River Processes Geography IGCSE - Revision Notes

Erosion

Erosion: Wearing down of surfaces.
Four processes that change the river channel:
- Hydraulic action: Force of water removing material from bed and banks.
- Abrasion: Materials carried by river scraping away the banks and bed.
- Attrition: Material hits each other, becoming rounder and smaller.
- Corrosion (solution): Rocks dissolved in slightly acidic water.
Vertical erosion: Dominant in upper course, increases river depth.
Lateral erosion: Dominant in middle/lower courses, increases river width.

Four processes:
- Traction: Larger rocks rolled along riverbed.
- Saltation: Smaller material bounces along riverbed.
- Suspension: Lighter material carried within flow.
- Solution: Materials dissolved in water.

Deposition: River drops materials it can't carry.
Causes:
- Reduced discharge.
- Decreased gradient.
- Slower flow in bends or shallower areas.
- Entering sea, ocean, or lake.
Bedload: Heaviest material deposited first.
Alluvium: Lighter materials carried further.
Bradshaw Model summarizes these changes.

Shows changes in river gradient from source to mouth.
Concave shape:
- Source: Upland area.
- Upper course: Steep, uneven surface.
- Middle course: Gradient decreases.
- Lower course: Almost flat.

Cross-sections from one bank to another.
Upper course:
- Shallow, steep sides, narrow.
- Low velocity, large bedload.
- Rough bed, high friction, vertical erosion.
Middle course:
- Deeper, gentle sides, wider.
- Greater velocity, material decreases in size.
- Smoother bed, lower friction, lateral erosion.
Lower course:
- Deeper, flat floodplains, wider.
- Greater velocity, mostly sediment and alluvium.
- Smooth bed, lowest friction, deposition dominant.