Integrated measures for urban flood control and disaster mitigation in Japan and their developments

An introduction is given to the formation and development of the urban flood control system in Japan, a country well known for its mountainous geography and humid climate. It is pointed out that the formation and the development of the flood control system are closely related to the Japanese socio-economy. The development of the economy provides a solid foundation for enhancement of the capacity in disaster prevention, while an improved flood control system stimulates land exploitation and utilization in river basins and further makes high requirement to the flood control system. Four major structural measures for urban flood control are presented, including reservoir/dam construction, channel improvement, underground canal excavation and construction of flood storage/detention regions and pumping systems. Countermeasures against urban flood disasters are classified into five categories: improving the accuracy of flood prediction and forecasting system, shortening the dissemination time of disaster information, raising the public awareness of disaster prevention, completing the flood hazard map for vulnerable areas, and implementing flood forecasting in medium and small sized rivers in major cities. Three major flood control and disaster relief organizations are introduced as well, i.e. fire and disaster control authorities, flood control communities/flood control affair cooperatives and the Japan succor self defense forces. It is found that the recent flood disasters induced by urban rivers have challenged the urban flood control system, and the system is further developed with emphasis placed on disaster prevention and disaster mitigation. In addition to conventional flood control expertise and works, a new system is put forward into schedule in which individuals, local communities and state government are expected to share different functions in flood control and disaster mitigation.