The impact of glacier recession upon the discharge of the Bow River above Banff, Alberta, 1951-1993

Three methods have been used to explore the volumetric change of glaciers in the Bow Basin above Banff for the years 1951 to 1993. Using aerial photography, the extent of glacier covers for the two years were mapped at a scale of 1:50,000. The first volumetric calculation of glacier loss was based on inventory criteria; the second a hyposgraphic curve method based on Young’s investigations in Mistaya Basin (1991) and the third stereo air photogrammetry and DEM comparisons using computer software. These methods were applied to the highly glacierized Hector Lake catchment within the Bow Valley and then extrapolated up to the whole basin above Banff. Reasonable agreement was achieved between the methods and the magnitude of glacier loss is estimated to be between 930 and 1400 m3 x 106 w.e. for the entire 42 year period. The bulk glacier “wastage” estimate was divided into proportions using the Peyto Glacier mass balance record. Unfortunately, the record began in 1966 and a back-cast to 1952 was necessary. The mass balance model proposed by Letreguilly (1988) was considered inappropriate for this task due to it not adequately representing the observations of recession on Peyto for 1952 to 1965. A new model utilizing Banff maximum summer temperature and Lake Louise snow course data was constructed. The proportions of seasonal wastage contributios to the river flow were estimated using a multiple regression model of monthly average temperature and precipitation with snow course data as the antecedent condition determinant. This model was used to predict the shape of the glacier (ice and firn) melt hydrograph from June to September. An estimate of the temporal variation of glacier recession inputs to the Bow River hydrograph at Lake Louise and Banff was facilitated by comparing known basin yields with the modelled “wastage” values. For 1952 to 1993 at Banff, the average annual wastage/basin yield ration is found to be around 2.3%; for 1965 to 1992 (years of available data) at Lake Louise the same ratio is 4.5%. For the extremely low flow year of 1970 these ratios increase to 12.5% and 16.2% respectively. The proportion of flow derived from glacier recession in August of this year is estimated to be around 53% for Banff and 84% for Lake Louise. It is thought that the basin scale extrapolation may lead to under-estimations of wastage but the mass balance back-cast is more likely to preferentially weight wastage contributions toward the latter part of the time series