ENGINEERING – HYDRAULIC & OPEN CHANNEL FLOW CALCULATOR
Side Weir Discharge
A precise tool.
What is the Side Weir Discharge & How does it work?
A side weir is a vertical plate installed on the side of an open channel to measure flow. Water rises above the plate and creates a hydraulic head, H, which drives the discharge through the weir opening. The geometry of the weir and the flow conditions determine the relationship between the measured head and the actual flow rate. The De Marchi coefficient, Cd, is an empirical factor that accounts for the contraction of the flow stream and energy losses at the weir edge. It varies with the shape of the weir and the Reynolds number of the flow, but for a sharp‑edged side weir a typical value lies between 0.55 and 0.65. Combining the head‑discharge relationship with the De Marchi coefficient yields the classic side‑weir formula. By measuring the head, H, and knowing the effective length of the weir, L, the discharge, Q, can be calculated directly.
Q = C_{d},L,H^{3/2}
Q = discharge (m³/s)
C_{d} = De Marchi coefficient
L = length of weir (m)
H = head over weir (m)
C_{d} = De Marchi coefficient
L = length of weir (m)
H = head over weir (m)
Parameters
Result
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Frequently Asked Questions
What is a side weir in open channel flow?
A side weir is a vertical plate installed on the side of an open channel to measure flow by creating a hydraulic head.
How does the De Marchi coefficient affect discharge calculation?
The De Marchi coefficient accounts for flow contraction and energy losses at the weir edge, affecting the accuracy of the discharge calculation.
What is the formula used in this side weir discharge calculator?
The formula typically uses head (H) over the weir and the De Marchi coefficient (Cd) to calculate the discharge.
Can I use this calculator for any type of weir?
This calculator is specifically designed for side weirs; other types may require different formulas or coefficients.
What units should I use for head and discharge in this calculation?
Head is usually measured in meters (m) or feet (ft), and discharge in cubic meters per second (m³/s) or cubic feet per second (ft³/s).
How do I determine the De Marchi coefficient for my specific weir?
The De Marchi coefficient varies with weir shape and flow conditions; it's often provided in engineering tables or can be estimated based on similar weirs.
What is the purpose of using a side weir in hydraulic engineering?
A side weir is used to measure the flow rate in open channels, helping engineers design and manage water systems effectively.
Results are for informational purposes only and do not constitute professional advice.