This document discusses a study that used field data and XBeach modeling to analyze washover processes on the Wadden Island of Schiermonnikoog in the Netherlands. The study used XBeach's 1D mode to model wave, tide, and storm surge conditions, and its 2D mode to model sediment transport under different washover geometries. The modeling showed that currents dominate sediment transport during inundation, which is influenced by the pressure gradient between water levels in the North Sea and Wadden Sea. The study also found that small, frequent inundation events are important for long-term sediment transport, and that sediment transport is sensitive to the dimensions of washover openings.

1. Washover processes at the Wadden Island
of Schiermonnikoog, the Netherlands:
Field data and XBeach modeling
D. Wesselman, M. van der Vegt, R. de Winter

2. Spiekeroog Wangeroog
Construction of sand-drift dikes prevents overwash

3. North Sea
Wadden
Sea

4. Schiermonnikoog

5. Research question
How is sediment transport during inundation influenced
by wave, tide and storm surge conditions, and by
washover geometry?
1. XBeach 1D mode => wave, tide and storm surge1
2. XBeach 2D mode => washover geometry
1Wesselman et al., 2017

6. XBeach 1D => model set-up + fieldwork
Boundary conditions
• Water level stations
in North Sea and
Wadden Sea
• Wave buoy in North
Sea
Parameter settings
• γ = 0.45 in Roelvink2
(wave breaking)
• Other: Default values

7. XBeach 1D => Validation

8. • 6 classes, based
on 25 years of
water level data
• Tidal phase
difference
• Larger water
level increase in
Wadden Sea
• Higher class =>
larger waves
XBeach 1D => Analysis of processes

9. XBeach 1D => Analysis of processes

10. XBeach 1D => Analysis of processes
• Currents => dominate sediment transport
• Currents => depend on pressure gradient between North
Sea and Wadden Sea
• Pressure gradient => interplay between tide, storm surge
and wave set-up
• Small but frequenly-occuring inundation events are
important for the net and long-term sediment transport

11. XBeach 2D => Model set-up
• Constant water level of 2.5 m in North Sea and Wadden Sea
• Constant waves: Class 5 previous study

12. XBeach 2D => Results
Currents
• Alongshore in shallow water
• Cross-shore through
washover opening
• Flow contraction leads to
acceleration

13. XBeach 2D => Results

14. XBeach 2D => Results

15. Take home messages
• We successfully validated the hydrodynamics in XBeach (1D)
during inundation for mesotidal storm conditions.
• Currents dominate sediment transport at Schiermonnikoog
in the inundation phase.
• Water levels (tide, storm surge, wave set-up) in both the
North Sea and Wadden sea must be taken into account.
• The hydrodynamics and sediment transport are sensitive to
the washover opening dimensions.

16. 1Wesselman D, de Winter R, Engelstad A, McCall R, van
Dongeren A, Hoekstra P, Oost A, van der Vegt M. 2017. The
effect of tides and storms on the sediment transport across a
Dutch barrier island. Earth Surface Processes and Landforms

17. Additional slides

23. Increasing washover opening width
Increasingwashoveropeningheight