Characterization and modeling of water movement and salts transfer in a semi-arid region of Tunisia (Bou Hajla, Kairouan) – Salinization risk of soils and aquifers

The semi-arid region of Bou Hajla (Kairouan – Central Tunisia) is exposed to the risk of soils and aquifers salinization. A characterization of water movement through the use of TDR probes installed at up to 4 m in depth, and of salts transfer by soil sampling was conducted to highlight this risk. At the same time, climatic parameters were monitored. The results were gathered over the period of approximately 1 year (June 12, 2006 to May 08, 2007). Water infiltration and evaporation, occurred at within distinct materials: two zero flux planes at 1 and 3 m, and a clay-silt layer at 2 m where the soil water content and electrical conductivity is highly varied. Saline profiles show salt accumulation at this layer where the electrical conductivity of soil paste extract exceeds 20 dS m−1. However, the additive salt balance between soil surface and a depth of 4 m highlights the salt transfer beyond the studied unsaturated zone, increasing the salinization risk of the aquifer. The water movement and salts transfer were simulated by Hydrus-1d model, and inverse modeling was used to optimize the required hydrodynamic parameters. It was found that the simulated profiles of volumetric humidity and the electrical conductivity of soil are close to those measured. The calculated RMSE values are low, indicating the reliability of Hydrus-1d for the simulation of the hydro-saline dynamics in field conditions.

► Semi-arid region of Bou Hajla is facing soils and aquifers salinization risk.
► Characterization of water movement and salt transfer highlighted this risk.
► Deep dynamic of water and salts are under the effect of irrigation and rain.
► Hydrus-1d was used successfully to model these processes.