Weir
A weir is a small dam built across a river either to reduce the speed of the river, or to provide a mill pond. Weirs are often fitted with sluice gates to regulate the flow, and on navigable rivers lock gates allow boats to pass.
Weirs are often used in small to medium sized streams and rivers to aid flow and water level measurement by hydrologists. By providing a stable fixture on the river bed, the weir is used as a control that will ensure that the water level will be the same for any given flow.
There are different types of weir, they may be a simple metal plate with a V notch cut into it or it may be a concrete and steel structure across the bed of a river.
While a weir will typically increase the oxygen content of the water as it passes over the crest, a weir can have a detrimental effect on the local ecology of a river system. A weir will artificially reduce the up-stream water velocity which can lead to an increase in siltation. The weir may pose a barrier to migrating fish.
Mill ponds provide a water mill with the power it requires, using the difference in water level above and below the weir to provide the necessary energy.
Weirs often double as convenient pedestrian crossing points for the river.
Weirs are also fences made of nets in rivers or along sea coasts used for catching fish.
Referenced By
Canal lock
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