Application of the SWAT model on the Medjerda river basin (Tunisia)

The Medjerda river basin (Northern Tunisia) is experiencing an intensification of agriculture and the irrigated area is increasing rapidly. The SWAT (Soil and Water Assessment Tool) model, a soil, water, sediment, and nutrient transformation and fate simulator for agricultural watersheds, was applied to this catchment to study the potential impact of land management scenarios. The model was able to represent the hydrological cycle even though some discrepancies were observed, probably due to a lack of sufficient rainfall data, and due to the lack of representation of reservoirs. It was predicted that converting all agricultural land to irrigated crop introduced significant changes on nitrate concentration in surface water. However, the concentration was still below the limit of potability. It was also predicted that drastic reduction in the load of ammonium and phosphorus could be achieved by collecting and treating wastewater from major urban areas.