Coupled modelling of permafrost and groundwater : a case study approach

• Main Author: Scheidegger, J.
• Format: Report
• Language: English
• Published: British Geological Survey 2016
• Subjects: Ice; permafrost
• Online Access: http://nora.nerc.ac.uk/id/eprint/519040/; https://nora.nerc.ac.uk/id/eprint/519040/1/CR16053NA.pdf; https://nora.nerc.ac.uk/id/eprint/519040/2/CR16053NB.pdf

This report investigates the sensitivity of simulated permafrost thickness and dynamics to a variety of climatic, geological and hydrogeological conditions for two geological environments, basement under sedimentary cover and a low permeability succession of Mesozoic shales and siltstones (Case 1 and Case 2 respectively). A combination of one dimensional heat conduction modelling, including the effects of freeze-thaw, and two dimensional heat conduction-advection modelling, including freeze thaw, has been undertaken to simulate permafrost development in these two contrasting geological environments. This enables an assessment of the sensitivities to a range of possible geological parameters, advective heat flow, and the effect of glaciation with and without the influence of glacial loading. In this report, permafrost is defined as the sub-surface in which ice is present even in very small amounts, i.e. ice content is greater than 0%, and in the model, this is at the zero degree isotherm. The maximum permafrost thickness is strongly dependent on the mean annual surface temperature, the presence of ice that will insulate the system and the duration of the cold phase. By scaling the minimum temperature of 57 Pliocene-Pleistocene globally distributed benthic δ18O records to temperatures of 14°C, 18°C and 25 °C below the present day mean annual temperature, the maximum permafrost thickness for Case 1 is simulated to reach 171 m, 248 m, and 475 m, and for Case 2 80 m, 138 m, and 238 m respectively. The difference in permafrost thickness between the two Cases is attributed to the variation in subsurface rock properties. Deeper permafrost depths than for Case 1 and 2 can be expected where the thermal conductivity is higher than for Case 1 and 2. A sensitivity study of the geological parameters has shown that there is a strong, non-linear, relationship between thermal conductivity, latent heat and geothermal heat flow for a series of temperatures representative of the glacial cycles of the past one million years. This is ...