Residual circulation and freshwater transport in the Dutch Wadden Sea: a numerical modelling study

Abstract

Abstract. The Dutch Wadden Sea is a region of intertidal flats located between the chain of Wadden Islands and the Dutch mainland. We present numerical model results on the tidal prisms and residual flows through the tidal inlets and across one of the main watersheds. The model also provides insight into the pathways of fresh water originating from the two sluices at the Afsluitdijk (enclosure dike) through the use of passive tracers. All these results are obtained from threedimensional numerical simulations carried out with the General Estuarine Transport Model (GETM), at a horizontal resolution of 200 m and with terrain-following vertical coordinates with 30 layers. We concentrate on the years 2009-2010, for which we impose meteorological forcing, freshwater discharge, and boundary conditions for tidal forcing and storm surges. Results from the model show an excellent agreement with various observational data sets for sea surface height, temperature, salinity and transport through the Texel Inlet. The simulations show that although tides are responsible for a characteristic pattern of residual transport through the inlets, the wind imposes a large variability on its magnitude and can even invert its direction during strong southwesterly winds. Even though these events are sporadic, they play an important role in the flushing of the Dutch Wadden Sea, as they strongly diminish the flushing time of fresh water. In addition, wind can force a residual transport across the Terschelling watershed of the same order, if not larger, than through any of the main tidal inlets, despite the fact that its tidal prism is much smaller than any of those of the inlets. For the pathways of fresh water, the Terschelling watershed turns out to be more important than was previously thought, while the opposite holds for the Vlie Inlet.

Variability of residual fluxes of suspended sediment in a multiple tidal-inlet system: the Dutch Wadden Sea

“…The model also solves for the equations of potential temperature and salinity and includes a flooding and drying algorithm. The resolution of the model employed in previous studies was 200 m for the horizontal coordinates and 30 sigma-layers in the vertical (Duran-Matute et al 2014;Sassi et al subm.). In this study, we lowered the resolution to 500 m and 10 sigma-layers, to render possible extensive sensitivity tests.…”

“…The hydrodynamic module has been extensively described in Duran-Matute et al (2014). Here, we discuss the most important characteristics.…”

“…Seasonal variability in residual sediment transport is about 10-50 % over the course of the year and these variations can be related to the seasonal variability of the amplitudes of M 2 and M 4 tidal constituents due to the seasonal stratification cycle of the North Sea. The freshwater outflow from the lake IJssel finds its way through the Marsdiep and Vlie inlets (Duran-Matute et al 2014), with typical mean annual freshwater discharge into the domain of about 500 m 3 s −1 .…”

Shifts in nursery habitat utilization by 0-group plaice in the western Dutch Wadden Sea

“…In this respect, water temperatures measured in the various intertidal stations were well within the physiological tolerance range described for 0-group plaice and, in addition, no clear differences in thermal regimes between the different habitats were found. We cannot exclude, however, that actual thermal environment experienced by 0-group plaice is insufficiently captured by the modelled temperature data, despite validation of the model against several observational datasets (Duran- Matute et al, 2014). Not only may the dynamic nature of shallow tidal areas such as the Dutch Wadden Sea lead to less precise estimates but also fine-scale habitat selection by individuals (van der Veer & Bergman, 1986;Hurst et al, 2010) and/or fine-scale spatial thermal heterogeneity (Budy et al, 2011) may occur hampering the possibility of linking species response to thermal conditions.…”

Production efficiency of mussel bottom culture

“…Abundance of sea stars in the study area is lower in winter, which is attributed to the lower salinity in winter (Agüera 2015). High temporal fluctuations in salinity occur in regions where water from Lake IJssel enters the Wadden Sea (Duran-Matute et al 2014). Areas with high temporal fluctuations in salinity are the areas where we find natural mussel beds ( Figure 6.6).…”