COMRISK Workshop Norden 12./13. May 2004

1. COMRISK Workshop Norden12./13. May 2004 Failure probability of the Ribe sea defence Andreas Kortenhaus Leichtweiß-Institut for Hydraulics (LWI) Dept. Hydromechanics and Coastal Engineering Beethovenstr. 51a 38106 Braunschweig

2. Contents • Introduction • Location of Ribe sea defence • Input parameter • Deterministic calculations • Uncertainties • Probabilistic calculations • Overall failure probability • Summary / concluding remarks

3. On the richness of English language • Question: how is the German word “schräg”, Dutch: “”, Danish “” translated into English • leaning (in terms of the tower of Pisa or the church in Norden) • oblique (in plan view for wave attack) • diagonal • sloping (in terms of slopes of a structure) • inclining (in terms of walls) • tilted (in terms of very large angles) • at an angle (in terms you do not know exactly)

4. Definition of risk Failure probability Pf Expected damage and consequences of flooding E(D) Flooding risk Rfc = ( Pf )S ·E(D)

5. Location of project area

6. N Map of Ribe area and sea defences Northern wing dike Contiguous dike line Outlet Darum Potential flooding area Outlet Konge-Å Main dike line Ribe Ribe-Å Sluice Ribe-Å Ribe Outlet V. Vedsted Ebb way Southern wing dike Mandø Contiguous dike line

7. Standard dike profile Bk= 2,50m 1:10 DWL = + 5,22 m 1:3 dfr db Clay layer d 1:100 hk= 6,88m Sandcore ht= 2,38m 0,00 m DVR90

8. Ribe sluice 5,88 m Outer flood gates (closed) 5,78 m DWL = 5,22 m 0 mDVR90 -3,60 m Sole paving Chamber walls Outer floodgates Inner floodgates

9. Outlet Konge-Å Stone mattress Clay layer Sandcore Grass layer Berm 6,88 m 1:3 1:2 5,22m DWL Storm gate 4,23 m 1:7 2,50 m 0 m DVR90 Filter gravel Drainage -2,00 m Sole (concrete) Floodgate Pavement

10. N Location of profiles analysed Outlet Darum 14499 Water levelmeasurements Outlet Konge–Å Fanø Wave rider Fanø 10403 Profile 290 Sluice Ribe-Å 9400 8422 Ribe 6644 Profile 270 Profile 250 Wind measurements 3156 Outlet V. Vedstedt Profile 1 Mandø Dike profiles Sluices / outlets

11. N Adaption of profile data to model – profile 3156 Ribe 3156

12. N Adaption of profile data to model – profile 6644 Ribe 6644

13. N Adaption of profile data to model – profile 8422 8422 Ribe

14. N Adaption of profile data to model – profile 9400 9400 Ribe

15. N Adaption of profile data to model – profile 10403 10403 Ribe

16. N Adaption of profile data to model – profile 14499 14499 Ribe

17. Typical input parameter for two sections Bk= 2,00m km 6644 Hs, Tp, θ 1:10 1:2,6 DWL = + 5,22 m dfr Clay: gK, gKr d 1:12 Sand: gS, gSr, qs hk= 7,08m ht= 2,66m 0,00 m DVR90 2 [KN/m ] H = 1,51 m d = 1,0 m c = 15,0 s fr u 3 g KN/m T = 4,89 s = 17,0 d = 0,05 [m] p K G 3 3 g g KN/m [KN/m ] θ = 20 ° = 20,0 = 19,0 Kr S 2 3 g KN/m [KN/m ] t = 6,5 h c = 35,0 = 22,0 s s Sr 2 KN/m d = 2,65 m c = 10,0  = 40,0 [°] ss s km 8422 Bk= 2,80m Hs, Tp, θ 1:11 DWL = + 5,22 m 1:3,1 dfr Clay: gK, gKr d 1:20 Sand: gS, gSr, s hk= 6,73m ht= 1,92m 0,00 m DVR90 2 [KN/m ] H = 1,47 m d = 1,0 m c = 15,0 s fr u 3 g KN/m T = 6,01 s = 17,0 d = 0,05 [m] p K G 3 3 g g KN/m [KN/m ] θ = 20 ° = 20,0 = 19,0 Kr S 2 3 g KN/m [KN/m ] t = 6,5 h c = 35,0 = 22,0 s s Sr 2 KN/m d = 3,3 m c = 10,0  = 40,0 [°] ss s

18. Failure modes for dike profiles Global failure modes: Overflow Overtopping Dike breach Dike slid Failure modes shoreward slope: Velocity overflow Velocity overtopping Gras erosion Clay erosion Infiltration Kappensturz Phreatic line Clay uplift Clay slid Bishop shoreward slope Sand erosion Failure modes seaward slope: Revetment stability Impact Revetment uplift Velocity wave run-up Gras erosion Clay erosion Phreatic line Cliff erosion Bishop shoreward slope Clay Layer Core Internal failure modes: Piping Matrix erosion

19. Failure modes Ribe sluice Global failure modes: Overtopping Overflow Hydraulic uplift

20. Results of deterministic calculations

21. Results of sensitivity analysis

22. Uncertainty analysis of water level

23. Correlation of water level and wave heights

24. Uncertainties of input parameter

25. Fault tree calculations

26. Probabilistic results (overview)

27. Probabilistic results of scenario approach (sect. 10403)

28. Probabilistic results (sensitivity analysis)

29. Definition of sections of Ribe sea defence

30. Overall failure probability for Ribe sea defence

31. Conclusions • study of input parameters • good representation of dike cross sections • soil parameters taken from measurements if possible • deterministic calculations of all cross sections and sluices • overtopping failure at sluice for design conditions • grass erosion failure for all sea dikes • uncertainty analysis of input parameters • detailed study of water level • correlation of water levels and wave heights • probabilistic calculations of all cross sections and sluices • reduction of scenario tree to most important elements • overall failure probability for dikes in the range of Pf = 10-5 • failure probability for sluice in the range of Pf = 10-1 • Overall failure probability of sea defence • sluice and outlets to be considered correctly • overall probability governed by dike failure probability

32. Thank you very much for your attention Andreas Kortenhaus Leichtweiß-Institut für Wasserbau Technische Universität Braunschweig Tel.: 0531 / 391-3981 E-mail: a.kortenhaus@tu-bs.de LWI