Floodplains - Any watershed begins with small trickles of water.

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Any watershed begins with small trickles of water. These small trickles gather and form larger streams, which gradually grow from brooks to creeks to rivers. As the volume of water increases in the stream channel, the stream channel has a greater cross-sectional area (there is an increase in stream size - width, depth, velocity, and flow volume).

As the river reaches the flat land around the base of the hill, the river will begin to meander. This slows the progress of certain areas of the river and speeds up others, meaning that one side is often eroded while the other is deposited – forming a floodplain.

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A floodplain is a mostly flat area of land bordering a river that is subjected to periodic flooding.  It is made up of silts and sands, which have been deposited over many years by the river.  Whilst some deposition takes place within the river channel, the bulk of the sediment is deposited when the river floods.  The reason for this is that as the river spreads over its floodplain, there is a sudden increase in both the wetted perimeter and the hydraulic radius.  This results in an increase in friction, causing a decrease in velocity and the deposition of material ...

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