Quantifying Heat Advection by Groundwater Flow in the Active Layer: Laboratory Simulations
Sabine Veuille1,2, Manuel Verpaelst
1,2, Simon Charbonneau
1, Katerine Grandmont
1,2 and Daniel Fortier
3, (1)Université de Montréal, Montréal, QC, Canada, (2)Centre d'études nordiques, Québec, QC, Canada, (3)University of Montreal, Montreal, QC, Canada
Contact First Author: Sabine Veuille; sabineveuille@gmail.com
English Abstract:
Rising temperatures due to climate change affect permafrost thermal regime through convective heat transfer at the air-soil interface. Surface run-off and groundwater flow also impact the ground thermal regime by convective heat transfer processes and must be taken into account to obtain an accurate global thermal balance. The magnitude of surface run-off and subsurface water flow is strongly related to topography, and both processes contribute to the thawing in the active layer. This phenomenon is even more pronounced where the active layer is ice-rich. Although the influence of heat advection has already been demonstrated, the efficiency of thawing by convection compared to thawing by conduction has been poorly quantified so far. This knowledge gap has been in part created by the impossibility to control all parameters in natural settings. The Peclet number is an indicator that can be used to determine which of the two phenomena is predominant. However latent heat is not included in the equation which limits the analysis, especially with very low flow.
To overcome field variability, experiments were carried out in a controlled environment to link field conditions with laboratory tests. To replicate physical permafrost models and compare the efficiency of thawing by convection versus thawing by conduction, eight cells were designed and filled with different saturated soils. The cells were submitted to two different air thawing conditions: 15 and 5°C. Four cells were thawed by conductive heat transfer whereas four others were submitted to sub-surface flow. Slope and water temperatures, 15 and 5°C, varied with the experimentations. Results show that the efficiency rate of thawing by convection in comparison to thawing by conduction is proportionally correlated with temperatures, water flow and slope. Convection is 2 orders of magnitude more efficient when temperatures are different (warmer water temperature) than when they are equal.
