HYDROGEOLOGICAL CONTEXT AND NUMERICAL SIMULATION OF REGIONAL GROUNDWATER FLOW IN THE ST. LAWRENCE LOWLANDS OF SOUTH-WESTERN QUEBEC

A numerical modeling study of regional groundwater flow in sedimentary rock aquifers was conducted within a groundwater resources assessment project in the St. Lawrence Lowlands of south-western Quebec. The main objectives of the study were to estimate the sustainability of the groundwater resource and to delineate zones suitable for future groundwater developments on the regional scale. The general approach was to describe the hydrogeological framework, to define the hydraulic properties of the aquifer units, to describe the groundwater dynamics parameters, to develop a numerical model and to simulate the flow under current and potential future stress conditions. The regional saturated steady-state flow was modeled using finite elements with an equivalent porous medium approach. The results show that the current pumping conditions provoke a median drawdown of 0.6 m. The results of various uniform withdrawal scenarios point out the recharge zones as the most vulnerable to groundwater extraction. The regional discharge zones are less sensitive as the drawdowns are compensated by the influx from the areas with higher groundwater elevations. Coupled with the groundwater quality zonation of the flow system, these results delineate the areas best suited for future groundwater use.