Index velocity methods for winter discharge measurement

Abstract

At present, the only truly accurate method of determining discharge under ice-affected conditions is by direct measurement. However, this is a costly undertaking that places technicians at personal risk. Because of this, the Water Survey of Canada often bases winter discharge hydrographs on as few as two direct measurements over the entire ice-affected season. This study explores the viability of using an index velocity approach to winter discharge measurement, which basically involves the determination of streamflow based on a very limited number of actual point velocity measurements in the cross section. Such an approach has the potential to reduce the amount of time required for a single discharge measurement, thus opening the potential for an increase in the number of discharge measurements that can be obtained per year at a given site. Also, a reduction in personal risk to those taking measurements on the ice cover is expected because of the reduction in the time spent on the ice cover for each individual measurement. Here, the viability of using a single point velocity, or alternatively a single panel velocity profile, is explored using detailed velocity measurement data collected by the Water Survey of Canada at a number of sites across Canada, on rivers of varying size. Results suggest that there is a definite potential to streamline winter discharge measurement protocols to increase both safety and frequency of measurement.Key words: winter streamflow measurement, rivers, ice.