2020 年 8 巻 1 号 p. 35-45
In the Higashi-Yokobori and Dotonbori Rivers, water quality is controlled by the inflow of relatively clean river water from above the upstream floodgate and outflowing polluted water to below the downstream floodgate. However, a hypoxic water mass occurs during high-temperature periods; therefore, there is room for further water quality improvement. In this study, field surveys, laboratory experiments, and simulations were conducted to determine the water quality characteristics of these two rivers.
The impacts of these water quality improvements resulting from the exchange of the water mass with water from outside the floodgates were evaluated, and more effective methods were proposed. It was shown that the main factor leading to hypoxia was dissolved oxygen (DO) consumption in the water. In order to maintain a satisfactory DO environment in the summer, it would be necessary to continuously allow water to enter from above the upstream floodgate at a rate of more than 2.0 m3/s.