Acoustic measurement of tidal bores in the Qiantang River, China

The repeat reciprocal sound transmission experiments for measurement of tidal bores were successful carried out in the upstream region of the Qiantang River in Hangzhou city, about 90 km from the mouth of the Hangzhou Bay during September 2009 to February 2010. Two Coastal Acoustic Tomography (CAT) Systems were set up at a distance of 3050 m for making a reciprocal sound transmission between the both banks of the Qiantang River. During the sound transmission experiments, the acoustic Doppler profiler and water level measurements were also performed. The range-averaged current velocities estimated from the acoustic data changed from 0.82 m/s to -1.18 m/s, and the water level changed from 0.18 m to 1.34 m, within a short period of about 20 minutes during the arrival of tidal bores. The mean propagation speeds of the tidal bores between two stations changed in the range of 5.76 m/s and 6.72 m/s with a mean of 6.33 m/s. The surge Froude numbers were estimated to be 0.82-1.13, which indicated the observed tidal bores were undular bores.