Page last updated at 16:01 GMT, Wednesday, 25 March 2009

Research reveals flood-risk areas

By Matt Precey
BBC News

Flood sign c/o PA
Research examined areas at risk from surface water flooding
More than 127,000 homes across the east of England could be within areas at risk from flash flooding, according to research carried out for the BBC.

Almost 1,500 electricity substations are also within vulnerable areas.

And in one county, Hertfordshire, almost a quarter of fire stations are situated in locations which may be at risk from the sort of intense rainfall which hit parts of the UK in the summer of 2007.

The analysis was undertaken by the company which is supplying the Environment Agency with the first maps identifying those locations likely to be vulnerable to what is termed surface water flooding.

The scenarios are based on rainfall volumes similar to that which caused the emergencies in Hull and Gloucestershire in which 55,000 properties were flooded, costing insurers an estimated £3 billion.

The report which looked at the lessons to be drawn from these events, the Pitt Review, described the floods as "the biggest civil emergency in British history".

Estimated numbers of homes in potential flash flood areas
Beds 11,351
Cambs 14,777
Essex 28,008
Herts 28,297
Norfolk 15,302
Northants 9,976
Suffolk 17,268

BBC East asked JBA Consulting to calculate the number of buildings in the region which lie within the risk areas of their surface water flood maps.

This was done by cross-referencing detailed topographic data with information which pinpoints the precise location of every building in the region.

JBA's analysts identified Essex and Hertfordshire as having the most number of buildings at risk from extreme rainfall events.

According to Jill Boulton, JBA's Technical Director, the proximity of these counties to London is probably the reason.

"Hertfordshire is most at risk because they built in areas you probably wouldn't because of population density - they've concreted over a lot of areas that were draining and now aren't."

Bedfordshire appears to have the highest proportion of domestic properties in risk areas - 6.6% of the total number of homes. Hertfordshire has the highest number with 28,297 (6.1%).

Computer modelling

This analysis does not take into account the built environment, flood defence measures or sewer capacity - it only identifies where rainwater is likely to collect.

The scenarios are based on flooding to a depth of 0.3m.

Last year's Pitt Review said such rare rainfall events will become more frequent over the next 30-100 years with the effects of climate change possibly becoming "more extreme than had previously been estimated", it said.

In particular, the potential increases in rainfall volume, intensity, and temperature, are greater making it "virtually impossible to assign a meaningful probability" to such events.

According to Pitt, the only certainty is that the risk will increase and that the authorities have to act now.

The flood maps the analysis is based on are part of a drive by the Environment Agency to implement the Pitt recommendations to better understand surface water behaviour and to identify the risk areas.

JBA said the figures were only estimates generated using computer modelling, several variables and data from a number of sources which could be subject to extensive variation.

Although its estimates could not be viewed as accurate, they "should be viewed as broadly predictive of what could happen given a coincidence of some of those variables".

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Northampton councillor Brendan Glynane said people should have flood plans for their homes



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