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Upper course (steep gradient)
- Vertical (downward) erosion
- Source; Tributaries; V-Shaped valley; Interlocking spurs; Waterfalls; Rapids; Gorges
Middle course (gentle gradient)
- Lateral (sideways) erosion starts; Transportation
- River beaches (slip off slopes); Meanders; River cliffs
Lower course (very low gradient)
- Flood plain; Ox-bow lakes; Levées; Delta; Estuary
- Wearing away of the river bed and banks by the load hitting against them.
- Wearing down of the load as the rocks and pebbles hit the river bed and each other.
* Hydraulic Action
- Breaking away of river bed and banks by the sheer force of the water getting into small cracks.
* Chemical Action (Corrosion)
- Water dissolves minerals from the rocks and washes them away.
* Traction -
Quite large stones can be rolled or dragged along the river bed by the force of the water.
- Small stones which the water cannot lift bounce off each other and are carried forward by the water above the river bed for short distances.
- If particles are small enough the river can lift them and carry them long distances.
- When the river dissolves minerals from the rocks they are carried in the water itself.
formation of a waterfall
- (a) River flows over an area where there are bands of softer and harder rocks,
- (b) softer rock is more quickly eroded,
- (c) the river undercuts the harder rock leaving an overhang,
- (d) the river forms a plunge pool below the waterfall,
- (e) overhanging rock is unsupported and falls into the plunge pool,
- (f) the waterfall is moved upstream,
- (g) as this process continues a gorge is cut back into the hillside.
formation of a vshaped valley
- the valley sides are steep so fragments of rock fall into the river by gravity
- the river has lots of energy in it's upper course and cuts downwards into the river bed by hydraulich action. the rocks it carries erode the bed banks by abrasion