The Wadden Sea’s intertidal flats modelled in 3Di for ecology study
- Partners
- Rijkswaterstaat, Delft University of Technology
- Researcher
- Reinder Boorsma
The Wadden Sea’s intertidal flats—home to millions of migratory birds and natural coastal defenses—are shifting under the forces of wind, waves, and tides. This graduation thesis, executed by Reinder Boonsma, unpacks these complex dynamics using advanced modeling, uncovering insights that enhance coastal resilience and ecosystem protection in the face of climate change. Understanding these flow patterns is key to preserving the Wadden Sea’s irreplaceable habitats for future generations. This research is done in collaboration with University of Technology Delft and Rijkswaterstaat.
The challenge
The Wadden Sea is ecologically important. Key elements in the Wadden Sea are the intertidal flats. These contain vast amounts of life, serve as feeding grounds for millions of birds, and provide ecosystem services such as coastal protection. Therefore, it is important to be able to understand and predict how these vital elements of the Wadden Sea change over time.
The evolution of intertidal flats relies on the balance between erosion and sedimentation caused by the forcing of wind, waves, and the tide. Exact horizontal flow patterns on intertidal flats are not fully understood, especially under the influence of wind.
Our solution
This study aims to investigate the tidally- and wind-driven flow patterns on the scale of an intertidal flat in the western Dutch Wadden Sea. To do so, a subgrid-based hydrodynamic model of the Dutch Wadden Sea is created. Simulations are run in which the following model settings are manipulated: computational grid resolution on the scale of the intertidal flat, whether subgrid modelling technique is applied, the phase of the spring-neap tidal cycle, and whether wind forcing is applied.
Simulations show that subgrid modeling technique is beneficial for representing the impact of small-scale bathymetric features on the flow pattern while using a coarser computational grid. The flow pattern is represented more accurately compared to standard practice simulations using averaged bed elevation per computational cell. The automatic wetting and drying of subgrid modelling technique is crucial for representing flow in shallow water layers.
The outcome
Results indicate that the flow patterns on intertidal flats follow from the water level gradient between surrounding channels and are influenced by the intertidal flat geometry (i.e. size, bed elevation, and degree to which the intertidal flat is intersected by tidal channels), hydraulic boundary condition (i.e. phase of the spring-neap tidal cycle, asymmetry of the tidal wave), and wind forcing (which can completely alter hydrodynamics at several scales).
This report contributes to the knowledge on flow patterns on intertidal flats. These insights benefit future studies into ecology, navigational maintenance, flood protection, and the ability of intertidal flats to keep up with sea level rise. However, the flow pattern is not solely responsible for morphological change. Moving forward, continued research into the drivers of the morphological change of intertidal flats will be crucial for informed management of ecologically valuable estuarine areas like the Wadden Sea.
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