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CDM . .CAMP DRESSER & McKEE INC, envirOflmental ftfIgineers, scientists, planners. & management consultants Write,'s Tower, Suite 1100 1660 South Albion Street Denver, Cololado 80222 303758.4351 January 26, 1981 Dear John: ;1J1~r- '"J2f!1LqF"'r--( }l"\,~!\_::,, i " . JAlI 6..:,. Iv 2 8 1981 (" ,; , Co., '~;)', ",)~'R\I.., r/~N i~,qR~ Dr. John Liou Federal Emergency Management Agency Denver Federal Center, Building 710 Lakewood, CO 80225 CDM has completed a review of the hydrology for Fountain Creek in the City of Colorado Springs and El Paso County, Colorado, which was per- formed by the Army Corp of Engineers in various existing studies. In response to your request that COM summarize the existing hydrologic information, we have prepared this letter which can supplement the Hydrologic Review for the Flood Insurance Study of Colorado Springs and El Paso County, prepared by COM in December, 1980. The hydrologic results which are contained in the Flood Plain Information Reports of Fountain Creek below Monument Creek (COE 1974) and Fountain Creek in Manitou Springs (COE, 1974), as well as the Manitou Springs Flood Insurance Study currently under review by FEMA (PRC, 1980), have all been obtained by means of a regional stream gage analysis. The two COE reports have both been designated by the Colorado Water Conservation Board and have been used by the respective communities for flood plain regulation. The hydrologic analysis con- tained in the current Fountain Creek FIS for Manitou Springs has been updated by the study contractor (i.e., PRC), by adding additional years of stream gage data to the existing COE data base. This analy- sis showed no changes in the peak flow rates from the original 1974 CaE study in Manitou Springs and therefore the hydrologic analysis presented by the COE ,ms used in the current FIS of Manitou Springs (accepted by FEMA in a letter to PRC dated March 1979). The peak flow rates for the 10-, 50-, 100- and 500-year frequency floods for specific locations on Fountain Creek from the El Paso/Pueblo county lines to the Colorado Springs/Manitou Springs city limits, are summarized in Table 1. These flow rates correspond to the COE's Lower Fountain Creek Study (1974) and PRC's Manitou Springs FIS (1980). The flow rates sho,m in Table 1 are recommended for use by COM in the El Paso County and Colorado Springs FIS. Since the hydrologic review conducted by PRC in the }ffinitou Springs FIS supplemented the 1974 CaE hydrologic analysis with gage data through 1977, and showed no appre- ciable changes in the peak flow rates, it is not believed that an additional two years of stream data (i.e., 1978 and 1979) will show any changes from the peak flow rates either. Therefore the peak flow rates obtained in the previous studies and summarized in Table 1 are suggested for use in the hydraulic review and analysis of Fountain Creek below Manitou Springs.