## (a) Comprehensive Flood Control Measures

With factors such as the concentration of population following the development of urban areas and peripheral areas as well as increased discharge from flooding rivers, for urban rivers where flood control safety is significantly compromised it is important to carry out comprehensive flood control measures, in addition to river development, such as securing the water retention and flood dissipation functions of the river basin, directing land use in regions at risk of disasters occurring, and establishing a precautionary evacuation framework. As part of these efforts, the development of rainwater harvesting facilities is being promoted through measures such as river basin storage and infiltration projects and tax breaks so that the relevant local authorities can

Example Measures Based on the 100mm/h Safe Plan for Hii River

○Hii River experienced close to 100mm/h rainfall in the flood of July 2009 where damages extending to 410 housing units being flooded but due to advanced urbanization, it was difficult to respond with river improvement alone

○For this, in addition to emergency river improvement, citizens, companies and government are working together to install facilities to store rainwater in houses, schools, etc.

$ ^{※} $ Establish the "Hii River Basin Flood Control Citizen Conference" including participants from citizens, academics, companies, government, and media. The Kyushu Regional Development Bureau gave technical advice based on domestic case studies.

cooperate to further suppress rainwater drainage and measures to reduce civil damages.

In addition, to prevent the disruption of urban functions due to flooding as well as the flooding of underground malls in accordance with the “Act on Countermeasures against Flood Damage of Specified Rivers Running Across Cities,” river administrators, sewage system administrators, and local government are working together to promote river basin flood damage countermeasures such as developing rainwater harvesting and infiltration facilities as well as regulations to suppress the drainage of rainwater.

## (b) Localized Downpours (Guerilla Rainstorm) Measures

For localized downpours that exceeds 50mm, 100mm per hour a “100mm/h relief plan” that stipulates measures carried out by the river administrator such as river development and flood basins, sewage development, as well as the placement of rainwater harvesting and infiltration facilities within the housing premises by residents to promote integrated heavy rainfall measures within the region so that the people can live with peace of mind.

## (c) Integrating Land Use Measures with Disaster Mitigation

In accordance with land use conditions, if it is more efficient and effective than developing a consecutive levee, integrated land use that combines the development of a circle levee $ ^{Note} $ and the regulation of land use through measures such as designation of disaster risk areas is combined in cooperation with local authorities to promote disaster mitigation measures.

## (d) Inner Water Measures

To prevent flooding through inner water inundation and strive for the healthy development of cities, the improvement of facilities such as sewer pipes and drainage pump stations are being promoted. However, in recent years, the frequency of concentrated downpours that far exceed planned scales, increased rainwater drainage due to the advancement of urbanization, the increased complexity of the urban landscape including the concentration of population and wealth as well as the increased use of underground spaces make the risk of damage due to inner water inundation even greater. For this reason, measures such as integrated projects for the reduction of sewer flooding damages and integrated projects for inner water emergency measures are being utilized with the cooperation of relevant parties including regional authorities and affected residents to carry out hard measures such as proactively implementing rainwater drainage reduction facilities; soft measures such as providing rainfall information, land use regulations, and creation of inner water hazard maps; and self-help initiatives such as the placement of water stops and sandbags as well as evacuation activities in combination for the promotion of integrated flood measures.