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Defending the Gateway
Contract Journal – 28 June 2005

Developers can heave a sigh of relief – the government has dropped plans to levy a flood defence tax on new housing in the Thames Gateway. Instead, they will be expected to incorporate sustainable, 'soft' drainage solutions into new developments. Mark Smulian explains

Flooding is an emotive issue for many people in the Thames Gateway area.

Even among those not born at the time the folk memory remains strong of the 1953 floods, Britain's worst peacetime disaster of the last century. Hundreds of lives were lost along the east coast, and homes and land were ruined, in the freak combination of high tides and winds.

Vast amounts of money have been spent to make sure nothing like it can happen again. The most visible manifestation is the Thames Barrier, but elsewhere embankments and sea walls have been used to keep the water at bay.

But the combination of climate change and the 'tilt' of Great Britain, so that the south east is slowly sinking, means that flooding remains a threat.

This situation might not immediately recommend the Thames Gateway as a sensible location for 120,000 new homes by 2016, as the government plans.

Some of these would be on the floodplain, an area which the Environment Agency admits "will become increasingly at risk of tidal flooding".

The agency, the official environmental watchdog, oversees flood protection and defences, and is leading a move away from 'hard' solutions such as building embankments to 'soft' ones of managing flood water.

As ever, there is mixed news for builders.

On the one hand, they will not have the agency coming round with a collecting tin for flood defence contributions. On the other, they will have to grapple with some unfamiliar concepts and design ideas to benefit from the 'soft' solutions.

According to the agency, the areas at risk on the gateway floodplain are those below the 5m contour line.

But rather than ban the construction of homes there, or order the erection of enormous walls to protect low-lying areas – as happened at Canvey Island after 1953 – it is moving from flood defence to flood resilience, from hard to soft.

In plain terms, this means enabling areas to survive floods without the need for large engineering works.

Guidance released by the agency at a conference in mid-July for developers working in the gateway firmly pointed out, "for too long we have been over-reliant on hard engineering, such as concrete walls and steel barriers, which requires maintenance and which can have an adverse impact on the surrounding area. Effective land use involves matching developments with flood risk".

The agency's suggestions for putting this 'soft' engineering approach to floods into effect included:

It is also concerned that remediation is carried out with an eye to future flood risk. Much of the gateway is brownfield land contaminated from previous uses.

Remediating this land to meet present hazards is all very well, but not if this means that contaminated material could surface in a future flood that was a consequence of climate change.

"Careful thought must be given the engineering solutions that will be used to remediate contaminated land, as if a site may become subject to flooding some engineering solutions may not be suitable," it says.

However, even the agency with its focus on the environment, generally maintains a sunny optimism about development in the gateway, noting that "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 the development".

Rachael Hill the agency's senior technical specialist on flooding, says the gateway floodplain "is protected to the highest standard in the country and the probability of flooding is very low".

There have been no serious floods since 1953 in the Thames estuary and not since 1928 in London, she points out. The protection is to a standard against all but a 'once in 200 years' flood level.

The agency requires flood risk assessments for all development in the floodplain area.

At the first stage, this is a strategic assessment for master plans of entire areas and looks at the likelihood of flooding, the sources of risk and the consequences.

This enables planners to reach informed decisions on suitable and unsuitable locations for development.

Flood resilience means that the most vulnerable facilities, such as schools and hospitals, should not be built on land most at risk.

For homes and other development, it is matter of "looking at where the water will go and not cause harm", she says.

This might mean, for example, that land most prone to flood is used for car parking or public open space, or that homes are built on raised ground or so that the ground floors do not contain living quarters.

Hill explains: "Flood resilience is a move away from flood defence and fixed protection to flood management and it does mean that there is some risk to property."

The second stage is a site-specific assessment for large individual developments that will look at "where gets wet, when, where, and then describe how to manage it".

It is an approach that does not rule out the construction of physical flood defences, but uses them only where unavoidable.

House builders and other developers have to ensure their developments are safe. The agency can object where this is inadequate or formally approve as satisfactory those that meet its standards.

But Hill says resilience techniques are "very cost effective and cheaper than traditional flood defences".

There is, she says, no issue of builders having to pay the Environment Agency to erect flood defences.

All of which is good news for the House Builders Federation, which was alarmed two years ago when environment minister Elliott Morley floated the idea that there should be a charge levied on developers to contribute to flood defence.

"We heard nothing about how it would work, and have nothing since," says the federation's spokesman Pierre Williams.

He points out that the reason that the gateway is a regeneration area in the first place is that it has a great deal of brownfield land but minimal infrastructure.

"If brownfield regeneration is going to happen as quickly and comprehensively as the government wants it will need significant public investment," he says.

"If they believe house builders will foot the bill for decades of under investment, it is just farcical."

The federation recognises that a builder who gains planning permission in an area of flood risk must ensure the site is safe, "but it better to look at this strategically and defend an area rather than to erect small flood defences all over the place", says Williams.

Increasingly, builders are turning to sustainable urban drainage systems, which, as far as possible, mimic nature in their disposal of water.

These can use gravel swales, reed beds and retention ponds among methods to collect water and release it slowly into rivers and ditches.

Williams points out that the problem with conventional concrete pipe sewers is that they "remove water at speed", leading to a rapid rise in river levels and exacerbating flood problems.

Normal flood defences can also have the effect of simply moving floodwater, so that effective defences at point A mean the water inundates point B.

In line with the agency's approach of managing floodwater rather than building defences, sustainable drainage gives builders a weapon that can allow marginal floodplain land to be built on without the need for excessively costly embankments and walls.

The fount of wisdom on this and related subjects is the Office of the Deputy Prime Minister's Planning Policy Guidance Note 25.

This says that "continued construction of hard-engineered flood defences to protect development in areas exposed to frequent or extensive flooding might not be sustainable in the long term.

"Soft engineering techniques such as creating, preserving and enhancing natural flood meadows and washlands can be of great value."

It notes: "In particular, as part of its strategy for sustainable development, the government wishes to avoid an unnecessary increase in the requirement to provide artificial defence against flooding."

Developers must satisfy local councils that they can manage any flood risk both to their own or adjacent sites, and are usually responsible for flood defence and mitigation works.

Public money is available normally only where flood works form part of some wider regeneration project.

Ian Cox, director for urban regeneration projects at Bellway Homes, says the use of water management schemes is being encouraged at the company's developments.

At the Barking Reach site in the Thames Gateway, where Bellway is working in a joint venture with English Partnerships, remediation of the site is compatible with the agency's strategy to avoid the risk of flooding and involves raising the level of the land.

There is also a large balancing pond to ensure that a low level of water flows into the local streams in the event of a storm surge, and is then released later so flooding is avoided.

The whole tenor of PPG25 is supportive of 'soft' sustainable drainage measures. Jon Offer, who works for Westbury Homes Central, is an expert in these systems.

He says the agency was at first "not very forward thinking in the Thames Gateway" because it assumed that floodplains could not be built on. "You can if you do the right thing," he says.

Sustainable drainage is about handling the water as close to its source as possible.

It helps also to embellish builders' 'green' credentials with the public because allowing water to be absorbed by the ground or in ponds, rather than being rushed away at once by pipes, helps to sustain groundwater supplies – a sensitive issue in the dry area around the gateway.

"It might be that homes are built in a floodplain but the ground floor is a garage," he says.

"While people would not want their car ruined by flood water if there is sufficient warning it could be moved and that is a risk people might accept."

Offer speculates that homes built on vulnerable areas would be sold at lower prices than those elsewhere and so would possibly attract first time buyers or key workers, both groups the government is keen to accommodate in the gateway.

"You can flood proof homes, for example by having the ground floors and walls tiled and the power supply above ground level, and if you are flooded you can hose it down and be back in business in a week if there are no timber floors," he says.

"It is matter of risk, and if I could have a home in the area where I need to live, and at a cheaper price than elsewhere, but had to accept a one in 30 years flood risk, I'd buy it."

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