Laboratory Study on 3D Flow Structures Induced by Zero-Height Side Weir and Implications for 1D Modeling

Side weir flows induce complex three-dimensional (3D) structures on the flow field in the main channel. Extensive experiments at the laboratory scale were conducted in order to investigate the flow field for the particular case of a side weir with a zero height crest in both fixed bed and steady flow conditions. Detailed measurements of the flow surface, discharge, and velocity field were performed in the main channel upstream, alongside, and downstream of the side weir location. They allowed detection and analysis of the three-dimensional flow structures. Elaborations of the measurements show the implications of such three-dimensional nature of the flow on integral quantities such as Coriolis and Boussinesq coefficients as well as the specific energy and discharge coefficient that are important in the widely used one-dimensional (1D) models. Moreover, the results may help to better understand other free-surface problems similar to the side weir flow, such as lateral diversions, river bifurcations, and levee breaches.