Christian Leduc, IRD, UMR G-EAU, Montpellier, France Presentation given during the 5th GEF Biennial International Waters Conference in Cairns, Australia (during the pre-conference workshop for freshwater ecosystems, Global Changes and Water Resources Workshop).

1. The Fifth GEF Biennial International Waters Conference, Cairns, 26-29 October 2009
Global Changes and Water Resources Workshop
The Merguellil catchment (central Tunisia):
towards an integrated study of
water resources and water uses
Christian LEDUC
Gestion de l'Eau, Acteurs,
IRD, UMR G-EAU, Montpellier, France
leduc@ird.fr

2. Impacts of the Global Change on the hydrological cycle
An attempt to integrate studies at a relevant scale
A situation typical of the Mediterranean environment
(and many other semi-arid cases)
GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

3. Tunis
250 mm
500 mm
Merguellil
National context: limited resources, highly variable in time and space
increasing demand for population, agriculture, tourism
decision of a maximum use of WR (goal of nearly 100 %)
Regional context: semi-arid catchment (> 2000 km2
)
increasing uses up to overexploitation
water export to the coastal region
GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop
Kairouan

4. Global change
Rainfall: 200 to 550 mm.yr-1
highly variable: ex 1969
no long-term trend
Increasing population
(0.25 % yr-1
1994-2004
2.3 % yr-1
1984-1994)
Intensified agriculture
grazing lands turned into fields
traditional crops replaced by irrigated crops
Many water and soil conservation works
Big dams
GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

5. Water and soil conservation works
Increasing number of Water/Soil Conservation works
(bench terraces, 48 small dams)
For limiting erosion on the slopes
silting up of the big El Haouareb dam
Rarely in agreement with local customs and wishes
Increase in green water, locally
Increase in stored water (small reservoirs)
Clear decrease in blue water at the catchment outlet
Fundamental maintenance of WSCW:
quick loss of efficiency
final result often worse than nothing
Limited development of new uses from the new storages
2003
1970
1988
GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

6. The El Haouareb big dam
Protection against floods + Provision of water to an irrigated scheme
Total change in groundwater recharge
(location, processes, flow, quality):
- no river flow downstream
- the dam is often dried up
- ≈ 60 % of the dam water infiltrates to
the karst
- tracing of the reservoir evaporation
(reservoir, downstream)

7. Groundwater upstream
3 "small" aquifers
1 deliberately overexploited by the State for
exporting drinking water to the coast
Enhanced leakage from the rivers to the aquifers
Increasing pumping for irrigation and potable water
Groundwater upstream
1 thick aquifer, overexploited for potable water, public and private irrigation
No enforcement of the law protecting
the aquifer
90
95
100
105
janv-92 janv-94 janv-96 janv-98 Janvier00 janv-02

8. Some technical remarks
Contradictory impacts of conservation works:
prevent siltation but decrease the exploitable water resource
The big dam is often empty, because of the unexpected karstic loss
Physical models propose contradictory explanations
Possible consequences of overexploitation:
deeper pumping more difficult and more expensive
resort to more salted water
GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

9. GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop
Socio-economical surveys
Typology of farms and farmers
Behaviour of farmers facing changes
in their physical environment (climate, soil fertility)
in the regulations (law, water price, technical constraints)
in the external market
Cooperation/competition between farmers
(land rental, water sale) (family vs speculators, large vs small)
Spatial scales of benefit: personal-local-regional-national

10. GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop
Socio-economical surveys
Proposal of measures for protecting the water resource
acceptability - efficiency
Unexpected impacts:
increasing irrigated areas after subsidising drip irrigation
Social equity vs profitability
Institutional analysis
lack of coordination inside the same Ministry
limited involvement in local top-down associations

11. Conclusion
To manage together water supply and water demand
To integrate technical and socio-economical aspects
To build long-term sustainable proposals
Natural and human complexity beyond our models
Already in official files:
interconnection of big dams in Central Tunisia
transfer channels from Northern Tunisia
GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop

12. GEF International Waters Conference, Cairns, Oct. 2009, Global Changes and Water Resources Workshop
Second International Conference on Climate, Sustainability and
Development in Semi-arid Regions - ICID 2010
Fortaleza, 16-20 August 2010
www.icid18.org
Contribution to the Rio+20 UN conference on development and environment
1) Climate and Environment
2) Climate and Sustainable Development
3) Governance and Sustainable Development
4) Policy Processes and Institutions.
Submissions of papers, panels, round tables welcome