The project was initially planned in 1968 by the local authorities, before the Government of Japan funded a study between 1985 and 1987 to further examine the hydroelectric potential in the upper reaches of Kotmale River. The feasibility study included five sites and eight alternative development schemes, and concluded with two sites which were more technically and economically feasible. The two sites were a conventional type at Caledonia, and a run-of-the-river type at Talawakele. The project at Caledonia involved the displacement of over 2,700 families and inundation of large areas of land used for tea plantations, and thus the Caledonia site was dropped. Further funding was then provided by Japan for the engineering study, which included a review of the feasibility study, selection of an optimal development plan, development of the detailed design, and the preparation of tender documents and an environmental impact assessment report. The environmental impact assessment report was completed in September 1994, with the final design report completed in March 1995. The environmental assessment identified key issues associated with the project, which includes impact on St. Clair's Falls aesthetics due to stream flow reductions, social impacts due to resettlement of affected people, possible effects on ground water due to tunnelling, impacts on downstream water uses due to de-watering of streams, and impacts on biodiversity. These impacts led large delays in project development. As per the National Environmental Act of 1998, the environmental clearance was then granted to the project. The project initially faced several objections, before being officially permitted by courts of law. Construction work on the project then began in 2006, and is expected to be completed by the end of 2011.
Construction and development
This project is estimated to cost a total of up to Rs.44 billion, of which Rs.5.931 billion was funded by the Ceylon Electricity Board, and ¥33.265 billion by the Japan Bank for International Cooperation. The entire project covers an area of approximately, and is developed in five phases:
Phase 1: Site preparations, construction of employers and workers living quarters, construction of access roads, and relocation of affected people.
Phase 2: All key civil engineering works, such as construction of tunnel, dam, underground power house etc. This takes about 50% of the project cost.
Phase 3: Hydro-mechanical works such as construction of spillways, penstocks, intake gates, etc.
Phase 4: Electro-mechanical works such as generation installations, construction of the switchyard, fire fighting system, communication system, etc.
A total of 2,250 construction workers are employed at the site, of which 2,100 are locals, and 150 are foreign.
Dam and reservoir
The gravity dam measures tall, and wide, impounding the Kotmale River and creating the Upper Kotmale Reservoir. Once filled, the reservoir will have a surface area of with an average storage capacity of. The minimum and maximum operating water levels are and AMSL respectively, while the tailwater level is AMSL. Water from the reservoir will be used for both irrigation development and hydroelectric power generation.
Tunnel
The diameter, long Upper Kotmale Tunnel, the longest excavated tunnel in Sri Lanka, will be used to deliver the water to the powerhouse. The tunnel begins at the dam site, and stretches north at a distance of approximately towards Pundaluoya, before stretching a further north-west towards Kumbaloluwa and ending up at its powerhouse at the Kotmale River near Niyamgamdora, at approximately, downstream of the confluence of Pundal River and the Kotmale River. Excavation on the tunnel was completed and ceremonially opened by PresidentMahinda Rajapaksa on 4 November 2010.
Powerhouse
The powerhouse measures long, wide, and tall, and is located underground at Niyamgamdora. It has installed electrical capacity of from two turbines, capable of producing up to of power annually. Water arrives at the powerhouse from the dam via the long Upper Kotmale Tunnel, which then feeds the penstock. The initial of the penstock is single-lane, while the latter splits into two lanes, feeding the two generators respectively. The powerhouse consists of the two three-phase, vertical-axis Francis turbine-generators, two three-phase transformers, and a 220kV Gas Insulator Switchgear substation. An outdoor switchyard measuring by.
Transmission line
The 220kV transmission line of the Upper Kotmale Hydro-power Project connects the power station located at Niyamgamdora, Kotmale, to the national grid via Kotmale switch yard located in Atabage, Gampola. The line consists of 45 towers and has a length of 15.5 km. The double circuit transmission line has a capacity of 220 MW per circuit.
Social and environmental impact
The construction of the dam, tunnel, and powerhouse, required the relocation of families from 495 houses. New homes were built away from the site with access to vital facilities such as water and power. The relocated families are provided with concessionary loans to start new self-employment ventures, while additional facilities such as the Talawakele Central College, places of worship, a cinema hall, a library, and a community centre, are being established. Similar most other dam's impacts on rivers around the world, the Upper Kotmale Dam will periodically stop the St. Clair's Falls, located downstream of the dam, and a further of the Kotmale River downstream of St. Clairs Falls, before the river is restored by water from the Devon River, the river forming the picturesque Devon Falls. As ordered by the Government Extraordinary, the St. Clair's waterfall will maintain a continuous flow of of water for 10 hours and 30 minutes daily, between sunrise and sunset.
