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, CDM · . CAMP DRESSER & McKEE INC. " environmental engineers. scientists, planners. & management COflsulrants Writer's Tower, Suite 1100 1660 South Albion Streel Denver, Colorado 80222 303 758.4351 March 17, 1981 !3'/ 1-11- )jj~' 1l'lJ.'f';;;,~ , "f';~ ;' ,~. Jr:-,r-,,,, c.: 1.14t;> ";!>/"'o.. , ., '",J <; J /f! Co'~ 19~'; 'A.S c V{, .v, C, " , I?v..q riO_ ' IV ' CDM has completed the review of the Army Corp of Engineers SO,,! hydro:ogic analyses for Kettle, Jimmy Camp and Cottonwood cree~ I?Q in EI Paso County and Colorado Springs. The hydrologic analyses reviewed for Kettle and Cottonwood creeks included th COE 1976 Report on Hydrologic Investigations in Colorado Springs and EI Paso County, the 1976 COE Floodplain Information Report for Cottonwood Creek and the 1979 Cottonwood Creek drainage study by Lincoln-Devore, Inc. The analyses reviewed for Jimmy Camp Creek are contained in the 1973 Flood Plain Information Report for Fountain and Jim~y Camp Creeks by the COE, the 1976 COE Report on HYGrologic Investigations, and the 1975 SCS Flood Hazard Analysis for Cottonwood Creek. ' Dr. John Li ou FEMA Denver Federal Center, Lakewood, CO 80225 Bldg. 710 Dear John: The 1976 COE hydrologic analysis for Kettle Creek used a unit hydrograph procedure and 1M-I to predict peak flows for the 10-, 50-, 100- and 500-year storm events. CDM has checked al I of the hydrologic parameters calculated by the COE and have found them to be accurately estimated. CDM recommends that the hydrologic results in the 1976 COE work on Kettle Creek at Colorado Highway 83 be util ized in the present Flood Insurance Study. An area reduction method will be used by COM to estimate the peak flow rates at other locations within the Kettle Creek basin. The suggested flow rates for Kettle Creek are presented in Table 1. CDM has reviewed the existing hydrologic information for Jimmy Camp Creek and have found that a small discrepency occurs in the peak lOa-year flow rates predicted between the 1973 and 1976 CaE stud'es. Similar methodologies were used (synthetic unit hydrograph procedures), however the 1976 work uti I ized 1M-I to check the unit hydrograph results. We feel that the use of 1M-I is the cause of the difference in peak flow rates at the Fountain and Jimmy Camp creeks confluence. The results of the 1973 COE FPIR and the 1975 SCS FHA for Jimmy Camp Creek compare favorably for all frequencies, indicating the similarity of the procedures used in each of these studies. Both the 1973 COE and the 1975 SCS studies have been designated by the Colorado Water Conservation Board and are currently being used by EI Paso County for floodplain regulation purposes. CDM recommends that the hydrologic results as contained in the 1973 COE Flood Plain