River Processes

Geomorphic processes (those processes operating at or near the earth's surface) that operate in the river system.

1. Weathering

        - Biological

        - Chemical

        - Physical / Mechanical

Biological - animals, plants and humans burrow or trample the soil and so cause the break up of the surface.

Chemical - slightly acidic water (rain or river) reacts with the rocks and dissolves them eg limestone or chalk as these rocks are Calcium carbonate (CaCo3).

Physical / Mechanical - eg Freeze thaw. Diurnal temperature change above and below freezing causes water to freeze and then thaw in cracks in the rock. Freezing widens the cracks as the water expands, on melting more water can enter the crack and then freeze again, as this is repeated. 

2. Processes of Erosion

• Hydraulic Action - the shear power of the water erodes the river bed and banks as water and air is forced into weaknesses in the rock.

• Abrasion / Corrasion - the river uses the load of the river to abrade or scrape away at the bed and the banks

• Attrition - pebbles and rocks knock into each other and break into smaller pieces (tools for abrasion)

• Corrosion / Solution - minerals such as Calcium in the rock are dissolved by the slightly acidic river water.

3. Processes of Transport

• Traction - the largest material, such as boulders in the river is rolled along the bed

• Saltation - smaller material, such as gravel (too large for suspension) bounces along the bed

• Suspension - silt is carried in the water. If there is a lot of suspended sediment then the river will look 'muddy'.

Tsavo River, Tsavo West

• Solution - dissolved material is carried by the river. Particularly in limestone or chalk areas.