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<br />-. <br /> <br />MEMORANDUM <br /> <br />COLORADO WATER CONSERVATION BOARD <br />DARIES C LILE <br />DIRECTOR <br /> <br />DATE: <br /> <br />April 18, 1996 <br /> <br />TO: <br /> <br />CSM Project Team Two <br /> <br />FROM: <br /> <br />Tom Browning - CWCB <br /> <br />RE: <br /> <br />Walsenburg Hydrology Study <br /> <br />In response to a conversation I had with Kevin, I am providing some information that should be <br />helpful for your study. Below are some regional regression equations that can be used for <br />determining peak flow values for your study. Try using these equations in addition to using the <br />Rational Method, and compare the results. <br /> <br />USGS Regression Equations: <br /> <br />QIO = 500(A)89 <br />QIOO = l550(Alo7 <br /> <br />Where: <br />QIO = lO-year peak flow (cfs) <br />QIOO = IOO-year peak flow (cfs) <br />A = Drainage Area (square miles) <br /> <br />CWCB Regression Equation: <br /> <br />QIOO = 3959.2(A) 366 <br /> <br />Where: <br />QIOO = lOG-year peak flow (cfs) <br />A = Drainage Area (square miles) <br /> <br />I am providing you with Time-Intensity-Frequency curves that were developed for the Denver <br />area. These curves will be good enough for use with your study. For the Rational Method, use <br />the curves to estimate the rainfall intensity. Assume a time of concentration (te) of 15 minutes. <br />Then, using the time of concentration and the curves for the lO-year and IOO-year events, <br />estimate the rainfall intensities. Calculate the lO-year and IOO-year flows using the equation Q = <br />CiA. You'll probably find that the Rational Method gives you higher values than the regression <br />equations. Please call me if you have any questions. <br />