Presentation byThijs Lanckriet, IMDC, Belgium, at the XBeach User Day 2018, during Delft Software Days - Edition 2018. Thursday, 15 November 2018, Delft.

1. Simulating the impact of alternative solutions
for marina inlet sedimentation
and coastal erosion
Thijs Lanckriet, Leen Baelus, Li Wang, Eleftheria Kragiopoulou,
Tim Franken & Annelies Bolle
XBeach User Day – 2018-11-15

2. 15 November 2018/ Blankenberge – Wenduine / slide 2
Project overview
• Blankenberge (Belgium):
inlet sedimentation
• Wenduine:
Beach erosion
Wenduine Blanken-
berge

3. 15 November 2018/ Blankenberge – Wenduine / slide 3
Blankenberge marina access channel

4. 15 November 2018/ Blankenberge – Wenduine / slide 4
Blankenberge marina access channel
www.nieuwsblad.be/cnt/dmf20130130_00451426

5. 15 November 2018/ Blankenberge – Wenduine / slide 5
Wenduine nourishments
First major nourishment in 2012 (720 000 m3)
Maintenance nourishments in 2014, 2016 and 2017
(160 000 – 300 000 m3)

6. 15 November 2018/ Blankenberge – Wenduine / slide 6
Study process
1. Feasiblity study / study of alternatives.
• Criteria:
• Morphology (effectiveness in reducing
sedimentation/erosion)
• Cost effectiveness
• Nautical access
• Swimmer safety
• Coastal safety
• Environmental aspects
• Architectural/planological aspects
2. Pre-design
• Activities involving XBeach
• Optimization of measures
• Coastal safety assessment
3. Final design
4. EIA
5. Construction
---> XBeach
---> XBeach
---> XBeach
---> XBeach
---> XBeach
---> XBeach

7. 15 November 2018/ Blankenberge – Wenduine / slide 7
XBeach models
2 grids:
• Blankenberge model
• Wenduine model
2 simulation types:
• Long term morphodynamics (1-5 years)
• Hydrodynamics (50 hours)

8. 15 November 2018/ Blankenberge – Wenduine / slide 8
Long-term morphological simulations
• Reduced wave climate
using OPTI
input reduction method
• Using 8 tidal cycles of
24h50 min to represent
1 year
• Morfac 36.5

9. 15 November 2018/ Blankenberge – Wenduine / slide 9
Hydrodynamics
Impact of groyne field during flood + waves from NNE

10. 15 November 2018/ Blankenberge – Wenduine / slide 10
Hydrodynamics
Reference during flood + waves from WNW

11. 15 November 2018/ Blankenberge – Wenduine / slide 11
Hydrodynamics
Impact of groyne field during flood + waves from WNW

12. 15 November 2018/ Blankenberge – Wenduine / slide 12
Morphodynamics
Impact of groyne field

13. 15 November 2018/ Blankenberge – Wenduine / slide 13
Morphodynamics
How to implement groynes in XBeach?
• Traditional way: simply raise 1 grid line in bathymetry
• For coarse alongshore grids:
groyne slope is not well represented
• Which fraction of littoral transport should a groyne block?
Groynes have sediment transport going
• Around the groyne (bypassing)
• Over the groyne  very little guidance in literature

14. 15 November 2018/ Blankenberge – Wenduine / slide 14
Morphodynamics
How to implement groynes in XBeach?
Effect of model resolution is rather limited.

15. 15 November 2018/ Blankenberge – Wenduine / slide 15
Morphodynamics
Optimizing groyne length using XBeach

16. 15 November 2018/ Blankenberge – Wenduine / slide 16
Morphodynamics
Foreshore nourishments
Very little onshore transport predicted by
XBeach
=> Can we use XBeach to assess
effectiveness of foreshore nourishments?

17. 15 November 2018/ Blankenberge – Wenduine / slide 17
Conclusions
• A feasibility & (pre-)design study was performed to develop
solutions for marina inlet sedimentation in Blankenberge and
beach erosion in Wenduine, Belgium
• XBeach was used extensively throughout the study to assess
morphology, swimmer safety and nautical access
• Innovative applications:
• Web-based visualization of currents for swimmers & lifeguards
• Optimization of groynes & groyne length
• Long-term morphology (5 years)

18. 15 November 2018/ Blankenberge – Wenduine / slide 18
Questions and philosophical remarks
• How to implement groynes?
• Little quantitative data available on groyne effects
• Long-term morphological modelling using XBeach
• Pros & cons vs Delft3D?
• Groynes? Why not soft solutions using sand?
• Both groynes & soft solutions were simulated and assessed
• A detailed cost-benefit analysis showed groynes to be
most cost-effective solution (!)
• More details at ICE Coastal Management 2019

19. 15 November 2018/ Blankenberge – Wenduine / slide 19
Morphology – new equilibrium coastline