The usable storage at Warragamba dam in Sydney, Australia has been increased by about 40B litres, by gaining access to a part of the reservoir previously considered as dead storage.

Usually this water, located below the lowest existing outlet point in the dam, cannot be extracted. Gaining access to dead storage at Warragamba is expected to supply an extra six months of water in very extreme drought conditions. As a part of this project, the Sydney Catchment Authority (SCA) is also refurbishing a disused pumping station 1500m downstream of the dam.

A team of international divers, who usually work on offshore oil rigs, spent over two weeks removing a 17 tonne concrete block from the base of the dam wall. The divers have cut a 2m hole through the wall to allow water at the bottom of the dam to be pumped into the Warragamba pipeline, in Sydney, New South Wales (NSW). The project was part of the NSW state government’s US$88.8M programme to access dead storage in reservoirs. Similar deep water projects are also being undertaken at Avon and Nepean dams.

The concrete block at Warragamba was removed using an underwater cutting machine that uses core drilling and a diamond impregnated cutting wire. Eight divers, known as aquanauts, worked in eight hour shifts, 24 hours a day and at a depth of 85m while being given food and supplies through an airlock. Competing with zero visibility and freezing conditions, the divers also constantly had hot water piped through tubes underneath their suits to keep them warm.