Hydrogeological characterization of an alpine aquifer system in the Canadian Rocky Mountains

Abstract

Groundwater storage in alpine regions is essential for maintaining baseflows in mountain streams. Recent studies have shown that common alpine landforms (e.g., talus and moraine) have substantial groundwater storage capacity, but the hydrogeological connectivity between individual landforms has not been understood. This study characterizes the hydrogeology of an alpine cirque basin in the Canadian Rocky Mountains that contains typical alpine landforms (talus, meadow, moraines) and hydrological features (tarn, streams, and springs). Geological, hydrological, and hydrochemical observations were used to understand the overall hydrogeological setting of the study basin, and three different geophysical methods (electrical resistivity tomography, seismic refraction tomography, and ground penetrating radar) were used to characterize the subsurface structure and connectivity, and to develop a hydrogeological conceptual model. Geophysical imaging shows that the talus is typically 20-40 m thick and highly heterogeneous. The meadow sediments are only up to 11 m thick but are part of a 30-40-m-thick accumulation of unconsolidated material that fills a bedrock overdeepening (i.e. a closed, subglacial basin). A minor, shallow groundwater system feeds springs on the talus and streams on the meadow, whereas a deep system in the moraine supplies most of the water to the basin outlet springs, thereby serving as a 'gate keeper' of the basin. Although the hydrologic functions of the talus in this study are substantially different from other locations, primarily due to differences in bedrock lithology and geomorphic processes, the general conceptual framework developed in this study is expected to be applicable to other alpine regions.

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

“…These findings agree with the conclusions of previous studies, indicating the important role of talus‐moraine features in controlling groundwater storage and release. The recent study of Christensen et al (2020) explored the role of moraine as a “gate‐keeper” in one of these features in the Canadian Rockies, talus being located upslope of the moraine. In the Tsalet catchment, moraine likely plays this role as well.…”

“…Finally, these results highlight the dominant role of Quaternary deposits to store water. The mechanisms explaining the importance of Quaternary deposits are the combination of moraine and talus with different permeabilities allowing the storage of enough water to release it slowly during drier years, as stated in the publications of Cochand et al (2019), Glas et al (2019), Hayashi (2020), and Christensen et al (2020). The high permeability of talus allows for the rapid infiltration of water and its connection to lower permeability moraine leads to deeper infiltration and a slower release of groundwater to streams, ensuring year‐round streamflow down‐gradient.…”

“…Cochand, Christe, Ornstein, and Hunkeler (2019) proposed a conceptual model highlighting the combination of different unconsolidated aquifer units to store groundwater. The recent study of Christensen, Hayashi, and Bentley (2020) identified that in a talus‐moraine feature in the Canadian Rockies, groundwater from the moraine supplies most of the water to the basin outlet springs and that moraine, located downstream the talus, could serve as a “gate keeper” of the basin. While knowledge alpine hydrogeology is advancing with more and more studies, current knowledge remains limited and difficult to extrapolate to other alpine areas (Christensen et al, 2020; Somers et al, 2019).…”

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 2: Future change in cryosphere, vegetation, and hydrology

“…This indicates that they will further recede to adjust their geometry to the current climate, with a typical response time of several decades for glaciers in western Canada (Marshall et al, 2011;Marzeion et al, 2018). Ongoing climate change is expected to further exacerbate the current imbalance and lead to additional retreat (Clarke et al, 2015).…”

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 2: Future change in cryosphere, vegetation, and hydrology

“…Groundwater plays an essential role in sustaining base flow in the mountain headwaters of large river systems (Paznekas and Hayashi, 2016), and may be of growing importance under climate change. Above the tree line in the Rocky Mountains, primary aquifers are sedimentary landforms such as talus, moraine, and rock glacier (Hood and Hayashi, 2015;Harrington et al, 2018;Hayashi, 2020;Christensen et al, 2020), except in areas with substantial karst systems. Groundwater storage in these landforms is relatively small compared to the SWE contained in the seasonal snow cover (Hood and Hayashi, 2015), and groundwater discharge exhibits a fast recession https://doi.org/10.5194/hess-2020-491 Preprint.…”