Hydrology of subarctic Canadian shield: bedrock upland

Runoff generation processes in the Canadian Shield were investigated to reconcile the considerable variability of runoff ratios noted by previous studies. Four bedrock plots near Yellowknife, Northwest Territories, Canada were studied between May 1999 and September 2000. Surface runoff increases with rainfall and snowmelt intensity because higher values of the latter can exceed fracture infiltration capacities. The size distribution of fractures affects infiltration while the fracture network controls the direction of surface flow. Frost has no effect on infiltration since the fractures are seldom ice filled. Storms of long duration and intermittent rainfall provide intervals between rainfalls during which evaporation can reduce the water available to runoff. Available storage in bedrock depressions, both empty and soil filled, retard surface flow and lengthen residence time, in turn enhancing evaporation and infiltration at the expense of runoff. The further downslope available storage is on the slope the more control it has on plot runoff magnitude. These field results show that rainfall–runoff relationships for bedrock slopes in the Canadian Shield should be considered in terms of microtopography, bedrock and soil characteristics and climate.