A dual-porosity approach to simulate groundwater flow in fractured porous media:: application in the Itxina karstic aquifer, Spain

Mathematical models are commonly used in groundwater studies as an attempt to represent processes through mathematical equations. In the case of fractured porous media, and especially when karstification processes occur, fractures contribute as a secondary porosity, adding to the original one. This makes the comprehension of the phenomenon and the characterization of the groundwater flow difficult. This is the case of the karst aquifer of Itxina, which presents a high degree of karstification, with particular emphasis on the exuberance and wealth of the exokarstic forms and the development of the underground cavities. The aim of this paper is, first, to present the conceptualization of the Itxina aquifer. The second part treats the modelling of the flows in the aquifer using the TRAFRAP model (TRAnsport in FRActured Porous media with water table boundary conditions, Huyakorn et al., 1994). It is a two-dimensional finite element model designed to simulate groundwater flow in a steady-state or transient form. Simulation results demonstrate the complicated nature of the karst system. With the different simulations and variations to the inputs (recharge), the system was characterized as a highly fractured system with a rapid response to events.