The most common types of weirs are the broad-crested weir, the sharp-crested weir, the circular-crested weir, and nowadays, the ogee crest weir. Advantages of the cylindrical weir shape include the stable overflow pattern, the ease to pass floating debris, the simplicity of design compared to ogee crest design, and the associated lower costs. In this study, the writers describe new experiments of circular weir overflows, with eight cylinder sizes, for several weir heights and for five types of inflow conditions: partially developed inflow, fully developed inflow, upstream ramp, upstream undular hydraulic jump, and upstream (breaking) hydraulic jump. Within the range of the experiments, the cylinder size, the weir height D/R and the presence of an upstream ramp had no effect on the discharge coefficient, flow depth at crest, and energy dissipation. But the inflow conditions had substantial effects on the discharge characteristics and flow properties at the crest. Practically, the results indicate that discharge measurements with circular weirs are significantly affected by the upstream flow conditions.
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Chanson et al. (1998) studied this question.
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