Broad Crested Weir Calculation

Calculate the Water Flow Rate in broad crested weir for given values:

Width of the Weir (b) m
Head 1 on the Weir (h1) m
Head 2 on the Weir (h2) m
Discharge Constant (Cd)



Water Flow Rate (q) m³/s

The calculator will calculate the water flow rate of a channel's full width using broad crested weir method for given values of discharge constant, width of the weir and both head (1, 2) on the Weir.


q = Cd × b × h2 × (2g (h1 - h2) )1/2


q = Water Flow Rate,

Cd = Discharge Constant,

b = Width of the Weir,

g = Gravity (9.81 m/s²),

h1, h2 = Head 1 and Head 2 on the Weir

Use of broad crested weir

The broad crested weir is a hydraulic structures widely used for depth control and flow measurement in field and laboratory canals. The geometry described as a flat-crested structure with a length (L) of crest large enough compared to the flow thickness over the crest of the weir.

Difference between broad crested weir and sharp crested weir

The sharp crested weir helps in measuring the discharge of the water from small rivers and canals and the weir is placed in the direction of the flow of water. The broad crested weir is one which the water flow discharge in measured from large water bodies like big canals and rivers.

Difference between weirs and Dams

Dams are big wall constructed across a valley to control the flow or raise the level of water held within a catchment area, whare as weirs are steel or concrete barrier constructed across a river or creek that regulates water flow and allows water to be released slowly.