Effect of the spatial variability of transmissivity on the groundwater flow and budget of the Takelsa multilayer aquifer, Tunisia

Groundwater models are vulnerable to uncertainties, especially those that are developed based on incomplete knowledge of the hydraulic parameters. Transmissivity is often the most uncertain parameter in groundwater modeling. This work evaluates the effect of the spatial variability of transmissivity on the outputs of the groundwater flow model of the Takelsa multilayer aquifer. The study was based on a combination of deterministic and stochastic modeling. Groundwater flow modeling and stochastic simulations were made using the PMWIN software (a version of MODFLOW). Initially, the groundwater flow model was developed in the steady state. The criteria used for the calibration process were based on the comparison between the observed and the simulated hydraulic level. Then, a stochastic approach was used and 100 simulations of transmissivity were performed. The simulated transmissivity values were used to recalculate the hydraulic head and the water budget of the Saouaf deep aquifer. Finally, the consequent 100 results obtained by running MODFLOW were analyzed. The results showed variations in the hydraulic head levels, but the flow direction remained the same. The impact of the spatial variability of transmissivity on the water budget shows a range of inflow and outflow rates of Saouaf aquifer, with special relevance to the sea intrusion which may cause a probable deterioration of the quality of the groundwater.