Groundwater flow and chloride transport modeling of the alluvial aquifer of lower Soummam Valley, Bejaia, North-East of Algeria

摘要

Resulting from lithological conditions and anthropogenic activities as fertilizers use and wastewater discharge, high concentrations of chloride ions were revealed in both surface water and groundwater in Lower Soummam valley, situated in the North-Eastern of Algeria. Using geological, hydrogeological and geochemical data, a conceptual model was designed in order to improve understanding of chloride mass movements within the aquifer. A groundwater flow using PMWIN, coupled with a solute transport numerical model using MT3D code was run. Following a steady state stress period, four transient stress periods were added in order to simulate groundwater level evolution from 2011 to 2030. Groundwater withdrawals, providing from the National Plan of Water, were increased and vertical recharge rate was progressively reduced. Respecting an optimal management of water resources suitable for arid and semi-arid watersheds, successive tests have been conducted in order to mitigate the influence of high pumping rates and low recharge conditions. Recognized as a major term in water budget, water inflows from lateral boundaries representing 54.4%. At the river-aquifer interface, water was exchanged in both upward and downward representing 18% of the total amount of inflow. In coherence with experimental data, simulations indicate an impact of exchange fluxes across the river-aquifer interface. The Cl model simulations show a substantial decrease of Cl loads. According to good hydraulic properties, 90% of simulated wells show a gradual decline in their calculated concentrations, almost located on El Kseur-Oued Ghir pathway. Simulation results could be integrated in the future water resource management plan of Soummam Valley. Such a predictive model, it will be used to lay down water quality restoration strategy.