Discharge increases downstream because of additional water from tributaries. Velocity increases due to the additional water from tributaries and less water is in contact with the bed and banks so there is less friction.

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The long profile shows the gradient of the river from its source to mouth.

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The steepest gradient in the long profile of a river is found in the upper course near to the source.

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It becomes narrow and steep-sided in the upper course due to vertical erosion.

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The increase in lateral (sideways) erosion.

Find out more about the long profile of a river.