As a part of their study of rivers in GCSE Geography students will look at flooding. This is the second of two quizzes on that topic and it looks at both the risk of floods and their management.
Flooding is a natural part of the yearly cycle of a river, creating flood plains, levees and various other features. Floods occur when the discharge volume of the river becomes too large for the channel to contain. They are commonly seasonal, as in the UK where in winter a combination of frozen, sodden ground and higher than average rainfall will lead to a river going into spate before overtopping its banks and causing a flood.
Before the Neolithic Age, during the winter hunter-gatherer populations would have retreated to higher grounds, only returning when the risk of flooding had passed. In later times we began to attempt flood management. In the 3rd and 4th millennium BC humans started creating canals, dams and channels to try and control the flow of the river. Since then we have been trying to manage and control river flow to prevent flooding. Until recently hard engineering systems were used, but lately the value of soft engineering to reduce the flood risk has been realised.
[readmore]Now that there are settlements built in the high risk areas for flooding, the management of rivers is a must if we want to prevent homes from flooding. Cases such as Boscastle, which flooded in 2004, and the Cumbria floods in 2009, along with the more recent flooding of the Somerset Levels in 2014, have shown that floods are a risk that is still very much present. For governments with a limited budget, even in MEDCs (more economically developed countries), cost effective protection from flooding is a growing area of science.
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You can find more about this topic by visiting BBC Bitesize - Flooding and flood management
The main increase to flooding caused by sheep farming comes from draining the marshlands to make it more suitable for grazing. The farmers are forced to add more field drainage to keep the fields from being waterlogged and harming the sheep. This water enters rivers and so increases the risk of floods
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Peat bogs can reduce discharge levels by up to 25% by drawing the water in and gradually releasing it as water levels fall
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Beavers make huge dams that act as natural pools and marshes, holding back water in times of flood and releasing it gradually as water levels fall
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Anything that requires building something or physically altering the river is commonly considered hard engineering
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The Levels are at a very low level meaning it is naturally flooded for part of the year. Drainage ditches have been cut, recut and extended since the prehistoric period to drain the water away. Soft engineering methods, as well as a lack of funding, mean that the channels have been allowed to silt up preventing the water draining
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Other rivers, such as the River Mersey that flows through Manchester and Liverpool, have been so heavily straightened that little of the original river remains. This means the water moves down river very rapidly and this dramatically increases flooding at the few sections that still meander
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Leaving areas to flood naturally along most of the length of the river can allow some areas where buildings have already been built at the rivers edge to be protected. This is an example of soft engineering
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In general, farming and playing fields are located closest to the river, with car parks coming next, followed by industry, then residential properties and finally critical infrastructure
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Flood proofing can be divided into dry proofing (i.e. stopping the water getting in) and wet proofing (i.e. reducing the damage done when the water gets in)
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One advantage of a dam is that discharge rates can be altered and controlled. Holding back water during periods of high flow and releasing them during periods of lower water levels, can reduce flooding and maintain a regular level in the river
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