Engineering geology of Sungai Piah hydro-electric project, Perak, Peninsular Malaysia

The Sungai Piah hydro-electric Project is s ituated some 57 km north-northeast of Ipoh. The area is mountainous and heav ily forested . The general outline of the project is for diverting water from Sungai Temor to Sungai Piah and then through a series of tunnels down to a lower elevation, thus developing an effective head of about 680 m and a generating capacity of 46.5 MW. Approximately 20 km of tunnel lines, comprising 2 stages of diversion and power tunnels , are proposed for the hydro-electric project. Preliminary geological mapping was conducted in October and November 1982 and a feasibility srudy consisting of surface mapping together with geotechnical investigation and a diamond drilling programme was undertaken from early August to November 1983. The area is underlain predominantly by coarse-grained porphyritic biotite granite with a 4 km x 7 km roof pendant to the northwest. The roof pendant consists of quartz-mica schist and calcsilicate hornfels. The Stage I scheme is expected 10 encounter more faults than the Stage ll scheme which would require more lining for the runnel. The Chier fault, which is the largest in the area, affected the location of both the tunnel portal si tes of the Stage ll diversion tunnel. They had to be relocated further downstrean1 away from the fault zone. INTRODUCTION The Sungai Piah Project is ode of the smaller hydro-electric schemes of the National Electricity Board. It is being investigated by the Shawinigan Engineering Company Limited, a consultantfirm from Canada. The Geological Survey ofMalaysia provides complementary services and support to this investigation. The project area which is located about 57 km north-northeast oflpoh is mountainous and heavily forested (Figure 1). It is accessible by metalled road to Lasah, beyond which only timber tracks exist. The proposed tunnel line is approximately 20 km long and comprises 2 stages of diversion and power tunnels. Stage I (Upper Scheme) would provide for the diversion of Sungai Piah at elevation 800 m to a conventional surface powerhouse near Sungai Toor at elevation 534 m thereby developing 266 m of head (Figure 2). Stage II (Lower Scheme) would involve a second diversion of the Sungai Piah immediately downstream of the Sungai ToorSungai Piah confluence, with the Piah flows being supplemented by a diversion from the Sungai Temor, to an underground powerhouse at elevation 120m. Stage II would provide development of 414 m of head. The combined gross head of the two stages of development is 680 m with a generating capacity of 46.5 MW. LEGEND Metalled road