Abstract
A prototype model experiment, covering the seabed with fly ash beans, has been in progress since June 2010 at the bottom of Kaita Bay, located in the innermost region of the larger Hiroshima Bay in Japan. In order to verify the effectiveness of sediment improvement, the site has been monitored over the approximately one and a half years since the experiment began, primarily in summer and winter. The experiment was conducted with three zones demarcated, covered with thicknesses of 5cm, 10cm and 20cm respectively, which were then assessed in comparison to one another and to the surrounding area. The assessment determined that covering the seabed with fly ash beans contributes positively in terms of trapping of suspended mud, improvement of sediment quality, and creation of an environment favorable to marine organisms, and that these improvements were being sustained.
However, the possibility of suspended mud accumulating in the covering layer and completely blocking its gaps, thereby detracting from the improvement of sediment quality, was also considered. In fact, it was found that in the zone with coating 5cm in thickness, the degree of improvement had declined considerably since the experiment began. In addition to clarifying the degree of sediment improvement through covering the seabed with fly ash beans, this experiment is intended to evaluate the sustainability of this improvement. Henceforth, the scale of the operation area will be expanded, and the relevant findings organized appropriately.
