The 600 MW Pergau hydroelectric project in Northern Peninsular Malaysia draws water from a reservoir on the Sungai Pergau impounded by the Kuala Yong Dam. Additional water for the Kuala Yong reservoir is drawn from local streams by way of a 24 km long aqueduct tunnel. Some 60 of this additional flow is pumped into the upstream end of the aqueduct from a pool created by a 8 m high concrete-faced rockfill weir on the Sungai Terang. Flood flows of over 1000 m~3/s pass over this weir and there is insufficient depth downstream to create a hydraulic jump. This paper describes the development of a roughened apron in a series of physical model studies. A staggered arrangement of blocks in double rows on the apron provided a satisfactory deceleration of the stream and acceptable flow patterns. A simple analytical technique using an estimated drag coefficient has been put forward as a rational approach to the design of roughness patterns.
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