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a 10-year, 24-hour precipitation event or less. <br /> Assuming no flow through the principal spillway (a very unlikely occurrence), Pond 007 is <br /> designed to safely pass the runoff from the 25-year and 100-year, 24-hour precipitation <br /> event through the emergency spillway without overtopping the dam. The top of the <br /> embankment is designed to be at elevation 5657.0. <br /> POND No. 007 - EAST DITCH <br /> In order to maximize coal recovery and to contain runoff from the proposed disturbance <br /> areas, a contour ditch is required along the disturbance areas east of Pond No. 007, <br /> flowing into Pond No. 007 (see Exhibit 13-5). <br /> For the design of this ditch, the SEDIMOT II model was used to predict runoff from the <br /> watershed (see Addendum D for the batch input and output). A 10-year, 24-hour <br /> precipitation event was used in the design, which is a conservative approach to a <br /> temporary ditch. <br /> Following is a list of the main input factors which were derived in a similar manner to <br /> the factors for Pond No. 007: <br /> Input East Ditch <br /> Precipitation 1.60 in. <br /> Drainage Area 304.7 ac. <br /> CN 85 <br /> L 7155 ft. <br /> y 4.65 % <br /> tc 1.08 hour <br /> Output <br /> Q (cfs) 67.1 cfs <br /> Based on this discharge, the Dodson and Associates, Inc.'s computer software was used to <br /> design the ditch based on Manning's equation calculations. <br /> Two ditch designs are proposed for the east ditch. Based on the critical slope <br /> 12 <br />