WASSCE SHS
A river erodes, transports and deposits. The work it does, and the valley it leaves, change from the uplands to the mouth.
Erosion happens in four ways. Hydraulic action is the force of the water itself, forcing into cracks. Abrasion, also called corrasion, is the load scratching and scraping the bed and banks. Attrition is the load knocking against itself, so stones become smaller and rounder. Solution, or corrosion, is minerals dissolving. In the upper course the gradient is steep, the valley is often V shaped, and waterfalls form where hard rock overlies softer rock. The soft rock is cut away, the hard rock is undercut, and the fall retreats upstream.
In the middle and lower courses the gradient is gentler. The river may meander. On the outside of a bend the water is faster and erodes. On the inside it is slower and deposits, building a slip off slope. A flood plain is the flat land built of silt beside the channel. An ox bow lake is a meander cut off when the neck is breached. Use the course the question names. A waterfall answer placed in the lower course is in the wrong part of the river.
The four processes are a standard list. Give the action, not only the name. Hydraulic action is water. Abrasion is the load on the bed. Attrition is stones on stones. Solution is dissolving. For a waterfall, hard rock over soft rock, undercutting, collapse, retreat. A labelled sequence in words scores the same ideas a diagram would score. Do not say the river flows faster in the lower course as a rule. The gradient there is gentler.
These are practice questions in the style of the paper, with a model answer and a mark scheme. They are not a promise of what your paper will ask.
4 marks
Describe two processes of river erosion. (4 marks)
Hydraulic action is the force of moving water breaking the bed and banks. Abrasion is the river's load scraping the channel as it is carried along.
4 marks
Explain how a waterfall forms where hard rock lies over soft rock. (4 marks)
The soft rock below is eroded faster than the hard rock above. The hard cap is undercut and eventually collapses. The fall is left standing, and over time it retreats upstream, leaving a gorge.
2 marks
On a meander, where does erosion take place and where does deposition take place? (2 marks)
Erosion is on the outside of the bend, where the flow is faster. Deposition is on the inside, where the flow is slower.
More questions on this topic are inside GLearn, marked as you answer, with the reason written out. The first ones need no account.
Practise Geography freeHydraulic action is the force of the water. Abrasion is the load scraping the bed. Attrition is stones breaking each other down. Solution is rock dissolving. Name the action, not only the label.
Where hard rock lies over softer rock, the soft rock is worn away faster. The hard rock is undercut and collapses. The fall retreats upstream and a gorge is left below. This is typical of a steep upper course, not of a flat flood plain. All WASSCE Geography past questions