Upper Kothmale Power Station
Upper Kothmale Reservoir/Dam
The Upper Kotmale Dam (also known as the Upper Kotmale Hydropower Project, or UKHP) is located in Talawakele, within the Nuwara Eliya District, in the Central Province of Sri Lanka. The dam feeds the third largest hydroelectric power station in the country.
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 the plant was commissioned and started generation in October 2012.
Social and Environmental Impact
The St. Clair’s Falls
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 2.2 km (1.4 mi) downstream of the dam, and a further 2.9 km (1.8 mi) 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 47,250 m3 (1,668,618 cu ft) of water for 10 hours and 30 minutes daily, between sunrise and sunset.
Technical Data (Dam and Reservoir)
Dam located close to the town of Talawakelle with a height of 35.5m and a crest length of 180m. It will have a gross storage of 2.5 MCM with an effective capacity of 0.8 MCM with a surface area of 0.25km2 (60 acres). Full supply level for the reservoir will be 1,194 metres above mean sea level (msl), the minimum operating level will be 1190m msl and the normal tail water level 703m msl.
Headrace tunnel 4.5m/5+.2m in diameter lined and unlined and 12.89km in length, running north from the dam towards the Pundal Oya Falls before turning to the northwest towards the existing Kotmale dam and reservoir. (The maximum gross head between the reservoir and the powerhouse will be 491m).
Upstream surge tank 12m in diameter and 98m high with a restricted opening, located on the crest of the power house.
The penstock formed by an underground incline shaft starting with a diameter of 4.5m and reducing to 1.45m. It will be 793m in length, consisting of one lane of 745m and two lanes of 48m.
Underground powerhouse is located at Niyamgamdora, (2km upstream of the confluence of Puna Oya and Kotmale Oya) with dimensions of 66.3m L x 18.8m W x 36.5m H to house two units of 77,000kW turbines, two vertical axis three phase 88,000kVA generators, two 3-phase, transformers and a 220kV Gas Insulator Switchgear (GIS) substation.
An outdoor switchyard, 36.5m wide and 130m long, located at Niyamgamdora, to connect the Power House to a 220kV double circuit transmission line.
220kV double circuit transmission line of 18km length to transmit power generated to existing Kotmale Substation and the associated switch yard extensions.
- Installed capacity 70 MW X 3
- Expected annual average energy 700 GWh
- Commissioned in 1984
- Main contractors
- Civil – Costain
- Electromechanical – GEC Large Machines
- Hydro mechanical – Boving
- Located 40 km south-east of Kandy
- Catchment area : 1891 km2
- Usable water volume : 688 MCM
- Maximum level : 438 m above MSL
- Minimum level : 370 m above MSL
- Circular concrete lined
- 6.2 m diameter
- 5800 m length
- Steel circular, 3 m diameter, 178 m length, With surge tank
- Length : VVV m ; Maximum level : 240 m above MSL; Minimum level : 230 m above MSL
- Generator (ASEA)
- Conventional vertical
- 70125 kVA, 0.85 PF, 12.5 kV, 3810 A
- 50 Hz, 18 poles, 333 ⅓ rev/min
- Exciter : 220 V, 1130 A
- Turbine (KAMEWA)
- Vertical Francis
- Output : 72 MW @ 190 m effective head (Rated), 83 MW @ 208 m effective head (Maximum)
- Rated discharge : 35 m3/sec
- 333 ⅓ rev/min