Thermal-hydraulic-mechanical modelling of groundwater dynamics in a permafrost basin

ABSTRACT: Despite a growing interest in predicting the dynamics of the thermal regime and groundwater flow systems subjected to freeze-thaw cycles, simulations addressing the evolution and its feedbacks among the thermal, hydraulic, and mechanical fields in permafrost terrain under a changing climate has received comparably little attention. Here we present a fully coupled thermal-hydraulic-mechanical (THM) model, which includes heat conduction and convection, water-ice phase change, groundwater flow driven by pressure and thermal gradients (cryosuction), and elastic stress-strain relationships. This THM model framework was 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, frost heave and thaw settlement, and groundwater discharge to surface water bodies over timescales of decades to centuries. Our results demonstrated that i) there is significant deformation of the land surface and aquifer consolidation as the freeze-thaw process advances in time, ii) disappearance of residual permafrost significantly changed groundwater and thermal flow paths and enhanced base flow to stream/rivers. These insights into changing patterns of groundwater dynamics, thermal regime and terrain structure (deformations) help explain observed changes in arctic wetland patterns and landscapes and are crucial for northern water cycles.