Characteristics of Flow over Rectangular Sharp-Crested Side Weirs

In this study, water flow over rectangular sharp-crested side weirs of various heights and widths was investigated. The distribution of the three-dimensional velocity over the crest and in the vicinity of the side weir was obtained using an acoustic Doppler velocity (ADV) meter. The structure of each component of velocity was examined separately. The velocity distributions showed that longitudinal velocity peaked near the beginning of the side weir, whereas velocity in the direction of spill flow was highest at the end of the weir. The observed values of vertical velocity showed that the direction of flow near the crest was upward, but at the highest depths, the flow direction was reversed and a downward flow was generated near the water surface. Analysis of the velocity profiles indicated that the local discharge increased along the crest of the weir; local discharge also increased as the relative width of the weir decreased. Since the angle of the spilling jet (phi) plays a large role in shaping the hydraulic characteristics of a side structure, variation in this angle was investigated, and an expression for estimating phi was developed. DOI: 10.1061/(ASCE)IR.1943-4774.0000433. (C) 2012 American Society of Civil Engineers.