Natural foreshores as an alternative to traditional dike re-enforecements

1. Ellis Penning, Henk Steetzel, Robbin van Santen, Jasper Fiselier,
Marieke de Lange, Vincent Vuik, Sonja Ouwerkerk, Jaap van Thiel de
Vries
NATURAL FORESHORES AS AN ALTERNATIVE
TO TRADITIONAL DIKE RE-ENFORECEMENTS:
A FIELD PILOT IN THE LARGE SHALLOW LAKE MARKERMEER,
THE NETHERLANDS

2. What are natural foreshores?
Long term safety:
Marshes grow
with SLR
reefs
Marshes, mangroves, reedbeds
Foreshore & beach sand nourishments
Use & produce
ecosystem services
Limited wave reduction
Enhanced wave reduction
Maximized wave reduction

3. What are natural foreshores?
Long term safety:
Marshes grow
with SLR
reefs
Marshes, mangroves, reedbeds
Foreshore & beach sand nourishments
Use & produce
ecosystem services
Limited wave reduction
Enhanced wave reduction
Maximized wave reduction

4. What are natural foreshores?
Long term safety:
Marshes grow
with SLR
reefs
Marshes, mangroves, reedbeds
Foreshore & beach sand nourishments
Use & produce
ecosystem services
Limited wave reduction
Enhanced wave reduction
Maximized wave reduction

5. From coastal to inland applications
Markermeer: 700 km2
Fetch: up to 40 km
Avg. Depth: 2-4 meters
No tides, substantial waves and water level
fluctuations due to wind
Managed unnatural water level:
-0,4 NAP winter
-0,2 NAP summer
Houtridbijk splits lake Markermeer from
lake IJsselmeer
Houtribdijk needs maintenance (26 km)

6. Considerations during design phase
Pilot under the National High water protection programme –
innovation funds:
• Only sand nurishments applied from water - cheaper and faster
• Stable slope – steeper is cheaper
• Account for sediment consolidation of the underground
• Can vegetation aid the stability of
the construction during normal
and extreme situations
• Legal requirements

7. Details design
Section 1 en 4 : sand
Section 2 en 3: top layer mixed with clay
Vak 1 Vak 2 Vak 4 RestvakVak 3
zand
zand
zand
zand
holoceen+zand holoceen + zand
zand
zand

8. • Each section half planted, half empty
• Willow mats with reeds (section 3 and 4)
• Exclosures to define effect of grazing
Role of vegetation
Section 1 Section 2 Section 4Section 3
zand
zand
zand
zand

11. Monitoring
4 years
• Hydrodynamics and meteorology (continuous)
wave- and flow patterns as forcing factor
• Morfodynamics (monthly)
consolidation, erosion/sedimentation due to hydrodynamics
and vegetation
• Vegetation development (2x year)
safety and biodiversity

12. Hs =
0.9 m

13. Water levels under influence of wind

15. Morfological developments - september

16. Morfological developments - october

17. Morfological developments - november

18. Morfological developments - december

19. Morfological developments - january

20. Morfological developments - februari

21. Morfological developments - march

22. Morfological developments- april

23. Morfological developments sept-march
Wind screen
Effect
interpolation
Interaction with dike
Slope
development

24. Analyses slope development

25. Analyses morphological developments
First impressions
• A stable, yet dynamic foreshore
• Steep slope (1 : 10) along the waterline
• Swash-berm up to NAP+0,5 m
• Underwater plateau nearly flat at -1m NAP
• Effect of coarse sand?

26. Sediment grain size

27. Role between mean grain size and slope
Design:
D50 = 200/250 µm  slope 1:30/40
Present:
D50 = 350/400 µm  slope 1:10

28. Next steps
• Monitoring until 2018
• Use of data for improvement and validation of models
• Extrapolation to other locations
• Need for testing of extreme conditions in controlled
flume experiment