Erosion within a river

Erosion Processes

Vertical erosion: This form of erosion deepens channels, aided by weathering mass movement and soil creep. Characteristics of a channel undergoing vertical erosion include large bed load comprising coarse hard particles. Potholes and deep narrow gorges are common.

Lateral erosion: This process increases a river’s width. A large sediment load has to be entrained for this process to work most effectively. It is responsible in conjunction with the processes of slope transport and mass movement for valley widening, meander migration and river cliff formation.

Headward erosion: This increases the length of a river. This process is most active in the source area of a river or where a bed is locally steep. It causes accelerated erosion and is commonly associated with waterfall formation.

Abrasion: Smaller material, carried in suspension, rubs against the riverbanks and wears it away.

Attrition: When bed load is moved downstream, boulders collide with other material and the impact break the rock into smaller pieces. In time, angular rocks become increasingly rounded in appearance.

Corrosion/ Solution: This occurs continuously and is independent of river discharge or velocity. When acids in the river dissolve rocks, which form the river’s bed/ bank. It is related to the chemical composition of the water e.g. the concentration of carbonic acid and humic acid.

Hydraulic action: The sheer force of the turbulent current hits riverbanks, pushes water unto cracks. The air in the cracks is compressed, pressure is increased and over time the back will collapse. Cavitation is a rare form of hydraulic action and the sudden and violent implosion of gas bubbles caused by this process shatters banks extremely rapidly. The resultant shockwaves hit and slowly weaken the banks. This is the slowest and least effective process.

Corrasion: Corrasion occurs when the river picks up material and rubs it along its bed and banks, wearing them away by abrasion. This process is most effective during times of flood and is the major method by which the river erodes both vertically and horizontally. If there are hollows in the riverbed, pebbles are likely to become trapped. Turbulent eddies in the current can swirl pebbles around to form potholes. This form of erosion occurs most often during times of higher river flow, bed load being used as an abrasive agent, scratching and scraping of the solid bedrock.