Modelling groundwater flow and advective contaminant transport in the Bou-Areg unconfined aquifer (NE Morocco)

A three-dimensional finite-difference groundwater flow model was implemented to investigate the variety of hydrogeological conditions and to simulate the behavior of the flow system under different stresses in the unconfined aquifer of Bou-Areg. The modelling package MODFLOW, employed in the Groundwater Modelling System (GMS), was applied for this purpose. The plain of Bou-Areg, located on the Mediterranean coast of northeastern Morocco, contains two sedimentary formations of Plio-quaternary age. The upper formation consists of thin silts and the lower one is formed of coarse silts with sand and gravels. The aquifer system is underlain by marly bedrock of Miocene age that slopes towards the Bou-Areg coastal lagoon. The two-layer model was calibrated with two steps: a steady state calibration, using observed groundwater levels from 1990, and a transient calibration and verification, using observed groundwater levels for 1990–2006. Estimation of the hydraulic conductivity distribution was optimized using a combination of trial-and-error and automated inverse methods. The simulation results show that the fluctuations of hydraulic heads are dependent on seasonal variation in recharge from natural infiltration of precipitation and irrigation. Also, the model can simulate the positive fluctuations of the hydraulic heads in Bou-Areg aquifer, with different responses of the hydrogeological system. Different scenarios were considered to predict aquifer system response under different conditions. Advective transport MODPATH was approximated using pathways of particles tracking originating from sources areas.