Stream-aquifer interactions: a combined field - methodological approach in fractured carbonate catchments

Stream-aquifer studies remain a challenge due to numerous factors impacting these interactions. They play a fundamental role in terms of quantity and quality of water, in particular on the ecological status of rivers. Field quantification of such interactions is a first step but it has to be in relation with the whole budgets of water and transported substances across the catchment in order to represent their importance on overall fluxes. Numerous complementary investigations have to be undertaken to achieve such understanding of catchment behavior, in particular to estimate specific indicators and to achieve representative data for modeling stream-aquifer interactions. From that situation, our study aims to characterize and quantify stream-aquifer interactions to assess reliability of diverse field experiments methodologies. A catchment has been studied for 3 years in quantitative and qualitative ways via a dense instrumentation and monitoring. Numerous complementary investigations (discharge measurements, hydrogeochemistry, distributed temperature sensing, base flow separation…) have been applied to reach the objectives. We achieved a large and diversified measurement dataset of groundwater-surface water interactions and whole water budget. This allowed reaching an improved understanding of the catchment behavior to quantify importance of the groundwater component on the dynamics and chemistry of the stream and on the consequences on river ecological status. The investigations on several subcatchments allows also to propose a general typology of stream catchment in terms of groundwater dependence based on the combination of various groundwater contexts and groundwater-stream interaction indicators. Methodologies applied in this study allow to emphasize strength and weakness of numerous investigations in a stream aquifer project and conclusions can be reproduced and generalized to other contexts.