River Processes

1. River Processes 5F Geographers 2013

2. Erosion Transportation Deposition

3. Erosion! Corrasion (abrasion) Corrosion (solution) Attrition HydraulicAction

4. Transportation Traction Saltation Suspension Solution

5. 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

6. 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

7. Attrition • Is the break up of rocks into smaller pieces due tocollsions between them • Whenthe 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

8. HydraulicAction • Isthe power of the water alone breaking down the bank and bed of the river • Thestronger and faster the river, the more hydraulic action occurs

9. 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

10. 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.

11. 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

12. 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

13. Deposition • When thesolid materials being transportedby theriver aredeposited 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

14. 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.