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<br />" <br /> <br />" <br /> <br />. <br /> <br />. <br /> <br />Dr. John Liou, FEMA <br />October 20, 1981 <br />Page 2 <br /> <br />CAMP DRESSER & McKEE INC, <br /> <br />plotting the 10-, SO- and 100-year rainfall on a log-probability <br />graph and extrapolating to obtain the SOD-year rainfall as advised <br />by the Soil Conservation Service. <br /> <br /> <br />r~esa Creek <br /> <br />All basin characteristics were obtained from the 1976 "Mesa Basin <br />Drainage Study," by Parker and Associates. Curve nwobers for each <br />sub-basin were al so obtained from thi s study and were co,l1bined at <br />each hydrologic point to calculate the 10-, 50-, 100-, and 500- <br />year discharges using the SCS method. <br /> <br />Peterson Fi el d <br /> <br />A review of the Army Corps of Engineers (COE) hydrologic analysis <br />for Peterson Field was performed by COM. This analysis is summar- <br />ized in the 1976 CDE Report on Hydrologic Investigations for Flood <br />Insurance Studies in El Paso County and Colorado Springs, <br />Colorado. All of the hydrologic parameters used by the COE for <br />calculating peak flow rates were checked and found to be accur- <br />'atelyestimated. <br /> <br />Rockrimmon Basin <br /> <br />All basin characteristics were obtained from the March, 1976, <br />"Rockrimmon North Drainage Basin Hydrologic Study," by United <br />Western Engineering. Discharges for each recurrence interval were <br />calculated using the SCS method. <br /> <br />Sand Creek <br /> <br />A review of the SCS hydrologic analysis contdined in the 1973 <br />"Flood Hazard Analysis of Sand Creek, City of Colorado Springs and <br />E1 Paso County," was perfonoed by COM. It was determined that <br />only develop'llent in the lower part of the basin has occurred si nce <br />the time of the 1973 report. However, the increased development <br />will not affect the peak flows of the 1973 report due to the much <br />larger area of the basin above the developed areas. It was there- <br />fore determined to use the existing development condition dis- <br />charges for the 10-, 50-, 100-, and SOD-year frequencies as pre- <br />sented in the 1973 report. <br /> <br />Spri ng Creek <br /> <br />No current studies were found to exist on Spring Creek in Colorado <br />Springs. COM therefore developed flows for the 10-, SO-, 100-, <br />and SOD-year recurrence intervals using the SCS method. Aerial <br />photographs, USGS quadrangle maps, SCS soils maps, and Colorado <br />