Xiang Huang, David L. Rudolph and Jiaqi Weng (2022). Thermal-hydraulic-mechanical-chemical modelling in a permafrost-affected groundwater system. Proceedings of the GWF Annual Open Science Meeting, May 16-18, 2022.

The continuous growing interest for predicting the dynamics of the thermal regime and groundwater flow systems subjected to freeze-thaw cycles is enhancing the need for a more comprehensive understanding of the integration and feedback among the thermal, hydraulic, mechanical, and chemical fields. This is of particular significance in discontinuous permafrost terrain under a changing climate. However, predicting those behaviours in permafrost-affected groundwater systems is challenging due to the inherent nonlinear interactions and coupling between subsurface mass and energy transport processes. Here we present a fully coupled thermal-hydraulic-mechanical-chemical (THMC) model, which includes heat conduction and convection, water-ice phase change, groundwater flow driven by pressure and thermal gradients (cryosuction), linear elastic stress-strain relationships, and solute transport with adsorption. This THMC model framework is first validated by lab experimental measurements from literature and then applied to an idealized aquifer system within a discontinuous permafrost environment in which groundwater flow is driven by topography. Simulations show the impact of climate warming scenarios on permafrost distribution, groundwater discharge to surface water bodies, frost heave and thaw settlement, and the transport of conservative, yet sorptive solutes over timescales of decades to centuries. Our simulation results showed that i) disappearance of residual permafrost significantly changed groundwater and thermal flow paths and enhanced base flow to stream/rivers; ii) the magnitude of thawing front moving rate in supra-permafrost is significantly higher than that in the sub-permafrost; and iii) the thawing-induced settlement/consolidation and solute-affected early thawing behaviour (lower freezing point) cause non-linear evolution trends of the increasing groundwater discharge as well as the solute mass flux to streams. These insights into changing patterns of groundwater dynamics, thermal regime, discontinuous terrain deformation and contaminant transport behaviour will help explain observed changes in arctic landscapes and are crucial for examining northern water cycles.

AOSM2022 Northern Water Futures/core modelling team First Author: Xiang Huang, University of Waterloo Additional Authors: David L. Rudolph and Jiaqi Weng, University of Waterloo