Major milestone as cut-off wall is installed at landmark reservoir2nd Feb 2026

A “major technical milestone” has been hit at Portsmouth Water’s multi-million-pound Havant Thicket Reservoir scheme courtesy of the installation of a 20-tonne steel wall.

The innovative barrier was constructed by Future Water MJJV Ltd, a joint venture between Jones Bros Civil Engineering UK and Mackley, with key contributions from Coffey Geotechnics Ltd, Keller UK, and GHD UK.

The culvert cut-off wall, which measures 13 metres wide and nine metres high and took 72 hours to install, will sit beneath the main reservoir embankment.

Constructed on site and lifted into position in a single piece using a 100-tonne crane, it is designed to seal the connection between the embankment and the culvert that holds the pipeline which will take water from the reservoir.

Requiring precision to within just 25 millimetres, the wall was lowered carefully into an eight-metre-deep trench filled with bentonite slurry mix, with the on-site team working around the clock in rotating shifts to combat the hardening of the special watertight mixture.

Deputy project director for Future Water and earthworks construction director Geraint Lloyd said: “It’s a major milestone for the team here at Havant, and one everyone is rightly proud of.

“To achieve the level of accuracy needed with a structure of that size and weight is a huge achievement, and that’s before considering the time constraints.

“It was a wonderful effort which required planning, teamwork, and exceptional focus throughout the 72 hours.”

Led by Portsmouth Water, the project is the UK’s first major water-storage reservoir since the 1980s.

Bob Taylor, chief executive officer of Portsmouth Water, said: “This is a major technical milestone for the Havant Thicket Reservoir project and an incredibly proud moment for everyone involved.

“Working continuously for 72 hours presented challenges and we were acutely aware of the need to keep disruption to a minimum for local residents. We made sure noise and lighting were reduced as far as possible and installed an acoustic barrier, to ensure as little noise as possible travelled from site. I would like to thank everyone for their patience and understanding while this key piece of work took place.

“This milestone marks significant progress for the Havant Thicket Reservoir project, which will play a vital role in protecting two globally rare chalk streams in Hampshire, by providing a new, sustainable source of water. Last year saw excellent progress on site, and we look forward to our main earthworks season starting in spring this year.”

Established in the 1950s, Jones Bros owns one of the largest plant fleets in the UK and employs approximately 550 people.

The company is currently working on contracts in various sectors including highways, flood and marine defence, reservoirs, waste management, and renewable energy around the UK.

The company runs an award-winning apprenticeship scheme, which has produced a large percentage of its current workforce, with several of its senior managers having started out as apprentices or in a trainee role. It has recruited hundreds of apprentices over the years.