Why are rivers dammed, and what are the benefits and problems of managing a river basin?
The physical and human factors in selecting a dam and reservoir site, the need for water management, and the social, economic and environmental consequences of a multi-purpose scheme.
An SQA Higher Geography answer on river basin management, covering the physical and human factors in choosing a dam and reservoir site, the reasons water management is needed, and the social, economic and environmental benefits and problems of a multi-purpose scheme.
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What this key area is asking
The SQA wants you to explain why a river basin is managed, what physical and human factors decide where a dam and reservoir go, and the social, economic and environmental consequences (good and bad) of a multi-purpose water scheme. Higher answers need a named scheme and a balanced judgement across all three dimensions.
Why manage a river basin
Management is needed where the water supply is unreliable (seasonal rainfall, drought or flood), where demand for domestic, farming and industrial water is rising with population and development, where there is potential for hydroelectric power, and where flooding threatens people and property downstream.
Choosing a dam and reservoir site
Consequences of a scheme
A multi-purpose scheme brings real benefits: a reliable water supply, clean hydroelectric power, flood control downstream, irrigation for farming, and new jobs and tourism at the reservoir. But it also creates problems:
- Social: valleys, farmland and villages are flooded and people are displaced; stagnant reservoir water can spread water-borne disease such as bilharzia.
- Economic: schemes are very expensive to build, and the reservoir slowly fills with silt, reducing its lifespan and the fertility of land downstream.
- Environmental: habitats are lost, the river flow and sediment supply downstream are altered, water quality can decline, and the weight of water can trigger landslides or minor seismic activity.
Examples in context
Example 1. The Three Gorges Dam, China. On the Yangtze, the Three Gorges Dam is the world's largest hydroelectric scheme, with a capacity of about . Its benefits are clean power, flood control on a river whose floods once killed thousands, and improved navigation. Its costs are heavy: around million people were displaced, towns, farmland and archaeological sites were drowned, the reservoir traps silt that once fertilised downstream fields, habitats were lost and the river dolphin declined, and there are landslide and seismic concerns. It is the SQA's standard scheme for balancing consequences.
Example 2. Highland hydro schemes, Scotland. Schemes such as Cruachan and the Loch Sloy and Tummel-Garry developments show good site choice: steep, narrow, glaciated valleys cut into impermeable rock, high reliable rainfall and large natural catchments make ideal reservoir sites with relatively few people to displace. They deliver reliable, storable renewable power (Cruachan is a pumped-storage station that releases water to meet peak demand) with smaller social costs than the Three Gorges, illustrating how physical site factors and low population combine for a successful UK scheme.
Try this
Q1. Explain the physical factors that make a good dam and reservoir site. [4 marks]
- Cue. A narrow, deep valley keeps the dam short and cheap; solid impermeable rock anchors it and prevents leakage; a large catchment with reliable rainfall keeps the reservoir full; a flat area upstream stores a large volume.
Q2. Discuss the environmental consequences of a multi-purpose river scheme. [4 marks]
- Cue. Flooding of land destroys habitats; the dam traps sediment so less reaches downstream; flow patterns and water quality change; the reservoir silts up over time.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher 20195 marksExplain the physical and human factors that influence the choice of a dam and reservoir site.Show worked answer →
Worth 5 marks. Both physical and human factors must appear, each with a reason. About four developed points reach the top band.
Physical factors (about 3 marks). A narrow, deep valley keeps the dam wall short and so cheaper to build, while a wide, flat area upstream allows a large reservoir. Solid, impermeable bedrock (such as granite) anchors the dam and stops the reservoir leaking. A large catchment with high, reliable rainfall keeps the reservoir full.
Human factors (about 2 marks). A site with few people, settlements or valuable farmland to flood reduces the cost and disruption of relocation. The site should be reasonably close to the towns, farms or industry that need the water and power, and accessible for construction. A balanced answer naming a scheme such as the Three Gorges or a Highland scheme earns full marks.
SQA Higher 20216 marksReferring to a named multi-purpose water management scheme, evaluate its social, economic and environmental consequences.Show worked answer →
Worth 6 marks. "Evaluate" means weigh benefits against problems across the three dimensions, with a named scheme such as the Three Gorges Dam.
Benefits (about 3 marks). The Three Gorges Dam in China generates huge amounts of clean hydroelectric power (about capacity), controls flooding on the Yangtze that once killed thousands, improves navigation, and supports irrigation and water supply.
Problems and judgement (about 3 marks). Around million people were displaced and historic towns and farmland were flooded (social cost); the scheme was hugely expensive and the reservoir traps silt, reducing fertility downstream (economic cost); habitats were lost, the Yangtze river dolphin declined, and there are landslide and seismic concerns (environmental cost). A balanced judgement weighing power and flood control against displacement and ecological harm reaches the top band.
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Sources & how we know this
- SQA Higher Geography Course Specification — SQA (2018)