Workreport 2020-4



Groundwater Flow Modelling Under Transient Ice Sheet Conditions in Greenland


Jaquet, O., Namar, R., Siegel, P., Harper, J., Jansson, P.



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The Greenland Analogue Project (GAP), an international field and modelling study of the Greenland Ice Sheet was established in 2008, collaboratively by the Swedish, Finnish and Canadian nuclear waste management organisations; namely, Posiva (Posiva Oy), SKB (Svensk Kärnbränslehantering AB) and  NWMO (Nuclear Waste Management Organisation). The aim of GAP is to advance the understanding of the impact of glacial processes on the long-term performance of a deep geologic repository. The Greenland Ice Sheet is considered to be a modern analogue with respect to size and conditions that could prevail in Fennoscandia and Canada during future glacial periods with ­continental-scale ice sheets.

Within the framework of the GAP project, this third phase of ground­water flow modelling under transient ice sheet conditions in Greenland has enabled the assimilation of transient data from the dynamic ice sheet model SICOPOLIS into the simulations over time frames relevant to safety assessment applications. Modelling density-driven groundwater flow, heat transfer and permafrost using transient boundary conditions representing ice sheet displacement was performed during a complete glacial cycle (from -115 to -1 ka before 2000 AD) in Greenland.

Detailed subglacial topography, subglacial layer, deformation zones, borehole data and talik locations were integrated in the model. For the first time, the choice for the subglacial boundary conditions (i.e. as ice overburden hydraulic pressure) could be justified by field data provided by ice boreholes drilled in the Greenland ice sheet during the GAP project. The impact of various hydraulic ­parametrisations for the rock domain and deformation zones was investigated based on data from three sites located in the Fennoscandian shield (Laxemar, Forsmark and Olkiluoto). Furthermore, the effect of specific glaciation scenarios given by the dynamic ice sheet model was investigated. The tracing of meltwater from the ice sheet was modelled in order to determine the depth range likely reachable by glacial meltwater for the various sensitivity cases. The subglacial layer plays a key hydraulic role in draining meltwater underneath the ice sheet. Below the surface, groundwater flow is governed by the hydraulic parametrisation of the rock domain, the deformation zones and the permafrost. Glacial meltwater is likely to reach depths that exceed 500 m in this modelling. During the periods of glacial build-up and retreat, solely the taliks located within a few kilometres of the ice margin can be reached by glacial meltwater. Whatever the glacial period considered, for the lower hydraulic parametrisation cases (Forsmark and Olkiluoto), the flux values remains below 10 mm/a at depth. The model shows that the mean depth of permafrost lies in the range 509 – 617 m when only a part of the domain is covered by the ice sheet during the periods of glacial build up and retreat. Finally, the presented groundwater flow modelling approach allowing assimilation of dynamic ice sheet model data leads to a reduction in uncertainty and consequently improves confidence when assessing selected measures of repository performance.


GAP, Greenland Analogue project, groundwater modelling, transient conditions


WR 2020-04_web (pdf) (11.1 MB)


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