The long profile and changing valley cross profile of a river, fluvial processes of erosion, transport and deposition, erosional and depositional landforms, and hard and soft flood management.

What this dot point is asking

This is AQA GCSE Geography (8035) Paper 1, Section C (3.1.3 Physical landscapes in the UK). AQA expects you to describe the river long profile and how the valley cross profile changes downstream, explain the fluvial processes (erosion, transport and deposition), describe and explain erosional and depositional landforms from source to mouth, and evaluate hard and soft engineering for flood management. Rivers is one of three landscape options.

Long profile, cross profile and processes

A river flows from its source (often in the uplands) to its mouth (where it meets the sea). The long profile is a side view from source to mouth: it is steep and irregular in the upper course, becoming gentler and smoother through the middle and lower courses. The valley cross profile (a slice across the valley) changes alongside it: a narrow, steep-sided V-shaped valley with interlocking spurs upstream, widening to a broad, flat floodplain with a wide channel downstream. As the river moves downstream its discharge, velocity and channel size all increase, even though the gradient gets gentler, because more water is added by tributaries and the channel becomes more efficient.

Erosional landforms

Depositional landforms

In the middle and lower course the river meanders (winds from side to side). On the outside of each bend the channel is deeper and the flow faster, so erosion undercuts the bank to form a steep river cliff; on the inside the flow is slower and shallower, so deposition builds a gentle slip-off slope of sand and shingle. Over time erosion narrows the meander neck; during a flood the river breaks straight across it, and deposition then seals off the abandoned loop to leave an ox-bow lake. When the river floods, it spreads over the flat floodplain, loses energy and deposits its load: the coarsest material is dropped first right beside the channel, building up raised banks called levees, while finer alluvium (silt) spreads across the floodplain and keeps it fertile. Where the river meets the sea and deposits its remaining load faster than it can be removed, an estuary or delta forms.

Flood management

A hydrograph shows how a river's discharge responds to a storm; urbanisation, deforestation and impermeable rock all produce a "flashy" hydrograph (a steep rising limb and high peak) that increases flood risk. Management aims to reduce that risk:

• Hard engineering: dams and reservoirs (store water and release it slowly), embankments (raise the banks), channel straightening (speeds water through) and flood relief channels (such as the Jubilee River near Maidenhead). Effective and reliable but expensive and can simply shift the problem downstream.
• Soft engineering: flood warnings, floodplain zoning (keeping high-value building off the floodplain), afforestation (trees intercept rain and slow run-off) and river restoration (returning a straightened river to its natural, meandering course). Cheaper and more sustainable, but offer less certainty of protection.

A flood risk assessment weighs the cost of protection against the value of what is protected, so dense urban areas get hard defences while low-value farmland may be left to flood (or used as washland) to protect towns downstream.

Try this

Q1. Explain how a waterfall is formed. [4 marks]

• Cue. Soft rock erodes faster than hard rock, creating a step; undercutting forms an overhang that collapses, and the waterfall retreats upstream.

Q2. Explain how an ox-bow lake forms from a meander. [4 marks]

• Cue. Erosion narrows the meander neck, the river breaks through during a flood, deposition seals off the old loop, leaving an ox-bow lake.