A field study of transport and mixing in a river using an Acoustic Doppler Velocity Profiler

摘要

A 3-D Acoustic Doppler Velocity Profiler (ADVP) is used for measuring closely spaced profiles across the river Poisine (on a straight river reach with mean water depth h ≈ 0.5 m, width B ≈ 12m, flat gravel bed with estimated D_(50) ≈ 6 cm). The mean streamwise velocity profiles show logarithmic profiles all across the half section, decreasing towards the bank. Most of the three turbulence intensities profiles between the center (y/B = 0.5) and y/B = 0.24 agree relatively well with laboratory profiles. Closer to the bank (y/B < 0.24) strong deviations in the profile form indicate "side-wall" effects. A cumulant discard method is applied and conditional statistics and conditional sampling are used to compare the experimental relative covariance contributions from the four quadrants. In the center (y/B = 0.5), all quadrant distributions correspond to those observed in laboratory open-channel flow. Near the bank (y/B = 0.04), significant differences between the results for different depths occur in all planes. Thus, the flow near the bank cannot be considered two-dimensional.