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. . . I: . . . . . . . . . . . . . . . . '. . I. . . . I: . . i. . . . . . I. . . . . . . . . . . . . I. . .. . . Table 4. USGS Station ID 09034500 Peak 100- ear Dischar e for Selected USGS Ga in Station Name Colorado River at Hot SuI hur S Stations 100-year Discharge (cfs 11,520 There are several reservoirs on the Colorado River which provide some incidental flood control. Because it is likely that spillway facilities have been designed to evacuate flood flows in excess of the IOO-year discharge, it has been assumed that reservoir will not affect downstream IOO-year flood discharge. In actuality, there will be some flood flow attenuation due to surcharge capacity in the reservoir and travel times from the reservoir inflow points to the spillway. Regardless, the gage records analyzed above implicitly consider reservoir storage in a general matter. Additional analysis of the reservoirs and basin would be needed to more accurately estimate peak discharges. Communities should regulate the approximate floodplains on a case-by-case basis. FEMA requires that a detailed floodplain analysis must be performed by a professional engineer and submitted by the developer or development proponent for development projects involving more 5 acres or more than 50 units (whichever is more restrictive), Hydraulic Analysis Hydraulic methods used for the approximate floodplain delineations shown on the Town of Hot Sulphur Springs FHBM panels are not available or have not been documented by FEMA. For future studies, an approximate IOO-year flood elevation at a particular location on the river may be obtained by using the 100-year peak flow value (as provided in this report) in conjunction with an acceptable hydraulic analysis. Hydraulic analyses for determining I DO-year water surface elevations for approximate floodplains may be performed using FEMA's Quick-2 computer program, the Corps of Engineers' HEC-2 computer program, Flowmaster, or other acceptable hydraulic methods. Channel and floodplain cross-sections may be obtained from detailed topographic mapping or from field surveys, For Heimbaugh Creek, a field visit was made to the Town of Hot Sulphur Springs and the basic geometry of the channel was approximated. Combined with the flow found using the regression equation (COl.-I), enough information was gathered to obtain a 100 year depth and approximate floodplain using normal depth calculations. The map and the normal depth worksheets can be found after Figure 2 in the back of this report. Floodplain Mappinl!: The existing FHBM for the Town of Hot Sulphur Springs depicts areas subject to 100-year flooding based on approximate technical methods. The map does not show flood profiles. base flood elevations, or sufficient detail in order for county and municipal officials. engineers, developers. and land owners to make floodplain determinations with any certainty. The Colorado Water Conservation Board can be contacted to request technical assistance for approximate floodplain analyses as needed. 7