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USGS CMG InfoBank: River Bars

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Comment: 09:17 - 10:02 (00:45)
Source: Annenberg/CPB Resources - Earth Revealed - 19. Running Water I: Rivers, Erosion and Deposition
Keywords: "James Sadd", river, stream, discharge, "flow velocity", turbulence, energy, erosion, transportation, sediment, deposition, "river channel", bar, sand, gravel, ripple

Our transcription: Because precipitation varies seasonally, as well as from year to year, the discharge and velocity of a stream also fluctuates.
As the river slows down, the turbulence of the moving water begins to subside, and the amount of energy available to erode and transport sediment, decreases abruptly.
Much of the sediment can no longer remain in motion and is deposited instead.
The sediment is usually deposited in the river channel itself in a series of piles called "bars."
Most river bars are ridges made of sand and gravel that are covered with small migrating ripples.
In fact, the bars themselves are actually large ripples that migrate downstream during sporadic cycles of erosion and deposition.

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