Flow Numerical Modelling in Thermal Karst Systems: The Case of Alhama de Aragón and Jaraba Springs

The underground flow of a karstic aquifer within one of Spain and Europe’s most important thermal systems (Alhama and Jaraba thermal springs, with a combined flow rate of 1200 L/s, 711 L/s at more than 30 °C) was simulated. In the simulation process, it was important to consider how temperature (a very sensitive parameter when calibrating the numerical model) and depth influence the variation in hydraulic conductivity in the aquifer. The location of previously unknown high recharge zones was also essential in the calibration. It was verified that some fault jumps break the hydraulic continuity of the aquifer, and the role of most of the existing faults in the regional flow is generally unimportant since they are incapable of explaining by themselves the large volume of water evacuated. It is relevant to highlight the importance of the orientation of the strata when calibrating the model, which become vertical in the area of the outcrops. In the end, the modelled regional flow as well as the simulated groundwater contour lines are consistent with the progressive increase in temperature, the age of the water, the mineralization, the piezometric values measured in the observation wells, and the springs’ flow through which the system discharges. The most significant finding is the validation of the conceptual hydrogeological model through regional flow simulations from numerical models, confirming the recharge area and supporting the inferred origins of the springs.