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TitleEvaluation of threshold freezing conditions for winter road construction over discontinuous permafrost peatlands, subarctic Canadian Shield
AuthorSladen, W E; Wolfe, S A; Morse, P D
SourceNorthwest Territories Geological Survey, Yellowknife Geoscience Forum Abstract and Summary Volume 2019, 2019 p. 87-88 (Open Access)
LinksOnline - En ligne (complete volume - volume complet, PDF, 6.60 MB)
Year2019
Alt SeriesNatural Resources Canada, Contribution Series 20190332
PublisherNorthwest Territories Geological Survey (Yellowknife, NT, Canada)
Meeting47th Annual Yellowknife Geoscience Forum; Yellowknife, NT; CA; November 19-21, 2019
Documentserial
Lang.English
Mediaon-line; digital
File formatpdf
ProvinceNorthwest Territories; Nunavut
NTS85I/09; 85I/10; 85I/11; 85I/12; 85I/13; 85I/14; 85I/15; 85I/16; 85P/01; 85P/02; 85P/03; 85P/04; 85P/05; 85P/06; 85P/08
AreaTibbitt Lake; Cameron River; Gordon Lake; Tibbitt to Contwoyto Winter Road
Lat/Long WENS-114.0000 -112.0000 63.5000 62.5000
Subjectssurficial geology/geomorphology; geophysics; Nature and Environment; Science and Technology; Transport; permafrost; ground ice; periglacial features; organic deposits; peatlands; ice conditions; ice thickness; snow; floods; temperature; ground temperatures; logging techniques; thermal analyses; surface waters; lakes; Canadian Shield; road construction; road safety; air-freezing degree-day index
ProgramClimate Change Geoscience, Permafrost
Released2019 11 01
AbstractWinter roads are important transportation corridors in northern regions. The Tibbitt to Contwoyto Winter Road (TCWR) traverses the subarctic Canadian Shield and is the most heavily used winter road in Canada. In addition to lake-ice thickness, trafficability on the TCWR depends on adequate freezeback of overland portages, which primarily traverse peatlands underlain by discontinuous permafrost. We investigate threshold requirements for the initiation of winter road operation and assess the use of a recommended 305 °C-day air-freezing index (FDD305a) value to predict ground freezing at 30-cm depth, the standard depth for initiating winter road construction. Snow compaction and flooding enhanced freezeback of portages and early winter overland water flow had a similar effect. The majority of winter road portages were not frozen to a depth of 30 cm by FDD305a. The results indicate that an FDDa threshold of 1100 °C-days is more appropriate for drained and wet peatlands in this discontinuous permafrost However, TCWR winter road operators presently plan the construction of the winter road by calendar date rather than by evaluation of the air-freezing index. This practice results in a conservative approach to the start of the construction season, close to 1100 °C-days, when a higher percentage of sites are frozen to 30-cm depth than would be if FDD305awas used. In addition, the use of low-pressure vehicles for snow compaction during the start of the construction season is an environment. effective adaptation practice to speed up ground freezing.
Summary(Plain Language Summary, not published)
Winter roads are seasonally constructed roads servicing remote communities and resource development sites in northern Canada. The lake ice and frozen ground provide stable surfaces for vehicular traffic that would otherwise not be possible. Guidelines require 30 cm of frozen ground to support heavy equipment and use 305 air freezing degree-days (FDD305a) as the threshold to start winter road construction over land. This paper investigates the ground thermal conditions at 30-cm depth in discontinuous permafrost peatlands on and off right-of-way along the Tibbitt to Contwoyto Winter Road (TCWR). During the study period, the FDD305a threshold was insufficient for frost penetration to 30-cm depth in wet peatlands typical of the subarctic Canadian Shield. The current calendar date threshold used by the TCWR does however, provide sufficient time for adequate frost penetration.
GEOSCAN ID321392