07 Feb 2023
 | 07 Feb 2023
Status: this preprint is open for discussion.

Current and future role of meltwater-groundwater dynamics in a proglacial Alpine outwash plain

Tom Müller, Matteo Roncoroni, Davide Mancini, Stuart N. Lane, and Bettina Schaefli

Abstract. Glaciated alpine catchments are rapidly evolving due to glacier retreat and consequent geomorphological and ecological changes. As more terrain becomes ice free, the interactions between surface and subsurface waters become gradually more significant, leading to potential changes in water storage and release, which in turn may impact ecological, geomorphological and hydrological processes. In this study, we aim to understand the hydrological functioning of outwash plains as glaciers retreat. These constitute a fluvial aquifer which appears as a focal point for water storage and alpine ecology and their dynamics have only rarely been studied. Based on geophysical investigations as well as year-round stream and groundwater observations, we developed a simplified physically-based 3D MODFLOW model and performed an optimized automatic calibration using PEST HP. By comparing the model results to field observations, we highlight the strong interactions between the upstream river and the aquifer, with stream infiltration being the dominant process of recharge. Groundwater exfiltration occurs in the lower half part of the outwash plain, balancing out the amount of river infiltration at a daily time scale. We show that hillslope contributions from rain and snow-melt have little impact on groundwater levels. We also show that outwash plain aquifers can maintain groundwater levels close to the surface even during long dry periods. From a hydrological perspective, we finally explore how new outwash plains may form in the future due to glacier recession and discuss what cascading impact the presence of multiple outwash plains may have in such catchments. We estimate the total dynamic storage of future outwash plains to be about 20 mm and we demonstrate their limited capacity to produce more stream water than what they infiltrate upstream, except for very low river flows (< 150 to 200 L s−1). Below this limit, they can provide limited baseflow on timescales of weeks, thus maintaining some moisture conditions potentially beneficial for proglacial ecosystems. Their role in attenuating floods also appears limited, as less than 0.5 m3 s−1 of river water can be infiltrated. Outwash plains appear therefore to play an important role for alpine ecosystems but have marginal hydrological effects on downstream river discharge.

Tom Müller et al.

Status: open (until 04 Apr 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • AC1: 'Pre-print submitted to HESS', Tom Müller, 07 Feb 2023 reply
  • RC1: 'Comment on egusphere-2022-1503', Anonymous Referee #1, 06 Mar 2023 reply

Tom Müller et al.

Data sets

Water table elevation and groundwater temperature from the outwash plain of the Otemma glacier forefield (Switzerland) from 2019 to 2021 Tom Müller

Stream discharge, stage, electrical conductivity & temperature dataset from Otemma glacier forefield, Switzerland (from July 2019 to October 2021) Tom Müller and Floreana Miesen

Electrical Resistivity Tomography (ERT) datasets from the Otemma glacier forefield and outwash plain Tom Müller

Weather dataset from Otemma glacier forefield, Switzerland (from 14 July 2019 to 18 November 2021) Tom Müller

Tom Müller et al.


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Short summary
We investigate the role of a newly formed floodplain in an alpine glaciated catchment to store and release water. Based on field measurements, we built a numerical model to simulate the water fluxes and show that recharge occurs mainly due to the ice-melt fed river. We identify 3 future floodplains, which could emerge from glacier retreat and show that their combined storage lead to some additional groundwater storage but contribute to little additional baseflow for the downstream river.