A river changes shape as it flows from its source (where a river starts) to its mouth (where a river flows into a sea or lake). The shape of the long profile (a slice through the river from source to mouth) shows how the rivers gradient, height, energy and load changes due to erosion processes such as abrasion, cavitation, attrition, hydraulic action and corrosion as well as how the rivers deposition rates fluxuate.
The source of the mouth is the part of the drainage basin where the river starts. It is usually high above base level, such as a mountain, and has a very steep gradient. As a river flows down steep slopes the water performs head ward and vertical erosion. This form of erosion cuts down towards the river bed and carves out steep-sided V-shaped valleys. This type of erosion is mainly abrasion which is the rubbing or scouring of the bed and banks by the sediment being carried along by the river. Hydraulic action is also present – this is the movement of sediment by the frictional drag of moving water. The channel is therefore very rough which causes turbulence so large angular bed load is scraped along the bed. This part of the river mainly transports large particles carried by traction or saltation during high energy conditions. Traction is large materials such as boulders and cobbles that are too heavy to be picked up by the current, so are rolled along the river bed, and saltation is the dissolved load (weak acids e.g. carbonic acids from precipitation, may act on more soluble rocks e.g. limestone and chalk and gradually remove material in solution). Saltation usually happens after the erosion proves known as corrosion. This is when some rocks dissolve into the water and are carried away. This process is most common where carbonate rocks such as limestone and chalk re exposed in the channel. At this point, the rivers deposition rates are very little, as the river is