C2 Fluvial Processes

Characteristics of Upper Course

• V shaped valley, narrow and deep

• Large sediments, predominantly bedload

• Erosion > deposition

Middle Course

• Wider valley with gentler sides

• Smaller sediments, consists of bedload, suspended and dissolved load

• Lateral erosion > Vertical erosion

Lower Course

• Widest and shallowest valley

• Very small/fine sediments, mainly suspended and dissolved load

• Deposition > Erosion

River capacity VS Sediment load

Erosion: RC > S
Deposition: S > RC

Erosion processes

1. Corrasion

   1. Coarse fragments of rock are entrained along the channel floor, scour the channel and undermine banks and valley slopes — extreme form: potholing due to strong eddy motions

2. Corrosion

   1. Chemical dissolving of carbonate rocks

3. Cavitation

   1. Formation and collapse of bubbles in water, as bubbles burst microjets are produced at high velocities that hammer the river bed or banks

Directions of Erosion

1. Vertical downcutting

2. Lateral erosion

3. Headward erosion

Transportation processes

1. Traction

   1. Coarse bedload move intermittently by sliding along the stream bed

2. Saltation

   1. Skipping motion of sand particles in a cumulative process

3. Suspension

   1. Fine particles are carried along by turbulence

4. Solution

   1. Soluble materials that dissolve in water

River capacity VS competence

Capacity: determined by transport velocity

Competence: determined by maximum size of load that river can transport

Hjulstrom Curve

Shows velocities needed for entrainment and movement of particles

Conditions for deposition

1. Excessive load of high calibre (load > velocity)

2. Deceleration of flow

Factors influencing Fluvial Processes

CGSRVH

• Climate (rainfall)

• SGC (permeability)

• Relief (steep vs gentle)

• Vegetation

• Human

Channel Level

• Type of channel flow

• Channel roughness

• Channel velocity