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Concrete variable radius arch dam explained

Updated: Aug 16, 2020

Definition 🧾:

A barrier constructed to hold back water and raise its level, forming a reservoir used to generate electricity or as a water supply.

"The dam burst after torrential rain"

An arch dam is a concrete dam that is curved upstream in a plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, compressing and strengthening the structure as it pushes into its foundation or abutments.


An arch dam is most suitable for narrow canyons or gorges with steep walls of stable rock to support the structure and stresses. Since they are thinner than any other dam type, they require much less construction material, making them economical and practical in remote areas.

Arch dams classified with respect to their structural height are:

  • Low dams up to 100 feet (30 m),

  • Medium-high dams between 100–300 ft (30–91 m)

  • High dams over 300 ft (91 m).

General dams classified based on base thickness and height relations:

  • Thin arch<0.2h

  • Medium arch0.2h - 0.3h

  • Thick arch>0.3h

  • Arch-gravity>0.5h

The Katse Dam, a 185m high concrete arch dam in Lesotho.

History: The 1st Arch Dam construction ⛲️

The first known arch dam, the Glanum Dam, also known as the Vallon de Baume Dam, was built by the Romans in France and it dates back to the 1st century BC.

The dam was about 12 metres (39 ft) high and 18 metres (59 ft) in length. Its radius was about 14 m (46 ft), and it consisted of two masonry walls. The Romans built it to supply nearby Glanum with water.


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Basic Design Types 🏗

There are two basic designs for an arch dam: constant-radius dams, which have a constant radius of curvature, and variable-radius dams, which have both upstream and downstream curves that systematically decrease in radius below the crest. A dam that is double-curved in both its horizontal and vertical planes may be called a dome dam

Advantages of Arch Dam

1. Arch dams are particularly adapted to the gorges where the length is small in proportion to the height.

2. For a given height, the section of an arch dam is much lesser than a corresponding gravity dam.

Hence, an arch dam requires less material and is, therefore, cheaper.

3. Because of much less base width, the problems of uplift pressure are minor.

4. Since only a small part of water load is transferred to the foundation by cantilever action,




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