Edexcel GCSE Geography A (1GA0) — The Physical Environment
Why do rivers in the Scottish Highlands behave completely differently from rivers in the South of England? The UK's temperate maritime climate drives a distinct regional divide in how rivers shape the landscape.
| Feature | North and West (Upland) | South and East (Lowland) |
|---|---|---|
| Climate | High precipitation (over 2,500mm annually) and lower temperatures. | Lower rainfall and higher average temperatures. |
| River Flow | Sustained periods of high river discharge and kinetic energy. | Higher evapotranspiration reduces discharge and energy. |
| Dominant Processes | High rates of vertical erosion (deepening channels). | Slower erosion rates; deposition is the dominant process. |
| Associated Landforms | V-shaped valleys and interlocking spurs. | Floodplains and meanders. |
Seasonal weather cycles also control how rock is broken down. In winter, low temperatures in upland areas trigger freeze-thaw weathering, where water enters rock cracks and expands by 9% when frozen. Unlike erosion, weathering breaks down rock in-situ and does NOT involve a moving medium transporting the material away. In summer, higher temperatures increase chemical weathering (like carbonation), while droughts can drastically lower discharge, causing rivers to lose energy and deposit their load.
The rain stopped days ago, so why is the river suddenly flooding today? The answer lies in the moisture already stored in the soil from previous weather.
When rain falls on previously saturated ground that has reached field capacity, the water cannot infiltrate the soil. Instead of moving slowly through the ground, the excess water travels rapidly as surface runoff over the land. This combination of antecedent rainfall and intense storm events creates "flashy" storm hydrographs, characterised by a steep rising limb and a short lag time. For example, antecedent rainfall in the Pennine catchments caused the soil around the River Ouse to reach field capacity, leading to a record-breaking peak discharge 5.4m above normal levels during subsequent storms.
This massive increase in river discharge significantly accelerates erosion. The increased volume and force of water trap and compress air in cracks along the banks, fracturing the rock through hydraulic action. The river can also transport a larger, heavier load, which grinds against the river bed like sandpaper in a process called abrasion.
The volume of water flowing through a channel is calculated using the river discharge equation:
Where:
Worked Example: Calculating River Discharge
Step 1: Identify the values given. A river is 5m wide with an average depth of 0.8m. Its velocity is 1.5 . Step 2: Calculate the cross-sectional area (). Step 3: Substitute into the equation to find .
A river might cut the base of a valley, but it takes gravity to build the familiar 'V' shape. Sub-aerial processes on the valley sides above the water line provide the sediment "fuel" that the river uses for further fluvial processes (erosion and transportation).
Heavy seasonal rain acts as a lubricant between soil particles, drastically reducing friction and increasing the weight of the valley-side material. This triggers mass movement, such as slumping (moving down in a block along a curved surface) or soil creep (extremely slow downhill movement). Mass movement is worse when permeable rock sits over impermeable rock, forcing the top saturated layer to slide.
The Formation of a V-shaped Valley:
A landscape that took thousands of years to form can be completely altered in a single weekend storm. Extreme weather is becoming a prominent driver of geomorphic change, with the UK experiencing 42 major storms between 2015 and 2020 compared to just 10 between 2010 and 2014.
During intense storms, rivers gain vastly increased power and surplus kinetic energy. This causes a temporary shift from vertical to lateral erosion. In the upper course, intense flood energy allows the river to undercut and "clip" the bases of interlocking spurs. This modification rounds off the sharp projections and widens the valley floor, while weathering creates scree slopes at their base.
In the middle and lower courses, lateral erosion allows a river to rapidly erode through a meander neck. Intense storms, like Storm Dennis in 2020, allow the river to adopt a shorter, straighter course, leaving behind an oxbow lake.
Conversely, sustained seasonal flooding modifies floodplains through vertical accretion. Each time the river overtops its banks, it deposits a new layer of alluvium, gradually increasing the floodplain's height. The sudden drop in velocity during an over-bank flood causes the river to immediately deposit its heaviest load close to the channel edge, building natural embankments called levees.
Students frequently confuse weathering with erosion. Weathering is the breakdown of rock in-situ (in one place, like freeze-thaw on valley sides); erosion involves the wearing away and removal of material by water.
In 8-mark 'Assess' questions, examiners expect you to weigh the importance of long-term climate (seasonal averages creating V-shaped valleys) versus short-term weather (extreme storms causing rapid meander cut-offs).
When describing storm hydrographs, using the precise term 'field capacity' to explain saturated ground will unlock higher-level marks than just saying the ground is 'soaked'.
To secure full marks on V-shaped valley formation, explicitly state that vertical erosion deepens the channel, while weathering and mass movement are responsible for widening the valley sides.
River discharge
The volume of water flowing through a river channel at a given point, measured in cubic metres per second (cumecs).
Evapotranspiration
The combined process of water evaporating from the ground and transpiring from plants into the atmosphere.
Vertical erosion
The downward wearing away of the river bed, which deepens the channel.
Deposition
The dropping of material being carried by a moving river when it loses energy.
Interlocking spurs
Projections of resistant rock that extend from alternate sides of a V-shaped valley, which a river is forced to flow around in its upper course.
Freeze-thaw weathering
A physical weathering process where water enters cracks in rocks, freezes and expands by 9%, forcing the rock apart.
Chemical weathering
The breakdown of rock in-situ through chemical reactions, such as carbonation dissolving limestone.
Field capacity
The point at which the soil is completely saturated with water and cannot absorb any more, leading to surface runoff.
Surface runoff
The rapid movement of excess water over the land surface when the ground is completely saturated or impermeable.
Antecedent rainfall
The amount of moisture already in the soil from previous precipitation, which dictates the ground's saturation level and flooding risk.
Lag time
The time delay between peak rainfall and peak discharge on a storm hydrograph.
Hydraulic action
The force of river water hitting the banks and bed, compressing trapped air in cracks and causing rock to fracture.
Abrasion
The wearing away of the river bed and banks by the river's load (sediment) scraping against them like sandpaper.
Cumecs
Cubic metres per second (), the standard unit of measurement for river discharge.
Sub-aerial processes
Processes occurring on the valley sides above the water line, primarily weathering and mass movement, which contribute material to the river.
Fluvial processes
Processes relating to the work of a river, including erosion, transportation, and deposition.
Mass movement
The downhill movement of weathered material (soil and rock) under the influence of gravity.
Slumping
A type of mass movement where a block of land moves downwards along a curved slip surface.
Soil creep
The extremely slow downhill movement of soil particles due to gravity, often caused by the expansion and contraction of wet and dry soil.
Lateral erosion
Erosion focused sideways into the river banks, which widens the river channel and valley floor.
Scree slopes
Accumulations of weathered rock fragments found at the base of steep valley sides or spurs.
Oxbow lake
A curved lake formed at a former meander where the main stream of the river has cut across the narrow neck and no longer flows around the loop.
Vertical accretion
The continuous build-up of sediment layers on a floodplain during repeated flood events.
Levees
Natural, raised embankments along the edges of a river channel formed by deposition during flood events.
Weathering
The breakdown and decay of rock in-situ (without movement).
Transportation
The movement of eroded material (load) by a river.
Put your knowledge into practice — try past paper questions for Geography A
River discharge
The volume of water flowing through a river channel at a given point, measured in cubic metres per second (cumecs).
Evapotranspiration
The combined process of water evaporating from the ground and transpiring from plants into the atmosphere.
Vertical erosion
The downward wearing away of the river bed, which deepens the channel.
Deposition
The dropping of material being carried by a moving river when it loses energy.
Interlocking spurs
Projections of resistant rock that extend from alternate sides of a V-shaped valley, which a river is forced to flow around in its upper course.
Freeze-thaw weathering
A physical weathering process where water enters cracks in rocks, freezes and expands by 9%, forcing the rock apart.
Chemical weathering
The breakdown of rock in-situ through chemical reactions, such as carbonation dissolving limestone.
Field capacity
The point at which the soil is completely saturated with water and cannot absorb any more, leading to surface runoff.
Surface runoff
The rapid movement of excess water over the land surface when the ground is completely saturated or impermeable.
Antecedent rainfall
The amount of moisture already in the soil from previous precipitation, which dictates the ground's saturation level and flooding risk.
Lag time
The time delay between peak rainfall and peak discharge on a storm hydrograph.
Hydraulic action
The force of river water hitting the banks and bed, compressing trapped air in cracks and causing rock to fracture.
Abrasion
The wearing away of the river bed and banks by the river's load (sediment) scraping against them like sandpaper.
Cumecs
Cubic metres per second (), the standard unit of measurement for river discharge.
Sub-aerial processes
Processes occurring on the valley sides above the water line, primarily weathering and mass movement, which contribute material to the river.
Fluvial processes
Processes relating to the work of a river, including erosion, transportation, and deposition.
Mass movement
The downhill movement of weathered material (soil and rock) under the influence of gravity.
Slumping
A type of mass movement where a block of land moves downwards along a curved slip surface.
Soil creep
The extremely slow downhill movement of soil particles due to gravity, often caused by the expansion and contraction of wet and dry soil.
Lateral erosion
Erosion focused sideways into the river banks, which widens the river channel and valley floor.
Scree slopes
Accumulations of weathered rock fragments found at the base of steep valley sides or spurs.
Oxbow lake
A curved lake formed at a former meander where the main stream of the river has cut across the narrow neck and no longer flows around the loop.
Vertical accretion
The continuous build-up of sediment layers on a floodplain during repeated flood events.
Levees
Natural, raised embankments along the edges of a river channel formed by deposition during flood events.
Weathering
The breakdown and decay of rock in-situ (without movement).
Transportation
The movement of eroded material (load) by a river.
