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',. 321 the largest increment of the annual total sediment load through the channel. The effective discharge at the Little Snake River near Dixon gage has been equaled or exceeded on the average of 5.1 days per year, or 1.4% of the time, during the period of streamflow record, 1939-1976. A number of other sig- nificant characteristics of the sediment discharge are shown in Fig. 5. Approx- imately 73% of the total sediment load at this station was transported by discharges between 57 and 156 m3/s. These discharges are equaled or exceed- ed on the average between 8.8 and 0.2% of the time, or between 32 and 0.70 day per year. Thus, neither the rare large floods nor the common streamflows have been significant sediment-transporting discharges at this station during the period of record. In particular, the mean-annual discharge has not been an important sediment-transporting discharge, as it has transported only a small fraction of the annual sediment load. More than 90% of the mean-annual sediment load has been transported by discharges larger than the mean-annual discharge. The effective discharge at all gaging stations was computed by the method described above. The effective discharges and their durations are summarized in Table I, columns 7 and 8, and compared in Fig. 6. The streamflow duration of the effective discharge varies between gaging stations. The observations range from 0.4 to 3.0% of the time or from 1.5 to 11 days per year. On the average, the effective discharge was equaled or exceeded 1.6% of the time or 5.8 days per year. These observations agree with the conclusion of Wolman and Miller (1960) that the effective discharge is a relatively frequent flow that occurs on an average of several days per year. NUMBER OF DAYS PER YEAR THE EFFECTIVE DISCHARGE IS EOUALED OR EXCEEDED o 2 4 6 8 10 11 6 I I I I I I I I I I T I I I I - - I- - - - <Jl Z Q .... <( 4 > a: w <Jl CD 0 u. 0 a: 2 w CD ~ ::> z o o 0.5 1.0 1.5 2.0 2.5 3.0 PERCENTAGE OF TIME THE EFFECTIVE DISCHARGE IS EOUALED OR ExceEDED Fig. 6. Streamflow duration of effective discharges at 15 gaging stations in the Yampa River basin.