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USGS CMG InfoBank: Dams

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Comment: 14:42 - 15:41 (00:59)
Source: Annenberg/CPB Resources - Earth Revealed - 19. Running Water I: Rivers, Erosion and Deposition
Keywords: "Douglas D. Rhodes", river, flood, dam, discharge, valley, stream, deposition, erosion, lake, sediment, reservoir, "river channel"

Our transcription: One way to reduce floods is by constructing dams through which a river's discharge can be regulated.
But while dams solve some problems, they can create others.
All manmade structures in a river valley have an effect upon the stream, the most profound effect being caused by dams.
A dam essentially creates an artificial base level.
Sea level for all practical examples that causes the stream to deposit all of the load that it's been moving.
The quiet water of the lake doesn't allow that sediment to continue to move, so it's dumped at the upper end of the reservoir.
The water which comes through the spillways of the dam is now without the sediment that has been transported and will go about eroding new sediment to replace that which has been lost.
A river replaces this sediment by eroding the river channel downstream from the dam.
Sometimes this erosion can be severe.

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