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<br />3.3 ESTIMATES OF PEAK FLOWS BASED ON REGRESSION EQUATIONS <br /> <br />(i) Regression Equation for Republican River Basin <br /> <br />Frenchman Creek is a tributary of the Republican River, The regression equation for the <br />Republican River basin (CWCB, 1999) gives, <br /> <br />QIOO (cfs) = 289,1 (A)0.667 = 289.1 x (247.5 )0,667 = 11,417 cfs <br /> <br />in which Q]OO (cfs) = 100-yr peak flow in cubic feet per second; A = drainage area (sq miles). <br />The standard error of this equation is 36%. So, the 100-yr peak flow may range from about <br />7,307 to 15,527 cfs. Regression equation for Q25 for the Republican River basin is not available, <br /> <br />(ii) Regression Equations for Region 2, Nebraska <br /> <br />The regression equations for Region 2, Nebraska, which is adjacent to the watershed of <br />Frenchman Creek in Colorado, are as follows (USGS, 1976; 1993): <br /> <br />QIOO (cfs) = 0,55 (A)O,872 sl.063 (124,50 _3)3,731 <br />Q25 (cfs) = 0,50 (A)0.854 SO.928 (h4,50 _3)3.501 , <br /> <br />in which A = drainage area (sq miles) = 247.5 sq miles; s = average basin slope (ft/mile) = 12.7 <br />ft/mile; and h4,50 = 50-yr 24-hr precipitation (inches) = 4.65 inches (USGS, 1993: USDOC, <br />1961), This gives QIOo (cfs) = 6,491 cfs and Q25 (cfs) = 3,379 cfs. The standard error of these <br />equations is 60% to 84%. Thus, the 100-yr and 25-yr peak flows for Frenchman Creek may <br />range from about 1,039 to 11,943 cfs and 540 to 6,217 cfs, respectively. <br /> <br />(iii) Regression Equations for Watersheds in Kansas <br /> <br />A single set of regression equations has been developed for watersheds in the entire state of <br />Kansas. The regression equation for 100-yr peak flow is as follows (USGS, 1987; 1993): <br /> <br />QIOO (cfs) = 16.0 (A)x (h) 2.651 SO.295 (SpyO.156 <br />X = 0.873 (AyO.04 <br /> <br />in which A = D,A. = 247.5 sq miles; h = 2-yr 24-hr precipitation = 2,2 inches; s = average basin <br />slope = 12.7 ft/mile; and Sp = average soil permeability = 1.3 inlhr, The standard error of this <br />equation is 36%, This results in a 100-year peak flow of 12,471 cfs with a range of 7,981 to <br />16,961 cfs for Frenchman Creek at Holoyoke, <br /> <br />Draft Letter Report <br />Independent Review of Hydrologic Analysis for Frenchman Creek <br />Contract No. D A CW 41-00- D-0026-000 1 <br /> <br />Flood Plain Management Services Special Study <br />Holyoke. Colorado <br />June 18,2001 <br /> <br />Page 11 <br />