Investigating groundwater flow components in an Alpine relict rock glacier (Austria) using a numerical model

Abstract

Relict rock glaciers are complex hydrogeological systems that might act as relevant groundwater storages; therefore, the discharge behavior of these alpine landforms needs to be better understood. Hydrogeological and geophysical investigations at a relict rock glacier in the Niedere Tauern Range (Austria) reveal a slow and fast flow component that appear to be related to the heterogeneous structure of the aquifer. A numerical groundwater flow model was used to indicate the influence of important internal structures such as layering, preferential flow paths and aquifer-base topography. Discharge dynamics can be reproduced reasonably by both introducing layers of strongly different hydraulic conductivities or by a network of highly conductive channels within a low-conductivity zone. Moreover, the topography of the aquifer base influences the discharge dynamics, which can be observed particularly in simply structured aquifers. Hydraulic conductivity differences of three orders of magnitude are required to account for the observed discharge behavior: a highly conductive layer and/or channel network controlling the fast and flashy spring responses to recharge events, as opposed to less conductive sediment accumulations sustaining the long-term base flow. The results show that the hydraulic behavior of this relict rock glacier and likely that of others can be adequately represented by two aquifer components. However, the attempt to characterize the two components by inverse modeling results in ambiguity of internal structures when solely discharge data are available.

Groundwater flow and storage processes in an inactive rock glacier

“…Regardless of the depositional processes responsible for the presence of a basal layer, both fine‐grained sediments and tills are expected to have a lower hydraulic conductivity than coarse sediments generally found in rock glaciers. The rising and lowering of the water table between a basal low‐conductivity layer and an overlying high‐conductivity layer (e.g., Pauritsch et al, ) could also explain the observed shifting hydraulic properties and threshold response behaviour, similar to the “transmissivity feedback” mechanism (Figure b; Bishop, Seibert, Köhler, & Laudon, ). The available data cannot determine which of these processes (or both) play the dominant role in the hydrological response of the rock glacier.…”

“…Little work has been done to date to examine how subsurface flow paths may control groundwater discharge from inactive and relict rock glaciers, except for recent studies in Austria (Pauritsch, Wagner, Winkler, & Birk, ; Winkler et al, ). These studies indicated the importance of understanding the internal structure of relict rock glaciers and how it affects groundwater storage and flow pathways.…”

Spatio‐temporal variability in contributions to low flows in the high Alpine Poschiavino catchment

“…Recent studies have shown that the majority of the sediment features, like thick talus slopes and moraine deposits, might never fill up, and instead drain rapidly due to the high permeability (Langston, Bentley, Hayashi, McClymont, & Pidlisecky, ; Muir, Hayashi, & McClymont, ). Long‐term storage in these sediment layers is restricted to a less permeable but relatively thin saturated zone on the bottom that is capable of storing (and releasing) water for longer periods (e.g., Pauritsch, Wagner, Winkler, & Birk, ; Volze, ; Winkler et al, ).…”

“…Long-term storage in these sediment layers is restricted to a less permeable but relatively thin saturated zone on the bottom that is capable of storing (and releasing) water for longer periods (e.g., Pauritsch, Wagner, Winkler, & Birk, 2017;Volze, 2015;Winkler et al, 2016).…”

Hydrogeologie im Tauernfenster – Fallbeispiel Rauristal, Salzburg

“…Tiefgreifend aufgelockerte Massenbewegungen an übersteilten Hängen bieten gute Durchlässigkeiten entlang der Bewegungsbahnen oder komplexe Fließsysteme durch die interne Auflockerung der Rutsch-oder Kriechmassen (Ronchetti et al 2009;Strauhal et al 2015;Vallet et al 2015). Blockglet-scher zeigen häufig eine interne Struktur, in der sich blockige grobe Komponenten mit feinkörnigeren Schichten abwechseln, was zu einem komplexen Fließgefüge mit kurzen bis mittleren Verweilzeiten und damit schnellen und langsamen Fließkomponenten führt (Winkler et al 2016;Pauritsch et al 2017;Jones et al 2019). Moränenablagerungen sind aufgrund ihrer schlechten Sortierung und ihres hohen Feinkornanteils, Grundmoränen zudem aufgrund der hohen Lagerungsdichte gering durchlässig und bilden damit lokale Stauhorizonte aus.…”