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7-6a-A D III'IIIII'II"II'11 <br />I ate.12/11/2001 <br />lvadge Scraper Plorth Fit - Oitch <br />• In order to maximize coal recovery and to contain runoff from the proposed <br />disturbance areas, a contour ditch is required along the slope below the <br />anticipated mining disturbance. This ditch will drain any runoff through <br />culvert No. 49b and back into the U02 sedimentation pond's watershed (see <br />Exhibit 7-7). <br />For the design of this ditch and culvert, the Sedimot II Hydrology <br />Computer model was used to' predict the runoff from the watershed (see <br />Tables 1 and 2 for the batch input and output, respectively). <br />A 10-year, 24-hour precipitation event, Type II storm, was used in the <br />design, which is a conservative approach to a temporary ditch. Following <br />is a list of the main input factors which were derived during the <br />analysis: <br />Precipitation = 1.60 inches <br />Drainage Area = 48.1 acres <br />Weighed CN: <br />Area <br />Vegetation Cover llydrologic Soils Group CPl (Acres) CI; x Area <br />Mixed Brush (w/Aspen) B 48 5.05 242.40 <br />Disturbed Area C 91 43.66 3973.06 <br />48.11 4215.46 <br />Wt. CN = 4215.46 = 86.5; Use 87 <br />48.7 <br />Time of Concentration (tc): <br />• <br />02/13/87 <br />A-1 <br />