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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />. United States Forest Service <br />(USFS) <br /> <br />-Mountain soils <br /> <br />· United States Geological Survey <br />(USGS) <br /> <br />-Electronic topographic base map (partial) <br />-Stream gage data <br /> <br />UDSWMM MODEL <br /> <br />Drawings 1 through 11 are electronic drawings which have USGS topographic (40 <br />foot contour interval) map bases for the entire watershed (Drawings 1 through 3), <br />and City/County topographic (5 foot/2 foot contour interval) and landscape feature <br />maps (Drawings 4 through 11). The subbasins, streams, combining or splitting <br />nodes, and reservoir elements which make up the UDSWMM hydrology model are <br />all located on these maps, with appropriate delineation of their linkage and general <br />routes of flow. <br /> <br />The hydrology models for the 10-, 50-, 100- and 500-year events are presented in <br />appendices A 1 through A4 under the file names: sbc_10td.out (1 O-year). <br />sbc_ 50td.out (50-year), sbc_1td.out (1 OO-year). and sbc _ 500td.out (500-year). All <br />standard input and output data are presented in the files. Hydrographs are not <br />printed to save paper. For those interested, electronic input files can be provided, <br />and the user can obtain the desired hydrographs. Representative hydrographs are <br />presented in Section V. <br /> <br />SUMMARY FLOW RESULTS AND COMPARISON WITH PREVIOUS HYDROLOGY <br /> <br />Table 1-1 is a summary comparison between the previous Corps' hydrology model <br />and the figures used in the current effective floodplain maps. <br /> <br />The summary table begins at Gross Reservoir and proceeds downstream. Stream <br />or node element numbers, given in the table, can be identified on the drawings. <br /> <br />At Highway 93 the flood flows split along two or more roughly parallel locations <br />down the floodplain. Since there are multiple parallel flow paths across the lower <br />watershed in the new model, it is complicated to make exact comparisons with the <br />old modeling, as the time to peak flow is different as each flow route crosses at a <br />reference line, for example, Highway 36 or Baseline. The table gives for <br />representative reference lines the peak flow for each flow path and then the peak <br />sum flow across all paths at a given time. Determination of this peak sum flow <br />was done by examining each of the flow path hydrographs at a given time. These <br />peak sum flows in the last column can be compared to the previous hydrology. <br />Generally the new model gives results that are 37 to 66 percent greater than the <br />previous. <br /> <br />1-9 <br />