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<br />0028~O <br /> <br />Daily stream-temperature data for Yampa River near Maybell (1951-73 <br />water years) and for Little Snake River above Lily (1951-69 water years) <br />yielded annual harmonic coefficients to which a trend-analysis procedure was <br />applied as documented in Steele, Gilroy, and Hawkinson (1974). No signifi- <br />cant trends in stream-temperature characteristics were revealed at either of <br />the sites for the indicated periods of record. <br /> <br />Continuous stream-temperature data have been collected by an engineering <br />consultant (Stearns-Roger, Inc., written commun., 1976) on the mainstem Yampa <br />River above the water intake for the electric power-generation plant near <br />Hayden, Colo. (site Y-47; fig. 1). Harmonic analysis of these data produced <br />coefficients similar to those obtained from periodic data collected by the <br />U.S. Geological Survey at or near this site. By continually decreasing the <br />number of observations included in the analysis, an assessment was obtained <br />for sampling alternatives which are less frequent than daily. In terms of <br />seasonal stream-temperature characterization, minimal loss of information was <br />indicated, even when only 3 percent of the data values were used. This sup- <br />ports a conclusion reached earlier by Gilroy and Steele (1972). <br /> <br />. <br />. <br /> <br />Harmonic coefficients developed from periodic data (generally one meas- <br />urement every 4 to 6 weeks) collected at 34 sites throughout the Yampa River <br />basin during the period 1960-75 have been correlated with selected basin <br />characteristics. Figure 3 is a plot of harmonic mean temperature versus <br />altitude for each site. A general inverse correlation between these two <br />variables is observed, indicating that regional patterns do exist. Regional <br />analyses for other areas of the United States (Steele and Dyar, 1974; H. W. <br />Lowham, written commun., 1976; Shampine, 1977) indicate similar results. <br />Thus, by estimating stream-temperature characteristics at unmeasured sites <br />this technique has potential for documenting changes resulting from man's <br />activities, even though pre-activity information may be sparse or lacking. <br /> <br />SUSPENDED SEDIMENT <br /> <br />Iorns, Hembree, and Oakland (1965) have made estimates of fluvial- <br />sediment discharge in the Yampa River basin. The analysis was based on daily <br />records at the Yampa River near Maybell, Colo. (fig. 1), for 1951-57 water <br />years and on data collected intermittently at 10 additional sites in the <br />basin during 1952-53 and 1957-58. The total suspended-sediment load of the <br />Yampa River basin was estimated to be 1.8 million tons (1.6 million t) per <br />year. <br /> <br />Based on daily records collected since the Iorns, Hembree, and Oakland <br />(1965) analysis, computed suspended-sediment loads from the basin are on the <br />order of 20 percent higher than that previously estimated. The cumulative- <br />frequency curve for suspended-sediment discharge at the Yampa River near <br />Maybell during water years 1951-58 shows the distribution of the sediment <br />load at this site (fig. 4). Recently calculated average annual suspended- <br />sediment concentrations of 270 mg/L (milligrams per liter) for the Yampa <br />River near Maybell and 2,890 mg/L for the Little Snake River near Lily are 38 <br />and 61 percent higher, respectively; than the estimates of Iorns, Hembree, <br />and Oakland (1965). Drainage areas of these two subbasin units are within 10 <br />percent of one another, being 3,410 mi2 (8,830 km2) for the Yampa River near <br />Maybell and 3,730 mi2 (9,660 krn2) for the Little Sn3ke River near Lily (see <br /> <br />6 <br /> <br />- j. ~ - , <br />