The state of excavation of the Tenguiwa Irrigation System was recorded in old documents such as the Jōmō Densetsu Zakki (1774) and the Shukin Roku (1798) and is still being handed down from generation to generation.

The right bank of the Tone River used to be unsuitable for rice cultivation due to the lack of water. In 1601, feudal Lord Akimoto, who ruled over the land, created a plan to build an irrigation canal to revive the barren land and develop new paddy fields. However, the land was at a higher elevation than the Tone River, making it impossible to divert water from the river to the area within the territory. Feudal Lord Akimoto requested Honda, the feudal lord who ruled over the upstream area of the river and was granted permission to establish a water intake port in the upstream river area. He promised the farmers that they would be exempt from land taxes for three years and took the lead in constructing the irrigation canal.

In 1604, the excavation of the Tenguiwa Irrigation Canal was completed and abundant water flowed into the territory. Once the water had wet the paddy fields in the territory, it flowed back into the Hachiman River (present-day Taki river).

At the time, feudal lord Ina, who ruled over the downstream river area, also planned to divert water from the Tone River. The leader of the local wealthy farmers living in the downstream river area, Ebara, who supported the excavation of the Tenguiwa Irrigation Canal, proposed to feudal lord Ina to create an irrigation canal that would use water from the latter.

In 1605, feudal lord Ina began expanding the Tenguiwa Irrigation Canal’s water intake port and excavating a new irrigation canal. In 1610, a canal about 23 km long, which included the Hachiman River (present-day Taki river), was completed. The irrigation canal excavated by feudal Lord Akimoto was called the “Tenguiwa Irrigation Canal” and the irrigation canal excavated by feudal lord Ina was called the “Daikan Bori.” In this application, the whole area, including these two canals, is now called the “Tenguiwa Irrigation System”.

The Tenguiwa Irrigation System, originally an irrigation canal, was excavated for farmers with the help of the neighbouring feudal lords. At the time, although the rice harvest yield was 900 tons, it increased to 4050 tons in the latter half of the 18^th century and this land became a rich paddy-producing region. In 1776, the farmers built a stone monument to show their gratitude for feudal Lord Akimoto. The stone monument that farmers built in appreciation of the feudal lord is a rare sight in Japan and its high historical value saw it designated as a cultural asset of Gunma Prefecture in 1950.

Today, the Tenguiwa Irrigation System takes its water from Tone River and supplies it to 1571 hectares of paddy fields spread throughout Maebashi City, Takasaki City and Tamamura Town.

Even now, four centuries on, the people are grateful to be able to live such rich lives. Since 1990, an annual festival is held honouring the Feudal Lord Akimoto and both he and the Tenguiwa Irrigation System are still loved by the people. While the Tenguiwa Irrigation System was being constructed, Feudal Lord Akimoto used a unique form of diversion technology known as an “echūwaku.” to protect the water intake port from flooding.

According to ancient records, when the Tone River rises, the wooden frame fixed to the river floats and the lumber on the other side weakens the momentum of water and when the water level exceeds a certain level, it automatically controls the intake of water to the Tenguiwa Irrigation System. Installing the “echūwaku” protected the area against flood damage and sustains the benefit of the Tenguiwa Irrigation System.

Water Heritage

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

• The amount of rice harvested in this area increased from 900 tons to 4050 tons due to the completion of the Tenguiwa Irrigation System.
• Engraved in the stone monument, erected in 1776, is a message of thanks to feudal lord Akimoto, thanks to whom the farmers prospered for over 150 years. This story has been passed down through the years.
• Illustrations drawn in 1838 show that approximately 70 villages in the early 19th century prospered due to the completion of the Tenguiwa Irrigation System.
• The Tenguiwa Irrigation System is an important structure that helps develop agriculture in the land as well as boosting food production.

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

• Representatives of farmers petitioned the Japanese government to “rank” feudal lord Akimoto’s achievements. In 1912, Emperor Meiji granted Akimoto a new rank.
• The Tenguiwa Irrigation System has been around for four centuries and it is a structure that made the farmers’ lives far more stable as well as helping the agricultural village develop.

The Tenguiwa Irrigation System was unique in some positive and constructive way;

• The Tenguiwa Irrigation System is a structure that was built using a unique method created by feudal lord Akimoto, who had less economic power, thus demonstrating his experience and knowledge.
• The construction method he used was a modified version of that used by Sengoku warlord Shingen Takeda and reformed to adapt to the fast-flowing Tone River. It was named “echūwaku,” after the feudal Lord Akimoto’s official rank.
• According to the petition addressed to Emperor Meiji, the “echūwaku” was a structure whereby when the Tone River’s main stem level rose, the wooden frame fixed to the river would automatically weaken the water’s momentum and when the water level exceeded a certain level, the intake of water to the Tenguiwa Irrigation System would be controlled and guided back into Tone River’s main stem.
• Installing the “echūwaku” meant that even if a flood occurred on one side of the Tone River, the land on the opposite side, which benefits from the Tenguiwa Irrigation System, would remain undamaged.
• Additionally, at nighttime, feudal Lord Akimoto would use paper lanterns to measure differences in elevation between the land and the Tone River. This method of using paper lanterns to measure the difference of elevation was frequently used in the mid-17^th century, but in the early 17^th century, when the Tenguiwa Irrigation System was excavated, examples of this form of measurement were exceedingly rare. “Chōken Inari” is a hillside shrine and a benchmark point of reference for measuring with paper lanterns.

The Tenguiwa Irrigation System bears the stamp of a cultural tradition or a civilization of past the past;

• Once the Tenguiwa Irrigation System was completed, the farmers would offer up harvested rice to feudal Lord Akimoto’s grave every year and hold festivals such as Yabusame (horseback archery) and the traditional Shishimai Dance at the shrine to show their gratitude to Akimoto, the feudal lord who enriched their lives.
• Even today, 400 years later, this festival is still held to honour and thank feudal Lord Akimoto for the rich life he brought to the farmers. At this festival, the Mayor of Maebashi City dresses up as the feudal lord and leads a warrior procession as they travel around the town and joins the citizens in giving thanks for the Tenguiwa Irrigation System and feudal Lord Akimoto.
• In 1893, the fifth oldest hydroelectric power plant in Japan was constructed by exploiting a drop area in Tenguiwa Irrigation System. Even today, there are still traces of the brick water intake port from that time.
• The history of the Tenguiwa Irrigation System is used in teaching materials for elementary schools in Maebashi City and 4^th-grade elementary school students visit this site for their social studies class.

Engineering utility vis-à-vis designed utility

The Tenguiwa Irrigation Canal was an unpaved water canal completed in 1604, which was 0.75 m deep, 1.2 m wide and about 3 km long. Excavating the Tenguiwa Irrigation System helped expand the paddy fields as well as increasing the irrigated area. To accommodate this expansion more effectively, the canal was rebuilt as a reinforced concrete structure 2 m deep and 5 m wide.

Present State of Conservation

The water intake facility of the Tenguiwa Irrigation System was built into the Tone River and has enriched the agricultural land that benefits from the same. However, flooding due to Typhoon Kathleen in 1947 and once again in 1948 due to Typhoon Ione saw the facility sustain serious damage.

In 1948, as a permanent measure to stabilize the water intake, an agreement was reached to form a joint water intake facility between the Tenguiwa Irrigation System and the Hirose Momonoki Irrigation System, thus forming the Bando Ōzeki Land Improvement District Association. In 1951, the Bando Ōzeki joint water intake port was created thanks to a disaster recovery project. Even now, the Bando Ōzeki water intake port is managed by the Bando Ōzeki Land Improvement District Association.