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~ ~ ,.,......,.;.~ ..:..;..., , "-.--, -..--<.".:~;:.' -~-",;;;,~,:.~~,;,;~;' ''.:~ " ,.:.:Ji.;;;;;::.Jl;'M'i. : . \ --;".;,:,. C0MPUTATIO~J OF ANNUAL SED1~\E~n LOADS AT SELECTED STREAMFLO\i-GAG I NG STAT IONS Pwailable Data The streamflow and sediment data aval lable at 17 stream-gaging stations within the YaGpa 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 differ-er,t times. In general, however, the s_,tre2mflow records used I^.'ere sufficient to approximate the) ong'-term average'1R-agn i tude and frequency of streamflm'/s, assuming tha.t there is no long-term -'trend in the annual streamflow time ~~riei. The gaging station on the ~ampa'Ri~er at Steamboat Springs (fig. 1) has- the 10ngesJ, ,streamflow"record in the basin. The annual time series of trus record-vIas tested using a technique developed by Conover (19~-e~ the results indicate there was no long-term trend in s t reamf 1 ow. - The sediment-load records summarized in table 1 include data for only the suspended part of the total-sedi~ent 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 streamflo\~. The bedload is co~posed or the relatively coarser sediment particles which move along the bed or 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-sediment concentration by the mean discharge 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 8ade in the Yampa River basin. Because the bedload fraction may be a substantia] 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. Dai ly suspended-sediment loads have been measured at only two gag1ng stations in the Yampa River basin for periods longer than a few months. These stations are the Yampa River near Maybell, Colo., rrom December 1950 through ~1ay 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 dai ly sediment IOdds. 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 or record at both ga~ing stations, however, is short relative to the observed year-to-year streamflow variation. The gaging stations on the Yampa River near Maybe] 1 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