Modelling of sediment transport and morphological evolution under the combined action of waves and currents

Abstract

Abstract. Coastal defence structures are often constructed to prevent beach erosion. However, poorly designed structures may cause serious erosion problems in the downdrift direction. Morphological models are useful tools to predict such impacts and assess the efficiency of defence structures for different scenarios. Nevertheless, morphological modelling is still a topic under intense research effort. The processes simulated by a morphological model depend on model complexity. For instance, undertow currents are neglected in coastal area models (2DH), which is a limitation for simulating the evolution of beach profiles for long periods. Model limitations are generally overcome by predefining invariant equilibrium profiles that are allowed to shift offshore or onshore. A more flexible approach is described in this paper, which can be generalised to 3D models. The present work is based on the coupling of the MOHID modelling system and SWAN wave model. The impacts of different designs of detached breakwaters and groynes were simulated in a schematic beach configuration following a 2DH approach. The results of bathymetry evolution are in agreement with the patterns found in the literature for several existing structures. The model was also tested in a 3D test case to simulate the formation of sandbars by undertow currents. The findings of this work confirmed the applicability of the MOHID modelling system to study sediment transport and morphological changes in coastal zones under the combined action of waves and currents. The same modelling methodology was applied to a coastal zone (Costa da Caparica) located at the mouth of a mesotidal estuary (Tagus Estuary, Portugal) to evaluate the hydrodynamics and sediment transport in calm water conditions and during events of highly energetic waves.

The effect of waves in hydrodynamics, stratification, and salt wedge intrusion in a microtidal estuary

“…where V represents the control volume, v H =(u,v) the horizontal velocity vector, v=(u,v,w) the velocity vector, n the normal vector to the bounding surface A, n H the normal vector related to the horizontal plane, υ T the turbulent viscosity, r the water density, p = g Z h z rdz +P atm the water presure, g is gravitational acceleration, P atm the atmospheric pressure, h the water level, W the earth rotation vector, and F is external forces, which include the wave induced force (gradient of radiation stress) computed by the wave model. The wave induced force was considered in the model MOHID in different systems (Malhadas et al, 2009;Malhadas et al, 2010;Delpey et al, 2014;Franz et al, 2017).…”

“…Filling The gap, the present work is focused on the effects of waves on hydrodynamics, processes such as stratification, circulation, and salt wedge dynamics are evaluated in the MRE. Field data and the coupling of the 3D MOHID finite volume model (Neves, 1985;Leitão, 2003;Franz et al, 2017), with the SWAN spectral wave model (Booij et al, 1999), previously calibrated and validated, were used. The low freshwater discharge seasons of 2018 and 2020 were taken as case studies, simulating current-only conditions (tidal and river), and comparing the results with simulations that include also the effects of waves on hydrodynamics.…”

An Analysis of Surface Ocean Currents from HF Radar Measurements in the Bali Strait and the Flores Sea, Indonesia

“…Thus, it is indicated that a lot of deposits might accumulate there, which in turn can change the morphology of the coastal zone. Sea currents and waves leading to the coast can contribute to the morphological changes in the coastal zone as in the form of sediments [53]. Specifically, Taniguchi et al [54] explain that residual currents affect sediment deposition on the coast.…”