Author(s): Ichiro Fujita; Ryota Tsubaki; Takeshi Okabe
Keywords: Non-intrusive flow measurement; Discharge measurement; Image analysis; Surface velocity measurement; STIV; HDV; LSPIV
Abstract: A non-intrusive river-surface flow measurement method using video images is applied for the measurement of a large flood occurred in the Yoshino River. The flood took place from September 6 in 2005, which is the second maximum flood observed in the river in the past several decades. The measurement field is located about 64km from the river mouth of the Yoshino River that flows in the Shikoku Island in Japan, where bamboo grove develops on the flood plane along the left bank. In the field observation, a high resolution video camera with a resolution of 1440 by 1080 pixels is used for improving the spatial resolution of the image. As for a non-intrusive measurement method, the space-time image velocimetry (STIV) developed by Fujita et al. (2005, 2007) is used for improving the efficiency of the image analysis. Although the flow of the flood peak which came during the midnight was difficult to capture due to the lack of enough lights, we could conduct a six-hour measurement after the passing of the flood peak. In the measurements, the maximum surface velocity of about five meter per second and the discharge of seven thousand cubic meters per second were successfully obtained by STIV. The measured discharge agrees well with those obtained by the conventional method using floats. The proper use of the image smoothing parameter in STIV is also discussed.