An adjustable air-regulated siphon spillway

The Pergau hydroelectric project was built as a design and construct contract in Northern Peninsular Malaysia by an Anglo-Malaysian joint venture with funding assistance provided by the British Government, A regulating pond providing 1.5 x 10(6) m(3) of live storage was constructed at the tailrace outfall to accept peak generation flows and release them back into the river in a controlled manner, Discharge from the pond is normally regulated by two hydraulically activated radial gates acting on signals from the project's automatic control system, An air-regulated siphon with a design capacity of 140 m(3)/s was provided to protect the embankment crest from overtopping in the event of gate malfunction or station generation flow continuing for longer than programmed, The spillway was developed with novel features in an extensive series of laboratory trials, Provision was made in the prototype to adjust the air intake area to compensate for scale effects in the model study and to ensure that the required head discharge relationship is obtained.