Hydraulic Performance of an Embankment Weir with Rough Crest

Abstract

An experimental study was conducted on a large embankment weir with smooth and rough crests for a range of flow conditions 0.011≤Q≤0.226 m3/s. Close agreement between the rough and smooth crest experiments was observed in terms of flow patterns, free-surface profiles, and pressure distributions. The crest roughness had effects on the velocity distributions, the boundary layer properties, and the shear stress. On the rough crest, the velocity distributions were shifted upwards, increasing the growth rate of the boundary layer. The calculation of the shear stresses with the law of the wall, outer flow region, and momentum integral methods showed consistent results of about τ/(ρ g H)≈0.0015–0.0018 for the smooth crest and of τ/(ρ g H)≈0.0024 for the rough crest. The crest roughness reduced the discharge performance, while upstream and downstream ramps did not have any effects. The present observations highlighted the relevance of roughness and scaling on the hydraulic performances of weirs.