Some Observations on Permafrost Distribution at a Lake in the Mackenzie Delta, N.W.T., Canada

HE THAWING effect of water in contact with permafrost is a problem of major concern to engineers engaged in northern construction. Improper drainage or disrupted natural drainage, which allows water to pond adjacent to or under structures such as buildings, roads, or airstrips, usually results in an increased depth of thaw of the perennially frozen ground. In many cases the performance of the structure is seriously affected - sometimes failure has resulted. The degradation of permafrost by water is of even greater con- cern when dykes or dams are constructed on perennially frozen ground and large areas are covered by the water impounded behind these embankments. The design and performance of these structures and the stability of the underlying foundation material is dependent on a knowledge of the rate at which thawing will take place and the depth to which the perennially frozen ground will thaw. One method of improving knowledge of the thawing effect of water on permafrost and of providing some guidance for future engineering design is to study the present level of permafrost under natural bodies of water in the north, such as lakes and streams. An investigation to determine the distribu- tion of permafrost under and adjacent to a lake in the Mackenzie Delta near the new townsite of Inuvik, N.W.T. was carried out by members of the Divi- sion of Building Research in April 1961. This study, although limited in scope, yielded interesting results, which are now reported. Some aspects of the thawing effect of water The occurrence and movement of surface and subsurface water exerts an important influence on the thermal regime of the ground. Because of the heat storage capacity of water, its movement from one area to another pro- vides the means to transfer substantial amounts of thermal energy. Moving or standing bodies of water that accumulate an excess of thermal energy inhibit the formation of permafrost and cause thawing of the underlying frozen ground.