Japan is located in the Asian monsoon climatic zone and these climatic conditions are favourable for growing rice in summer. In every age, rice fields have produced the staple food of the Japanese people and have also been the source of the multifunctional roles of agriculture. This paper describes the evolution of rice field drainage in Japan focusing on the last 60 years.
The productivity-oriented drainage policy has been shifted to place emphasis on coping with discharge from expanding rural areas, corresponding to the social and economic background of the country. In recent years, irrigation and drainage facilities that take the environment into consideration have been actively introduced. This leads a new agricultural policy to conserve and improve the land, water and environment, the key factor of which is the creation of new local organizations including non-farmers.
In view of technical aspects, various methods have been developed and applied in order to plan, design and install/improve main drainage facilities, field surface drainage, and field subsurface drainage. Various examples of restoring the ecosystem inherent to rice fields are introduced, including simple fish ladders and stairway-like fish passages. Technical standards are also introduced in terms of drainage system layout, structure of subsurface drainage and design drainage rate.