Snow cover extent during spring snowmelt in the south-central interior of British Columbia

Abstract

The H60 contour elevation (i.e., elevation above which 60% of the watershed lies) is commonly used in hydrologic impact assessments of snowmelt-dominated watersheds in the interior of British Columbia. The H60 concept assumes that the upper 60% of a mountainous watershed is snow-covered and is contributing meltwater during the time of peak flow; thus, peak streamflow is assumed to be more sensitive to forest harvesting above the H60 contour elevation. However, the concept has not been well-verified by field data. This study tested the H60 concept for the Mission Creek watershed in the Okanagan region of British Columbia. Snowlines were mapped during spring freshet (snowmelt runoff) for 5 years (1999–2003). These data were analyzed with corresponding runoff data to determine, for each year, the snowline that best represents the lower extent of snow cover upon commencement of the peak flow period. It was found that, on average, 38% of the Mission Creek watershed was snow-covered at the start of the peak flow period, which represents an average contour elevation of 1520 m; the H60 elevation is 1300 m. These results suggest that the H60 concept overestimates the extent of snow cover during the spring peak flow period and, therefore does not reasonably represent the snow-sensitive zone of the Mission Creek watershed. This may be important in the assessment of potential forest harvesting impacts in the watershed.