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Show 6 Water Quality in the Great Salt Lake Basins, Utah, Idaho, and Wyoming, 1998- 2001 Major Findings Water development affects quantity and quality of water resources Streamflow regulation, such as that in the Bear River Basin, alters daily and seasonal flows Regulation of streamflow for power generation and irrigation substantially alters daily flow in some streams in the Great Salt Lake Basins Study Unit. For example, streamflow in the Bear River at the Utah/ Idaho State line, downstream from the Oneida Narrows hydroelectric dam, fluctuated from about 400 to more than 1,600 ft3/ s ( cubic feet per second) over a 7- day period in August 2000. Flow in the Bear River near Cokeville, Wyoming, which is not affected by power generation, remained nearly constant at 180 ft3/ s during the same period ( fig. 7). Seasonal fluctuations in flow in a regulated stream in the basins also are demonstrated in the Bear River. During the winter months, when large amounts of water are not stored in reservoirs or diverted into canals, flow naturally OCC ,800 ,600 ,400 ,200 ,000 800 600 400 200 0 - i 1 1 r • Bear River at Utah/ Idaho State line. 12 3 4 5 6 TYPICAL DAYS IN AUGUST 2000 Figure 7. During atypical week in the summer, streamflow at sites below hydroelectric dams ( such as Bear River at Utah/ Idaho State line) have large daily fluctuations, while sites unaffected by power generation ( such as Bear River near Cokeville) have steady flow. • 1,400 MILES DOWNSTREAM FROM HEADWATERS Figure 8. The flow of the Bear River in February approaches that of a natural river, increasing from upstream to downstream. The flow in August is dramatically altered by release and diversion of stored water for downstream irrigators. increases in a downstream direction ( from about 50 to more than 1,000 ft3/ s) ( fig. 8). In the summer months, when water is released from reservoirs and diverted into canals for irrigation, flow changes substantially ( from nearly no flow in some stream segments, to more than 1,200 ff3/ s in others) ( fig. 8). Periodic low flow in streams can affect recreation, ground- water recharge, March aquatic life, and fish and wildlife habitat. To avoid such effects, minimum instream flow requirements, maintained through purchased water rights or legislation, have been established for some streams in the Great Salt Lake Basins. Segments of other streams with no requirements, including some in the Bear River Basin, however, can be completely dewatered by diversions. Reductions in water quantity also affect water quality in streams Identifying and understanding daily and seasonal fluctuations in streamflow is important because the amount of water in a stream can directly affect the quality of the water. Specifically, the magnitude and timing in transport of sediment, nutrients, and other contaminants is affected. For example, concentrations of total phosphorus in the Bear River in March 2001, when flow regulation was minimal, increased downstream from less than 0.004 mg/ L at the UtahAVyoming State line ( near the EXPLANATION Total phosphorus concentration, 2001 0 Low ( less than 0.05 milligrams per liter) 4n O Moderate ( 0.05 to 0.099 milligrams per liter) % High ( 0.1 milligrams per liter or greater) ^• Dam Figure 9. In the Bear River, contributions from tributary streams have a large influence on total phosphorus concentration in March. Reservoir management and canal diversions affect concentrations in July and August. |