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002398 spring flood below the lake's surface, but as fall progresses, this mass becomes colder and eventually sinks. The late summer salinity plume is convectively mixed with the colder bottom hugging flow; which we have dubbed the fall SWARM bottom flow because of it's high Salinity and relative WARMth (compared to other bottom layers). Oxygen levels are typically low due to high oxygen demand from the inflow. This cell of water is the greatest contributor of salinity to the hypolimnion on an annual basis. As the SWARM plug flows downlake, it incorporates-- through diffusion, dispersion and entrainment --the previous winter's underflows that have remained relatively stagnant since the spring flood first appeared. When this saline mass of water reaches the dam (between February and March), it contributes to the state of meromixis if of sufficient salinity to resist subsequent mixing. Deep Winter FRESCO: During the deepest cold of winter, convective mixing is most extensive. In the inflow area, the winter river inflow is at its coldest, most oxygen saturated, and saline. This cold saline winter inflow is mixed (convective mixing and entrainment) with the last of the spring flood near the inflow. A relatively FRESh plug of the lake's COldest most oxygenated water results. The FRESCO bottom flow follows the SWARM plug down the bottom of the lake, typically set in motion in January and February. The FRESCO's downlake momentum will eventually reach the SWARM which has made contact with the dam. The momentum of the FRESCO rocks the hypolimnion like a lever, moving the uplake chemocline downward as the chemocline at the dam moves upward. It is at this time that the highest conductivity, lowest temperature and lowest dissolved oxygen levels are discharged from the penstocks, as seen in Lees Ferry water quality (Figs. 12-15). At this point uplake, the fresh cold bottom plug typically has three options. I) Hvpolimnetic Overflow: If the FRESCO flow is not sufficiently cold or the chemical gradient between it and the meromictic salty warm bottom plug is too great, its momentum will carry it over the hypolimnion where it is entrained by the penstock 06/02/98 DRAFT Pe, .1 of 62