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Water is released from the upper resevoir during periods of high demand and is used to generate electricity. What makes this different from other hydroelectric dams is that during times of low demand, power is taken from coal, nuclear, and other power plants and is used to pump water from the lower to the upper resevoir. Although this plant use more power than it generates, it allows these other plants to operate at close to peak efficiency for an overall cost savings. Back Creek and Little Back Creek, the water sources used to create the resevoirs, have a relatively small flow rate. However, since water is pumped between the resevoirs equally, the only water taken from these creeks now that the resevoirs are full is to replace the water lost to evaporation. During operation, the water level fluctuates by over 105 feet in the upper resevoir and 60 feet in the wider lower resevoir.