GCSE Geography | River Management: Hard Engineering (River Landscapes 10)

Many rivers are protected by hard engineering - this is when structures are built to reduce the risk of flooding.

Dams and reservoirs

A dam is a concrete barrier built across a river to control the flow of water (by using sluice gates to release water) - restricting the level of water downstream and lowering the risk of flooding. Behind the dam the river valley will flood to create a reservoir.

Advantages:

• Minimal risk of flooding - releases of water are highly controlled
• Can be used to generate hydroelectric power (renewable and doesn't emit carbon dioxide)
• Reservoir is used for water storage - supplies water for domestic and industrial uses
• Reservoir can also be used for leisure, e.g. water sports - so boosts tourist income

Disadvantages:

• Flooding behind the dam causes displacement and loss of farmland
• Extremely expensive
• Less water downstream can affect farming, e.g. less flooding downstream means less alluvium being deposited, decreasing soil fertility
• Impact on fishing - fish get trapped behind the dam, as does sediment - silt build up
• Sudden releases of water can cause erosion downstream
• Impact on marine habitats - the deep reservoir is much colder than the original river and many species will struggle to adapt

Channel straightening

With channel straightening the original river is engineered to be wider, straighter and deeper - this makes the river travel faster through an area, so water is removed more quickly, reducing the risk of flooding.

Advantages:

• Water is moved out of the area more quickly (less friction with the river bed and banks to slow down flow)
• Faster flowing water stops sediment from building up so there is less need for dredging
• Can improve navigation which improves travel and trade links
• Local properties are protected, which lowers home insurance premiums in the area

• Water is fast flowing through the straightened sections, and has to slow considerably when it starts to bend downstream. This loss of energy causes deposition to occur, and the sedimentation can increase the risk of flooding and need for dredging
• This is a very expensive solution as it requires a lot of engineering
• The additional dredging that is needed downstream is also expensive
• Impact on the river ecosystem which can destroy habitats and lower biodiversity
• Straightened rivers are often lined with concrete which is unnatural and stops animals burrowing into the river bank

Embankments

An embankment is an artificially raised river bank made by building up mounds of impermeable soil. By making the river bank higher the river channel is able to hold more water before it floods, so the flood risk is reduced. Embankments may be reinforced by gabion cages or lined with concrete (particularly in large urban areas).

Advantages:

• Increased capacity means the river is less likely to burst its banks so protects homes and businesses along the river
• Much cheaper than other hard engineering strategies (although this is dependent on type of embankment)
• Embankments made from earth provide important wildlife habitats (concrete ones do not!)
• Leisure facilities - concrete embankments are good for walking and cycling

Disadvantages:

• Embankments interfere with access to the river
• Less reliable than other methods of hard engineering - embankments are often breeched
• Need continual monitoring and repairs so maintenance costs are considerable
• Earth embankments are prone to erosion - which causes sedimentation of the river bed which will eventually need expensive dredging
• If it does flood it is hard for the water to drain back into the river over the raised river bank
• Gabions and concrete reinforcements are unattractive and destroy river habitats

Flood relief channels

If a river frequently floods it may have an artificial channel built as a back-up. The man-made channel is parallel to the main river and works like a bypass and in times of high discharge a gate will automatically close off the main river and divert water through the artificial spillway to reduce the risk of the main river flooding.

Advantages:

• Protects home and businesses from flooding so reduces insurance premiums and increases property values
• Leisure amenities, such as cycle paths along the new channel, and calm water for swimming, paddle boarding and kayaking
• Often have reed beds planted which provide important wildlife habitats

Disadvantages:

• Can cause displacement if people live along the path of the relief channel
• Increased flood risk downstream as the merging of water from the flood relief channel and the main channel increases discharge
• Very expensive to build, and need constant maintenance and repair, which is also expensive
• Very time consuming to construct
• Disturbance to habitats
• In times of low flow the relief channels look unpleasant as all the concrete is exposed - this is also bad for wildlife