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Various Hydraulic structures are constructed across the river to function as a retention for upstream water, used for different purposes. In general, dams, weirs, and barrages function to help generate electricity, used in irrigation, and for common human needs, especially during times of flood or overflowing water. There is some confusion around the difference between weirs and barrages, more particularly how they fit in the spectrum of dams category as a whole. Effectively, both weirs and barrages are what’s called headworks that are used to increase the head of water on the upstream side.
In this article, you will learn the differences between a weir and barrage.
A weir is simply a concrete or masonry structure that is built through an open channel, for instance, a river. In most cases, it is built to control water flow, measure the discharge, prevent flooding and make rivers navigable. It can be built with different materials such as wood, concrete or a mixture of rocks, gravel, and boulders depending on age and purpose.
On the other hand, a barrage is a concrete structure that consists of a series of large gates that can be opened or closed to control the amount of water that flows through them. This allows the structure to adjust and stabilize the elevation of the upstream water for irrigation and other systems. The valves are positioned between the pillars that have the task of supporting the water load of the pool created.
A weir is an impermeable barrier that is built across a river to raise the water level on the upstream side. Here, the water level is at the required height and excess water then can flow over the weir.
It is usually built on the other side of a flooded river.
On the other hand, a barrage involves adjustable gates installed over a dam to maintain the water surface at different levels and at different times. The water level is adjusted by opening the valves or gates. These gates are supported by pillars at both ends and are also positioned at different levels. They are usually operated by cables from the cabin.
Both weirs and barrages are obstacles to the watercourse, but the barrage is an expensive structure, while the weir is a relatively cheap structure.
Barrages are built near cities so that the amount of water flowing in the river can be controlled by opening and closing the gates to save the city from flooding. A weir, in contrast, is built, for example, in tourist destinations and preservation areas to allow the fish to swim upstream.
They’re both used to control floods.
Both help to make a river navigable.
Both measure discharge.
Kentchurch Weir was located on the River Monnow in the Kentchurch estate near Hereford, where the river marks the border between England and Wales (counties of Herefordshire and Monmouthshire respectively).
In 2008, EA Wales, supported by Atkins, built a fishing route at Osbaston Weir, also located on the River Monnow, about 3 km upstream of the confluence with the River Wye. This project has restored the connectivity of habitats in the lower watershed of the River Monnow after centuries of fragmentation.
In the upper part of Monnow, there is excellent fluvial habitat, however, the potential of this habitat has not been fully exploited, as it is inaccessible due to the two-meter height threshold. The removal of the weir was preferable to the creation of an on-site fishing route and restore the full connectivity of the habitat, with a significant improvement in biodiversity and allowing for the transport and uninterrupted supply of river gravel downstream. A weir is a barrier built across a river that changes the flow of the river. Depending on the design, some pose a problem for fish since the fish cannot get across the weir.
Routine surveys of fish prior to sampling have confirmed the absence of upstream salmons. Three years earlier, before the removal, it was a natural passage of fish around the other spillway on the mainstream. The migratory salmon was observed to jump to the spillway at Kentchurch, although they were unable to cross.
The effect of the weir was studied before removal, and it showed a significant change in river morphology with reduced erosion.
The ecological status of the Monnow River was well equipped for fish migration.
Sukkur Barrage is a barrage on the Indus River near the town of Sukkur, in the Pakistani province of Sindh. The barrage was constructed during the British Raj from 1923 to 1932 and was called Lloyd Dam. The Sukkur barrage is in fact, the pride of Pakistan’s irrigation system since it is the largest irrigation system of its kind in the world. It irrigates Sukkur district in the north, and Mirpurkhas districts in the south. It is located about 300 miles northeast of Karachi and 3 miles below Sukkur Gorge. The introduction of an irrigation system controlled by a dam has made it possible to supply the existing cultivated areas in the Pakistani province of Sindh more quickly.
The idea of the Sukkur Dam was conceived by Mr. C.A. Fife in 1868. However, the project was finally approved in 1923. It was built under the general direction of Sir Charlton Harrison, CIE, as chief engineer, while Sir Arnold Musto, as the architect and project engineer. Work on the head and canals was completed in 1932. Once completed, it was opened by His Excellency the 1st Count of Willingdon, Viceroy of India.
Sindh survives almost entirely on water from the Indus. This is because groundwater is very limited. Rainfall in the province averages between 150 to 200 mm per year, while the evaporation rate is between 1,000 and 2,000 mm. Thus, Sindh is arid and it is the only barrage that irrigates other barren lands.
The Sukkur Dam is used to control the flow of water into the Indus for irrigation and flood control. It is the backbone of the economy as it allows water to flow through what was originally a network of seven channels that fed the world’s largest irrigation system. The second-largest channel is the Rohri channel which, although slightly shorter than the Nara channel, still absorbs a much larger flow than the first. Its arable area amounts to 2.6 million hectares for irrigation. Cotton, wheat, and sugar cane are the main crops of this system of canals.
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