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a02615 COMPUTATION OF ANNUAL SEDIMENT LOADS AT SELECTED STREAMFLOW-GAGING STATIONS Avai lable Data The streamflow and sediment data avai lable at 17 stream-gaging stations within the Yampa River basin are summarized in table 1. The records of daily mean streamflow for the gaging stations used in this study are for periods of different lengths. and different times. In general, however, the streamflow records used were sufficient to approximate the long-term average magnitude and frequency of stream flows, assuming that there is no long-term trend in the annual streamflow time series. The gaging station on the Yampa River at Steamboat Springs (fig. 1) has the longest streamflow record in the basin. The annual time series of this record was tested using a technique developed by Conover (1971) and the results indicate there was no iong-term trend in streamflow. The sediment-load records summarized in table 1 include.data for only the suspended part of the total-sediment load transported by streamflow at these stations. The sediment load of a river is commonly divided, for computation purposes, into two fractions--the suspended load and the bedload. The suspended load is composed of the relatively finer sediment particles which are transported within the streamflow. The bedload is composed of the relatively coarser sediment particles which move along the bed of the stream. The concentration of suspended sediment in the streamflow is measured by collecting a discharge-weighted sample of the streamflow. The suspended~ sediment load for a given period may be computed by multiplying the mean suspended-sed i ment concent rat i on by the mean d i scha rge and then by 0.0027 times the number of days in the period. All sediment-load data included in the records 1 isted in table 1 were computed in this manner. These data do not include the bedload fraction. Although the bedload-transport rate may be sampled separately, no bedload-transport measurements have been made in the Yampa River basin. Because the bedload fraction may be a substantial part of the total-sediment load in many rivers, it is desirable to obtain an estimate of the bedload fraction. As wi 11 be discussed later, the bedload-transport rate at each station was computed from a bedload-transport formula. Daily suspended-sediment loads have been measured at only two gaging stations in the Yampa River basin for periods longer than a few months. These stations are the Yampa River near Maybe 11 , Colo., From December 195D through May 1958, and the Little Snake River near Lily, Colo., from May 1958 through September 1964. Annual sediment loads for these gaging stations may be calculated by summing the measured daily sediment loads. A reasonable estimate of the mean-annual sediment load may be calculated by averaging the measured annual sediment loads at each of these two sites. The period of record at both gaging stations, however, is short relative to the observed year-to-year streamflow variation. The gaging stations on the Yampa River near Maybell and the Little Snake River near Lily are located near the confluence of these rivers. Therefore, the respective records are indicative of the sediment and water yields of the 4 ~i