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. . . . . . ENGINEERING METHODS . . Hvdrolol!:ic Analvsis . . Table 1 lists the two streams and reaches for which approximate or detailed floodplain boundary . information is contained in the September 27, 1985 FIS. Detailed analysis was carried out only . for the Uncompahgre River and was based upon log-Pearson Type ill statistical analysis of 54 . years of streamflow records. Discharge rates for the Uncompahgre River are presented in the FIS . for the 10-, 50-, 100- and 500-year events. . . Approximate analysis of flood hazards was carried out for one flooding source, Cottonwood . Creek. Hydrologic analyses and discharge rates for Cottonwood Creek are not documented by . FEMA in the 1985 FIS. As previously discussed, Colorado statutes require that this information . be provided in order for floodplain studies to be "designated" and thus made legally usable for . floodplain regulation. For the purposes of this HA, a 100-year discharge rate has been computed . for Cottonwood Creek using regional regression equations developed by the CWCB and . documented in Guidelines for Detennining 100- Year Flood Flows for Approximate Floodplains . in Colorado (CWCB, January 1999). Regression equations presented in this publication . compute 100-year peak discharge rates and are based upon data from floodplain studies . previously designated by the CWCB. Regression equations have been developed for nine major . river basins within the state and a number of subbasins. The appropriate equation from these . guidelines for Cottonwood Creek is as follows: . . Q = 180.8(A)o578 . . A = Drainage area in square miles (2<A<8,000 sq mi) . Q = IOO-year peak discharge in cfs . . Table 2 presents the laO-year discharge rate determined for Cottonwood Creek using the CWCB . regression equation. . . . . . . . . . . . . . . . . . . 4 . ...