The hidden impact of a drought on the ground beneath our feet
More than two-thirds of England are now in drought. What does that mean for the built environment?
After the UK’s fifth heatwave of the year, and the driest July since records began in 1836, 45 million people are now living in a drought area in England. M more parts of Scotland are moving into water scarcity, and other climate crisis effects such as wildfires, tearing through the UK, Ireland and Europe.
The effects are being felt across public health, farming and the natural environment. But there is another, less visible impact to consider - what is happening to the ground beneath our homes, infrastructure and developments?
Gabby O’Reilly is our new associate in our earth & environment team. Joining the team last month, she brings over 15 years’ experience of geoconsultancy engineering with specialisms geotechnical consultancy and geohazard assessments.
We caught up with Gabby to find out more about what’s actually happening to the land beneath our feet, and what it could mean for the way we develop our towns and cities.
What actually happens to the ground during prolonged drought?
The UK has large areas of clay-rich soils, that can absorb vast amounts of water after rainfall. But when prolonged dry weather removes that moisture, the soil can shrink and crack. This is known as ‘shrink–swell’ behaviour.
Where buildings, roads or utilities sit on this type of ground, changes in soil volume can affect how they perform, and in some cases, their stability.
The risk isn’t only that the ground is too dry today, it’s how it will respond to repeated cycles of becoming wetter and drier - something we expect to see more of according to British Geological Survey (BGS).
Is this something design teams are increasingly having to consider in projects?
Yes. Historically, ground investigations and design have largely focused on understanding the present conditions of a site, then designing appropriately for them.
But climate change means we can’t assume that those conditions will stay the same throughout the lifetime of a development. The ground could behave differently in the future, creating risks that need to be considered alongside the other more familiar geotechnical risks.
New research from the BGS highlights the potential scale of the issue. By 2070, around 5% of British properties - more than 1.8 million - are projected to be highly or extremely likely to be susceptible to clay shrink-swell under a medium-emissions scenario. Under a higher-emissions scenario, that rises to around 11%, or more than 4.2 million properties.
These are projections rather than predictions, but they show why understanding how the ground could change over time is becoming increasingly important for the built environment.
Are conventional ground investigations assumptions still sufficient?
Traditional ground investigations tend to only tell us about the conditions we have today. But if those conditions are changing, we also need to think about how the ground could behave over the lifetime of a development.
New Construction Industry Research and Information Association (CIRIA) guidance, C824, provides a framework for assessing and managing climate change and extreme weather related geo-based risks in land development. It encourages project teams to consider these risks throughout the development process, rather than treating climate change as something to address separately at the end of the design process.
There is also updated guidance from the Society of Brownfield Risk Assessment (SoBRA) on considering future climate change when assessing risks to controlled waters from land contamination.
Ultimately, understanding ground risk increasingly means looking beyond what the ground is doing now, and considering what it could do in the future.
Does climate change need to be factored into ground risk assessments earlier?
Absolutely. The earlier climate-related ground risks are identified, the more opportunities there are to manage them throughout the design process of a development.
That could mean:
- Seeking specialist advice before major works begin
- Considering ground conditions when developing the site layout
- Managing vegetation where tree roots could influence soil moisture
- Designing foundations with future changes in sinkable clay behaviour in mind
It also requires a system thinking approach with geologists, built environment engineers, environmental and climate risk consultants, hydrogeologists and other specialists that can contribute to understanding how a site may respond to changing climate conditions.
What are the wider implications for infrastructure and construction?
The implications go beyond building foundations and sink-swell behaviour.
Drier conditions can affect soils, vegetation and how sites are managed during construction. For example, increased dust generation may need to be considered during planning, while sensitive materials such as topsoil and peat, need to be carefully managed because of the carbon they store.
As this extreme weather becomes more frequent, understanding how the ground is responding now and how it could respond in the future, will become an increasingly important part of creating resilient places and infrastructure.
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