How a dam drawdown works
Varying drawdown elevations serve different purposes. Deep drawdowns are the most effective for improved fish passageway.
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The problem: Fish injury or death
The solution: Deep water drawdown
Dam
Power house with generator
Spillway
Penstock
Regulating outlet
Spring and summer reservoir elevation
Most juvenile chinook and steelhead fish pass through the spillway.
Waterflow
1
2
3
winter season flood control drawdown
Regulating outlets are too deep. Passage through turbines leads to fish injury and mortality.
Turbine
Effective spillway fish passage
Deep drawdown for improved fish passage
Reservoir is shallow enough for juvenile chinook and steelhead to find outlets and pass through.
SOURCE: U.S. Army Corps of Engineers
