Assessment by multivariate analysis of groundwater–surface water interactions in urbanized Mediterranean streams

SummaryStreams in Mediterranean areas are characterized by a variable discharge regime with annual floods and droughts. Natural flow perturbations result in permanent and temporary rivers and, as a consequence, unique ecosystems. Human pressures such as treated and non-treated waste water discharge impact severely on these streams, since waste water dilution depends on river flow dynamics. Furthermore, their hydrological status worsens with the capture of stream discharge by surface or groundwater exploitation.Multivariate analysis has been widely used to analyze large sets of variables in environmental studies. In the present work, a hydrological study reinforced by principal component analysis (PCA), followed by cluster analysis of the PCA results, has been used to determine surface water origin and its interactions with groundwater in Mediterranean streams.The results show that hydrological observations are supported by PCA and cluster analysis. Additionally, this joint analysis makes it possible to observe the significance of the interaction between streams and aquifers in anthropized Mediterranean Basins. Groundwater exploitation can seriously impact on permanent streams, reducing their dilution capacity, and can even cause the capture of the whole stream discharge. Furthermore, good quality water contributions allow continuous stream flows and better waste water dilutions all year long. Finally, the results show that the presence and quality of surface water in temporary reaches during dry periods directly depends on groundwater contributions.