Determination of Optimal Velocity Ranges Based on the Shape Profiles of Two Passive Surface Water Flux Meters

A method is presented for direct measurement of cumulative surface water flux (discharge) and solute flux using a Passive Surface Water Flux Meter (PSFM). Both the water velocity and the shape, or bluntness, of the device are important for determining the flow profile around a submerged body. Theoretically, the PSFM should provide the most precise cumulative flux measurements when the shape of the device is as blunt as possible without creating a separation region or a downstream wake. This study examined how the shape of the PSFM affects the accuracy of the cumulative flux data and determined the optimal velocity ranges under which each shape profile could be used. In this experiment, blunt (cylindrical) and streamlined (Joukowsky profile) shapes were tested. Both of these devices were examined under a range of velocities in a laboratory flume. Results showed that the blunt shape provided more accurate water and solute flux measurements at lower velocities, whereas the streamlined shape provided more accurate measurements at higher velocities. These findings indicate that the shape profile of the PSFM may be adjusted to provide the most accurate cumulative water and solute flux measurements when deployed in known flow regimes.