Numerical modelling of integrated processes in cryo-hydrogeological systems: Applications in Nunavik, Quebec, Canada

Numerical simulations of coupled groundwater flow, heat and mass transport have been carried out for better understanding of cryo-hydrogeological system behavior under climate change.

Simulations are based on conceptual models of two well-monitored field sites at Umiujaq and Salluit, in Nunavik, (northern Quebec), Canada. The Umiujaq site contains discontinuous permafrost as discrete mounds within a marine silt bounded by unconfined and confined sand aquifers, while the Salluit site includes a bedrock river-talik system within continuous permafrost.

All simulations are run with the finite element HEATFLOW/SMOKER code which includes density-dependent groundwater flow, advective-conductive heat transport and advective-dispersive microparticle transport. Water-ice phase change, latent heat, ice-fraction dependent relative permeability and temperature-dependent thermal parameters are integrated in the solution. The thermal-hydraulic system is driven by ground surface recharge/discharge conditions which depend on the thermal state of the shallow subsurface (frozen or thawed), and by coupling with air-ground temperature gradients. Microparticle transport includes thaw-dependent particle suspension and velocity-dependent downgradient retention in heterogeneous porous media.

At the Umiujaq site, the two-dimensional vertical-plane simulations through a permafrost mound show how supra- and sub-permafrost groundwater flow can affect permafrost thaw which can lead to the release of microparticles, contributing to increased groundwater turbidity. At the Salluit site, supported by cross-sections of electrical resistivity tomography, the simulated 3D river-talik system follows the river meanders and responds dynamically to seasonal changes in air temperature and groundwater pumping.  The groundwater pumping rate needs to be managed for sustainable use, especially in winter when the talik is hydraulically disconnected from the river bed.