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Opening the floodgates

Flood protection - Thames Gateway

Solving the conflict between flooding and development will be crucial to build 120,000 new homes in the Thames Gateway, says Paul Wheeler.

The government wants to see as many as 120,000 homes built in the Thames estuary corridor within the next 12 years. Scarred by decades of industrial activity and postindustrial decay, the idea of regenerating the Thames Gateway as a place to live and work holds huge appeal.

But the idea is not without problems: Half the new homes could be located within the Thames floodplain (NCE 10 June), and the prospect of rising sea levels coupled with a recent increase in incidence of flooding, has forced many to question the wisdom of such a plan.

The Green Party, for example, describes the proposals as 'premature and potentially reckless'.

Others have raised concerns over whether home-buyers will be able to secure mortgages and insurance on properties within the Gateway. If flood risk is not managed sustainably, the insurance industry says it will be unable to provide affordable cover for development in the floodplain.

Threat of flooding has meant that the Thames Barrier is being closed more and more frequently - 57 times in the past six years, compared to four times between 1983-1989.

The Environment Agency believes flood-related closures have increased, in particular, over the past four years.

However, Environment Agency senior technical specialist Rachael Hill says that flooding of the Thames does not pose a major obstacle to the Thames Gateway project. Hill is a member of the Agency's Thames Estuary 2100 project, which is assessing how best to tackle the risk of inundation in the flood plain over the next 100 years.

Thames Gateway will be a major test for the Environment Agency and its new strategy for limiting flood risk, which moves away from the traditional focus of defending against floods to managing them.

'Our aim is to put flood risk into perspective, ' says Hill.

'It is about highlighting flood probability and consequence, and ensuring that land-use planners do not put the most vulnerable developments in the areas most at risk.'

The strategy is already obligatory under planning policy guidance PPG25, but is poorly understood and implemented by planners and developers.

It involves identifying where risks come from, determining their probability, assessing the consequences of a flood event and then making a decision on the siting of new development.

'The whole premise is that you must understand the risk before you can mitigate and manage it, ' says Hill. Where the probability of flooding is high, you need to select a land use that can tolerate the risk.

Alternatively, a number of flood management measures can be incorporated to reduce the impact of a flood event.

This is an area where under the new risk-based regime, housing developers could get very smart; in the Netherlands, for example, houses have been built that are designed to float when the area floods.

Flood management is all about common sense and making informed decisions, Hill says.

Radical thinking at the heart of the Thames Gateway plan involves creating a 'green grid' of open space. This will provide parkland, sports facilities and wildlife habitats that will also serve as flood storage capacity or 'manageable washlands'.

Alex Nickson, environment and sustainability officer with development agency London Thames Gateway Partnerships (LTGP), believes this introduces a level of sophistication to treatment of the urban landscape that has been missing.

'In adapting to climate change, we could actually improve the environment, ' he maintains.

Manageable washlands could vastly improve the biodiversity of dense new urban centres where they are built, he believes.

The Thames Gateway, he adds, should embrace the river: 'It's one of the region's greatest assets and the last thing you should be thinking about doing is raising the river walls.'

This requires a shift in public expectations of the consequences of flooding. While some land uses, such as hospitals and electricity substations, should never be located in areas at risk of flooding, parkland does not need to remain dry at all times - especially if it is designed to double up as flood storage.

Nickson envisages multi-level landscaped parks within the green grid. The lower level would be the storage basin with reed beds, a middle level could contain cycle paths and open spaces, while an upper level might include a perimeter footpath.

The Environment Agency last month opened the first green space designed along these principles at Sutcliffe Park in Lewisham (see box above).

There is, as yet, uncertainty over who pays for this 'green infrastructure', although a possible solution would be to view the grid as essential infrastructure - as important as, say, roads, services and schools.

It would then be part-funded by developers through planning gain, which is already used to provide social housing, to compensate for damage to wildlife habitats, or provide local transport, for example.

The Association of British Insurers (ABI) is also taking a radically new 'can-do' approach to flooding, says policy advisor on natural perils Sebastian Catovsky.

ABI next month publishes guidance setting out good development principles on the basis of which insurers will offer cover for developments within flood risk areas.

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