Hydrological processes and streamflow in a lake dominated watercourse

This paper discusses results of a nested basin study investigating run-off responses along the watercourse in a 137 km(2) subarctic Canadian Shield watershed. Catchment areas contributing surface run-off to the basin outlet shrink after a maximum during spring snowmelt because of storage demands in headwater wetlands and lakes. This decrease is significant as summer contributing areas to the basin outlet are only 4% the size of spring melt contributing areas. This reduction in contributing area and decrease in antecedent lake levels lead to a two order of magnitude decrease in run-off ratios from spring snowmelt to midsummer. Furthermore, the attenuating influence of lakes on the run-off hydrograph increases the opportunity for evaporative losses, which prevents small run-off events from maintaining a measurable flood wave through the basin. The location at which a run-off event is interrupted in the watercourse is a function of lake size relative to upstream run-off inputs. Run-off is more susceptible to evaporative losses in large receiving lakes where inflow per unit area is less. These processes cause intermittent streamflow through the basin. These results have repercussions for coupled atmospheric/hydrological models whose resolution is approaching the basin scale. The incorporation of lateral transfer schemes that encompass these processes and physiographic influences on streamflow response is encouraged. Copyright (c) 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.