Landmark incorporates the first groundwater flood risk map available for England and Wales

Environment Agency maps show that about 5 million properties in England lie within areas at risk of flooding, but this does not include the greater risk posed by potential groundwater floods. Until now, there has not been any authoritative information to show where property is at risk of flooding by groundwater, with the only data available for the purpose merely showing susceptibility. However, with the publication of the ESI National Groundwater Flood Risk Map it is now clear that only half the areas thought to be susceptible to groundwater flooding are actually at risk, with just 12% of the land area of England and Wales situated within areas at risk of groundwater flooding (Scotland will be released spring 2014).

We are pleased to report that the problem is more localised than previously thought - around 50% of that suggested by previous data - where groundwater flooding does occur it can lead to longer duration impacts and increased damage to property than other causes of flooding.  By combining information on likelihood and severity, the new map provides vital data to indicate for the first time where property is at risk.

The findings are presented in a comprehensive series of new data sets that are being leveraged by us in partnership with environmental consultancy ESI.  Our reports will have a major impact not only on the way in which land is assessed and prepared for development, but also the speed at which property purchase transactions can take place.

Based on scientific and quantitative groundwater flood risk models, including data from the British Geological Survey national geoscience database and calibrated to the best available field evidence of flooding incidence, this is the first risk data set focusing purely on groundwater. The data will be incorporated into our proprietary risk assessment reports, thereby playing an integral role in sales transactions and land-use planning by facilitating even more detailed site evaluations, together with advice around a suitable programme of protection measures where appropriate.

One of the key benefits of the data is that it specifically assesses risk, rather than susceptibility to flooding. This means that it is significantly more accurate than other data sources, due to the fact that it gives fewer ‘false positive’ results. In turn this means that, for the residential market, conveyancing solicitors can more accurately highlight risk to new homebuyers, facilitating quicker transactions because properties will not be unduly blighted by less accurate flood data. Furthermore, from the very outset environmental consultants can more correctly identify, mitigate and avoid potential development in areas that are confirmed as being exposed to groundwater flooding.  

Groundwater flooding typically occurs after long periods of sustained high rainfall and takes longer to dissipate than surface water, meaning that groundwater floods can persist for several weeks and even months following severe flooding. Recently, many locations have seen groundwater levels rise by more than 10 metres thanks to prolonged and persistent rainfall conditions[1], and recent groundwater flooding events have proven the value of this new map by confirming the validity of the risk model.

Chris Taylor, Director at Landmark Information Group, commented: “With extreme weather conditions threatening to become ever more prevalent, the ability to more accurately assess risk promises to become an increasingly important tool in first stage prevention. Not only will it act as a powerful screening tool in the early stages of planning, but the ability to clarify different levels of risk will play a huge role in helping people locally in planning ways to avoid exposure to flooding wherever possible.”

Mark Fermor, from ESI added: “There are areas where groundwater flood risk is significant, and it is important for those contemplating purchasing property or developing land to understand the risks and how to manage them.  There will be local or site-level features that are not included in these preliminary assessment maps but will act to prevent actual flooding, so it is also important to review the detailed guidance provided in the reports to put the findings in context.  Groundwater flooding is a significant problem and these new reports provide the advice needed to understand the data and what action, if any, is appropriate to address the risk.

We will be incorporating the groundwater flood risk data into a wide range of its risk assessment reports, including Homecheck Flood, Envirosearch Residential, SiteSolutions Residential, Sitecheck Combined, SiteSolutions Commerical and SiteSolutions Combined. 

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[1] Thames Water