Groundwater development effects on different scale hydrogeological systems using head, hydrochemical and isotopic data and implications for water resources management: The Selva basin (NE Spain)

Abstract

Hydrogeological resources in regional, large-scale groundwater systems are conditioned by their specific geological setting, which defines their capacity to supply human demand and their potential to recover from human-induced stress factors such as water withdrawal. In this paper, the hydrogeology of a range-and-basin hydrogeological system is described, based on potentiometric, hydrochemical and isotopic data, in order to fulfill a twofold objective: to characterize the alteration brought about in the hydrogeological system by intensive groundwater withdrawal, where tectonic elements such as fault zones play a significant role in the flow behaviour, and to define groundwater hydrodynamics under current human pressures as a necessary step to achieve appropriate groundwater management. Hydraulic head data indicate the relationships between geological formations in the range areas and the sedimentary infill of the basin. In this set-up, fault zones and a fracture network have a direct effect on the recharge, and allow upward vertical flow from the basement to the sedimentary aquifers. Hydrochemical and isotopic data support this observation. The use of fluoride and nitrate as tracers for the contribution of deep and shallow flow systems provides a detailed portrait of the effects of pumping on the flow path distribution. Isotopic data depict seasonal trends in the water captured by wells. In this connection, we can differentiate between two distinct flow systems: a regional, large-scale, longer residence time system, originating in the surrounding ranges, and a local flow system constituted by infiltration in the lower areas of the basin. The two systems, with specific water qualities, contribute differently to the resources that are withdrawn, and their specific contributions, in the frame of the basin water budget, determine the potential for present sustainable water exploitation