Weichselian permafrost depth in the Netherlands: a comprehensive uncertainty and sensitivity analysis

Abstract

Abstract. The Rupelian clay in the Netherlands is currently the subject of a feasibility study with respect to the storage of radioactive waste in the Netherlands (OPERA-project). Many features need to be considered in the assessment of the long-term evolution of the natural environment surrounding a geological waste disposal facility. One of these is permafrost development as it may have an impact on various components of the disposal system, including the natural environment (hydrogeology), the natural barrier (clay) and the engineered barrier. Determining how deep permafrost might develop in the future is desirable in order to properly address the possible impact on the various components. It is expected that periglacial conditions will reappear at some point during the next several hundred thousands of years, a typical time frame considered in geological waste disposal feasibility studies. In this study, the Weichselian glaciation is used as an analogue for future permafrost development. Permafrost depth modelling using a best estimate temperature curve of the Weichselian indicates that permafrost would reach depths between 155 and 195 m. Without imposing a climatic gradient over the country, deepest permafrost is expected in the south due to the lower geothermal heat flux and higher average sand content of the post-Rupelian overburden. Accounting for various sources of uncertainty, such as type and impact of vegetation, snow cover, surface temperature gradients across the country, possible errors in palaeoclimate reconstructions, porosity, lithology and geothermal heat flux, stochastic calculations point out that permafrost depth during the coldest stages of a glacial cycle such as the Weichselian, for any location in the Netherlands, would be 130-210 m at the 2σ level. In any case, permafrost would not reach depths greater than 270 m. The most sensitive parameters in permafrost development are the mean annual air temperatures and porosity, while the geothermal heat flux is the crucial parameter in permafrost degradation once temperatures start rising again.

Numerical modelling of permafrost spring discharge and open-system pingo formation induced by basal permafrost aggradation

“…The total fractions of soil or rock ( ), water ( ), and ice ( ) are described respectively as; = 1 − , = • , and = − with being the total porosity. The effective thermal conductivity was calculated as root-square-mean, as done by Mottaghy and Rath (2006) and Govaerts et al (2016). When temperature change occur between and , freezing or thawing results in the release or absorption of latent heat, = 333.6 kJ kg -1 (Mottaghy and Rath, 2006).…”

“…When temperature change occur between and , freezing or thawing results in the release or absorption of latent heat, = 333.6 kJ kg -1 (Mottaghy and Rath, 2006). The latent heat of fusion was included in the expression of the equivalent volumetric heat capacity [J (m 3 K -1 ], (same approach as Govaerts et al, 2016):…”

Numerical modelling of permafrost spring discharge and open-system pingo formation induced by basal permafrost aggradation

“…This implies, for ex-ample, an increased outflow of deeper groundwater to rivers and lakes (Bense et al, 2012), increased rates of biogeochemical processes (Grosse et al, 2016), and potentially increased fluxes of methane or other compounds into the surface environment and atmosphere (Schuster et al, 2018). The surface discharge of sub-permafrost groundwater is currently exemplified by springs in the high Arctic (Andersen et al, 2002;Grasby et al, 2012;Haldorsen et al, 1996;Williams, 1970). If conditions are favourable, spring outflow may instead freeze below the active layer and initiate the growth of an ice-cored hill or pingo.…”

Potential Use of Time-Lapse Surface Seismics for Monitoring Thawing of the Terrestrial Arctic

“…For permafrost that is typically a matrix, water, ice, and air (in the following defined by subscripts m, w, i, and a, respectively). We also need to include latent heat L (kJ/kg) when one or more of the materials involved changes phase (here: water/ice, L = 333.6 kJ/kg), and following [21], we do this by replacing C with an equivalent heat capacity C eq that includes latent heat:…”

“…Combining this knowledge with Equation (1), we can now determine how ice saturation evolves with time and depth. Figure 1 shows the freezing point isotherm computed using Equation (1) for a simple model consisting of quartz sand with initial temperature T0 = −5 • C throughout the sediment column for three different assumptions of surface temperature: T1 is +1 • C, T2 is +5 • C, and T3 is +10 • C. We use typical values for the physical properties of the constituents from [21,24]. All three scenarios are displayed for a high-porosity ( Figure 1a) and a low-porosity sand ( Figure 1b) and for high-salinity (solid line) and low-salinity pore water (dashed line).…”