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3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge- frequency relationships for each flooding source studied in detail affecting the community. The peak flow figures for the four different frequencies used in the hydraulic analysis of this study were obtained from a regional log-Pearson Type III analysis. The 1957 peak flow for the SOuth Arkansas River was obtained from a set of correlations that resulted in a relationship obtained from the period of common records between the South Arkansas River near Salida and the Arkansas River at Salida. Except for a water-stage recorder at Marshall Pass, which records transmountain diversio.,s via the Larkspur Ditch, there are no active streamflow gaging stations in any of the study area drainage basins. The historical streamflow records show that two stations have recorded flows in the study area. The first station, located on the South Arkansas River approximately 0.25 mile upstream from its confluence with Poncha Creek, recorded flows during the 1911-1917 and 1971- 1973 periods. The second station, located on Poncha Creek approxi- mately 0.25 mile upstream from its mouth, recorded flows during the 1912-1917 period (Reference 1). peak discharge-drainage area relationships for Poncha Springs are shown in Table 1. 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the eleva- tions of floods of the selected recurrence intervals. Digitized cross secticn information was provided by the Colorado Water Conservation Board in cooperation with Chaffee County. It was necessary to adjust the digitized cross sections to truly reflect the channel invert elevations. The minimum elevation given for the digitized cross sections is that of the water-surface elevation in the stream channel at the time the aerial photography was taken (November 4, 1975). The flows in the study reaches on November 4, 1975, were obtained from the streamflow records for the SOuth Arkansas River near the Salida gaging station; and the ditch diversions for the Harrington, Murry, and Rosedale Ditches. Next, the average depth of flow at each cross section was computed based on the con- structed streamflow for November 4, 1975. The computed values ranged from 0.1 to 0.6 feet with approximately 72 percent of the cross sections having an average value of 0.2 to 0.3 feet. This depth was subtracted from the minimum channel elevation given on the digitized cross sections to obtain the channel invert eleva- tions that were incorporated into the digitized cross section infor- 7