Water movement in the Dutch Wadden Sea
When we think about the water movement in coastal areas, we often picture waves hitting the coast, and periodic rise and fall of the water levels due to the tides.
But, just like the weather, no two days in the sea are the same. This is also the case in the Dutch Wadden Sea, where water movement is much more dynamic than previously thought. This unique coastal area with multiple inlets is the Dutch part of the largest system of intertidal flats in the world, namely the Wadden Sea.
Numerical simulations
For his PhD research, Jeancarlo Fajardo Urbina used sophisticated numerical simulations of currents, salinity, and temperature and AI-based models to understand and predict the water movement.
This is important for the sustainability of the region and for making informed management decisions since water ultimately influences the transport of sediments, marine species, and pollutants.
Movement of water
It was believed that tides were the dominant force controlling the water movement in the Dutch Wadden Sea. However, recent research based on computer simulations of currents for three years (2009-2011) showed that winds play a much more important role than expected, especially during storms.
Given the large variability in the water transport during these three years, it was concluded that long-term trends can only be identified by considering several decades.
By extending the previous simulation to cover the years 1980-2015, Fajardo Urbina studied the movement of water in the Dutch Wadden Sea by releasing and tracking billions of particles that follow the currents.
Main findings
Fajardo Urbina found that stormy winds (mainly from southwest to west) move groups of particles for several kilometers as if they were stuck to each other.
Meanwhile, tides are especially important for the spread of the particles and break these groups apart. So, particles that start close together will spread and end up in different places. Since this spread depends on the tide, it is related to astronomical motions such as the moon phases and the moon鈥檚 proximity to the earth along its elliptical orbit.
Seasons also influence water movement. In the windy seasons (common in autumn and winter), water parcels leave the Dutch Wadden Sea into the North Sea faster than during calmer seasons (typically in spring and summer).
In addition, year-to-year variations, influenced by large-scale climate patterns, also change the rate at which water exits the Dutch Wadden Sea.
One key finding is that once a water parcel leaves, it rarely returns because it is carried away by North Sea currents. Recent campaigns with drifters released in the DWS that simulate floating debris, like plastic, agree with this last statement. However, the data emphasized that specific oriented simulations are required to better represent the transport of such floating material.
Finally, by developing an AI-based model in combination with the physical knowledge from my previous results, it is now possible to predict the transport of particles around 100 times faster than traditional numerical simulations.
This approach is especially useful for advancing tools to plan the response to marine accidents that require actions in real time.
Future
The findings from this research not only improved our knowledge of the Dutch Wadden Sea but can also help us understand similar coastal systems worldwide.
As climate change continues to alter wind patterns, storm intensities, sea levels, and currents, studies like this are crucial for adapting to future changes in our coastal environments.
Title of PhD thesis: Supervisors: Matias Duran Matute and Herman Clercx.