The confluence region downstream of the Katsura River, the Kizu River and the Uji River in Kyoto displays complicated flow patterns depending on which watershed undergoes larger precipitations. The flow characteristics at this location have not been clarified so far due to the complexity of the combining streams. In the present study, in order to obtain the flow features in normal flow conditions, surface flow measurement by using a helicopter is performed. The surface flow is visualized by biodegradable tracers and they are videotaped from a helicopter hovering at about 300 meter height following the cloud of tracers. A high-vision video camera is used for recording the images and the velocity of the tracers are analyzed by applying PIV with subtracting background movement. At the same time, distributions of temperature, pH, and other parameters related to water quality are measured by multi-purpose instrument installed on a boat. It was found that water quality of the Ktsura River is quite different from the other rivers and the longitudinal dispersion of tracers is evident at the location.
