Prior to 1620, agriculture in the Kanuki area suffered from chronic water shortages, with rainfall and reservoirs as the only water sources. Therefore, Ueda Naizen, who lived in Kamikanuki Village, made a plan to build an irrigation canal using the Kano-gawa river that ran nearby as an intake and began construction work on the project. The irrigation canal extended from east to west on the north side of Kanuki-yama mountain, with an upper canal extending from Yazakinohana to Kamikanuki (about 1,200 m long and 3.6 m wide) and a lower canal to Shimokanuki (about 3,818 m long, 3.6 to 5.5 m wide, and 1.5 to 4.5 m deep). Water was successfully drawn despite the difficulties involved in the construction, such as building a stone weir at the intake to raise the water level, together with work such as mixing furnace ash with earth to prevent water from seeping into the sandy soil irrigation canal. As a result, the Kanuki area became free from drought, and it became the foundation of the agricultural development known as the “2,000 koku of Kanuki” (with one koku being about 150 kilograms of rice). Currently, although the area under irrigation has decreased with the urbanization of the region, it now plays a stronger role in local disaster prevention as a drainage canal during heavy rains and the like. As a result of the progress of repair work such as culverting, it has lost its former appearance, but it has been passed down in the region for about 390 years.

An overview of the Kanuki Irrigation Canal as it currently remains is as follows.

Structure: Concrete canals (U-shaped, box-shaped, etc.)

Irrigated area: 7.13 ha

Extension: 19.85 km (irrigation canal: 9.96 km; drainage canal: 9.89 km)

Water level control facilities: 9 locations

The structure represents a milestone / turning points in development of irrigated agriculture and bears an exceptional testimony to development of agriculture and increase in food production along with the improvement of economic condition of farmers;

In the 1620s, when the Kanuki Irrigation Canal was constructed, the Edo shogunate (national government) and the various clans (local authorities) were encouraging the development of new rice paddies throughout the country, and the same was true in the Kanuki area. Under these circumstances, solving the water shortages through the establishment of the Kanuki Irrigation Canal system marked an important turning point in the development of agriculture in the Kanuki area.

The structure made outstanding contribution to enhancing food production, livelihood opportunities, rural prosperity, and poverty alleviation in a region;

Comparison of before and after the completion of the Kanuki Irrigation Canal at that time

Before completion: Paddy field area: 191.27 ha (harvest: approx. 267 tons)

After completion: Paddy field area: 224.73 ha (harvest: approx. 306 tons)

(1777 Kamikanuki Village Record Book, 1777 Shimokanuki Village Record Book)

Agriculture in the Kanuki area had been suffering from chronic water shortages, but with the completion of the Kanuki Irrigation Canal from around 1620 to 1629, the Kanuki area became free from drought, which laid the foundation for the development of agriculture known as the “2,000 koku of Kanuki.” The total yield was 306 tons, consisting of 153 tons in Kamikanuki Village, 135 tons in Shimokanuki Village, and 18 tons in Zendayu-shinden. Water from the Kanuki Irrigation Canal was also directed to Ganyudo Village, and the four villages of Kamikanuki Village, Shimokanuki Village, Zendayu-shinden, and Ganyudo Village benefited from the Kanuki Irrigation Canal. In addition, land with a yield of 21 tons in Kamikanuki Village was opened up as new rice paddies due to the Kanuki Irrigation Canal.

Today, the city, the agricultural cooperative, and local water commissioners attend a memorial service for Ueda Naizen, which is held every year on August 15 at Reizanji Temple. In addition, the facility contributes to providing a good living environment for residents, such as the maintenance of the local community through waterway cleanup activities by neighbourhood residents, and plays a role in preventing ambient water pollution and preserving the beauty of the landscape.

The structure was an example of engineering marvel or excellence at the time of its construction;

A crescent-shaped stone weir was set up at the water intake, and a “Kawakura” structure (three logs assembled in the shape of a triangular pyramid, with a bamboo rope stretched over it, on which grass or straw mats are hung) was placed as an extension of the stone weir to raise the water level. In addition, three places called “Sunaharai” (sand conduits) were established in the stone weir where the stones were lower than the ones around them as a measure to prevent the accumulation of sand. During the rice planting season, it is necessary to take in a lot of water, so a sand conduit about 1 m wide near the bank was covered with boards to dam the water flow, and the two sand conduits about 5 m wide far from the bank were covered with horizontal log poles, on which bamboo was placed vertically like stakes with grass and straw hung to dam the water flow. This was an ingenious way of securing the water level at the intake.

The structure was unique in some positive and constructive way;

Initially, when Ueda Naizen built a weir at Otaki on the Kano-gawa river and constructed an irrigation canal to draw in water, the water did not flow because of the sandy soil near the water intake sluice gate. Therefore, at a time when cement was not widely used, furnace ash was mixed with soil and spread on the irrigation canal to prevent water from seeping in, which succeeded in bringing long-awaited agricultural water to the Kanuki area.

Engineering utility vis-à-vis designed utility

Due to flooding of the Kano-gawa river in June 1945, the upstream bend of a 50-meter section of the bank of the stone weir collapsed over a width of about 10 meters, preventing water from entering the irrigation canal, so an axial-flow pump was installed at Zentokubo, where the Kise-gawa river joins the Kano-gawa river. Since the water is now pumped, there is no longer a need to repair the stone weir or insert the “Kawakura” structure.

Due to a land readjustment project in the Nakase and Nakahara areas that began in FY 1968, the upper and lower canals of the irrigation canal in some sections were backfilled, and a levee was constructed along the Kano-gawa river. As a result, the lifting pump at Zentokubo was removed, and its location was moved downstream on the Kano-gawa river, where the current Kanuki pumping plant was established, and water is taken year-round as water to maintain the irrigation canal. The water intake method has changed since its construction, the irrigated area has decreased, and its role as a drainage canal has increased, but it still plays an important role as agricultural water for the area and contributes to the promotion of agriculture in the area.

Present State of Conservation

Operation and inspection of the Kanuki irrigation pumping station and water level control facilities (such as the Futasegawa sluice gate and Miyahara pump) and repairs to other sluice gates are performed by Numazu City facility manager. Otherwise, daily management of the irrigation canal (patrols at ordinary times and removal of garbage, etc.) and sluice gate operation (at times of heavy rain) are carried out by the Kanuki Irrigation Canal Committee, which is organized by local farmers. In addition, Numazu City responds to requests and suggestions from local residents through onsite inspections, repair work, and so on.