River Processes
5F Geographers 2013
Erosion
Transportation
Deposition
Erosion!
Corrasion (abrasion)
Corrosion (solution)
Attrition
Hydraulic Action
Transportation
Traction
Saltation
Suspension
Solution
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 pick
up material from the river bed
(entrainment). As the river discharge
and velocity increases so does the
amount of load it can transport
(capacity) increase and the largest size
of material it can transport increase
(competence).
The greater the river velocity the larger
the material that can be transported.
When the river slows down the Settling
velocity curve shows in what order the
different sized materials are deposited.