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W.H. LIZER & ASSOCIATES <br /> Engineering Consulting and Land Surveying <br /> • 576 25 Road, Unit 18 <br /> Grand Junction,Colorado 81505 <br /> 241-1129 <br /> March 20, 1995 �I <br /> DRAINAGE REPORT <br /> FOR <br /> RAPID CREEK RIP-RAP_ QUARRY . <br /> LOCATED IN THE SW 1/4 SW 1/4 <br /> SECTION 35, T10S, R98W, 6th PM, <br /> MESA COUNTY, COLORADO <br /> GENERAL <br /> The Rapid Creek Rip-Rap Quarry is located in the SW 1/4 SW 1/4 of <br /> Section 35, T10S, R98W; 6th P.M. in Mesa County, Colorado. <br /> S-N7" 14 irlh <br /> The site drains form Zaet to West at approximately 6.8%. The method <br /> of mining will be excavation and removal of material from�t to1-1-Alk <br /> There will not be any hard surfaces implemented into the process, <br /> therefore this report will deal with historic runoff only and methods of <br /> erosion control . <br /> The site is vacant now but at one time may have been irrigated. <br /> METHOD OF ANALYSIS <br /> The Rational Method was used to determine the amount of storm runoff, <br /> using the formula, Q = CCfIA, since this is a very small area, <br /> where Q = runoff in cfs <br /> C = runoff coefficient <br /> i <br /> Cf = rainfall frequency factor = 1 for a 10-year storm <br /> I = rainfall intensity (in./hr. ) <br /> A = area in acres <br /> For historic runoff, a value of 0.37 was used for "C". <br /> I <br /> Ten-year and 100-year free,�:ency sto-ms were ^alculated. <br /> Values of "I" were determined from intensity duration curves for the <br /> Grand Junction Area (graph attached). <br /> Computations attached. <br /> I <br />