Relative importance of weathering profiles and major fracture zones to fit the water balance of a hydrogeological catchment in hard rocks

Hard rocks constitute complex hydrodynamic structures in which both weathering products of hard rock and fractures play a major hydrodynamic role. The characterization of the relative importance of weathering products and fractures in groundwater flow is assessed through a numerical groundwater simulation. The methodology employed focuses first on the capitalization of all geological and hydrogeological information available in the Dimbokro catchment. Secondly, all geological and hydrodynamic data obtained are incorporated in a flow simulator. To estimate and possibly quantify the relative importance of weathering profiles and major fractures zones, two approaches of modeling are adopted: Equivalent Continuum (accounting for the weathering profile without fractures) and Continuum/Discrete fractures (incorporating discrete fractures). In the two approaches, the adjustments of simulated and observed hydraulic head are sensibly the same. However, the Equivalent Continuum model shows disequilibrium in the water budget due to the fact that the model is not able to reproduce the drainage condition of the aquifer. The presence of fractures in the Continuum/Discrete fractures approach allowed balancing the water budget. Although the fractures do not show any influence over hydraulic head distribution, they play a major role in groundwater circulations within the flow paths of the aquifer which allows balancing the water budget.