Numerical simulations of microparticle transport in a thawing permafrost environment

ABSTRACT: Suspension, transport, and deposition of microparticles in a porous medium are important processes to consider when studying the response of a porous medium to physical perturbations. Permafrost thaw resulting from climate change, for example, can disturb the soil network structure and mobilize fine particles, presenting long-term risks to ground stability, and increasing groundwater turbidity and sediment loading to streams. Furthermore, groundwater pathways can be reactivated and soil matrix connectivity can be modified, enhancing groundwater flow and discharge rates. To date, the behavior of such systems and the consequences of such perturbations on particle transport have not been well-documented. In this context, to better understand the complex processes involving particle transport through a porous medium, we adapted the finite element numerical model Heatflow/Smoker for coupled groundwater flow and heat transfer to include the mobilization, transport and deposition of microparticles. The particle transport processes were simulated based on a modified advection-dispersion-deposition equation accounting for the influence of flow velocity and porous media grain size distribution. The model was tested against an analytical solution, calibrated to laboratory experimental data then up-scaled to a 2D conceptual model containing discontinuous permafrost based on observed conditions in the Tasiapik Valley near Umiujaq, Nunavik, Quebec. The conceptual model includes a thawing permafrost block within a 2D flow system, advective-conductive heat transport, heat exchange at ground surface, ice-water phase change with latent heat, as well as particle suspension during permafrost thaw, particle transport and deposition. Our simulations highlight the role of hydrodynamic conditions and the physical characteristics of the soil on the transport of suspended particles and on depositional mechanisms, and the susceptibility of the porous medium to thermo-suffosion in permafrost environments.