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For Sutherland Creek, Williams Canyon, and Ruxton Creek, discharges were determined using the regression equations described in Manual For Estimatinii Flood Characteristics of Natural-Flow Streams in Colorado (Reference 21), The equations for the Plains Region were applied to the portion of each drainage area below an elevation of 9,000 feet. Above an elevation of 9,000 feet, the equations for the Mountain Region were applied, It was found that the Plains Region portion of each drainage yields much higher discharges than the Mountain Region portion, Consequently. the 10-. 50-. 100-. and 500-year flood discharges from the respective Plains Region equations were used, For Beckers Lane Tributary, discharges were determined using the methodology outlined in the Drail1l\l:e Criteria Manual for Colorado Springs and El Paso County (Reference 27), This manual requires the determination of 2- and 24-hour storms using the SCS method, The storm producing the most severe evem for a given recurrence imerval was selected, Final calculations were carried out using the USACE HEC-l hydrologic computer program (Reference 28), The flood discharges for the upper portions of Beckers Lane Tributary and Williams Canyon were interpolated from a drainage area-discharge curve developed from computed discharges for Williams Canyon and Sutherland Creek, The hydrologic analysis used for Crystal Creek and Dirty Woman Creek in the Town of Monument was obtained through the Colorado Urban Hydrograph Procedure. developed by the Urban Drainage and Flood Control District. This method is specified for ungaged drainage areas greater than 160 acres in the (preliminary) Storm Drainage Criteria Manual for the Town of Monument. Significant parameters used in the hydrologic calculations are rainfall values for the 10-, 50-, and lOO-year I-hour rainfalls. the SCS soil type, and the percent impervious area, The 500-year peak flow for each basin was derived by an extrapolation of a plotting of the 10-, 50-, and lOO-year peak flows for each creek on log probability paper. Hydrology for Crystal Creek was consistent with a hydrologic analysis of the lOO-year peak flow performed by Tri-Consultants for Casey's subdivision located along Crystal Creek between Interstate Highway 25 and Beacon Light Road, Tri-Consultants used the SCS method to determine the lOO-year peak flow, Peak discharge-drainage area relationships for streams studied by detailed methods are shown in Table 3. 3,2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals, Water-surface elevations were developed with the USACE HEC-2 water-surface profile computer program (Reference 29), Flood profiles were drawn showing computed water- surface elevations for the 10-,50-, 100-, and 500-year recurrence intervals, Hydraulic analyses were not carried out to provide water-surface elevations for the 10- and 50-year recurrence intervals for Dry Creek and its tributaries, Cross sections for the backwater analyses of the streams studied in detail were obtained from aerial topographic mapping compiled between 1972 and 1983 (References 30 through 36), 22