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<br />State line were based on a statistical analysis of annual peak <br />discharges recorded at the following USGS gaging stations: <br /> <br />Gaging Station <br /> <br />Period of Record <br /> <br />Colorado River: <br />near Cameo <br />near Palisade <br />near Fruita <br />near Colorado-Utah State Line <br /> <br />1934 - 1985 <br />1902 - 1933 <br />1911 - 1923 <br />1951 - 1985 <br /> <br />Gunnison River: <br />near Grand Junction <br />(after Blue Mesa Dam) <br /> <br />1965 - 1985 <br /> <br />The frequency analysis was performed using the log-Pearson Type III <br />Method, in accordance with criteria outlined in Bulletin 178 <br />(Reference 12). <br /> <br />The peak flow series that were analyzed represent primarily <br />snowmelt floods which peak between late April and June. Following <br />COE guidel ines, a regional skew of zero was used for the Cameo <br />gage. The results of the computation compared favorably with the <br />results of the COE hydrology report and are shown in Table 3. <br /> <br />To estimate peak discharges for the various recurrence intervals on <br />the Gunnison River near Grand Junction, records from the long-term <br />gage on the Gunnison were analyzed, using the log-Pearson Type III <br />distribution (Reference 12). The entire period of record was not <br />used because Blue Mesa Dam, completed in 1965, significantly <br />affects downstream flows. The results of flood flow frequency <br />analysis performed for the period 1966 to 1985 are shown in <br />Table 3. <br /> <br />A comparison of the flood hydrographs for the Colorado and Gunnison <br />Rivers was made. It can be assumed that flood peaks on the <br />Colorado and Gunnison Rivers occur at the same time since the <br />hydrographs are nearly parallel. Thus, for study reaches <br />downstream of the mouth of the Gunnison River, the peak discharges <br />on the Colorado River are added to the flood peaks computed for the <br />Gunnison River. For reaches upstream of the Gunnison River, <br />results of the 1985 COE hydrologic study on the Colorado River <br />(Reference 10) were used. <br /> <br />The smaller drainage areas that were studied by detailed methods <br />required the use of the COE HEC-l rainfall-runoff computer program <br />(Reference 13). Peak flows from the computed flood hydrographs <br />were compared to values obtained from the regional frequency curves <br />and adjustments were made to the computed flood hydrographs to <br />assure their consistency with the frequency curves. <br /> <br />The City of Grand Junction conducted a hydrologic study of Horizon <br />Drive Channel in 1988 (Reference 14) in order to determine the <br />effects on the IOO-year flood peak of a newly constructed detention <br /> <br />18 <br />