Long and Changing Cross profiles

What does a 'long profile show?

A long profile shows how the height of a river changes along its course typically from its source, to where it meets the sea. 

How does a theoretical long profile change from the source to the mouth of the river?

There is generally a steep reduction in the height of a river from its source to a more gradual reduction in height further downstream to the mouth of the river. Traced on a diagram, the profile would have a concave appearance. 

However, long profiles are rare as there are a number of geographical factors that can interfere with this. For example, the land can be uplifted along the course of the river and can be affected by different bands of hard and soft rock crossing the path of the river. Also the sea level can change. 

How does a river change downstream? 

Upper: Shallow narrow channel

In the upper channel, the river carries a large load causing abrasion. At the high flow, there is some saltation and traction. Large boulders are transported by the river and some are in suspension. There is little solution. The large load is deposited. Mostly vertical erosion occurs with Hydraulic action and attrition. 

Middle: Wider, deeper channel

The channel is deeper and wider. Vertical erosion decreasing in importance. More lateral erosion and deposition occurs. Suspension is the main transportation type. Saltation and traction are still present. The land becomes smaller and less regular. 

Lower: Widest, Deepest channel

The channel is at it's widest and deepest, and may be tidal. Fine Material is deposited. There is only a little lateral erosion - deposition is more important than erosion. There is a large amount of load, but the size is very small and rounded. Suspension is the dominant process. 

What is the cross profile of a river? 

The cross profile of a river shows the shape of a river valley which will change and generally become wider and flatter at the mouth of the river.