Repeated Glacier Mapping for Hydrological Purposes: Water Power Planning

Abstract

Good hydrological knowledge is necessary for the planning of a hydro-electric power installation. Observations of daily discharge in Norwegian streams are available for several decades, but for glacierized basins there is a lack of information. Either the observation period is too short or it comprises mainly years when glaciers retreated and thus produced extra amounts of melt water – a direct result of negative mass balance. Consequently, many discharge figures are too ‘optimistic” — they indicate larger average run-off than would be the case if glaciers were in a steady state, or, even worse, if they started to grow and then started to reduce their melt-water contribution to rivers. Our means of correcting actually observed discharge figures for glacier influence is to perform annual mass-balance measurements. This has been done since 1948 for one glacier and since 1962 for several glaciers and results have been used in the planning of power stations. The method is, however, relatively costly. Another method is now being developed. Repeated glacier mapping makes it possible to calculate the average change (decrease) in glacier volume between the years when air photographs were taken. Therefore, several glacier maps have been produced based upon older vertical photographs and new maps are constructed from repeated air photography of the same glaciers. By subtraction, the total decrease in ice volume can be calculated and, hence, corrections of observed discharge be made. This method is quicker and cheaper than conventional mass-balance measurements. Large potentials for this method lie in future digital maps. Almost all the detailed (1:10 000) Norwegian glacier maps are printed in four colours and they have a standard UTM coordinate grid and 10 m contours. An example of a recent map is enclosed in the map pocket on the rear cover of this volume.