Managing Floods - hard engineering

Dams and reservoirs are widely used around the world to regulate river flow and reduce risk of flooding. Most dam projects are multi-purpose, having several functions, for example:

• food prevention
• irrigation
• water supply
• hydro-electric power generation
• recreation

Dams can be very effective in regulating water flow. During periods of high rainfall, water can be stored in the reservoir. It can then be released when rainfall is low. But the construction of dams can be very controversial. They cost huge amounts of money and the reservoir often floods large area of land. Many people may have moved from their homes.

River straightening involves cuttibg through meanders to create a straight channel. This speeds up the flow of water along the river. Whilst river straightening may protect a vulnerable location from flooding, it may increase the flood risk further downstream. The problem is not really solved but shifted somewhere else.

In some places straightened sections of river are lined with concrete. This speeds up the flow and prevents the banks from collapsing, which can cause the channel to slit up. But the concrete channels create a very unattractive and unnatural river environment and can damage wildlife habitats.

An embankment is a raised riverbank. Raising the level of a riverbank allows the river channel to hold more water before flooding occurs.

Hard engineering structures involving concrete walls or blocks of stone are frequently used in towns or cities to prevent flooding of valuable property. Sometimes mud dredged from the river may be used. This is cheaped and more sustainable and looks more natural.

A flood relief channel is a man-made river channel constructed to by-pass an urban area

During times of high flow, sluice gates can be opened to allow excess water to flow away into the flood relief channel and reduce the threat of flooding.