M.Sc. Project: Longshore Currents and Eddies near Beaches

Longshore currents and eddies are the primary carriers of sediment and
pollution at our beaches. Longshore currents arise when obliquely incident
waves offshore break near the beach and then deposit their momentum.
Eddies or vortices arise due to wave breaking over intricate beach topography
(see Figure 1), e.g. causing the infamous rip currents through sand bars, and
due to instabilities of the longshore currents. While the classical explanation
of these phenomena is rooted in averaging over the short waves, an exciting
complimentary explanation is rooted in a vortex anomaly generation mechanism of
each breaking wave (Peregrine and Bokhove 1998, Bokhove and Peregrine 1999).

The principal aim of this M.Sc. research project is:
(i) to analyse these potential instabilities of longshore currents in a shallow-water
model, and
(ii) to find shallow-water vortex solutions near beaches and to perturb these vortices
with incoming surface waves or bores. An example of a vortex solution ---valid to
leading order in a Froude number expansion--- is given in figure 2.

The research project will be characterized by an enhancing combination of analytical
(e.g. perturbation theory) and numerical methods for finding solutions in linear and
nonlinear coastal surf-zone hydrodynamics.

Figure 1. Vortices at the confluence of Berkel and Slinge rivers (courtesy of Valerie Zwart).

Literature