The Bakun AC hydroelectric plant in the north of the Philippines provides much needed electricity while reducing the need to import foreign fuel such as coal and petroleum.
It is the first hydropower project in the Philippines to be built on a build-own-operate-transfer (BOOT) basis, and Halcrow’s expertise was invaluable in making the scheme a success.
Halcrow was initially engaged to prepare a due diligence report and assist the turnkey contractor, Transfield, to prepare a competitive bid. During that process we reviewed existing feasibility studies for three separate schemes and recommended that they be combined into a single 70MW hydro scheme that generates 98.5% of the annual energy of the three schemes, but at a cost of 10% less per kWh.
We were subsequently appointed by the design and build contractor for the detailed design of the project.
The AU$95 million plant sits on the Bakun River, in the Cordillera Central mountain range in northern Luzon, one of the wetter regions in the Philippines, with annual rainfall of approximately 3.1m.
The site's steep topography - with a drop in elevation of 500m - combined with this abundant rainfall makes it an ideal location for "run-of-river" hydroelectric production, which harnesses the natural flow of the river to produce electricity and, therefore, does not involve constructing an impounding dam and reservoir.
The head works consist of an 11m high mass concrete weir incorporating a 21m long crest intake and a bypass spillway. The intake diverts 20 cumecs of water from the Bakun River, augmented by diverting a downstream tributary through a 100m long diversion tunnel and 80m long pipeline.
To reduce maintenance, all water entering the power station passes through a 75m long, underground "desanding" basin, which slows the water flow and allows particles up to 0.5mm in size to settle out.
After passing through the desander, the water travels 9.5km along tunnels, the first 6.5km of which is 3.4m in diameter and supported by rockbolts and steel fibre reinforced sprayed concrete. The remaining 3km of tunnel is steel lined to withstand the high head.
The power station has a reinforced concrete substructure and a structural steel superstructure. Its installed capacity of 70MW comes from two horizontally mounted generator sets driven by 17.5MW twin jet Pelton turbines.
Construction of the hydro plant eliminates the environmental consequences of burning approximately 330,000 barrels of oil a year.