How river landscapes change along the long profile and the erosion, transport and deposition processes that form fluvial landforms; storm hydrographs and the factors that affect them; rising flood risk; and the costs and benefits of hard and soft flood management.

What this dot point is asking

This is Edexcel GCSE Geography B (1GB0) Paper 2, Section A (Topic 4, The UK's evolving physical landscape), the river processes and pressures depth study. Edexcel expects you to explain how river landscapes contrast between the upper, middle and lower courses and how channel shape, gradient, discharge, velocity and sediment change along a named UK river; the erosion, transport and deposition processes that form fluvial landforms (meanders, waterfalls, flood plains, levees, ox-bow lakes, deltas); how storm hydrographs and lag times are affected by physical factors; the rising risk of river flooding; and the costs and benefits of hard and soft flood management.

The long profile and fluvial processes

A river's character changes from source to mouth along its long profile.

The river shapes the land through erosion (hydraulic action, abrasion, attrition, solution), transport (traction rolling, saltation bouncing, suspension carrying fine sediment, solution dissolved load) and deposition when it loses energy. A meander forms because the river erodes the outer bank (forming a river cliff) and deposits on the slower inner bank (a slip-off slope); when the neck is narrowed and the river cuts through during a flood, deposition seals off the loop to leave an ox-bow lake.

Storm hydrographs

A storm hydrograph shows how a river responds to a rainfall event.

Flood risk and management

River flood risk is rising because of more frequent and intense storms (linked to climate change) and land-use change. Urbanisation is a major factor: impermeable concrete and tarmac stop infiltration, so rain runs off quickly into drains and rivers, shortening lag time and raising peak discharge. Deforestation has a similar effect by reducing interception.

Flooding is managed with two approaches. Hard engineering uses built defences: flood walls and embankments (raise the channel banks), and flood barriers (close off rivers or estuaries during surges). These are effective and protect property but are expensive and can look unnatural, and they may shift the problem downstream. Soft engineering works with natural processes: flood plain retention (keeping the flood plain free of building so it can flood safely) and river restoration (returning a straightened river to a natural, meandering course to slow flow). These are cheaper and more sustainable but offer less certain protection to dense settlement. A cost-benefit analysis weighs the value of what is protected against the cost.

Try this

Q1. 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 then seals off the old loop, leaving a curved ox-bow lake cut off from the main channel.

Q2. Explain one physical factor that shortens the lag time on a storm hydrograph. [3 marks]

• Cue. Impermeable geology, steep slopes, a circular basin shape, or already-saturated (antecedent) ground all speed runoff to the river, shortening lag time and raising peak discharge.