Delaying seasonal snowmelt with avalanche activity: some results from the Cascade Mountains, southern British Columbia

Winter-time avalanche activity has the potential to delay a portion of annual snowmelt runoff from high elevation basins, if enough avalanche transported snow is deposited in sites where it is protected from subsequent ablation. In the Cascade Mountains of southern British Columbia, streamflow after the main snowmelt period in three years from a small (5 sq km) avalanche prone basin is substantially greater than from an adjacent forested, avalanche-free basin. The total excess of discharge over an eleven week period after the complete disappearance of undisturbed snow cover totals 80,000 cubic meters/sq km (80 mm) in 1992 and 1993, and 130,000 cubic meters/sq km (127 mm) over a thirteen week period in 1994. Despite much lighter than normal avalanche activity in all three winters, the delayed melting of avalanche show accounts for 18 to 30% of this excess and 12 to 21% of the total streamflow from the avalanche prone basin over these summer periods. Other factors which might play a role in producing these differences in basin yield are also discussed.