A CFD Description of the Breach Flow of an Overtopped Embankment Dam ^†

We investigate the flow over a breached dam through combined measurements and numerical simulations, revealing key topological features of the mean flow, including separation and stagnation surfaces, attached vortices, secondary currents, and boundary layer development. PIV measurements of velocities are complemented with simulations with the interFoam solver of OpenFOAM-v2106 (URANS with k-ω SST closure model and rough-wall corrections). We show the development of the boundary layer over the crest, influenced by the breach crest wall curvature and strong lateral flow convergence. Three-dimensional separation is observed in the plunging pool. Two different attached vortices develop along the bottom and side walls of the breach, where underscouring is known to be strong. The first is associated with an adverse pressure gradient while the second results from the flow curvature imposed by the evolving geometry of the plunging pool. A counter rotating vortex pair is observed in the flow exiting the dam breach channel. We discuss the significance of these structures for hydraulic erosion and underscouring. We also provide recommendations for CFD modeling of dam breaches.