Ranking suitable sites for irrigation with reclaimed water in the Nabeul-Hammamet region (Tunisia) using GIS and AHP-multicriteria decision analysis

The present study describes an innovative methodology to rank suitable sites for irrigation with TWW using fuzzy-AHP based on GIS where the Nabeul-Hammamet aquifer catchment (Tunisia) is selected as the target area. The model is relatively simple and is extendable worldwide. Several influential parameters are identified considering simultaneously technical, social, economical and environmental aspects. They are grouped in five main criteria, namely land suitability for irrigation, resources conflicts, cost effectiveness, social acceptance and environmental impact. Each criterion is subdivided into several sub-criteria. A pair-wise matrix is used to compare these criteria and sub-criteria and to rank them according to their relative importance for site evaluation. Using GIS, geographical layers are obtained for the sub-criteria, leading to mapping and ranking the suitable sites for TWW irrigation. The results show that the total suitable area covers 11,426 ha which represents 31% of the total Nabeul-Hammamet aquifer watershed. This constitutes quite a large zone that can absorb the entire volume of available treated wastewater, thereby increasing the region's agricultural production. The best sites to receive the surplus amount of TWW, produced by the treatment plants of the region, are located near these plants and inside agricultural lands. In addition, all these sites are located around the districts already irrigated by TWW, which underlines the role these districts may play in encouraging neighbouring farmers to change their attitude towards TWW and to accept it as an alternative resource for irrigation.