Modeling of Breaching Due to Overtopping Flow and Waves Based on Coupled Flow and Sediment Transport

Abstract

Breaching of earthen or sandy dams/dunes by overtopping flow and waves is a complicated process with strong, unsteady flow, high sediment transport, and rapid bed changes in which the interactions between flow and morphology should not be ignored. This study presents a depth-averaged two-dimensional (2D) coupled flow and sediment transport model to investigate the flow and breaching processes with and without waves. Bed change and variable flow density are included in the flow continuity and momentum equations to consider the impacts of sediment transport. The model adopts the non-equilibrium approach for total-load sediment transport and specifies different repose angles to handle non-cohesive embankment slope avalanching. The equations are solved using an explicit finite volume method on a rectangular grid with the improved Godunov-type central upwind scheme and the nonnegative reconstruction of the water depth method to handle mixed-regime flows near the breach. The model has been tested against two sets of experimental data which show that it well simulates the flow characteristics, bed changes, and sediment transport. It is then applied to analyze flow and morphologic changes by overtopping flow with and without waves. The simulated bed change and breach cross-section shape show a significant difference if waves are considered. Erosion by flow without waves mainly occurs at the breach and is dominated by vertical erosion at the initial stage followed by the lateral erosion. With waves, the flow OPEN ACCESSWater 2015, 7 4284 overtops the entire length of the dune to cause faster erosion along the entire length. Erosion mainly takes place at the upper layer at the initial stage and gradually accelerates as the height of the dune reduces and flow discharge increases, which indicates the simulated results with waves shall be further verified by physical experimental evidence.

Calculated Potential Bedload Versus Real Transported Sands along the Guadiana River Estuary (Spain–Portugal)

“…In recent years, some of these equations have been used for calculations in spatial grids by means of mathematical models of transportation [19][20][21]. These models can couple together different modules, thereby generating 2D and 3D patterns of flow circulation and sediment transport [22].…”

A Non-Equilibrium Sediment Transport Model for Dam Break Flow over Moveable Bed Based on Non-Uniform Rectangular Mesh

“…Based on the projection step, the Godunov-type schemes generally fall into two categories: upwind schemes (Riemann solver schemes) [9,12,14,[17][18][19][20]27] and central schemes [6,[28][29][30]. Central schemes do not require any Riemann problem solvers and characteristic decomposition, which is a powerful black-box solver for the hyperbolic partial differential equations (PDEs).…”

“…Liu et al [15] further shows that the central-upwind scheme is less expensive than other popular Riemann solvers while still capable of tracking wet/dry fronts accurately. The central-upwind schemes are widely used in numerical models to simulate dam break flow over fixed [6,30] and movable bed [15,21,29,32], and satisfactory simulation results are achieved. However, most of these existing models are based on uniform Cartesian grids or triangular mesh, and limited studies are dedicated to non-uniform rectangular or quadtree grids.…”

Role of Beach Morphology in Wave Overtopping Hazard Assessment

“…The morphological response of a beach to storm events has been shown to be mostly dependent on wave action [8,9], with other parameters including surge duration, pre-existing morphology and still water level also being capable of influencing storm-driven morphodynamics [10,11]. This research aims to determine the role of the initial beach profile and storm-driven changes in beach morphodynamics in controlling wave overtopping volume through a sea defence breach.…”