The document discusses changes over time in the dynamic management of foredunes in the Netherlands. It describes how policy shifted from defensive to offensive, allowing coastal retreat to be stopped and sand supply to the foredunes to increase. Graphs show increases in sand volumes in foredunes from nourishment projects over time. The document also contrasts short and long sand transport gradients between the beach and foredune and different foredune development types. It evaluates dynamic projects like the Sand Engine and foredune remobilization, and concludes a dynamic approach is preferable to allow foredunes to grow and adapt to sea level rise while noting some risks to consider.

1. Bas Arens, Bureau for Beach and Dune Research
Amsterdam
Dynamic foredune
management in the
Netherlands

2. Change in policy
= change in foredune development
• From defensive to offensive
• Coastline retreat was stopped
• Sand supply to (fore)dunes

3. 0
20
40
60
80
100
120
1100
1150
1200
1250
1300
1350
1400
1965 1975 1985 1995 2005
nourishedvolume(m3/m)
volumeforedunes(m3/m)
volume foredunes beach nourishment shoreface nourishment

4. 0
10
20
30
40
50
60
S R P
percentageofcrosssections(%)
Foredune type
Dutch Coast
1966-1988 1988-2008

6. foredune
2130 Grey dunes
2120 White dunes
2110 Embryonic dunes
beach
wind
salt
sand (from beach)
Short gradient – no sand sharing

7. Foredune
development
Schouwen
1997-2012

9. © RWS www.kustfoto.nl
Response: sand sharing system

10. foredune
2130 Grey dunes
2120 White dunes
beach
wind
salt
sand (from beach and foredune)
beach (wave erosion)
zand (wind erosion)
Long gradient – transfer zone

11. 1
10
100
1000
10000
100000
0 200 400 600 800
trappedweight(gr)
distance from dunefoot (m)

12. 0
10
20
30
40
50
60
70
80
Delta Holland Wadden NL
percentageoftotal(%)
stable, no dynamic processes moderate sand exchange intensive sand exchange

13. “Dynamic” projects
• Sand engine
– Offensive strategy
• Noordwestkern
– Foredune remobilisation

14. ©: Rijkswaterstaat/Joop van Houdt

15. Sand catchers Sand engine (Zandmotor)

17. Changes in height 2013-2014

18. Sand catchers Noordwestkern

19. Conclusions
• Dynamic foredunes preferable?
– Long transport gradient
– White dunes need sand
– Grey dunes need (a little) sand
– Stop acidification of soils
– Dunes can grow with sea level rise
• Offensive strategy
– Risk for block in sand transfer
– Long term effects on dunes unclear