AN ADJUSTABLE AIR-REGULATED SIPHON SPILLWAY

The Pergau hydroelectric project was built as a design and construct c ontract in Northern Peninsular Malaysia by an Anglo-Malaysian joint ve nture with funding assistance provided by the British Government, A re gulating pond providing 1.5 x 10(6) m(3) of live storage was construct ed at the tailrace outfall to accept peak generation flows and release them back into the river in a controlled manner, Discharge from the p ond 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 mal function or station generation flow continuing for longer than program med, The spillway was developed with novel features in an extensive se ries of laboratory trials, Provision was made in the prototype to adju st the air intake area to compensate for scale effects in the model st udy and to ensure that the required head discharge relationship is obt ained.