 Broad Crested Weir refers to the flow measurement and regulation of water depth in rivers, canals and other natural open channels. Broad Crested Weirs are a robust structure used to measure the full width of the channel. A broad crested weir is normally a flat topped object which obstructs and extends across the entire channel.

m
m
m
m3/s

Formula

q = Cd × b × h2 × (2g (h1 - h2)) 1/2

Where,
q = Water Flow Rate
Cd = Discharge Constant
b = Width of the Weir
g = Gravity (9.81 m/s2)

An overflow structure on which the nappe is supported for an appreciable length in the direction of flow is called as broad crested weir. It is a flat-crested structure, with a long crest compared to the flow thickness of water in canals and rivers.

Example:
Calculate the Broad Crested Weir for the given details.
Width of the Weir (b) = 5 m
Head 1 on the Weir (h1) = 3 m
Head 2 on the Weir (h2) = 1 m
Discharge Constant (Cd) = 10

Solution:
Apply Formula:
q = Cd × b × h2 × (2g (h1 - h2)) 1/2
Water Flow Rate (q) = 313.20919526731655 m3/s