• Flood plain zoning - This attempts to organise the flood defences in such a way that land that is near the river and often floods is not built on. This could be used for pastoral farming, playing fields etc. The areas that rarely get flooded therefore would be used for houses, transport and industry.
• Flood relief channels - Building new artificial channels that are used when a river is close to maximum discharge. They take the pressure off the main channels when floods are likely, therefore reducing flood risk.
• Flood risk - The predicted frequency of floods in an area.
• Flood warning - Providing reliable advance information about possible flooding. Flood warning systems give people time to remove possessions and evacuate areas.
• Hard engineering - Involves the building of entirely artificial structures using various materials such as rock, concrete and steel to reduce, disrupt or stop the impact of river processes.
• Soft engineering - Involves the use of the natural environment surrounding a river, using schemes that work with the river's natural processes. Soft engineering is usually much cheaper and offers a more sustainable option as it does not interfere directly with the river’s flow.
• Channel straightening - Removing meanders from a river to make the river straighter. Straightening the river (also called channelising) allows it to carry more water quickly downstream, so it doesn’t build up and is less likely to flood.
• Dam and reservoir - A barrier (made on earth, concrete or stone) built across a valley to interrupt river flow and create a man‐made lake (reservoir) which stores water and controls the discharge of the river.
Rivers are managed in a huge variety ways and for a variety of different reasons. We use rivers for collecting water for drinking, industry and farming, and we manage then to prevent damage caused by deposition, erosion and flooding. Management can be split into 2 areas - HARD and SOFT ENGINEERING. These 2 methods have many BENEFITS for people and the ENVIRONMENT, but can also have associated COSTS or negatives.
Hard engineering involves the building of entirely ARTIFICIAL structures using various materials such as rock, concrete and steel to reduce or stop the impact of river processes.
DAMS & RESERVOIRS
Figure 17 - Three Gorges Dam in China - By Source file: Le Grand Portage Derivative work: Rehman via Wikimedia Commons
One way in which we manage rivers is to build huge concrete and steel structures called dams. These dams block rivers and cause the water carried by rivers to back up and flood the valley upstream of the dam creating a RESERVOIR. This water can then be used or released through the dam to produce Hydro Electric Power (HEP). By building a dam it allows engineers to control the flow of a river - this can therefore be used to prevent flooding during high rainfall periods. Newcastle is protected in part by the Kielder Water dam, and China has just completed construction of the World's largest dam at 3 Gorges. This dam has reduced the risk of flooding downstream of the dam from one in 10 years to one in a 100. Recent flooding prior to dam construction affected millions of people and ruined farmland because of clay that was deposited on the fields. The dam will protect over 25,000ha of farmland downstream. The dam has a huge series of locks running up one side to aid navigation, and will generate huge amounts of electricity. However, 1.4 million people had to be displaced (moved) to make way for the 600km lake that has formed behind the dam, there are expected to be problems with the huge amounts of sediment that will be deposited behind the dam and waste has been a problem. The city of Chongqing puts around 1 billion tonnes of untreated waste into the lake very year.
FLOOD RELIEF CHANNELS
Flood Relief Channels can also be used. Here, water is taken out of rivers and moved through artificial concrete channels away from vulnerable areas of valuable land use such as housing or industry.
Another way that rivers can be managed is to straighten meanders. This involves digging a straighter shorter channel in areas where rivers meander. The logic behind this is to speed up water flow in flood prone areas, and stop water from "hanging around". This has occurred on the Mississippi river and in York, but can cause flooding in downstream areas - a knock on consequence.
FLOOD WALLS AND EMBANKMENTS
A final hard engineering scheme is to build flood walls or embankments in flood risk areas. These strategies involve raising the banks of the river so that it can hold more water - thus reducing the risk of a flood. Morpeth has flood walls that will now be improved following flooding there, whilst it was the failure of floodwalls in New Orleans that caused so much damage during Hurricane Katrina.
SOFT ENGINEERING is a contrasting approach. It involves managing a river using natural materials and mimicking natural processes to protect more vulnerable areas. One technique used is to encourage the growth of reed beds which are allowed to flood and slow down river water. Another technique is known as floodplain zoning. Here, the areas closest to rivers are only used for low cost uses, such as playing fields and grazing. Higher cost land uses are kept away from the river on higher land.
A final approach is a flood warning system. In the UK if you live in a flood risk zone your details are kept on a database. In the event of a flood the Environment Agency will contact homeowners at risk via text message, phone call or a visit from a flood warden.