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<br />a. Comparison of Colorado River Discharges at Several Locations <br />along Study F:each <br /> <br />To determine if the discharges estimated by the Corps downstream <br />of Plateau Creek (listed in Section No. II A) were appropriate to <br />use at palisade and points downstream, gauging station records at <br />several points were examined. Figures 2 and 3 compare flows at <br />the State Line gauge during the 1983 and 1984 snowmelt flood with <br />flows computed by adding records of mean daily flows at the <br />Cameo, Plateau Creek. and Gunnison-Gl~and Junction gauges. (The <br />Plateau Creek gauge did not record any flows during 1984.) <br /> <br />It is apparent that the sum of the flows of the three upstream <br />gauges. is nearly equal to the recorded values at the State Line. <br />Therefore, one may conclude that since there are no major <br />tributaries on the Colorado between Plateau Creek and the <br />Gunnison or between the Gunnison and the State Line, any <br />additional runoff from intervening drainage al:eas is balanced by <br />channel and overbank storage and diversions into irrigation <br />ditches in the area. Thus, there is no overall change in peak <br />discharges and it is reasonable to use the peak flows estimated <br />by the Corps below Plateau Creek for the stream reach between <br />Plateau Creek al: Palisade to a point just: upstream of the <br />Gunnison River. <br /> <br />b. Analysis of Gunnison River Flood Flows <br /> <br />Downstream of the mouth of the Gunnison, peak discharges on the <br />Colorado River increase significantly. To determine how much <br />effect the Gunnison River has on floods on the Colorado, two <br />questions were addressed: 1) what are the magnitudes 'of the <br />floods on the Gunnison; and 2) when do peak discharges on the <br />Gunnison occur, relative to peaks on the Colorado. <br /> <br />Records from the long-term gauge on the Gunnison were analyzed, <br />using the log Pearson Type III distribution to estimate peak <br />discharges near Grand Junction. The entire periOd of record was <br />not used because Blue Mesa Dam, completed in 1965, significantly <br />affects downstream flows. The flood flow frequency analysis <br />performed for the period 1966 to 1985 gives the following <br />results. <br /> <br />Return Interval <br /> <br />Results of <br />Frequencv AnalYeis <br /> <br />Previous FIS <br /> <br />10-year <br />50-YE!ar <br />100-year <br />500-year <br /> <br />17,700 cfs <br />28,700 cfs <br />34.400 cfs <br />50,400 cfs <br /> <br />15.000 <br />16,600 <br />19,000 <br />25,000 <br /> <br />-5-- <br />