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<br />~~t~ ~ <br /> <br />'I <br />I, / <br /> <br />then applied to the May 30-31, 1935 storm and results compared against USGS discharge <br />measurements at Kiowa Ck nr Elbert. <br /> <br />Basin parameters were based on previous studies of small basins having both rainfall and <br />discharge data within the Kiowa Ck Basin, Because only three sub-basins were considered for <br />this study, rainfall was calculated via area-weighted average over each basin, Precipitation <br />distribution was based on data and information provided by Mr, John Henz for storm cells A-2 <br />and A-3, However, due to further investigation of both storm cells, and discussion between Mr, <br />Henz, Mr, Don Jensen, and the author, Mr. Henz recommended that the mass curve for storm <br />cell A-2 be applied throughout the basin. <br /> <br />RESULTS <br /> <br />June 17, 1965 Storm <br /> <br />Table 1 indicates favorable comparison between HEC-I modeling results and USGS discharge <br />data for West Kiowa Ck at Elbert and Kiowa Ck at Kiowa,. However, HEC-l results are <br />somewhat low for Kiowa Ck at Elbert; that may be due to inaccurate reported rainfall over that <br />basin. Also, a precipitation distribution for the storm was not available; in lieu of that, an SCS <br />Standard Emergency Spillway (6-hr) distribution was applied. That was chosen because it is <br />representative of a fairly short duration, high-intensity storm. <br /> <br />Based on the results, it was felt that the HEC-l model for Upper Kiowa Ck basin can reasonably <br />simulate its hydrology for the purpose of this evaluation, and thus could be applied to other <br />storms (e.g., the May 30-31, 1935 storm), <br /> <br />May 30-31,1935 Storm <br /> <br />Table 1 indicates a very large discrepancy between HEC-l results and USGS discharge, data for <br />Kiowa Ck nr Elbert, The difference, 43,500 vs 130,000 cfs for USGS measured data and HEC-I <br />modeled results, respectively, is well beyond the range of hydrologic uncertainty and errors due <br />to RF/RO modeling. <br /> <br />For the purpose of illustrating the difference in rainfall (area-weighted average) needed to <br />simulate the measured discharge at Kiowa Ck nr Elbert, the area-weighted rainfall was <br />proportionally reduced for each sub-basin above Elbert via trial and error and input into HEC-l <br />until the measured value of 43,500 cfs was obtained for Kiowa Ck nr Elbert. That resulted in <br />area-weighted average values of5.8 in and 7,7 in (originally, 12.8 in and 18 in, respectively), for <br />Kiowa Ck at Elbert, and West Kiowa Ck, respectively - a reduction of about 42.5 percent of the <br />initial value. <br /> <br />It is not known if the rainfall reduction discussed in the above paragraph should be applied to <br />rainfall amount. spatial distribution. or a combination of both. Because ofthe linear relationship <br />of the computed area-weighted precipitation, a proportional 42.5 percent isohyetal reduction in <br />storm area (i,e., the area between each isohyetal would be reduced by 42.5 percent) would also <br />produce the same results. <br />