Changing river environments
Connect drainage-basin processes to river landforms, flooding and pollution, then compare management choices using scale and sustainability.
Section Paper 1 · Physical Geography · Topics 1–5
Exam scope and assessment notes
Cambridge IGCSE Geography 0460, 2027–2029 syllabus, Topic 1. The syllabus does not prescribe one universal set of named detailed specific examples: centres select places suited to their learners. Sixteen optional StudyForA evidence packs now cover all sixteen example objectives, but the centre's choices are unconfirmed. Match each pack to your centre's chosen place and replace any mismatch before treating the course as complete. Original StudyForA explanations and self-check practice are not Cambridge papers, official grades or teacher-marked coursework. Map, graph and written answers are not automatically assessed. Paper 4 practice uses supplied or invented data and cannot certify safe fieldwork, equipment use or real data collection. Centre-set coursework and specialist teacher review remain pending.
Before you begin
- No previous Geography course is assumed. Use the supplied map, data or scenario; distinguish observation from explanation and support conclusions with evidence.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which is a water transfer from land to atmosphere: infiltration or evaporation?
What you will learn
- Locate and describe drainage basins, river channels and long profiles
- Use the Bradshaw model and water-cycle stores and transfers
- Explain erosion, transport and deposition and the landforms they create
- Assess river opportunities, hazards, flood causes and impacts
- Evaluate flood and pollution management with a named example
A drainage basin transfers water
A watershed is the drainage-basin boundary. Rain can be intercepted, infiltrate and percolate through soil, move as throughflow or groundwater, or travel overland to a channel. Evaporation and transpiration return water to the atmosphere; precipitation is the input. Land cover, soil, slope and rainfall intensity affect the route and timing of runoff.
Discharge is the volume of water passing a channel cross-section per unit time. For a simplified rectangular channel, discharge = width × mean depth × mean velocity. The Bradshaw model describes downstream tendencies: channel width, depth, velocity and discharge usually rise, while gradient and bedload size tend to fall. It is a model, not a rule for every river.
Processes build and reshape landforms
Hydraulic action, abrasion, attrition and solution erode channels. Traction, saltation, suspension and solution transport material; when a river loses energy it deposits sediment. Resistant rock can help create waterfalls and gorges; lateral erosion and deposition develop meanders and oxbow lakes; deposition can form floodplains, levees and deltas.
A meander's faster outer-bank flow erodes a river cliff, while slower inner-bank flow deposits a slip-off slope. Continued neck narrowing and a high-flow cut-off can leave an oxbow lake. The explanation should link process, location and resulting shape.
Flood and pollution management involves trade-offs
Flood risk reflects both hazard and exposure. Intense or prolonged rain, saturated or impermeable ground, steep slopes and urban surfaces can increase rapid runoff; deforestation and building on floodplains may increase exposure or alter flows. Floods may damage homes and infrastructure, but floodplains also offer fertile soils, water, transport and recreation.
Hard engineering such as dams, levees and channel straightening can protect some places but transfer risk downstream, disrupt ecosystems or require high costs. Warning, floodplain zoning, wetland restoration and afforestation can reduce risk through planning or storage. River pollution may come from sewage, industry, farming and waste; management needs source control, treatment, enforcement and monitoring. Evaluate who benefits, at what scale, and whether impacts are sustainable.
Pause and explain
A flood wall protects one town but raises water levels downstream. What should an evaluation consider?
Worked example
A channel is 18 m wide, has a mean depth of 2 m and mean velocity of 1.5 m/s. Estimate discharge.
Show the worked solution
- Cross-sectional area = width × depth = 18 × 2 = 36 m².
- Discharge = area × velocity = 36 × 1.5.
- Include the unit: cubic metres per second.
Answer Discharge = 54 m³/s under the simplified rectangular-channel estimate. A real cross-section is irregular, so width × mean depth is an approximation.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A river's discharge rises from 45 m³/s to 72 m³/s after a storm. Calculate the percentage increase and suggest one basin factor that could explain a rapid rise.
Give me a hint
Find the change, divide by the original value, then multiply by 100.
Compare my reasoning
- Increase = 72 − 45 = 27 m³/s.
- Percentage increase = 27/45 × 100 = 60%.
- For example, saturated soil can reduce infiltration and increase overland flow.
Discharge increased by 60%. Saturated ground is one possible cause of faster runoff; the rainfall pattern and other basin conditions also matter.
Look for these in your work
- Change calculated
- Original value used as denominator
- A process-based cause stated
Explain how a meander can develop an oxbow lake. Include erosion, deposition and a change in the channel route.
Give me a hint
Compare flow and erosion on the outer and inner banks, then describe a high-flow cut-off.
Compare my reasoning
- Faster flow erodes the outer bank; slower flow deposits material on the inner bank.
- The meander neck narrows as lateral erosion continues.
- A high-flow event may cut through the neck; deposition can seal the old loop.
Outer-bank erosion and inner-bank deposition enlarge the meander until a high-flow cut-off creates a shorter channel. Deposition may then isolate the former loop as an oxbow lake.
Look for these in your work
- Both banks explained
- Neck narrowing described
- Cut-off and deposition linked
A town is choosing between higher levees and restoring an upstream wetland. Compare one benefit and one limitation of each, then state what local evidence would help decide.
Give me a hint
Compare where each option stores or redirects water and identify people or ecosystems affected.
Compare my reasoning
- Levees can protect developed land locally but may move risk downstream and need maintenance.
- A wetland stores some water and can support habitats, but its storage capacity and location may not protect every settlement.
- Use flood levels, land use, costs, downstream flow and habitat data before deciding.
Levees may offer direct local protection but can transfer risk; wetland restoration can slow and store runoff and add habitat, but may be insufficient alone. A decision needs evidence about flood flows, exposed people, costs and downstream or ecological effects.
Look for these in your work
- Both strategies compared
- Trade-offs recognised
- Relevant evidence identified
Common mistakes
- Treating every Bradshaw trend as a guaranteed observation
- Confusing erosion with transportation or deposition
- Explaining a flood by rainfall alone
- Calling an embankment sustainable without considering downstream effects
- Giving a case-study claim without a named place or evidence
What can you explain now?
Why can rapid urbanisation increase a river's peak discharge after heavy rain?
Compare with the explanation
Impermeable surfaces reduce infiltration and can send water to channels more quickly
The mechanism links land cover to faster runoff; the size of the effect depends on drainage and basin conditions.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do discharge and velocity usually change downstream, and why should the Bradshaw model be checked against local evidence?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.