BGS Groundwater Flooding Susceptibility: helping mitigate one of the UK’s most costly hazards

Groundwater flooding occurs when the water table rises to meet the ground surface. This hazard often goes unnoticed because it commonly occurs alongside river and surface water flooding, but it can substantially exacerbate the effects of flooding events.
Without dramatic images of burst river banks or breached sea defences, groundwater flooding rarely makes the headlines, yet in England and Wales it is estimated that groundwater flooding accounts for on average £530 million in damage per year. This represents 30 per cent of the total national annual economic loss due to flooding (Allocca et al., 2021).

A significant contributing factor to the high costs associated with groundwater flooding is the effect on underground infrastructure, such as basements and buried assets. Generally, the water table response to rainfall is much slower than rivers. Persistent rainfall over weeks and months can raise groundwater levels to a tipping point, where even a short period of low-intensity rainfall can unexpectedly trigger a flooding event. The mechanics of groundwater flooding also result in flood water lingering for longer than other forms of flooding as the water table slowly recedes, causing an estimated 2.5 times greater damage than those incurred from other flood types (Allocca et al., 2021).

The BGS Groundwater Flooding Susceptibility dataset highlights which areas of England, Scotland and Wales are most susceptible to groundwater flooding, based on geological and hydrogeological conditions at a 50 m resolution. Models of groundwater flooding originating from both superficial and bedrock aquifers are combined creating zones of susceptibility which are classified as:

• the potential for groundwater flooding to occur at surface
• the potential for groundwater flooding of property situated below ground level (basements, etc.)
• limited potential for groundwater flooding to occur
  

A complementary dataset providing a measure of confidence in the susceptibility classification (based on the hydrogeological setting) is included, which considers the groundwater flooding mechanism, susceptibility class and locations of previous groundwater flooding. The data is recommended as a screening tool for scoping and planning rather than for site-specific risk assessments.

Feedback from existing data users demonstrates the wide-ranging applications of this data:

• desk-based scoping studies by environmental and engineering consultants
• informing local planning authorities and property developers when compiling local development plans
• informing lead local flood authorities compiling their strategic flood risk assessments
• assessing infrastructure networks and assets, such as rail lines, highways and water treatment facilities, for susceptibility to groundwater flooding
• research by conservation and academic institutes
• informing water companies of areas that may be affected by planned reductions in groundwater abstraction activities
• informing climate reports for Ministry of Defence sites  

Many home insurance providers do not provide cover for the effects of groundwater flooding and ensuring awareness of an area’s susceptibility to this hazard is an essential component of any property conveyancing report.

A more granular view of groundwater flood risk can be gained by combining this data with other information such as elevation, previous instances of groundwater flooding, rainfall, property type, and land drainage information. A number of BGS’s data resellers have used the BGS Groundwater Flooding Susceptibility dataset alongside some of our other datasets to develop their own flood modelling tools, predicting groundwater flood risk at a finer scale.

Contact

If you would like to discuss how this data can support your organisations groundwater flooding decision making please get in touch with the digital data team (digitaldata@bgs.ac.uk).

About the author

Rob Shaw

Geospatial data analyst

BGS Keyworth

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