A weir, as defined in the USBR measurement manual, is simply an overflow structure built perpendicular to an open channel axis to measure the rate of flow of water. In other words, a weir is essentially a partial dam. It works by raising the water level upstream of the weir, and then forcing the water to spill over. The more water is flowing over the weir, the deeper the water will be upstream of the weir. So measuring flow rate (CFS) can be done by simply measuring the depth of the water upstream. The biggest difference between a weir and a flume is that a weir creates a pond upstream of the weir, while a flume requires much less upstream depth. This often prevents weirs from being used in flat canals or ditches, or canals with little head upstream.
Weirs are available in a variety of shapes and sizes, but the most common and most simple are the Rectangular, Cipolletti, and the V-Notch weirs. The style of weir required depends on your particular application.
We offer weirs made of fiberglass or steel. We can also design a weir for you that can be built of concrete on-site. To learn more about weirs and for assistance in selecting the correct type please contact us for a no-obligation consultation.