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First published on 08/09/25

Scientists have found hidden features beneath Cardiff that could play a major role in the city’s future energy and infrastructure planning. For the first time the British Geological Survey (BGS) has used long-term monitoring at the Cardiff Urban Geo-Observatory to study how heat moves through the ground. Tracking 62 boreholes across the city, which are narrow shafts drilled in the ground either vertically or horizontally, they collected detailed readings every 30 minutes between 2014 and 2018. What they ended up finding was localised cracks and channels in the south of Cardiff hidden beneath layers of clay.

These cracks act like “pathways”, according to the BGS, that allow rainwater to seep deep underground, recharging the groundwater system. In geological terms these are known as recharge routes and until now they were not thought to exist in this part of the city.

Ashley Patton, engineering geologist at BGS and research lead, said: “Using time-system data for the first time in Cardiff has provided vital information to further our understanding of what lies beneath our feet.

“The discovery of geological recharge pockets in an area where they were previously not thought to occur is an important consideration for future infrastructure projects.

“It’s essential that geothermal developers take this research into account before installing a shallow ground-source heat pump to ensure it runs as effectively as possible and is not impacted by recharge.”

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