Large-Scale Coastal Maintenance using Sand Experiences and Experiments in The Netherlands

Large-Scale Coastal Maintenance using SandExperiences and Experiments in The Netherlands

MODEG meeting, March, 11, 2011

Ad van der Spek

Content

1. Introduction

2. Coastal system of The Netherlands

3. Coastal maintenance using sand

fighting structural erosion !

4. Results coastal maintenance

5. Future developments

6. Lessons learned, experiments

data needs

7. Concluding remarks

March 11, 2011Coastal Maintenance in The Netherlands 2


Introduction: sand budget


Introduction: coastal cells


Introduction: coastal profile in dynamic equilibrium

Active coastal zone


The Netherlands: sandy coast

350 km

• Amsterdam

Young dunes

Old dunes

Young dunes

Old dunes

Netherlands• The Hague

March 11, 2011Coastal Maintenance in The Netherlands

How were The Netherlands built?

7


Long-term coastal evolution

supply > demand :

regression

Demand tidal basin

vs.

Supply coast

supply < demand :

transgression

8


Paleo-geography of The Netherlands

5000 BP

demand > supply

2600 BP

demand < supply

9


Holocene sediment budget

1.

2.

2.

3.

4.

sources & sinks

10


Total volume Holocene coastal deposits

( in billion m3 )

lithology volume percentage

----------------------------------------------------------------------------------

sand 151 - 157 67 -70 %

mud 59 - 65 26 - 29 %

peat 11 5 %

----------------------------------------------------------------------------------

Total 226 100 %


Holocene sediment budget - Infilling with time

period perc. volume vol. / yr

(billion m3) (million m3)

----------------------------------------------------------------------------------------

8000-5000 BP 60 % 136 41

5000-3000 BP 30 % 67 27

Since 3000 BP 10 % 23 7

----------------------------------------------------------------------------------------

12

“The Hague, we have a problem !”


Sediment balance Dutch coast

Western Scheldt

Coastal

Foundation

Wadden Sea


Solution: we do it ourselves !!

Keeping up by nourishing sand

14


What to do ?

Coastal Maintenance Programme

Yearly monitoring of coastline: jarkus

Bring sand where you need it

Yearly nourishment budget: 12 Mm3 sand

Why nourishing sand?1. Compensating sand deficit

2. Feeding sediment fluxes

3. Building sand buffer


Soft sea defence

Hard defence

Soft defence

Hard defence

Soft defence

350 km

• Amsterdam


Why nourishing?

1. Fighting structural erosion• Sand balance Dutch coast negative• 1965-1990: -6,5 Mm3 / yr• Dynamic Maintenance (preferably sand …)

2. Reinforcing the coast• upfront compensation SLR• upscaling: mega-nourishments, Sand Engine

3. Land reclamation• near future ?


How to nourish ?

1. Beach

2. Shoreface

3. Channel

4. Combinations

Future: directing natural processes ?


Nourishment policy since 1990

1990 – 2000:

6 Mm3/year

2001 - :

12 Mm3/year

1990 – 2000:

6 Mm3/year

2001 - :

12 Mm3/year

19


0

5

10

15

20

jaar

Su

pp

letie

ho

ev

ee

lhe

de

n (

10

6 m

3)

0

10

20

30

40

BK

L-o

ve

rsc

hri

jdin

ge

n (

%)Onderwaters uppleties

Strands uppletiesBKL-overs chrijdingen

refe

rence

coas

t lin

e pro

ble

ms

(%)

1991

2006

0

5

10

15

20

jaar

Su

pp

letie

ho

ev

ee

lhe

de

n (

10

6 m

3)

0

10

20

30

40

BK

L-o

ve

rsc

hri

jdin

ge

n (

%)Onderwaters uppleties

Strands uppletiesBKL-overs chrijdingen

refe

rence

coas

t lin

e pro

ble

ms

(%)

1991

2006

Result 1: coast line position maintained

20


Result 2: outbuilding of coastal dunes !!

Wassenaar

Katwijk aan Zee

Noordwijk aan Zee


dune growth 1998 - 2007pro-active

nourishment approach is succesfull

from: Arens, 2010

22


today 1990

Prograding dune at Bergen aan Zee

23


Safety against flooding

residual strengthdays / meters

MSL

- 20mdunes

beach

shore face

dunes

Am sterdam

The Hague

Rotterdam


basal coast line

coastal foundation

years / km

decades – centuries / 10’s – 100’s km

MSL

- 20m

days / metersdunes

coast line

coastal foundation

SustainableSafety against flooding

residual strength

pro-active

nourishment policy

Conclusion:

• The balance concept works

sea-level rise ≠ coastal erosion !• Outbuilding: we can tip the balance• Future: maintaining coast with sand

• Strict monitoring:• Coastline position: decision on nourishing• Development shoreface nourishments: learning• Coastal foundation: yes, but how ??



Coastal Foundation

Western Scheldt

Coastal

Foundation

Wadden Sea

active sand sharing coastal system


Challenge: explore feasible ways of upscaling

12 Mm3/year

20 Mm3/year

85 Mm3/year


Building a sand buffer …


Kijkduin 2


The new Delfland coast


Pilot Sand Engine

• Surplus of sand, distributed by tide/waves/wind• 20 mln m3• Initial design: Ca 100-150 ha,

1000 m seaward• Total budget 70 Meuro• Realisation planned 2010-2011

Artist impressionwww.kustvisiezuidholland.nl/zandmotor

Holland Coast

Sand Engine


• Joint initiative:• Province• National government• Water Board• Local authorities• NGO’s

Pilot Sand Engine

ambition agreement

Co-financing:• 17 %• 83 %

Sand Engine objectives

Long-term: guarantee coastal safety by promoting dune development

Medium-term: knowledge development, innovation

Short-term: create space for nature and/or recreation



Sand Engine design

• Dynamic design ( not a well defined end result )

• Dynamic optimization of different functions

• Balance between long term benefits (safety against flooding) and short term benefits (nature and recreation)

• Challenge: management of expectations with different stakeholders

(zeetorenhvh)


Monitoring and evaluation

monitoring morphology hydrology ecology

tourism management risks

(zeetorenhvh)

evaluation 5 years: 2015 10 years: 2020 20 years: 2030

Lessons learned (1): data needs

• System analysis• Reconstruction coastal evolution• Sediment balance

• Volume nearshore sand resources

Information enables design maintenance strategy

• Monitoring

• Relative sea-level rise• Coastal state (yearly)• Frequent monitoring large nourishments

(learning by doing)


Lessons learned (2): sand as a resource

• Sufficient nearshore sand resources only on certain stable broad shelves

• In other cases sand resources insufficient or sufficient only for nourishing coastal hot spots

• For most shelves sand resources have not yet been investigated



Sea-level low-stand river deposits

Sand deposits can be unexploitable:

• too far from the coast

• at too deep water

• buried under non-sandy sediments


Global nearshore sand resources

Sand resource > 1 km3 / 100 km

Sand resource between 0,1 and 1 km3 / 100 km

Lessons learned (3)

Learning by doing:• Step by step• Co-operation with other countries

• EU-programmes:> NOURTEC: shoreface nourishing> COAST3D: nearshore processes> SANDPIT: effects of sand extraction> SAFECOAST, EUROSION, CONSCIENCE etc.

• Data availability• Central storage?• Flexible formats?

> Fitting in relevant, extra information• Monitoring programmes or project-related acquisition?



Concluding remarks: What is nourishing ?

Compensation of sand deficits

Feeding of sediment fluxes

Building a sand buffer

• Flexible• Tailor-made• Relatively cheap• Swift reaction to unexpected changes


Concluding remarks

Analysis sediment balance crucial

Available resources?

Sand volume?

potential resources? > sand captured in reservoirs> restoring sediment supply

Sand Engine experiment

case study for european coastal community?


Thank you for your attention !

Large-Scale Coastal Maintenance using Sand Experiences and Experiments in The Netherlands

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