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Run of River
A run-of-river hydro project uses the natural power created by the flow of a river to produce electricity. It means we don’t need to build an impounding dam with a large reservoir and that the project will hardly disrupt the natural environment or the water quality.
Our Bakun Hydro Project in the Philippines is a perfect example of this. Water from the upper reaches of the Bakun river is diverted by a small concrete wall into a 9.5km tunnel and steel pipeline that exits at the power station almost 550m below the intake. You can see its four major components on the diagram below: the diversion weir, desanders, a high pressure tunnel, and the power plant itself.
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1. The Diversion Weir
The weir is a concrete water trap designed to divert water. As it doesn’t create a reservoir of any size or significance, flooding is kept minimal and the impact of the project on both the environment and the local communities is limited. The weir is about 10 m deep and 20 m wide and is made of reinforced concrete firmly joined to solid rock below the riverbed. It redirects the water from the river channel into a screened intake. Steel rails line the weir's inner surfaces to protect it from damage by gravel and other waterborne debris. From here the water flows through a short tunnel into two large V-shaped underground chambers called "desanders’. |
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2. The Desanders
The desanders slow the flow of water and allow the collection and removal of any pebbles, sand and silt. Each unit has special sensors which detect the build-up of this kind of rubble. When it reaches a set level, the drainage vents automatically open to flush the system clean. This operation, as well as the maintenance of the water level in the desanders, are controlled by state-of-the-art systems of hydraulics, electronic sensors and computerized switches. The monitoring and control of these systems can be done manually at the weir site or by remote commands from the power station. |
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3. The Pressure Tunnel
After the sand, silt and pebbles are removed, the clear water is allowed to flow into the 4 m high and 3.5 m wide main tunnel. This diversion tunnel extends 9.6 km through the Cordillera mountains before ending up at the power plant almost 550 m lower than the weir elevation. The first 6 km of the tunnel are not very steep and pass through good rock requiring little structural support. The remainder of the tunnel dips more sharply and passes through weaker rock, so extra steel rock bolts and reinforced concrete were required. |
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4. The Power Station
A steel pipe extends from the tunnel into the power station where it directs the water through high-pressure jets, onto the blades of four Pelton turbines. The turbines operate in pairs and rotate like steel waterwheels at very high speeds. With each pair driving a 35-megawatt generator, the total station capacity is 70 megawatts. All operations in the power plant, including those of the weir and desanders, are linked by state-of-the-art computer technology allowing the whole system to be controlled by just one person from the central operations room. All the energy produced is delivered to the National Power Corporation and fed into the north Luzon sector of the Philippine national power grid. |
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