1. 1 Futureproof design of flood defences A wide approach… ISFD 2008 – Toronto W.L.A. ter Horst – INFRAM / Delft University of Technology Dr. P. Bernardini – CUR Building & Infrastructure Prof. J.K. Vrijling – Delft University of Technology May 8 th 2008

2. 2 Outline presentation Introduction System analysis of a wide coastal zone Case studies Field tests on the strength of dikes Results and conclusions

3. 3 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

4. 4 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 SeaLand Landward measures

5. 5 Degrees of freedom when designing a flood defence Land Sea

6. 6 System analysis Cause – consequence diagram

7. 7 System analysis (continued) In this study: assumption: infinite strong dikes Storage capacity of transitional zone

8. 8 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

9. 9 Testing strength of grass revetment

10. 10 Applicable in New Orleans? System of two dikes + breakwater (Dijkman, MSc-thesis, DUT) Breakwater

11. 11 Applicable in New Orleans? System of two dikes + foreland (Dijkman, MSc-thesis, DUT) Landreclamation

12. 12 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

13. 13 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 Safety standard 1/10000-years

14. 14 Hondsbossche Seadefence (continued) Future development (based on a sea level rise of 60cm / century) Safety standard 1/10000-years Preliminary overtopping tests show that a allowable overtopping discharge of 30 – 50 l/s/m is feasible

15. 15 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

16. 16 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

17. 17 Thanks for your attention! Report and more information available on: www.comcoast.org www.infram.nl www.hydraulicengineering.tudelft.nl