River gauging using PIV techniques: a proof of concept experiment on the Iowa River

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An image-based approach for discharge measurements is evaluated for river gauging in an experiment on the Iowa River at Iowa City, Iowa. Over a twenty-day period, ten discharge measurements were made using the image-based approach. A ten-minute video recording was made of the river flow for each measurement. Particle image velocimetry (PIV) was used to estimate surface velocities for the imaged area using naturally occurring foam as a flow tracer. The surface velocities were then estimated along a surveyed river section, and river discharge was computed using standard velocity–area methods over a selected cross-section. Several unique aspects of this experiment were the use of PIV for unseeded flow conditions, and the evaluation of discharge estimates over a range of flow conditions. A comparison of the PIV discharge measurements with traditional current meter measurements, which have been made at the site since 1984, showed that the PIV measurements were consistent with the observed stage–discharge relationship. Discharge for the experiment ranged from 50 to 300 m 3s −1, which covers a large portion of the existing rating curve. The experimental results suggest that image-based approach may be a reliable way of establishing a stage–discharge relationship at a site, perhaps even remotely, by making repeated measurement with a camera mounted at the site. Still, there are inherent limitations with the approach. These limitations include the need for recognizable tracer particles or flow patterns to detect motion, problems associated with shadows and reflections on the water surface, as well as the common the problem for all discharge measurement of the need for survey information on the channel cross-section.