Direct and inverse modelling of the groundwater flow in porous media

This article shows the role of mathematical simulation in the understanding of complex and heterogeneous aquifers. The coastal aquifer of the western Morocco is an example that reflects the spatial distribution of permeable and impermeable bodies. Hence the need to know its hydrological functioning in terms of numerical modelling. The hydrodynamic model proposed is based on solving the direct and inverse problem. In the steady state, the groundwater flow simulation (direct problem) showed the persistence of major differences between the measured and calculated heads. This calibration anomaly is mainly explained by heterogeneity and fissures, that are incompatible with the derivation of the diffusivity equation, which assumes a continuous and a laminar rather than turbulent flow. Two key maps have been obtained: (a) a map of hydraulic conductivity polygons whose values vary between 50 x 10 super(-4) and 80 x 10 super(-4) m/s; and (b) a map of recharge polygons whose values vary between 4.5 x 10 super(-9) and 5 x 10 super(-9) m/s. Calibration of the flow model, that was investigated in the solution of the inverse problem, leads to identification of the parameters of the aquifer from the known piezometric data. The inversion code PEST (Parameter ESTimation) was used to create maps of hydraulic conductivity and recharge polygons with values very similar to the results of the conceptual model.