water control structures. <br /> <br />TRAPEZOIDAL CROSS-SECTION <br /> <br />PARABOLIC CROSS-SECTION <br />FIGURE 4.17 TYPICAL INTERCEPTOR DIKES AND SWALES <br />(Modified from State of Maryland, 1983) <br />F nd Whe?to seThem <br />7h7en:a <br />Interceptor dikes and swales are generally built around the perimeter of a construction site before <br />any major soil disturbing activity takes place. Temporary dikes or swales may also be used to <br />protect existing buildings; areas, such as stockpiles; or other small areas that have not yet been <br />fully stabilized. When constructed along the upslope perimeter of a disturbed or high-risk area <br />(though not necessarily all the way around it), dikes or swales prevent runoff from uphill areas from <br />crossing the unprotected slope. Temporary dikes or swales constructed on the down slope side of <br />the disturbed or high-risk area will prevent runoff that contains sediment from leaving the site <br /> <br />C? <br />4-70