Sediment transport via dam-break flows over sloping erodible beds

Abstract

When a semi-infinite body of homogeneous fluid initially at rest behind a vertical retaining wall is suddenly released by the removal of the barrier, the resulting flow over a horizontal or sloping bed is referred to as a dam-break flow. When bed resistance is neglected the exact solution, in the case of a stable horizontal bed, may be obtained on the basis of shallow-water theory via the method of characteristics and the results are well known. Discrepancies between these shallow-water based solutions and experiments have been partially accounted for by the introduction of flow resistance in the form of basal friction. This added friction significantly modifies the wave speed and flow profile near the head of the wave so that the simple exact solutions no longer apply. Various asymptotic or numerical approaches must be implemented to solve these frictionally modified depth-averaged shallow-water equations. When the bed is no longer stable so that solid particles may be exchanged between the bed and the fluid, the dynamics of the flow become highly complex as the buoyancy forces vary in space and time according to the competing rates of erosion and deposition. It is our intention here to study dam-break flows over erodible sloping beds as agents of sediment transport, taking into account basal friction as well as the effects of particle concentrations on flow dynamics including both erosion and deposition. We shall consider shallow flows over initially dry beds and investigate the effects of changes in the depositional and erosional models employed, in the nature of the drag acting on the flow, and in the slope of the bed. These models include effects hitherto neglected in previous studies and offer insights into the transport of sediment in the worst case scenario of the complete and instantaneous collapse of a dam.

Two‐dimensional two‐layer shallow water model for dam break flows with significant bed load transport

“…He investigated the influence of the lock gate raise, the bed roughness and the suspended sediment concentration. Emmett and Moodie [46] accounted for the suspension load defining mass deposition and erosion rates that depend on the particle volume fraction. Capart and Young [13] chose lightweight artificial pearls of uniform size as granular bed material in a horizontal flume.…”

“…These models are closed with formulas for the energy slope and for the bed load transport (see [45] for a comparison of these formulas). Emmett and Moodie [46] accounted for the suspension load defining mass deposition and erosion rates that depend on the particle volume fraction. In addition, a failure operator could be included into these shallow water models to predict bank morphological evolution [47].…”