Six BGS datasets for assessing shrink–swell subsidence hazards

Many towns, cities and major infrastructure corridors in the UK are founded on clay-rich soils, especially in the south-east of the UK including much of London. Differences in the properties of underlying geology and regional climate across the UK result in localised changes in susceptibility due to shrink–swell subsidence (Jones and Jefferson, 2012; Jones et al., 2020). It is predicted that climate change will also have a significant effect on the magnitude and frequency of shrink–swell subsidence incidents.

Outlined here is the full range of BGS shrink–swell subsidence data products, which are designed to offer complementary assessments of susceptibility at a range of scales for a range of different uses and users. These include:

General users:

• BGS GeoSure
• BGS GeoClimate Shrink–swell

Specialist users:

• BGS GeoSure Insurance Product
• BGS Property Subsidence Assessment
• BGS GeoSure Extra Shrink–swell 3D
• BGS GeoSure Extra Shrink–swell Subsurface

The importance of BGS datasets

It is important to understand where shrink–swell hazard might be present to assess, adapt and mitigate for it. Natural ground instability may lead to financial loss if it is not correctly identified and infrastructure constructed accordingly.

This suite of data products from the UK’s premier geoscience institute can support the identification of this geohazard and the implementation of preventative measures, the cost of which may be very low compared to the cost of the repair following ground movement.

BGS GeoSure

What is it?

BGS GeoSure comprises natural ground stability data and consists of six data layers, including shrink–swell. Each layer is a national hazard susceptibility map for the following ground instability hazards:

• collapsible deposits 
• compressible ground
• landslides 
• running sand 
• shrink–swell subsidence 
• soluble rocks 

What information does it provide?

This dataset shows areas of susceptibility for each hazard on a scale of A to E (low to high susceptibility) along with a class description. A free, open-source version of the BGS GeoSure datasets is available as a 5 km hex grid, which provides a generalised, national to regional overview of hazard susceptibility.

Coverage

• Great Britain

Suitable uses

This dataset can be used to assess the potential presence of geohazards that might affect low-rise buildings, and for the identification and classification of those geohazards.

Users could include:

• architects and surveyors
• developers
• home owners
• insurers and loss adjusters
• local government and regional planners
• solicitors

BGS GeoClimate Shrink–swell

What is it?

BGS GeoClimate Shrink–swell comprises national datasets showing potential change in subsidence due to changes in climate for the next century.

How is it different to GeoSure?

GeoClimate provides added detail for the potential effects of climate change. This is demonstrated through a number of different climate scenario thresholds.

What information does it provide?

UKCP18 climate projections and groundwater models are combined with GeoSure Shrink–swell hazard maps to model future shrink–swell susceptibility for two time periods: 2030s (2025 to 2035) and 2070s (206 to 2075). GeoClimate provides a ‘hot spot’ map of susceptible areas, which can inform mitigation strategies, prioritise works and aid risk reduction.

An assessment of the likelihood to experience an increase in susceptibility is provided for three scenarios for each time period. These represent wetter, drier and average future climate conditions, and convey the variation and uncertainty within the scenario modelling. This allows the user to consider the best- and worst-case scenario according to their needs.

A difference map is also provided to allow for comparison, detailing the relative change in GeoClimate classification compared to a modelled baseline period.

An open version of GeoClimate is freely available and consists of the average scenario for future climate conditions for the two time periods, provided on a 2 km grid.

Coverage

• Great Britain

Suitable uses

GeoClimate is of use to a broad range of market sectors dealing with resilience to future climate change including:

• heritage
• infrastructure operators
• local authorities
• planning and development
• utilities

BGS GeoSure Insurance Product

What is it?

The BGS GeoSure Insurance Product (GIP), designed specifically for use in the insurance sector, is an index-level assessment of the potential for a geological deposit to create financial insurance loss due to natural ground movement.

What information does it provide?

GIP incorporates the combined effects of the six BGS GeoSure hazards on (low-rise) buildings and links these to a postcode database. This database contains a normalised hazard rating for each of the six hazards (that is, each hazard has been balanced against each other). Full vector data is available for property assessment, whilst a combined unified hazard rating is available for each postcode in Great Britain.

Coverage

• Great Britain

Suitable uses

This dataset was developed for the insurance sector to quantify ground instability susceptibility in a way that is comparable between hazards and considers the potential effect on a building. It is also applicable to other financial sectors, such as banking or mortgage providers, for quantifying susceptibility of asset portfolios.

BGS Property Subsidence Assessment

What is it?

BGS Property Subsidence Assessment (PSA) offers property and postcode-level assessments of shrink–swell susceptibility, considering the potential influences of geological and building characteristics.

How is it different to GeoSure?

PSA focuses solely on the shrink–swell subsidence hazard, providing a higher resolution, specialised assessment. It considers key influencing factors (building characteristics; tree proximity) in its assessment. It is complemented by BGS GeoSure and the BGS GeoSure Insurance Product, which provide assessments of susceptibility for a much broader range of ground instability hazards.

What information does it provide?

This dataset uses a combination of geology, tree location and building characteristics to assess shrink–swell susceptibility. These factors are combined to calculate a subsidence hazard score at the building and postcode scales. A recent BGS blog outlines the features of this dataset in greater detail.

Coverage

• England and Wales

Suitable uses

PSA includes a risk element for the housing stock at postcode and building level, making it ideal for use in the property report and insurance sectors.

BGS GeoSure Extra Shrink–swell 3D

What is it?

The BGS GeoSure Extra Shrink–swell 3D dataset identifies the shrink–swell potential for subsurface or concealed deposits in the London area.

How is it different to BGS GeoSure?

BGS GeoSure provides information on shrink–swell hazard susceptibility in the shallow subsurface (upper 5 m). The 3D model data provides additional information at greater depth, to 20 m.

What information does it provide?

Plasticity ranges in line with GeoSure A to E ratings are applied to data extracted from the London 3D geological model and provided in GIS format. The product identifies areas of potential shrink–swell hazard, in 3D space, down to 20 m in the London Lithoframe area of Great Britain. Shrink–swell/plasticity is provided on a 50 m grid at various depths below surface (1, 2, 3, 4, 5, 10, 15 and 20 m) but can be varied depending on need.

Coverage

• London and the Thames Valley

Suitable uses

This product is designed for the ground engineering markets and infrastructure sectors. Operators for infrastructure such as deep cuttings, tunneling, deep foundations for major construction projects, etc. will find this detailed information useful at a planning stage.

BGS GeoSure Extra Shrink–swell Subsurface

What is it?

BGS GeoSure Extra Shrink–swell subsurface provides information on shrink–swell potential for shallow subcrop (up to 10 m) clays.

How is it different to BGS GeoSure?

BGS GeoSure provides shrink–swell hazard susceptibility for the upper 5 m of geology only. BGS GeoSure Shrink–swell Subsurface provides a deeper assessment of susceptibility, found beneath other deposits, at a much coarser resolution.

What information does it provide?

This product extends the BGS GeoSure Shrink–swell values into the shallow subsurface, providing information for the eight major clay formations across Great Britain that are underneath another solid formation and therefore hidden from the surface. These are analysed up to 10 m depth for deeper foundation structures.

Coverage

• Partial Great Britain coverage (limited to the main clay formations)

Suitable uses

BGS GeoSure Shrink–swell Subsurface is suitable for screening and desk-based assessments of:

• construction of deep foundations, basements and other such large infrastructure
• infrastructure networks (road and rail)
• utility development
• scoping for civil engineering projects

Contact

If you have any questions or would like to discuss which of these datasets is best suited to your needs, please email the digital data team (digitaldata@bgs.ac.uk).

References

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