Inaoigawa Irrigation Canal located on the left bank of Osaka River in Japan is recognized for its organized operation and maintenance by local people thereby helping transform the Sanbongi area in Japan from a barren plain to one leading in rice production and serving as a source of spiritual home. Inaogawa irrigation canal is loved by people in the community and handed down to the present generation as a structure which recalls achievement of ancestors.
Inaogawa irrigation canal serves as the lifeblood of agriculture for Towada City, the fourth largest city and one of leading rice producers in Aomori Prefecture. Sanbongihara which is the former name of the area including Towada City was an alluvial fan covered with volcanic ash generated from the eruption of Mt. Towada. The volcanic ash impaired the soils ability to retain water resulting in immediate seepage of rainwater into the ground. The project faced many difficult hurdles requiring high technical capabilities to overcome, such as, construction of two tunnel weirs and a land weir.
The project was taken up more than 160 years ago when the planning design and construction of most civil engineering works in Japan depended heavily on foreign engineers. This reclamation project was carried out primarily by Nanbu tsuchikatasyu, a group of construction technicians and completed by Japanese techniques only. This group of tunneling workers, having the most excellent special techniques in the domain, carried out construction in an extremely organized manner with the level, the Azimuth instrument and the rope measure used at that time. It is considered that the technician group used traverse calculation using Hassen table; a Japanese style of trigonometric function table. The project was constructed using man power only. Inaogawa irrigation canal has helped transformation of Sanbongi from a barren plain 160 years ago to one of leading rice producers in Aomori Prefecture and has contributed to development not only in agriculture but also of other sectors of the entire region.
In 1855, the rulers launched a large-scale reclamation project in Sanbongihara with the construction of Kuradeyama weir and Tenguyama weir and a canal through which water was passed on a trial basis on April 24, 1858. After repair work, on May 4, 1859, about four years after the start of the project, water was successfully taken to Sanbongihara and in 1860, the canal was named Inaogawa irrigation canal.
Though the Irrigation system of Sanbongihara was successfully completed, but it did not have sufficient supplies of water to reach up to the Pacific coast. Accordingly, another plan was developed to build an intake further upstream which comprised of three tunnel weirs and an additional canal meeting Inaogawa irrigation canal. Tunneling work was started from the north side of Kuradeyama tunnel weir, but could not be completed. Subsequently the second water diversion plan was undertaken as a national reclamation project and finally completed in 1866.
The project has undergone several changes over the years. Modernization and development projects have been implemented since then, converting Sanbongigahara into one of the most productive areas of rice production in Aomori Prefecture, which now covers approximately 5,300 hectares of field. The canal reaching to the Pacific Ocean was completed during the period 1937 to 1966. Then, from 1978 to 2006, the national farm irrigation project on the left bank of Osaka River was implemented to solve constant water shortage and poor drainage and to ensure stable supply of water and reduce the workload for operation and maintenance. Farmers, local residents and relevant organizations such as National Federation of Land Improvement Associations are working together to take new operation and maintenance measures for the canal.