Samanalawewa Dam
Encyclopedia
The Samanalawewa Dam is a dam that is primarily used for hydroelectric power generation
in Sri Lanka
. Commissioned in 1992, the Samanalawewa project is the second-largest hydroelectric scheme in the country, producing 405 GWh of energy annually. It was built with financial support from Japan
and the United Kingdom
. It is notable for a large leak on its right bank. Power production continues as planned despite the leakage, and the water from the leak now provides two thirds of the water issued by the reservoir for agriculture in downstream areas.
and 160 kilometres (99.4 mi) southeast of Colombo
, the capital. The ground of the project area is karstic.
rapidly increased. When it became clear that it would not be possible to meet the demand with coal fired power plants
, the government of Sri Lanka decided to initiate another hydroelectric power project. A reservoir type hydroelectric power plant was planned to be constructed across the Walawe river, which would address the shortage of electricity in the country. Detailed investigations for a hydroelectric power plant in this area have been carried out since 1958, but the scheme was initiated only in 1986. The financing for the project was given by the governments of Japan
and the United Kingdom
.
The cost of the project was estimated to be 60,176 million yen, but with the remedial measures taken to control the leak, the cost increased to 74,313 million yen. The Samanalawewa power plant was commissioned in 1992. The Samanalawewa project is the second largest hydroelectric scheme in Sri Lanka after the Mahaweli project.
of the dam has three gates, each 14 metres (45.9 ft) high and 11 metres (36.1 ft) wide. It can discharge water at a rate of 3600 cubic metres (127,132.8 cu ft) per second. Its tunnel is 4.5 metres (14.8 ft) in diameter and 5159 metres (16,925.9 ft) in length.
The reservoir created by the dam has a total live storage capacity of 218000000 cubic metres (7,698,597,234.4 cu ft). Its gross storage capacity is 278000000 cubic metres (9,817,477,207.1 cu ft), of which 60000000 cubic metres (2,118,879,972.8 cu ft) is dead storage. The reservoir's full supply level is 460 metres (1,509.2 ft) above main sea level, and the reservoir spreads 8 kilometres (5 mi) upstream at this level. The reservoir is u-shaped. It covers an area of 897 ha
. However, with the water leakage the water level was reduced to 430 metres (1,410.8 ft). It is one of the largest reservoirs in Sri Lanka.
The power house contains two Francis turbine
s, each with a capacity of 62 MW, and generates 405 GWh of energy annually. The powerplant is managed by the Ceylon Electricity Board
.
The leak is constantly monitored. If the leak remains stable and does not increase further, it does not pose a threat to the sustainability of the project. The karstic ground has created complex geological conditions, and as a result the exact mechanism of the leak cannot be established, so remedial measures have been unsuccessful.
However, the necessity to constantly release water for agriculture in the downstream areas was reduced due to the leak. Of the water released from the Samanalawewa dam for agriculture in the downstream areas, two-thirds is from the leak and only one-third has to be supplied via the IRV.
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...
in Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
. Commissioned in 1992, the Samanalawewa project is the second-largest hydroelectric scheme in the country, producing 405 GWh of energy annually. It was built with financial support from Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. It is notable for a large leak on its right bank. Power production continues as planned despite the leakage, and the water from the leak now provides two thirds of the water issued by the reservoir for agriculture in downstream areas.
Location
The Samanalawewa dam is located in the Uda Walawe basin. It was built at the confluence of the Walawe river and the Belihul Oya, a location 400 metres (1,312.3 ft) above mean sea level. It is near the town of BalangodaBalangoda
Balangoda is a town in Sabaragamuwa Province of Sri Lanka. Its 143 km away from Colombo and 43 km away from Ratnapura. It is the one of biggest towns of the Ratnapura District which is one of the two districts belonging to Sabaragamuwa Province . According to the 2001 census Balangoda has a...
and 160 kilometres (99.4 mi) southeast of Colombo
Colombo
Colombo is the largest city of Sri Lanka. It is located on the west coast of the island and adjacent to Sri Jayawardenapura Kotte, the capital of Sri Lanka. Colombo is often referred to as the capital of the country, since Sri Jayawardenapura Kotte is a satellite city of Colombo...
, the capital. The ground of the project area is karstic.
Background and development
With the Mahaweli and Laxapana hydroelectric power projects implemented, the demand for electricity in Sri LankaSri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
rapidly increased. When it became clear that it would not be possible to meet the demand with coal fired power plants
Fossil fuel power plant
A fossil-fuel power station is a power station that burns fossil fuels such as coal, natural gas or petroleum to produce electricity. Central station fossil-fuel power plants are designed on a large scale for continuous operation...
, the government of Sri Lanka decided to initiate another hydroelectric power project. A reservoir type hydroelectric power plant was planned to be constructed across the Walawe river, which would address the shortage of electricity in the country. Detailed investigations for a hydroelectric power plant in this area have been carried out since 1958, but the scheme was initiated only in 1986. The financing for the project was given by the governments of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
.
The cost of the project was estimated to be 60,176 million yen, but with the remedial measures taken to control the leak, the cost increased to 74,313 million yen. The Samanalawewa power plant was commissioned in 1992. The Samanalawewa project is the second largest hydroelectric scheme in Sri Lanka after the Mahaweli project.
Dam, reservoir and the power station
The Samanalawewa dam is 110 metres (360.9 ft) in height and has a length of 530 metres (1,738.8 ft) at crest level. The volume of the dam is about 4500000 cubic metres (158,915,998 cu ft). Rainfall in the area has an annual average of 2867 millimetres (112.9 in), and the catchment area is 372 square kilometres (143.6 sq mi). The dam is of rock fill, central earth core type. The spillwaySpillway
A spillway is a structure used to provide the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed. In the UK they may be known as overflow channels. Spillways release floods so that the water does not overtop and damage or even destroy...
of the dam has three gates, each 14 metres (45.9 ft) high and 11 metres (36.1 ft) wide. It can discharge water at a rate of 3600 cubic metres (127,132.8 cu ft) per second. Its tunnel is 4.5 metres (14.8 ft) in diameter and 5159 metres (16,925.9 ft) in length.
The reservoir created by the dam has a total live storage capacity of 218000000 cubic metres (7,698,597,234.4 cu ft). Its gross storage capacity is 278000000 cubic metres (9,817,477,207.1 cu ft), of which 60000000 cubic metres (2,118,879,972.8 cu ft) is dead storage. The reservoir's full supply level is 460 metres (1,509.2 ft) above main sea level, and the reservoir spreads 8 kilometres (5 mi) upstream at this level. The reservoir is u-shaped. It covers an area of 897 ha
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
. However, with the water leakage the water level was reduced to 430 metres (1,410.8 ft). It is one of the largest reservoirs in Sri Lanka.
The power house contains two Francis turbine
Francis turbine
The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts....
s, each with a capacity of 62 MW, and generates 405 GWh of energy annually. The powerplant is managed by the Ceylon Electricity Board
Ceylon Electricity Board
The Ceylon Electricity Board , is the largest electricity company in Sri Lanka. With a market share of nearly 100%, it controls all major functions of electricity generation, transmission, distribution and retailing in Sri Lanka. It is one of the only two on-grid electricity companies in the...
.
Leak
A permeable area of ground was found during the construction of the dam in 1988. Curtain grouting was used in an effort to remedy this. However, as the reservoir was being filled, a large leak occurred on the side of the right bank, about 300 metres (984.3 ft) downstream from the dam, causing a landslip. Subsequent measures taken to control the leakage were largely ineffective. The leakage of approximately 1800 litres (395.9 imp gal) per second continues, but has not affected power production at the plant, which has been in full operation since its commissioning in 1992.The leak is constantly monitored. If the leak remains stable and does not increase further, it does not pose a threat to the sustainability of the project. The karstic ground has created complex geological conditions, and as a result the exact mechanism of the leak cannot be established, so remedial measures have been unsuccessful.
Impact
The project was planned as a single purpose hydropower project. Therefore the effects on the agriculture and the environment of the area were taken into consideration very little during the development. Although an irrigational release valve (IRV) is there in the dam to supply water to the farmlands in the downstream areas, the yield and cultivable acreage has declined since the Samanalawewa project was commissioned.However, the necessity to constantly release water for agriculture in the downstream areas was reduced due to the leak. Of the water released from the Samanalawewa dam for agriculture in the downstream areas, two-thirds is from the leak and only one-third has to be supplied via the IRV.