Numerical modelling of intra-wave sediment transport on sandy beaches using a non-hydrostatic, wave-resolving model

Giulia Mancini,Riccardo Briganti,Fangfang Zhu,Robert McCall,Nicholas Dodd

doi:10.1007/s10236-020-01416-x

Giulia Mancini, Riccardo Briganti + Show 3 more

Open Access

https://doi.org/10.1007/s10236-020-01416-x

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Abstract

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 performance of the model. Numerical results show overall better performance in simulating single waves rather than wave trains. For the latter, the modelling of the morphodynamic response improves in the swash zone compared with the existing sediment transport modelling approach within non-hydrostatic XBeach, while the need of including additional physical processes to better capture sediment transport and bed evolution in the surf zone is highlighted in the paper.

Highlights

Sandy beach evolution plays a key role in coastal vulnerability, influencing the stability of ecosystems and coastal communities’ economy and safety
The present study focuses on modelling the dynamics of sediment in the nearshore zone in all stages of the flow both for solitary waves, i.e., isolated waves, and wave trains, with significant swash-swash interactions
The XBNH-Intra-Wave Sediment Transport (IWST) modelling of sediment transport and morphodynamics is discussed by comparing the results of numerical simulations of the Alsina et al (2016) case obtained in the present study with those of Ruffini et al (2020) using the XBNH-Wave-Averaged Sediment Transport (WAST) approach

Summary

Introduction

Sandy beach evolution plays a key role in coastal vulnerability, influencing the stability of ecosystems and coastal communities’ economy and safety. Wave-resolving hydro-morphodynamic models are needed to provide an accurate description of these complex dynamics because they include intra-wave physical processes, which make these models suitable to fully solve swash morphodynamics The models of this type in the literature use as governing hydrodynamic equations one of the following alternatives: the Non-Linear Shallow Water Equations (NLSWE) (e.g., Li et al 2002, Postacchini et al 2012, Zhu and Dodd 2015, Incelli et al 2016, see Briganti et al 2016 for a review), the non-hydrostatic NLSWE (e.g., Smit et al 2010, Ma et al 2012, Ruffini et al 2020), or Boussinesq-type equations To enable the computation of morphodynamics, these models would require sub-models that compute suspended and bed load sediment transport based on intra-wave hydrodynamics, from which in turn bed level change can be computed

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