4.11 Case Studies

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Objective 1: The Impact of a Named Multipurpose Dam Scheme

What is a Multipurpose Dam?

A multipurpose dam is a large dam built across a river that serves more than one purpose at the same time. Instead of doing just one job (like storing water), it does several — for example, generating electricity, supplying water for drinking, controlling floods, and helping with irrigation (watering farmland).

The case study used here is the Three Gorges Dam on the Yangtze River in China. It is the largest dam in the world and a clear example of a multipurpose dam scheme.

Background: What Is the Three Gorges Dam?

• Located on the Yangtze River in central China.
• Construction began in 1994 and the dam became fully operational in 2012.
• It is 2.3 km wide and 185 metres tall.
• The reservoir (the large lake of water that forms behind the dam) stretches back approximately 600 km upstream.
• It was built to solve serious problems: devastating floods along the Yangtze had killed thousands of people over the centuries, and China needed more electricity as its population and industries were growing rapidly.

Purposes of the Three Gorges Dam

The dam was designed to do several things at once — that is why it is called multipurpose:

• Flood control — stopping the seasonal Yangtze River floods that used to destroy villages and farmland downstream.
• Hydroelectric power (HEP) — using the force of falling water to spin turbines and generate electricity. The dam produces about 22,500 megawatts of electricity, making it the world's largest power station. This supplies electricity to hundreds of millions of people.
• Improved navigation — the reservoir made the river deeper, allowing large cargo ships to travel further inland, boosting trade and transport.
• Water supply — the reservoir stores enormous amounts of freshwater that can be used for drinking and irrigation during dry periods.