In the wake of Hurricane Katrina, insurers have warned about the flood risk in the Thames Gateway

Flood experts are urging the government to consider ways to protect the Thames Gateway in the wake of the New Orleans disaster.

The Association of British Insurers is lobbying London’s authorities to reduce building on brownfield land to prevent the capital suffering from catastrophic flooding. Other experts say no ground-level accommodation should be built.

The ABI wants local authorities to consider building on greenfield land after a government study last year showed that flood risk could only be effectively reduced by developing sites that have a lower risk of flooding.

In a submission to the London Assembly on Monday, the ABI said: “The ABI supports a policy to develop on appropriate brownfield sites, but this must be balanced against other considerations, including the impact on flood risk. Because many brownfield sites are in the flood plain, their redevelopment could substantially increase the risk.”

The ABI has suggested that vacant banks of low-quality greenfield land could be developed instead of building in high-risk areas. It has floated the idea of a “land swap” to prevent overbuilding on the brownfield land that is needed to act as a natural flood plain where water could be directed in a major flood.

Dr Sebastian Catovsky, head of the ABI’s natural perils department, agreed that the Thames Gateway was highly susceptible to flooding.

He said: “Ninety-one per cent of the new housing in east London would be in the flood plain. In north Kent, 65% is in the flood plains, in Kent Thameside 45% and in Essex 35%.

“The probability of such an event is lower but if it happened it could have just as serious effects as New Orleans. The chance of it happening is once in a 1000 years, but if it did it could flood as suddenly, or even more suddenly. Thamesmead, for example, is 3 m below sea level.”

Any major flooding in the Thames flood plain could cause between £40bn and £50bn of damage, with addional disruption costs put at 30-50% of that figure.

Roland Grzybek, flood risk expert at engineer Halcrow, said the flood risk in the Gateway could be countered by not using the lower floors of buildings for housing.

He said: “The house types for rebuilding New Orleans will need to be specifically designed to cope with flood events. In the Thames Gateway planners are looking at schemes in which the lower two floors would not be used for accommodation, and this will almost certainly be considered in New Orleans.”

However, he added that problems could arise with this in the USA because, although most property would be condemned, some properties would not be demolished completely. This contrasts with the situation in the Thames Gateway, where developments are being constructed from scratch.

Despite the potential problems, Grzybek said the UK was better prepared for flooding even in risk areas, as it had better flood risk management procedures in place than the USA. He said: “In the USA it is difficult to understand who is responsible for planning flood-plain developments and who is responsible for responding to events like New Orleans.

“Nobody knows whether it is in the remit of the federal, state or local government. The USA will need to reappraise, as we did five or six years ago.”

The eventual bill of the recovery and reconstruction operation in New Orleans is expected to run to £25bn. Among firms involved in the city, engineer Parsons Brinckerhoff has been contracted by the Federal Emergency Management Agency to work on the reconstruction. Kellogg Brown & Root is assessing the city’s infrastructure and pumps under a contract it has with the US Naval Facilities Engineering Command.