FIELD MEASUREMENTS AND MODELLING OF NEARSHORE CURRENTS AT A HIGH-ENERGY GEOLOGICALLY-CONSTRAINED BEACH

We present field measurements of nearshore currents at a high-energy mesotidal beach with the presence of a 500-m headland and a submerged reef. Small changes in wave forcing and tide elevation were found to largely impact circulation patterns. In particular, under 4-m oblique wave conditions, our measurements indicate the presence of an intense low-frequency fluctuating deflection rip flowing against the headland and extending well beyond the surf zone. An XBeach model is further set up to hindcast such flow patterns.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/EiqnjBIkWJE

A PRELIMINARY EXPERIMENT OF NEARSHORE CURRENT GENERATED DUE TO TRANSVERSE PHASE DIFFERENCES

The vorticity generation due to the ends of wave crests and its resultant rip current have been studied (Johnson and Pattiaratchi, 2006; Clark et al., 2012; Choi et al., 2015; Peregrine, 1998; Postacchini et al., 2014). Recently, a laboratory experiment was conducted to observe rip currents formed between the ends of breaking wave crests (Choi and Roh, 2020) by using the wave generation method of pseudo intersecting wave trains. In this method, regular waves were generated by running two parts of wave maker out of phase. Their pseudo intersecting wave trains was compared with the intersecting wave trains generated by regular waves having the same wave period and the slightly different two wave directions. However, the pseudo intersecting wave trains, i.e., out-of-phase wave trains, could be formed in the field by the transformation of long-crest waves propagating over a specific change of topography in an intermediate water depth, for example, a submerged semi-infinite straight seamount range parallel to the shoreline. The long-crest wave train can be divided into two wave trains with phase difference because of the different wave speeds over the end of the submerged structure. To understand the evolution process of nearshore currents generated due to transverse phase differences, a laboratory experiment was planned. This study showed the preliminary laboratory experiments in which two wave trains with phase differences and its resultant nearshore currents were observed using the optical flow method.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/SaMl6rspZmw

Wave Fields and Nearshore Currents in the Coastal Region Opposite San Mauro Cilento (Italy)

In this paper in order to simulate nearshore currents in computational domains representing the complex morphology of real coastal regions we use a model based on a contravariant integral form of the fully nonlinear Boussinesq equations (FNBE). The contravariant integral form, in which Christoffel symbols are absent, of the continuity equation does not contain the dispersive term. The Boussinesq equation system is numerically solved by a hybrid finite volume-finite difference scheme. The wave breaking is represented by discontinuities of the weak solution of the integral form of the nonlinear shallow water equations (NSWE). The capacity of the proposed model to correctly simulate the wave train propagation on a highly distorted grid is verified against test case present in the literature. The simulation of wave fields and nearshore currents in the coastal region, opposite San Mauro Cilento (Italy) in presence of a system of T-head groins, is numerically reproduced by using the proposed model.

Nonlinear waves and nearshore currents over variable bathymetry in curve-shaped coastal areas

Irregular coastlines and variable bathymetry produce nonlinear effects on wave propagation which play a significant role on the formation of nearshore currents. To protect the coastline from the erosional action of nearshore currents, it is usual to adopt coastal defence works such as submerged breakwaters. If properly designed, they give rise to circulation patterns capable to induce sedimentation of suspended material at the nearshore region. To numerically simulate the hydrodynamic effects of submerged breakwaters in irregular coastal areas, we use a numerical model which is based on an integral contravariant formulation of the three-dimensional Navier–Stokes equations in a time-dependent coordinate system. These equations are numerically solved by a non-hydrostatic shock-capturing numerical scheme which is able to simulate the wave propagation from deep water to the shoreline, including the surf zone and swash zone.

Evaluation of beach nourishment works on Miyazaki coast in Japan

Miyazaki Coast have been suffering from severe erosion problem due to the shortage of sediment supply from rivers and the change of waves and nearshore currents by the construction of an offshore breakwater at Miyazaki Port. In order to reproduce a wide sandy beach, a beach nourishment project has been done since 2008 in combination with the installation of Sand-Packed containers that were placed in front of dune. A certain volume of nourishment sand has been installed for the sand fill works that cover Sand-Packed containers, and the rest has been dumped off the coast. The purpose of this research is to evaluate the effectiveness of beach nourishment works with using long-term bottom sounding data. This study discussed the effect of the beach nourishment on longshore sandbar evolution. The change of the sand volume in research area was also discussed in this study.