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'''''')C)?7 \J _. '. . . CONCLUSIONS The use of thermal mixing by either mechani- cal pumping or compressed air appears to have important potential for evaporation suppression on deep reservoirs. This concept does not involve many of the problems associated with monolayer suppression. It is independent of wind; it does not produce a concentration of excess heat near the surface; it provides a mechanism for net sup pres. sian on an annual rather than only a seasonal basis (warmed outflow); and it does not involve environmental problems associated with adding chemicals to the reservoir surface. There are, in fact. several environmental benefits claimed for the destratification procedure. Significant improvement in dissolved oxygen, taste and odor, algae production. and many other quality parameters occur in the hypolimnion water. In addition to these human related benefits, fish habitat may be improved both in the reservoir (because of increased DO) and downstream from it. Below Flaming Gorge Dam, for example, the water being released is presently so cold that native species of fish in the area are becoming endangered. The warmed outflow from a thermally mixed reservoir would help this situation. The necessary conditions for significant evaporation suppression appear to be as follows: I. Sufficienl depth (usually more than 60 feet) to produce a marked nalural thermocline and to provide a relatively large volume of cold hypolimnion water for mixing. 2. An outlet that is below the thermocline and sufficient outflow in relation to storage to transport a significant amount of excess heat from the reservoir. The model developed in connection with this research appears to produce reasonably accurate but conservative estimates of suppression for impoundments in an arid climate but the model error increases rapidly as average humidity increases. The estimated average annual potential volume of water salvageable by destratification of Utah reservoirs is 172,000 acre feet. Of this amount, 140,200 acre feet is represented by Lake Powell. This potential at Lake Powell exceeds the total amount of water proposed for development by the Bonneville unit of the Central Utah Project. Because of the major potential for water consen'ation in general and water for energy production and salinity control in particular, additional research on destratification of deep reservoirs should be undertaken. 49