Water Resources in Tunisia

Surface water

Tunisia is among the driest countries in Africa and is characterized by limited water resources. Average annual rainfall ranges from less than 100 millimetres per year (mm/yr) in the south to 1,500 mm/yr in the north-west. Surface water resources total 2,700 million cubic metres (MCM) and are distributed between the country’s major watersheds as follows:

The north covers about 26% of the total area of the country, provides regular and important surface water evaluated at 2,190 MCM from the major basins of the Medjerda River (1,000 MCM/yr), the extreme north (585 MCM/yr), Ichkeul and Bizerte (375 MCM/yr) and Cap Bon and Meliane (230 MCM/yr). These basins contribute 81% of the country’s total surface water potential.[1]

The centre covers the same area as the north and provides irregular surface water resources of 320 MCM/yr from the basin rivers of Nebhana, Marguellil, Zeroud as well as the Sahel of Sousse and Sfax.

Figure 1: Surface water variability for the period 1984-2016.[5] [6]

These resources represent 12% of the country’s total surface water potential [2].

The south, which covers about 62% of the total area of the country, is the poorest region in terms of surface water and has only very irregular resources. It provides 190 MCM/Yr or 7% of the country’s total surface water potential from chotts and the Djeffara basin.[3]

Surface water resources are also constrained by the irregularity in rainfall between months and years. Moreover, surface water resources have a very high inter-annual variability, with a minimum of 780 MCM/yr, as observed in 1993-1994, and a maximum of 11,000 MCM/yr, as observed in 1969-1970.[4]

Groundwater

The groundwater resources in Tunisia are associated with both shallow and deep aquifers, including both renewable and weakly renewable or fossil reserves. The total exploitable reserves are estimated at nearly 2,100 MCM, distributed sparsely across the entire country. These are composed of 1,486 MCM of renewable resources, representing about 69.6% of the total groundwater potential, and 650 MCM of weakly renewable resources, found mainly in the south and representing 30.4% of the total groundwater potential. [7]

Renewable groundwater resources are available at 55% in the north of the country, 30% in the centre and 15% in the south of the total renewable groundwater resources potential. However, deep aquifers are more available in the south, with a potential of 58%, and to some extent in the centre and the north, with 24% and 18% respectively.[8]

Figure 2: Groundwater mobilization and development for the period 1980-2015.[10] [11]

Even though groundwater resources are important in the south, their use remains limited, mainly due to the low water quality.

The mobilization and development of groundwater resources has been accelerated over the last decades, almost to the limit of available resources.[9] At the same time, the rate of groundwater extraction in many aquifers is unsustainable (Cap Bon in the north, the central region, Kebili in the south). This problem is exacerbated by an inconsistent institutional framework to ensure the sustainability of groundwater use and unauthorized drilling for aquifer exploitation.

Non-conventional water resources

The use of non-conventional water resources, including desalinated water and wastewater, helps to save the limited conventional resources and could play an increasingly important role in satisfying the growing water requirements.

Desalination

With its limited energy and water resources, Tunisia considers desalination as a way to bridge the gap between water supply and demand within an integrated water resources management framework, rather than a solution to solve water scarcity. Some 110 desalination plants have been constructed, mainly for domestic water supply, and have a capacity of about 200,000 cubic metres per day (m3/day).[13] Desalination was introduced gradually, even though it is the only possible alternative for the production of fresh water for domestic use. Its cost is still high, mainly because of the initial investment required and subsequent operation and maintenance costs.

Figure 4: Distribution of the overall desalination capacity by sector (2016).[14]

Water reuse
Reclaimed water reuse has been an integral part of the National Water Resources Strategy since the 1990s. In the early 2000s, the Ministry of Agriculture, Water Resources and Fisheries developed a National Strategy for Wastewater Reuse to promote reuse for agricultural irrigation and other purposes. About 260 MCM of water were treated in 2017, representing 7% of the total volume allocated to irrigation and 5% of available water resources. The main wastewater treatment plants are located along the coast to protect coastal resorts and prevent marine sea pollution. About 50% of treated wastewater is produced in the capital Tunis and its suburbs. Currently, 119 treatment plants are in operation: 110 for urban wastewater treatment, nine for industrial wastewater and eight for rural wastewater. They operate biologically up to a secondary treatment stage, consuming a large amount of energy. Currently, no further treatment is carried out due to economic constraints. Tertiary treatment is being undertaken at pilot scale.[15]

More than 75% of treated wastewater is not yet reused and is discharged into the environment to become part of the hydrological cycle as well as of wastewater from communities unconnected to the sewerage network.[16] The volume of treated wastewater is projected to keep growing as urbanization and efforts to preserve the environment increase. This volume constitutes about 10% of the available groundwater resources and could be used to recharge some aquifers in irrigation areas where groundwater overdraft is causing saltwater intrusion in coastal aquifers.

Total water availability and per capita availability

Potential conventional water resources for the whole country are estimated at 4,800 MCM/yr, including an average of 2,700 MCM/yr of surface water and 2,100 MCM/yr of groundwater. The variability of these resources is apparent over the past few decades, with a maximum potential volume of surface water of 11 billion cubic metres (BCM) in 1969-70 and a minimum of 780 MCM in 1993-94. These resources are expected to become more variable and less predictable between and within years, due to the increasing incidence of extreme weather events, which can have an adverse impact on people’s socio-economic situation.

Despite the slight increase in per capita water resources during the last decade, total availability has declined. The total per capita availability was estimated at 450 m3 in 1995 and had decreased to 433 m3 in 1998. In 1999, with the exploration and exploitation of new deep-water resources, availability increased to reach 444 m3 but fell again to 426 m3 in 2004. In other words, per capita availability has decreased by about 5% over a decade.[17] [18] It is expected to continue declining, reaching 359 m3/cap/yr in 2030.[19]

Table 1: Evolution of per capita water availability between 1995 and 2004.[20]