Unsteady Stage-Discharge Relationships for Sharp-Crested Weirs

Abstract

Currently, discharges passing measurement devices and structures in unsteady flow conditions are determined based on relationships developed for steady flow condition due to lack of sufficient data. In this study, the operation of triangular and rectangular sharp-crested weirs in unsteady flow conditions was experimentally investigated. The compiled data indicated the presence of looped rating curves, but with transposition of the rising and falling limbs compared to that commonly observed in stream gauge ratings. The presence of such looped rating curves was justified, and the validity of the steady rating curve relationships, which are presently being applied to unsteady flow conditions, was questioned. Accordingly, relationships for evaluating unsteady discharge passing different rectangular and triangular sharp-crested weirs were presented. The proposed formulas considerably improve the discharge measurements accuracy in unsteady flow conditions and could be incorporated in hydrodynamic models.