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<br />flooding potentials based on conditions existing in the community at the <br />time of completion of this study, Maps and flood elevations will be <br />amended periodically to reflect future changes, <br /> <br />3,1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak discharge- <br />frequency relationships for each flooding source studied in detail <br />affecting the community, <br /> <br />Peak discharges for the 10- and; 100-year floods for Tributary M of <br />Niver Creek were developed using the Colorado Urban Hydrograph <br />Procedure (CUHP) (Reference 3) and U.S. Army COrps of Engineers <br />HEC-l (Reference 4) computer models, The watershed was subdivided <br />into six subbasins, For each s~bbasin, peak flow hydrographs were <br />developed using the CUHP model, Parameters for the hydrograph <br />development include rainfall data (Reference 5), soil type, land <br />use, basin area, and basin geom~try (References 6, 7, and 8). The <br />outflow hydrographs derived for; the subbasins were then used for <br />the HEC-l model, which has channel and storage routing capability <br />using the Modified Puls methods', <br /> <br />The result from the HEC-l analy~is shows that the upper pond near <br />Elm Circle attenuate the 100-year peak flow from 226 cfs to 200 <br />cfs, The flows vary from 200 efs upstream to 1,086 cfs at Pecos <br />Street, <br /> <br />Peak discharge-drainage area relationships for Tributary M of Niver <br />Creek are shown in Table 1, <br /> <br />3,2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />sources studied were carried o~t to provide estimates of the eleva- <br />tions of floods of the selecte~ recurrence intervals, <br /> <br />Cross sections for the backwater analyses for Tributary M of Niver <br />Creek were obtained from topographic maps, provided by the city, <br />at a scale of 1.1,200, with a contour interval of 2 feet (Refer- <br />ence 8), All bridges and culverts were field surveyed to obtain <br />elevation data and structural geometry, <br /> <br />Locations of selected cross seqtions used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1), <br /> <br />Roughness factors (Manning's .~.) used in the hydraulic computations <br />were chosen by engineering judgment and based on field observations <br />of the stream and flood plain areas, Roughness values for the <br />main channel ranged from 0,02 to 0,04, and overbank roughness values <br />ranged from 0,02 to 0,07, <br /> <br />6 <br />