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0024J2 while the diversion tunnel drew off the deepest hypolimnetic waters. The result was rapid turn-over of the lake? s volurne in 1965 with pronounced refreshment of the hypolimnion. The diversion tunnel was permanently sealed in September 1965. The bi-Ievel epilimnetic withdrawals that followed in 1966 and strong SWARM currents that followed in the late 1960?s resulted in an exceptionally persistent and very saline hypolimnion-meromixis-- that dominated the lake through 1971. Oxygen levels for this period remained fairly high. Although the early dissolved oxygen data was sometimes noisy, the pattern of winter oxygenation predictable under the circumstances. Although ,quite saline, the winter bottom flows were cold and well oxygenated. Furthermore, these flows were entering a smaller lake and the cold, oxygenated FRESCO plume had less distance to travel to the dam than in later years when the lake was deeper and longer. b. Drought Cycles For the purposes of this assessment, basin-wide drought is measured by the total inflow to the lake and not local weather patterns. At least 5 major drought cycles can be observed in the long term forebay plots in Fig. 3a, denoted by a low inflow (as well as outflow) hydrograph, decreasing or low lake levels, and generally increasing salinity levels. Some of the droughts may have consisted of only one or two year, such as 1964, 1972, 1976 to 1977 and 1981, yet it can be seen they had an immediate and persistent effect upon the hypolimnion. Other droughts continued for years, such as the 3 sub-normal years from 1966 through 1968, and the most recent drought from 1988 to 1992. These longer droughts produced greater meromixis in the hypolimnion, as well as substantially higher levels in the epilimnion. As happened in 1966, the effects of a strongly saline SWARM bottom current, such as typically follows a dry year, has an immediate and strong influence on hypolimnetic conductance. 06/02/98 DRAFT 1'. ,0 25 of 62