Underwater temporary works

Inspection and repair of leaking valvegear to the service spillways at Lake Vyrnwy, Severn Trent Water's large supply reservoir in Mid Wales, required design and installation of a temporary closure to the service intakes.

Working in conjunction with specialist underwater contractor Divemex, SADLEIR technical consultancy prepared detailed design and fabrication drawings for the 1.5m diameter “lightweight” thin plate cap (1.6m∅ x 30mm thick, weighing approximately half a tonne in air).

Careful advance planning and rapid design turnaround meant that the fabricated cap was delivered to site for installation within a week of the initial dimensional survey, carried out on the first dive.

Site survey and all installation work was carried out by diver-constructors, using surface-demand breathing apparatus, at depths of up to 25m. Closed-circuit colour television was used throughout the progress of the work, for surface-based technical supervision and recording purposes.

Safety, both of the divers involved in installation of the closure, and of Client's personnel subsequently dependent upon its security and structural adequacy, was a prime consideration at all times.