Development of a Flow and Transport Model for Drainage Network Conception in Northern Tunisia

Abstract

In Tunisia, the salinization phenomenon in irrigated areas is frequently worsened by poor drainage. In this context, the irrigated area of Cebala Borj-Touil was studied in order to conceive an efficient drainage network. The characterization of the shallow groundwater was based on depth and salinity observations. Three selected piezometers were equipped with sensors (CTD Diver) for automatic measurement of groundwater depth and salinity. A finite difference model was developed to simulate groundwater flow and solute transport in the irrigated area. The model results showed a limited effect of the present design of the drainage network, particularly downstream in the central axis of the drainage system (the CPII canal). Various management alternatives were modeled: (1) a CPII canal performance decrease, (2) a 1 m deepening of the CPII canal level compared with the present level, and (3) a 1.5 m deepening of the CPII canal level compared with the present level. The results of scenarios 1 and 2 showed a piezometric level lowering, a drainage flow rise and a rate evaporation and salt concentration decrease. The improvement of the drainage network efficiency is more significant with an important deepening of the CPII canal level.