Discharge Measurements in Open Channels using Compound Sharp-Crested Weirs

Compound sharp-crested weirs have been widely used for measuring discharges in open channels accurately with a reasonable sensitivity over a wide flow range. The flow characteristic over a compound sharp-crested weir is completely different to that over a single sharp-crested weir. The most common type of compound sharp-crested weir used in irrigation canals is the combination of a rectangular notch and a 'V notch with a small notch angle. However, the continuity of flow and precision of this type of compound weirs are reported to be poor in the transition region between two sections. As an improvement, a compound sharp-crested weir composed of two triangular parts with different notch angles has been designed and experimentally validated which proved to be accurate in measuring a wide range of discharges without any discontinuity. Several methods are also proposed to estimate the flow over the double 'V notch compound sharp-crested weir and one method is experimentally validated as most suitable.