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ABSTRACT ~~_'~9r) .' -' ,~--,.... WATER-QUALITY AND SEDIMENT-TRANSPORT CHARACTERISTICS IN KENNEY RESERVOIR, WHITE RIVER BASIN, NORTHWESTERN COLORADO By Robert L. Tobin and Caroline P. Hollowed The construction of Taylor Draw Dam and filling of Kenney Reservoir during 1984 were done in response to increased water-management needs in northwestern Colorado. To evaluate possible processes and changes that may occur in the reservoir after filling and the effects of sediment transport to the reservoir, physical, chemical, and biological data needed to be collected to define seasonal variations in vertical and areal water-quality character- istics. Physical, chemical, and biological data collected during the first 3 years of reservoir operation (1985-87) are presented and summarized for two sites in Kenney Reservoir. Related water-quality data and sediment character- istics during 1983-87 are summarized for one site on the White River about 8 miles upstream from the reservoir. Data from the three sites were compared for changes in water-quality characteristics that were caused by impoundment. In addition, fluvial sediment loads were determined for the White River upstream from the reservoir for 1983-87, and sediment retention in the reservoir was estimated. During 1983-87, the mean annual discharge in the White River (site 3) was about 174 percent of the mean annual discharge for the period of record (1973-81) at a discontinued streamflow-gaging station near the present dam site. Changes in water temperature, specific conductance, pH, and dissolved oxygen with depth were measured at the dam (site 1) and near the reservoir inlet (site 2). Some thermal stratification developed during summer when temperatures at site 1 generally decreased 3 to 5 oC from the surface to the bottom. Maximum surface temperatures in the reservoir were 23.8 oC at site 1 and 24.4 oC at site 2. Surface temperatures in the reservoir during summer were similar to temperatures measured in the White River at site 3 during summer. Specific-conductance values in the reservoir were similar to values in the White River and ranged from 374 to 932 microsiemens per centimeter. Except during a phytoplankton bloom in June 1987, values of pH generally ranged from 7.4 to 8.8, and concentrations of dissolved oxygen generally ranged from 2.3 to 10.1 milligrams per liter. Values of pH that exceeded 9.0 and concentrations of dissolved oxygen that exceeded 200 percent saturation were measured in near-surface waters that contained concentrated growths of phytoplankton in June 1987. Values of pH and dissolved oxygen decreased with depth in summer. Light penetration and turbidity values indicated increasing water clarity from the inflow end of the reservoir to the dam as suspended solids settled in the reservoir. 1