How does a river change course downstream?

A river changes shape as it flows from its source to its mouth. A section of the course of a river drawn from source to mouth is known as a long profile.

Long profiles

Illustration showing a long river profile Long profile of a river

The source of a river is often, but not always, in an upland area. Near the source, a river flows over steep slopes with uneven surfaces.

It often flows over a series of waterfalls and rapids.

As a river flows down steep slopes, the water performs vertical erosion. This form of erosion cuts down towards the river bed and carves out steep-sided V-shaped valleys.

As the river flows towards the mouth, the gradient of the slope becomes less steep.

Eventually the river will flow over flat land as it approaches the sea.

As the river moves from the source to the mouth – both the depth of the river and the width of the river will both increase.

The load of a river will also change as it is transported and eroded along the river's profile.

As a result, the size and shape of stones will change as they journey through the river profile.

The discharge will increase as the river approaches the sea.

The discharge is usually calculated as the cross sectional area (depth x width) multiplied by the velocity or speed of the water.