HYDROGEOLOGY OF A SMALL WATERSHED LOCATED IN THE DISCONTINUOUS PERMAFROST ZONE OF NORTHERN CANADA

Groundwater was recently recognized as an important component of the water cycle in cold environments. In a warming climate, groundwater base flow has an important control on river discharge. Groundwater can also have an important control on permafrost dynamics due to advective heat transport. Thawing permafrost due to climate warming is also expected to allow the development of active groundwater flow systems and to increase groundwater availability as a source of drinking water for northern communities. In this context, groundwater distribution and flow dynamics were studied in a small watershed located in the discontinuous permafrost zone at Umiujaq in Nunavik (Québec), Canada, to assess the seasonal variations and perform a quantitative analysis of the water cycle in a subarctic watershed. Due to the complexity of the subsurface geology within the watershed, an integrated investigation was instrumental to provide a detailed understanding of the hydrogeological context as a basis for the water balance. The investigation revealed a complex stratified groundwater flow system with two aquifers separated by a thick layer of deep marine sediments (silt) in which discontinuous permafrost is found. A thin water table aquifer perched over the silt unit is found in the upper part of the valley, while a confined aquifer below the silt unit is found in the lower part of the valley, with upward flow toward a small stream. While permafrost has limited impact on groundwater availability in this watershed, it exerts an important control on groundwater flow dynamics since it limits surface and groundwater interaction through the silt unit. Projected permafrost degradation will likely increase stream baseflow, especially in winter, as it will be easier for groundwater from the lower aquifer to flow upward across the silt unit.