GROUNDWATER CONTRIBUTION TO WINTER STREAM FLOW IN THE CANADIAN ROCKIES

Alpine watersheds represent an important source of freshwater in western Canada. Urbanization is beginning to push further into alpine environments, putting increased stress on the water supply. For this reason, our understanding of headwaters in alpine environments is crucial in order to manage and allocate our water considering the potential effects of climate change on river flow regime. Much of the previous research on mountain rivers has focused on summer flows that provide water supply during the high-demand season, however late fall and winter flows are also important as they maintain the critical baseflow during the majority of the year. Since rainfall, snowmelt, and glacier melt make little contributions to alpine streams during winter months, essentially all winter baseflow is provided by groundwater discharge. Therefore, the analysis of winter baseflow provides valuable information regarding the occurrence of groundwater in alpine watersheds. We will analyze the baseflow records in 20 watersheds (14-3900 km²) in the southern parts (< 53° N) of the Canadian Rockies. Preliminary results indicate that winter baseflow is remarkably consistent (0.25-0.5 mm d^-1) among most of the watershed, and has little sensitivity to inter-annual variability of precipitation and air temperature. This suggests that the groundwater storage and release in these watersheds are primarily controlled by stationary factors such as geology and topography. We will examine the influence of various geological and topographical factors on winter baseflow and propose a conceptual framework for understanding groundwater processes in the Canadian Rockies. These results are compared with detailed field-based process studies of three sub-watersheds within the Lake O’Hara Research Basin (14km²) in the Rockies, which has similar winter baseflow (0.2 mm d^-1) to further our understanding of the hydrological processes controlling winter baseflows.