The future of deltas in the perspective of environmental

changeHarmonizing human interests and

environmental interest is one of the largest challenges for human

mankind

6th Lustrum of theWaterbouwdispuut

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)

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 damPhuoc Hoa dam

Tri An dam

Cai Mep/ Thi Vai

Dong Thap Muoi

Thu Dau Mot

The problems of HCM City

March 29 2011Hanoi

Main stakeholders

Shipping

NatureAgriculture

City

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 damPhuoc Hoa dam

Tri An dam

Cai Mep/ Thi Vai

Dong Thap Muoi

Thu Dau MotDam

Vung Tau – Go Cong: the IJssellake

solution

March 29 2011Hanoi

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

Basin

Dam with valve

No dam, original situation

...... and keeps salt water

outside

Simplified approach

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

Real situation more complex:

Effect over

whole period

Effect during

springtideNo dam

With valve

ShippingMaximum permissible velocity ~ 4 knots = 2

m/s

Necessary width ~ 200 – 300 m

But: valve closed during flood → locks

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 damPhuoc Hoa dam

Tri An dam

Cai Mep/ Thi Vai

Dong Thap Muoi

Thu Dau Mot

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

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 damPhuoc 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

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

The Dutch Southwestern Delta

Perceived problems

The Dutch Southwestern Delta

Perceived problem: no

salt-fresh water gradient

The Dutch Southwestern Delta

Perceived problem:Stagnation due to

absence of fresh/salt water

gradient

The Dutch Southwestern Delta

Perceived problem:Starving intertidal

areas

The Dutch Southwestern Delta

Perceived problem:Restoration of intertidal, low-

dynamic regions

The Dutch Southwestern Delta

Solution: restore intertidal areas by depoldering but

polictically unacceptable

The Dutch Southwestern Delta

Political solution: restore intertidal areas by creating these areas in the current outerdike

space!Nonsense!

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