A hydrostratigraphic simplification approach to build 3D groundwater flow numerical models: example of a Quaternary deltaic deposit aquifer

The construction of 3D hydrogeological models for unconsolidated sedimentary aquifers remains particularly challenging, especially in Quaternary deposits. Simplifications at small or large scale are part of groundwater flow modeling and are often required due on the usual inherent complexity of the stratigraphic systems. This study analyzes the effects of hydrostratigraphic simplifications on the accuracy of 3D numerical groundwater flow models. Such investigation is conducted from an initial detailed model of an aquifer located in the Saguenay-Lac-St-Jean region in Canada and the considered simplifications are based on using the equivalent hydraulic conductivity concept. Different levels or approaches of simplification are applied to numerical simulated models and the results of the different scenarios are compared. A root mean square (RMS) calibration result of 3.79 m on the groundwater levels is obtained for the most detailed model, while the RMS ranges between 4.01 and 4.83 m with the simplified models. Such results illustrate a gain obtained in the calibration of the model with increasing level of hydrostratigraphic details, but that this gain is relatively limited. The proposed methodology for simplifying the hydrostratigraphic settings could be used by hydrogeological modellers for a wide variety of aquifers constituted of sedimentary granular material.