An Adaptation of Diagnostic Numerical Model of Residual Current to Bungo Channel, Japan

Abstract

Residual current (RC) in the Bungo Channel, the Seto Inland Sea, where fishing ground development is ongoing to locally augment upwelling induced by the man-made structures, is estimated using a six-leveled diagnostic numerical model. This model developed can handle the density-driven current, wind-driven current and tide-induced residual current.
To assume the situation that the upwelling effects of the structures are most depressed by stratification, the density field in August is considered. Water temperature and salinity in August from 1989 to 1993 are objectively interpolated to get the density field from the results of field observations by the Prefectural Fisheries Experimental Stations. Wind stress distribution in the same period are also calculated by the objective analysis method from the data of the Automated Meteorological Data Acquisition System, the Meteorological Agency. Moreover the tidal stress is computed from the result of numerical tidal current simulation. Incorporating these conditions obtained into the model, the RC simulation is conducted.
The computed RC field is verified by some field observations conducted in August. In particular, the RC measured directly around the structures was toward the southeast and its velocity was within the range of 15 to 20cm/s. Compared to the data, the computed current is a little small in magnitude, but the same in direction. However, it is considered that the computed RC field can be accepted as a hydraulic environment set in numerically investigating the transport of upwelled nutrients.