Environmental Monitoring and Research

Phase Change and Water Movement in Shallow Permafrost Inferred from Borehole Observations of Liquid Water Content and Temperature near Yellowknife, Canada

Thursday, November 22, 2018 - 11:40 to 11:59 Theatre 3


S. Gruber (Presenting)
Carleton University

Three experimental installations for measuring temperature and liquid water content as well as surface heave/subsidence were made in summer 2017 near Yellowknife. All three quantities are measured with hourly resolution. The measured depths for temperature and liquid water content extend from 0.1 to around 2 metres. Temperature is calibrated to +/- 0.02 ºC except for one borehole that is accurate to only +/- 0.1 ºC. Water content is measured with a repeatability of a fraction of a percent, but absolute calibration is a work in progress. Surface heave/subsidence is measured with an accuracy of +/- 0.5 mm. This contribution will show results based on data from July 2017 to June 2018, possibly to November 2018.

The derived freezing characteristic curves, although limited by the temperature range experienced at each depth, are of high quality and predominantly show clear hysteretic behaviour. Water movement in the frozen soil can be inferred during periods when the experimental freezing curves (volumetric liquid water content as a function of temperature) deviate from their otherwise smooth exponential shape. Additionally, short episodes of increasing liquid water content occur in cooling permafrost. This contribution will present the major phenomena observable from the combined data set of temperature, liquid water content and subsidence. Inferred water content in freezing soil will be discussed in more detail.

This work contributes to better understanding the behaviour of near-isothermal permafrost. This is important because permafrost in many locations is subject to thaw i.e., the gradual loss of ground ice. Here the relevant changes of material properties are incompletely understood based on temperature observation alone.