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Flood prevention is not all about new defences

Portsmouth City Council said this week that it plans to impose a Community Infrastructure Levy (CIL) on new developments in the city to raise money for much-needed coastal flood defences (see News). It’s a clever way of making new developments work for the city.

But existing developments are also capable of helping to reduce flood risk − and if local authorities take a leadership role on retrofitting and what is termed “undevelopment”, existing developments can be made to work equally hard against flooding.

Existing developments

Undevelopment is the redevelopment of a brownfield site on a smaller scale. This doesn’t necessarily mean banning new buildings, but it might mean that a project on a brownfield site would be designed with as much green space and sustainable drainage systems (Suds) as possible, to optimise surface water management and create safe flood pathways.

Surface water management discussion tends to focus on new developments − and with the impending Flood and Water Management Act demanding that all new developments have Suds approved by a local authority, it’s easy to see why.

“You can minimise flood risk, but no flood risk is quite hard to do.”

David Balmforth, IIFRMG

But the bigger challenge − and bigger rewards − may be found in retrofitting surface water management systems.

The Inter-Institutional Flood Risk Management Group (IIFRMG) − made up of bodies including the ICE, the Royal Town Planning Institute and the Chartered Institution of Water and Environmental Management (Ciwem), among others − champions the idea that development should not increase flood risk.

“That’s quite a tough one,” says IIFRMG chair and ICE vice president David Balmforth. “You can minimise flood risk, but no flood risk is quite hard to do.”

The best way to achieve it, he says, is to be prepared to reject many developments in significant flood risk areas.

Current planning rules allow these developments to go ahead if the right hoops are jumped through.

“In some cases, maybe the development [shouldn’t] go ahead at all.”

David Balmforth, IIFRMG

“We kind of don’t agree with that. We want it to be tougher than it is at the moment,” says Balmforth. “In some cases, maybe the development [shouldn’t] go ahead at all.”

This is all part of making space for water, shifting the flood engineering focus from defence to resilience, and learning to live with the more frequent and severe floods that are predicted in future, thanks to climate change.

But where it is too late to prevent inappropriate development, there may yet be opportunities to undo the development of the past − provided planning authorities are converted to the cause.

“We want to see the potential for undevelopment fully realised,” says Balmforth, describing the concept of undevelopment as a carefully managed reassignment of space when a plot comes up for redevelopment.

Brave choices

Even so, imposing such requirements on developers could be tough for local authorities. They might fear that demanding flood-friendly redevelopment could limit economic growth in their regions, or deter developers from the area altogether.

These brave choices will only be made if elected representatives and council personnel are persuaded to put flood risk management “right up at the top of the urban design agenda”, says Balmforth. “It’s got to be built into their strategic planning.”

Equally, retrofitting existing developments with Suds is crucial if surface water is to be managed efficiently, and surface water flood risk reduced.

Pioneer projects

If existing developments can be retrofitted with Suds to the point where they can be disconnected from the wastewater network, there is an added benefit of freeing up sewer capacity to deal with new development elsewhere.

But the benefits of doing this must be demonstrated by a number of pioneer projects if the idea is to take hold.

“Where are the examples where that’s been done? I don’t think we’ve exploited it enough,” says Balmforth. “There are still tiny pockets of good news, but I’d like to see more.”

Here, too, success will depend on local authority figures driving such schemes forward.

Construction Industry Research & Information Association (Ciria) associate Paul Shaffer told a Ciwem surface water management conference last week that retrofitting measures can be successfully done on a piecemeal, opportunistic basis − such as in The Dings, Bristol, where a street has been retrofitted with permeable paving − or as a more strategic mix of solutions across a whole site.

Either way, he said, there must be “leadership to take the bull by the horns”, accompanied by guidance from professional institutions and − hopefully − the government’s water White Paper, due later this year.

These leaders must demonstrate that no space is useless, and that even the most developed spaces have a part to play. “Good places are never finished,” he said.

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