Tidal and wind-driven spatiotemporal variability in the residual displacement and dispersion of Lagrangian particles in a system of intertidal basins

Abstract

This study identifies and quantifies the distinct contributions of wind and tides to the variability of Lagrangian residual transport in the Dutch Wadden Sea (DWS), a mesotidal system of interconnected tidal basins of high ecological relevance. A three-dimensional hydrodynamic model and offline particle tracking were used to simulate the transport of particle patches over individual tidal periods of the record 1980-2015 using depth-averaged currents. This transport was decomposed into the net displacement of their center of mass (advection) and the tidally averaged rate of change of dispersion from their center of mass (the dispersion coefficient). The results reveal that advection is predominantly wind-driven on the temporal scale of events. Strong winds from the North Sea aligned with the topographical orientation of the system trigger advection comparable to the width of the basins. Although the role of tides in advection is secondary, they induce residual circulation cells near the inlets, particularly evident during weak wind conditions. In contrast, dispersion is controlled by the tides and exhibits filamentous structures with large values around all the DWS inlets. The strength of these structures has a linear correlation with the tidal amplitude, which is mainly modulated by the spring-neap cycle. However, the location of these structures changes predominantly from shallow areas surrounding the channels when particles are released at high tide to within the channels when released at low tide. These findings underscore the distinct separable roles of wind and tides in Lagrangian residual transport within event-driven, multi-inlet coastal systems such as the DWS.