8 - Alluvial river large river of very low channel gradient...

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The rapids are eroded until their gradient is closer to the stream’s average gradient. The main stream branches into higher parts of the original land mass carving out many new small drainage basins. With a graded stream, floodplains develop. The river wanders sidewards, cutting into side slopes—curved path Alluvium (sediment laid by a stream) collects on the inside of each bed. As cutting continues, the floodplain widens. Channels develop sweeping bends or alluvial meanders. The floodplain becomes a continuous belt of flat land between steep valley walls. Once the floodplain had developed, the river attacks the adjacent valley wall less frequently. Weathering, mass wasting, and overland flow act to reduce the steepness of the valley side slopes. Fluvial Landscapes Alluvial Rivers and Their Floodplains Over time, a floodplain is widened and is called an alluvial river.
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Unformatted text preview: Alluvial river : large river of very low channel gradient It flows on a thick floodplain of alluvium constructed by the river itself in earlier stages of its activity. Typical landforms: • Bluffs • Ox-bow lakes • Natural levees • Backswamps Fluvial Landscapes Meanders are smooth rounded bends of rivers that increase in size as the river grows and its floodplain widens. They grow outward and migrate downstream. When meanders touch, the river quickly takes the shortcut leaving a meander scar or ox-bow lake. Large floods can change the shape of the rivers course. Alluvial Fans Alluvial fan: gently sloping, conical accumulation of coarse alluvium deposited by a braided stream resembling an open fan. They are built by streams carrying heavy loads of coarse rock waste from a mountain or upland region. The central point of the fan lies at the mouth of a canyon or ravine....
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