The London Problem
The Thames Estuary has one of the best tidal defence systems in the world. There is not just the Thames Barrier, but also over 200 miles of sea walls and embankments, which were upgraded and raised by 2.5 metres in the 1980s.

The effects of climate change will erode this protection gradually, and many of the sea walls and embankments will come to the end of their design life at approximately the same time. However, even if the Barrier were to be overtopped, this would only happen for a short period - for example during a high tide combined with a severe storm surge, so it will still give a high level of protection for many years.

London was one of the first "Mega cities" and has a population that will soon exceed 8 million. Attempts to limit urban sprawl with greenbelt regulations mean that there is a high concentration of people and wealth in a relatively small area. This means that it is very exposed to hazards, and its ageing infrastructure makes it vulnerable.

Overall in London the value of property in the floodplain is around £80 billion. The Thames Barrier alone protects property worth around £30 billion. If the Barrier were to be put out of commission by accident, terrorism or sabotage, London could be at risk of flooding, although there are many precautions taken to prevent this happening.

The Barrier will protect London against the 1,000 year flood until 2030, but it will have to be raised more often. Between its opening in 1982 and August 2001, it was raised 63 times. Most of these events have been in recent years: in the winter of 2000/2001 alone, it was raised 24 times, mainly in response to unprecedented freshwater flows. As at Jan uary 2003, the Barrier had been used a total of 82 times following its use in a record 14 consecutive tides to help to alleviate fluvial flooding in the Thames catchment, when flows in the Thames reached their third-highest value, a more-severe event than in Autumn 2000. By 2030, due to sea level rise and other factors, it has been estimated that it will need to be raised 30 times a year on average. It seems to be generally accepted that further protection will be needed at some point in the next 30 to 50 years. The Environment Agency has therefore extended its planning horizon by 70 years to the year 2100, and has started a project called "Planning for Flood Risk Management in the Thames Estuary" to develop a strategy for the tidal Thames from Teddington to Sheerness/Shoeburyness. Preliminary estimates of the cost of providing a 1,000 year standard in flood defences up to the year 2100 produce a figure of £4bn which will need to be spent in the next 40 years.

Upstream, along the non tidal stretch of the Thames , some 12,000 houses are within 500 metres of the river bank, and their riverside location adds £580m to the value of these properties. Along the tidal stretch of the Thames , 800,000 people live within a ten minute walk of the river.

London 's infrastructure is near full capacity, yet the growing demand for houses means that many more houses are to be built. According to the Thames Gateway web site, for example, the Planning Framework estimates that in due course Thames Gateway might provide over 110,000 new dwellings, with 70,000 anticipated by the year 2006. Of these, it was revealed at a recent conference in London , some 86,000 could be built in the Thames floodplain by 2015.

Local authorities have been asked to ".give priority to the redevelopment of vacant and under-used urban sites before the release of greenfield land, and to foster sustainable relationships between homes, workplaces and community facilities"

Nevertheless, most of the new housing will lie in certain major sites, including the Royal Docks, Barking Reach, Thamesmead, Chafford Hundred and Chatham Maritime, together with, in due course, Greenwich Peninsula , Kent Thames -side, and Havering Riverside.

One aspect which may really concern insurers is that in the Thames Gateway area it is planned to have a high concentration of dwellings: around 120 dwellings per hectare compared to a normal level of around 30 dwellings per hectare even in Southeast England . Therefore, while the Thames flood hazard may be low because it is has the best standard of protection in Britain , the exposure is set to increase enormously, threatening insurers' ability to carry such a high concentration of risk.

The value of property protected by the Thames flood defences is therefore set to continue to rise rapidly, and while the Barrier itself gives a high standard of protection, a weak link in the 200 miles of associated defences could cause localised problems.

While London may be well protected from coastal and river flood, there is still a problem with pluvial flooding from severe rainfall events. On 7th August, 2002 , an inch of rain fell in central London in 30 minutes during the evening "rush hour", resulting in the closure of five mainline railway stations, and considerable disruption. London 's drainage infrastructure is too old and overloaded to cope with such events. More than 50% of drainage and sewage overflow problems in England take place in London as will be seen in the next section.

Of course the problem of inadequate sewage and drainage systems is not confined to London .

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