Sharp Crested Weirs
In the field of hydraulics, sharp crested weirs are thin solid barriers that allow water to flow above their crests, and through openings, which may have different shapes. Common shapes of weirs are rectangular, triangular and trapezoidal.
A V-notch weir measuring the overflow from the Blaydon Hazard Shaft, an abandoned coal mine near Newcastle upon Tyne, UK. (Photo by Younger & Wolkersdorfer, 2004)
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Weir ApplicationsThe basic function of a weir is to control the relation between the level of the backed up water upstream (i.e. head of water above the crest) and the discharge over the weir. This relation is known as the head-discharge equation, and is the most important property of a weir.
Depending on the shape of the head-discharge equation, a weir can be useful in many applications. The most common applications of weirs are: flood control, water level control, water quality control, discharge measurement and surface skimming. Below are head-discharge equations of polynomial weirs, which are different than those of simple weirs. They can be applied for flood control and water quality applications.
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Leonardo da Vinci circa 1500 proposed a set of weirs, seen in his drawing below, which can be suddenly opened. Da Vinci’s idea was to create a water surge downstream, as a weapon to submerge advancing enemies down the valley. In doing so, Da Vinci appears to be the first to describe what is now known as the dam-break problem.