The Project has a gravity dam by means of RCC construction method, which creates about 70 km long reservoir. Reservoir water will be used by two units of turbine at the powerhouse located on immediate downstream of the main dam.
The general layout of the main dam is shown in Figure 2. The facilities around the main dam are composed of one lane of river diversion tunnel, a gated spillway, an intake structure and penstock, a surface type powerhouse, outlet facilities, related accessory equipment, etc. The dam is 148 m high and 540 m wide and the total volume is around 2.3 MCM. Further, the re-regulation dam is installed at 6 km downstream from the main dam to release the 16-hour peaking inflow from the main dam evenly on a 24-hour basis.
The river water will be diverted by one diversion tunnel driven through the left abutment, together with two cofferdams to be installed at the upstream and downstream sides of the main dam. After completion of its function as river diversion the tunnel will be permanently plugged with concrete.
Figure 2 Layout of the main dam facilities
The spillway is a gated overflow structure on the main dam. Maximum outflow equivalent to 1,000-year flood can be discharged through the spillway at Food Water Level.
Power intakes, intake gates and penstocks are installed in the main dam body. The powerhouse will be located at the downstream of the main dam, semi-underground type of power house.
Transmission lines of the Project will be comprised of a double-circuit 230 kV line for the electricity exportation to Thailand and a single-circuit 115 kV line for the domestic electricity supply (Figure 3). The 230 kV transmission line will be from Nam Ngiep (Main Dam Switchyard) to Nabong substation. The length of the transmission line is approximately 130 km. The 115 kV transmis sion line will be from Nam Ngiep (Re-regulation Dam Switchyard) to the existing Pakxan Substation. The length of the transmission line is approximately 40 km.