Edexcel GCSE Geography A (1GA0) — The Physical Environment
A river's journey from source to mouth is rarely a perfectly smooth, concave curve. While a typical river's long profile decreases in gradient downstream as discharge increases, the underlying rock type drastically alters this shape.
Differential erosion provides the causal mechanism for these changes. Resistant igneous rocks, such as Whinstone, erode much more slowly than softer sedimentary rocks like clays, shales, or mudstones. When a river crosses a boundary from hard to soft rock, the softer rock is eroded vertically at a faster rate, creating a steep "step" in the profile known as a knickpoint.
To investigate this, geographers use a BGS map to identify the lithology (rock type) beneath the river. By overlaying BGS data onto an OS map, you can pinpoint exactly where the river crosses a geological boundary. If the map contour lines are tightly packed at the exact point the rock type changes from hard to soft, this explains the presence of a waterfall or rapids.
When interpreting maps, it is easy to focus only on the blue line of the river, but the real story of the landscape is hidden in the shape of the land around it. Edexcel requires you to recognise landforms on both 1:25,000 maps (which show micro-details) and 1:50,000 maps (which are more generalized).
To identify specific river valley features, follow this step-by-step descriptive guide:
When referencing these landforms in an exam, always use a 6-figure grid reference to locate the exact 100m by 100m square. You can also draw a cross-section to prove the valley shape by placing a straight-edged piece of paper across the valley on the map and marking where each contour intersects it. If the plotted heights increase rapidly, it is a narrow V-shaped valley; if they remain low and flat, it is a floodplain.
Every time a new housing estate is built or a river is engineered, the natural flow of water is fundamentally altered. Geographers use GIS (Geographic Information Systems) to layer spatial data and analyse how human modifications impact river catchments.
Historical spatiotemporal analysis can be performed using "Spy" viewers to overlay 1930s OS maps onto modern satellite imagery, revealing both physical changes (like meanders turning into oxbow lakes) and human changes (urban sprawl). Human interventions are directly identifiable on maps: channelisation appears as unnaturally straight blue lines, while dams are mapped as large blue polygons labelled "Resr".
To analyse the specific impact of urbanisation using GIS, geographers follow a layered breakdown:
This rapid routing of water results in a "flashy" storm hydrograph, characterised by a shorter lag time and a higher peak discharge. Hard engineering structures like levees or the Cow Green Reservoir on the River Tees may regulate local flow, but they often displace flood risk or increase erosion further downstream.
Confusing the direction of the contour "V" in a V-shaped valley. Remember: the "V" shape points uphill (towards the source), while the water flows out of the V (downhill).
Examiners rigorously differentiate between the river channel (the water) and the river valley (the surrounding relief). When asked to describe the "landscape", focus on contour patterns and valley shape, not just the blue line.
For 4-mark questions explaining human impacts, you must construct a step-by-step causal chain (e.g., "urbanisation creates impermeable surfaces, which leads to increased surface runoff, resulting in a shorter lag time").
Mark schemes frequently award points for understanding that hard engineering (like levees or channelisation) may solve local flooding, but inevitably displaces the problem downstream by discharging water at higher velocities.
Long profile
A line representing the change in a river's gradient from its source to its mouth.
Differential erosion
The process whereby softer, less resistant rocks wear away at a faster rate than harder, more resistant rocks.
Knickpoint
A sharp change in the gradient of a river's long profile, often marking the location of a waterfall or a transition between different rock resistances.
BGS map
A British Geological Survey map showing the distribution of bedrock and superficial deposits.
Contour lines
Lines on a map joining places of equal height above sea level; their spacing dictates the gradient of the land.
Spot height
A specific point on a map with its exact altitude in meters written next to it.
6-figure grid reference
A precise coordinate used to locate a feature within a 100m by 100m square on an OS map.
Cross-section
A diagram showing the side-on view of the land's relief, drawn by plotting heights from a map along a straight transect line.
GIS (Geographic Information Systems)
A digital framework for capturing, managing, and analysing spatial data in layered formats.
Channelisation
Deliberate engineering of a river channel, such as straightening or deepening, to increase flow velocity and reduce local flood risk.
Impermeable surfaces
Artificial materials like concrete or tarmac that prevent water infiltration, thereby increasing surface runoff.
Lag time
The temporal delay between peak rainfall and peak discharge on a storm hydrograph.
Put your knowledge into practice — try past paper questions for Geography A
Long profile
A line representing the change in a river's gradient from its source to its mouth.
Differential erosion
The process whereby softer, less resistant rocks wear away at a faster rate than harder, more resistant rocks.
Knickpoint
A sharp change in the gradient of a river's long profile, often marking the location of a waterfall or a transition between different rock resistances.
BGS map
A British Geological Survey map showing the distribution of bedrock and superficial deposits.
Contour lines
Lines on a map joining places of equal height above sea level; their spacing dictates the gradient of the land.
Spot height
A specific point on a map with its exact altitude in meters written next to it.
6-figure grid reference
A precise coordinate used to locate a feature within a 100m by 100m square on an OS map.
Cross-section
A diagram showing the side-on view of the land's relief, drawn by plotting heights from a map along a straight transect line.
GIS (Geographic Information Systems)
A digital framework for capturing, managing, and analysing spatial data in layered formats.
Channelisation
Deliberate engineering of a river channel, such as straightening or deepening, to increase flow velocity and reduce local flood risk.
Impermeable surfaces
Artificial materials like concrete or tarmac that prevent water infiltration, thereby increasing surface runoff.
Lag time
The temporal delay between peak rainfall and peak discharge on a storm hydrograph.
