A barrage is a type of low-head, diversion

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

which consists of a number of large gates that can be opened or closed to control the amount of water passing through. This allows the structure to 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. The term '' barrage'' is borrowed from the French word "barrer" meaning "to bar".

Dam construction

Barrage dams have a series of gates that control the amount of water passing through. A barrage dam can be used to divert water for irrigation needs or limit the amount of water downstream. In most cases, a barrage dam is built near the mouth of the river. The site of dam construction needs to be thoroughly investigated to ensure that the foundation is strong enough to support the dam and has low possibility of failing. When dams are created, they are given a safety rating depending on the type of dam, location, and the possible effects in case of failure. The ratings are from one to five, five having the highest danger rating. The rating of five would be given to dams built with a town or city downstream, which would have higher possibility of injury to people in the case of dam failure. New designs have been made that are able to sustain greater amounts of water. An improved wedge-shaped block technology was developed by Rafael Moran and Miguel Toledo. The new structure is able to withstand severe

flooding A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant concern in agriculture, civi ...

and uses less materials, reducing the production cost.

Environmental impacts

Dam construction has several effects on the

economy An economy is an area of the Production (economics), production, Distribution (economics), distribution and trade, as well as Consumption (economics), consumption of Goods (economics), goods and Service (economics), services. In general, it is ...

and the environment. Specifically, there are several ways in which the environment can be affected by dam construction. Species richness is usually measured to determine the effect of a dam on the

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

surrounding it. To observe the species richness, scientists collect data on the fish and animal populations before and after construction of the dam. With that data, they are able to see how the population size increased or decreased. In some cases, it was found that the species richness was less downstream from a dam compared to further upstream. Inhibiting the volume of water was shown to be detrimental to species diversity and richness. Also, at the entrance of dams, there are fewer nutrients due to the high-water flow reducing the ecosystem's reproduction standard. Along with species richness, plankton diversity can be an indicator of the ecosystem's ability to handle the newly-built dam. It has been shown that dams can have an effect on the

migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...

of fish, leading to less reproduction. There are many small factors that can have a relatively large effect on the river ecosystems, such as species richness, water volume and nutrient levels. Different experiments have been done that looked into each of these individually and were able to determine why some dams cause such effects. While there is substantial evidence, including case studies, that points to dam construction having

environmental impact Environmental issues are disruptions in the usual function of ecosystems. Further, these issues can be caused by humans ( human impact on the environment) or they can be natural. These issues are considered serious when the ecosystem cannot reco ...

, there are also studies that show less damage than expected. Looking at plankton near some dams has shown that plankton is able to continue to live through changes to its habitat. Changes such as the pH levels near dams have been recorded, and plankton was minimally affected. Other species, however, such as trout, are affected more, due to the physical dam inhibiting their migration and reproduction paths. Barrage dams control the amount of water going through them, leading to differences in the amount of water upstream and downstream from the dam. This discrepancy has different effects on different species native to the area. While there can be reduced flow downstream, there can also be problems upstream. Dams can have buildup of pressure that fish are not accustomed to, and they migrate further upstream, causing part of the river to have reduced population sizes. Although there are environmental effects that come with building new dams, there are also economic benefits from a dam. Without dams, it would be much harder to farm and grow livestock. The irrigation technology that comes with building a dam can exceed the risk factor.

Terminology

According to the

World Commission on Dams The World Commission on Dams (WCD) existed between April 1997 and 2001, to research the environmental, social and economic impacts of the development of large dam, dams globally. The self-styled WCD consisted of members of civil society, academia ...

, a key difference between a dam and a barrage is that a dam is built for water storage in a

reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

, which raises the level of water significantly. A barrage is built for diverting water, and raises the water level by only a few feet. The latter is generally built on flat terrain across wide, often

meander A meander is one of a series of regular sinuous curves in the Channel (geography), channel of a river or other watercourse. It is produced as a watercourse erosion, erodes the sediments of an outer, concave bank (cut bank, cut bank or river cl ...

ing 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.Raye R. Platt, Mohammed Bahy Hefny,
Egypt: A Compendium
, p.198,

American Geographical Society The American Geographical Society (AGS) is an organization of professional geographers, founded in 1851 in New York City. Most fellows of the society are United States, Americans, but among them have always been a significant number of fellows f ...

, 1958. Barrages are usually larger than the

headworks Headworks is a civil engineering term for any structure at the head or diversion point of a waterway. It is smaller than a barrage and is used to divert water from a river into a canal or from a large canal into a smaller canal. at Web archive An ...

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 Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods. Although not yet widely used, tidal energy has the potential for future electricity generation. T ...

from tidal flows are known as tidal barrages.

Etymology

The English usage of the term ''barrage'' originates from the Delta Barrage across the

Nile The Nile (also known as the Nile River or River Nile) is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa. It has historically been considered the List of river sy ...

branches north of Cairo, built between 1833 and 1862 by the French Linant de Bellefonds and Eugène Mougel employed by the Egyptian Public Works Department, with assistance from Barthélemy Prosper Enfantin and with the blessing of the Egyptian Viceroy of the

Ottoman Empire The Ottoman Empire (), also called the Turkish Empire, was an empire, imperial realm that controlled much of Southeast Europe, West Asia, and North Africa from the 14th to early 20th centuries; it also controlled parts of southeastern Centr ...

Muhammad Ali Muhammad Ali (; born Cassius Marcellus Clay Jr.; January 17, 1942 – June 3, 2016) was an American professional boxer and social activist. A global cultural icon, widely known by the nickname "The Greatest", he is often regarded as the gr ...

. 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 provinces of India, earlier presidencies of British India and still earlier, presidency towns, were the administrative divisions of British governance in South Asia. Collectively, they have been called British India. In one form or another ...

, the term ''barrages'' made its way to present-day India and Pakistan, as well as to the Middle East and thus generally into English.

References

External links