Ultrasonic velocity profiling (UVP) was applied to an environmental flow attempting an efficient measurement of river flow with higher accuracy in comparison with current measurement methods. Applicability of the method on measurement of an open channel flow was confirmed in a laboratory experiment; namely, the cross sectional velocity distribution of the channel was measured; the flow rate was obtained by integrating the velocity distribution; this showed high accuracy, around 4% in relative error. The method detecting the bottom position of the channel from a single velocity profile was also established and was demonstrated by various boundary conditions at the bottom of the channel. Actual river measurements were performed at a creek flowing out of a small pond in the campus of Hokkaido University; the width of the creek is approximately 1700 mm. Measured velocity distribution at a cross section of the river represents well the flow field. The bottom position of the river detected by the established method corresponds to that measured by a ruler excluding a place covered by waterweed. The flow rate determined by integrating the velocity distribution is in good agreement with that estimated by a weir mounted at the inlet of the river.

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