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 Management ETH Zurich, Switzerland
Algeria
Tunisia
Libya Recharge through
precipitation
Pumping
Evaporation from 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 exploitation
One big well field in vicinity of users
Low transport cost, high pumping cost, early exhaustion due to local
drawdown
Spread-out well fields at distance from the users
High transport cost, low pumping cost, well-distributed drawdown
1 2 3
5 4 6
Pumping from IC requires larger capital investment than pumping from TC
IC contra TC Alternating 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, Salts
Water 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 Point
Kaidu River
Bostan Lake
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
Kongque River:
30 m3/s 5 m3/s Bostan Lake
40 m3/s
Irrigation: 35 m3/s
ET crop: 20 m3/s ET 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
Zimbabwe
Mohembo
PhD thesis Peter Bauer (2004)
Goal of modeling
Model to predict size and dynamics of the delta for alternative scenarios
Water
300 m3/s
10 m3/s
Dissolved solids
300 000 t/a
30 000 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 compromise seems 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.
