Characterizing the current and future groundwater storages in a highly glaciated catchment : a synthesis of 3 years of field observations and modelling results

Alpine glaciated catchments are rapidly changing with glacier retreat. Combined with future earlier snow melt and more liquid precipitation, the importance of high alpine catchments to provide essential water resources for downstream uses will increase. In this context, groundwater storage may play a critical role in maintaining baseflow during drought events. In this study, we provide an overview of the hydrogeological functioning of the Otemma glacier catchment, a typical glaciated catchment in the Swiss Alps. Based on three years of field data, we provide a complete conceptual model of the volumes and timescales at which different landforms store and release water and compare those results with a catchment-scale analysis of the winter discharge recession. Based on water isotopes and geochemical data, we show the strong spatial heterogeneity in the water sources that recharge those landforms and how they are interconnected. Finally, we present results of a 3D model of the groundwater-surface water interactions in the proglacial outwash plain, discuss where potential new floodplains may form in the future and show a rather limited potential storage of the order of 20 mm. We conclude that superficial landforms have a limited potential to provide significant baseflow for downstream users but can provide significant moisture for high alpine ecosystems. Nevertheless, we show that bedrock infiltration likely represents the largest groundwater reservoir but more research is needed to characterize its role in the future.