impact of surface roughness on discharge coefficient of crump weirs: an analytical investigation

Objective: this study examines the impact of surface roughness on the discharge coefficient (cd) of crump weirs through a comparative analysis of smooth-surface and rough-surface configurations. material and methods: the experimental investigation utilized laboratory-scale crump weir models with controlled surface roughness conditions. different roughness regimes were created by applying uniform coatings of sand and gravel particles with varying grain sizes (ks). results and discussion: the results demonstrated significant effects of roughness, particularly under low-head conditions. a maximum cd reduction of 12.8% was observed with minimal upstream head (h/p < 0.2) for high-roughness conditions. the influence of roughness exhibited progressive attenuation with increasing h/p ratios, and at h/p > 0.5, the effects of surface roughness became negligible. conclusions: these findings suggest that smoother weir surfaces are preferable for low-flow precision, whereas roughness effects can be disregarded in high-flow conditions. future research should investigate additional factors, such as slope variations and field-scale validation, to refine hydraulic modeling.