WSP02851 - Laserfiche WebLink

Home Browse Search

.+::0- o en ~~ It thus appears that the ideal strategy for reducing evaporation from Lake Mead would be to continue operating Glen Canyon Dam from a deep discharge and shift Hoover Dam to a surface discharge. This could result in a combined reduction in water loss of 213,155 acre-feet (2.63 x 108m3)/yr, at the 1977-78 lake levels. Such reductions in water loss would constitute one of the best water conser- vation programs available for the Colorado River. Influences on Reservoir Salinity Reductions in evaporative water losses from Lake Mead would result in significant decreases in salinity of the reservoir. Inflows of cold water from Glen Canyon Dam are probably already causing reductions in salt concentrations ~n tlw Upper Basin of Lake Mead, although data are not av"i~lable to estimate the magnitude. \;a tel' loss reductions derived from operating Hoover Dam with a surface discharge would act to further decrease salinity, especially in the IJo'tier Basin.. Dissolved solids concentrations at the Hoover Dam intake towers in Lake Mead averaged 676 mg/l during water year 1978. Evaporation reductions of 120,000 acre-feet (1.48 x 108m3), achieved with a surface discharge at Hoover Dam; or 213,000 acre-feet (2.63 x 108m3), achieved with a cold- water discharge on Glen Canyon Dam and a surface discharge on Hoover Dam, would reduce salinity in Lake Mead by 9 mg/l and 16 mg/l, respectively (Figure 7). These salinity reduc- tions would occur wi thin a five-year period and are compar- able to those which will be achieved by the Las Vegas Wash, Nevada (8 mg/l) and Grand Valley, Colorado (19 mg/l) Salin- ity Control Projects (Figure 7) [3J. This would serve to effectively augment salinity control projects on the Colo- rado River. Feasibility of Operating Hoover Dam from a Surface Discharge 1'here are several potential problems associated with operation of Hoover Dam from a surface discharge [4J. First, this ~Tould require modifying the intake structures. Hoover Dam is currently equipped with intake gates at 895 ft (273 m) (lower gates) and 1045 ft (319 m) (upper gates) eleva- tions. At the 1978 lake elevations of 1186 ft (361 m), oper- ation from the upper gates would still result in withdrawal of cold, hypolimnion waters [12J. Intake gates would have to be installed at higher elevations to permit withdrawal of warm water. Engineering studies would have to be done to evaluate the feasibility and cost-effectiveness of such modifications. Hydraulic studies should also be conducted to insure that the intake structures would indeed withdraw sur- 13