Flow discharge computation over compound sharp-crested side weirs

Side weirs are generally rectangular sharp-crested in form, but for accurate flow measurement and management in a wide range of flow discharges, compound side weirs perform better. Such a commonly used one is rectangular compound side weir, which has a small rectangular weir in lower section for measuring low flow discharges, and a wide rectangular section alongside for measuring higher flows. Determination of discharge coefficient for such a compound side weir is difficult and needs to be calibrated using a large set of laboratory tests. In this paper, based on the practical design method of May et al., a new approach was proposed for predicting flow discharge over compound side weirs. This new approach has been evaluated against experimental data in subcritical flow conditions, and has shown very good agreement with the experimental data, with the mean overall and absolute relative errors being 1.6 and 7.8%, respectively. Because the proposed method is independent of discharge coefficient for overflow rate computation, it will provide a reliable and convenient tool for flow measurement of compound side weirs and their water surface profiles.