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<br /> <br /> Type of Event <br /> INumber of Annual Peak Flows <br /> Years of Rain during <br />Location Record Snowmelt Rain Snowmelt Runoff <br />Colona 57 48 4 5 <br />Delta 58 31 21 6 <br /> <br />The snowmelt runoff analysis resulted in frequency curves with skew <br />coefficients of -.08 for peak flow and -.01 for maximum l-day flow at <br />Colona, and -.90 for the peak and -.50 for the maxi~um l-day flow at Delta. <br />A skew of 0.0 was adopted for both sites because; <br /> <br />(1) Three low flow events biased the curves. <br /> <br />(2) A curve with a 0.0 skew fits the plotted data satisfactorily <br />(except for the three low flow events). <br /> <br />(3) There is insufficient evidence to support a trend of negative skew <br />coefficients in the Uncompahgre River drainage, which has runoff character- <br />istics unique from the rest of the Gunnison River basin (see skew coeffi- <br />cients for upstream gaging stations in Appendix B). <br /> <br />The resultant frequency curves are shown on Charts 8 and 11. <br /> <br />The rainfall runoff analysis produced frequency curves with skew co- <br />efficients of .36 at Colona and -.57 at Delta. This indicates that flows <br />higher than those at Delta can be expected at Colona during 25-year and <br />less-frequent rainfloods. This contradicts the historical record because <br />rainfall events have caused higher flows at Delta more often than at Colona. <br />Since there is insufficient regional evidence to support either positive or <br />negative skew coefficients for rainfall events, and a curve with a 0.0 skew <br />readily fits the plotted data at Colona and at Delta (with low outlier <br />omitted). skew coefficients of 0.0 were adopted for both stations. Charts <br />9 and 12 show the resultant frequency curves. <br /> <br />All-event peak flow-frequency curves were developed by combining the <br />rainfall and snowmelt peak runoff-frequency curves for each station. The <br />all-event curves are shown on Charts 10 and 13. Since the all-event curves <br />are nearly identical for the two stations, it can be assumed that the com- <br />bined peak flow frequencies do not change between Colona and Delta. This <br />is generally true since the attenuation and stream diversions are about <br />the same, givin6 consideration to tributary inflow between the stations. <br /> <br />9 <br />