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Futureproof design of flood defences

A wide approach…

ISFD 2008 – TorontoW.L.A. ter Horst – INFRAM / Delft University of Technology

Dr. P. Bernardini – CUR Building & Infrastructure

Prof. J.K. Vrijling – Delft University of Technology May 8th 2008

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Outline presentation

• Introduction

• System analysis of a wide coastal zone

• Case studies

• Field tests on the strength of dikes

• Results and conclusions

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Introduction

• Future• Climate change• People living in flood prone areas• Focus on environment• Technical & scientific development

• How do we make our flood defences future proof?• Both safe and liveable

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A wide coastal defence zone• Aim:

• Flood defences in a wider perspective• Multifunctional use of flood defences• Gradual transition from sea to land

• Focus on overtopping phenomenon

SWL

Foreland Transitional area Secondary dike

Wide coastal zone

Seaward measures

Primary dike

Sea Land

Landward measures

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Degrees of freedom when designing a flood defence

LandSea

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System analysis

Cause – consequence diagram

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System analysis (continued)

Failure coastal Defence Zone

Failure secondary dike

P I E

Failure primary dike

P I E

Failure water storage

Failure secondary dike due to (wave-)overtopping (causing

erosion of the inner slope)

Water level polder

Overtopping primary

dike

OR

OR

OR

OR

R

In this study: assumption: infinite strong dikes

Storage capacity of transitional zone

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Case study: Applicable in New Orleans?

System of two dikes, primary dike is overtopping resistant (Dijkman, MSc-thesis, Delft University of Technology)

Overtopping resistant dike

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Testing strength of grass revetment

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Applicable in New Orleans?

System of two dikes + breakwater (Dijkman, MSc-thesis, DUT)

Breakwater

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Applicable in New Orleans?

System of two dikes + foreland (Dijkman, MSc-thesis, DUT)

Landreclamation

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Case study: Hondsbossche Seadefence

• Freeboard: +/- 7m in extreme conditions!!• Not enough to fulfill safety standards

Based on a admittable overtopping discharge of 1 l/s/m• Heightening dike or searching for other options!

Current situation

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Hondsbossche Seadefence (continued)

• Calculation based on application of a wide coastal zone failure when there is a considerable amount of

water in the transitional area

1,E-08

1,E-07

1,E-06

1,E-05

1,E-04

1,E-03

1,E-02

8,0 9,0 10,0 11,0 12,0 13,0 14,0

Crest level primary dike [m]

Fai

lure

pro

bab

ility

[-]

Safety standard1/10000-years

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Hondsbossche Seadefence (continued)

Future development (based on a sea level rise of 60cm /

century)1,E-06

1,E-05

1,E-04

1,E-03

1,E-02

2000 2020 2040 2060 2080 2100 2120

Year [-]

An

nu

al f

ailu

re p

rob

abili

ty [

-]

Traditional dike

Overtopping criterion: 50 l/s/m

Coastal defence zone

Safety standard1/10000-years

Preliminary overtopping tests show that a allowable overtopping discharge of 30 – 50 l/s/m is feasible

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Concluding remarks• This study shows the applicability and potential of a

wide coastal defence zone

• Whether the coastal defence zone is the best suitable option for dike improvement is strongly dependable on area specific characteristics

• Effectiveness of a certain measure should be leading?• What’s the influence of the measure on the level of

safety? And on environment and on other aspects concerning liveability

• Which design option to choose? It’s all about optimalisation

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Concluding remarks (continued)

• Which design option to choose? It’s all about finding an optimal solution, taking into account:

- Costs- Environmental aspects- Societal aspects

• Remaining questions:• When can a dike be considered breachfree?

ongoing research in the Netherlands

• How to communicate to the public?one of the main issues in the ComCoast-project

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Thanks for your attention!

• Report and more information available on:

www.comcoast.org

www.infram.nl

www.hydraulicengineering.tudelft.nl