New homes could increase flood risk without 'sustainable drainage systems'

Building new properties to ease the housing crisis could increase flood risk for existing homes by overwhelming already-stretched drainage systems, a report warns.

The Government has a target to build a million new homes by the end of the decade to meet rising demand.

But current planning laws make it too easy to connect new developments to existing mains drainage, which are already above capacity, instead of putting in more sustainable systems that reduce flood risk, the report said.

With sustainable drainage systems, rainfall running off new roofs, driveways and roads is caught in ponds, bog gardens or other natural features that release it slowly into the ground.

Such systems can be installed affordably and without delay in nearly all developments, and are cost-effective when included early in the planning process, according to the report by Chartered Institution of Water and Environmental Management (CIWEM) and the Wildfowl and Wetlands Trust (WWT).

But a survey of 539 industry professionals conducted by organisations including CIWEM and WWT found 70% think planning policies do not sufficiently encourage sustainable drainage systems.

Almost two-thirds (65%) thought the Government's non-statutory standards for sustainable options were not effective.

And three quarters thought local authorities did not have the in-house expertise to check and advise on sustainable options, or challenge proposals that could increase flood risk.

Overwhelmed drains are the most common type of flooding in towns, costing the economy £260 million a year, with water in heavy rainstorms rushing off roads, roofs and other hard surfaces and into the drains or watercourses which cannot cope.

New developments can worsen that flood risk not just locally, but for communities downstream, the report said.

It is a growing problem, with more people living in towns and changing weather patterns delivering more intense rainstorms.

After the devastating 2007 floods, much of which were caused by surface water, laws were passed to require developers to exhaust "sustainable drainage system" options before connecting to the mains, but they have largely not been implemented.

The CIWEM and WWT are calling for the Government to strengthen planning law so that all new developments would use sustainable drainage where possible.

There should be better standards to ensure developers build quality schemes that improve local water quality and wildlife, and the Government should review the wider impacts of such projects with a view to rolling them out to older buildings.

CIWEM chief executive Terry Fuller said: "We recognise the urgent need for one million new homes but it is pointless to build in a way that creates flood risk for the future."

He said the analysis showed the main obstacles to sustainable drainage schemes were "political and institutional rather than technical or financial".

WWT chief executive Martin Spray said: "It is time for clarity: developers must include good natural drainage systems for our homes, and Government must make sure they are maintained.

"We can make this change affordable and quickly, delivering new defences and new habitats, without slowing down house-building."

A Department for Communities and Local Government spokesman said: "We've put in place strong safeguards to stop inappropriate development in areas at risk of flooding, and we are clear that sustainable drainage systems are critical for reducing surface water flood risk.

"Planning authorities have to make sure new buildings are flood-resilient and we expect sustainable drainage systems for all new developments with 10 or more homes."