Water resources in Tunisia

Introduction

Because of its geographical location, Tunisia undergoes the influence of two climate types : the Mediterranean type in the north and the Saharan type in the south which are at the origin of space time variability in water resources. Therefore, the annual rainfall average varies from less than 100mm in the extreme south to more than 1500 mm in the extreme northern parts of the country. Tunisia is, then, a country with relatively limited renewable water resources.

Despite such a restrictive situation, Tunisia could satisfy the requirement of water for all sectors even during drought periods. The rate of drinking water supply reached 100% in urban areas and more than 80% in rural areas without rationing even in shortage periods.

Because of its rooted traditions and political will, Tunisia managed to successfully implement an ambitious strategy to mobilize and develop water resources to satisfy the increasing needs which arise in relation with the demographic rise and the socio-economic development.

In fact, the management of water demands represents a fundamental axis in the general water policy for the future in order to control water demands of various sectors mainly in agriculture (using 80% of water resources) and to delay, as far as possible, the reuse of non-conventional water resources. Management tools are based on saving, developing and rationalisation of water use particularly in agriculture.

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Water potential

In Tunisia, water resources were evaluted in 2000 to 4825 Millions of Mm³, with 2700 Mm³of surface water and2125 Mm³ of ground water.

Surface water

Throw out of all the country, the mean of the rainfall is about of 230 mm/year, i.e. 36 billions of m³/year. It varies in time and space from less than 100 mm in the extreme south to 1500 in the extreme north-west (Map of Tunisian inter-annual isohyets).

Surface water comes from four natural distinguished areas. The extreme northern part representing only 3% of all four areas provides an average of 960 Mm³/year of surface water, i.e. 36% of all the country. The northern part provides an average of 1230 Mm³/year, i.e.46 % of the total surface water potential. The central part, including the catchment basins of Nebhana, Marguellil, Zéroud and the Sahel, prove an average of 320 Mm³/year, i.e. 12 %. The southern part, which represents 62 % in area, 190 Mm³/year, and only i.e.(190/2700) %.

The amount of surface water of 2700 Mm³, is the average calculated of a 50-year period. Resources which can be mobilized are estimated at 2 170 Mm³, 85% of which come from the rain off and 15% from basic flow inputs. Today, 1800 Mm3 are already mobilized, i.e. 83%.(See the map of Tunisian Dams).

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Ground waters

Ground water ressources are estimated at 2125 Mm3 out of which 745 Mm3 come from aquifers and 1380Mm3 from the confined aquifers of witch 650 Mm3 are non renewable resources.
The north of Tunisia has 55 % of ground water resources, the central part contains 30%, whereas the south contains only 15%. For deep waters, the south contains 58 % of esresources, the centre contains 24 %, whereas the north contains only 18 %.
Ground water abstraction reached 780 Mm3 in 2000, i.e. 105% ( from more than 90000 shalow wells).
Concerning the confined aquifers, they are exployted in the rate of 1100 Mm3 in 2000, by 3500 deep wells.
The global rate of resources mobilization in Tunisia is, then, 1800 Mm3 for surface water and 1880 Mm3 for ground water, i.e. a total of (rate of 86%) 3680 Mm3.

The following table gives us a global report on surface and ground water:

		Global potential (in millions of m3)	Resources which can be mobilized ( millions of m3)	mobilization by abstraction (millions m3)	Ratio of mobilization
Surface water		2700	2170	1800	83%
Ground waters	Shallow aquifers	745	745	780	105%
	Deep aquifers	1380	1380	1100	80%
TOTAL		4825	4295	3680	86%

In order to successfully implement its policy of water resources sustainable development , Tunisia instaured a developed system of networks to controle its water resources:

• Rainfall network with 800 rainfall stations;
• Hydrometric network with 80 main stations and 100 measuring points;
• Flood announcing network to manage any flood hazard with 60 automatic hydrology stations and 12 stations of remote data transmission;
• Piezometric network with more than 2000 dug wells and more than 1100 deep-wells;
• Network for ground water quality with more than 1200 measuring points.

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