WSP05260 - Laserfiche WebLink

Home Browse Search

. o to IV .... . . OTHER WATER QUALITY ASPECTS (Continued) show that the dissolved-oxygen concentrations in the Colorado River Basin are generally above established standards. A marked reduction in the concentration can be found during the summer months, however, below some municipal and industrial discharges and in some streams with very low flows. A 1966 investigation indicated that there might be a wide diurnal variation in the oxygen concentrations in some reaches because of the large amount of algae in the streams with oxygen saturation being reached during a sunlit day and minimal concentration occurring at night when oxygen is used by the plants. Samples also have indicated that at some of the lower depths in Flaming Gorge Reservoir anaerobic conditions exist. Releases are made, however, through the powerplant at higher elevations where the oxygen content is greater, thus maintaining suf- ficient oxygen in the stream below for fish life. 2. Temperature The Colorado River Basin water temperatures vary widely, reaching the greatest difference during the swnmer months when they vary from near freezing in the high mountains to above 900 F (32 Oe) in the lower reaches. Warmer temperatures may increase the rate of growth and decomposition of organic matter and of chemical reactions, resulting in had odors and tastes, and also decrease the dissolved oxygen concentra- tion available to sustain a fishery. Changes in water temperature in the basin result primarily from natural climatic conditions. The large reservoirs, however, may affect the stream temperatures for a considerable distance below the reservoir. Temperature records indicate that Flaming Gorge Reservoir has little effect on winter temperatures but cools the summer temperatures of the Green River up to 50 F (3 Oe) at the Green River, Utah, station. The temperature immediately below Flaming Gorge Dam had been too cold for maximum growth and propagation of fish life. Modification of the outlet works has recently been completed to improve this condition. The effect of this modification remains to be seen. Navajo Reservoir appears to have no effect on the temperatures of the San Juan River at the near Bluff station. Lake Powell appears to warm the winter temperatures of the Colorado River at the Grand Canyon station by up to 100 F (6 OC) and cool the summer temperatures by about the same amount. Thermal springs, wastewater discharges, and irrigation return flows may increase the temperatures in the receiving water, but the added heat is usually dissipated in a relatively short distance from the source. Flow depletions and changes in stream channel characteristics may also increase the effects of natural climatic conditions causing cooler or warmer water temperatures. Temperature increases due to municipal and industrial waste dis- charges have been minimal; however, the construction of large thermal 102