Sustainable Water Management

Examples from Sahara, Xinjiang(China) and Okawango (Botswana) regions

Wolfgang Kinzelbach, Tobias Siegfried, Philip Brunner, Peter Bauer, Fritz Stauffer

Institute for Hydromechanics and Water Resources ManagementETH Zurich, Switzerland

Algeria

Tunisia

Libya

Recharge throughprecipitation

Pumping

Evaporationfrom Chotts

~80 m3/s

~10 m3/s

~30 m3/s

~5 m3/s

Outflow to sea

N

~ 100 km

Overexploitation of the North-West Sahara Aquifer System (SASS)

PhD thesis Tobias Siegfried (2004)

What counts is the price of exploitation

• Investment cost and operational costs– Energy for pumping and conveyance

– Lift of more than 200 m not economically feasible

• Deterioration of water quality– Brine back flow from Chotts (gradient reversal )

– Saline intrusion from underlying aquifer

– Saline intrusion from the Mediterranean Sea

At present pumping, the Nefzawa oases are doomed

Oasis

Backflow of brine from Chotts …

... leads to die-off of oases

What can be done ? • Continue present exploitation

– Economically infeasible drawdown and unacceptable deterioration of water quality before 2050.

• Rational exploitation over limited time– Minimizing the price of the resource under quality

constraints over a given time horizon.– Gaining time for real solutions.

• Real solutions– Alternative water sources: e.g. desalination.– Structural change: water saving and decrease of irrigated

perimeters.

Tool: Model to predict consequence of strategies

Strategies for exploitationOne big well field in vicinity of users

Low transport cost, high pumping cost,early exhaustion due to local drawdown

Spread-out well fields atdistance from the users

High transport cost, low pumping cost,well-distributed drawdown

12

3

45

6

Pumping from IC requires larger capital investment than pumping from TC

IC contra TCAlternating between well fields

Actively pumping

Recovering

TC

IC

Conclusions Example 1 • Minimize costs of water over given time period

and fulfill constraints, gain time.• Provision cost is growing in time (while wells

spread areally and to IC and alternating).• International cooperation in utilizing the resource

brings slight advantages.• Real long-term solution yet to be found.• Main problem is of social and political nature.

Conservation of oases culture at present level is in the long run only possible through high subsidies.

Causes

Water, SaltsWater vapor

Without drainage: Salt accumulation

natural

irrigated

Groundwater table rise, capillary rise,high evaporation, salt deposition

Water, Salts

Relevant mechanism in Yanqi

Soil salinization and ecological water demand in Yanqi Basin, Xinjiang(China)

PhD thesis Philip Brunner (ongoing)

First Control PointKaidu River

BostanLake

Kongque River

Qing Shui River

Second Control Point

Huang Shui River

Decline of water level in lake

Die-off of fish

Increase of salinity in lake

(due to doubling of population over the last 50 years)

Soil salinization

Groundwater table rise due to irrigation

Drying up of ”Green Corridor“

Yanqi Basin and its problems

Kaidu River: 100 m3/s

KongqueRiver: 30 m3/s

5 m3/sBostan Lake

40 m3/s

Irrigation: 35 m3/s

ET crop: 20 m3/sET fallow: 10 m3/s

Water balance

Groundwater

Soil

• Reduction of irrigated area• Change to alternative crops• Increase efficiency of irrigation• Deep drainage and other drainage measures• Replace river water by groundwater in irrigation

• Lowering of lake level- Increase of outflow (Salinity control of lake water and power generation)

- Diversion of water around lake (to feed “Green corridor“)

Possible measures

Tool: Model to predict impact of measures

Conclusions Example 2• Solutions for the salinization problem in Yanqi

without production loss exist.• They imply increased production cost.• For the single farmer there is no incentive to change

behavior if water supply is not limited.• A solution for the whole system requires regulation

by the state.• Prediction of ecological consequences of lake

manipulation and monetarization of “Green Corridor”are the most difficult tasks in cost-benefit analysis.

Management of the wetlands of the Okavango Delta (Botswana)

The upstream-downstream problem

The local resource allocation problem

tourism

households industry

mining

and nature ...

Angola Zambia

Namibia

Botswana

Zim

babw

e

Mohembo

PhD thesis Peter Bauer (2004)

Goal of modelingModel to predict size and dynamics of the delta for alternative scenarios

Water

300 m3/s10 m3/s

Dissolved solids

300 000 t/a30 000 t/a

• Water balance components• Area of flooding• Temporal distribution of flooding• Fate of dissolved solids

• Water abstraction of above 30 m3/s upstream of Mohembo seems critical.

• Main impact: Increase of years with extremely small flooded area.

• Dams result in a downstream redistribution of flooded areas.

• Some major impacts cannot be influenced by the riparians (climate and tectonics).

• Solution by upstream-downstream compromiseseems possible through transfer payments.

Conclusions Example 3

Concluding remarks• New techniques: Remote Sensing, modeling,

environmental tracers, geophysics, DGPS, DTM.

• Water management in arid regions is inseparably coupled to salt management.

• All problems have an economic and political dimension, purely technical solutions are rare.

• Water saving in agriculture presents the largest potential resource, at higher price of food.

• Long-term management methods are in high demand.