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<br />002339 <br /> <br />withdrawal plume suction from dam releases pull it up toward the penstocks. The penstocks will <br /> <br />continue to draw on this layer (as well as others) until the following winter when the next SWARM <br /> <br />reaches the dam. This is the most common scenario, occurring 14 of the past 33 years. 2) <br /> <br />Hvoolimnetic Underflow: If it is sufficiently cold and dense, the FRESCO will continue downlake <br /> <br />on the bottom, displacing the hypolimnion upward toward the penstocks and perhaps not stopping <br /> <br />until it reaches the dam if of sufficient magnitude. An underflow that reaches the dam is the most <br /> <br />efficient process for removing meromixis and restoring oxygen to the hypolimnion without non- <br /> <br />powerplant releases. This is also the least common scenario, occurring only 6 times since Powell's <br /> <br />filling (1973, 1983, 1984, etc.). 3) Hvpolimnetic interflow: Several factors can contribute to this <br /> <br />process. rfthe advective forces are removed from the bottom currents through diversion to surface <br /> <br />flows in the spring, the bottom currents stall and the plumes substantially slow or cease to move <br /> <br />toward the dam. The discharge from the dam may continue to pull the FRESCO through the <br /> <br />SWARM at a depth that corresponds to the relative density and momentum of the respective flows. <br /> <br />Furthermore, if the chemical or thermal gradients are insubstantial, the FRESCO and SWARM <br /> <br />plugs may mix through diffusion and dispersion. This interflow is more common-occurring <br /> <br />approximately IZ"ofthe past 33 years. The amount of meromictic removal is a function of the depth <br /> <br />of the interflow. <br /> <br />Late Winter SCOOL: The final of the three bottom hugging winter plumes, the late winter <br /> <br />SCOOL plug has higher salinity concentrations than FRESCO but is not as cold. There are less of <br /> <br />the previous spring's floodwaters left to convectively mix with the saline but warming riverine <br /> <br />water. This Saline and COOL flow forms around March and follows the FRESCO plume down the <br /> <br />lake's bottom. Its progress is typically stalled by April or May when warming and the advective <br /> <br />flow forces are diverted to the spring flood at the surface. Organic and chemical oxygen demands, <br /> <br />low light availability, and prolonged stagnation keep oxygen lewls low in this cell. It typically does <br />06/02/98 DRAFT Page 22 of 62 <br />