Today in Japan, 20 or so projects are in progress, including (i) the embankment raising by approximately 12 meters for the existing Katsurazawa Dam, (ii) the modification to increase the capacity of flood control and add spillways by cutting out the dam body for the Nagayasuguchi Dam, (iii) the project to increase the capacity of flood control and newly construct a tunnel spillway for the Kanogawa Dam, and (iv) the project to newly construct a sediment bypass tunnel for the Miwa Dam.

Especially in the Tsuruta Dam redevelopment project, the floating cofferdam construction method has been developed as a technique for construction while operating the reservoir, in which temporary steel facilities are floated and constructed on the water, and then mounted onto the dam body in bulk. The method was recognized for cost reduction, shortening of construction periods, and safety realized by eliminating deep sea diving operations and diverting the cofferdam facilities to other purposes, and for the possibility of overseas development, so the Prime Minister's Award in the Monodzukuri Nippon Grand Award was granted to the engineers.

## (ii) Preventing the Reoccurrence of Flood Disasters

In recent years, within regions that experienced flooding, river channels are excavated and levees are being built to improve the flow capacity of rivers, drainage pump stations are developed to prevent inside water flooding among other measures are being implemented intensively in a short time span to prevent or mitigate flooding.

## (iii) Flood Control Measures Tailored to River Basin Characteristics

For rivers that experience a significant decline in flood control safety due to river basin development or existing urban areas regularly subject to flood damage, it is important to ensure the water retention and flood dissipation functions of the river basin. Rivers such as these require the promotion of river basin measures and a variety of methods that taken into consideration regional characteristics to ensure safety and comfort.

## (A) Comprehensive Flood Control Measures

With factors, such as an increase in the impermeable land area following the development of urban areas and peripheral areas, as well as an 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 high 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 cooperate to further suppress rainwater drainage and measures to reduce civil damage.

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 Measures

In recent years, due to flood damage caused by phenomenon such as concentrated heavy rains in localized areas, to ensure that residents can live safely even during localized heavy rains exceeding planned levels, a plan created with the support of residents (groups), private sector companies, and others that stipulates a comprehensive approach implemented to reduce flood damages known as the “100mm/h security plan” is registered and initiatives to promote mitigation measures against flood damages are being implemented in addition to the development of rivers and sewerage.