The Head Tank and Spillway
The head tank and spillway of the Former Yaotsu Power Plant Facilities (旧八百津発電所施設) are hydroelectric waterworks of 1911 on the high ground above the right bank of the Kiso River in Yaotsu, Yaotsu Town, Kamo District, Gifu Prefecture, and they were designated an Important Cultural Property in 2005 (Agency for Cultural Affairs).
The head tank, at the end of the headrace canal, regulated the flow of water heading down to the generators; the spillway carried overflow from the tank to the river (Agency for Cultural Affairs). Both were built in the same Yaotsu hydroelectric project as the main building and were added to the same designation of the Former Yaotsu Power Plant Facilities, number 02346.
The Head Tank
The head tank of the Former Yaotsu Power Plant Facilities lies on high ground about 200 meters east of the main building. It is a brick and concrete structure 73 meters long and 36 meters wide (Agency for Cultural Affairs).
Six control gates with iron doors line its west wall, and two sluices for flushing out sediment open in the south wall; on the slope below the control gates stands a brick retaining wall (Agency for Cultural Affairs). From the gates, penstocks dropped the water to the generators, which is why five sets of penstock channels survive in the main building.
The Spillway
The spillway starts at an overflow weir along the south wall of the tank and curves down the slope in a bow to the Kiso River. It is about 270 meters long, built of stone and concrete (Agency for Cultural Affairs).
It let water the plant could not use escape safely to the river, and its long line following the contours from hilltop to riverbank is the most legible trace of how the Former Yaotsu Power Plant Facilities coped with changes in flow.
Why It Is an Important Cultural Property
The Agency designated the head tank and spillway for their high historic value: together with the main building they preserve the layout of one of Japan's earliest large canal-type hydroelectric plants.
A powerhouse alone does not explain such a plant. With the tank that received the water and the channel that returned the surplus, the Former Yaotsu Power Plant Facilities now show the whole path of the water, and the land that forms their historic setting is protected with them.
Visiting
Since December 29, 2018, the grounds beyond the gate of the Former Yaotsu Power Plant Facilities have been closed (Yaotsu Town). Whether the head tank and spillway lie inside that area, and how much of them can be seen from public roads, has not been confirmed.
If you are travelling specifically to see them, check with the Yaotsu Town Board of Education first. Directions and parking are given on the page for the Former Yaotsu Power Plant Facilities as a whole.
Q&A
- What is the head tank of the Former Yaotsu Power Plant Facilities?
- A brick and concrete basin, 73 meters long and 36 meters wide, at the end of the headrace that regulated the water sent to the generators (Agency for Cultural Affairs).
- How long is the spillway of the Former Yaotsu Power Plant Facilities?
- About 270 meters, curving down the slope from the tank to the Kiso River (Agency for Cultural Affairs).
- When were the head tank and spillway of the Former Yaotsu Power Plant Facilities built?
- In the same project as the main building; the Agency dates them to 1911.
- Can I see the head tank and spillway of the Former Yaotsu Power Plant Facilities?
- The area beyond the gate is closed, and visibility from outside is unconfirmed, so ask the Yaotsu Town Board of Education.
- When were the head tank and spillway of the Former Yaotsu Power Plant Facilities designated an Important Cultural Property?
- On July 22, 2005 (Agency for Cultural Affairs).
Basic Information
| Name | Former Yaotsu Power Plant Facilities (旧八百津発電所施設), Head Tank and Spillway |
|---|---|
| Location | Yaotsu, Yaotsu Town, Kamo District, Gifu Prefecture |
| Designation | Important Cultural Property (Structure) |
| Year Designated | Designated 2005/07/22 (Heisei 17) |
| Quantity | 2 structures (head tank, spillway) |
| Dimensions | Head tank: brick and concrete, 73 m long, 36 m wide / Spillway: stone and concrete, 270 m long |
| Owner | Yaotsu Town |
| Public Access | Area beyond the facility gate closed since 2018/12/29; visibility of the tank and spillway unconfirmed |
References
- Former Yaotsu Power Plant Facilities, Head Tank (Database of National Cultural Properties, Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/bsys/maindetails/102/00004059
- Former Yaotsu Power Plant Facilities, Spillway (Database of National Cultural Properties, Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/bsys/maindetails/102/00004060
- Former Yaotsu Power Plant Facilities, Main Building (Database of National Cultural Properties, Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/bsys/maindetails/102/00004061
- Former Yaotsu Power Plant Museum (Yaotsu Town, Japanese)
- https://www.town.yaotsu.lg.jp/1518.htm
- Suspension of interior access (Yaotsu Town, Japanese)
- https://www.town.yaotsu.lg.jp/item/6896.htm
Last verified: 2026.11.12
Cultural Treasures in the Same Area
All are within walking distance in the same area, so we recommend visiting them together.
- Former Yaotsu Power Plant Facility spillway 0.00 km
- Former Yaotsu Power Plant Facility aquarium 0.15 km
