Avalanche Snow Melting and Summer Streamflow Differences between High-elevation Basins, Cascade Mountains, British Columbia, Canada

Abstract

Unit-area discharge after late May in 3 yr from an avalanche-prone basin (5 km²) in the Cascade Mountains, southern British Columbia, is significantly greater than that from an adjacent forested, avalanche-free basin (12 km²). Some of this difference is attributable to later melting of undisturbed snow cover in the avalanche-prone basin. Following the disappearance of this snow cover in all years, unit-area discharge continues to be greater than from the avalanche-free basin, the difference totalling 80 to 130 mm runoff over a period of 11 to 13 wk. The delayed melting of avalanche snow in the avalanche-prone basin accounts for 16 to 35% of this difference and 10 to 24% of the total basin yield during the period. When only the period between the disappearance of undisturbed snow cover and all avalanche snow is considered, the proportions in 1 yr are in the order of 48% of the runoff difference and 34% of the total yield. These results were obtained after three winters of very low snow accumulation and corresponding avalanche activity. A substantially greater effect on streamflow might be produced by more intense avalanche activity.