Calculate flow in channels, weirs and pipes

The flow in an open channel or a part-full pipe is calculated from the water level: in a calibrated structure (Parshall flume, Venturi or Khafagi flume, V-notch, rectangular or Cipolletti weir), with the Manning formula (rectangular or trapezoidal channel and part-full pipe) or, if velocity is also measured, by area-velocity. Enter the measured level and the dimensions of your installation to get the flow in m³/h.

Flow (Parshall flume)

Level (m)Zero level (m)Throat (1, 2, 3, 6, 9, 12, 18, 24 or 36 inches) (in)

CALCULATE

Flow (Venturi / Khafagi flume)

Level (m)Zero level (m)Throat width (m)Coefficient

CALCULATE

Flow (V-notch weir)

Level (m)Notch level (m)Angle (°)Discharge coefficient

CALCULATE

Flow (rectangular weir)

Level (m)Crest level (m)Width (m)With end contractions (1 = yes, 0 = no)

CALCULATE

Flow (Cipolletti weir)

Level (m)Crest level (m)Crest width (m)

CALCULATE

Flow (Manning, open channel)

Level (m)Bottom level (m)Bottom width (m)Side slope (horizontal per 1 vertical; 0 = rectangular)Slope (m/m)Manning roughness

CALCULATE

Flow (Manning, pipe)

Level (m)Inside diameter (m)Slope (m/m)Manning roughness

CALCULATE

Flow (area-velocity)

Level (m)Water velocity (m/s)Inside diameter (m)

CALCULATE

Indicative result. For a diagnosis of your installation, measure continuously or contact us.

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How it is calculated

• Flow (Parshall flume): Q = K · h^n, with K and n from the flume table for the throat width (ISO 9826).
• Flow (Venturi / Khafagi flume): Q = k · b · h^1.5 (rectangular throat flume, ISO 4359).
• Flow (V-notch weir): Q = 8/15 · Cd · √(2g) · tan(θ/2) · h^2.5 (ISO 1438).
• Flow (rectangular weir): Francis: Q = 1.838 · (b − 0.2·h) · h^1.5 (without end contractions, b instead of b − 0.2·h).
• Flow (Cipolletti weir): Q = 1.859 · b · h^1.5 (trapezoid with 1:4 side slopes).
• Flow (Manning, open channel): Q = (1/n) · A · R^(2/3) · √S, with A = (b + z·h)·h and R = A / (b + 2·h·√(1+z²)) of the rectangular (z = 0) or trapezoidal channel at that level.
• Flow (Manning, pipe): Q = (1/n) · A · R^(2/3) · √S, with A and R of the part-full pipe at that level.
• Flow (area-velocity): Q = v · A, with A = wetted area of the pipe at the measured level.

Measure these data continuously

With our IoT probes, sensors and equipment you have the data in real time on any device, and the panel calculates this value on its own and warns you before problems appear.

• Modbus Transmitter (BQC-TRANSMITTER)
• Sonda de nivel y velocidad 4-20 mA (BQS-LEVEL420)
• Ultrasonic flowmeter with probe for flow measurement and water sheet, with 7 meters of cable (BQD-US-Caudal)

Applications whose panel (dashboard) calculates it continuously: Prevention of blockages and overflows in manholes (panel · ROI)

See the panel model · Applications · Langelier index

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