All rivers have an upper, middle and lower course. The long profile of a river is basically the changes in gradient at these different stages in the river, every river is trying to achieve a smooth, concave, long profile.

The river begging in the upper course, normally in the hills and mountains. Here the river is smaller, the flow is fast and load and water volume are slow. The river erodes a v-shaped valley. At this stage the channel is inefficient as it has a large channel surface compared with channel surface area. There will be more friction as more water touches the river bed. A steep gradient is needed to maintain the rivers energy levels. The path of the river is fairly straight.

A river can erode the soil...