River cross profiles show you a cross-section, taken sideways, of a river’s channel and/or valley at certain points in the river’s course.

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A channel cross-profile is a cross-section of only the river channel.

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In the upper course, the river erodes its bed by hydraulic action and abrasion. As the river flows downstream it is joined by tributaries, increasing the volume of water, velocity and therefore its erosive power. This enables it to cut a deeper channel as it flows downstream.

Downstream, the channel becomes wider as the gradient becomes more gentle leading to less vertical erosion. By the middle course of the river lateral erosion becomes the dominant type of erosion. The channel becomes wide because of lateral erosion.

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In the upper course, the valley cross-profile is narrow and steep-sided. The river takes up most of the valley floor. In the middle course, the valley becomes wider due to lateral erosion. By the lower course, the valley is almost flat, consisting of a wide flood plain.

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A valley cross-profile includes the channel, the valley floor and the sides of the valley.

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