The way rivers shape the land depends on how fast they flow and the sort of rocks they flow over. In its upper course in the mountains, the river carves out a narrow, steep- sided valley which is usually in the shape of the letter V. The river bed has a steep slope, or gradient, and the water cuts down into the land because the force of the water breaks up the rocks beneath it. Loose pebbles, stones and bits of grit bounce along the river bottom, rubbing against the rocks and wearing them away even more.

Braided rivers look rather like a plait in a person's hair. They appear in places where valley slopes are steep, or in dry areas where there is a lot of sand and gravel. The river threads its way around bars of gravel, sand and other coarse sediment. In the upper river, braiding usually happens where a river works loose a lot of material that it cannot carry away.

Picture: Tony Bomford