Cofferdam – Definition, Application, Limitations & Working of Coffer Dams


The multiple-stage method of diversion over the tops of alternate low construction blocks or through diversion conduits in a concrete dam requires shifting of the cofferdam from one side of the river to the other during construction. During the first stage, the flow is restricted to one portion of the stream channel while the dam is constructed to a safe elevation in the remainder of the channel.

In the second stage, the cofferdam is shifted and the stream is carried over low blocks or through diversion conduits in the constructed section of the dam while work proceeds on the un-constructed portion. The dam is then carried to its ultimate height, with diversion finally being made through the spillway, penstock, or permanent outlets.

Coffer Dam

cofferdam can be defined as “A watertight construction designed to facilitate construction projects in areas which are normally submerged”, such as bridges and piers.

A cofferdam is installed in the execution area and the water is pumped out in order to facilitate work for workers and enable them to work in dry conditions and can construct structural supports, enact repairs, or perform other types of work in a dry environment. In some regions of the world, a cofferdam is better known as a caisson. Working inside a cofferdam can be hazardous if it is installed improperly or not safely pressurized, but advances in engineering have led to increased safety for workers using this unique work environment.

A cofferdam is a temporary dam or barrier used to divert a stream or to enclose an area during construction. The design of an adequate cofferdam involves the problem of construction economics. When the construction is timed so that the foundation work can be executed during the low-water season, the use of cofferdams can be held to a minimum. However, where the stream flow characteristics are such that this is not practical, the cofferdam must be so designed that it is not only safe, but also of the optimum height.

Height Limitations for Cofferdam

The height to which a cofferdam should be constructed may involve an economic study of cofferdam height versus diversion works capacity. This may include routing studies of the diversion design flood, especially when the outlet works requirements are small. If outlet works requirements dictate a relatively large outlet conduit or tunnel, diversion flows ordinarily may be accommodated without a high cofferdam. It should be remembered that the floodwater accumulated behind the cofferdam must be evacuated in time to accommodate another storm.

The maximum height to which it is feasible to construct the cofferdam without encroaching upon the area to be occupied by the dam must also be considered. Furthermore, the design of the cofferdam must take into consideration the effect that excavation and de-watering of the foundation of the dam will have on its stability, and it must anticipate removal, salvage, and other factors.

Generally, cofferdams are constructed of materials available at the site. The two types normally used in the construction of dams are

  1. Earthfill cofferdams and
  2. Rockfill cofferdams

Whose design considerations closely follow those for permanent dams of the same type. Other less common cofferdam types are concrete cribs filled with earth or rock, and cellular-steel cofferdams filled with earth or rock. In this case, the major portion of the cofferdam consists of an earth and rock embankment, and steel sheet piling was used to affect final closure in swift water. Cellular steel cofferdams and steel sheet piling are adaptable to confined areas where currents are swift.

If the cofferdam can be designed so that it is permanent and adds to the structural stability of the dam, it will have a decided economic advantage. In some embankment dams the cofferdam can even be incorporated into the main embankment. In such instances, the saving is twofold-the amount saved by reducing the embankment material required and the amount saved by not having to remove the cofferdam when it is no longer needed.

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The Girder Bridge


The Girder Bridge.

The 5 Biggest Dams in India


After independence we have made lots of progress in Dam and water reservoirs, Now India is one of the world’s most prolific dam-builders. Around 4300 large dams already constructed and many more in the pipeline, Almost half of which are more than twenty  years old. These dams are major attraction of tourists from all over India.

Some facts about the Indian dams are:

  • Tehri Dam is the eighth highest dam in the world.
  • The Idukki dam is the first Indian arch dam in Periyar River Kerala and the largest arch dam in Asia.
  • The Grand Anicut, Kallanai, located on Holy Cavery River in Tamil Nadu, is the oldest dam in the world.
  • Indira Sagar Dam is the Largest Reservoir in India. These dams with the channel provides an ideal environment for wildlife.

Tehri Dam -Uttaranchal

Tehri Dam

Tehri Dam located on the Bhagirathi River, Uttaranchal Now become Uttarakhand. Tehri Dam is the highest dam in India,With a height of 261 meters and the eighth tallest dam in the world. The high rock and earth-fill embankment dam first phase was completed in 2006 and other two phases are under construction. The Dam water reservoir use for irrigation, municipal water supply and the generation of 1,000 MW of hydroelectricity.

  • Height: 260 meters
  • Length: 575 meters
  • Type: Earth and rock-fill
  • Reservoir Capacity: 2,100,000 acre·ft
  • River: Bhagirathi River
  • Location: Uttarakhand
  • Installed capacity: 1,000 MW

Bhakra Nangal Dam -Himachal Pradesh

Bhakra-nangal-dam

Bhakra Nangal Dam is a gravity dam across the Sutlej river Himachal Pradesh. Bhakra Nangal is the largest dam in India, with a height of 225 meters and second largest Dam in Asia. Its reservoir, known as the “Gobind Sagar Lake” it is the second largest reservoir in India, the first being Indira Sagar dam.

  • Height: 226 meters
  • Length: 520 meters
  • Type: Concrete gravity
  • Reservoir Capacity: 7,501,775 acre·ft
  • River: Sutlej River
  • Location: Punjab and Himachal Pradesh
  • Installed capacity: 1325 MW

Hirakud Dam -Orissa

Hirakud-Dam

Hirakud dam built across the Mahanadi River in tribal state Orissa. Hirakud Dam is one of the longest dams in the world about 26 km in length. There are two observation towers on the dam one is “Gandhi Minar” and another one is “Nehru Minar”. The Hirakud Reservoir is 55 km long used as multipurpose scheme intended for flood control, irrigation and power generation. It was one of the major multipurpose river valley project after Independence.

  • Height: 60.96  meters
  • Length: 25.8 km
  • Type: Composite Dam
  • Reservoir Capacity: 4,779,965 acre·ft
  • River: Mahanadi River
  • Location: Orissa
  • Installed capacity: 307.5 MW

NagarjunaSagar Dam -Andhra Pradesh

Nagarjuna-sagar-Dam

Nagarjuna Sagar Dam is the world’s largest masonry dam with a height of 124 meters, built across Krishna River in Andhra Pradesh. Nagarjuna Sagar Dam is certainly the pride of India-considered the largest man-made lake in the world. The 1.6 km long with 26 gates dam was symbol of modern India’s architectural and technological triumphs over nature.

  • Height: 124 meters
  • Length:1,450 meters
  • Type: Masonry Dam
  • Reservoir Capacity: 9,371,845 acre·ft
  • River: Krishna River
  • Location: Andhra Pradesh
  • Installed capacity: 816 MW

Sardar Sarovar Dam -Gujarat

Sardar_sarovar_dam

Sardar Sarovar Dam also known as “Narmada Dam” is the largest dam to be built, with a height of 163 meters, over the Sacred Narmada River in Gujarat. Drought prone areas of Kutch and Saurashtra will get irrigate by this project. The gravity dam is the largest dam of Narmada Valley Project with power facilities up to 200 MW. The dam is meant to benefit the 4 major states of India Gujarat, Madhya Pradesh, Maharashtra and Rajasthan.

  • Height: 163 meters
  • Length:1,210 meters
  • Type: Gravity Dam
  • Reservoir Capacity: 7,701,775 acre·ft
  • River: Narmada River
  • Location: Gujarat
  • Installed capacity: 1,450 MW