A new process-based, wave-resolving, 2DH circulation model for the evolution of natural sand bars: The role of nearbed dynamics and suspended sediment transport

We study the migration of natural sand bars that evolve in the nearshore by means of a new process-based waveresolving, 2DH circulation model. In order to perform reliable and accurate computations, the robust Nonlinear Shallow Water Equations (NSWEs) hydro-morphodynamic solver of Brocchini et al. (2001) and Postacchini et al. (2012) implements a detailed description of the Bottom Boundary Layer (BBL) dynamics and a new predictor for the Suspended Sediment Transport (SST) based on the solution of a Depth-Averaged Advection-Diffusion Equation (DAADE) for the sediment concentration. The robustness and accuracy of the enhanced model are validated against literature theoretical, experimental, and numerical results, all comparisons highlighting good performances and clarifying the role of both BBL and SST contributions, the former one having a larger positive influence than the latter one on the results. Both original and enhanced models are, then, used to predict the evolution of the sand bar system that characterizes the nearshore of Senigallia (AN). The analysis leverages the field observations collected at such a site by means of the Sena Gallica Speculator video-monitoring system. Modeling of the storm-forced sand bar migration patterns reveals that: 1) the enhanced model can adequately reproduce the seaward migration of the sand bars of the system; 2) the process of shoreline retreat in coincidence with the generation of a new-born bar is well described; 3) inclusion of the BBL improves quantitative prediction of the bar crest migration; 4) the SST, beyond improving the prediction of the bar crest location, induces some smoothing of the bar profile, in line with the literature findings of SST being a stabilizing factor for the bar emergence.