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 ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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 ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô subsidence incidents.

Outlined here is the full range of BGS ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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:

• 51ÁÔÆæ GeoSure
• 51ÁÔÆæ GeoClimate Shrink–swell

Specialist users:

• 51ÁÔÆæ GeoSure Insurance Product
• 51ÁÔÆæ Property Subsidence Assessment
• 51ÁÔÆæ GeoSure Extra Shrink–swell 3D
• 51ÁÔÆæ GeoSure Extra Shrink–swell Subsurface

The importance of BGS datasets

It is important to understand where ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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 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.

51ÁÔÆæ GeoSure

What is it?

51ÁÔÆæ GeoSure comprises natural ground stability data and consists of six data layers, including ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô. Each layer is a national hazard susceptibility map for the following ground instability hazards:

• collapsible deposits 
• compressible ground
• landslides 
• running sand 
• ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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

51ÁÔÆæ GeoClimate Shrink–swell

What is it?

51ÁÔÆæ 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?

and groundwater models are combined with GeoSure Shrink–swell hazard maps to model future ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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

51ÁÔÆæ GeoSure Insurance Product

What is it?

The 51ÁÔÆæ 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.

51ÁÔÆæ Property Subsidence Assessment

What is it?

51ÁÔÆæ Property Subsidence Assessment (PSA) offers property and postcode-level assessments of ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô susceptibility, considering the potential influences of geological and building characteristics.

How is it different to GeoSure?

PSA focuses solely on the ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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 ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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.

51ÁÔÆæ GeoSure Extra Shrink–swell 3D

What is it?

The 51ÁÔÆæ GeoSure Extra Shrink–swell 3D dataset identifies the ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô potential for subsurface or concealed deposits in the London area.

How is it different to BGS GeoSure?

51ÁÔÆæ GeoSure provides information on ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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 ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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.

51ÁÔÆæ GeoSure Extra Shrink–swell Subsurface

What is it?

51ÁÔÆæ GeoSure Extra Shrink–swell subsurface provides information on ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô potential for shallow subcrop (up to 10 m) clays.

How is it different to BGS GeoSure?

51ÁÔÆæ GeoSure provides ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô 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

51ÁÔÆæ 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

About the author

Shrink–swell in clay soils is a major geohazard in the UK and costs the economy over £400 million a year. This is predicted to rise to over £600 million by 2050, due to climate change-driven weather extremes (Harrison et al., 2012). Research predicts a 50 per cent increase in ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô subsidence events across Europe by 2040 (Swiss Re, 2011).

Many towns, cities and major infrastructure corridors in the UK are founded on clay-rich soils, especially in the south-east, including most of London. Volume change of clay minerals within these soils is the primary cause of ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô and is controlled by mineralogy, temperature and rainfall. As such, some areas of the UK are more susceptible than others, depending on their underlying geology and regional climate (Jones and Jefferson, 2012; Jones et al., 2020).

Between January and June 2022, the UK experienced the driest weather in over 40 years, culminating with the hottest days on record in July when temperatures exceeded 40°C for the first time. These unprecedented hot, dry conditions will have resulted in levels of clay shrinkage never previously experienced in the UK and significant rainfall will be necessary to promote their recovery.

The BGS Property Subsidence Assessment dataset

The identification of ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô-related subsidence-prone buildings, alongside the inclusion of potential additional factors that could exacerbate this phenomenon, can better inform insurers and homeowners and form the basis to make decisions concerning prevention and remediation.

The BGS Property Subsidence Assessment (PSA) dataset provides insurers and homeowners access to a better understanding of the ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô hazard at both the individual property and postcode level for England and Wales. It builds upon the BGS GeoSure ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô data, which highlights the susceptibility of the local geology to shrink and swell, by mapping the hazard to the individual building polygon and considering the following additional susceptibility or influencing factors.

Building type and number of storeys

Building type and height influence the potential extent of structural damage, should movement occur. Damage to a structure is possible when as little three per cent volume expansion takes place, especially when these movements are unevenly distributed beneath a foundation or property.

Building age

Due to changes in foundation design and building regulations, the age of a property gives an indication of the potential foundation depth likely to be associated with the building and how that could be affected by ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô.

Drainage

Building practice changed from the use of clay to plastic pipes in 1950. Clay pipes have a higher propensity to crack as a result of ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô and resulting ground movement and therefore exacerbate possible movement in the vicinity of any cracks and leaks.

Tree proximity

Many subsidence insurance claims are linked to tree damage. Damage may occur as tree roots take up water from the soil, causing the ground to dry out and shrink, resulting in uneven settlement. This occurs predominately during the spring and summer months. Areas with many older houses and old-style shallow foundations can be seriously affected.

Using the dataset

PSA users receive GIS building polygons with an overall susceptibility to subsidence score between 1 and 100, with one being lowest susceptibility. Scores are also grouped into five classes, ranging from ’non-plastic’, indicating the absence of plastic clays (therefore the lowest susceptibility), to ‘very high’. Each building polygon is also scored from 1 to 10 for each of the individual subsidence factors, so users can identify the potential main causes of subsidence.

Postcode data is available as a table showing the generalised PSA score for all the buildings within each postcode.

More information

Please visit the BGS PSA data product web page for more details and the data user guide. Keep an eye out for our upcoming blog on the full suite of BGS ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô subsidence data products for an overview of all the subsidence solutions BGS has to offer and how these can be best used together.  

References

About the author

Debris flows are landslide hazard that are of particular concern to transport infrastructure managers and local authorities. They occur when poorly sorted debris mixed with water rapidly flow downslope and are potentially very destructive. Debris flows can cause considerable disruption and financial loss, particularly for owners or managers of infrastructure assets (for example  road or rail), utilities or property. With increases in rainfall combined with dry weather anticipated, the (2021) specifically highlights future risks to transport networks from slope and embankment failure, particularly on routes in more rural areas of the UK that follow natural features such as steep-sided valleys.

In response to increasing demand for knowledge about where debris flows may potentially occur in Great Britain, BGS  developed  a debris flow susceptibility model for Great Britain (BGS DFSM-GB), which has been updated recently. This dataset is designed for those interested specifically in debris flow susceptibility at a regional or national planning scale, such as those involved in construction or maintenance of infrastructure networks (road, rail or utilities), other asset managers, loss adjusters, surveyors or local government.

Armed with knowledge about potential debris flows, preventative steps can be put in place to alleviate the impact of the hazard to people and assets.

About debris flow hazards

Debris flows are a widespread phenomenon in mountainous terrain. They are distinct from other types of landslides as they can occur periodically on established paths, usually gullies or existing drainage channels. Periods of prolonged and intense rainfall are a common trigger for this type of hazard and, with changes in seasonal UK precipitation patterns generally accepted as a likely consequence of ongoing climate change, the magnitude and frequency of debris flows are likely to change.

In Great Britain, most disruptive debris flow events are recorded on the Scottish road and rail network. For example, the A83 ‘Rest and Be Thankful’ Pass suffers regular blockages and closures and, although event magnitudes are usually relatively small, the disruption caused can have significant economic effects. The pass is a strategic link road to the Kintyre peninsula and other remote regions of western Scotland, and regular closures force a 55-mile diversion. A study, ‘’, suggests that the direct and indirect economic effects of a single event there in 2007 were estimated at £1.2 million over a 15-day closure.

Real-life incidents

As well as issues such as economic costs and inconvenience caused by disruption to travel networks, debris flows pose a threat to public safety. Near-miss examples highlight the dangers this landslide hazard poses. In August 2004, two debris flows blocked the A85 in Glen Ogle, stranding 57 people between them, some of whom required rescue via airlift. In June 2012, a debris flow blocked a railway near Loch Trieg; it was struck by a freight engine resulting in derailment of the engine and injury to the driver.A similar incident occurred in January 2018, when after hitting a debris flow deposit.

About the dataset

Despite debris flows being relatively commonplace throughout upland regions of Great Britain, previous debris flow susceptibility assessments and modelling efforts by BGS had focused on Scotland. This new debris flow susceptibility model contains newly acquired data and more accurately calculated parameters.

As the national geological survey for Great Britain, our stakeholders were interested in a regional-scale susceptibility assessment of this potential hazard for other parts of the country besides Scotland. In response to this, we developed a debris flow susceptibility model in 2017 for the whole of Great Britain, building on research conducted over the previous 15 years, using the most recent data holdings available to us. When BGS acquired a new 5m national coverage digital terrain model in 2021, we incorporated it into a new debris flow susceptibility model, which calculates slope measurements and channels more accurately.

Catherine Pennington, BGS Engineering Geologist and landslide specialist.

The BGS DFSM-GB (v6.1) is a 1:50 000-scale raster dataset of Great Britain, providing 50 m ground resolution information on potential for a debris flow to be initiated given the ground conditions present. The product is supplied as an additional layer alongside the 51ÁÔÆæ GeoSure landslides product.

The BGS DFSM-GB represents an interpretation of where debris flows could occur given natural (rather than anthropogenic) geological, hydrogeological and geomorphological properties determined by geological experts and identified through the underpinning data. It was designed to identify potential source areas for debris flows rather than identify the locations where material may be deposited.

Claire Dashwood, BGS Engineering Geohazards Geologist.

Elements considered in the model include properties and characteristics of geological materials (permeability, material availability and characteristics when weathered), slope angle and proximity to stream channels as indicators of susceptibility. Building on existing knowledge, the model also considers the presence or absence of glacial scouring which, where present, can greatly reduce the material available to flow.

Comparison of the BGS DFSM-GB against mapped debris flow occurrences from within the 51ÁÔÆæ National Landslide Database at the time of publication showed that 90 per cent of debris flows in the inventory occurred in the areas the model had identified as having high potential for instability.

Contact

For more details on this dataset, as well as a case study detailing its use in a national assessment of landslide hazards for the rail network of Great Britain, please consult the debris flow susceptibility model product user guide. If you have any further questions, do not hesitate to contact the team.

Shrinking and swelling of the ground, often reported as subsidence, is already one of the most damaging geohazards in Britain, costing the economy an estimated £3 billion over the past decade. Subsidence may lead to financial loss for anyone involved in the ownership or management of property, including developers, homeowners or local government. These costs could include increased insurance premiums, depressed house prices and in some cases, engineering works to stabilise land or property.

How does climate change affect ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô?

Many soils contain clay minerals that absorb water when wet (making them swell) and lose water as they dry (making them shrink). Dry weather and high temperatures have been found to be a major factor in the emergence of subsidence in clay soils. However, every summer can be completely different to the last; summer 2018 had the hottest, driest June for years whereas summer 2019 had one of the wettest Junes on record. Looking to the future, warmer, drier summers and increases in annual temperature and rainfall variability are suggested for the UK. What is considered a heat wave today may be the norm in the 2050s and cool in the 2080s!

What does the data show?

The rock formations most susceptible to ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô behaviour are found mainly in the south-east of Britain. Here, many of the clay formations are too young to have been changed into stronger mudrocks, leaving them still able to absorb and lose moisture. Superficial deposits, such as alluvium, peat and laminated clays, can also be susceptible to soil subsidence and heave (e.g. in the Vale of York and the Cheshire Basin).

Clay rocks elsewhere in the country are older, hardened by burial deep in the Earth and less able to absorb water. In some areas (e.g. around The Wash and under the Lancashire Plain) they are deeply buried beneath other soils that are not susceptible to ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô behaviour.

By combining the BGS GeoSure dataset and applying the UK Climate Projections (UKCP) scenarios for rainfall and temperature changes in the UK for the next century, maps have been produced for Great Britain showing areas with varying vulnerability to ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô and thus subsidence in the future due to climate change. The maps show that areas with clay soils that shrink and swell with changes in moisture are going to become increasingly susceptible in the coming century and beyond.

The 51ÁÔÆæ GeoClimate UKCP18 datasets show an obvious increase in the amount of ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô potential across the south-east of England, due to climate change. Of particular interest are the clay-rich formations that are currently of low-moderate susceptibility. Buildings on these rock types might not have the robust foundations suitable to withstand subsidence hazard.

How might this affect my home?

As reported by the (2018), the effects of subsidence in a property can usually be seen as cracks in walls that:

• are more than 3 mm thick
• run diagonally across the wall
• are wider from top to bottom
• are visible from inside and outside
• occur near doors and windows
• cause rippling in wallpaper

What can I do about it?

If you are in an area that shows an increased susceptibility under future climate conditions, you should get specialist advice from a suitably qualified expert such as a structural surveyor, geotechnical engineer or chartered engineering geologist.

If active clay shrinkage or swelling is not affecting your property but the area has ²õ³ó°ù¾±²Ô°ì–s·É±ð±ô±ô clay potential, this should be taken into account before planning new buildings, extensions or modifications, or any other changes in land use.

• Take specialist advice before starting major building work.
• Consider the effect of laying impermeable drives, paths or hardstanding on the rainfall reaching the soil below and changing its moisture content.
• Seek expert advice before planting trees near to a house. The safe planting distance will depend on the tree species, the type of foundation and soil composition.
• Ensure foundations of new constructions or extensions are designed for any shrinkable clay soil conditions that could be present or  forecast under future climate conditions.
• Do not plant potentially large trees next to a house.
• Do not remove mature trees that pre-date the construction of the house before taking advice. Tree management by crown reduction or thinning may be better than removal because it will maintain a stable soil moisture profile.

About the author