DAM-BREAK FLOW IN A CHANNEL WITH A 90° BEND AND MOBILE BED: EXPERIMENTAL AND NUMERICAL SIMULATIONS

Predicting the morphological changes induced by fast transient flows such as flash floods or dam-break flows is still a challenging task, especially when sediment transport is considered. In order to validate numerical simulation tools designed for such flow conditions, reliable experimental data is needed. In this paper, dam-break flow experiments over a mobile bed made of coarse uniform sediments are presented. The initial conditions consist of a constant water-depth in the upstream reservoir and a saturated sediment bed downstream. Due to the strong reflection of the flow in the bend, complex morphological patterns can be observed, with significant erosion and deposition. Measurements were obtained using non-intrusive devices to capture the free-surface evolution as well as the bed morphological evolution. The free-surface evolution was measured using ultrasonic probes at several locations. The bed morphological evolution was measured using digital imaging devices and a laser-sheet to isolate given cross-sections of the flow on the images. Such a technique proved its efficiency in slower flow conditions, but its application to the present case with a fast flow involving significant sediment transport is challenging. These measurements are then compared to numerical simulations performed using a finite-volume scheme with a lateralized HLLC scheme for the flux predictions. This scheme solves in a coupled way the system composed by the shallow-water equations and the Exner equation for the bed morphology, closed by the Meyer-Peter and Müller formula for sediment transport. Finally, a discussion of the numerical results is proposed, through the comparisons with the experimental data