Over-all length of the weir 650m Maximum width 45m Over-all length of the trunk canal extended from the weir 7km It is the largest existing stone weir for irrigation for agricultural purposes in Japan. While still actively utilized, its stone-paving in the Edo period (1603 – 1868 CE) was maintained in good condition and was designated as the Selected Civil Engineering Heritage by the Japan Society of Civil Engineers, Public-Service Cooperation, on November 18, 2012.

Reservoirs were the source of water to paddy fields in the region, but many of them were destroyed by heavy floods that occurred throughout Bizen Province in the 1600s. In an agricultural society, it is obvious that obtaining irrigation water directly from the Asahi River would stabilize wetland paddy rice farming. The Okayama feudal domain lord in Bizen Province ordered the construction of the weir and irrigation channels. The oldest document indicated the presence of Takebe Weir in 1721. Therefore, it must have been built before that, although documents regarding its construction have not been verified. A hypothetical theory claims that it was built around the time because rice production in the related region increased considerably in 1628 – 1630.

Since the center line of the Asahi River was at the border between Bizen Province and Mimasaka Province on the other side, it was impossible to intercept the river crossing at a right angles. Therefore, it has the structure of a diagonal weir in the “Katamochi Method,” which did not ground the neighboring province and broke off the center of the river. The borders at the time were guarded rigidly even with cannons, and the existence of the encampment housing of the Okayama feudal domain lord was left as evidence in this Takebe region, the northern tip of Bizen Province, in 1632. These facts draw speculation that there must have been no room for negotiation with neighboring provinces. Hence, the “Katamochi Method” was their only option, and Takebe Weir, which is a diagonal weir, was lengthened for taking in a large volume of water. In addition, most of its main structure was built parallel to the river flow direction to reduce the water resistance. Moreover, to protect the weir in the “Katamochi Method” from flood disasters, solid stone-paving covered the entire weir, which made it an extremely rare structure for irrigation.

In addition, the massive weirs constructed all over Japan during this period were improved/renovated into fixed concrete dams or ferroconcrete weirs with gates, and appearances from those days have been lost. However, Takebe Weir has kept its stone-covered surface as it was originally constructed and is the largest stone-built weir for irrigation in Japan among all existing ones.

Thanks to the construction of Takebe Weir, rice field agriculture changed in the area from the previous style of using a reservoir to directly using river water by the weir and irrigation ditch. Taking advantage of the abundant water from the river, secondary or tertiary canals / ditches were laid out from the main canal, which provided water to most of the rice fields on the plain in the six villages concerned. Moreover, according to a document indicating the amount of rice production around the time Takebe Weir was constructed, as the sum of the four villages benefitted by the weir considerably agricultural yields increased from 286 tons in 1628 to 322 tons in 1630, but levelled off thereafter. Based on these facts, it is evident that the construction of Takebe Weir contributed to the stabilization of rice paddy farming in the area.

As the other side of the river belonged to other clans, they could not build a weir that across the Asahi River. Instead, they built a diagonal weir using the “Katamochi Method,” in which only one side was connected to the land. Because of the “Katamochi Method,” the length of the weir became as long as 650 m in order to take more water, and also to reduce the water pressure against the weir, almost the entire weir was constructed along the river. To protect this “Katamochi Method” weir from water damage, a solid stone cover was layered throughout the weir.

Since the weir was constructed, people have changed their paddy farming to utilize river water directly, and they were no longer concerned about the water shortage in the reservoir to produce rice. This led to the stabilization of rice and wheat productions.

Since the other side of the river belonged to other clans, they could not build a weir which across the river so it was made diagonal referring the “Katamochi Method,” in which only one side was connected to the land. To allow this diagonal weir by the “Katamochi Method” to function effectively, people elongated the weir and built it to the shape to stably irrigate more water. In addition, to be ready against water disasters, almost the entire weir was built horizontally along the river flow direction to reduce the water pressure, with a solid cover of stones over the entire weir.

In addition to being a diagonal weir to reduce water pressure, a round surface was created by combining the stones into long parenthesis-shapes, lowering the resistance of the current flowing over the weir.

Because this diagonal weir did not block the flow of the river, boats could convey materials by using the river, and fish could migrate from downstream to upstream or upstream to downstream.

Because they did not have a rock-breaker or combustive powder to break rocks around the time it was built, some people said that the Abura-Nagashi Method, which burned oil to make rocks breakable, was employed. Utilizing this method, people combined stones into long parenthesis-shapes and made the surface round and succeeded in reducing water resistance. Around the beginning part of the weir, the sturdy structure with giant rocks as big as almost 5m2 was laid against water disaster and it still has kept its original shape for more than 300 years.

The Structure is quite unique going parallel to the river except for the very first part even though it was built as a diagonal weir. Thus, the prolonged weir would not make the irrigation system nonfunctional. There were 2 facilities to release sediment like dirt, and upon flooding, the wooden part which held back the current was constructed to be pulled up in order to release water and dirt.

Around the era Takebe Weir was built, it was planned that the water would overflow on the arranged stones all the time since the water level of the river was higher. Even so, the level went down after the volume of water was well-controlled by the dam constructed upstream in 1954, and then the arranged stones of the weir became exposed. However, it did not affected the water intake function and it has been providing water to the rice fields in the Takebe region for over 300 years.

The massive weirs for irrigation constructed all over Japan during this era were improved/renovated to fixed concrete dams or ferroconcrete weirs with gates and appearances from those days have been lost. However, Takebe Weir has kept its stone-covered surface as it was originally constructed and is the largest stone-built weir for irrigation in Japan among all existing ones. In addition, its very small part was reinforced with concrete for recovering from the flood disaster damage in 1936, although people in the region minimized the reinforcement of concrete with their strong will. Their point of view toward Takebe Weir has not changed yet.