Kaptai dam is the one and only dam of Bangladesh that is used to generate hydro-electric power. The only hydropower plant in the country is located at kaptai, about 50 km from the port city of chittagong. This plant was constructed in 1962 as part of the 'Karnafuli Multipurpose Project', and is one of the biggest water resources development project of Bangladesh. The water storage capacity of the Kaptai dam is 11000 km2.
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| Kaptai Dam |
After being commissioned in 1962, the plant could feed the national grid with 80 MW of electricity. In later years, the generation capacity was increased in two phases to a total of 230 MW. The plant not only plays an important role in meeting the power demand of the country but is also vital as a flood management installation for the areas downstream.
Under the guidance of then Chief Engineer (Irrigation) Khwaja Azimuddin, the construction site was chosen at present location of the dam in 1951. The International Engineering Co. Inc. (IECO) was engaged for a study on the project. Utah International Inc. was selected as construction contractor.
The earth-filled dam Kaptai is an earth-fill dam. It is 45.7m (36m MSL or mean sea level) high and 670.6m long. The maximum width is 7.6m and width at the foot is 45.7m. The 16-gated spillways, each 12.2m by 11.3m, can together pass a flow of 625,000 cusec. The average annual flow in the reservoir is approximately 15,646 MCM. The flood absorption capacity is 8.25 million Ac-ft and the flooded area at 33m MSL is 777 sq km.
In 1962, the the dam, spillway, penstock and two units of powerhouses were built. Each of the powerhouses was capable of generating 40MW of electricity. In November 1981 another 50MW generating unit was completed. In October 1988 the 4th and 5th generating units were installed which raised the total generation capacity to 230MW. The total cost of Unit 1, Unit 2 and a part of Unit 3 was Rs. 503 million and the total cost of extension was Tk. 1,900 million. The spillways was constructed on the left side of the main dam. The 16 gated (each 12.2 m X 11.3 m) spillway have discharge capacity of 625000 cusec. The construction of these system (dam, spillways and others) required to excavate 113400 cubic m. The dead storage at 23.16m above MSL is 1.18 million ac-ft. Flood storage capacity is 0.83 million ac-ft.
Climate
The project area lies in the path of heavily moisture-laden monsoon winds. The rainy season extends from June through November and about 80% of the annual rainfall is concentrated in this season. The annual rainfall in the area is estimated at 2,200 mm to 3600 mm. Although the humidity is 35-45% from November through March, it becomes 80% or even higher during the rainy season. Most of the evaporation is concentrated in the dry season. The average annual evaporation is about 500 mm. Wind is generally considered to be mild except during strong thunderstorms and cyclones. The maximum wind velocity recorded is 96.54 km/h.
Flooding
Normally, large floods occur during the monsoon from June to October. High floods stay for periods of 4 to 5 days and are likely to occur during spring high tides. The flood condition is aggravated by typhoon rainstorms, which tend to raise the tidal level. The major cause of severe flooding in low-lying areas downstream is synchronization of the flood peaks of the karnafuli and the relatively sluggish halda river.
Power generation
The project was inaugurated in early 1962, with two of its three planned generators putting 80 MW of electricity into the national power grid. The third generator of 50 MW started power generation in January 1982. A feasibility study revealed that the reservoir had a 25% higher capacity than what was originally computed. The operating data also revealed a higher value of inflow than had initially been calculated. In order to exploit this additional potential, two more generators having 50 MW capacity each was installed in 1988.
The power available from this dam has accelerated the establishment and expansion of industries in Bangladesh and has resulted in an appreciable saving in foreign exchange required for the import of manufactured goods. The power generated also permits pumping of water to achieve widespread irrigation and drainage. The reservoir storage designed to prevent serious flood has already saved the city of Chittagong from severe damage. Fishing in Kaptai reservoir annually produces more than 7,000 tons of freshwater fish. Right above the dam there is the unending vista of a smooth sheet of water up to all conceivable corners of chittagong hill tracts made negotiable by launches, boats and other craft to the farthest Barkal rapids to the east and Kasalong forest reserves to the north, past rangamati. At Kaptai, all floating cargoes are transported across the dam by electric overhead trolleys.
Kaptai dam can reduce the downstream flood peak in the Karnafuli river by 50% by storing water in the reservoir. Kaptai dam is 670.56m long and 45.7m high. The width at the foundation level is 45.7m and at crest level 7.6m. The crest level is 36m above mean sea level (MSL).
The 11000 km2 catchment area of the reservoir of the Kaptai dam claims 220 km2 of cultivable land of which 40% cultivable land in this area and displace 18000 families submerging a total of 655 km2.