Open Channel Flow Measurement Principle

The common method of measuring flow through an open channel is to measure the height or HEAD of the liquid as it passes over an obstruction (a flume or weir) in the channel.

Using ultrasonic level technology, Open channel flow meters include a non-contacting sensor mounted above the flume or weir.

By measuring the time from transmission of an ultrasonic pulse to receipt of an echo, the water level or “Head” is accurately measured.

Open Channel Flow Measurement

Open Channel Flow Measurement Animation

Animation Credits: greyline

Flumes and weirs are specially designed channel shapes that characterize the flow of water.

Common types are

  • Rectangular Weirs,
  • V-Notch Weirs,
  • Parshall flumes and
  • Palmer Bowlus flumes.

The choice of flume or weir type depends on the application: flow rate, channel shape, and solids content of the water.

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3 thoughts on “Open Channel Flow Measurement Principle”

    • Normally in power plant, this type of arrangement is installed. River/reservoir water coming to plant is measured.

      Flow measurement through parshall flume depends on flume geometry (e.g converging, diverging and throat section : height, slop and length)

      Q = C*H^n

      Q is flow rate
      C is the free-flow coefficient
      H is the head at throat section
      n varies with flume size

  1. Good day! We are working on a project study that will prove Bernoulli’s Principle. Do we need to place two ultrasonic level sensors before and after it passes the weir? Where is the right place of the sensor for the second weir?


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