River Processes

5F Geographers 2013

Erosion

Transportation

Deposition

Corrosion (solution)

Hydraulic Action

Corrasion (abrasion)

Attrition

Erosion!

Saltation

Solution

Traction

Suspension

Transportation

Corrosion/Solution

• Particles dissolve in water• Maximum rates occur in fast flowing rivers• In the lower course, a large amount of the

load is carried as the solute load

Corrasion/Abrasion

• The force of the flowing pushes stones and pebbles along the river bed and against the river bank. This causes some of the river bed and bank to be eroded away

• This erosion process happens when there is a lot of energy in the river flow

Attrition

• Is the break up of rocks into smaller pieces due to collsions between them

• When the velocity of the river is higher, more rocks are moved, and there are more collsions

• This process happens almost entirely in the upper and middle courses of the river

• The sands, clays, and silts found in the lower course of the river are a product of this type of erosion

Hydraulic Action

• Is the power of the water alone breaking down the bank and bed of the river

• The stronger and faster the river, the more hydraulic action occurs

Traction

• The force of the river rolls rocks along the river bed• The largest boulders can only be

moved in times of flood when the competence of the river increases hugely

Saltation

• Is a “leap frog” movement in which pebbles bounce along the river bed

• The pebbles are too light to be rolled (traction) but too heavy to be carried in suspension.

Suspension

• This is when sold particles are light enough to be fully suspended in the flow of the river

• These particles would only de deposited on the river bed or floodplain when the river had slowed down to the settling velocity for the size of the particle

Solution

• Solution is when the particles are dissolved in the water

• These particles are too small to de deposited even if the river stands still

• Material carried in this way is called the solute load. The solute load reaches the sea where it helps to keep sea water salty

Deposition

• When the solid materials being transported by the river are deposited in the river channel or on the floodplain

• It occurs when the river loses energy. As river velocity decreases the largest materials are deposited first

The Hjulstrom curve

The river must have energy to pickup material from the river bed (entrainment). As the river discharge and velocity increases so does theamount of load it can transport(capacity) increase and the largest sizeof material it can transport increase(competence). The greater the river velocity the largerthe material that can be transported.When the river slows down the Settlingvelocity curve shows in what order the different sized materials are deposited.