Sustainable management of the coastal aquifers underlying the Gabès Oases

Since 2011, in Tunisia's Gabès region, the BRGM has been contributing to an important programme to introduce better water resource management. The aim is to draw up a coordinated management plan to cover needs over the long term while preserving the oasis ecosystem.

The Gabès oases in south-eastern Tunisia, the only coastal oasis system in the Mediterranean region, have seen a considerable surge in human activity in recent decades, especially in agriculture, which is putting severe pressure on water resources.

Over time”, explains Jean-François Vernoux, the BRGM project manager, “overabstraction, especially for irrigation, has dried up springs, sometimes permanently, and lowered the water table, with saline intrusions into the aquifer as a result. With agricultural drainage and pollution from
various sources compounding the problem, these factors are threatening not only the hydrosystem but the entire oasis ecosystem

The Djeffara de Gabès aquifer system, which lies in a transition zone between desert and coastal steppe, is recharged naturally from the vast Saharan water tables but very little by rainwater, and is particularly vulnerable. Preserving the balance of this fragile system is crucial.

Gravity-fed (or surface run-off) irrigation in a public area in the Gabès oasis. © BRGM

A hydrodynamic model

In 2011, the regional agricultural development commission (CRDA) launched a major programme, with funding from the French development agency (AFD) and support from the BRGM, on “Management of the Gabès oases coastal aquifer system”.

The aims”, explains JF Vernoux, “are to improve our knowledge of the geology and hydrogeology of the Gabès oasis system and the socio-economic factors affecting it, and to put forward sustainable management solutions that will maintain the right balance between resources and needs.”

In close cooperation with Tunisian geoscientists, the project team undertook a major effort to compile, analyse and synthesise data collected since the 1970s (location and description of boreholes, piezometric monitoring of water tables, maps of irrigated areas and changes over time) with, in parallel, the acquisition of new data (remote sensing of water abstraction, irrigated areas outside the oases).

Several geological and hydrogeological models and a database were produced and incorporated into a Water Information System (WIS). These have provided the scientific foundations for the hydrosystem model, which will be completed by the end of 2016.

Thanks to this hydrodynamic model”, says JF Vernoux, “we will be able to simulate the behaviour of the aquifers under different use scenarios, according to sectors and needs and taking climate change impacts into account. The simulations run with the model will contribute to the  development of an integrated water resource management programme (IWRM).”