What happened
What residents saw on 30 July 2026, and what the Health and Safety Executive found.
On the afternoon of Thursday 30 July 2026, a large volume of water carrying mud, sludge and debris from historic mine workings ran down through Gwaelod-y-Garth. Fifteen properties were affected. Thirteen homes had to be evacuated. Roads, fields and public spaces were left under mud and debris.
What residents saw
It had been a prolonged dry spell with Wales officially in a drought, which is part of why the water came as such a shock.
Residents describe hearing what several of them called an explosion, followed within a few minutes by water arriving through the village. One resident described her whole house shaking, like a mini earthquake. Another described seeing a wall of water at the back of his garden, brown and up to his waist, and being pushed off his feet by the force of it.
Reports of shaking were not limited to Gwaelod-y-Garth. Residents have also described tremors being felt in surrounding communities, including Pentyrch, Radyr, Ty Rhiw and Taffs Well. Reports include books falling from shelves, houses visibly rocking and, in Taffs Well, damage including cracked walls.
These accounts are being gathered to help establish how widely the effects of the incident were felt.
In some homes the water reached around five feet deep. Others spent hours bailing to keep it below the electrics so they could stay in their houses.
The water was heavy with sediment. It carried material out of the old mine workings and picked up more as it went, tearing up ground and carrying it down into the village. It left a tide mark around the walls of people’s homes.
The response
Crews from six fire stations attended. South Wales Fire and Rescue Service asked people to avoid Heol Berry and Heol y Nant while it dealt with the incident. A neighbouring industrial estate was also evacuated.
Cardiff Council has coordinated clean up work in the community. Dŵr Cymru Welsh Water said the flooding was not related to its pipe network.
What the investigation found
On 5 August 2026 the Health and Safety Executive set out what its investigation had found. It said:
This is an isolated incident where a substantial quantity of rock from a planned blast entered one of four interconnected known bodies of water collected in the old iron mine workings. A substantial volume of that water was displaced out of an existing mine adit.
Health and Safety Executive, 5 August 2026
An adit is a horizontal tunnel driven into a hillside to reach the workings.
The HSE said that mine and quarry inspectors had confirmed that the underground rock voids holding the water, and the tunnel, had not been compromised in the incident. It said it recognised the concern the incident had caused for local residents, particularly those living close to the quarrying operations.
The quarry operator confirmed that there had been an incident at its quarry, and said it was working closely with the relevant authorities while engaging with the local community as it responded to the situation.
What is still open
The HSE has said that the information used in the blast design, which was developed by specialist blasting contractors, is the focus of its continuing investigation. That investigation has not yet reported.
A number of questions matter a great deal to people living below the hill and remain unanswered. Whether the risk to homes outside the quarry boundary was ever assessed. What monitoring was required, and by whom. What residents were told, and when. Whether there is any continuing risk from the workings above the village.
These are set out on our concerns and questions page.
Were you affected?
Register your damage and tell us what you saw. It helps us build a picture of how far the water reached.