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The 'tr;anainen and Warren method of detention facility design is the same method <br /> used by King Ccunty. This method can be used for tributary areas up to 30 arres. <br /> Where tributary areas are greater than 30 acres, the Soil Conservation Service method <br /> must be used. Also, in general, on-site detention will not be required in the lower <br /> one-third of any drainage ba:,in. A step by step description of the Y 6c W method <br /> fol!ows: <br /> Step 1. Runoff Coefficient <br /> The runoff coefficient, "c", represenis the fe'action of rainfall that contributes � <br /> to runoff during a rainstorm. The more intensely an area is developed, <br /> the higher its c will be. Table 1 lists several c factors for varying ground <br /> cover conditions; it can be used as a guide for selecting your runoff coefficient. <br /> Runoff ccefficients oftentimes will ha•.c to be "area weighted". For examp➢e, <br /> if a site haz 1 acre of paved parking and rooftops and 1 acre of landscaping, <br /> the area weighted c would be: 1 (0.9) + I (0.21., In the rest of the discussion, <br /> 2 _. <br /> Cexist and Cdev will refer to ?he runoff coet:icients beiore and after <br /> development, respcctively. <br /> l <br /> � <br /> {' <br />