It has long been told that construction of the Naganoseki Irrigation Canal began about 1000 years ago. Its completion can be confirmed nearly 400 years ago at the latest, as the canal is clearly depicted in a hand-drawn map of Gunma prefecture from 1645 (National Diet Library Collection).
Later the Shirakawa Inverted Siphon was constructed. The Gunma-gun Shi (an historical report of Gunma county in 1925) records that “in 1814, the cross culvert was excavated 2 meters below the bed of the Shirakawa River (present-day Haruna-Shirakwa River)”. This is shown in another hand-drawn map dating to around 1830. This proves that a high of knowledge standard and advanced engineering techniques in the early times.
The Naganoseki Irrigation Canal passed through middle of Takasaki City from west to east. The head works draws irrigation water from the Karasugawa River. The maximum water intake capacity is 6.8m3/s. The main irrigation canal is 8.6 kilometers in length from the head works to the cylindrical proportional distributor. Between the head works and the cylindrical proportional distributor, the canal distributes water to 15 beneficiary areas by branch irrigation canals. Moreover, the cylindrical proportional distributor divides the water into 4 downstream areas in proportion to extent of them.
Withdrawing additional water from Haruna lake through a tunnel of 283m and going through the modernization, the canal irrigated over 1700 hectares of paddy fields in 1904. Though paddy fields in beneficiary areas is decreasing due to urbanization, it irrigates about 430 hectares these days. It also fulfils function of regional drainage.
Elementary school students in Takasaki City are taught the history of the canal and its contribution to agricultural products and to the improvement of living standards of people in the area.
In 2006, the Naganoseki Irrigation Canal was listed as one of the Top 100 Irrigation Canals in Japan.