1. The future of deltas in the perspective of environmental change Harmonizing human interests and environmental interest is one of the largest challenges for human mankind 6th Lustrum of theWaterbouwdispuut

2. The future of deltas Ho Chi Minh City and its estuarine and tidal river delta (a typical example of a growth economy in SE Asia) The Southwestern Dutch delta (a typical example of an established protected delta seeking for harmony with nature)

3. Sai Gon Long Tau Vam Co Vam Co Tay Vam Co Dong Dong Nai Soai Rap Can Gio Vung Tau Ho Chi Minh City Nha Be Go Cong East Sea Be Can Thanh Hiep Phuoc Dau Tieng dam Phuoc Hoa dam Tri An dam Cai Mep/ Thi Vai Dong Thap Muoi Thu Dau Mot The problems of HCM City March 29 2011 Hanoi

4. Main stakeholders Shipping Nature Agriculture City

5. Sai Gon Long Tau Vam Co Vam Co Tay Vam Co Dong Dong Nai Soai Rap Can Gio Vung Tau Ho Chi Minh City Nha Be Go Cong East Sea Be Can Thanh Hiep Phuoc Dau Tieng dam Phuoc Hoa dam Tri An dam Cai Mep/ Thi Vai Dong Thap Muoi Thu Dau Mot Dam Vung Tau – Go Cong: the IJssellake solution March 29 2011 Hanoi

6. Idea: “valve” lowers water levels...... River flow Tide 5.000 m3/s river flow, valve 10.000 m2 30.000 m3/s river flow, valve 10.000 m2 Basi n Dam with valve No dam, original situation...... and keeps salt water outside Simplified approach

7. Result depends on: River flow Valve size Basin size No dam, original situation Basin 200 km2 Basin 300 km2 River flow 30.000 m3/s

8. Real situation more complex: Effect over whole period Effect during springtide No dam With valve

9. Shipping Maximum permissible velocity ~ 4 knots = 2 m/s Necessary width ~ 200 – 300 m But: valve closed during flood → locks

10. Sai Gon Long Tau Vam Co Vam Co Tay Vam Co Dong Dong Nai Soai Rap Can Gio Vung Tau Ho Chi Minh City Nha Be Go Cong East Sea Be Can Thanh Hiep Phuoc Dau Tieng dam Phuoc Hoa dam Tri An dam Cai Mep/ Thi Vai Dong Thap Muoi Thu Dau Mot Possible alternative 1 combination of IJssellake and Haringvliet solution Idea: Lowering level HCMC Lowering salinity Dong Thap Muoi Maintaining tide and salt Can Gio Maintaining shipping route Cai Mep

11. Sai Gon Long Tau Vam Co Vam Co Tay Vam Co Dong Dong Nai Soai Rap Can Gio Vung Tau Ho Chi Minh City Nha Be Go Cong East Sea Be Can Thanh Hiep Phuoc Dau Tieng dam Phuoc Hoa dam Tri An dam Cai Mep/ Thi Vai Dong Thap Muoi Thu Dau Mot Possible alternative 2 Idea: Lowering level HCMC Lowering salinity Dong Thap Muoi Maintaining tide and salt Can Gio Maintaining shipping route Cai Mep

12. Provisional conclusions Idea promising for lowering water levels with moderate river flows For extreme river flow, it will be difficult For detailed studies consistent data needed (salt, velocities, discharges, ….) Take other issues into account, e.g. subsidence Dutch experience: soil subsidence more important than sea level rise

13. The Dutch Southwestern Delta Perceived problems

14. The Dutch Southwestern Delta Perceived problem: no salt-fresh water gradient

15. The Dutch Southwestern Delta Perceived problem: Stagnation due to absence of fresh/salt water gradient

16. The Dutch Southwestern Delta Perceived problem: Starving intertidal areas

17. The Dutch Southwestern Delta Perceived problem: Restoration of intertidal, low- dynamic regions

18. The Dutch Southwestern Delta Solution: restore intertidal areas by depoldering but polictically unacceptable

19. The Dutch Southwestern Delta Political solution: restore intertidal areas by creating these areas in the current outerdike space! Nonsense!

20. Conclusions Growth economies are facing a challenging time: how to combine economic growth with environmental concerns Established economies are facing a challenge as well: how to restore environmental values against economic interests