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<br />SLA used the Environmental Protection Agency SWMM (Reference 10) in <br />determining discharges for the original report. SLA assumed that <br />all irrigation ditches and canals would already be full from <br />upstream runoff and would not have the capacity to intercept <br />additional runoff. The NRCS found that one exception to this <br />assumption is Windsor Ditch, which crosses the basin upstream of the <br />Town of Wellington. The NRCS determined that 200 cubic feet per <br />second would be diverted from Coal Creek by Windsor Ditch. The 10~, <br />50-, 100-, and 500~year~f1ood peak discharges are shown in Table 1, <br />"summary of Discharges." <br /> <br />Water-surface profiles for the return frequencies were determined <br />using the U. S. Army Corps of Engineers HEC-2 computer program <br />(Reference 11). Roughness coefficients (Manning's un" values) were <br />determined from field inspections and ranged from 0.040 to 0.070 in <br />the channel and from 0.050 to 0.070 in the overbanks. <br /> <br />The Flood Insurance study for the unincorporated areas of Larimer <br />County, Colorado (Reference 15), was updated concurrently with this <br />restudy. These studies are in agreement with one another. <br /> <br />Exhibit 1, "Flood Profiles," was revised to reflect changes as a <br />result of the restudy. <br /> <br />12 <br />