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See also:LEVEE (from Fr. See also:lever, to raise)
, an See also:embankment which keeps a See also:river in its channel
.
A river such as the See also:Mississippi (q.v.), draining a large See also:area, carries a See also:great amount of sediment from its swifter See also:head-streams to the See also:lower ground
.
As soon as a stream's velocity is checked, it drops a portion of its load of sediment and spreads an alluvial See also:fan in the lower See also:part of its course
.
This deposition of material takes See also:place particularly at the sides of the stream where the velocity is least, and the See also:banks are in consequence raised above the See also:main channel, so that the river becomes lifted bodily upwards in its See also:bed, and flows above the level of the surrounding See also:country
.
In See also:flood-See also:time the muddy See also:water flows over the river's banks, where its velocity is at once checked as it flows gently down the See also:outer See also:side, causing more material to be deposited there, and a See also:long alluvial See also:ridge, called a natural See also:levee, to be built up on either side of the stream
.
These ridges may be wide or narrow, but they slope from the stream's outer banks to the See also:plain below, and in consequence require careful watching, for if the levee is broken by a " See also:crevasse," the whole See also:body of the river may pour through and flood the country below
.
In 1890 the Mississippi near New See also: |
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