Use a V Notch Weir to Measure Open Channel Flow Rate

The v notch weir is widely used to measure open channel flow rate. It is especially good for measuring a low flow rate, because the area of flow through the v notch becomes quite small while the head over the v notch is still a measurable value. When a v notch weir is used to meter flow, the weir equation Q = 2.49 H^2.48 can be used to calculate Q, the flow rate over the weir (and through the channel), as a function of the head of water over the crest of the v notch, H. In order to use this equation, the v notch angle must be 90 degrees and the water flow over the weir must be fully contracted. If the v notch angle isn't 90 degrees, then a somewhat more complicated v notch weir equation is available to use.