Towards a hydrogeomorphological understanding of proglacial catchments: review of current knowledge and assessment of groundwater storage and release in an Alpine catchment

Abstract. Proglacial margins form when glaciers retreat, and create zones with distinctive ecological, geomorphological and hydrological properties in Alpine environments. There is extensive literature on geomorphology and sediment transport in such areas as well as surface and glacial hydrology; but there is much less research into the specific hydrological behavior of the landforms that develop after glacier retreat in and close to proglacial margins. Recent reviews have highlighted the presence of groundwater stores even in such steep, rapidly draining environments. It remains however largely unclear where groundwater recharge and storage occurs and the limited studies of the hydrological functioning of specific landforms has not been put into the perspective of the catchment-scale storage-discharge behavior driven by proglacial margins. Here, we provide a detailed literature review of the geomorphological structure of proglacial landforms in the context of their hydrological processes, as well as a summary of the timescale of their hydrological response. We then propose a recession-analysis based framework to understand how different landforms contribute to catchment-scale discharge. We applied the proposed methods to the case of a Swiss proglacial alpine margin and summarize the insights that follow from a complete perceptual model of how such a proglacial catchments works. We identify the relative groundwater storage volumes of different superficial landforms and show how steep zones only store water on the timescale of days, while flatter areas maintain baseflow in the order of several weeks. We show that those geomorphological landforms themselves fail to explain the catchment-scale recession analyses and discuss the presence of an unidentified storage compartment of the order of 40 mm which releases water during the cold months, which we propose to attribute to deeper bedrock flowpaths. Finally, the key insights on the interplay of different landforms as well as the analysis framework is readily transferable to other similar proglacial margins and should contribute to a better understanding of the future hydrogeological behavior of such catchments.