Author(s): Kiyoshi Kawanishi; Satoshi Watanabe; Arata Kaneko
Linked Author(s): Kiyoshi Kawanishi
Keywords: Coustic tomography; Tidal river; Flow rate
Abstract: New technology for water discharge measurement is required for attainment of water control system corresponding to new social needs. In the present study, a FAT (fluvial acoustic tomography) system, which overcomes the previous problems, has been developed. It is difficult to measure water discharge with conventional method in wide tidal rivers because of the large changes in water depth and complexity of flow structures. The FAT system has the following breakthroughs: 1) Sound is simultaneously transmitted from both banks. Using GPS clock signals lead to high-precision measurement of sound travel time 2) Attainment of high signal-to-noise ratio as a result of transmission signal modulation by 10 th order M-sequence 3) Low cost, light weight and low power (Alleviating restrictive depth, reducing the cost of installation and maintenance, portability). In addition to the cross-sectional averaged velocity and discharge, cross-sectional averaged salinity and water temperature are calculated from cross-sectional averaged sound speed. Moreover, fresh water runoff is calculated from the cross-sectional averaged salinity. Sound paths are not capable of penetrating into bottom layers when the position of salt wedge is lower than the transducer. The flow velocity is somewhat overestimated in this case. In this situation, calculated discharge should be corrected applying an analytical solution of twolayer flow. To assess the fundamental performance, the FAT observation was conducted in 9km upstream of the Ohta Floodway, Japan. The calculated discharge is compared with the results measured by an ADCP (Acoustic Doppler Current Profiles). The result showed acceptable with the observed data by ADCP, which indicates that FAT system is applicable to various tidal flow conditions
Year: 2010