The Inaoigawa Irrigation Canal at the “Scanty land” Sanbongihara Plateau

Abstract

The Inaoigawa irrigation canal was constructed by Tsutou Nitobe and Jyujirou Nitobe in 1855, the grandfather and a father of Inazo Nitobe. It was a huge civil engineering work with the purpose of irrigating the “Scanty land” Sanbongihara Plateau, about 50-90 m above sea level. The ~800 m tunnel water way would have required high-level technology for geographic measurement and tunnel construction for the Edo period. We conducted a field excavation of the tunnel water way in 2012, and surveyed the constructive structures and measured the inclination ratio of the water way. We found many similarities in the methods of tunnel construction between the Inaoigawa irrigation canal and the Persian qanat irrigation systems of central Asia.