Sea level rise and its danger for the Belgian coast

1. Sea level rise and its danger for the Belgian coast ir. Toon Verwaest ODINAFRICA course – 13 november 2006 – Oostende

2. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 What is Flanders Hydraulics Research? Definition(s) sea level rise Measurements sea level rise Coastal defence from the perspective of sea level rise The coastal landscape from the perspective of sea level rise

3. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 What is Flanders Hydraulics Research? • service of the Flemish administration (ministry Mobility and Public Works) • internal consulting • knowledge area is “water” (ship maneuvring in undeep water, coastal defence, ports, navigable waterways, sluices…) • physical models, numerical models, measuring networks in situ, databanks, laboratory experiments

4. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Definition(s) sea level rise • Reference level on land : “relative sea level” (3 different reference levels) • Relative sea level movements (ca. 10 different phisical processes, taking place on very different timescales and spatial scales) • time scale < 1 year • time scale > 1 year  “mean sea level”

5. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006

6. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006

7. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006

8. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Bewegingen relatieve zeespiegel op tijdsschaal < 1 jaar

9. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Bewegingen relatieve zeespiegel op tijdsschaal > 1 jaar

10. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Measurements of relative sea level rise • Relative to the top of quay walls in harbours : maregraphs (100 year data set) • Relative to the top of pleistocene subsoil : quartair-geology (10.000 jaar data set)

11. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 18 cm / eeuw

12. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 7 cm / eeuw 70 cm / eeuw

13. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006

14. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Coastal defence from the perspective of sea level rise • Scenarios of relative sea level rise in 21st century : from only 10 cm to almost 100 cm • …and the next centuries of the 3rd millenium : ~ 10 m in the year 3000 • Increase floodable land (the coastal lowlying areas) • Increase failure probability of the coastal defence

15. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Increase floodable land :

16. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Increase failure probability of coastal defence : ca. 0,5 m higher sea level translates into a factor 10 increase in failure probability ! [ this is because the failure probability of a coastal defence is determined (in large part) by the storm surge level] … in addition, there are expactations that the storm climate in the North Sea will worsen : more (frequent) extreme winds

17. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 COASTAL DEFENCE POLICY = GROW WITH THE SEA using SAND NOURISHMENTS • To protect 1 km of coast ~ for every 10 cm sea level rise 100.000 m3 sand • flexibel technique (<-> hard coastal defences such as sea dike structures) • maximum societal benefits : • + recreational beach • + ecology • + landscape • Work with nature : sedimentation of natural sand transport • Important increase of finances for coastal defence (~ factor 3 in 2050 !) • “seaward solution”

18. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 The coastal landscape from the perspective of sea level rise • 21st century : • Damages of the coastal defence caused by storm surge (erosion of dunes, damages to buildings on the coastal defence…) • “seaward solution” with sand nourishments (to grow with the sea) • 3rd millenium : • managed retreat = change the functions of the land near the coastline (~ a different spatial planning) = “landward solution” (<-> “seaward solution”)

19. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 SAND NOURISHMENT, example : De Haan

20. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 SAND NOURISHMENT, example : Oostende

21. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 MANAGED RETREAT, example : UK : nature areas in stead of farmland

22. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 MANAGED RETREAT, example : COMCOAST european project

23. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Other type of MANAGED RETREAT : Controled flooding areas alongside rivers, Thereby also decreasing the water level in the river

24. Sea level rise and its danger for the Belgian coast – ir. Toon Verwaest – 13 november 2006 Other type of MANAGED RETREAT: Projects to create nature areas (not triggered by a coastal defence problem) Sea inlet “slufter” (~1 ha) near borderwith France Increasing the “Zwin” salt marches (~100 ha) near border with The Netherlands