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<br />probability distribution for the period from 1921 to 1986 to assign a return period <br />to the mean annual flow as follows: <br /> <br />Low flow year = 1.25 year return period = 1,530 cfs (43 m3/s) <br />Average flow year = 2 year return period = 2,140 cfs (61 m3/s) <br />High flow year = 5 year return period = 2,750 cfs (78 m3/s) <br /> <br />Butler (1988b) used the period 1941 to 1986 to conduct his sediment budget <br />analysis because of missing records. It shoula be noted that these records were <br />missing from the computer data base W A TSTOR but were not missing from the <br />USGS Water Resource published records. Future analyses should use the entire <br />record. <br /> <br />Another valuable contribution in this work was Butler's discussion and use <br />of the bias correction factor to adjust the sediment loads predicted with regressed <br />power functions as previously discussed for the Lily and Maybell gage data. Butler <br />(1988b) estimated a mean annual sediment load of 2.6 million tons per year at <br />Deerlodge Park. O'Brien (1987) estimated the average annual suspended load of <br />2.02 million tons per year at the Lily gage. Adding an average annual Yampa River <br />suspended sediment load of 389,000 tons and a 5% bedload, the total sediment <br />load for the combined rivers will be in excess of 2.5 million tons per year. It <br />should be noted that the application of the bias correction is not valid for all data <br />bases if the data are not normally distributed, if the log-transformed rating curve is <br />not linear, or if the scatter does not have the same residual variance at all <br />discharges (Ferguson 1986). <br /> <br />Butler (1988b) recognized that the sediment budget analyses are only as <br />accurate as the rating curves on which they are based. The rating curves <br />produced by O'Brien (1987) and Elliott et al. (1984), for example, were based on <br /> <br />40 <br />