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NatureWater Lesson Plans
Problems & Solutions:
GRAVEL AUGMENTATION

Areas below big dams often do not have enough spawning gravel. Gravel in the riverbed is pushed out by flowing water over time, with replacement gravel in short supply because of the dam. Under natural conditions rocks errode from the surrounding watershed, fall into the stream, and grind down from bolders to gravel to sand as the water tumbles the stone seaward. Dams stop this process by blocking the downstream progress of gravel and other sediment, and by preventing the high water flows that perform most of the moving.

When suitable spawning gravel is limited, fish are forced to spawn on existing redds. Digging a new hole in a spot already claimed dislodges the previous eggs, which drift away and are eaten by other animals. This unfortunate competition for scarce nesting space reduces the rate of successful reproduction.

Solution:

A black and white drawing of a winding river, with trees and rocks along the banks.
In the Sacramento and Trinity Rivers, people have tried dumping gravel into stream channels. This solution works only with sites accessible to dump trucks. During low flow conditions the gravel is placed in piles. When flows increase, the power of moving water distributes the gravel downstream.

More pictures of gravel augmentation
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