RECTANGULAR WEIR

Rectangular Weir – Flow Calculation

This section estimates the flow rate over a rectangular weir based on the geometry of the weir and the height of liquid flowing over it. Rectangular weirs are commonly used for open-channel flow measurement in hydraulic and environmental applications.

Inputs Used
  • Flow over weir (Fv) (ft3/s) – Calculated volumetric flow rate
  • Width of weir (L) (ft) – Effective horizontal length of the weir crest
  • Height of liquid over weir (H) (ft) – Head of liquid above the weir crest
How the Flow Is Calculated
  1. Establish liquid head: The height of liquid above the weir crest (H) represents the driving energy for the flow.
  2. Apply rectangular weir relationship: The flow rate is calculated using the standard rectangular weir equation, where flow is proportional to the weir width and the head raised to the 3/2 power.
  3. Compute flow rate: The result is expressed as volumetric flow in ft3/s.
Outputs
  • Flow over weir (Fv) is reported in ft3/s.
Interpretation
  • Higher liquid head (H) significantly increases the flow rate.
  • Wider weirs (L) allow more flow for the same head.
  • Rectangular weirs are most accurate when the flow is free-flowing and not submerged downstream.

Use this tool to estimate open-channel flow rates and evaluate weir dimensions for flow measurement applications.

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Height (H)
Length (L)

Flow over weir (Fv)
{{Flow_over_weir:Integer}} ft3/s