Surface water – groundwater interactions in alluvial contexts: constraints using single and multi-isotope tracers

Abstract : Surface water and groundwater have been considered as separate waters bodies for a long time by hydrologists and also decision makers, so that the relevance of interconnections between groundwater and surface water has frequently been underestimated. Since the last decades, rivers and aquifers are no more considered as physically independent entities, and are now approached as integral components of an aquifer-river-continuum with strong mutual influences between river, aquifer and the interconnecting hyporheic zone. Numerous research approaches were developed to identify and quantify the river-aquifer exchanges that can be in both directions depending on the river profile and the seasonal water levels and hydraulic gradients. The understanding of the links between hydrological, biogeochemical, and ecological process dynamics in hyporheic zones and their implications for river water quality and ecology are also of major concern for water management and decision makers.