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The regression equation for 25-yr peak flow for watersheds in Kansas is (USGS, 1987; 1993), . Q25 (cfs) = 4.43 (A) Y (h) 3.339 S0.310 ( SprO.l56 x = 0.864 (ArO.04 The standard error of this equation is 29%. This results in a 25-year peak flow of 5,930 cfs with a range of 4,210 to 7,650 cfs for Frenchman Creek at Holoyoke. (v) Regression Equation for Plains Region of Eastern Colorado The regression equation for plains region of eastern Colorado is as follows (USGS, 1993; CWCB,1976): QIOO (cfs) = 1770 (A)0.463 SO,086 The standard error of this equation is -24 to + 32 %. This gives a value ofQlOo (cfs) = 28,257 cfs with a range of 21,475 to 37,299 cfs, Regression equation for Q25 for watersheds in the plains region of eastern Colorado is not available, 4.0 CONCLUSIONS AND RECOMMENDATIONS Estimated peak flows of Frenchman Creek at Holoyoke using different model parameters and methods are shown in Table 8, The estimates of peak flows included in the previous study (US ACE, 1980) are "based on statistical analyses of the streamflow records of several drainage basins in the same geographical region as the North Fork Republican River basin", The number of years of data, range of drainage areas, and watershed characteristics for the streams included in these statistical analyses are not known. Extrapolation based on these estimates results in a 100-yr peak flow of 8,940 cfs at Holoyoke. Between the time of this study (July 1980) and the present (June 2001), higher peak flows may have occurred due to urbanization in the sub-watersheds and randomly occurring storm events some of which may have been more severe than those experienced prior to 1980, As shown in Figure 1, the estimated values shown in Table 7 almost exactly fit a lognormal distribution. Usually, the actual data would have some scatter above and below the fitted straight line. So, there must have been a standard error of estimate associated with these estimated values, These arguments suggest that the estimate of 8,940 cfs may not be sufficiently conservative for current conditions. The regression equations for southwest Nebraska (Region 2) result in a 100-yr peak flow ranging from about 1,039 to 11,943 cfs (with an average of 6,491 cfs) and a 25-yr peak flow ranging from 540 to 6,217 cfs (with an average of 3,379 cfs). These equations have a relatively high standard error of 60% to 84%, Therefore, the estimates based on these equations are deemed to have a relatively low accuracy. Draft Letter Report Independent Review of Hydrologic Analysis for Frenchman Creek Contract No. DACW41-00-D-0026-0001 Flood Plain Management Services Special Study Holyoke, Colorado June 18,200 I Page 12