River Processes

Erosion:

Headland: makes river longer using throughflow and surface runoff. Valley head. Vertical: Deepens. Upper course. Lateral: widens, middle/lower.

5 ways in which erosion happens:

1) Hydraulic action: pressure of water breaks rock particles away from the bed & banks. Strongest in rapids & waterfalls.

2) Abrasion: eroded rock scrapes/rubs agains b&b, removes material. Most common.

3) Attrition: Smash into each other. Small pieces. Don't erode, just smoothens.

4) Cavitation: Air bubbles implode. Causes shockwaves that break pieces of rock of b&b.

5) Corrosion: Dissolution of rock due to chemical processes. CO2 dissolves to form a weak acid. Reacts with some rock to break down.

Process of eroded material being carried in a river.

Velocity of river provides energy to transport material. The material it carries is called its load. It can be carried in 4 ways:

1) Solution: if they can dissolve then they are carried in the water.

2) Suspension: very fine material is whipped up by turbulence and is carried. This is the most common type.

3) Saltation: large particles can't be carried, so the water force causes them to bounce along the river bed.

4) Traction: very large particles e.g. boulders are pushed along the river bed by the force of the water.

Material that is transported by traction or saltation is called the river bedload.

Process of dropping eroded material.

It happens when the river loses energy. It drops its load. Can happen in 5 ways:

1) Reduced rainfall = less discharge. The river slows down, so energy is lost.

2) Increased evaporation.

3) Friction. Shallow areas that are close to the banks, reduces the speed.

4) Bottlenecks. The river is forced to slow down.

5) When the river meets the sea. The sea absorbs the energy.

Total amount of material a river can carry. 

Capacity is total load that a river can transport at a time.

It can be divided into different categories  according to particle size. These can vary from silt to boulders.

Competence is maximum particle size that a river can transport  at any time.

Shows the relationship between river velocity and competence. Also shows how the river processes vary with velocity.