WEIRS
V-Notch
A V-notch weir measures water flow rates in open channels. It consists of a vertical plate or wall across the channel with a V-shaped notch or opening.
Calculating the flow rate involves determining the water height flowing over the notch. People commonly use V-notch weirs for small-scale water flow measurement, such as in laboratories or field research.
These weirs accurately measure low flow rates and people can construct them using stainless steel, plastic, or fiberglass materials. The V-notch angle typically remains at 90 degrees, although specific applications may require other angles.
Rectangular
Rectangular weirs serve as structures for measuring water flow rates in open channels. They comprise a rectangular notch or opening installed across the channel, allowing for the calculation of the flow rate based on the water’s height over the weir crest.
People determine the discharge coefficient experimentally, taking into account the weir’s shape, size, water velocity, and depth. Water treatment plants, irrigation systems, and environmental monitoring stations commonly employ rectangular weirs. Although suitable for measuring both low and high flow rates, they may not be appropriate for high sediment concentrations or high velocities.
To ensure accurate flow rate measurements, it is essential to properly calibrate and regularly maintain the weirs. This involves determining the discharge coefficient and ensuring the weir opening remains clean and free from debris.
Broad-crested Weir
A broad-crested weir measures water flow rates in open channels. People install it across the channel and it consists of a rectangular weir with a crest width relatively wider than the depth of the water flowing over it.
Broad-crested weirs, unlike rectangular weirs, are used for subcritical flow in the channel. In this flow condition, the water velocity is less than the velocity of waves. People commonly use them in irrigation systems, water treatment plants, and environmental monitoring stations.
Compared to rectangular weirs, broad-crested weirs can handle a wider range of flow rates. They are suitable for use in channels with irregular shapes or non-uniform flow conditions, as long as people design the weir to fit the channel geometry.