MODELING RAPID BEACH CHANGE SURROUNDING A COASTAL STRUCTURE IN OBLIQUE WAVES

Sandy beaches are typically in equilibrium with the wave climate, and changes occur when the system is perturbed. However, changes to nearshore morphology can occur when coastal structures are built and the system adjusts to a new equilibrium. An example of this is the construction of a shore-perpendicular groin that is designed to trap sediment . We investigate the capability of Delft3D model to simulate wave transformation, nearshore circulation and morphology change around a structure, driven by relatively small breaking waves at a very high incident angle.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/q_rnSiaP7WM

Rhythmic patterns of shoreline contour in the gulf of Terpenya of Sakhalin Island

The results are discussed of the long-term observations of the system of mega-cusps (large-scale shoreline cusps) revealed on the coast of the Gulf of Terpenya of Sakhalin Island. Typical spatial step of the rhythmic forms is about 800 m and the amplitude of shoreline undulations is of tens of meters. Despite of significant changes in temporal scales of the seasons, years and decades the main morphological features of mega-cusps are kept over the period of more than 60 years. The model is suggested explaining creation of rhythmic shoreline patterns by self-organization of bottom relief under the wave impact. Development of mega-cusps is shown to be connected with generation of nearshore circulation cells. Due to flows within the cells a small initial perturbation of shoreline contour can increase in time. A positive feedback between the coastal morphology and the hydrodynamics arises when a certain relation is established between the length of perturbation, the width of surf zone and the velocities of nearshore currents. It is concluded that the system of mega-cusps in the Gulf of Terpenya is mainly supported by the moderate waves of significant wave height about 1.6 m.

VORTEX FORCE ANALYSIS OF WAVE-DRIVEN NEARSHORE CIRCULATION

In this presentation, we examine 3-D structure of nearshore circulation driven by short-crested wave breaking using the 3-D Smooth Particle Hydrodynamic model, GPUSPH (Hérault et al., 2010). The alongshore variation of incident wave field has been imposed by using the method of intersecting wave trains proposed by Dalrymple (1975). We use the 3-D vortex force formalism to analyze the various forcing mechanisms of the observed circulation. Of particular interest is the relative importance of the vortex force compared with the other wave-averaged forces. The accuracy of the depth-averaged vortex force based on the formulation of Smith [2006] is also examined.

Christopher N. K. Mooers (1935–2018)

This passionate physical oceanographer, a leader and catalyst in coastal studies, explored many facets of nearshore circulation and advanced the modeling and forecasting of coastal dynamics.

Different approaches to model the nearshore circulation in the south shore of O'ahu, Hawaii

The dynamical interaction between currents, bathymetry, waves, and estuarine outflow has significant impacts on the surf zone. We investigate the impacts of two strategies to include the effect of surface gravity waves on an ocean circulation model of the south shore of O'ahu, Hawaii. This area provides an ideal laboratory for the development of nearshore circulation modeling systems for reef-protected coastlines. We use two numerical models for circulation and waves: Regional Ocean Modeling System (ROMS) and Simulating Waves Nearshore (SWAN) model, respectively. The circulation model is nested within larger-scale models that capture the tidal, regional, and wind-forced circulation of the Hawaiian archipelago. Two strategies are explored for circulation modeling: forcing by the output of the wave model and online, two-way coupling of the circulation and wave models. In addition, the circulation model alone provides the reference for the circulation without the effect of the waves. These strategies are applied to two experiments: (1) typical trade-wind conditions that are frequent during summer months, and (2) the arrival of a large winter swell that wraps around the island. The results show the importance of considering the effect of the waves on the circulation and, particularly, the circulation–wave coupled processes. Both approaches show a similar nearshore circulation pattern, with the presence of an offshore current in the middle beaches of Waikiki. Although the pattern of the offshore circulation remains the same, the coupled waves and circulation produce larger significant wave heights ( ≈ 10 %) and the formation of strong alongshore and cross-shore currents ( ≈ 1 m s−1).

Different approaches to model the nearshore circulation in the south shore of Oahu, Hawaii

The dynamical interaction between currents, bathymetry, waves, and estuarian outflow have significant impacts on the surf-zone. We investigate the impacts of two strategies to include the effect of surface gravity waves on an ocean circulation model of the south shore of O'ahu, Hawaii. This area provides an ideal laboratory for the development of nearshore circulation modeling systems for reef protected coastlines. We use two numerical models for circulation and waves: Regional Ocean Modeling System (ROMS) and Simulating Waves Nearshore (SWAN), respectively. The circulation model is nested within larger-scale models that capture the tidal, regional, and wind-forced circulation of the Hawaiian archipelago. Two strategies are explored for circulation modeling: forcing by the output of the wave model and online, two-way coupling of the circulation and wave models. In addition, the circulation model alone provides the reference for the circulation without the effect of the waves. These strategies are applied to two experiments: (1) typical trade-wind conditions that are frequent during summer months, and (2) the arrival of a large winter swell that wraps around the island. The results show the importance of considering the effect of the waves on the circulation and, particularly, the circulation-wave coupled processes. Both approaches show a similar nearshore circulation pattern, with the presence of an offshore current in the middle beaches of Waikiki. Although the pattern of the offshore circulation remains the same, the coupled waves and circulation produce larger significant wave heights (10 % to 20 %) and the formation of strong along- and cross-shore currents (~ 1 m s−1).