1.3 River channel processes and landforms Flashcards
List and define main 3 types of river processes
- Erosion: involves the wearing away of rock and soil found along the river bed and banks. Erosion also involves the breaking down of the rock particles being carried downstream by the river.
- Transportation: the process where sediments are are entrained and moved by the water
- Depostion: the geological process in which sediments, soil and rocks are added to a landform or land mass - These processes require energy
List and define 4 types of erosion (upper and middle course)
- Abrasion: rocks carried along by the river wear down the river bed and banks. Mechanical impact
- Hydraulic action: the force of the river against the banks causes air to be trapped in cracks and crevices (cavitation). The pressure weakens the banks and gradually wears it away
- Attrition: rocks carried by the river smash together and break into smaller smoother particles
- Solution: soluble particles are dissolved into the river
Factors affecting rate of erosion
- Load
- Velocity
- Gradient
- Geology
- pH
- Human impact
Difference between erosion in the upper course and lower course
- Upper course: tends to be more vertical, mainly abrasion and hydraulic action - Lower course: more lateral and more frequent, happens outside of the bend, mainly abrasion and attrition
List 4 types of transportation (middle course)
- Suspension
- Saltation
- Traction
- Solution
- 2 factors that determine whether a particle is transported or not: size of particle and velocity of water
Define suspension
smallest particles such as silts and clays are carried as a suspended load
Define saltation
sands, gravel and small stones are being transported by a series of hop. Small particles are thrust up from river bed and fall back to the bottom when they dislodge other particles upwards => causes more bouncing
Define traction
large particles are shunted,dragged and rolled along the bed as a tracted load. Mainly happens during a period of high discharge
Define solution (transportation)
In areas of calcerous rocks, materals are carried in solutionas a dissolved load
Define capacity
The largest amount of debris that a stream can carry
Define competence
The diameter of the largest particle that the river can carry at a given velocity
Causes of deposition (middle and lower course)
- a shallowing gradient which decreases velocity and energy
- an increase in friction between water and channel
- a decrease in the volume of water in channel
- an increase in size of loads
- when river floods
Factors affecting the energy available
- Weight and velocity of water/ Discharge
- Gradient - height above sea level (greater potential energy)
- Channel roughness: amount/size of rocks and vegetation
- Shape of river (Meander/straight)
- Hydraulic radius (cross section/wetted perimerter) the higher the ratio the more effective a river is
The long profile (upper, middle and lower course)
- Upper: Vertical erosion (hydraulic and attrition), transportation (mostly traction)
- Middle: Lateral erosion (abrasion and attrition), transportation (suspension and traction), deposition on slip off slopes.
- Lower: Transportation (suspension and solution), mostly small particles deposited. Levées and slip off slopes formed.
What does the Hjulstrom curve show?
Shows the relationship between the 3 river processes and the velocity for particles of different size