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Home and dry
Housebuilder – May 2005

The Thames Gateway lies beyond the protection of the Thames Barrier and there is no denying it is largely a floodplain. Mark Smulian considers the implications for stakeholders involved with the government's housing growth plans, and how they plan to tackle the risk

Water is a splendid thing in the right place. Most housebuilders will be well aware that a house with a river view can be sold at a premium price. The problem comes when the view of the water becomes rather too close; when a river has burst its banks and flooded the house.

Potential purchasers are wary of buying a home built in any area known to be prone to flooding, and the insurance industry has talked about refusing cover for homes in such places, which would in effect make them un-mortgagable. Despite this, the government wants 120,000 new homes built in the Thames Gateway, an area notoriously at risk from floods. The vast swathe of brownfield sites available is too tempting a source of building land to be ignored, even if just over a third of the homes are due to be built on a floodplain. Thus, the water has to be tamed - the question for builders is how rather than whether this must be done.

Floods can be a sensitive issue around the Thames estuary. Older residents remember the 1953 floods, Britain's worst peacetime disaster in which hundreds of lives were lost.

With flood defences plainly obvious to anyone who cares to look - from the Thames Barrier to ordinary sea walls - there is no getting away from public concern about whether houses built in the Gateway might face inundation. Traditional flood defences have depended on embankments to contain water, but the Environment Agency's thinking is increasingly changing towards socalled "soft" defences.

This is mixed news for builders: they will not face so many demands to make costly contributions towards the construction of flood defences, but they will have to get their heads round some new concepts in "soft" defences and convince purchasers that these will be effective.

Soft defences can include, for example, buffer zones adjacent to water, perhaps parks or playing fields that can absorb the immediate flood and so allow less water to reach inhabited areas, where smaller and cheaper defences can then be built.

Another approach is to build homes in which the ground floor is a garage so that a flood would not damage living rooms, or perhaps to design homes so that electrical connections are not vulnerable to floods.

For surface water floods, sustainable drainage systems (SUDS) with ponds can be designed to reduce the rate at which water runs off to drains and watercourses.

This means that rivers are not overwhelmed during heavy rainfall, and the ponds provide an amenity and wildlife refuge in normal times.

The Environment Agency is quite optimistic about the potential of the Gateway, noting in guidance last year: "Provided all of the issues are carefully considered and planned for, there is no reason why [flood hazard] should be seen as a barrier to development".

change of thinking

Peter Borrows, the agency's Thames estuary strategy manager, explains: "There is a change in thinking from hard to soft defences where appropriate, and in future the emphasis on softer will be greater, though there are already hard defences in the estuary and they must be improved and strengthened when necessary."

Whether developers would have to contribute towards the cost of these is an issue that has "not bottomed out," says Borrows. He points out that flood defences in the Thames Gateway "are already provided to the highest standard in the UK, so the chances of a flood are very low."

Little or no-cost flood prevention measures include simple planning concepts such as, "do not put vulnerable groups' buildings such as schools or old peoples' homes right by the river," he says. "Most people, including insurers, are coming round to the view that these approaches make sense."

Longer term, the agency is developing a policy to take account of the effects of climate change, rising sea levels and the south east's gradual "tilt" to 2100.

The largest development facing decisions on flood prevention is Barking Riverside, a joint venture between Bellway and English Partnerships to build a 10,000-home new town between the River Thames and Barking town centre.

Project director Stuart Stockdale admits: "In the public mind flooding is a very high concern because of the amount of publicity about this in the press. That is a problem as people start to believe it, but from what I know the Environment Agency is confident."

Consultant Hyder is undertaking a detailed flood risk assessment, looking among much else at what to do with two streams that flow through the site and which have their outlets to the Thames blocked at high tide. "We have to work out how high the water could come and design around that," says Stockdale.

Modelling suggests that the worst case for which Stockdale should plan is a long gradual storm that built up water, rather than a short intense cloudburst, although the latter can be the main hazard elsewhere. The site will use ponds to contain this water for slow release in the way suggested by the agency.

Barking Riverside already has a 7.4m river embankment and this will be raised slightly to 8m to meet the agency's new requirement to plan against a predicted once-in-1,000-years severe flood. "We will keep a half metre above the flood level and raising the defences on our 2km river frontage is something we have to do anyway as a responsible landowner," says Stockdale.

One potential customer for housebuilders in the Thames Gateway, were he thinking of moving home, is Colin Green, professor of water economics at Middlesex University.

He says: "You always have to think about a bigger flood than one that has happened, but I would buy a house in the Thames Gateway floodplain because one in 1,000 years flood protection is pretty OK and I'd be happy with that, its an acceptable risk."

Professor Green says the government will need to spend generously to ensure defences are in place for its 2025 to complete the bulk of Gateway development. Soft defences are cheaper, he says, and do less damage to the environment than, say, the construction of huge dykes around sites.

Green explains: "For example, a mudflat on the seaward side means waves lose height as they go across that and your physical flood defences can be smaller. "Parks alongside the river certainly help, but you need space for that and I imagine housebuilders hope it will not be them who have to find the space."

insurance issue

The insurance issue is bedevilled by economics, he says. In the past insurers offered cover everywhere on the assumption that claims in flood-prone areas would be balanced by premiums from customers in areas not at risk. "Now, you have direct sellers who can provide flood cover at cheaper premiums by cherry picking customers in low-risk areas leaving conventional insurers with policies in areas at risk, which of course concerns them," says Green.

Last February, the Association of British Insurers published recommendations to mitigate risks of building on floodplains. Planning policies that emphasised floor protection, "could reduce flood risks by half in Thames Gateway," it argues.

The insurers say the government should ensure that new developments are built on the lowest-risk sites first, that councils should make flood risk assessments so that risks could be reduced before building began, and that flood defence spending should be targeted towards vulnerable sites.

Keith Hill, the planning minister, announced a consultation on flood risk policy just before the general election. In its new guise as Planning Policy Statement 25 this is expected to say that major development applications in areas prone to floods would be called in by Whitehall if a council wanted to give planning permission against the agency's advice. Hill said he was "concerned at the number of instances where planning permission is still being granted against Environment Agency advice."

About half of the agency's objections arose where no flood risk assessment had been made, and Hill said the new policy would clarify guidance on risk assessments, with a stronger requirement to match types of development against levels of flood risk.

It is clear from both the government and insurers that gaining planning permission for developments on floodplains - and not just in the Thames Gateway - will be an increasingly demanding process, potentially requiring builders to commit themselves to flood alleviation measures that may be costly, unpopular with buyers, or both.

But since "water before your eyes" will always be a more potent sales slogan than "water under your feet," flood protection will be a growing issue as constraints on greenfield building brings more marginal land into play.