Model and map of English flood data fail to match says NAO

The Environment Agency's model of the risk of flooding from rivers and the sea does not match up with a map designed to raise awareness of flood risks, according to the National Audit Office (NAO).

"The Agency's national flood risk assessment and its flood map currently do not present consistent information," says its new report called Flood Risk Management in England.

The purpose of the flood risk model is to provide national and regional risk assessment to guide large-scale investment decisions, while the aim of the flood map is to raise the awareness of flood risk. It is also used by property owners and local authorities for development planning.

Unlike the national flood risk assessment, the map does not take into account any flood defences and does not show the distribution of the level of risk within the areas potentially affected.

The NAO's concerns come as the public sector ICT organisation Socitm calls for a higher priority to be given to ensuring useful government data is properly captured and readily available in a timely fashion to decision-makers.

The NAO also found that flood risk management authorities have "developed information over the years on a piecemeal basis, with the result that users of this information can find it inaccessible and difficult to understand."

Flood risk information needs to be brought together and made clearer and simpler, says the NAO, adding that it is not known how the different sources of flood risk combine and interact.

The NAO acknowledges that the Agency intends to develop a tool that combines information about flood likelihood from all sources by 2013 although this tool will not consider how the different sources of flood risk interact.

In addition, the NAO points out that England's flood defence infrastructure for smaller rivers and surface water is not fully known and approaches to build up this knowledge are not integrated.

The Agency is an international pioneer in developing a national model covering the long-term risk of flooding from rivers and the sea, but work is required to make it more effective, says the NAO.

The Agency does not routinely analyze the impact that data uncertainties may have on its risk assessment, making it less effective than it could be.

Over 5.2 million, or one in six, properties in England are at risk of flooding from rivers, the sea, or surface water. The annual cost of flood damage in England is more than £1.1 billion and is expected to rise.

The Environment Agency has contested some of the NAO's findings, in particular about its flood map. A spokeswoman for the agency told the press, "We currently use our flood map to raise public awareness of flood risk and encourage them to take action to reduce their risk.

"This map shows the entire area of land that could be flooded, and how those areas benefit from flood defences. The National Flood Risk Assessment shows the likelihood of those areas of land flooding, taking the reliability of defences into account."

She said the agency takes its strategic overview role seriously, so it is important that it has an understanding of the risks from groundwater and surface water as well as rivers and sea, and how they interact.

"We are the first country in the world to model surface water nationally," she said. "So the science for predicting surface and ground water flood risk isn't as mature as it is for predicting flooding from rivers and the seas, and it is much more complex. Interactions are modelled in areas of high risk, but are not included in our national scale products.

"This is why we are working with local authorities and academia to develop new scientific methods for predicting surface and groundwater flooding, and build up a bank of data from previous flood events that will help in these predictions," she concluded.