Dam-break flow on mobile bed in a channel with a sudden enlargement

This paper presents a dam-break flow experiment on mobile bed, made of uniform coarse sand, carried out in a channel with a sudden enlargement. Due to this enlargement, the resulting flow was typically two-dimensional. Important scouring was observed at the corner of the sudden enlargement, while deposition of sand occurred close to the sidewalls of the enlarged channel. Measurements of the flow were obtained using ultrasonic sensors and digital-imaging techniques that have all the advantage to be non-intrusive. Available experimental data consist of water level evolution in time at a given number of gauging points and topographical survey of final bed eleva-tion at a given number of cross-sections. The experimental data are compared to two finite-volume numerical models: (1) a one-dimensional model developed for cross-sections of arbitrary shape, and (2) a two-dimensional model aimed at simulating fast transient flows over movable beds. In both models, the flow is described by the Saint-Venant equations for the water continuity and momen-tum, and by the Exner equation for the sediment continuity. Both models satisfactorily simulate the water levels, while bed levels are captured only by the 2D model, though with some underestima-tion of erosion / deposition phenomena.