Hydraulics of Embankment Weirs

Abstract

Embankment weirs, often found in engineering applications with a side slope 1V:2H, are considered in this paper. For free overflow, the discharge coefficient is determined in terms of relative crest length for long broad-crested, broad-crested, short-crested, and thin-crested weirs. A considerable increase of capacity is noted when compared to broad-crested weirs with vertical faces. For submerged overflow, four regimes are identified: (1) A-jump; (2) plunging jet; (3) surface wave; and (4) surface jet. Particular attention is focused on plunging jets and surface waves. The flow regimes are discussed in terms of submergence, crest length, and modular limit. A description is given of the forward and backward (recirculation) zones with indications of typical lengths. Also, the entire velocity field is described, including the maximum forward and backward velocities, and the velocity distribution in arbitrary sections of the tailwater region. It is found that plunging jets and surface jets are hydraulically similar, and that the profile of one regime can be transformed into the other profile by inversion about the median. All results are generalized and can be directly applied.