Ocean Environmental Survey on Influence of River Inflows on Current within a Harbor

Abstract

The waters facing the Marine Training and Research Center (MTRC) at the National Institute of Technology (NIT), Toyama College consist of a mixture of inflows from the Shinbori River, a timber pond and the open sea. In this study, we examine a particular current that is influenced by the combination of inflows and open seawater occurred in summer. This slow current, which flows westward at the speed of approximately 0.1-0.3 m/s, influences handling of small boats and the college training ship Wakashio-maru (231 GT) that operate from the MTRC pier. Accordingly, the authors conducted Conductivity, Temperature and Depth profiler (CTD), Electromagnetic current meter, and Acoustic Doppler Current Profiler (ACDP) observations of the marine environment of the flow in order to gain an understanding of the inflow waters such as their vertical formulations, seasonal variations, water structure, temperature, and salinity. The results of those observations revealed that the waters consisted of three layers, with the upper layer most influenced by the Shinbori River and the lower layer most influenced by the open sea. The middle layer was a mixture of both the upper and lower layers. It was also found that the borders of layers changed according to seasons, and that the flow was influenced by the tidal current at lower layer, the river water at upper layer and the topography.