The Nam Ngiep 1 Project is designed to harness the energy potential of the lower part of the Ngiep River by creating a reservoir that will supply water to a power station situated below a 167-metre high dam. The electricity generated at this facility will be exported to Thailand.
A second dam and small reservoir are to be built downstream of the main facilities in order to regulate water flows and so minimize disturbances to the river and people living further along the Nam Ngiep. A smaller power station located at this Re-Regulating Dam will supply electricity for use in Laos.
The 167-m high Main Dam will create the Nam Ngiep 1 Main Reservoir, with a surface area of 70 square kilometers when at full supply level. The height and volume of the reservoir has been limited in order to reduce the number of people affected by the water level but it will still have an effective storage capacity of 1,192 million cubic metres of water. The average depth of the reservoir will be about 74 m, ranging from a maximum of 167 m at the Main Dam, to just a few meters at the furthest point from the dam, approximately 70 km upstream.
At the Main Dam, which is a roller-compacted concreted gravity dam approximately 530 m in length, water from the reservoir will drop around 132 m to the Main Powerhouse, located on the left bank of the river when looking downstream. The Main Dam also features a spillway with four gates to enable extra release if the reservoir approaches full capacity. The ski-jump type spillway mitigates the effects of discharged water around the immediate downstream area and is designed to release up to 5,200 cubic metres of water per second, enough to deal with a 1,000-year maximum flood event.
The Main Powerhouse features two Francis Unit turbines that can together generate 272 MW of power, supplying 1,546 GWh per year to the nearby substation.
Water discharged from the Main Powerhouse will flow into the Re-Regulating Reservoir, created so that a smooth discharge of water can be released on a daily basis downstream. By storing discharged water from the Main Dam during power peaks, re-using it for domestic power generation and releasing it downstream evenly on a 24-hour basis on weekdays, the re-regulation system helps to mitigate potential environmental impacts caused by fluctuations in water level.
The water can be released either directly through the Re-Regulation Dam, located 6.2 km downstream from the main dam, or through the Re- Regulation Powerhouse. The Re-Regulation Dam is a free-overflow type concrete gravity dam approximately 90 meters long and 20 meters high.
The Re-Regulation Powerhouse will have an 18-MW capacity, able to generate 105 GWh of power annually through a single bulb type turbine. This power station will generate energy for delivery to EDL.