Portsmouth Water is celebrating the successful completion of a key milestone at Havant Thicket Reservoir, the first major new UK reservoir in over 30 years.

At the start of 2026, the project team worked continuously for 72 hours to install a 20 tonne steel wall, known as the Culvert Cut Off Wall, that will sit beneath the main reservoir embankment.

The Culvert Cut Off Wall measures 13 metres high and 9 metres wide. It is designed to seal the connection between the reservoir embankment and the large concrete tunnel, known as a culvert, that holds the pipeline which will take water from the reservoir.

The steel wall was constructed on site and lifted into position in a single piece using a 100 tonne crane. It was carefully lowered into a deep trench filled with a special water-tight mixture, with precision to within just 25 millimetres.

Because the mixture hardens quickly, teams worked around the clock in rotating shifts to complete the installation safely within 72 hours. The embankment will then be built over the top later this year, with construction due to start in the spring.

The innovative underground barrier was installed by the main reservoir works contractor, Future Water MJJV Ltd, with significant contributions from Coffey Geotechnics Ltd, Keller UK and GHD UK, whose expertise was key in making this a success.

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.”

The reservoir itself is being constructed by Future Water MJJV Ltd, a joint venture between leading civil engineering contractors Mackley and Jones Bros, with over 150 years of combined experience in complex civil engineering projects.