Author(s): David S. Mueller; Michael S. Rehmel; Chad R. Wagner

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Abstract: The StreamPro acoustic Doppler current profiler is a moving-boat discharge measuring instrument designed for use in shallow streams with depths less than 4meters. Because moving-boat ADCP discharge measurements based on bottom tracking do not require a compass, an internal compass was not implemented in the Stream Pro. This lack of a compass has caused two problems when using the instrument in moving-bed conditions. First, during stationary moving-bed tests the StreamPro often tends to swim or kite from the end of the tether (the instrument rotates then moves laterally in the direction of the rotation). Because the StreamPro does not have an internal compass, it cannot account for the rotation. This rotation and lateral movement of the StreamPro on the end of the tether generates a false upstream velocity, which cannot be easily distinguished from a moving-bed velocity. Second, the common techniques (use of GPS or the loop method) for correcting measured discharges biased by a moving-bed cannot be used with the StreamPro because the StreamPro has no compass. A solution has been developed to address these two problems. The vector dot product of the boat velocity and the unit vector of the depth-averaged water velocity was found to be an effective method for calculating an accurate moving-bed velocity from a stationary moving-bed test. The discharge measured by a StreamPro in moving-bed conditions can be corrected by collecting multiple moving-bed tests and processing the data through a computer program. The computer program uses linear regression to develop a relation between the computed moving-bed velocity from the dot product algorithm and the near-bed water velocity from the moving-bed tests. This relation is then applied to the measured velocities in each ensemble of each transect and thus, the measured discharge is corrected for the effect of the moving-bed.

DOI:

Year: 2009