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<br />111-11 <br /> <br />, <br /> <br />The analysis of the existing runoff conditions for the 100 year storm, based <br />on a thunderstorm type rainfall pattern, resulted in a peak discharge value of <br />1470 cfs for a 90-minute duration storm with a maximum five-minute increment <br />of 0.72 inches. The excess precipitation was calculated to be 1.55 inches <br />or 67% of the total precipitation of 2.3 inches, which agrees reasonably well <br />with the May 1973 storm. <br />The conclusion of the comparison of the May 1973 storm to the results of <br />the present analysis is that the runoff model used in this study appears to <br />be a good representation of the runoff phenomenon if proper consideration of <br />the difference in types of storm and antecedent moisture content are made. <br />6. Special Considerations <br />The hydrology for portions of the Clear Creek basin where significant <br />areas of ponds exist, required a separate analysis. For the sub-basin to <br />be considered isolated or self-contained, the ponds were required to store the <br />100 year 24-hour total precipitation within a maximum water surface rise of <br />six inches. These rather severe constraints were imposed to account for the <br />uncertainties of pond operation and antecedent precipitation. Based on this <br />criteria, then sub-basins H-10, C-1 and C-2a are self-contained and do not <br />contribute to the design flows of the remainder of the basin. <br />An additional consideration imposed upon sub-basin H-10 was the overflow <br />volume from the flow splitting at the 0 & RGW Railroad and Tennyson Street. <br />The surface area of the ponds in basin H-10 available for storage of the over- <br />flow volume is 28 acres. The potential overflow volume for the 100 year future <br />development conditions storm is approximately 18 acre-feet. Therefore, an <br />additional one foot of available storage area in the ponds would be necessary <br /> <br />o. <br />