River processes and landforms, flood risk, hydrographs and management.
Notes and quizzes readyOptional · choose 2 of 3
Named examples on this page are revision choices. Use your school’s examples if they differ.
Revise the key ideas
Profiles and river processes
A river's long profile shows how height changes from source to mouth. It is usually steep near the source and becomes gentler downstream, giving a broadly concave shape.
In the upper course, vertical erosion deepens a narrow valley. Farther downstream, lateral erosion widens it, and a broader floodplain commonly develops.
Channel width, depth and discharge generally increase downstream as tributaries join. The bedload often becomes smaller and rounder through attrition and sorting, although local conditions can interrupt these trends.
Hydraulic action is erosion by the force of water. Abrasion is the bed and banks being worn by transported sediment. Attrition makes transported particles smaller and rounder as they collide.
Solution dissolves soluble minerals in rocks. Vertical erosion cuts down into the bed; lateral erosion attacks the banks and widens a valley.
Traction rolls large particles along the bed. Saltation bounces smaller particles; suspension carries fine sediment in the water; solution carries dissolved substances.
Deposition occurs when a river loses the energy needed to carry some of its sediment. This can happen when flow slows on a floodplain, enters still water or discharge falls.
Upper-course landforms
Interlocking spurs form where a river winds around projecting hillsides while mainly eroding downwards. Weathering and mass movement help create the steep sides of a V-shaped valley.
A waterfall can develop where resistant rock overlies less resistant rock. Faster erosion of the softer rock creates a step and a plunge pool; abrasion and hydraulic action enlarge the pool.
Undercutting leaves an unsupported overhang, which collapses. Repeated collapse makes the waterfall retreat upstream, leaving a steep-sided gorge.Waterfall retreat. Undercutting and collapse move the falls upstream. The diagram simplifies the rock structure and is not a measured section of High Force.
At a meander, faster flow near the outside bend causes erosion and a river cliff. Slower flow near the inside bend deposits sediment, building a slip-off slope. Helical flow helps move sediment across the channel.
Erosion can narrow a meander neck. During high flow the river may cut through, taking a shorter route; deposition blocks the old loop's ends, leaving an ox-bow lake.
Floodplains develop through lateral channel movement and deposition during floods. Repeated flooding leaves layers of sediment across the valley floor.
Natural levées are raised banks beside a channel. When floodwater spills over, it slows and deposits coarser material first near the banks, while finer material travels farther across the floodplain.
An estuary is the tidal mouth of a river where freshwater meets seawater. Tides, river flow and sediment deposition can create mudflats and salt marshes.
Flood risk and hydrographs
A flood occurs when water covers land normally dry, often because discharge exceeds channel capacity. Discharge is the volume of water passing a point each second, measured in m³/s.
Heavy or prolonged rain increases water input. Saturated ground, frozen ground or impermeable rocks reduce infiltration, sending more water rapidly towards channels.
Steep slopes encourage rapid runoff. Urban surfaces and drains can speed water into rivers; removing vegetation can reduce interception and water storage.
A storm hydrograph shows river discharge changing after rainfall. Peak discharge is the highest flow, and lag time is the time between peak rainfall and peak discharge.Rainfall and river response. Bars show relative rainfall and the line shows relative discharge. There are no numerical units because these are separate normalised schematic series.
A short lag time and high peak often indicate a rapid catchment response and greater flood risk. Basin size, shape, rainfall pattern and antecedent conditions (how wet it was beforehand) also matter.
Hard engineering
Dams and reservoirs can store floodwater and release it gradually. They may also supply water or electricity, but are costly, flood land and alter downstream sediment and habitats.
Channel straightening can move water through a location faster, but may increase flood risk downstream and reduce habitat diversity.
Embankments increase the amount of water held within a channel. They need maintenance, and failure or overtopping can cause dangerous flooding.
Flood relief channels divert some flow away from vulnerable areas. They require land and careful design so they do not shift risk to another community.
Soft engineering
Flood warnings and preparation help people move belongings, evacuate or use barriers. Warnings reduce harm but do not prevent the river from rising, and people need time and support to act.
Floodplain zoning limits vulnerable development in high-risk areas. It avoids future exposure but can restrict building opportunities and does not protect existing homes by itself.
Planting trees can increase interception, infiltration and surface roughness, slowing some runoff. Its effectiveness depends on location and storm conditions; it cannot guarantee protection from every extreme flood.
River restoration can reconnect a river with its floodplain and create space to store water. It can benefit habitats but may require changes in land use and compensation.
Evaluate a scheme using social, economic and environmental effects. Ask which places gain protection, whether risk moves elsewhere, and how costs and benefits change over time.
UK river valley example: the Tees
The River Tees rises on the eastern side of the Pennines and flows towards the North Sea. Upper Teesdale has steep valley sections and waterfalls, while the lower river has broader lowland areas and an estuary.
At High Force, the Tees flows over resistant Whin Sill dolerite above older sedimentary rocks. Erosion creates the waterfall and gorge, and the falls retreat over time. Real geology is more complex than a two-layer textbook sketch.
Near Yarm, bends illustrate meandering in the lower valley. Lateral erosion and deposition help move bends over time; nearby floodplain land is exposed when river levels exceed capacity.
At Teesmouth, river sediment, tides and marine processes shape mudflats and salt marsh. Industrial development and management also influence the modern estuary, so it is not an untouched natural landscape.
UK flood-management example: the Jubilee River
The Jubilee flood relief channel opened in 2002 as part of the Maidenhead, Windsor and Eton flood alleviation scheme. It addresses flood risk from the Thames to homes, businesses and infrastructure in these communities.
The channel is 11.6 km long. Gates at Taplow divert some Thames water through it during high flows; the water rejoins the Thames at Datchet. The wider scheme reduces risk to about 3,000 properties.
Lower flood risk benefits households and businesses and reduces potential disruption. Building and maintaining the channel has substantial costs, and protection is limited by the scheme's design and capacity.
The channel includes naturalistic habitats and paths, providing environmental and recreational benefits. Gates, weirs and channel works still modify flows and require ecological care and maintenance.
Communities outside the scheme remain at risk, creating questions about how investment is shared. The Environment Agency states that the Jubilee does not adversely affect upstream or downstream communities; do not present downstream flood damage as proof that the channel caused it.
This example shows why social, economic and environmental evaluation matters: protection, cost, access, habitats and the limits of coverage all need consideration.
Test yourself
50 questions · Random sets of 10. These quick checks support revision; practise longer explanations and justified judgements too.
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