INVESTIGATION OF FLOW VELOCITY AND SALINITY BEHAVIOUR IN OTA RIVER ESTUARY USING ACOUSTIC TOMOGRAPHY METHOD AND NUMERICAL MODELING Mochammad Meddy DANIAL Kiyosi KAWANISI Masoud Bahraini MOTLAGH Mohamad Basel Al SAWAF Takayuki WAKABAYASHI Dept. of Civil and Environmental Engineering, Graduate School of Engineering Hiroshima University

Current velocity is essential parameter in tidal channel network to carry sediment, nutrients and contaminant. The behaviour of velocity pattern mostly influenced by topography or geometrical shape (such as hypersyncronous or hyposyncronous). In this study, we want to know the Influence or effect of tidal junction or asymmetric river branch towards the inequality of flow division in which current velocity in one branch is different than that of another branch. Salt transport is an important phenomena and has significant implication on the estuarine area such as water use, sedimentation and pollutant dispersion. Mean salinity measurement in tidal estuary with including cross-sectional area is rare. Study of salinity pattern in tidal junction is also needed. Background

This paper focuses on investigating the behaviour of current velocity and salinity in tidal channel network, particularly in tidal junction. To quantify the ratio of current velocity, particularly in asymmetric tidal junction between Tenma and Kyu Ota and investigate the salinity behaviour during spring and neap tide Current velocity is essential parameter in related to sediment transport process in estuary, whereas salinity parameter is an important indicator of water quality and has environmental effect on the estuarine area. Purpose of the study Significance of the study

Methodology Source: Ministry of Land, Infrastructure, Transport and Tourism (MLIT) Study Area Equipment of measurement : 1.4 Transducers 30 Khz and 53 Khz 2.4 FATS 3.2 ADCPs 4.2 CT sensors Mesh of bathymetry of Ota river

Methodology FATS = Fluvial acoustic tomography system

( b) Computed and observed water level: (a). Misasa gauging station.; (b) Gion gauging station. Spring and neap tide is represented by blue and orange arrow above figure, respectively. Result Simulation of tidal fluctuation in tidal junction of Ota river

ADCP and model in Kyu Ota river ADCP and FATS in Kyu Ota river ADCP and model in Tenma river ADCP and FATS in Tenma river. Comparison of velocity pattern in tidal junction of Ota river

Velocity vector during Flood tide Velocity vector during Ebb tide Velocity comparison in Kyu Ota and Tenma river; Residual velocity using 33 h low-pass filter analysis between Kyu Ota and Tenma river Comparison of velocity pattern in tidal junction during flood and ebb tide Comparison of velocity pattern in tidal junction between Kyu Ota and Tenma river

Salinity comparison in Kyu Ota river between FATS and C-T sensor. Comparison of salinity in Kyu Ota (red line) and Tenma (green line) during spring and neap tide. Comparison of velocity pattern in tidal junction between Kyu Ota and Tenma river

Velocity behaviour in tidal junction shows interesting result where current velocity during ebb tide is higher that that during flood tide. The influence of tidal junction toward velocity also indicate that the current velocity in Kyu Ota river is higher than that in Tenma river at the ratio of ± 62%. Behaviour of salinity pattern in Kyu Ota and Tenma river during neap and spring tide indicates that salinity during neap tide is greater than that during spring tide. However, there is no significant difference of salinity pattern in tidal junction. Conclusion

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