River Channel Processes Flashcards
What is erosion?
Erosion is:
- The break-up of rocks and soil.
- Due to the action of moving water and solid particles.
What is transportation?
Transportation is:
- The movement of solid particles from the site of erosion to the site of deposition.
What is deposition?
Deposition is:
- The dropping of solid particles as sediment.
- Within a river or on the sea floor.
What factors determine a river’s total energy?
- The mass of water in the channel.
- The height of the river above sea level (base level).
- The steepness of the channel.
- The amount of friction in the channel.
Which processes are the dominant processes in high and low energy rivers?
High Energy
- Erosion
- Transportation
Low Energy
- Deposition
What are the 4 main erosional processes?
- Hydraulic Action
- Abrasion (corrasion)- the pebbles being transported wear away the bed and banks.
- Attrition- particles get hit together making them rounder, smoother and reduced in size.
- Corrosion
Which direction of erosion dominates each part of the rivers course?
Upper Course - Vertical
Middle Course - Vertical & Lateral
Lower Course - Lateral
What processes use up a rivers energy?
- Erosion
- Transportation
- Friction (drag between water and channel)
What are the main sources of sediment that form a rivers load?
- Sediment washed into the river from the sides of the valley.
- Sediment eroded from the bed and banks of the river.
What are the 4 types of river transportation?
- Traction - rolling large stones and boulders along the river bed.
- Saltation - bouncing small stones along the river bed.
- Suspension - small sand and silt particles carried along in the flow of the river.
- Solution - dissolved minerals carried within the moving water.
What is the definition of capacity?
Amount of material that the river can carry i.e. the total volume of the load.
What is the definition of competence?
Competence is the size of the largest particle that the river can carry.
What is a Hjulström graph?
A Hjulström graph shows the relationship between river velocity, particle size (competence) and processes of erosion, transportation and deposition
Why are small silk/clay particles more difficult to transport than sand?
Cohesion - small clay/silt particles tend to stick together, meaning that larger velocities are required to lift them.
Why do load particles get smaller the further downstream the river travels?
The rivers velocity is usually faster in the upper course and slower in the middle and lower courses.
This drop in velocity leads to a drop in competence as the river moves down valley.
This leads to progressive deposition of the largest particles.
Attrition - during load transport acts to break large particles in the flow into small pieces.
