Calculate water flow rate (discharge) over a broad-crested weir.
Input Parameters
m
m
Calculation Results
Enter dimensions to calculate flow
Quick Reference
bWidth of weir crest
HHead relative to crest
CdDischarge coefficient
g9.81 m/s²
Overview
A broad-crested weir is a flat-crested structure with a length (in direction of flow) large enough to maintain a hydrostatic pressure distribution over some distance. It is used to measure flow in open channels.
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Pro Tips
The hydraulic head (H) is the height of water upstream above the weir crest.
The discharge coefficient (Cd) typically ranges from 0.5 to 0.62, with 0.385 being a common theoretical base for some formulas.
Ensure the crest is wide enough compared to the head for the 'broad-crested' assumption to hold (L > 2H).
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Fun Facts
"Broad-crested weirs are less sensitive to upstream turbulence than sharp-crested weirs."
"They are often used in irrigation systems and dam spillways."
"The flow over the weir is typically critical flow, which allows for a simple relationship between head and discharge."
