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List of some major dams across the world: 1. The Bhakra Dam (Gravity Dam) 2. Idduki Dam (Arch Dam) 3. Nagarjuna Sagar Dam (Masonry Dam) 4. The Hirakud Dam (Earth Dam) 5. Grand Coulee Dam (Gravity Dam – USA) 6. Kariba Dam (Double Curvature Arch Dam – Zambia) 7. Grand Dixence Dam (Gravity Dam – Switzerland) 8. Mangla Dam (Earthfill – Pakistan).
1. The Bhakra Dam (Gravity Dam):
The Bhakra Dam, which is a multipurpose gravity dam, is built across river Sutlej in district Hoshiarpur of Himachal Pradesh State of India. It was completed in 1963 and is 226 meters in height and 518 m in length at the crest (about 100 m at the base). Its spillways have a discharge capacity of 8372 cubic meter per second. The reservoir called Gobind Sagar has an area of 16,6000 × 103 m2.
The gorge in the dam area is made up of alternating layers of fairly hard and thick-bedded sandstones and light-red clays. The sequence has a steep down-stream dip varying between
70°-80°. In the foundations and abutment rocks, a large number of shear zones and fault zones were encountered.
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Three types of shear zones were very abundant – bedding shear zones (parallel to bedding planes), diagonal shear zones and the cross or transverse shear zones cutting the bedding planes at right angles. These zones were treated thoroughly by conventional methods of excavation and backfilling and grouting, wherever necessary.
The question of suitability of the present site for a dam was studied as far back as 1915.
In 1925, Dr. C.S. Fox, a top geologist of Geological Survey of India, had summarized that:
(i) The rocks in the proposed site are somewhat crushed;
(ii) There are potentialities for a landslip to occur just below the northwest part of the gorge owing to steep downstream inclination of the strata and their striking across the gorge.
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The site is located in the foot hill of Himalayas which falls in the zone of highest seismic intensity in the country. But because of its topographic situation, the dam which is one of the highest gravity dams in the world was constructed taking all the precautions and incorporating high safety factors in its design.
It has already stood the test of time for about 45 years (in 2008) and played a signal role in the development of the country especially in the fields of food production and industrialization. Its irrigation potential is 10 million acres and power generation capacity is 1200 MW.
2. Idduki Dam (Arch Dam):
This is one of the major dams of Kerala state constructed over Periyar River. It is a storage type project with an installed capacity of 780 MW in six units of 130 MW each. The dam was completed in 1974 and is the only major Arch dam of the country at the close of the 20th century with a height of 169 meters above the lowest foundation and length of 366 meters.
3. Nagarjuna Sagar Dam (Masonry Dam):
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The Nagarjuna Sagar Dam is named after Buddhist Savant, Acharya Nagarjuna and is constructed over river Krishna in Nalgonda district of Andhra Pradesh (India). The main dam is a stone masonry dam, 124 m high from the deepest foundation and 1446 m long. The main dam is flanked on either side by an earth dam.
The left bank earth dam is 2554 m long and the right bank dam 851 m long. Seen in totality, the Nagarjuna Sagar Dam forms one of the longest masonry – earth dams of the world as in 2003. It is also a multipurpose dam. The reservoir has a gross storage capacity of 9.37 million acre feet and power generation capacity of 300 MW. The dam was inaugurated in 1967.
4. The Hirakud Dam (Earth Dam):
This is one of the longest earth dams of India constructed over river Mahanadi near Sambalpur in Orissa state. The dam was completed in 1957 and has a length of 4800 meters and height of 59 meters. The reservoir created by the dam has a gross storage capacity of 1841 million cum and live storage capacity of 5822 million cum.
It has irrigational facilities for 251 thousand hectares of land and power generation capacity of 150 MW. It is one of the oldest multipurpose hydro- power-irrigation projects of the country which has contributed tremendously toward the food production and power generation.
5. Grand Coulee Dam (Gravity Dam – USA):
The dam is located on the Columbia River (USA) and is example of a dam constructed safely in a glaciated area. The dam is 168 m high, has a crest length of 1270 m and is founded on coarse grained granite that was overlain by 15 to 100 meters of silts and gravels. The dam was completed in 1942 and is a multipurpose dam with a capacity to generate more than 2000 MW power and a reservoir extending for more than 240 km.
6. Kariba Dam (Double Curvature Arch Dam – Zambia):
The Kariba dam has been constructed across the Zambezvi River which forms frontier between Rhodesia and Zambia in 1960. It is one of best examples of a double curvature arch dams and has a height of 128 m. The crest length is 620 m. The site is made up of metamorphic rocks, primarily gneisses and quartzites, the latter being highly fractured, sheared and weathered to a great depth. The dam provides an example of improving the quality of rocks to the desired extent by artificial treatment.
7. Grand Dixence Dam (Gravity Dam – Switzerland):
The Grand Dixence Dam with a height of 285 m is certainly one of the greatest dams of the world. It is constructed to impound water from Rhone River and is of gravity type with a crest length of 695 m. The site rocks belong to metamorphic group, being predominantly of the type quartz-rich mica-schist of hard type. The dam is considered as an example of highest gravity dam resting satisfactorily on Schists which are otherwise generally considered poor quality site rocks. The dam has a capacity to generate 1440 MW of hydroelectric power.
8. Mangla Dam (Earthfill – Pakistan):
The Mangla Dam is an important multipurpose dam of Pakistan constructed over Jhelum River in 1968. It has a capacity of generating 800 MW power and has created a reservoir 64 km in length. The Mangla Dam is of an earthfill type having a maximum height of 138 m, crest length of 2450 m and a crest width of 12 m.
The dam and the reservoir are located in sandstones, siltstones, clays and gravel beds of Siwalik System, and are tectonically disturbed besides being soft and friable. Hence the dam posed lot of geological problems during construction.