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<br />. <br /> <br />. <br /> <br />. <br /> <br />ENGINEERING METHODS <br /> <br />Hvdrolol!ic Analvsis <br /> <br />There is no published hydrology to support the FIRM. Fortunately Engineering Professionals, Inc. <br />performed a detailed hydrologic analysis as part of the Town of Otis Master Drainage and Flood <br />Study. Norton, Underwood & Lamb also used that hydrologic analysis in the fmal design of the <br />storm drainage and flood control project that included the map entitled Project Layout, Drainage <br />and Floodplain Improvements. The CWCB used the same detailed hydrologic analysis in revising <br />the FIRM. It is, therefore, consistent with the approximate floodplain information included on the <br />revised FIRM. <br /> <br />Engineering Professionals, Inc. performed a standard detailed hydrologic analysis for Otis. The <br />Southwest Drainage was divided into smaller sub-basins, and rainfall amounts from the federal <br />rainfall atlas were used to represent IO-year and IOO-year design storms. The Corps of Engineers <br />computerized hydrologic model, HEC-I, with some modifications developed by the Denver Urban <br />Drainage and Flood Control District, was used to calculate IO-year and IOO-year peak flows. The <br />IOO-year flow for the Southwest Drainage is listed below in Table I. <br /> <br />Table 1 <br /> <br />Peak Flows for Drainages in Otis, CO <br /> <br />Drainage Location <br /> <br /> <br />lOO-year Peak Flow <br />cfs <br />1618 <br /> <br />Northwest Drainage at Dade Street <br />tributa to Brunker Creek) <br />Southwest Drainage at railroad culverts <br />art 0 Brunker Creek <br /> <br />9.96 <br /> <br />18.42 <br /> <br />2456 <br /> <br /> <br />* <br /> <br />The 62.8 square miles of the Brunker Creek watershed that drains into Brunker Lake <br />have not been included. Only the area downstream of Brunker Lake has been included. <br /> <br />The IOO-year flow for streams within the Republican River Basin can be estimated by utilizing a <br />regression equation developed by the CWCB as part of a publication entitled "Guidelines for <br />Determining IOO-Year Flood Flowsfor Approximate Floodplains" (Guidelines). The use of the <br />Guidelines methodology was unnecessary because of the detailed hydrologic analysis described <br />above. <br /> <br />Hvdraulic Analvsis <br /> <br />6 <br />