Vulnerability and Mitigation of the Dempster Highway to the Impacts of Climate Change

In 2013, a team made up of representatives from the government of Northwest Territories Highways, government of Yukon Highways, EBA Engineering and Carleton University began the first phase of a project aimed to assess the vulnerability of the Dempster Highway to the impacts of climate change. Surveys for the road began in 1958 and it was opened in 1979. It is a very remote, gravel road that provides the only year-round highway connection between Inuvik and the rest of Canada’s highway network, and was built on continuous permafrost for 90% of its 736 km. The road structure is an embankment, designed to maintain permafrost and prevent thaw subsidence. Over the past decade there has been an increase in the frequency and severity of issues related to drainage, erosion, and permafrost degradation. As the climate continues to warm, rising streams and increasing numbers of extreme weather events will put additional strain on the aging drainage system. With much of the highway located in the continuous permafrost zones, the warming climate also has a direct impact on the performance of the road, and can result in settlement, sinkhole formation, embankment failure, and other geohazards. Although there are no communities along the Yukon section of the highway, it is a critically important route to the Beaufort Delta Region in the Northwest Territories, serving as a long-haul transport route for food, fuel, supplies, and other goods. The remote location and length of the highway, coupled with the challenging terrain and ground conditions result in relatively high maintenance costs, considering the low traffic volumes (63 vehicles per day).

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Identifying Actions

Recognizing the need to ensure year-round availability of the Dempster Highway in the context of increasing traffic and a changing climate, Yukon Government Department of Highways and Public Works (HPW) has initiated a project to create a functional plan that specifically considers contributions of climate change to geohazards along the highway. Research and analysis required to assess climate and geohazard vulnerability have been carried out by the Northern Climate ExChange, part of the Yukon Research Centre at Yukon University, feeding into the functional planning process carried out by an engineering consultant. This project included various activities. The first step consisted of a preliminary assessment and literature review, where data and reports from previous surveys and studies pertaining to the study area and its surroundings were reviewed. Additional information such as articles, air photos, satellite imagery, geological and surficial geological maps were reviewed to gain insight about the geomorphologic and surficial geologic conditions of the area. The preliminary assessment was followed by field assessments which took place during the summer and fall, 2017. Field work included a combination of drilling, electrical resistivity tomography (ERT), and installation of ground temperature monitoring instruments. Core samples collected during drilling were kept frozen and returned to the Northern Climate ExChange (NCE) lab in Whitehorse for further analyses including soil grain-size analysis, cryostructure, volumetric excess ice content and gravimetric ice content. Ground temperature data were downloaded in the fall from monitoring instruments installed earlier in the summer, and from those installed in previous years.

Implementation

The objective of this project was to understand the issues contributing to identified geohazards along the Dempster Highway. To achieve this objective, a combination of desktop studies and field investigation were used. Surficial geology maps prepared by the Yukon Geological Survey and aerial and satellite images were interpreted as part of the project. These data were supplemented with geotechnical reports from consultants and discussion with civil engineers and maintenance crew from Highways and Public Works (HPW). Data and personal communications were combined, analyzed, and interpreted to complement previous efforts. Field investigation was focused largely on the acquisition of new geophysical information using electrical resistivity tomography (ERT) surveys. Shallow drilling was used to verify interpretations of geophysical information and to develop cryostratigraphic logs. Importantly, the work focuses on areas proximal to the highway embankment either in the field parallel to the highway, or at the toe and on the shoulder of the embankment, where minimal information is currently available. This information is key because it will allow project researchers to infer the probability of permafrost presence under the highway embankment. Electrical resistivity tomography (ERT) is a geophysical method that passes electrical current through stainless steel electrodes that are driven into the ground surface. A central “station” measures the resistivity distribution of the subsurface between electrode pairs. Mineral materials (except for specific substances such as metallic ores) are mostly non-conductive. Therefore, variation in the resistivity of a soil or rock profile is governed primarily by the amount of pore water or ice present in the profile, and the arrangement of the pores. ERT is very well suited to permafrost and hydrology applications because most water in frozen ground is in the solid phase and has a higher resistivity than liquid water. Permafrost distribution can then be inferred based on changes in resistivity between frozen and unfrozen ground.

Outcomes and Monitoring Progress

The NTAI has established four sites along the Dempster Highway in Yukon and the Northwest Territories to describe ground thermal regimes near and beneath the road and to monitor their response to climate change. At each site an automatic weather station records air temperature, relative humidity and windspeed and direction. Ground temperatures are measured to 10m depth beneath the road surface and at target depths of 8 m at the embankment toe and in undistributed ground. The data is collected every 4 hours and transmitted via the GOES system. Monitoring has continued since site installation in winter 2013-14.

Next Steps

Improved climate and weather information in the NWT is critical to inform adaptation planning. In December 2019, the GNWT signed a memorandum of understanding with ECCC to share weather and climate information and formalize the establishment of the Canadian Council for Weather and Climate Monitoring. The sharing of real time data allows for better weather forecasting and work will continue in 2020/21 to develop options to enhance climate monitoring in the NWT. Work is also being done to establish a better model between biophysics and economics to choose the best strategy that will ensure the a more sustainable maintenance cost.

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