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<br /> <br />002549 <br /> <br />The sampling was done during a 24-hour period to obtain the approximate <br />diel variation for most of the constituents. Only two BOD and nutrient <br />samples were collected at the 11 tributary locations because few diel varia- <br />tions were expected, The main-stem sites YM-9, YM-10, YM-11, YM-12, and YM-13 <br />(fig. 6) ,are located downstream from the Elk River which contributes approx- <br />imately 40 percent of the total flow of the Yampa River at the confluence. <br />These sites were sampled only for BOD and nutrients because water from the Elk <br />River was expected to further dilute the wastewater effluent in the Yampa <br />River below the confluence. <br /> <br />A second <br />cember 1976. <br />of these data <br />analyze the <br />also to serve <br /> <br />data-collection effort for ,a 24-hour period was made during De- <br />Because of the time constraints of this investigation, analysis <br />is not included in this report. The second effort was made, to <br />yearly variability of water-quality and flow characteristics and <br />as a check of model results during winter (December) conditions. <br /> <br />Steady-state conditions can be assumed for most streams during low flows <br />by dividing a reach into subreaches. Such was the case during the calibration <br />sampling period for the study reach of the Yampa River. To help define depth, <br />velocity, and traveltime data for each sub reach of the Yampa River, 15 <br />discharge measurements were made. These measurements were made so that <br />average depth-velocity conditions of the stream in the general vicinity of <br />each measurement could be determined. The discharge of each tributary and <br />wastewater-treatment plant also was measured. <br /> <br />Stream-Reach and Diel Variations <br /> <br />Profiles of the mean values of DO concentrations, stream temperature, and <br />5-day CBOD (CBODs) are shown on figure 7. This summary is based on data <br />collected during the 24-hour sampling period. The mean DO concentrations in <br />the study ,reach were within 15 percent of saturation, with the mean DO concen- <br />tration exceeding 8 mg/L (milligrams per liter) at each location. Mean DO <br />concentrations were larger just upstream and downstream from the main <br />wastewater-treatment plant at Steamboat Springs (sites YM-2 to YM-5, fig. 7 <br />and table 2). These large concentrations may be due, in part, to the large <br />number of algae and submerged vascular plants at the sites. Stream <br />temperatures during the 24-hour sampling period averaged about 100 to 110C <br />from Steamboat Springs to Sage Creek. Downstream from Sage Creek (downstream <br />from site 'YM~ll), the stream temperature in the Yampa River increased to <br />approximately 130C. The discharge from Sage Creek (site YT-15), which was, <br />receiving thermal-heated effluent from the Hayden Power Plant, had an average <br />temperature of 160C and contributed to the, increased temperature in the Yampa <br />River downstream from Sage Creek (sites YM-12, YM-13, and YM-14, fig. 6). The <br />slope of the Yampa River decreases between Sage Creek and Hayden. As a <br />result, the mean river velocity decreases, creating larger pools in this part <br />of the study reach. This results in a longer residence time per unit length <br />of stream and allows the water in the stream to approach its equilibrium tem- <br />perature more quickly for a given length of stream reach. <br /> <br />14 <br />