The long profile is a side view of a river from source to mouth; the cross profile is a slice across the valley and channel at one point. The long profile is concave — steep at the source, gentle at the mouth — while the cross profile widens from a narrow V-shaped valley to a broad, flat floodplain.
Two different views of the same river
Students mix these up constantly, so fix the difference first with a simple image.
- Long profile: imagine walking beside the river the whole way and drawing the height of the water against the distance travelled. You are looking at the river lengthways, from the side.
- Cross profile: imagine standing on one valley side, walking straight across the valley and the channel to the other side, and drawing the shape of the ground you cross. You are looking at the river across, in section.
The long profile shows how gradient changes along the river. The cross profile shows how the shape of the channel and valley changes — and you draw a different cross profile for the upper, middle and lower course.
The long profile
A typical long profile is concave: it drops steeply near the source, then flattens progressively towards the mouth.
| Course | Gradient | Dominant process |
|---|---|---|
| Upper | Steep | Vertical erosion — the river cuts downwards |
| Middle | Moderate | Erosion turns increasingly lateral — sideways |
| Lower | Very gentle | Deposition dominates |
The base level is the lowest point to which a river can erode, usually sea level. Over long periods a river tends to smooth its long profile towards this level, which is why the curve flattens out at the mouth. Irregularities interrupt it — a band of harder rock can produce a step in the profile, often marked by a waterfall or rapids, and these features gradually retreat upstream as the softer rock beneath is undercut.
The cross profile in each course
Upper course. The river is close to its source, high in the landscape. It has little water and carries large, angular boulders, so much of its energy goes into overcoming friction. What energy remains is directed downwards, producing vertical erosion. The result is a narrow, shallow channel with a rough, rocky bed, set in a steep-sided V-shaped valley, often with interlocking spurs where the river winds between areas of higher ground.
Middle course. More tributaries have joined, so discharge is greater. The gradient eases and erosion becomes more lateral, widening the valley floor. The channel is wider and deeper, meanders begin to develop, and the valley cross profile becomes noticeably broader with gentler sides.
Lower course. The river is at its largest and closest to the sea. The channel is wide, deep and smooth-bedded, carrying a large volume of water and a fine, well-rounded load. The valley is very wide and flat — a floodplain — often with levees along the banks, and the river meanders freely across it.
| Upper | Middle | Lower | |
|---|---|---|---|
| Valley shape | Narrow, steep V | Broader, gentler sides | Very wide and flat |
| Channel width | Narrow | Wider | Widest |
| Channel depth | Shallow | Deeper | Deepest |
| Bed roughness | Very rough — boulders | Moderate | Smooth — silt and sand |
| Load size | Large, angular | Medium, becoming rounded | Small, rounded, fine |
| Landforms | Waterfalls, gorges, interlocking spurs | Meanders, river cliffs, slip-off slopes | Floodplains, levees, oxbow lakes, deltas |
The misconception worth correcting
Almost everyone assumes a river flows fastest in the upper course, because the slope is steepest and the water looks dramatic — tumbling, white, noisy. In fact average velocity generally increases downstream, and this counter-intuitive result is a favourite exam question.
The reason is friction. In the upper course the channel is shallow and full of large boulders, so a great deal of the water is in contact with a very rough bed and banks. Energy that could move water is spent overcoming that resistance. In the lower course the channel is deep, wide and smooth, so a much smaller proportion of the water touches the bed. Less friction means more of the river's energy goes into flow. Geographers describe this using the hydraulic radius — roughly, the ratio of the channel's cross-sectional area to the length of bed and bank in contact with the water. A high hydraulic radius means an efficient channel.
The white water in the upper course is turbulence, not speed. It looks fast because it is chaotic.
Putting it together: the Bradshaw model
The Bradshaw model is a diagram summarising how a set of river characteristics change from source to mouth. It shows, moving downstream:
Increasing — discharge, channel width, channel depth, average velocity, load quantity, channel efficiency (hydraulic radius).
Decreasing — gradient, load particle size, channel bed roughness.
It is a model, which means it is a simplification. Real rivers depart from it constantly: a tributary joining can change discharge abruptly, a band of resistant rock can steepen the gradient midway, human structures such as dams and channelisation alter everything downstream of them, and a river in flood behaves quite differently from the same river in dry weather. Saying so in an answer demonstrates that you understand what a model is for.
How this appears in exams
Three question types recur, and each has a reliable approach.
- Describe the long profile / cross profile. Use the shape words — concave, V-shaped, wide and flat — and give a comparison between at least two courses. Describe only; save the reasons for the next question type.
- Explain why the cross profile changes downstream. Link process to shape: vertical erosion produces the V, lateral erosion widens the valley, deposition builds the floodplain.
- Explain why velocity increases downstream. Friction, hydraulic radius, smoother bed. This is the discriminating question, and knowing the friction argument properly is worth learning once and keeping.
Draw the diagrams. A labelled sketch of a V-shaped valley or a river's long profile earns credit quickly and organises your written answer at the same time.
Frequently asked questions
What is the difference between the long profile and the cross profile?
The long profile is the view from the side along the river's whole length, showing how its height falls from source to mouth; it is a single curve for the whole river and it is concave. The cross profile is a slice straight across the river and its valley at one particular point, showing the shape of the channel and the valley sides; it is different in the upper, middle and lower course, changing from a narrow V to a wide, flat floodplain. One tells you about gradient along the river; the other tells you about shape across it at a chosen place.
Why does a river not flow fastest at the source?
Because friction dominates in the upper course. The channel there is shallow and narrow with a bed of large, angular boulders, so a very high proportion of the flowing water is in contact with a rough surface, and much of the river's energy is used overcoming that resistance rather than moving water forward. Downstream the channel becomes deep, wide and smooth, so proportionally less water touches the bed and banks and the flow becomes far more efficient. The turbulence and noise of an upland stream are signs of resistance, not of speed.
What causes a V-shaped valley?
Vertical erosion by the river, plus weathering and mass movement on the slopes above it. In the upper course the steep gradient directs the river's energy downwards, so it cuts into its bed, deepening the channel. That leaves steep valley sides, which are then attacked by weathering — freeze-thaw is common in upland Britain — and the loosened material slides or creeps down towards the river, which carries it away. The result is the characteristic narrow V. Where the river winds around areas of higher ground, the ridges left projecting into the valley from alternate sides are interlocking spurs.
Is the Bradshaw model always accurate?
No, and it is not meant to be. It describes the general tendency of an idealised river, and real rivers deviate for entirely predictable reasons: a large tributary can raise discharge sharply at one point rather than gradually, resistant rock bands can steepen the gradient partway down, and human interventions such as reservoirs, straightened channels and abstraction change flow substantially. Conditions vary with the weather too, since a river in flood has a very different velocity and load from the same river in a dry spell. Recognising that a model is a useful simplification rather than a rule is itself a piece of geographical thinking examiners reward.
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