This deep dive covers How Rivers Transport Load: The Four Methods within River Processes and Landforms for GCSE Geography. Revise River Processes and Landforms in Physical Landscapes in the UK for GCSE Geography with 21 exam-style questions and 22 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 4 of 18 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
🚛 How Rivers Transport Load: The Four Methods
Transportation is the movement of eroded material (the load) downstream. The type of transport depends on the size of the particle and the velocity (energy) of the river. A river's ability to transport load depends on two properties: its capacity (the total amount of load it can carry) and its competence (the maximum size of particle it can carry). Both increase when velocity increases.
1. Traction
Traction moves the largest, heaviest particles — boulders and cobbles — by rolling them along the riverbed. The particles never leave the bed; they are simply dragged forward by the force of the water. You can sometimes see this happening in a fast-flowing upland stream after heavy rain: large stones visibly rolling and grinding along the bottom.
2. Saltation
Saltation moves medium-sized particles — pebbles and coarse sand — in a hopping or bouncing motion. The current lifts a particle briefly off the bed, carries it a short distance, then drops it. When it lands, it may dislodge another particle, sending it into saltation in turn. This creates a characteristic "bouncing" movement along the bed, visible in shallow upland streams.
3. Suspension
Suspension carries the finest particles — silt and clay — within the body of the flowing water itself. These particles are so light that the turbulence of the flow keeps them permanently lifted off the bed. Suspended load is what makes rivers look brown or cloudy during and after rainfall. It represents the largest proportion of total load carried by most rivers — the River Thames carries millions of tonnes of suspended sediment to the sea each year.
4. Solution
Solution carries dissolved minerals — the products of corrosion — invisibly within the water. There is no visible evidence of this form of transport; the river simply carries dissolved calcium carbonate, sodium chloride and other minerals as ions within the water. Solution transport is particularly important in limestone and chalk catchments.
The Hjulström Curve: Competence and Deposition (Higher Tier)
The Hjulström curve shows the relationship between flow velocity and whether a particle is eroded, transported, or deposited. The key insight is that deposition occurs when velocity drops below a threshold — the river no longer has the competence to carry a particle and drops it. This explains why deposition occurs in three key situations:
- On the inside of meander bends, where flow is slower (deposition builds point bars)
- Where a river enters the sea or a lake, and velocity falls suddenly (deposition builds deltas)
- When floodwater recedes after a flood event (velocity drops, load is deposited across the floodplain)
Interestingly, the Hjulström curve also shows that clay and silt are harder to erode than fine sand, even though they are smaller — this is because clay particles clump together (cohesion) and require a higher velocity to detach them from the bed.
Test yourself: how rivers transport their load
Apply the four transport processes to changing river conditions.
A river's velocity decreases significantly near its mouth. Explain what happens to load being transported by traction.2 marks
As velocity and therefore energy or competence falls, the river no longer has enough energy to roll or drag large boulders along the bed, so this material is deposited. It settles first because it needs the most energy to keep moving.
The link examiners want is energy or competence falling BEFORE deposition. 'The river slows so material is dropped' without that link loses a mark.
Explain why a river carrying dissolved calcium carbonate can still transport this load even when flowing very slowly.2 marks
It is transported in solution, dissolved within the water itself, so unlike traction, saltation and suspension its movement does not depend on velocity or energy. It is only deposited through a chemical change, not because the river slows.
Most confused with suspension. The distinguishing point is that solution transport is independent of velocity.
During a flood a river's discharge and velocity increase rapidly. Explain how the load being transported changes.3 marks
Higher velocity gives more energy and higher competence, so the river can now move larger material it could not before — pebbles and small boulders that were static now move by traction or saltation. More turbulent flow also erodes more fine sediment from the banks and bed, increasing the material carried in suspension.
Full marks needs at least two named processes and an explanation using competence or energy. 'The river carries more' with no named process scores at most 1 of 3.
Practice questions for River Processes and Landforms
Which of the following best describes the erosion process of abrasion?
Explain how hydraulic action erodes a river's bed and banks.