Dams in Japan Japan Commission on Large Dams Past, Present and Future

Abstract

The geographical features of Japan are quite distinct, especially when compared with those of continental countries. Collision of four tectonic plates brought about the narrow archipelago of Japan, its high orogenic and volcanic activities, complicated geological structure, and frequent occurrence of large-scale earthquakes. The existence of backbone mountain ranges formed many small river basins. Plentiful precipitation characteristic of the Asian Monsoon climate fostered rich forest zones with clear streams on mountain sides. It is remarkable that two thirds of the national land of Japan, one of the most industrialized counties in the world, is still covered by green forests. This precipitation also resulted in the development of alluvial plains along the downstream parts of rivers through repeated flooding. These plains are now the major areas of social and economic activities for the Japanese. The high productivity of paddy cultivation, which suits natural conditions in Japan, supported Japanese society as its key industry for more than ten centuries until the achievement of industrialization. Its experience and innovations in water management and flood disaster mitigation including construction and management of irrigation ponds became an important part of the social framework of Japan. The modernization of Japan started in the latter half of 19th century, and was successfully achieved within a short period of 100 years or so. This progress was accompanied by the urbanization and industrialization of the alluvial plains. One infrastructure development important for this success was protection from flood disasters by large-scale river improvement works and dam projects, and the supply of necessary water and energy by dams. The society and economy of Japan are now mature, following a period of rapid economic growth. The general public now holds a harsh view of major social infrastructure such as dams. The population of Japan dramatically increased from 40 million at the end of 19th century to 128 million at the beginning of 21st century, and the Japanese are now facing a new phase: population decline. Dam construction projects in Japan peaked about ten years ago. The effective use and redevelopment of existing dams and prolonging their operational life are major tasks for the coming years. In addition, measures to adapt to climate change accompanying the global warming are emerging as world-scale challenges. In the face of fear