Precipitation‐Runoff and Storage Dynamics in Watersheds Underlain by Till and Permeable Bedrock in Alberta's Rocky Mountains

Abstract

Abstract The complex mechanisms driving runoff dynamics in mountainous watersheds with thick glacial till and fractured bedrock are not well understood. We examined long‐ and short‐term precipitation‐runoff relationships and quantified subsurface storage in watersheds on the eastern slopes of Canada's Rocky Mountains to develop a conceptual understanding of runoff generation processes in this region. Fractured permeable bedrock (bedrock storage) and glacial till deposits (soil and till storage) collectively result in large dynamic storage (hydrologically active storage). The transition from multiyear dry to multiyear wet patterns increased specific discharge due to less bedrock storage opportunity but did not influence event‐scale rainfall‐runoff responses. Rather, event‐scale rainfall‐runoff responses were governed by snowmelt and soil and till storage capacity. While winter snowfall was an important predictor of annual runoff ratios, storage at the end of the previous fall also influenced runoff ratios. These complex subsurface dynamics and large storage capacities are important for understanding how mountainous watersheds with glacial till deposits may respond to disturbance or climate change.