The causes & consequences of flooding
A flood is a devastating natural hazard that severely affects the lives of people, each year all over the world floods will be ruining the lives of someone by causing damage to their houses or crops or by killing them. Around 5 million people, in 2 million properties, live in flood risk areas in England and Wales. An example of a river that floods quite often is the River Severn in the United Kingdom.
The Severn is known for rising quickly. Being a long river there are many tributaries feeding in, helping to increase the amount of water in the Severn. On October 31, 1998, many towns and villages along the River Severn were badly flooded. There had been a lot of rainfall over three days. Forty flood warnings had been issued to areas along the river Severn. Ten of these were severe flood warnings. This meant that people should be ready to evacuate their homes. The centre of Shrewsbury was completely flooded.
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The causes of the floods in the Severn Valley in 1998 can be split into two sections: human and physical causes. The human causes are urbanisation; by concreting over the land humans have increased the rate of surface runoff and decreased the saturation levels of the ground. When surface runoff is high rainwater reaches the river faster. In 1998 the speed at which it reached the river was too fast for it to handle and flooded. The river filled up overflowing its banks onto the flood plain. The flood plain of the river Severn is built on, therefore, when the river floods it floods onto peoples homes.
Urbanisation can also affect the river level because it reduces the amount of vegetation in the areas surrounding the river. This will affect the river by reducing the amount of interception, which will increase the speed of runoff to the river.
One of the physical factors that caused the flood was the vast amount of rainfall that had fallen over the months of October and November. In these months many areas received huge amounts of rain that meant that the river did not have enough time to get rid of all the excess water, making the river rise to such a level that it flooded. The upstream area of the river was worse affected than the lower area of the river.
Another physical factor that caused the floods is the actual physical features of the river and surrounding areas such as the flat and low-lying areas that are around the river. This meant that as the water went over the banks it just spread out across the land.
The floods of 1998 caused major devastation to peoples lives. Many people in the areas where the floodwaters hit had to be rescued from their houses. They were trapped on the top floor of their houses as the ground flood was flooded with water from the Severn that was polluted. Elderly people were the worst affected. The floods led to at least twelve deaths.
Farmers had to move their cattle and other animals to higher ground to keep them safe and thousands of homes were marooned by floodwater. Some people estimated the damage to be over ï¿½100 million pounds. Shrewsbury suffered it worst flood in over thirty years. Two bridges in the town were closed. The wet weather also caused major problems for sporting events.
River basin management is the management of the area surrounding the river. This may include; hydroelectric power stations, dams, building of levee’s, the dredging of a river bed and river walls. These things will be done for many reasons but the most popular reason for river basin management is the prevention of flooding. Other reasons for river basin management may include a clean water supply, a good efficient power supply and straightening of the channel for navigation.
An example of a river basin management scheme is the River Tees in NE England. There are 3 different schemes that are set-up on the river tees these are:
> The Upper Tees Basin
> The Yarm Flood defence system
> The Lower Tees
The reason that the river tees needed the flood defence system is that the rainfall reaches the river tees very quickly so that discharge is high. The River Tees is also known as an area for flash flooding. The steep sided valleys that surround the basin of the River Tees also make the flood risk factor worse.
The aims of the overall river basin management scheme were to; reduce the impact of flooding, supply a growing water demand, reduce water pollution and improve its quality and to increase the recreational use of water.
In the upper Tees there is the Cow Green Reservoir that holds back up to forty million cubic metres of water. There are also reservoirs on the tributaries such as the River Lune, River Hury and the River Baldershead. The council also discourages new developments in the low-lying areas to even more reduce the risk of flooding. They also built a tunnel connecting Kielder water via the River Tyne is used to add excess water to the River Tees at times of low flow.
In Yarm they spend ï¿½2.1 million on a defence system that included; reinforced concrete walls clad with stone as a boundary around Yarm. Flood gates to allow access by people and cars. Landscaped earth embankments to protect the local school. Also they used gabions to reduce the erosion along the embankments and used pipes to redirect floodwater. At the time they also improved the amenities and environment by improving the street lighting, flower beds, street furniture and fishing platforms.
In the lower Tees they improved the flood warning systems and discouraged any new developments on undeveloped land. They also constructed the Tees Barrage to minimise the risk of both river and tidal flooding.
To conclude the scheme set up in the river Tees was mainly to prevent flooding but had other reason aswell.