River profiles - cross profiles and long profiles

Long profile

A long profile shows how the river changes over its course from its source (where it starts) to its mouth (where it meets the sea).

Upper part of river has larger bed load, more roughness, turbulence and friction. Lower part of river has greatest cross-section, the highest hydraulic radius, greatest velocity and discharge.

Upper course - this is where the river starts and is usually an upland area. The river's load is large in the upper course, as it hasn't been broken down by erosion yet.

Lower course - - the final course of the river is where the land is a lot flatter. The river's load is fine sediment, as erosion has broken down the rocks.

Cross profile

A cross profile is a view of the valley from one side to another.

A - as the river flows downhill there is an increase in vertical erosion. The channel is shallow and narrow because there is not a lot of water in the channel.

B - as the river flows into the middle course, there is some vertical erosion but more lateral erosion. The channel is wider and deeper as a result.

C - in the lower course there is a lot less erosion, with only some lateral erosion. The channel is at its widest and deepest.

The river channel is narrow at the source (A), wider in the middle (B) and wider still at the mouth (C).
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