Bas Arens, Bureau for Beach and Dune ResearchAmsterdam

Dynamic foredunemanagement in the

Netherlands

Change in policy= change in foredune development

• From defensive to offensive

• Coastline retreat was stopped

• Sand supply to (fore)dunes

0

20

40

60

80

100

120

1100

1150

1200

1250

1300

1350

1400

1965 1975 1985 1995 2005

no

uri

sh

ed

vo

lum

e (

m3/m

)

vo

lum

e f

ore

du

ne

s(m

3/m

)

volume foredunes beach nourishment shoreface nourishment

0

10

20

30

40

50

60

S R P

pe

rce

nta

ge

of

cro

ss

se

cti

on

s (

%)

Foredune type

Dutch Coast

1966-1988 1988-2008

foredune

2130 Grey dunes2120 White dunes

2110 Embryonic dunes

beach

wind

salt

sand (from beach)

Short gradient – no sand sharing

Foredune development

Schouwen1997-2012

© RWS www.kustfoto.nl

Response: sand sharing system

foredune

2130 Grey dunes2120 White dunes

beach

wind

salt

sand (from beach and foredune)

beach (wave erosion)

zand (wind erosion)

Long gradient – transfer zone

1

10

100

1000

10000

100000

0 200 400 600 800

tra

pp

ed

we

igh

t (

gr)

distance from dunefoot (m)

0

10

20

30

40

50

60

70

80

Delta Holland Wadden NL

perc

en

tag

e o

f to

tal

(%)

stable, no dynamic processes moderate sand exchange intensive sand exchange

“Dynamic” projects

• Sand engine

– Offensive strategy

• Noordwestkern

– Foredune remobilisation

©: Rijkswaterstaat/Joop van Houdt

Sand catchers Sand engine (Zandmotor)

Changes in height 2013-2014

Sand catchers Noordwestkern

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