A socio-hydrological journey around the Wadi Merguellil in central Tunisia

The Wadi Merguellil, the main watercourse of the Merguellil basin in central Tunisia, has experienced an extremely marked socio-hydrological evolution. It is currently intermittent over most of its course, but the statements of farmers and archival records reveal that this was not the case at the beginning of the last century. They testify their nostalgia for a past when water was easily mobilized from the wadi using traditional irrigation canals. As well, the spatial patterns of irrigation and the organization of social groups around the Wadi look very different from what it is now.  Wind back the clock 100 years to the early 20th century, the Wadi Merguellil base flow was fed by the overflow of regional aquifers and the agriculture development was maintained thanks to the irrigation from this flow. However, things came to a head in the 1975’s, an exploitation scheme was implemented in order to drop the groundwater level of the regional aquifers to a target depth so as to reduce '' losses '' by evaporation in the Wadi Merguellil. This scheme was based on a simple resource displacement to limit water "losses" but around the wadi, there are also farmers for which the wadi represents a means of subsistence. Thus, drying up of the Wadi Merguellil has forced farmers to abandon the irrigation canals and opt for the installation of pumps and deep wells. This retroaction of farmers to the hydrological change contributed to further disturb the hydrological budget and led to a generalized groundwater level drop of 37 m over the last 50 years and an inversion of hydraulic gradients. In fact, the exploitation scheme was intended to satisfy all stakeholders but it was based exclusively on hydrodynamic considerations without taking into account the evolution of society around the wadi. The results of this work are in line with researches in socio-hydrology that call for a deeper integration of social aspects into management plans to ensure the sustainable development of water resources.