Snowmelt runoff processes in a headwater lake and its catchment, subarctic Canadian Shield

Abstract During the snowmelt season, surface runoff into northern Canadian Shield lakes is governed by the distribution of snow and its ablation, storage in catchment slopes and valleys, and flow delivery from uplands, bottomlands and from upper lakes. For the lake studied, time lags exist between the commencement of snowmelt and the arrival of runoff to the lake, with evaporation from the uplands and bottomlands consuming some of the meltwater produced. Inflow from an upper lake is delayed. With all these inputs, the lake becomes flooded, first forming a moat, followed by an expansion of the open water areas, which are subject to evaporation loss. Lake outflow begins when water level rises above the outlet threshold. For the snowmelt season, outflow constitutes 40% of total melt and rainfall. The lake itself is a major storage that continues to maintain outflow until the lake level drops below the threshold in early summer, after which flow ceases. Snowmelt is the main period when runoff is generated from the headwater catchment to replenish storage depleted in the previous summer, and to produce flow along the Shield valley that contains a chain of lakes. Copyright © 2006 John Wiley & Sons, Ltd.