Hyakutaro Ditch, also known as Hyakutaro Weir, is a historic irrigation waterway that runs through Taragi Town, Asagiri Town, and Nishiki Town in Kuma District, Kumamoto Prefecture. For centuries, it has played an important role in supplying water to local farmland and supporting agriculture in the Kuma region.
Hyakutaro Ditch extends for approximately 18 kilometers. According to one account, it was completed in 1710, during the Hoei era. The waterway was excavated by local farmers and has long been used to irrigate the surrounding agricultural land.
The first excavation work is said to have begun in the late 16th century, although few records survive and the details remain unclear. A second phase of construction took place in 1680. The third phase was carried out between 1696 and 1697, followed by a fourth phase in 1704–1705. The main waterway was completed on August 20, 1710. A fifth phase was planned for the area west of the Harada River, but it remained unfinished, and its exact date is unknown.
Construction continued over approximately a century. The completed waterway eventually reached a total length of about 19 kilometers and served an irrigation area of approximately 1,400 hectares. It made a major contribution to the development of rice paddies on the region’s alluvial fans.
Together with the Kono Ditch, Hyakutaro Ditch helped transform the Upper Kuma area into productive rice-growing land. The canal was especially notable because it was dug by local farmers without the support of the feudal domain or the direction of a specially appointed leader. Their collective effort made the waterway an important part of the region’s agricultural history.
The name “Hyakutaro” is associated with legends about a man named Hyakutaro who was sacrificed as a human pillar in an attempt to protect the water-control structures. These stories have become an enduring part of the canal’s local history.
Construction of Ichifusa Dam began in 1957, accompanied by a major land-improvement project led by Kumamoto Prefecture. As part of this project, Hyakutaro Ditch and Kono Ditch were renovated into modern concrete waterways. The improvement works were completed in 1968.
The former Hyakutaro Weir had suffered from serious water leakage. Its old sluice gate, built from enormous stone blocks, has been preserved beside Mito Shrine. The surviving structure offers a tangible reminder of the engineering challenges faced by the people who built and maintained the historic canal.
Several local traditions explain the origin of the name Hyakutaro Ditch. Although their details differ, they all reflect the difficulties of controlling floods and securing a reliable water supply for agriculture.
One well-known story tells of repeated river floods that swept away fields and farmland. According to the legend, villagers received a divine message instructing them to offer as a human pillar someone wearing a garment with two lines along its hem. Hyakutaro happened to be wearing such clothing and was selected.
He was tied to a bridge pillar, and his cries were said to have echoed throughout the village that night. The following day, the flooding subsided. In this telling, his sacrifice brought an end to the disasters that had troubled the community.
Another version places the story during the construction of the canal. The work was repeatedly disrupted because the weir gates were washed away. Hyakutaro is said to have received a message from a water deity who appeared to him in a dream. Following this revelation, he willingly became a human pillar and was buried alive beneath the gate. From that point onward, the gate was believed to have remained secure.
A third tradition describes Hyakutaro as an engineer who was ordered by the feudal authorities to direct construction of the canal and weir. When a heavy overnight rain destroyed a gate he had designed, he reportedly took responsibility by committing suicide or volunteering to become a human pillar. A large pine tree beside the weir is regarded in this story as his grave marker.
These accounts are legends rather than verified historical records, but they reveal how deeply the canal’s construction and the sacrifices associated with it have been remembered in local culture.
Hyakutaro Ditch continues to be valued as an irrigation waterway and as a historical site. The remains of the former Hyakutaro Weir beside Mito Shrine preserve the memory of the people who worked to bring water to the region’s farmland. Visitors interested in local history, traditional irrigation engineering, and rural landscapes can explore the site as part of a wider visit to the Kuma area.
Hyakutaro Ditch runs through Taragi Town, Asagiri Town, and Nishiki Town in Kuma District, Kumamoto Prefecture. The area can be reached by car or public transportation. Because the canal extends across several municipalities, visitors may wish to combine a visit to the former sluice gate and nearby Mito Shrine with other local attractions.