Evaluation of the distribution of salinity in the different recharge zones of the lower Llobregat River aquifer and its impact in groundwater

Abstract

The salinity of surface water and groundwater of the Lower Valley of the Llobregat basin has experienced a significant decrease in the last decades. This project aims to establish a traceability between the evolution of salinity in surface water and its impact on the aquifer, relating it with the structural modifications of the area, as well as the existing infrastructures and the natural evolution of the environment. Historical information on the quality of surface and groundwater is available. Making a selection of wells and sampling points, we work in the analysis of the evolution of chloride concentrations (a clear indicator of salinity) and we use several tools such as Piper diagrams or the relationship of conservative parameters (chlorides / bromides), trying to find, through all this information, the impact of the different sources of recharge in the water of the left and right margins of the Lower Valley of the Llobregat. Apart from the natural recharge with rainwater, the aquifer of the Lower Valley of the Llobregat River receives mostly contributions from the waters of the Llobregat River, of the Anoia River and of the Rubí Stream, affecting the two margins of the Llobregat River in different ways, that is: each margin is recharged with water of different origin and in different proportions. Using the methods mentioned above, it has been shown that the decrease in salinity in recent years has been caused by changes in the infrastructure of this system and for a higher rainfall regime, now reaching values below the established limit of 250 mg/L of chlorides. Other effects such as the saline intrusion produced during the drought period have also had a clear footprint which has lasted for a long time in specific areas of this system