Thames Gateway and flooding: going with the flow

After centuries of trying to keep floods out of developments, we should begin to let them in.

That’s one of the messages architect Robert Barker will give at the Thames Gateway Forum.

With some of the Thames Gateway lying on flood plains the question of how to balance housing with water is an important one.

Barker’s practice, Baca Architects, has come up with models for handling flooding in three areas: an urban site in Hackbridge in Sutton at the upper end of a river, a suburban site in Peterborough midway along and a rural, riverside site near the sea in Littlehampton, Sussex. The project, Long-term Initiatives for Flood-risk Environments or LIFE, was sponsored by the Department for the Environment, Food and Rural Affairs’ Making Space for Water programme.

At the Forum he will talk about the model with the greatest similarities to the Gateway, the Littlehampton site.

Water everywhere

The area is on an estuary and so has the largest number of sources of flood risk: sea level rise, tidal flooding, fluvial river flooding and flooding from rain.

“It is a common misconception that flooding is all the same but there are various different sources,” says Barker.

The team looked beyond Littlehampton to the whole of the lower end of the River Arun to see where development opportunities were, the high flood risk areas and the popular areas for living. The scenarios for the site looked at sea level rises from 1m, currently predicted by the end of the century, to 7m and the design should be able to handle a 2m rise in sea levels across the region.

Open the floodgates

The key to the design is that it does not try to keep every drop of water out but allows part of the development to flood in a controlled way so that property is not damaged and people are protected.

“It takes a more naturalistic approach to flood risk management to reduce dependency on defences,” says Barker. “It works with a more natural cycle and allows area of sites to flood on occasion.”

The conceptual masterplan for the site allows people to get down the river’s edge so on the river promenade there would be kiosks and cafes.

Behind this is a 1.5m high bank, landscaped to look natural rather than have the concrete and steel appearance of a flood barrier, which stands in front of the development. The land between the buildings is interlaced with channels that can fill with water as needed and could take up water if the defences failed.

A larger strip connects the river to two lagoons beyond the development. Soil dug out to build the lagoons would be used to raise the height of the harbour above flood level. The lagoons, which would have walkways, boardwalks and a marina would be a habitat for wildlife and a recreational area.

The development is landscaped to be a variety of heights. The residential areas have retail, light industrial and office space on the ground floor. Nobody would sleep on the lower levels of the development and interlinked corridors would make the buildings easy to evacuate. “If we build resistance into the buildings themselves then if the sea level rise is greater than predicted we will be prepared for it,” says Barker.

Forms of defence

The scheme is designed to have a series of flood mitigation measures.“I was in New Orleans and I saw the devastation of just having one line of defence,” says Barker. “The first port of call is to divert water to the lagoon but if there is a failure of the defences the water would be directed into the lower channel area.”

He says the chances of a flood coming into the building is less than one in a thousand – the same level as areas defined as at low risk of flooding.

The development could also have land-based wind turbines or generate energy from tidal flow.

A regional bulwark

Developments like this could protect larger towns by providing a place to store flood water. A river flood would create about £164m of damage to Littlehampton.

“The idea of living with water is a new idea,” says Barker. The government has been looking at the idea through reports and research programmes since 2004, but the public’s attitude is still usually that water should be kept at bay.

“We are trying to demonstrate there is a way of managing flood risk and creating a fantastic environment,” he adds.

He points out that he is not advocating building in flood prone areas, but at least 2 million homes are already on flood plains and, as sea levels rise, other areas already earmarked for development will flood more easily. There are also contaminated brownfield sites which need to be cleaned and built on otherwise flood water would wash the pollutants into the water system, he adds.

Baca will publish a set of principles and a guidebook to its approach in February 2009.