A national study of groundwater flooding risk by a leading UK groundwater specialist has revealed the potential cost to property in England from this ‘hidden hazard’ to be £530 million.

Groundwater flooding is a risk which is excluded from many insurance policies and was missed from the recent National Flood Resilience Review and Department for Environment Food & Rural Affairs (Defra) Select Committee reports. Our company, ESI Consulting, believes that flood risk analysis and recommendations from recent government reviews have, to date, been too ‘rivers-centric’ and that a more robust risk management plan is needed to understand and tackle this costly, but largely ignored natural hazard.

ESI has completed national mapping and developed preliminary economic analysis of the risk of groundwater flooding to property and infrastructure. Using this, combined with other flood risks, we have created the first ‘Flooding from All Sources’ dataset using advanced modelling techniques on a five-metre grid.

Now, drawing on available Environment Agency, Ordnance Survey and British Geological Survey data, and the national groundwater flood risk maps created by our sister company Geosmart, we are discussing with Defra how these ‘flood risk from all sources’ maps may be made available for public use. We are advocating an immediate increase in the Environment Agency’s flood risk management function, with more focus on groundwater science on a catchment basis.

Our national modelling has revealed the scale of the problem but also highlights very large uncertainties, partly because the UK’s regulatory structure is not looking at the issues from a catchment flow perspective. Groundwater is classed as ‘local flooding’ and part of ‘surface water flooding’, assigning risk management to local authorities within administrative rather than catchment boundaries. This is a serious barrier to a clear and objective understanding of the risk. Most of the water in our southern English rivers is derived from groundwater, so it is obvious that a catchment approach is essential.

Local authority boundaries and river catchments do not match up, so it is unfair to expect a council or unitary authority to be able to assess flood risk effectively.

We should empower the Environment Agency, our catchment specialists, to take on this role, and provide updated risk management plans as a matter of urgency before we are faced with another difficult winter. Without detailed groundwater flood risk mapping at present, they cannot make vital strategic planning decisions.

Many insurance policies exclude groundwater. We believe that clearer recognition of the risk to property and the role that groundwater plays in driving catchment flood risk will help the householder and hence the insurance industry wake up to the need for appropriate cover.

Homeowners and businesses remain vulnerable and potentially face potentially over £500 million's worth of economic loss to property every year, according to our preliminary analysis. Infrastructure impact and consequential losses add to this. Groundwater flood risk maps are now available, which for the first time enable a joined up approach to understanding threats to property and infrastructure from flooding from all sources.

A Technical Summary on the preliminary economic impact of groundwater flood risk is now available for download here.