The nearshore zone extends from the landward limit of the swash to the seaward point at which incident waves commence breaking. This zone encompasses a large range of scales and types of fluid motion, including short and long waves, currents, turbulence and vortices. Sediment transport in the surf and swash zones control the nearshore and beach morphology. Numerical models of processes in these zones include many simplifications. The main objective of this project is to develop further understanding of the sediment transport in the nearshore zone.
The major areas to investigated were:
- Numerical simulation of surf-swash zone hydrodynamics including turbulent flow and sediment transport;
- Numerical modeling of wave-beach groundwater interaction and its effects on nearshore sediment transport and beach profile changes;
- Temporal and spatial profiles of sediment concentration and velocity for various grain sizes and wave conditions;
- Time-varying and time-averaged sediment flux distributions for different beach and flow conditions;
- Net on/off-shore sand transport rates varying with flow conditions;
- Influence of wave conditions on groundwater dynamics and salinity beneath granular beaches; and
- Extent of mixing between fresh groundwater and seawater in the nearshore region.
The project included model formulation and development, and model validation. A comprehensive two-phase, onshore/offshore flow model was developed. The model, built on an existing research codes, was based on the Euler-Euler coupling of the governing equations for the sediment and fluid phases. Each phase was modeled using the Navier-Stokes equations, with the coupling between the phases accounting for interphase mass and momentum conservation. Other model elements included were: (i) k-ε closure model for turbulence generation and translation processes; (ii) free-surface motion modeled using the Volume-of-Fluid technique; and (iii) saturated-unsaturated density-dependent groundwater flow in an unconfined aquifer.
Fig. 1: Schematic illustration of the nearshore (Elfrink and Baldock, 2002).
Fig. 2: Tide-induced (a) salt distribution, (b) oxygen distribution with no natural oxygen-consuming processes and (c) oxygen distribution with natural oxygen consumption in a tidally-influenced near-shore aquifer. The upper saline plume (USP), saltwater wedge and freshwater discharge zone (FDZ) are denoted in (a). The arrows represent the groundwater flows averaged over a tidal cycle. After Robertson et al. (2008).
Robinson, C.E., Li, L., Barry, D.A. 2007. Adv Water Resour 30, 851-65.
Elfrink, B., Baldock, T.E. 2002. Coast Eng 45, 149-67.