Abstract
The Shira. River, one of the rivers that flow into the Ariake Sea, has well mixed estuary. In the estuary of the river, turbidity maximum is observed. Turbidity meter, conductivity meter, Acoustic Doppler Profiler and head rotating side scan sonar (Simrad Mesotech MS-1000) were installed in the River. Turbidity, water temperature, conductivity and vertical distribution of the horizontal current were measured in every 10 minutes. Moreover, longitudinal vertical 2-D acoustic image was observed continuously using Sonar. Water samples were collected intensively when the density current passed. The acoustic imagery of the front of the density current was successfully obtained. The front consists of saline water and high concentration of SS. From the acoustic imagery, it was found that the form of the front of the density current was inflated and Kelvin-Helmholtz instability was observed at the boundary layer of the density current
