Barrage dam

A barrage is a type of low-head, diversion dam which consists of a number of large gates that can be opened or closed to control the amount of water passing through the structure, and thus regulate and stabilize river water elevation upstream for use in irrigation and other systems. The gates are set between flanking piers which are responsible for supporting the water load of the pool created. While the term is borrowed from the French word meaning a dam generally, its usage for such a structure in English is chiefly in Pakistan, India, Egypt, Iraq, and other countries in the Middle East.

According to the World Commission on Dams, a key difference between a barrage and a dam is that a dam is built for water storage in a reservoir, which raises the level of water significantly. A barrage is built for diverting water, and raises the water level only a few feet; they are generally built on flat terrain across wide, often meandering rivers. Similar distinctions are used in Egypt, where it is noted: "In this system a "dam" is a structure that forms a reservoir for the storage of water during the annual flood period of the Nile in order to supplement the natural flow of the river during the low-water period; a "barrage" merely raises the river or canal level, when necessary, to the height required for adequate flow into the canals that take off above it. Barrages are usually larger than the headworks of irrigation and navigation canals, with which they are associated.

Barrages that are commonly used to dam a tidal lagoon or estuary as a method to capture tidal power from tidal inflows are known as tidal barrages.

The English usage of the term barrage originates from the Delta Barrage across the Nile-branches north of Cairo, built between 1833 and 1862 by the French Linant de Bellefonds and Eugène Mougel employed in the Egyptian Public Works Department. When the British, after 1882, had to look after these structures generally referred to as barrages, they adopted the term in their language and continued to use it for similar structures built by themselves across the Nile (Zefta Barrage and Assiut Barrage both completed in 1902). Since the British in the Egyptian Public Works Department kept close relations to their counterparts in British India, the term barrages made its way to present day India and Pakistan as well as to the Middle East, and thus generally into English.

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