Stream discharge measurement using a large-scale particle image velocimetry (LSPIV) prototype

New technologies have been developed for open-channel discharge measurement due to concerns about costs, accuracy, and safety of traditional methods. One emerging technology is large-scale particle image velocimetry (LSPIV). LSPIV is capable of measuring surface velocity by analyzing recorded images of particles added to the stream surface. LSPIV has several advantages over conventional measurement techniques: LSPIV is safer, potentially automated, and produces real-time measurements. Therefore, the goal of this study was to evaluate the accuracy and feasibility of using LSPIV to measure instantaneous discharge in low-order streams. The specific objectives were: (1) to determine optimum operating parameters for applying LSPIV under various conditions, (2) to design, develop, and test a prototype under controlled laboratory conditions, and (3) to develop and test the field equipment for a variety of streamflow conditions. The laboratory experiment results indicated that LSPIV accuracy was influenced by camera angle, surface disturbances (Froude number), and flow tracer concentration. Under field conditions, the prototype acquired consistent images and performed image processing using accepted input parameters. The accuracy of LSPIV for use infield applications was evaluated using a permanent weir. Overall, 18 discharge measurements were taken with each measuring device. The LSPIV prototype was accurate, with a mean error of -1.7%, compared to the weir measurements. The root mean square error (RMSE) was similar for LSPIV and current meter discharge measurements with the area-velocity method when compared to the weir. Finally, the LSPIV discharge measurements had an uncertainty of approximately +/- 14% (at a 95% confidence level). Therefore, LSPIV showed the potential to become competitive with conventional discharge measurement techniques.