St Helier, the capital of Jersey, was prone to flooding during extreme rainfall. To alleviate this, a vast underground storage chamber was dug beneath Fort Regent in the 1990s. The contents are then pumped out over several days to the sewage treatment plant.
The tank is approached via a vehicle-sized curving ramnp and there is also a 52 metre high pump shaft which also forms part of the forced ventilation system. The vast main chamber holds 25,000 cubic metres of liquid. The excavation is fully shotcreted - the entrance tunnels with a smooth finish. The whole has automated ‘washdown’ facilities and automated methane detection.
Further tunnels were constructed in 2012/13 to provide additional protection.