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<br />I <br />I <br />I <br />I <br />I <br />I <br />J <br />I <br />I <br />I <br />I <br />I <br />I <br />. <br />I <br />I <br />J <br />I <br />1 <br /> <br />For streets, a resistance coefficient of 0,020 was used, For storm sewers, ihe resistance coefficient was <br />determined according to the type of pipe, 0,016 for concrete and 0,035 for corrugated metal. For existing <br />channel sections', the resistance coefficient values were determined based on the criteria outlined in the <br />UDSWM Users Manual (Reference 3) and from site visits, The SWMM routing element parameters used for this <br />study are summarized in Appendix C, The SWMM routing elements are shown on Figure 111-5, A SWMM <br />schematic routing diagram is shown on Figures 111-6 through 111-11, Peak flows at key locations are shown in <br />Table 111-2. <br /> <br />The sub-watershed runoff hydrographs were combined and routed down to Cherry Creek, In addition to <br />the four drainageways (KC, FD, NP, and SP), 20 direct inflows into Cherry Creek were computed within the <br />study limits, However, the inflows were not combined and routed in Cherry Creek since the combined flows will <br />not represent the total flows in Cherry Creek, <br /> <br />A sample UDSWM-2000 input file is included in Appendix C, The sample input file is representative of <br />model configurations for all relevant return periods, The summary of UDSWM model outputs for the 10~, 50-, <br />and 1 OO-year future land use conditions along with the 1 OO-year existing land use conditions are included in <br />Appendix D, <br /> <br />The 500-year storm event was not formally hydrologically modeled, A regression analysis of peak flows <br />at several locations in the Denver Metropolitan area indicates thatthe 500-year flood event typically exceeds <br />the 1 OO-year flood event by a factor of 1,7 to 1,9, For this study a factor of 1,7 was used to obtain the 500-year <br />flood peak flow estimate, <br /> <br />Several publicly owned and maintained detention ponds were included in the hydrologic models, The <br />stage versus discharge relationships for the detention ponds were generated utilizing the design plans provided <br />by Douglas County and 2' topographic mapping and field survey information provided by UDFCD, The flow <br />attenuation effects of the detention ponds are reflected in the UDSWM-2000 output. The Detention Pond <br />Storage Discharge relationships are included in Appendix E. <br /> <br />III-2 <br />