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<br />in the catchment. Estimates of 500-year flood peaks were obtained using frequency <br />analysis. The updated hydrologic analysis was reviewed and approved by the City and <br />UDFCD and was used for the LOMR for Fourmile Canyon Creek. <br /> <br />The LOMR uses surveyed cross sections, aerial topography, and revised 10-, 50-, 100-, <br />and 500-year flood peak estimates to update the Fourmile Canyon Creek FIS. The <br />LOMR begins downstream at Boulder Creek in the county and extends upstream to the <br />upstream City Limits. <br /> <br />The hydraulic model used for the FIS did not include an analysis of the spills which leave <br />Foumlile Canyon Creek. The HEC-RAS model used for the LOMR analyzes the spill <br />discharges, and, since some of the spills pelmanently leave the channel, flood peak <br />discharges for the 50-, 100-, and 500-year events are reduced in the LOMR compared to <br />the regulatory model. A flow division at 61 st Street which was not analyzed in the FIS <br />was analyzed in the LOMR. <br /> <br />The existing condition subcritical hydraulic model developed for the LOMR will be used <br />by the City to define the impact of any future projects on the Fourmile Canyon Creek <br />floodplain. <br /> <br />2.1.2 Wonderland Creek <br /> <br />Similar to Fourmile Canyon Creek, 10-, 50-, and 100-year flood peak estimates for <br />Wonderland Creek were updated using the most recent version of CUHP and routed <br />using UDSWM. Hydrologic parameters in the models were updated using recent <br />topographic information and data in the City's GIS system. Estimates of 500-year flood <br />peaks were obtained using frequency analysis. The updated hydrologic analysis was <br />reviewed and approved by the City and UDFCD and was used for the LOMR for <br />Wonderland Creek. <br /> <br />The LOMR uses surveyed cross sections, aerial topography, and revised 10-, 50-, 100-, <br />and 500-year flood peak estimates to update the Wonderland Creek FIS. The LOMR <br />begins downstream at the confluence with Goose Creek and extends upstream to <br />Wonderland Lake. Wonderland Lake, which was originally modeled in the regulatory <br />hydrologic model, was revised in the LOMR model using "as-constructed" information <br />for Wonderland Lake obtained from the State of Colorado State Engineers Office in the <br />LOMR. The LOMR analyzes flow divisions at 28th Street and at Foothills Parkway <br />which were not analyzed in the regulatory model. <br /> <br />The HEC-RAS model used for the LOMR incorporates the spill discharge from Fourmile <br />Canyon Creek, and, as a result, flood peak discharges for the 50-, 100-, and 500-year <br />events are higher in the LOMR compared to the regulatory model. <br /> <br />-5- <br />