ncident management and repair of a ruptured scour main at Talybont dam caused by a pressure wave

Talybont reservoir is impounded by a 30 m high earthfill embankment dam. A 760 mm diameter water supply main and 635 mm diameter scour main are located in a tunnel that passes beneath the dam. A branch off the scour main supplies a hydropower turbine.

When the power to the turbine pump failed one evening, a pressure shock wave in the scour main caused a section of the pipe to rupture catastrophically. The incident was detected when the reservoir level dropped by an unusual amount overnight. The repair was undertaken in difficult conditions due to the confined space environment of the tunnel and manual handling issues of heavy pipe sections; the inability to isolate the main due to the guard valve being jammed in a partially open; the supply-critical main having some corrosion and weakened pipe joints near the section of scour main that was to be repaired; and the unknown condition of the remainder of the scour pipework and valve, which had been subjected to the pressure wave.

This paper describes how the incident was managed; it presents the options considered to undertake the emergency repair and the post- incident analysis and lessons learnt.