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SA Schumm. Ph.D <br />M.D. Harvey Ph.D. <br />CC WNSOn, PE. Ph.D. <br />• <br />419 Canyon, Surte Z25 <br />Fort Collins. Coloratlo 80521 U.SA <br />I-303-482-8201 <br />Colorado Yampa Coal Co. <br />29588 Routt County Road X27 <br />Oak Creek, Colorado 80467 <br />Attention: Mr. Rick Mills <br />July 27, 1988 <br />I A 111 <br />Mr ii <br />Re: Eckman Park 51 West Permit Drawings <br />(WET Project 47-702-88) <br />• <br />Enclosed are 5 sets of preliminary permit drawings for riprap <br />channel improvements for the Eckman Park 51 West area. These drawings <br />bear the seal of a Colorado Professional Engineer, and were prepared <br />under his supervision. <br />Dear Rick: <br />Hydrologic information was developed for an evaluation of the <br />proposed channel improvement at the Eckman Park 51 West Tract and is <br />reproduced here as follows: <br />Drainage Area: 333.5 acres <br />10-yr, 24-hr Rainfall: 1.8 inches <br />Peak Rate of Discharge: 230 cfs/inch of runoff <br />Runoff: 0.52 inch/inch of rainfall <br />Basin Slope: 14% <br />Slope Adj. Factor: 0.96 <br />Q10~ 115 cfs <br /> <br />where Q10 indicates the 10-year, 24-hour peak flowrate. Hydrology was <br />evaluated using criteria in the 1984 SCS Publication, Peak Flows in <br />Colorado. Runoff rates were evaluated assuming an antecedent soil <br />moisture condition classified as AMC II with a curve number of 82. <br />An in-house computerized procedure for sizing riprap on steep slopes <br />was utilized to evaluate rock size. The methodology employed utilizes a <br />