The action of rivers

The action of rivers


* Rivers are the most widespread agents of denudation and deposition.
* The amount of erosion, transportation and deposition of the river is dependent on the energy of the river which in turn is dependent on:
o The gradient of the slope
o The volume of water
o The shape of the channel
* Generally, the volume of the river increases from the source to the mouth. Exceptions may be such as when the river passes through a hot desert.
River Erosion
* River erosion involves 4 processes:
1. Abrasion/Corrasion: The wearing away of the sides and the bed of a river by the impact of the load.
2. Hydraulic Action: Erosion by the force of moving water.
3. Atrrition: The breaking down of the load by particles hitting against each other.
4. Solution/Corrossion: When minerals dissolve in water.
River Transport
* The material a river carries is referred to as its load.
* A river transports its load in 4 main ways:
1. Traction: The rolling of huge particles along the bed.
2. Saltation: The bouncing of particles on the bed of the river
3. Suspension: The movement of particles held up by river turbulence.
4. Solution: The movement of particles dissolved in water.
River Deposition
* Deposition takes place when a river has insufficient energy to transport its load. It takes place at all stages of a river.
* Larger particles are deposited first.
* Deposition is greatest in the lower course of a river. It is also greater during floods.
* Deposition will occur when the speed of a river is reduced. This may happen in:
o areas with a sudden increase in gradient
o the inside of meanders
o places where the river enters a sea/lake.
The Development of a River Transport System
* Surface run-off forms small streams.
* These streams join together to form larger streams.
* These largers streams join to form a river.
* The junction of 2 streams is called the confluence. When a smaller flow joins a larger flow it's called a tributa