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Flooding can cause damage to homes, businesses, infrastructure and communications. Hard engineering involves building artificial structures which try to control rivers. They tend to be expensive. Each hard engineering strategy has its advantages and disadvantages.

Dams and reservoirs

A dam traps water, which builds up behind it, forming a reservoir. Water can then be released in a controlled way.

Advantages

• Can be used to produce electricity by passing the water through a turbine within the dam.
• Reservoirs can attract tourists.

Disadvantages

• Very expensive.
• Dams trap sediment, which means the reservoir can silt up and hold less water.
• Habitats are flooded, destroying ecosystems and often leading to rotting vegetation. This releases methane which is a greenhouse gas.
• Settlements are lost leading to the displacement of people. In some countries locals are not always consulted and have little say in where they are relocated.

River straightening and dredging

Straightening the river speeds up the water, so high volumes can pass through an area quickly, therefore reducing the chances of a flood. Dredging makes the river deeper so it can hold more water.

Advantages

• More water can be held in the channel.
• It can be used to reduce flood risk in built-up areas.
• Improves the river as a shipping route.
• Silt from the river makes an excellent fertiliser.

Disadvantages

• Dredging needs to be done frequently.
• Speeding up the river increases flood risk downstream.

Embankments

Embankments raise the banks of a river so that it can hold more water.

Advantages

• Cheap with a one-off cost.
• Allow for flood water to be contained within the river, protecting particular areas of high value from flooding.

Disadvantages

• Looks unnatural and reduces access to the river.
• Water speeds up and can increase flood risk downstream.

Flood relief channels

The floodwater flows into the relief channel and is taken either to an area where it can be absorbed, or re-enters the river further down its course.

Advantages

• Remove excess water from the river channel to reduce flooding.
• Does not affect the river ecosystem.

Disadvantages

• Expensive to build.
• If water levels continue to rise, the relief channel may also flood.