The Cross Profile of a River Flashcards

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What is the cross profile of a river?
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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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What is the cross profile of a river?
Why does the valley cross-section change downstream?
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A steep, V-shaped cross-profile is typical in the upper course. This is because of vertical erosion by the river combined with weathering and mass movement of the valley slopes.

In the middle course, the river is flowing through lower-lying land. The gradient is gentler, so the river begins to meander (bend). As it does this the dominant type of erosion becomes lateral, eroding the valley sides. The makes the valley broader. Also, the rate of weathering increases on the softer rocks of the valley sides.

In the lower course, the river is passing through the low-lying country. Flooding results in deposition building up the flood plain and this, along with migrating meanders builds up and widens the valley further.

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Why does the valley cross-section change downstream?
Why does the channel cross-section of a river change downstream?
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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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Why does the channel cross-section of a river change downstream?
How does a channel cross-section change downstream?
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In the upper course, the channel is very narrow and very shallow. By the middle course, the channel becomes wider and deeper usually over 1 m. By the lower course, the channel becomes wider still and the channel is much deeper.

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How does a channel cross-section change downstream?
How does the valley cross-section change downstream?
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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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How does the valley cross-section change downstream?




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