Geography Hard Engineering

Hard Engineering

Structural Approaches to Flood Management

Levees, Embankments

and Flood Walls

Clywedog, Wales

Dams and Storage Reservoirs

These three are all designed to increase the height of the channel, and therefore increase the amount of water a channel can hold before it floods, giving homeowners and farmers a chance to move their possessions/livestock before the water spills out over the floodplain. They are commonly used in towns and cities and are made of either concrete or earth with rubble fill. Some examples of artificial levees are the Mississippi, the Rhine and the Ganges. Although effective forms of flood prevention, they are however costly, at around £2500 - £5000 per foot, they are to be built strategically. Levees also need lots of maintenance and if breached, can prevent water returning to the channel, causing a long standing body of water, and saturation of the surrounding land.

A dam is any barrier that holds back water and is primarily used to save, manage and or prevent the excess flow of water into specific regions, which may be inhabited, or else are crucial agricultural/industrial sites. Some dams are also used to create Hydro Power, while many are used mainly as reservoirs, this is an artificial lake used to store water. Dams are good examples of hard engineering as they are crucial in countries such as Egypt, where the Nile river floods year upon year, they are however extremely expensive to construct, many coming to a total of tens of millions of pounds. Some negatives of a dam are that as the river is abruptly stopped in the lake, the sediment is dropped also as the competence of the river decreases, this leads to layers of alluvium on the resivour floor. Dam construction can also lead to the displacement of residents, for example, during the build of the Three Gorges dam in China, more than 1.2 million people were moved out of their homes.

Mississippi

Vancouver

River Exe, Exmoor

Channel Improvements

Flood Interception and Diversionary Spillways

Relief Channels

Channel improvements attempt to restrict flood water from damaging properties and land by either creating a smoother channel by removing vegetation or boulders which restrict water movement, this would allow for faster and more efficient flow, or by artificially deepening or widening the channel, to create a greater capacity for the water flow. Although this method does have benefits as it could be relatively cheap depending on the type or amount of object removed, channel improvements are generally hard to maintain because of the continually changing state of the river channel (deposition and erosion), and could cause flooding downstream. An example of this method being used is the Columbia river, Vancouver

A flood interception channel may be constructed to re-route a river to bypass a town, while diversionary spillways are overflow channels used to store excess water in times of flood. These methods of hard engineering are places on low value land which will have minimal impact to the local community if flooded. These can be expensive to build as they require movement of land, but are effective means of storing and moving water as they can be built on a large scale, one disadvantage however, is that if the diversionary spillways were to be overwhelmed, this could lead to widespread flooding in areas not usually affected.

A relief channel is designed to change the course of some of the water in the channel to an area away from a settlement, by sending the excess water through an artificial channel, water then rejoins the main channel after the diversion and continues on its course. This can reduce the flood risk by taking the pressure off the main channel and many can be controlled so they are only accessible in times of peak flow. This method is however expensive, for example the proposed relief channel for Oxford, England, is expected to cost £100 million.