Contribution of icing ablation to streamflow in a discontinuous permafrost area Sharon Reedyk, Ming-ko Woo, and Terry D. Prowse Abstract: Icings, present in many small streams in the discontinuous permafrost environment, alter the seasonal water balance by redistributing a component of flow from the winter to the spring. Icing ablation continues to contribute to streamflow after the disappearance of the snowpack and constitutes an additional source of runoff. The temporal variability and significance of icing ablation to streamflow were examined with a combined water balance and isotope study in a tributary of Manners Creek, Northwest Territories. Icing accounted for 20% of the surface water available for melt. Over the spring study period, icing ablation accounted for 6% of total streamflow, while the total surface-water flux provided 8 % . Shallow subsurface flow, which consisted of infiltrated snow meltwater and premelt groundwater, contributed the most to streamflow. At the end of the melt period, icing ablation was the only source of surface runoff to the stream and was similar in magnitude to the estimated evapotranspiration loss. Comparison with other studies revealed that on a regional scale, the hydrologic role of icing ablation is controlled by the interaction between the timing of melt, the magnitude of groundwater recharge, the spatial extent of permafrost, and the depth of seasonal frost. R6sum6 : La formation de lentilles de glace superficielle, apparaissant dans de nombreux petits affluents en region de pergCliso1 discontinu, modifie 1'Cquilibre hydrique saisonnier en redistribuant, de l'hiver jusqu'au printemps, une partie de 1'Ccoulement. Suite a la disparition de l'accumulation annuelle de neige, l'ablation des lentilles de glace superficielle procure une source additionnelle d'eau de ruissellement qui entretient 1'Ccoulement fluviatile. La variation temporelle et les effets de I'ablation des lentilles de glace superficielle sur 1'Ccoulement fluviatile ont CtC examines de concert avec une Ctude de l'tquilibre hydrique et des isotopes dans un affluent de Manners Creek, des Territoires du Nord-Ouest. Les lentilles de glace constituaient l'tquivalent de 20% des eaux de surface disponibles aprks la fonte. Durant la ptriode printanibre de l'ktude, l'ablation des lentilles de glace superficielle a fourni 6% du total de 1'Ccoulement fluviatile, tandis que la contribution du flot total des eaux de surface Ctait de 8%. L'Ccoulement de subsurface i faible profondeur, incluant l'eau de fonte infiltrCe et celle dCji emrnagasinke sous forme d'eau souterraine, represente la principale source de 1'Ccoulement fluviatile. A la fin de la pCriode de fonte, l'ablation des lentilles de glace superficielle Ctait l'unique source qui alimentait 1'Ccoulement de surface de I'affluent, et sa production Cquivalait sensiblement la perte estimCe due ?i I'Cvapotranspiration. La comparaison de nos rCsultats avec ceux de d'autres Ctudes a rCvClt qu'i une Cchelle rCgionale, le rBle hydrologique de l'ablation des lentilles de glace superficielle est dtterminC par I'interaction entre I'Cpisode de la fonte, la magnitude du rCapprovisionnement en eau de la nappe souterraine, I'Ctendue spatiale du pergClisol et la profondeur du gel saisonnier. [Traduit par la rCdaction] Introduction valent in many small streams in the discontinuous permafrost Icing is defined as a "sheetlike mass of layered ice formed on zone where base flow and seepage persist throughout the the ground surface, or on river or lake ice, by freezing of winter (Carey 1973; Kane and Slaughter 1972; Van Ever- successive flows of water that may seep from the ground, dingen 1982). Reported mean depths of icing range from < 1 flow from a spring, or emerge from below river ice through to 10 m (Grey and Mackay 1979; Kane and Slaughter 1972). fractures" (Permafrost Subcommittee 1988). Icings are pre- Reported surface areas and volumes of icings range from 0.01 to 40 km2 and 14 000 to > 100 x lo6 m3, respectively Received October 25, 1993. Accepted October 5, 1994. S. Reedyk' and M.-k. Woo Department of Geography, McMaster University, Hamilton, ON L8S 4K1, Canada. 1 T.D. Prowse National Hydrology Research Institute, 11 Innovation Boulevard, Saskatoon, SK S7N 3H5, Canada. ' Present address: Department of Zoology, University of Alberta, Edmonton, AB T6G 2E9, Canada. (Froehlich and Slupik 1982; Grey and Mackay 1979; Van Everdingen 1982). Descriptive accounts of large icings in northern Russia indicate that their ablation may contribute to streamflow well into the summer (Froehlich and Slupik 1982; Sokolov 1978). Kane and Slaughter (1972) estimated that 40% of winter base flow in a small Alaskan watershed was stored as icing, which, when melted, contributed up to 4% of annual strearn- Can. J. Earth Sci. 32, 13-20 (1995) Printed in Canada / ImprimC au Canada Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by McMaster University on 12/05/14 For personal use only.