A Simple Model of Sediment Transport in the Nearshore Zone (original) (raw)
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A numerical model of nearshore waves, currents, and sediment transport
Coastal Engineering, 2009
A two-dimensional numerical model of nearshore waves, currents, and sediment transport was developed. The multi-directional random wave transformation model formulated by Mase [Mase, H., 2001. Multi-directional random wave transformation model based on energy balance equation. Coastal Engineering Journal 43 (4) (2001) 317] based on an energy balance equation was employed with an improved description of the energy dissipation due to breaking. In order to describe surface roller effects on the momentum transport, an energy balance equation for the roller was included following Dally-Brown [Dally, W. R., Brown, C. A., 1995. A modeling investigation of the breaking wave roller with application to cross-shore currents. Journal of Geophysical Research 100(C12), 24873]. Nearshore currents and mean water elevation were modeled using the continuity equation together with the depth-averaged momentum equations. Sediment transport rates in the offshore and surf zone were computed using the sediment transport formulation proposed by Camenen-Larson
Coastal Engineering Journal,
This study investigates the coupling eld of grouped wind waves and their associated long waves in the surf and swash zones. Based on the calculated wave elds, the contributions of the wind waves and the long waves on the sediment transport eciency are discussed. Spatial variations of the incident grouped wind waves propagating over a plane slope are calculated based on time-dependent mild slope equation. Generation of the long waves is reproduced based on a time-varying breakpoint model proposed by Symonds et al. [1982]. In order to obtain the long wave solutions extending over the landward region from the still water shoreline, calculations using nonlinear shallow water equations are connected to the Symonds' model invoking a moving boundary treatment. The Shields parameters under composition of the grouped wind waves and the associated long waves are evaluated to assess the mobility of the bottom sediment. The results show that the long waves have greater sediment transport eciency over the grouped wind waves in the swash zone.
Ocean Dynamics, 2020
The mutual feedback between the swash zone and the surf zone is known to affect large-scale morphodynamic processes such as breaker bar migration on sandy beaches. To fully resolve this feedback in a process-based manner, the morphodynamics in the swash zone and due to swash-swash interactions must be explicitly solved, e.g., by means of a wave-resolving numerical model. Currently, few existing models are able to fully resolve the complex morphodynamics in the swash zone, and none is practically applicable for engineering purposes. This work aims at improving the numerical modelling of the intra-wave sediment transport on sandy beaches in an open-source wave-resolving hydro-morphodynamic framework (e.g., non-hydrostatic XBeach). A transport equation for the intra-wave suspended sediment concentration, including an erosion and a deposition rate, is newly implemented in the model. Two laboratory experiments involving isolated waves and wave trains are simulated to analyse the performa...
The effect of bottom sediment transport on wave set-up
In this paper we augment the wave-averaged mean field equations commonly used to describe wave setup and wave-induced mean currents in the near-shore zone, with an empirical sediment flux law depending only on the wave-induced mean current and mean total depth. This model allows the bottom to evolve slowly in time, and is used to examine how sediment transport affects wave setup in the surf zone. We show that the mean bottom depth in the surf zone evolves according to a simple wave equation, whose solution predicts that the mean bottom depth decreases and the beach is replenished. Further, we show that if the sediment flux law also allows for a diffusive dependence on the beach slope then the simple wave equation is replaced by a nonlinear diffusion equation which allows a steady-state solution, the equilibrium beach profile.
Modelling the rip current flow on a quadratic beach profile
Wave transformation in the surf zone is the dominant factor in the hydrodynamics of the nearshore circulation, and consequent sediment transport. A global description in terms of the spatial variation of such quantities such as wave action, wave action flux and wave radiation stress are the driving entities we have used to describe the generation by waves of mean currents in the nearshore zone. Studies on the interaction between waves and currents span nearly half a century. Mainly driven by a combination of engineering, shipping and coastal interests, there has been much research on shoaling nonlinear waves, on how currents affect waves and how waves can drive currents. This last aspect is the main concern in this paper.
Modelling the effect of bottom sediment transport on beach profiles and wave set-up
Ocean Modelling, 2012
In this paper we augment the wave-averaged mean field equations commonly used to describe wave setup and wave-induced mean currents in the near-shore zone, with an empirical sediment flux law depending only on the wave-induced mean current and mean total depth. This model allows the bottom to evolve slowly in time, and is used to examine how sediment transport affects the beach profile and wave setup in the surf zone. We show that the mean bottom depth in the surf zone evolves according to a simple wave equation, whose solution predicts that the mean bottom depth decreases and the beach is replenished. Further, we show that if the sediment flux law also allows for a diffusive dependence on the beach slope then the simple wave equation is replaced by a nonlinear diffusion equation which allows a steady-state solution, the equilibrium beach profile.
Nearshore sediment dynamics computation under the combined effects of waves and currents
Advances in Engineering Software, 2002
An integrated computational structure for non-cohesive sediment-transport and bed-level changes in near-shore regions has been developed. It is basically composed of: (1) three hydrodynamic sub-models; (2) a dynamic equation for the sediment transport (of the Bailardtype); and (3) an extended sediment balance equation. A shallow-water approximation, or Saint-Venant-type model, is utilized for the computation and up-to-date ®eld currents, initially and after each characteristic computational period. A Berkhoff-type wave model allows us to determine the wave characteristics in deep water and intermediate water conditions. These computations make it possible to de®ne a smaller modeling area for a non-linear wave±current model of the Boussinesq-type, including breaking waves, friction effects and improved dispersion wave characteristics. Bed topography is updated after each wave period, or a multiple of this, called computational sedimentary period. Applicability of the computational structure is con®rmed through laboratory experiments. Practical results of a real-world application obtained around the S. Lourenc Ëo forti®cation, Tagus estuary (Portugal), with the intention of preventing the destruction of the Bugio lighthouse, are shown. q
Sediment transport models in Generalized shear shallow water flow equations
HAL (Le Centre pour la Communication Scientifique Directe), 2022
The classical sediment transport models based on shallow water equations (SWE) describes the hydro-morphodynamic process without horizontal velocity shear along the vertical and considers that the fluid velocity is equal to sediment velocity. The classical shear shallow water (SSW) with friction and topography source terms assumes that the fluid density is uniform in all the space. Nevertheless, for the coastal flows with sediment transport we are interested in it seems essential to consider these shear effects, the phase lag effect and the nonhomogenous ness of fluid density. In this paper, we develop new sediment transport models incorporating the shear velocity along the vertical, the phase lag effect and the spatial variation of the fluid density. The starting point is the 2D equations for the evolution of mixing quantities and sediment volume rate. These equations describe the motion of fluid mixing in a domain bounded by a dynamical water surface and water bed. Contrary to the classical sediment transport models, the second-order vertical fluctuations of the horizontal velocity are considered. Considering the kinematic conditions on the moving surfaces, we apply an average along the depth on the three-dimensional equations to obtain simplified equations. The resulting model has a wider range of validity and integrates the morphodynamic processes proposed in the literature. The proposed mathematical derivation is in the context of recent developments with the additional presence of sediment and a dynamic bed.
New Practical Model for Sand Transport Induced by Non-Breaking Waves and Currents
Coastal Engineering Proceedings, 2011
Many existing practical sand transport formulae for the coastal marine environment are restricted to limited ranges of hydrodynamic and sediment conditions. This paper presents a new practical formula for net sand transport induced by non-breaking waves and currents, and currents alone. The formula is based on the semi-unsteady, half wave-cycle concept, with bed shear stress as the main forcing parameter. Unsteady phase-lag effects between velocities and concentrations are accounted for, which are especially important for rippled bed and fine sand sheet-flow conditions. Recently recognized effects on the net transport related to flow acceleration skewness and progressive surface waves are also included. The formula is calibrated against a large dataset of net transport rate measurements from oscillatory flow tunnels and a large wave flume covering a wide range of flow and sand conditions. Good agreement is obtained between observations and predictions, and its validity is shown for ...
Coastal Engineering Journal, 2016
In this paper, we propose a model for the simulation of the bed evolution dynamics in coastal regions characterized by articulated morphologies. An integral form of the fully nonlinear Boussinesq equations in contravariant formulation, in which Christoffel symbols are absent, is proposed in order to simulate hydrodynamic fields from deep water up to just seaward of the surf zones. Breaking wave propagation in the surf zone is simulated by integrating the nonlinear shallow water equations with a high-order shock-capturing scheme. The near-bed instantaneous flow velocity and the intra-wave hydrodynamic quantities are calculated by the momentum equation integrated over the turbulent boundary layer. The bed evolution dynamics is calculated starting from the contravariant formulation of the advection-diffusion equation for the suspended sediment concentration in which the advective sediment transport terms are formulated according to a quasi-three-dimensional approach, and taking into account the contribution given by the spatial variation of the bed load transport. The model is validated against several tests by comparing numerical results with experimental data. The ability of the proposed model to represent the sediment transport phenomena in a morphologically articulated coastal region is verified by * Corresponding author.