Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Geography & Environmental Studies

Program Name/Specialization

Environmental Science

Faculty/School

Faculty of Arts

First Advisor

Dr William Quinton

Advisor Role

Supervisor

Second Advisor

Michael Braverman

Advisor Role

Expert Engineering Advisor

Abstract

Northwestern Canada is one of the most rapidly warming regions on Earth. The southern limit of the discontinuous permafrost zone is highly sensitive to small climatic fluctuations and presently experiencing a rapid landscape change due to accelerated permafrost thaw, which is further exacerbated by anthropogenic disturbances such as seismic exploration. Recent research has begun to examine both natural and mechanical approaches to minimize permafrost loss, although the utility of such methods in peatland environments is not well understood. This study explored the efficiency of natural and artificial ground cooling processes in a peatland environment by evaluating snow exclusion and thermosyphon methods. Ground-freezing devices have been used at the Scotty Creek Research Station in the Northwest Territories, Canada, since 2013 for experimental studies on permafrost stabilization and regeneration. Data arising from these studies were used in the present study to evaluate the effectiveness of specific designs and applications of such devices. The effect on ground freezing was evaluated for 7 freezing systems deployed along the seismic line: (a) two-phase, passive, 7-thermosyphon configuration, (b) single-phase, active thermosyphon, (c) single-phase, active, 4-thermosyphon configuration, (d) single-phase, passive, coaxial, non-insulated thermosyphon, (e) single-phase, passive, coaxial, insulated thermosyphon, (f) single-phase, active thermosyphon conjoined with the snow shading cone and, (g) four individual snow shading cones. It was found that the single-phase, active thermosyphon conjoined with the snow shading cone was the most effective ground freezing system in a highly saturated peat environment, reaching minimum ground temperatures between -13.3 to -14.2 o C 80 cm below the ground surface. Natural ground cooling by direct coupling of air and ground temperatures is strongly limited by the presence of snow however, average ground temperatures in the snow-reduced areas remained lower by only 0.7-1.2 o C within an 80 cm vertical profile than in the snow-covered areas, which suggests that other factors such as moisture content may exert dominant control over ground cooling range. Nonetheless, at the end of the summer snow-reduced areas maintained a 15 cm thick frozen layer at 60 -75 cm below the ground surface. We are proposing that systematic monitoring of snowpack development and decay can be used as a proxy for ground thermal profile evaluation. This study supports the feasibility of low cost, readily deployable ground freezing systems that can mitigate permafrost thaw and improve the adaptability of engineering designs to changing environmental conditions.

Convocation Year

2020

Convocation Season

Spring

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