Keynote Dynamic Dunes Congress 2015: Gerben Ruessink - Beach-dune interaction for dynamic coastal management

1. Faculty of Geosciences
Faculty of Geosciences
Beach-dune interaction
for dynamic coastal
management
Gerben Ruessink

2. Faculty of Geosciences
Beach-dune interaction
Urgency:
• nature restoration
• long-term coastal safety
No sand sharing: (1) loss in geomorphological dynamics
(2) loss in biodiversity
(3) no vertical growth with sea-level rise
Dune erosion Dune growth

3. Faculty of Geosciences
Building with Nature: Sand Engine
5 July 2011 10 January 2012
1 October 2013 1 oktober 20134 May 2015

4. Faculty of Geosciences
Building with Nature: Sand Engine
Beach-dune interaction:
• Short gradients (new embryo dunes)
• Foredune growth ~ 15 m3/m/year
• No dune erosion

5. Faculty of Geosciences
Building for Nature: NWNKern

6. Faculty of Geosciences
Building for Nature: NWNKern
Trenches:
V- to U-shape
Construction After 2 years
Foredune
scarping
Sedimentation
lobes

7. Faculty of Geosciences
Combination: HPZ

8. Faculty of Geosciences
Questions
• How much sand is actually blown toward the dunes?
• Which factors affect this amount?
• What to expect from dune remobilization?
• Are present-day large-scale measures effective?
• Can nourishments and dune remobilization be combined?
• …

9. Faculty of Geosciences
Needs
• Experiments: Learning by doing
• Long-term (years) monitoring with high resolution (seasons)
• Close co-operation between stakeholders and scientists
• Models with different complexity
• …

10. Faculty of Geosciences
Beach-dune interaction: models
Keysers et al. (2014)
Plos ONE
Poseidon Aeolus

11. Faculty of Geosciences
My projectBeach-dune interaction: models
Need
Accurate predictive
model of aeolian sand
supply
Challenges
Supply limitation
1. How wet?
2. When?
3. How much?
4. Upscaling

12. Faculty of Geosciences
Timing of aeolian events
Potential transport
• Events (4 hrs > 8 m/s)
• Hsu (1974)
Observed transport
• Sand-strip activity

13. Faculty of Geosciences
Timing of aeolian events
Mismatch between potential and actual events:
• Moderate wind speeds: considerable aeolian activity
• Large speeds are large: no aeolian activity

14. Faculty of Geosciences
Considerable aeolian activity under moderate,
shore-oblique/parallel winds
Timing of aeolian events

15. Faculty of Geosciences
Timing of aeolian events
No aeolian activity under strong shore-normal
/ oblique winds because of surge

16. Faculty of Geosciences
Summary
• From preventing dune-erosion to beach-dune interaction
• Building with and for Nature
• Practice-inspired questions and scientific ideas
• Pilot experiments: ‘Learning by doing’ with long-term
monitoring to eventually predictively understand
Only then ready for the challenges of the decades to come

17. Faculty of Geosciences

18. Faculty of Geosciences
Surface moisture content
saturated
Reflection (dB)
Moisturecontent(%)
dry

19. Faculty of Geosciences
Surface moisture content

20. Faculty of Geosciences
Mismatch between potential and actual events:
• Moderate wind speeds: considerable aeolian activity
• Large speeds are large: no aeolian activity
Timing of aeolian events

21. Faculty of Geosciences
Transport magnitude

22. Faculty of Geosciences
Results (Xaver)
-80 -70 -60 -50 -40 -30
0
5
10
15
20Elevation(mMSL)
-80 -70 -60 -50 -40 -30
0
5
10
15
20
Elevation(mMSL)
Distance (m)
before
after
I. Destruction of new foredune and embryo dunes
-80 -70 -60 -50 -40 -30
0
5
10
Elevatio
-80 -70 -60 -50 -40 -30
0
5
10
15
20Elevation(mMSL)
Distance (m)
-80 -70 -60 -50 -40 -30
0
5
10
15
20
Elevation(mMSL)
-80 -70 -60 -50 -40 -30
0
5
10
15
20
Elevation(mMSL)
Distance (m)
II. Failure of dune front with successive rotational slides
before
after

23. Faculty of Geosciences
-80 -70 -60 -50 -40 -30
0
5
10
15
20
Elevation(mMSL)
-80 -70 -60 -50 -40 -30
0
5
10
15
20
Elevation(mMSL)
Distance (m)
before
after storm
recovery
Results (post-Xaver)