Observation and dynamics of the tidal bore in the Qiantang River, China

Abstract

To measure the tidal bore the repeat reciprocal sound transmission experiments were 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 water level measurements were also performed. The range-averaged current velocities estimated from the acoustic data changed from 0.12 to 0.82 m/s and −1.18 to 0.08 m/s, before and after the arrival of the bores, 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 5.1 m/s and 8.4 m/s with a mean of 6.33 m/s. The surge Froude numbers were estimated to be 1.1–1.5, which indicated the observed tidal bores were undular bores.