Innovative & Challenging Dam Isolation

Talybont Reservoir in South East Wales was constructed between 1932 and 1939. Now more than 80 years old, its Victorian infrastructure required essential valve and pipework maintenance and refurbishment.

EDS was commissioned to provide isolations on the wet side of the dam so repair and maintenance work could be carried out safely. The reservoir supplies the Talybont Water Treatment Works, which in turn serves around 45,000 properties. Cutting off this supply entirely would have been enormously expensive and disruptive — a solution nobody wanted to use.

Key Challenges:

  • The brief required isolating three intakes on a tower with top, middle and bottom sections. The most challenging was the bottom section, which involved diving to a depth of 30 metres and then reaching a valve located at the end of a 60-metre tunnel
  • From a health and safety perspective, the client initially believed isolating the third intake would be impossible. EDS, however, saw an opportunity to apply innovation, collaboration and forward thinking to achieve what seemed unachievable
  • Before isolation works could begin, a temporary water supply was established using siphons and pumps to divert water from the tower to the treatment works
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Solutions:

  • First isolation: Divers created a double isolation from the water outside to make it safe for personnel working inside the tower. A plug was inserted into the pipework, and the penstock was used as secondary isolation
  • Second isolation: This intake was buried in concrete. A ‘Hatton Garden Robbery’ style drill was used to break into the concrete to access the valve and place a plug on the outlet. As this concrete had not been shown on any historic drawings, EDS had to work carefully to ensure safe access without damaging the tower
  • Third isolation: The most difficult but most exciting part of the brief. EDS proposed the design of a Remotely Operated Vehicle (ROV), built locally in Llandow, to travel the 60-metre pipe carrying a ‘top-hat’-style plug to seal the wet side of the dam. To minimise environmental impact, the ROV ran on biodegradable, fish-friendly oil. The ROV was intended to avoid a diver entering the tunnel, but sonar survey revealed that historic drawings were inaccurate. A dive would therefore still be required. To reassure the client, EDS requested an independent audit by Roger O’Kane, former secretary of the Association of Diving Contractors (ADC), who confirmed a dive survey into the tunnel could safely proceed
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A floating pontoon dive station was erected above the tunnel entrance. The ROV was lowered to the bottom of the reservoir using a winch and portable gantry. At the tunnel entrance, concrete beams initially prevented entry with the ‘top-hat’ attached. Drawing on years of experience and creative problem-solving, EDS adapted the approach: the ROV was driven up the tunnel in nil-visibility conditions, directed by a smaller video ROV with sonar guidance from an operative positioned more than 100m away on the pontoon. The ‘top-hat’ was successfully sealed, and work to replace the pipework could begin.

This project is one EDS will always be proud of. It demonstrates our determination, innovation and team ethos: we never give up.

If you have a problem or project that seems tricky — or even impossible — head over to our Contact Us page and give us a call.

“Talybont was an industry first which proved difficult isolations underwater can be achieved safely. Working closely with our clients and giving them the confidence to invest in our ideas was a milestone for everyone involved with the project. The Dam has been given a new lease of life for generations to come.”

Paul Edwards, Managing Director