Characterizing seasonal groundwater storage in alpine catchments using time‐lapse gravimetry, water stable isotopes and water balance methods

Abstract

Alpine areas play a major role in water supply in downstream valleys by releasing water during warm and dry periods. However, the hydrogeology of alpine catchments, which are particularly exposed to the effects of climate change, is currently not well understood. Increasing our knowledge of alpine hydrogeological processes is thus of considerable importance for any forward-looking hydrological investigations in alpine areas. The objectives of this study are to quantify seasonal groundwater storage variations in a small Swiss alpine catchment and to evaluate the capabilities of time-lapse gravimetry in the identification of zones of high groundwater storage fluctuations. Time-lapse gravimetric measurements enable rapid localisation of zones of dynamic groundwater storage changes and help to highlight aquifers with a higher storage decrease. Temperature sensors enable measurement of the temporal trend in stream and spring drying in the post-snowmelt period. Stable isotope measurements allow us to identify the origin of surface water exiting the catchment. The results improve our comprehension of a conceptual schema highlighting two different hydrogeological systems: (a) a shallow, rapidly depleted one fed directly by snowmelt and (b) a deeper one, with a slower recession, fed by main recharge during peak snowmelt and emerging at the lower part of the catchment below the talus and moraine of the catchment where bedrock is exposed. These dynamics confirm the high variability of storage in the talus and moraine aquifers and highlight the dominant role of Quaternary deposits and their connectivity to store water over seasonal and multi-year timescales. The mechanisms explaining the importance of Quaternary deposits are the combination of moraine and talus with different permeabilities allowing the storage of sufficient quantities of water permitting continuous release during drier periods of the year.

Toward a definition of Essential Mountain Climate Variables

“…Current records are too few and sparse to permit the analysis of groundwater level trends, for instance. Developing spatially integrated estimates of subsurface phenomena, such as MBR or total or dynamic (i.e., the component that contributes to streamflow) catchment groundwater storage, directly from data is challenging (but see Arnoux and coworkers 102,103 ), although such estimates are often in high demand. Simulation-based approaches-especially fully integrated surface-subsurface modeling-provide an alternative option to quantifying mountainous water balances in a physically based, spatially explicit fashion.…”

Hydrological response to warm and dry weather: do glaciers compensate?

“…The buffering effect of glaciers has been analyzed at different spatial and temporal scales. In general, studies indicate that glaciers provide an important source of water during warmer and drier periods throughout the year and during drought years specifically (e.g., Ayala et al, 2020;Jost et al, 2012;Kaser et al, 2010;Anderson and Radić, 2020).…”

“…During extreme drought years, runoff from melting glaciers was estimated to contribute 55 %-100 % to summer runoff in the Maipo river basin in Chile (7.8 % glacierized) (Ayala et al, 2020), and during the 2003 European drought and heat wave event, streamflow in glacierized catchments in the Alps was up to 40 %-60 % higher than normal during August, depending on glacier cover fraction of the catchment and catchment elevation (Zappa and Kan, 2007;Koboltschnig and Schöner, 2011). For the whole High Mountain Asia region, Pritchard (2019) also found high relative monthly glacier melt contributions to streamflow in drought years but mainly attributed this to a decrease in precipitation amounts.…”

Simulating fully-integrated hydrological dynamics in complex Alpine headwaters: potential and challenges

“…Allen et al, 2007), this being a generally uncertain water balance component, and estimates of seasonal groundwater storage determined via gravimetry (e.g. Arnoux et al, 2020), which would provide more spatially integrated, representative information that the piezometer measurements used here (see also Schilling, Cook et al, 2019). Employing the temporal evolution of the observed stream network as it expands and contracts (e.g.…”