Shiraito plateau, Kumamoto, Japan

Consideration about community’s history in the regional management – Case Study on the Shiraito plateau, Kumamoto, Japan –

Tsujun irrigation canal is an agricultural irrigation canal built in 1854 to supply water to Shiraito Plateau which previously had water conveyance difficulties due to being surrounded by low lands and rivers on four sides. Since then, the canal system has been supplying water to the terraced rice paddies of Shiraito Plateau for about 160 years. In 2008, part of Shiraito plateau was selected at the national level as the first terraced rice paddy for the Important Cultural Landscape, as Landscape with Tsujun irrigation channel and rice terraces in Shiraito plateau. In 2011, all of Shiraito plateau is included in the Important Cultural Landscape area. The Tsujun irrigation system, having a unique local history, designed in line with the natural environment, and supporting local business (agriculture) and living, deserves to be described as the foundation of this cultural landscape.

Cultural landscape system in Japan has been since 2004. Cultural landscape is “Landscapes formed by people‘s lives or work in a given region and the climate of the region are indispensable for understanding the lives and work of the Japanese people.” In the UNESCO’s world cultural heritage, the cultural landscape especially about the Continuing landscape is “Current society tries for the activation in acknowledgment of the importance of the traditional lifestyle, and the evolution of the landscape goes on.” So, the preservation of Cultural Landscape is sustainable community development based on their awareness of local identity.

  • Characteristics of the Tsujun irrigation channel

Tsujun irrigation system was built by Yasunosuke Futa, So-joya [Yabe tenaga’s chief village headman]. Futa conducted many civil engineering works during his term such as road improvements, bridge construction, irrigation canals and weirs, and so on. Permission from the feudal domain was given for an estimated reclamation of about 42ha of land in November 1852, and the Tsujun irrigation canal and Tsujun Bridge were completed in 1854. Agricultural productivity dramatically improved with the construction of the irrigation canal, and close to the estimate was reclaimed in the Meiji period; 180ha at its peak, and currently about 118ha of terraced rice-paddies are supplied with the water.

The irrigation canal consists of the headwork of the Sasahara River as the base, then cylindrical water division, Tsujun Bridge, Upper-Ide, Lower-Ide, and each branch channel, and is a mountain channel of about 49.2km in total length. The waterway consists of open channels and tunnels, and a hydraulic structure called sabuta is installed at various places along the waterway. The waterway splits into two: the main channel conducts water from the headwork of the Sasahara river, via the main body of the Tsujun bridge to the Upper-Ide that runs into the southern edge of Shiraito Plateau; and the Lower-Ide has its water inlet on the right bank of the Gorogataki river over which Tsujun Bridge was built, and flows 20m lower than the Upper-Ide in elevation. Some water flows directly by small dams in rice paddies. The water fork at the Upper-Ide goes to the branch channels via rice paddies, and then drops to the Lower-Ide for recycling. The main channel was basically contoured, and the water incline is kept even. The channel was tunneled when construction along the contour was impossible and the tunneled section is about 20 percent. Thus the irrigation networks built about 160 years ago have hardly changed.

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  • Transition of the operation and maintenance system

Water distribution management of the canal is supply-driven where the Land Improvement Association takes the initiative. The combination of this system and the water level control system with open channels and fixed weirs requires a longer response time in the downstream water division point, in response to the increase of water at the headwork. In order to prevent this, a reservoir is needed. In the Tsujun system there is no regulating reservoir, and the terraced rice paddies between the Upper-Ide and Lower-Ide function as regulating reservoirs.

It is characteristic of the Tsujun canal that there are many unwritten rules about the operation and management and that the site manager’s position tends to be hereditary. We will assess the real status of the current activities of the Land Improvement Association, and clarify the characteristics of the system in the Tsujun canal.

(1) Operation by the Tenaga (1854-1872)

(2) Operation by Kami-mashiki-gun (1873-1888)

(3) Operation by Shiraito Village (1889-1949)

(4) Operation by users (1950-now)

The following is a summary of these phase four characteristics: firstly, the Irrigation Rights Union was reformed into the Land Improvement Association, and it became possible for users to propose land improvement projects. Secondly, with technical advancement, renovation work on the channels and Tsujun Bridge became easier. And then, as Tsujun Bridge was designated a cultural asset, conservation activity began. Above all, the realization of projects in response to user requests became possible, and the organization is run mainly by users to the present day.

Maintenance of the Tsujun irrigation canal is currently operated by the Tsujun Area Land Improvement Association. This association is configured of members who pay union dues of 2,500 yen, 1 board chairperson, 9 directors, and 3 supervisors. The chairperson is selected from the directors, then, each district has a fixed number of personnel and the directors and supervisors are elected by discussion. Regular meetings are held five times a year to discuss water distribution and repair works for channels.

  • Recent activities for community development

“Machi-zukuri” means sustainable community development. These activities take bottom up style and are based on the collaboration of these three stakeholders; inhabitants, local collectivities and association. For the sustainable preservation of cultural landscape create system, it is important to share the outstanding universal value of the region. For sharing the value of local identity, there are two key concepts. One is Autonomy; based on the preservation of cultural landscape, this local area have to maintain the system by itself. The other is Integrate; several sectors have to cooperate for the preservation of cultural landscape. In the preservation of cultural landscape, the participation is important step of community development. Now, three philosophies; Diversity, Dynamism and Sustainability are important in these activities.

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Naoto TANAKA, Kumamoto University, naotot@kumamoto-u.ac.jp

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