Numerical Modeling of Secondary Flow in Meandering Estuarine River

The developed transversal flow in a river, known as secondary flow, is induced due to the instability of centrifugal forces along the vertical line of water body. In a saline environment, secondary flow undergoes further change by the presence of stratification throughout the water body. Furthermore, the existence of a structure such as sluice gate might further impose an alteration to the dynamics of secondary flow. The study herein takes place on the Ota Diversion Channel in Hiroshima City, Japan that belongs in the Ota River system. This channel has its water flow blocked with a sluice gate. A numerical model was used to investigate the transformation of secondary flow. Two scenarios were simulated by 10 σ layers, the first scenario incorporates the existence of sluice gate and the second exempts it from the simulation. This study solely focused on the spring tide period to eliminate the effect of increasing river discharge and spring to neap alteration. The numerical results show that the secondary flow is stronger with the existence of sluice gate rather than without it. The intrusion of saltwater could go further upstream without the existence of sluice gate thus generates a homogenous water body during high tide and ebb that dismisses the presence of stratification. Further evaluation by lateral momentum equation terms also manifest the transformation of baroclinic pressure gradient and centrifugal acceleration throughout the water body. These indicate that the presence of sluice gate indeed alters the structure of secondary flow.