NWT RESEARCH DATABASE

Regions: Sahtu Settlement Area, Dehcho Region

Tags: physical sciences, climate change, environmental baseline, thermokarst, permafrost mapping, airborne geophysics

Objective(s): To use airborne geophysics (helicopter-based surveys) flying the central Mackenzie Valley corridor along the existing winter road to map permafrost across different landforms and terrain types.

Project Description: This licence has been issued for the scientific research application No. 5160. The research team will use airborne geophysics (helicopter-based surveys) flying the central Mackenzie Valley corridor along the existing winter road to map permafrost across different landforms and terrain types. The objectives of this study are to: 1) Fly multiple lines of airborne electromagnetic geophysical data (between 2 and 4 parallel lines 100 m apart) between Wrigley and Norman Wells, NWT along the existing winter road corridor; 2) Using the geophysical and existing geological data, produce maps of the Mackenzie valley corridor of permafrost thickness and ground ice distribution; 3) Using these data, the research team will produce maps of ground hazards (areas of potential thaw) along the corridor. These data will be used by graduate students at the University of Alberta and University of British Columbia as part of their PhD Research in Earth Sciences and Geophysics. The research team will use airborne geophysics—Airborne Electromagnetic Methods (AEM) – an approach used successfully in Alaska to map permafrost, areas of thawed ground (taliks), groundwater interactions with permafrost, and ground ice. AEM geophysical surveys allow 3-D snapshots, over large distances quickly, and identify relations between surface water and geological features and the underlying permafrost and ground ice. One of the main insights has been to understand the influence of surface water and groundwater on permafrost and how that affects permafrost distribution and potential thaw areas. The AEM method works by having pairs of coils in a sensor (fibre glass and Kevlar tube about 10 m long) that is suspended below a helicopter that flies about 60 m above the ground surface. Each pair of coils operates at a different frequency (400 Hz to 140,000 Hz) but at levels safe to humans and animals and well below Health Canada and U.S. IEEE guidelines for exposure to electromagnetic signals. In an AEM survey the sensor transmits an electromagnetic signal at multiple frequencies and reads back the reflection from the ground. Longer wavelengths penetrate deeper into the earth while shorter wavelengths image shallower layers. More conductive layers return a stronger signal while less conductive (more resistive) layers return a weaker signal. In permafrost areas, frozen ground is strongly resistive while thawed ground and water is much more conductive. Combining these measurements with knowledge of the geology (from existing borehole and earlier geological work) the ground subsurface, including whether permafrost is present, its thickness and ground ice content can be mapped. Relations between surface features and subsurface geophysical data (real data from Alaska) allow understanding of the connection between subsurface permafrost, ground ice and taliks with surface features not available by other methods. The research team will utilize the Resolve system from XCalibur MultiPhysics which uses multiple frequencies close to radio waves (from 400 and 140,000 Hz). These are transmitted and measured from a sensor suspended below the aircraft. Typically, the aircraft will fly at relatively low speed (a few 10s of m/s). The helicopter will fly at about 60 m above the ground surface (and any obstacles) with the sensor suspended about 30 m below the aircraft. These flights will take place between 7 am and 8 pm usually in 3 trips lasting 2.5-3 hours each. The helicopter flying crew is supported by a ground crew that aids with calibration of the sensor. The pilot is guided by a GPS navigation system and radar altimeter in the helicopter. The survey lines are pre-programmed in the navigation system and provide guidance to the pilot. The surveys consist of 2-4 closely spaced lines flown in blocks (as shown in the attached maps). These blocks will be analyzed to produce a 3D image of each block. The helicopter is equipped with a satellite phone system allowing ground to air communications. Survey flights follow Transport Canada regulations for underslung load operations. The helicopter pilot will avoid overflight of people, vehicles or structures that could contain people. Following the AEM surveys, the research team will pair these data with the existing geological studies that they have been carrying out within the region. A Geophysics PhD student, Keytash Moshtaghian, will be working on the geophysics parts of the project. The research team will utilize the geological data, collected previously in the area over the last 7 years, with existing drilling data that has been produced in the past from earlier pipeline projects. The team estimates that they will fly about 800 km of AEM surveys between Wrigley and Norman Wells. Once the research team has these data and has developed the relations to the geology and permafrost conditions, they will use these data to map larger areas of the central Mackenzie valley outside of the immediate transportation corridor. These data will be especially valuable as we try to understand why some areas of permafrost are changing rapidly while other areas are relatively stable. Ultimately the research team believes these data will become valuable for future planning through the region. The research team would like to give community presentations on the work either in person (or remote), depending on community interest and timing, following the same approach they used communicating their past work in the Sahtu region. This would include in-person presentations in the communities closely associated with the proposed permafrost surveys (Norman Wells, Tuli´t'a and Wrigley), or remote presentations that coincide with existing meetings. The team used both methods this past year in the Sahtu region, and found both methods to be effective opportunities to present research but also to hear about community concerns, input and observations related to changing permafrost conditions. This past year, for example, the team gave community presentations in Tuli´t'a and Déline (late September 2022). In those communities they hosted a community dinner and a day in the schools with high school youth. The team also gave presentations on permafrost and spent time outside looking at permafrost with grade 10-12 students in the community. The students were very receptive and asked very good questions. The team would also offer to give updates on the work in the local environmental forums. This past December, the team made a presentation, answered questions, and were given direction by community members in the Ne? K’? Dene Ts’i?li? Forum in December 2022 regarding the team’s permafrost work in the Sahtu. This was well attended and seemed to reach a different audience than the community presentations. The surveys and all the data will (likely 2024) be published in an Open File Report by the Northwest Territories Geological Survey ensuring the data are available to anyone interested in permafrost within the areas that were flown in our surveys. The fieldwork for this study will be conducted from August 7, 2023 to September 30, 2023.