Earth:Wajū

Short description: Hydraulic engineering and flood control structure

An agebune (上げ舟) punt with a setting pole kept in the rafters of a wajū building in case of rising water

Early 20th century wajū pump built by Meidensha at the Museum of History and Folklore in Kaizu

A wajū (輪中, lit. inside the circle) is a hydraulic engineering and flood control structure unique to the alluvial floodplain of the Kiso Three Rivers in central Japan . It is comparable to the European polder, although a wajū is typically not reclaimed. The hardships endured for centuries by farmers whose lives revolved around the wajū has given rise to the term "wajū spirit" (輪中根性, wajū konjō).

History

Since prehistoric times, sudden freshets in late spring caused by snowmelt in the Japanese Alps along the course of the major rivers of Owari and Mino created great suffering for agricultural communities. The wajū was developed to protect fertile riparian farmland from becoming submerged by rising water levels during these freshets. Wajū are known to have been in use since at least the 16th century, but some wajū are reputed to be much older, such as Takasu wajū which was allegedly completed in 1319.

To develop a wajū, an area of land, usually a river island, was enclosed by a levee ring. In the event of a levee failure, most wajū incorporated structures allowing for vertical evacuation. One evacuation system was the inochizuka (命塚, lit. life [preserving] mound), an artificial earthen high ground similar to the terps of Northern Europe or the cattle mounds built on American ranches.

See also

• Ōgaki Castle, which is protected by a wajū
• Johannis de Rijke
• Tatsuta wajū sluice gates
• 1754 Hōreki River incident

Further reading

• Shinomoto, Etsuko. "Waju: Ethos for Water Use and Flood Control". Nanzan University. https://rci.nanzan-u.ac.jp/jinruiken/publication-new/item/ronshu_10_07_shimomoto.pdf.