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

Three methods were used to determine the net volumetric loss (wastage) of glacier cover within the Bow Valleyabove Banff, Alberta between 1951 and 1993 (see Hopkinson, 1997). It was estimated that between 1100 and 1650 m3 x 10 to the 6th of ice volume was lost during this time period. The median value of 1375 m3 x 10 to the 6th was converted to a water equivalence value of approximately 1170 m3 x to the 6th by assuming a glacier ice (including firn and voids)/water ratio of approximately 85%.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. Banff maximum summer temperature and Lake Louise snow course data were used as surrogates for summer and winter glacier mass balance, respectively. Seasonal wastage contributions to river flow were estimated for 1967 to 1974 using modelled values of glacial melt (ice and firn only) generated for Peyto Creek by Young ( 1982).An estimate of the temporal variation of glacier recession inputs to the Bow River hydrograph at Banff was facilitated by comparing known basin yields with the modelled wastage values. For 1952 to 1993, the average annual wastage/basin yield ratio is found to be around 2.3%. For the extremely low flow year of 1970 this ratio increases to 12.5%. The proportion of flow derived from glacier recession in August of this year is estimated to be around 53%. It is thought that the mass balance back-cast may slightly under-estimate wastage values in the early part of the time series, therefore, leading to an over-estimation later on.