Laserfiche WebLink
<br />~ <br />o <br />O'J <br />0') <br /> <br />Warm-water discharges from Hoover Dam could also result <br />in increased evaporation from Lake l~ohave and Lake Havasu, <br />the d01<nstream reservoirs. The temperature structure in <br />upper Lake Mohave is currentl<: influenced by cold-water <br />discharges from Hoover Dam [5J. However, the river forms an <br />underflow in Lake Mohave and mixing is not sufficient to <br />advectively cool the entire reservoir. Surface temperatures <br />in Lake Mohave frequently exceed those in Lake Mead, and <br />discharges of warm water from Hoover Dam will probably not <br />contribute more heat to the reservoir than it currently <br />assimilates from solar radiation. Temperature data are too <br />limited to allow for speculations on how evaporation could <br />be altered in Lake Havasu. However, the surface area of Lake <br />Mohave and Lake Havasu are each roughly one-third that of <br />Lake Mead. Net water losses and salinity in the river would <br />,prohllbly still be reduced, even if warm-water releases did <br />in(,~-I~pase evaporation rates in these reservoirs. <br />Finally, operation of Hoover Dam from a surface dis- <br />charge would alter the nutrient budget for Lake Mead. Total <br />nitrogen retention in Lake Mead would increase by 66% and <br />total phosphorus by 60% with a surface discharge on Hoover <br />Dam [11J. This, in turn, would elevate productivity in the <br />reservoir, particularly in the Lower Basin where wastewater <br />inflows from Las Vegas Wash contribute large amounts of <br />phosphorus to the reservoir [15J. However, this could be <br />beneficial to the largemouth bass population which has <br />undergone a serious decline in Lake Mead. This decline <br />appears to be related to a decrease in reservoir fertility <br />that occurred after Glen Canyon Dam was constructed in 1963 <br />[16,17J. High nutrient losses from the deep-water discharge <br />at Hoover Dam have further contributed to this decline in <br />fertility. A surface discharge could help sustain greater <br />fertility in Lake Mead, and perha~s provide a better food <br />base for the bass populations [11J. <br />The environmental and engineering problems associated <br />with operation of Hoover Dam from a surface discharge do not <br />appear to be insurmountable. Some of the environmental ques- <br />tions are being addressed in limnological studies currently <br />being conducted for the Office of liater Research and Tech- <br />nology, or in fisheries investigations being conducted by <br />the regional fisheries biologists and the U.S. Fish and <br />Wildlife Service. The engineering problems, however, will <br />clearly require additional investigations to determine <br />whether the existing intake structures can be modified to <br />cost-effectively withdraw surface waters from Lake Mead. <br />In addition, further limnological studies should be <br />done in Lake Mead to determine if the present methods of <br />estimating evaporation are accurate, evaluate estimates of <br />water loss savings made in this paper, and better assess the <br />relationship of salinity to evaporation in the reservoir. <br /> <br />15 <br />