Effective Application of a Mechanical Circulator for Reducing Hypoxia in an Estuarine Trench

Application of a mechanical circulator was considered to reduce hypoxia and anoxia in an estuarine trench by numerical examination in terms of the required flow rate and direction along with the physical mechanism of its effectiveness. We then developed a prototype of the circulator, generating downward flow by an impeller attached to the main body of the circulator floating on the surface, in which the surface water is being transported to the bottom through a flexible draft tube connected to the floating body. The effectiveness of the proposed mechanical circulator was verified by performing field tests in a dredged trench in Tokyo Port of Tokyo Bay, while monitoring current and water and sediment quality. The field test results showed that the mechanical circulator achieved the desired effects, including reduction in hypoxia and improvement of water and sediment quality in the trench. We also applied a primitive equation model and found that the model can successfully reproduce the field test results. The present study shows the availability of a mechanical circulator and an effective application methodology in the field.