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• SEDIMENT POND N0. 004 <br />The design of Sediment Pond 004 was evaluated to answer the questions <br />and concerns raised by the Division in their preliminary adequacy <br />comments (5/29/86). The storage capacity and detention time of the <br />10-year, 24-hour storm event was calculated and the principal spillway <br />was modified to meet the requirements for sedimention pond (4.05.6). <br />The total drainage area of Pond 004 is 392.79 acres, see Exhibit "7-7", <br />Surface Hydrology Map, Drainage Area I. For design purposes, 65.08 <br />acres is considered to be undisturbed ground and 327.91 acres is <br />anticipated to have been disturbed and reclaimed during the life of Pond <br />U04. The weighted curve number was calculated to be 75 and the weighted <br />"k" factor was determined to be 0.27 (see Table 1 and 2). The curve <br />number and "k" factor for the individual soil types were taken from <br />Tables 7-6-1 and 7-6-2, respectively. <br />The unit hydrograph type that was selected to be used in the SEDIMOT II <br />computer model was for a disturbed drainage condition. <br />The time of concentration, tc, is defined as the time required for water <br />to flow from the hydraulically most remote point in the watershed to the <br />watershed outlet (pond). The runoff time of concentration was <br />calculated using the following equations. <br />tc = LO'8 S + 1 0.7 <br />1140 Y <br />where L = hydraulic length of watershed = 5333 ft. <br />Y = average watershed slope = 20.8% <br />S = maximum retention <br />s = 1000 - 10 = 1000 - 10 = 3.33 <br />then tc = (5333)0'8{3.33 + 1)0'7 = 0.515 hrs. <br />1140 (20.8) ' <br />The particle size-percent finer distribution of the sail types in the <br />Pond 004 watershed was determined from a soil sample taken from a <br />reclaimed area in April of 1986 and the input particle distribution is <br />as follows: <br />7-6c-2 Revised 8/27/86 <br />