Century-Old Geological Survey Revived to Strengthen Flood Defences Along the River Tweed

The British Geological Survey (BGS) has embarked on an ambitious four-year project to remap the River Tweed catchment, combining cutting-edge technology with traditional field geology to improve understanding of groundwater movement and help communities better prepare for future flooding.

The programme marks the first comprehensive geological survey of the Tweed catchment in more than 100 years and is expected to provide new insight into one of the least understood contributors to flood risk—groundwater.

Stretching 156 kilometres from the Scottish Borders into northern England, the River Tweed supports hundreds of thousands of residents, businesses and critical infrastructure, making it one of the UK's most important cross-border river systems.

Looking beneath the surface

While river flooding often dominates headlines, scientists say water rising from beneath the ground can be equally destructive.

Groundwater flooding occurs when underground water levels rise high enough to emerge at the surface, often alongside river or surface water flooding, making it difficult to identify as a separate hazard.

According to the British Geological Survey, groundwater flooding is estimated to cause around £530 million of damage every year across England and Wales, yet its behaviour remains far less understood than other forms of flooding.

The new survey aims to close that knowledge gap.

Combining traditional geology with modern technology

Field teams began work this spring in the Cheviot Hills, with surveys progressing to the Tweedsmuir Hills during the summer before moving towards Melrose and Galashiels later in the year.

Working on foot, geologists are recording rock exposures, sediment layers, peat depth and landform characteristics using digital mapping technology supported by aerial imagery.

The information will then be combined with artificial intelligence, high-resolution terrain modelling and modern geological interpretation techniques to create an entirely new understanding of how groundwater moves through the catchment.

Mapping what earlier surveys missed

The previous geological mapping of the area dates back to the early twentieth century, long before modern understanding of glacial geology had developed.

Researchers will examine how different geological deposits—including weathered bedrock, glacial tills, slope deposits and peat—affect the storage and movement of water beneath the landscape.

These differences can significantly influence how quickly groundwater responds to heavy rainfall and where floodwater may eventually emerge.

Peatland areas are also receiving particular attention because of their natural ability to absorb rainfall before gradually releasing water back into the wider environment.

Supporting future flood resilience

Once completed, the updated geological maps will provide an important resource for organisations involved in flood risk management, planning and environmental protection.

The information will support local authorities, engineers, environmental consultants and land managers responsible for infrastructure and communities across a catchment serving around 450,000 people.

The findings will also become part of the national geological mapping programme and will be made publicly available through the British Geological Survey's online mapping services.

A new understanding of a changing landscape

Project lead and BGS Quaternary Geologist Sam Roberson said geological science has advanced dramatically since the Tweed catchment was last comprehensively surveyed.

"Our understanding of glacial systems has evolved enormously in the hundred years since the Tweed catchment was last surveyed."

He explained that while early surveys relied entirely on field observations, today's researchers are able to combine traditional geological expertise with sophisticated Earth observation technologies to build a far more detailed picture of the landscape.

Roberson added that the updated mapping could play an important role in future land-use planning and flood management by improving understanding of the ground conditions that influence how water moves through the catchment.

As climate change increases the frequency of extreme rainfall events, projects such as this are expected to become increasingly important in helping communities anticipate not only flooding from rivers and surface water, but also the often-overlooked threat emerging from beneath the ground.