Thames Barrier System - Case Study Example

DEFINITION OF WATER CATCHMENT: THAMES ESTUARY AND THAMES BARRIER STRATEGY Introduction For along time in the history of the world, there have been many incidences of conflicts between the environment and humans. In most of those cases it is the human being who suffers because the nature comes in uncontrollable forces. From the historical point of view, there are many incidences where human have suffered from storms, floods, and other water related calamities. This paper will look at Thames Barrier which is one of the solutions taken to shield the city of London from flood. Thames barrier is one of the UK's major estuaries. It expands from the tidal limit in river Thames at Teddington Lock passing through the heart of London and out to the North Sea. The development of an estuary at this site was chosen for the simple reason that there was more danger that was posed by the flooding every year in the city of London. In this regard, it is estimated that around 500,000 properties which houses more that 1.25 million people in London face a danger of losing their lives and property due to flooding. It has also been found out that a good proportion of London's essential infrastructure were also at a risk from the floods. This area is a habitat to a variety of species owing to its tidal salt march and extensive mudflats which are exposed at low water. (Soh and Tran, 2008) The Thames Barrier and other existing defenses have been providing a high level of protection against the risk of flooding but it has been predicted that this level of protection will decrease with time. It has been shown that there is an increasing risk of floods in London due to the failure of the existing defense mechanism. The character of flooding in the estuary changes from fluvial dominance at the upper side which reaches to the hazards that are caused by storms as they surge, and which are also caused by waves as they travel downstream. It has also been shown that the estuary has a dynamic sediment regime which comes with sequences of erosion from the upstream and deposition in the down streams every time there is a tide in the estuary. Development of Thames Barrier System The main idea behind the development of Thames Barrier was due to the risk that has been posed by floods. There was an increasing risk that was posed by the changes that were taking place in the environment which saw an increased level of sea water. As the ocean warm the level of the seas in the British coast, there has been increasing rise of the coast and intense rainfall coupled with stormy conditions poses more risk. There has also been land level lowering especially in the south-east of England which is slowly sinking to the sea. The flood defense that had been put in place has been aging with time. The existing barrier has become ineffective and costly to maintain as well. There has also been increasing development of new homes within the tidal flood plain which has increased the risk of many live. (Richard, 2003) Thames Barrier was first developed after the 1953 flood in London which killed approximately 300 people. The government then saw the importance of creating such a barrier that would protect the inhabitants of London from floods and was designed to protect the city till 2030 which was based on the estimates of the rising sea levels. It was designed in order to protect the surge of tides in the land. The first barrier was constructed at Woolwich Reach between 1974 and 1984. This is the largest world movable barrier. But since then there has been risks of flooding again posed by the changes that we have described above. There has been a review of the whole barrier and there is an agreement that there is need to upgrade the barrier or construct a new barriers altogether. Therefore the Thames Barrier 2100 had been proposed as the best method that can be used to protect the city of London for the next 100 years and over. Monitoring integrity and height of defenses along Grater Thames estuary The barrier is made up of 10 separate movable floods gates which are positioned end to end in 520 meters span. These gates are then mounted on pivots and are supported between concrete piers. In the normal sea condition, six of the gates are not seen resting on concrete sills on the riverbed. The four biggest gates have a weight of 3,700 tones each one and they leave apart a navigable span of about 61 meters. There are some 32 km of flood defense which have been built downstream of the barrier and in level with banks levels of storm 3 m higher than they had previously existing. Therefore the defense is a 60 meter high barking barrier. The defense has a drop gate which is not used and is used only when there is an imminent danger of flooding. When not in use, the drop gate is held out of the water which allows for uninterrupted passage of commercial ships by the use of the Barking Creek. The flood gates can be raised when needed by powerful electro-hydraulic machinery. These gates are raised in order to stop the encroaching water from reaching the lower side of London. The piers are covered by a stainless steel which looks like billowing sails. If any dangerous high tidal surge at a rate to attack, the rising sector gates are always moved up to about 90 degrees from the riverbed position. The four radial gates are also brought down and closed into the defense position. Therefore they form a continuous steel wall which face down the river and are ready to stern the tide. (Brownie and Simons, 2003) There can be further rotation of the gates to the horizontal maintenance position which renders them accessible for routine maintenance in order to make it stronger to protect the city from flooding. Under the improved 2001 Thames barrier, the defenses upstream of Putney on the South Bank and on Hammersmith in the northern bank have been raised in order to give similar degree of protection like it has been done in Central London. This has been effective in reduce the risk of flooding in time when high up-rive flows are consistent with tides and which are not dangerous enough to warrant closer of the barriers. Forecasting Water levels within the estuary In the event of waves the flood defense is triggered by tides forecast in the Northern Sea or a high flow of water from the rivers. These two conditions can cause the water level to exceed 4.87 meter in Central London. Therefore the Teddington weir has been set at the main indicator of the level of rising water in the sea. However a more accurate forecast of the levels of water in the sea is done by the Met office computers. These computers have been programmed to monitor the rise of the sea level and once it reaches an alarming rate, then the action to trigger the defense system is implemented. These computers forecast the level of water at the mouth or Tames Estuary. However there are model which are on the Thames forecasting and telemetry computer systems. This computer system has also been extensively used to monitor the level of rising water in the estuary that triggers the defense mechanism. The monitoring system is such that 9 hours before a high tide reaches barriers of the defense system, the closer of the barriers begins. There is also a warning to halt all the river traffic activities, close all the subsidiary gates, and alert those who live near the river of an impending danger. There is also an action to close the small gates which have been constructed along Thames Tideway in Barking Barrier, King George V Lock Gate, Dart ford Barriers and other small gates and Tilbury Docks and Canvey island. The moment all the navigations in the river are stopped, all the other subsidiary gates are closed and then the Thames barrier begins to close. Therefore the small gates are closed first and then the big ones are close later. (Environmental Agency, 2008b) Necessary data to modify existing defenses There are many solutions that have been proposed as a possible way to raise the defense of the barriers. In the new construction there has been an interim measures which have been aimed at improving the defense of London against flooding and at the same time ensures that there is construction of the main defense which is 80 km of the banks raised mainly between Putney and Purfeleet. There are many advantages of the proposed solution that can lead to the raising of the wall. First the walls are permanent and will be easy to maintain and are not likely to lead to a failure due to a human error as it has been before. But there have also been criticism that though raising the wall will be advantageous to the river, it will have a risk of hiding the whole of Thames River to the visitors of London thereby hiding the beauty of London river line to the viewers. There have also been a number of ways that have been proposed as possible to modify the current defense mechanism in the Thames barrier. One of such has been controlled inundation where areas will be crated which will be flooded when it is necessary and which will also serve as water storage. Under this proposition, excess storage areas will be built which will be used as flood sites in order to prevent the risk of flooding in the main city. There have also been a proposition about manage realignment. This has been described as a movement of flood defenses and buildings in order to improve the levels of protection by partially creating an area which can be inundated and which will be built between positions of the new defenses. This has been proposed in line with the need to come up with a managed upstream flow. There have been fears from many quarters that the Thames barrier will not meet its expected role by 2030. Since it was completed in 1982 the barrier has closed more that 100 times in order to protect London city and for all that time it has proved to be a good defense mechanism. But there has been increasing change in the climate and also there have been several other changes that have been taking place in the social life of the people and increased rise of the tourism sector which has become one of the most important economic sectors in London. These are some of the factors that have been proposed as possible barriers that are limiting the expansion of the wall in order to offer more protection. (Environmental Agency, 2008a) Originally the Thames Barrier and the 300km string of associated defenses were designed in order to provide 0.001% likelihood of flooding in London which was a standard of protecting up to 2030. The design considered the rate of rise of the sea level and it gave a greater allowance of the rise of sea level than what is being experienced currently. It is with this kind of dangers posed by the rising sea levels that the Environmental Agency has been working toward the creation of Thames 2100 in order to come up with a tidal flood risk management plan that will make the Thames more efficient in protecting the people and the city of London. The new plan is looking into the data on the climate change, rising sea level, natural aging of the infrastructure that has been providing the defense, the changes that is being experience in the land levels, and the new development in the tidal flood plain. References Brownie, A. & Simons, P. (2003): Flood fear forces Thames Barrier rethink. The Times online; Retrieved from, http://www.timesonline.co.uk/tol/news/uk/article859254.ece on 12th May 2008 Environmental Agency, (2008a): The facts behind fiction, Retrieved from, http://www.environment-agency.gov.uk/te2100/1853640/1854240/version=1&lang=_e on 12th May 2008 Environmental Agency, (2008b): Operating the barrier, Retrieved from, http://www.environmentagency.gov.uk/regions/thames/323150/335688/341764/341781/lang=_e on 12th May 2008 Richard, G. (2003). The development of the Thames Barrier; Retrieved from, http://www.ewell-probus.org.uk/archive/thames_barrier.htm on 12th May 2008 Soh, M. & Tran, P. (2008): Thames Barrier. Retrieved from, http://www.mech.uwa.edu.au/kamy/Thames%20Barrier.htm on 12th May 2008 Read More