Scilly proposes floating intake solution to sediment challenge

The Scilly Isles’ council has submitted plans to the Marine Management Organisation for a new seawater intake for the islands’ St Mary’s desalination plant. A novel floating arrangement for the intake is designed to leave the seabed undisturbed to limit filter blockage by sediment.

The council proposed the installation of a floating pump system, some 200m from the shore at Pelistry Bay, to take water from the open sea after an onshore borehole feed developed problems. The seawater intake will sit one metre below the water surface and will be connected to the desalination plant by a flexible pipe.

A £500,000 (US$ 780,000) water purification system, installed in 2013, has struggled to meet demand after onshore boreholes that provide feedwater became contaminated with iron pyrite. Unblocking the filtration is costing up to £ 20,000 (US$ 31,000) a month.

Last month the islands’ Inshore Fisheries and Conservation Authority (IFCA) raised concerns about the location of the inlet, in a Marine Special Area of Conservation and close to a colony of rare sunset cup coral. But the IFCA has now agreed to the plans, saying the water intake “won’t present an environmental problem.” There has also been no objections from Natural England and Scilly’s Wildlife Trust who were consulted on the plans.

In February, Scilly’s senior manager for infrastructure, Craig Dryden, said the cost of the new seawater intake could be as high as £ 300,000 (US$ 468,000). Councillors have raised water charges by 12% in response. But the current plans indicate that the cost of the scheme is likely to be only £ 25,000 US$ 39,000).