As the government presses on with its ambitious Thames Gateway housing development, Michael Hammond asks whether enough consideration has been given to the risks of flooding in these days of rising sea levels, global warming, and erratic rainfall
As devastating floods swept through Southern France at the tail end of 2003, the British government was rolling out the first phase of its 120,000-home Thames Gateway vision at Barking Reach, east of London, where it plans to build 10,000 properties on a flood plain.
It is no coincidence that London's peripheral development has organically grown out to the west. The wet marshes and meadows to the east were - and still are - largely unsuitable for building. Ignored by settlers since Roman times, this desolate windswept area was once the scene of Dickens' rotting prison hulks, housing people pushed to the margins in the UK's damp equivalent of Siberia. Nothing much has changed. The east marshlands remained 'undiscovered' until an increasingly desperate government needed to find homes for hundreds of thousands of migrants and key workers expected to swell London's already growing population in next few decades. The increase in land costs means that the once prohibitive costs of incorporating flood defences may now be acceptable.
Wet and wild
Estuaries are unique, at risk from both river and sea. Rainfall-swollen rivers can burst their banks. The lunar cycle creates two high tides each day of approximately 6m range, even higher at the equinoxes. Sea surges, caused mainly by the action of wind on the surface, effectively 'lump' it up, making the waves higher and more threatening. Sea level is also related to atmospheric pressure, rising by one centimetre with each millibar decrease in pressure. The unique topography of the Thames Gateway amplifies the risks, its low-lying lands and the inherent form of the estuary creating a funnel, open to the North Sea which, under easterly winds, can further increase the height of surges. A strong wind coupled with very low pressure can raise the sea level of eastern England by more than 2m. Without getting embroiled in the global warming debate, it is generally acknowledged that sea levels are steadily rising, adding again to the risk.
During a violent storm on the night of 31 January 1953, the sea defences protecting Canvey Island failed and 58 people died.
This was not a one-off freak occurrence, according to the Met Office website: 'Since time immemorial, coastal areas of eastern England have been inundated repeatedly.'
The first recorded flood in the region was in 1099, with many reoccurrences since. Yet since the 'great tide', as the disastrous Canvey Island flood became known, its population increased from 5,000 to nearly 50,000. This increase led to Canvey's evacuation procedure being abandoned in the 1990s, when police warned of the possibility of fatalities in the panic to get off the island.
Even with today's technology and sophisticated measuring techniques, assessment of flood risk can never be absolute; more a juggling of probabilities and variables. In its bid to gain acceptance for the development, the government constantly refers to the 'accepted risks' of a 100-year storm, but also concedes that 'the current one-in-100-year high-water on the east coast may be expected to be exceeded every 20 years by 2050. There may also be secondary impacts such as changes in wave height and frequency/duration of storm events.' This one statement seems to undermine all the base calculations.
According to Ray Kemp of the Environment Agency (EA), we had a 'near miss' as recently as 1999. 'On the night of Christmas Eve, we were only two hours away from an almost hurricane-force wind hitting the south coast. The storm was going to coincide with high tide, bringing potential disaster, but a couple of hours before it was going to hit, it suddenly veered towards the north of France. There it caused over 100 deaths.'
When designed in the 1970s the Thames barrier was predicted to be raised some 10 times a year, but in the winter of 2000/01 it was activated 24 times. But sea and river defences are a double-edged sword. On one hand they decrease the risk of flooding, but the other, should a breach occur, as in the case of Canvey, the consequences are much more serious when large quantities of water are released en masse. PPG 25 states: 'Development on land protected by sea defences would be extremely vulnerable in the event of any overtopping or breaching of those defences because of the speed of flooding in such circumstances. A breach with tidal surge, for example, might involve high risk of loss of life.'
Sarah Lavery, the EA civil engineer heading a team of 15 designing the next generation of Thames flood defences, said to James Meek of the Guardian: 'There is a risk, a very small risk, of a catastrophic event.' The Thames Barrier will have exceeded its design life by 2030 and a whole new array of defences are being planned, including protection for the Thames Gateway development. But, as Lavery continued, 'it seems to us that in the future it is going to be impossible to protect all these houses'.
The wrong type of rain
Richard Houghton, Thames Gateway project manager for the EA, has other concerns.
Bizarrely, water supply is a major concern of his. 'Nationally it's the driest area of the country, so you are starting from a low base point. You've then got the most densely populated area of the country so you've got high demand.' The same climate change that increases flood risk is also responsible for a severe water supply crisis. Shorter bursts of heavy rain as opposed to steady persistent precipitation over long periods is, to misquote British Rail, 'the wrong kind of rain'.
Coupled with the dramatic increase in demand this creates a big gap in the supply/demand equation. 'We are already very close to imposing restrictions, and that is before Thames Gateway.'
Houghton is also concerned about land contamination and waste disposal, both industrial and human. The 14 zones of change along the banks of the Thames have seen a cocktail of polluting industries: oil refineries, gas works and power stations to name a few. Traditional methods of burying waste cannot be used on flood plains, and increasingly stringent EU regulations could have a major impact on costs.
The cost of flooding ranges from emotional trauma through financial loss and property blight to risk of loss of life itself. So what reassurance does the government have for prospective purchasers of Thames Gateway homes? The second report of the Environment, Transport and Regional affairs committee HC64 'Development on, or Affecting, the Flood Plain' recommends local authorities carry a disclaimer in their responses to search enquiries, 'that the information (supplied) is not a wholly reliable measure of the likelihood of flooding'.
In its relentless pursuit of its building targets, the government seems to have pushed aside the fundamental principles of prudent construction.
PLANNING AND POLICY GUIDE 25 (PPG 25)
PPG 25 sets out the framework for defining flood risk for planning purposes.Due for re-assessment later this year, the ongoing consultation and redrafting process provides an interesting insight into the government's thought process and objectives.On investigation it soon becomes apparent that small manipulations of the flooding probability ratio enable vast tracts of land to become 'buildable'. The definition of the functional flood plain (the high-risk areas vulnerable to flooding) is based on an annual probability of 1per cent for rivers and 0.5 per cent for coastal areas, ignoring defences. The reason for the difference is that storm surges make coastal flooding more dynamic. The government's eagerness to release the flood plains into the development land pool is evident at every paragraph: '[the river flood probability] was thought unduly restrictive and could preclude development on brownfield sites in the flood plain'. Further, it was believed, 'that this could lead to economic and social blight'. Boundaries are further blurred by recommendations that allow the risk factor to be relaxed if flood defence measures are incorporated in development proposals.
As if mitigating its policy of building in high risk areas, PPG 25 even goes as far as attempting to alleviate the resultant damage by recommending that 'flood-proof construction techniques should be encouraged for use in developments at risk from flooding and incorporated into the building regulations'. These techniques included having power outlets above the flood line and requiring electrical safety to be added to the building regulations. The use of perishable floor coverings such as carpets was also to be discouraged.
Malcolm Tarling of the Association of British Insurers reports that 'ABI members will look to provide cover wherever possible notwithstanding that premiums and terms and conditions have to reflect the risk'. He describes the current system of flood defences and management as 'aged', and claims that the ABI has repeatedly called for action from the government.