The coastal area at the head of Osaka Bay, which is highly urbanized, has been developed into an enclosed area with complicated artificial islands and breakwaters. In order to clarify the processes of anoxic water in this enclosed area, field surveys were done to measure currents inside the ports of Amagasaki-Nishinomiya-Ashiya and Kobe. Numerical computations to simulate currents and water quality in summertime were also carried out using the Princeton Ocean Model (POM) and a water quality model.
Hypoxia, which is often defined by the low concentration of dissolved oxygen, is one of the main subjects of environmental research in the estuaries of Japan. Hypoxia compromises the survival of marine life and biodiversity, and the volume of the hypoxia never decreases in contrast with the reduction of the polluting load from land areas in recent decades. Osaka Bay is surrounded by industrially developed and highly urbanized areas. The number of people in the river basins that flow into the bay is 17 million. Most of the coast line is developed with ports which create large sections of calm water and closed harbor spaces. Hypoxia in Osaka Bay occurs in early summer, spreads to the head of the bay and decreases in October. In the harbor of the bay, it occurs earlier and remains in November. It spreads from the ports to outside of the ports. Obviously, improvement in the water quality in the harbor is a start to the improvement of the whole bay. In the present paper, field surveys have been conducted to clarify the dynamics of water mass with the low concentration of DO. One of the main surveys is to measure currents in two ports in the northern part of the bay. The simulation of currents and water quality using the threedimensional flow and water quality model were also carried out.
