Physical geography · GCSE Geography
Rivers
Erosion, transport and deposition from source to mouth, the landforms they create, and how we manage flood risk.
Energy decides: high energy carves, low energy dumps.
The important bits
What you need to know
- 1
A river’s long profile steepens in the upper course and flattens towards the mouth. Discharge usually increases downstream as tributaries join. Velocity is not simply “faster at the source”: channel efficiency matters.
- 2
Erosion: hydraulic action, abrasion, attrition, solution — same names as coasts, different fluid. Vertical erosion dominates upland; lateral erosion dominates meanders.
- 3
Transport: traction, saltation, suspension, solution. When energy falls (inside bend, below a waterfall, when a river meets the sea), deposition begins with the heaviest load first.
- 4
Upper-course landforms: V-shaped valleys, interlocking spurs, waterfalls and gorges (High Force on the Tees: hard Whin Sill over softer limestone/sandstone). Middle/lower: meanders, oxbow lakes, floodplains, levees, estuaries.
- 5
Meander mechanics: fastest flow on the outside bend (thalweg) erodes a river cliff; slow flow on the inside deposits a slip-off slope. Necks narrow until a flood cuts through; the old loop becomes an oxbow.
- 6
Flooding is physical plus human: prolonged rain, saturated or impermeable geology, steep slopes, snowmelt, plus urbanisation (drains, tarmac), deforestation, and building on floodplains. Hydrographs get flashier in towns.
- 7
Boscastle 2004 is a compact UK case: intense rainfall, steep catchment, saturated ground, debris-blocked channel, then later management (widened channel, debris screens). Somerset 2014 shows prolonged floodplain inundation and political row over dredging.
- 8
Management: hard (dams, embankments, channelisation, flood-relief channels) versus soft (warnings, land-use zoning, afforestation, river restoration). Upstream storage can protect a town and flood a valley — another winners-and-losers story.
Go deeper
High Force and the waterfall logic
A waterfall needs a cap of resistant rock over a weaker band. On the Tees, the Whin Sill (dolerite) sits above limestone and sandstone. Hydraulic action and abrasion undercut the softer rock; the cap collapses; the waterfall retreats, leaving a gorge. Plunge-pool erosion is violent because kinetic energy concentrates. This is the same structural idea as a coastal stack — weakness plus energy — in a vertical rather than horizontal frame. If a question gives an OS map with close contours crossing a river in the uplands, look for the waterfall symbol and think cap rock, not “the river got tired”.
Go deeper
Why cities make floods flashy
A storm hydrograph plots discharge against time after rain. Urban catchments have short lag times and high peaks because tarmac and storm drains skip soil storage and rush water to the channel. Deforestation and compacted farmland do a milder version of the same thing. Floodplain building puts people in the way of the overflow that used to be the river’s natural safety valve. Boscastle’s 2004 peak was about intense rain in a steep, saturated, debris-choked valley — physical first — but any urban 9-marker should add land use. Management that only raises walls in town without slowing water upstream often passes the flood to the next parish.
See the idea in action
Question: explain how an oxbow lake forms. Start with a meander: outer bend erosion, inner bend deposition, neck thinning. During high discharge the river cuts the neck, taking the steeper, shorter path. Deposition seals the ends of the abandoned loop. Locate if you can (a named meander belt on the Tees or Mississippi). End with the landform sitting on the floodplain as a crescent lake that may dry into a meander scar.
Exam technique
Turn knowledge into marks
Upper, middle and lower course is a scaffold, not a law. Use it to organise landforms, then mention that a single valley can show mixed features after rejuvenation or hard-rock bands.
Common mistakes
Do not give these marks away
- 01
Saying rivers are fastest at the source because the slope is steep, ignoring friction in a shallow, rocky channel.
- 02
Forming waterfalls with no hard/soft rock contrast.
- 03
Listing flood management strategies with no link to a named flood or to who pays.
Where is erosion strongest in a meander?
AOn the inside bend, where the slip-off slope builds
BOn the outside bend, where the current is fastest
CEvenly across the bed at all discharges
DOnly at the waterfall plunge pool
Show the answer
On the outside bend, where the current is fastest. The thalweg swings to the outer bank, so hydraulic action and abrasion cut a river cliff. The inner bend is slower and deposits the point bar or slip-off slope.
Quick questions
If this is the bit you searched
What is a levee?
A raised bank of coarser sediment deposited next to the channel during floods, when the river first loses energy as it spills onto the floodplain. Artificial embankments copy the idea, not always wisely.
Is dredging the solution to UK floods?
It can increase channel capacity locally and is politically popular. It is expensive to repeat, can damage habitats, and does not store water upstream. Somerset 2014 showed how contested the evidence and interests are.