Abstract
The Great East Japan Earthquake and recent major floods have revealed the limitations of gray infrastructure and point-based thinking in disaster prevention. In response to this situation, green infrastructure is being promoted at the national level, including its use in watershed flood control. However, the number of developments is not large at this time, possibly due to the fact that it is not clear how to develop a wide variety of green infrastructure. Therefore, this study investigated the maintenance of rain gardens in Kumamoto Prefecture, with the aim of clarifying the characteristics of rain gardens and how they should be maintained with a view to expanding their maintenance in the future. As a result, it became clear that rain gardens are in line with the concept of “green watershed flood control” triggered by the torrential rains in July 2020, and that they are currently being developed in cooperation with industry, academia, and government. In addition, it became clear that rain gardens have variable characteristics, that their form is determined by policy issues other than flood control, and that even in public-private partnerships, there are differences in the stage of participation of the entities in each case. Focusing on the process from introduction to maintenance and management, it is necessary to first clarify policy issues and position rain gardens as a solution to these issues in higher-level plans, to have key persons take the lead, and to have the participation of entities that have a close relationship with the companies. Next, at the maintenance stage, it is necessary to lower costs through the participation of local residents and establish a subsidy system, while for maintenance and management, existing systems should be utilized is needed. Since these are highly versatile initiatives that could be implemented in any municipality, it is believed that the analysis in this study has provided an understanding of some of the effective methods for rain garden maintenance.
