The future of deltas in the perspective of environmental change

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

4. Main stakeholders City Shipping Nature Agriculture

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

6. Simplified approach River flow Basin Idea: “valve” lowers water levels ...... Tide Dam with valve No dam, originalsituation 30.000 m3/s riverflow, valve 10.000 m2 ...... and keeps salt water outside 5.000 m3/s riverflow, valve 10.000 m2

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

8. Real situation more complex: Effect over wholeperiod Effect duringspringtide No dam Withvalve

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

10. Phuoc Hoa dam Dau Tieng dam Be Tri An dam Thu Dau Mot Dong Nai Sai Gon Possible alternative 1combination 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 Ho Chi Minh City Vam Co Dong Nha Be Hiep Phuoc Long Tau Dong Thap Muoi Cai Mep/ Thi Vai Soai Rap Vam Co Tay Can Gio Vam Co Can Thanh Vung Tau Go Cong East Sea

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

12. 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 Provisional conclusions 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