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. . . ENGINEERING METHODS Hvdrolol!ic Analvsis There is no published hydrology to support the FIRM. Fortunately Engineering Professionals, me. performed a detailed hydrologie analysis as part of the Town of Otis Master Drainage and Flood Study. Norton, Underwood & Lamb also used that hydrologie analysis in the fmal design of the storm drainage and flood eontrol projeet that included the map entitled Project Layout, Drainage and Floodplain Improvements. The CWCB used the same detailed hydrologie analysis in revising the FIRM. It is, therefore, eonsistent with the approximate floodplain information included on the revised FIRM. Engineering Professionals, me. performed a standard detailed hydrologie analysis for Otis. The Southwest Drainage was divided into smaller sub-basins, and rainfall amounts from the federal rainfall atlas were used to represent 10-year and 100-year design storms. The Corps of Engineers eomputerized hydrologie model, HEC-I, with some modifieations developed by the Denver Urban Drainage and Flood Control Distriet, was used to ealculate 10-year and 100-year peak flows. The 1 DO-year flow for the Southwest Drainage is listed below in Table I. Table 1 Peak Flows for Drainages in Otis, CO Drainage Location lOO-year Peak Flow cfs 1618 Northwest Drainage at Dade Street tributa to Brunker Creek) Southwest Drainage at railroad culverts art 0 Brunker Creek 9.96 18.42 2456 * The 62.8 square miles of the Brunker Creek watershed that drains into Brunker Lake have not been included. Only the area downstream of Brunker Lake has been included. The 1 DO-year flow for streams within the Republiean River Basin ean be estimated by utilizing a regression equation developed by the CWCB as part of a publieation entitled "Guidelines for Determining IOO-Year Flood Flowsfor Approximate Floodplains" (Guidelines). The use of the Guidelines methodology was unnecessary because of the detailed hydrologic analysis described above. Hvdraulic Analvsis 6