Hydrodynamic Modeling of the Impact of a Proposed New Coastline Groyne Structure on Floating Debris Pathways at Paget Farm, in Saint Vincent and the Grenadines

Abstract

To accommodate an increasing number of tourists visiting Bequia, the second largest island of Saint-Vincent and the Grenadines, the local government constructed an airport, through a major coastline land-reclamation project. However, due to the prevailing ocean current patterns in the area, an inlet created on the east side of the new airport is prone to trapping significant amounts of ocean-borne debris. This litter accumulation creates a health risk to local fishermen who clean their daily catch using water from the inlet. It is proposed to install a rubble-mound groyne structure on the eastward side of the new inlet to address this problem. The utilisation of a coastline groyne in this case is somewhat unorthodox, as the latter is normally employed to mitigate against coastal erosion. The goal of this study is to optimise the groyne design with the assistance of a 3D numerical model. The ‘Delft3D’ open-source model (WAVE and FLOW modules) was selected to examine the effects of different orientations and lengths of the proposed groyne on the movements of floating debris. Included in the initial phase of the study was a field investigation to collect certain data which were necessary for model calibration and validation. This involves the use of an Acoustic Doppler Current Profiler (ADCP) to measure local shore bathymetry and also current velocities over a range of tidal cycles.