Broad‐Crested Weir

Abstract

The flow features over the broad‐crested weir with vertical upstream wall and sharp‐crested corner are analyzed experimentally. Only the long‐crested weir is considered, for which the discharge coefficient remains practically constant. For a relative overflow depth between 10% and 40%, the surface profile, the bottom pressure profile, the boundary separation profile, and the velocity profiles close to the upper corner are self‐similar, provided effects of scale may be dropped. For extremely long‐crested weirs, undular flow occurs. The first wave profile is shown to be identical with the solitary wave profile. The main properties of the undular hydraulic jump are explored. The broad‐crested weir is characterized by insensitivity to tailwater submergence. The modular limit is found practically constant at 75% of the tailwater level, independent of the relative head on the weir. The discharge‐head relation for submerged flow is analyzed under a novel approach. Finally, recommendations are specified under which a broad‐crested weir may be used as a discharge measurement structure.