If you drop a paper boat into a tiny, turbulent mountain stream, it will eventually float out into a vast, flat estuary. The journey between these two points involves massive changes to the shape of the river and the surrounding landscape.
A river's long profile shows its gradient from the source to the mouth and typically follows a concave shape. It is steepest at the high-elevation source and gradually decreases to become almost completely flat at sea level.
In the upper course, approximately 95% of a river's energy is lost to friction against the rough bed and banks. This forces the river to focus its remaining energy downward through vertical erosion, creating distinct landforms. As the river moves downstream, it shifts to lateral erosion (sideways erosion), completely changing the cross profile of both the entire valley profile and the specific channel shape.
The characteristics of a river change dramatically as it travels from source to mouth. The table below compares these key differences.
| Feature | Upper Course | Middle Course | Lower Course |
|---|---|---|---|
| Valley Profile | Steep-sided, V-shaped valley with a narrow floor and interlocking spurs. | Wider valley with gentler slopes (U-shaped) and a small developing floodplain. | Very wide, flat valley floor dominated by an extensive floodplain. |
| Channel Shape | Narrow and shallow. | Wider and deeper than the upper course. | Widest and deepest (can exceed 1km wide in major UK rivers). |
| Dominant Process | Vertical erosion. | Lateral erosion. | Deposition and lateral erosion. |
| Transport | Heavy bedload moved by traction. | A mix of traction and suspension as sediment gets smaller. | Fine alluvium carried effortlessly in suspension. |
| Landforms | Waterfalls, gorges, interlocking spurs. | Meanders, slip-off slopes. | Large meanders, oxbow lakes, levees, estuaries. |
| Sediment / Bed | Rough, uneven bed with large, angular boulders. | Smoother bed with smaller, rounded pebbles. | Smooth bed made of fine alluvium (silt and clay); does not contain large angular rocks. |
It might seem obvious that a steep mountain stream flows much faster than a flat lowland river, but the reality is exactly the opposite. The Bradshaw Model is a geographical framework that predicts how these hydrological variables change with distance downstream.
According to the model, several factors increase downstream: discharge, occupied channel width, channel depth, average velocity, and overall load quantity. Conversely, load particle size, channel bed roughness, and slope gradient all decrease downstream.
Discharge increases continually as water flows downstream. This happens due to the cumulative addition of water from joining tributaries and groundwater flow. We calculate this using a specific formula:
Where:
Velocity increases downstream despite the flatter gradient due to improved hydraulic efficiency. In the lower course, the channel is deeper and smoother, meaning a smaller proportion of water is in contact with the wetted perimeter (the bed and banks). Because there is less friction dragging the water back, the average velocity reaches its peak.
The rocks found in a river do not stay the same size forever. As sediment moves downstream, it becomes significantly smaller, rounder, and smoother.
This transformation is driven primarily by attrition. This is a process of erosion where transported particles crash into each other over long distances, slowly wearing each other down into smaller fragments. Because heavier particles are deposited as soon as the river loses energy, the sediment also becomes better sorted (more uniform in size) downstream.
The type of sediment transport also shifts. In the upper course, heavy bedload is moved via traction (rolling along the riverbed). By the lower course, the smaller, lighter alluvium is carried effortlessly in suspension within the water column.
To see these changes in action, we can trace the 137 km journey of the River Tees from the Pennines to the North Sea. The river perfectly illustrates the Bradshaw Model, starting with a tiny discharge of cumecs in its headwaters and ending in a massive tidal estuary.
In the upper course (Cross Fell to Middleton-in-Teesdale), the river drops roughly 750m in elevation over a very short distance. Sediment here consists of large, angular boulders often exceeding 1m in diameter. It features the UK's tallest waterfall, High Force Waterfall (21m drop). This formed where a highly resistant igneous rock called Whin Sill (dolerite) sits over softer limestone and sandstone, creating a gorge as it retreats.
In the middle course (near Barnard Castle), channel depth increases to between 0.46m and 1.7m. Discharge rises significantly here because major tributaries, including the River Lune and River Greta, join the main channel. Sediment size reduces to pebbles and gravel, with most bedload visibly rounded by 5km from the source due to attrition.
By the lower course (Stockton-on-Tees to Middlesbrough), the depth reaches between 2.61m and 3.20m. The river carries fine silt and alluvium in suspension, forming extensive mudflats at Seal Sands in the estuary. However, the natural downstream progression has been heavily modified by human intervention, including the Cow Green Reservoir in the upper course and the Tees Barrage near the mouth to regulate flow.
Students frequently state that velocity is highest in the upper course due to steep gradients; you must explicitly state that velocity peaks in the lower course due to reduced friction and higher hydraulic efficiency.
When answering 'Contrast' questions, always use paired statements to secure marks (e.g., 'The upper course has a rough bed with angular boulders, whereas the lower course has a smooth bed with fine alluvium').
In 8-mark 'Discuss' or 'Evaluate' case study questions on a UK river, examiners strictly look for specific numerical data (e.g., depths of 3.20m at Stockton) and named features (e.g., Whin Sill) to award Level 3 marks.
Long profile
The gradient of a river from its source to its mouth, which typically follows a concave shape.
Cross profile
A section taken sideways across a river channel and/or its surrounding valley.
Valley profile
The cross-section of the entire valley, including the channel, valley floor, and the slopes of the valley sides.
Channel shape
The specific cross-section of the river bed and banks itself, measuring its width and depth.
Vertical erosion
Downward erosion which deepens the river channel, dominating in the upper course and creating V-shaped valleys.
Lateral erosion
Sideways erosion which widens the river channel and valley, dominating in the middle and lower courses.
V-shaped valley
A steep-sided, narrow valley found in the upper course of a river, formed primarily by vertical erosion.
Floodplain
A wide, flat area of land adjacent to a river in its middle and lower courses, prone to flooding.
Levees
Raised banks of sediment along the edges of a river channel in the lower course, formed naturally by repeated flooding.
Bradshaw Model
A geographical model illustrating how different river variables, such as velocity and discharge, change with distance downstream.
Discharge
The volume of water flowing through a river channel at a given point, measured in cubic metres per second (cumecs).
Velocity
The speed at which water travels through the channel, measured in metres per second.
Tributaries
Smaller rivers or streams that flow into and join a larger main river.
Wetted perimeter
The total length of the river bed and banks that is in direct contact with the water.
Channel bed roughness
A measure of the friction caused by rocks and sediment on the riverbed, which is highest in the upper course.
Hydraulic efficiency
The ability of a river channel to move water with minimal friction; deeper, wider, smoother channels are more efficient.
Attrition
A process of erosion where transported particles crash into each other, wearing each other down into smaller, rounder fragments.
Bedload
The heavier material, such as rocks and boulders, carried by a river along its bed.
Alluvium
Fine-grained, fertile soil made of silt and clay that is deposited by flowing water in a lower course valley or delta.
Traction
A method of transportation where large, heavy rocks are rolled along the riverbed.
Suspension
A method of transportation where fine, light material is carried along within the water column.
Whin Sill
A layer of hard, resistant igneous rock (dolerite) responsible for the steep drop at High Force Waterfall on the River Tees.
Cow Green Reservoir
A human-made reservoir in the upper course of the River Tees built to regulate the river's flow.
Meanders
Pronounced bends or curves in a river channel, typical of the middle and lower courses.
Oxbow lakes
Curved, U-shaped lakes formed when a wide meander is cut off from the main river channel.
Estuaries
The wide tidal mouth of a river where it meets the sea, often featuring mudflats.
Interlocking spurs
Projections of high land that alternate from either side of a V-shaped valley, forcing the river to wind around them.
Gorges
A narrow, steep-sided valley, often formed as a waterfall retreats upstream.
Waterfalls
A steep drop in the bed of a river, typically formed where hard, resistant rock overlays softer rock.
Slip-off slopes
The gentle slope formed by deposition on the inside bend of a meander.
Put your knowledge into practice — try past paper questions for Geography A
Long profile
The gradient of a river from its source to its mouth, which typically follows a concave shape.
Cross profile
A section taken sideways across a river channel and/or its surrounding valley.
Valley profile
The cross-section of the entire valley, including the channel, valley floor, and the slopes of the valley sides.
Channel shape
The specific cross-section of the river bed and banks itself, measuring its width and depth.
Vertical erosion
Downward erosion which deepens the river channel, dominating in the upper course and creating V-shaped valleys.
Lateral erosion
Sideways erosion which widens the river channel and valley, dominating in the middle and lower courses.
V-shaped valley
A steep-sided, narrow valley found in the upper course of a river, formed primarily by vertical erosion.
Floodplain
A wide, flat area of land adjacent to a river in its middle and lower courses, prone to flooding.
Levees
Raised banks of sediment along the edges of a river channel in the lower course, formed naturally by repeated flooding.
Bradshaw Model
A geographical model illustrating how different river variables, such as velocity and discharge, change with distance downstream.
Discharge
The volume of water flowing through a river channel at a given point, measured in cubic metres per second (cumecs).
Velocity
The speed at which water travels through the channel, measured in metres per second.
Tributaries
Smaller rivers or streams that flow into and join a larger main river.
Wetted perimeter
The total length of the river bed and banks that is in direct contact with the water.
Channel bed roughness
A measure of the friction caused by rocks and sediment on the riverbed, which is highest in the upper course.
Hydraulic efficiency
The ability of a river channel to move water with minimal friction; deeper, wider, smoother channels are more efficient.
Attrition
A process of erosion where transported particles crash into each other, wearing each other down into smaller, rounder fragments.
Bedload
The heavier material, such as rocks and boulders, carried by a river along its bed.
Alluvium
Fine-grained, fertile soil made of silt and clay that is deposited by flowing water in a lower course valley or delta.
Traction
A method of transportation where large, heavy rocks are rolled along the riverbed.
Suspension
A method of transportation where fine, light material is carried along within the water column.
Whin Sill
A layer of hard, resistant igneous rock (dolerite) responsible for the steep drop at High Force Waterfall on the River Tees.
Cow Green Reservoir
A human-made reservoir in the upper course of the River Tees built to regulate the river's flow.
Meanders
Pronounced bends or curves in a river channel, typical of the middle and lower courses.
Oxbow lakes
Curved, U-shaped lakes formed when a wide meander is cut off from the main river channel.
Estuaries
The wide tidal mouth of a river where it meets the sea, often featuring mudflats.
Interlocking spurs
Projections of high land that alternate from either side of a V-shaped valley, forcing the river to wind around them.
Gorges
A narrow, steep-sided valley, often formed as a waterfall retreats upstream.
Waterfalls
A steep drop in the bed of a river, typically formed where hard, resistant rock overlays softer rock.
Slip-off slopes
The gentle slope formed by deposition on the inside bend of a meander.