In this article, we rehabilitate the integrating rising bubble techniqueas an effective means of obtaining discharge measurements. Since Sargent (1981, 1982a),the technique has not been applied widely, mainly as a result of practicaldifficulties. We hypothesize that modern image processing techniquescan greatly improve the rising bubble technique. We applied the techniquein both a laboratory setup and a field study, after determining thebubble rising velocity for our nozzles in the specific case. Duringour measurements, we captured digital photographs of the bubble envelopeat the water surface, each picture being a single measurement of thedischarge. The photographs were corrected for lens distortion andreprojected so that accurate distances on water surface level couldbe obtained. This easy digital procedure resulted in accurate dischargemeasurements, even when turbulence was involved and the averages ofmultiple image analyses yielded good results. The study shows thatthe rising bubble technique can be a preferable discharge gaugingtechnique in some situations. Recent developments in image processingfacilitate the method substantially.
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