January 2008
Parts of south-eastern England narrowly avoided a potential catastrophe last November.
A storm surge – the worst since 1953 – raised sea levels by three metres. There was localised flooding in Norfolk and Suffolk and the Thames Flood Barrier was raised in case high tides came surging into central London.
With climate change forecast to bring higher sea-levels, experts are now warning that even more needs to be done to protect London in the future. New defences will most likely need to be built. Meanwhile, a new film – Flood – gives us a glimpse of what might happen if London is not given better protection.
The East Anglian coast survived an extreme weather event on November 9 2007.
In parts of the region, waters rose by 9m – the highest mark since the 1953 floods that killed 300 people.
100s of kilometres of coastline were under threat, including the settlements of Great Yarmouth, Lowestoft, Southwold, Ipswich and Felixstowe.
Police knocked on 7,500 doors to tell residents in the most at-risk areas that they should consider evacuating.
Hundreds spent the night in shelters, such as schools and leisure centres, or with friends away from the danger zone.
Luckily, none of the area’s major defences were breached. Minor flooding occurred in some low population density regions.
The village of Walcott on Norfolk experienced 4m waves that breached the sea wall and damaged caravans and conservatories (The Guardian, 10 November 2007). Some people had to be rescued by fire crews using dinghies in Lowestoft, Suffolk. And some important bird breeding grounds were flooded, according to the RSPB.
However, fears of wide-spread over-topping of defences were averted. At their maximum, sea-levels were 20cm lower than experts had predicted and this was enough to mean that the majority of sea-walls withstood the extreme waves that battered the coastline.
However, the event is a reminder of the perpetual danger of flooding that East Anglian and London home-owners are exposed to. It is a risk that is set to increase further if IPCC predictions of climate change-driven sea-level rises are proven correct.
During the surge, the Thames Flood Barrier was raised as a precaution in case excessive levels of tidal water were funnelled too far inland into central London. The film Flood, featuring Robert Carlyle, gives us a glimpse into what might happen if a truly extreme weather event were to occur over the North Sea and lead to the over-topping of the Thames Barrier. Watch the film trailer and see images on the film website.
The photograph above shows the “stratigraphy” of flood defences in London. Various additional layers that have been added to river defences over time, following various key flood events.
However, the flooding that took place in 1953 was so severe that a new approach to defending London was introduced: The Thames Flood Barrier.
The 1953 North Sea storm surge had brought flooding of large areas of the east coast, including areas of Essex close to the London conurbation, killing 307 people.
A very deep depression had resulted in unusually low pressure over the sea (which allows water levels to rise).
With strong surface winds driving water levels even higher, this extreme weather event coincided with the regular high spring tide - which maximised the worst effects of the surge.
The disaster provided the impetus for The Thames Barrier to be built in order to protect London from any future storm surges of similar or greater magnitude.
Finally completed in 1984, it is a moveable structure. Basically, the barrier is a series of ten separate movable gates positioned end-to-end across the river. Each gate is pivoted and supported between concrete piers that house the operating equipment.
Closing the barrier seals off part of the upper Thames from the sea and unusually high tides that might push sea-water into central London. When not in use, the six rising gates rest out of sight on the riverbed, allowing free passage of river traffic though the openings between the piers.
If a dangerously high tidal surge threatens, the rising sector gates are moved up though about 90° from their riverbed position, and the four radial gates are brought down into the closed defence position. The gates thus form a continuous steel wall facing down river ready to stem the tide (source: Environment Agency).
The width of the barrier from bank to bank is about 520m with the four main openings each having a clear span of 61m.each gate is 20m high, weighs 3,700 tonnes and is capable of withstanding an overall load of more than 9,000 tonnes.
Read more and watch a short animated film of the barrier in action on the BBC website
The Thames Barrier was originally designed to offer 1:1000 protection, meaning that it is only expected to be overwhelmed once every thousand years.
This estimate is based upon our statistical knowledge of previous storm surges.
However, if global climate is changing then in future the barrier may no longer offer the level of protection it was originally designed to give.
This is worrying news for the population of London. If flooding did occur, Westminster would be under two metres of water, and 68 underground and Docklands railway stations would be flooded, as would 16 hospitals and 400 schools.
As well as the risk to the physical body of London, the flooding of London would have a major impact on the economy of the UK and in turn, a potentially damaging effect to the world economy.
Meanwhile, London’s total level of risk is growing all the time, as more people migrate there and new housing developments increase the total value of vulnerable property.
With 200,000 new homes planned by the government below the high tide mark in the Thames Gateway area by 2016, the issue of dependable flood defence has become a major concern for policy-makers.
As climate change and sea level rise have become a reality, a new consensus has emerged that additional measures now need to be taken to protect London.
Estimates of sea-level rise due to climate change are wide-ranging. Conservative estimates suggest it will be less than 1m. However, some scientists think change is occurring more rapidly than previously suspected and that a rise in sea level of around 4m is possible by 2100. The Environment Agency has to prepare for all possibilities and has drawn up a plan that shows the measures that will need to be taken for a range of sea-level rises up to 4.2 metres (see the Flow Diagram below).
This new project to defend London is called Thames Estuary 2100. It addresses increasing flood risk due to climate change, sea-level rise, ageing flood defences and new development on the flood plain.
Using the Flow Diagram:
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Examine the x-axis. It shows possible sea-level rises up to 4.4m.
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Study the boxes. Each contains a possible flood defence method.
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Look at where each box ends and read off the corresponding sea-level rise on the x-axis. This tells you what rise in sea-level each proposed measure will offer protection for.
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For instance, “New barrier, raise defences” will work up to, but not beyond, a 2.6 m rise in sea levels.
Using the Flood Risk Management Map (Flood Risk Management Map Download), label the defences and areas that are shown on the Flood Risk Management PowerPoint Slide. Use this as Figure 1.
Study Figure 1.
(a) Describe the economic and social impacts a major storm surge might bring to London. (10)
(b) Examine the range of strategies employed to save lives in areas that experience extreme weather events. (10)
(c) Explain how primary and secondary sources could help you investigate potential flood risks along a named stretch of river. (15)
This article is written by Dr Simon Oakes, a Principal Examiner in A-level geography and regularly works as a flood hazard consultant for Middlesex Flood Hazard Research Centre. The RGS-IBG would like to thank Tim Reeder of the Environment Agency for assisting with the production of these resources (he is Project Scientist for the Thames 2100 project, which is looking at the future of the Thames barrier and flood risk management in the Thames Estuary).