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Coastal Flooding Case Study London

The Thames Barrier spans 520 meters across the River Thames near Woolwich, protecting 125 square kilometers of central London from flooding caused by tidal surges and storms from the North Sea. The barrier became operational in 1982 with 10 steel gates that can be raised into position across the River Thames. When raised, the main gates stand as high as a 5-story building, are as wide as the opening of Tower Bridge, and weigh about 3,300 tons. The barrier is closed under storm surge conditions to protect London from flooding from the sea, but may also be closed during periods of high flow, to reduce the risk of fluvial (river) flooding in some areas of west London including Richmond and Twickenham. The Environment Agency (the agency responsible for the barrier operation) receives information on a potential surge from a variety of sources including weather satellites, oil rigs, weather ships, and coastal stations. At the onset of a predicted surge, the Thames Barrier will close just after low tide, or about 4 hours before the peak of the incoming surge tide reaches the barrier, a process that takes about 1.5 hours for all 10 gates. The Barrier will remain closed until the water level downstream of the Thames Barrier has reduced to the same level as upstream. As of March 2014, the Environment Agency has closed the Thames Barrier 174 times since it became operational in 1982. Of these closures, 87 were to protect against tidal flooding and 87 were to alleviate river flooding.

How does the Thames Barrier work? Thames Flood Barrier (6:00)

Figure 9.12: The Thames Barrier is one of the largest movable flood barriers in the world. The Environment Agency runs and maintains the Thames Barrier as well as London’s other flood defenses.

Credit: Environment Agency, UK

LEDC case study: coping with flooding in Bangladesh

Bangladesh is an LEDC. The land is densely populated. Most of the land forms a delta from three main rivers - Ganges, Brahmaputra and Meghna - and 25 per cent of Bangladesh is less than 1 m above sea level. Flooding is an annual event as the rivers burst their banks. This seasonal flooding is beneficial as it provides water for the rice and jute (two main crops in the area) it also helps to keep the soil fertile. Bangladesh also experiences many tropical cyclones [tropical storm: A low pressure system in the tropical latitudes which has high winds and rainfall. Can be called a cyclone or hurricane. ]. The low-lying land means it is easily flooded. Half the country is less than 6m above sea level. The snowmelt in the Himalayas adds water into the main rivers. There are human causes too - building on the floodplains and cutting down trees both increase the effects of flooding.

There are advantages to living here:

Rice farmer in Bangladesh

  • The flat floodplains of the delta are very fertile [fertile: A soil which is rich in nutrients. ]. Rice is grown.
  • The area can also be used for shrimp farming.

There are disadvantages too:

  • The low-lying islands are very vulnerable and flood easily. It is difficult to protect them.
  • There are poor communications. Many locals do not own their own telephone or television so it is difficult to give successful flood warnings.

How can the risk of flooding be reduced?

Bangladesh is an LEDC and therefore does not have money to implement large schemes.

It is always going to be threatened with flooding, so the focus is on reducing the impact.

The Flood Action Plan is funded by the world bank. It funds projects to monitor flood levels and construct flood banks/artificial levees [levee: Ridges or banks formed by deposits of alluvium left behind by the periodic flooding of rivers. Can also be artificially constructed banks or walls. ].

More sustainable ways of reducing the flooding include building coastal flood shelters on stilts and early-warning systems.

Now try a Test Bite.

House on stilts, on low lying land

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