A Cylinder of Cut Stone on the Hillside
The Unit 1 Head Tank of the Kyushu Electric Power Myoken Power Station (九州電力妙見発電所１号機ヘッドタンク, Myōken Hatsudensho Ichigōki Heddotanku) is a stone water tank at Makizono-cho, Kirishima City, Kagoshima Prefecture, built in 1921 and entered on the national register of Tangible Cultural Properties on 26 January 2011 under registration number 46-0093. The Agency for Cultural Affairs classifies it as one unit of construction work rather than a building, and records its area as 76 square metres.
It stands partway up the steep slope behind the powerhouse. Water taken from the Nakatsugawa in the Amorigawa watershed arrives here by canal, settles in the tank, and then drops through a steel penstock more than 150 metres long to reach the Unit 1 turbine below. The tank itself is cut stone laid up in a cylinder, the courses stepping inward as they rise so that the wall in section resembles a shallow staircase. On either side of the penstock line, masonry retaining walls hold the slope in place, and a flight of steps runs beside the pipe for maintenance access.
Seventy-six square metres is not large. A backyard swimming pool would cover more ground. The point of a head tank is not volume but position: it is the reservoir that keeps the pressure in the pipe steady when the turbine's demand fluctuates, and its value lies in sitting at exactly the right height above the machine it feeds.
What a Head Tank Actually Does
Run-of-river hydroelectric plants of this generation do not store water behind a dam. A weir upstream diverts part of the flow into a canal that follows the contour of the valley, losing as little elevation as possible, until it reaches a point directly above the powerhouse. There the water has to change direction from horizontal travel to a controlled vertical fall, and that transition is where the head tank sits.
Two problems need solving at that junction. First, the canal delivers water at a roughly constant rate while the turbine takes it in variable amounts, so a buffer is required to absorb the difference without letting air into the pipe. Second, silt and debris carried down from the mountain must settle somewhere other than inside the machinery. A tank of modest surface area, deep enough to keep the penstock intake permanently submerged, handles both.
Understanding this makes the cylindrical form legible. A round tank distributes water pressure evenly through the wall, which matters when the wall is stone rather than steel or concrete, since masonry resists compression far better than tension. The stepped courses, wider at the base and narrowing upward, follow the same logic: the load increases with depth, so the stone thickens where the water pushes hardest. The mason who set these blocks in 1921 was solving a structural problem with the same reasoning an engineer would apply today, using the material at hand.
Registered in 2011, and Why That Category Fits
Registration as a Tangible Cultural Property is not the same thing as designation as an Important Cultural Property. The register was created in 1996 as a lighter framework: owners notify the authorities of changes rather than seek permission, and the system was aimed at buildings and structures from the Meiji period onward, particularly those still in working use. The criterion applied to the Myoken structures is contribution to the historic landscape of the country, the broadest of the three grounds available and the one commonly used for engineering works.
For a water tank belonging to an operating power station, no other category would work. This is equipment, not a monument. Water still runs through it, the penstock still carries pressure, and the owner still has to maintain the masonry against a century of wet and freeze. The register acknowledges heritage value without freezing the object in place.
The Unit 1 tank was registered on the same day as two companion structures: the stone powerhouse at the foot of the slope, registration number 46-0092, and the larger head tank serving Units 2 and 3, number 46-0094. The Agency's descriptions cross-reference each other. Read together, they treat the site as a single stone-built water system rather than three separate objects that happen to be neighbours.
Two Rivers, One Site
One detail in the official record repays attention. The Unit 1 tank takes water from the Nakatsugawa, while the tank serving Units 2 and 3 draws from the Amorigawa itself. The site therefore operates two intakes on two watercourses within the same watershed, feeding tanks at different elevations on the same hillside, with the Unit 1 tank set higher.
That arrangement tells you something about how the plant grew and how its designers thought. Rather than enlarging a single intake and a single canal, they tapped a second source at a different height and gave it its own tank and its own penstock. Available flow in either stream varies with rainfall and season, and two independent supplies at two elevations give an operator more room to manoeuvre than one large system would.
Walking up the slope, the difference between the two tanks is immediately visible: the upper one round and compact, the lower one rectangular and roughly six times the area. Same site, same year, same material, two quite different answers, each shaped by the flow it was built to hold.
Seeing It on the Ground
The tank stands on private land belonging to Kyushu Electric Power, on a steep slope above an operating power station, and it is not open for public visits. There is no admission gate, no signage for tourists and no set opening hours. The penstock line and the stone retaining walls beside it can be picked out from public roads in the vicinity, and photography from outside the property presents no problem, but the steps beside the pipe are a maintenance route rather than a footpath. Anyone hoping to get closer should contact the company in advance.
The site lies on the Amorigawa near the Myoken Onsen hot spring area of Makizono-cho. Kagoshima Airport is about fifteen minutes away by car, as is the Mizobe Kagoshima Airport interchange on the Kyushu Expressway. From the railway, the Myoken route bus takes roughly seventeen minutes from Hayato Station on the JR Nippo Line and about ten minutes from Kareigawa Station on the JR Hisatsu Line. Airport buses between Kokubu Station and Kagoshima Airport also stop at Myoken Onsen.
Once here, the surroundings deserve time. Riverside inns at Myoken Onsen draw naturally rising hot spring water at the water's edge, the gorge colours in November, and sweetfish anglers work the shallows in early summer. Kareigawa Station, a wooden station building of 1903 and itself a Registered Tangible Cultural Property, sits ten minutes down the road and makes a natural pairing: two registered structures from the same era of infrastructure building, one carrying passengers and one carrying water.
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Q&A
- What is the Myoken Power Station Unit 1 Head Tank, and what does a head tank do?
- It is a stone water tank built in 1921 on the slope above the Myoken Power Station in Kirishima City. A head tank sits where a canal delivering water horizontally meets the top of a penstock that drops it to the turbines. It buffers the difference between steady canal inflow and variable turbine demand, keeps the pipe intake submerged, and lets silt settle before the water reaches the machinery.
- Can visitors see the Myoken Power Station Unit 1 Head Tank up close?
- No. It stands on Kyushu Electric Power property on a steep slope above a working power station, with no public access, no admission and no opening hours. The penstock line and adjoining stone retaining walls can be seen from public roads nearby, and photography from outside the property is unrestricted. Requests for closer access should go to the company beforehand.
- How large is the Myoken Power Station Unit 1 Head Tank, and how is it built?
- The Agency for Cultural Affairs records it as stone construction with an area of 76 square metres, counted as one unit. Cut stone is laid up in a cylinder with the courses stepping inward as they rise. Masonry retaining walls flank the penstock on both sides, with a flight of steps alongside the pipe.
- Where does the water in the Myoken Power Station Unit 1 Head Tank come from?
- From the Nakatsugawa in the Amorigawa watershed. It reaches Unit 1 through a steel penstock more than 150 metres long. The separate head tank serving Units 2 and 3, lower on the same slope, draws instead from the Amorigawa, so the site works two intakes on two watercourses.
- When was the Myoken Power Station Unit 1 Head Tank registered, and how does registration differ from designation?
- It was registered on 26 January 2011, registration number 46-0093, in the 69th round. Registration, introduced in 1996, applies a lighter regime than designation as an Important Cultural Property: owners give notification of changes rather than seek permission, which suits modern structures still in daily operation.
Basic Information
| Name | Kyushu Electric Power Myoken Power Station Unit 1 Head Tank (九州電力妙見発電所１号機ヘッドタンク) |
|---|---|
| Location | 4224-6 Hakiri, Shukukubota, Makizono-cho, Kirishima City, Kagoshima Prefecture |
| Designation | Registered Tangible Cultural Property (Buildings), registration number 46-0093, 69th registration round, category of other structures |
| Year Designated | Registered 26 January 2011 (Heisei 23) |
| Quantity | 1 unit |
| Dimensions | Stone construction, area 76 square metres; cylindrical tank of cut stone with stepped courses; penstock exceeding 150 metres in length |
| Owner | Kyushu Electric Power Co., Inc. |
| Public Access | Not open to the public; located on company land above an operating power station. Built 1921 (Taisho 10) |
References
- National Database of Cultural Properties, Agency for Cultural Affairs: Kyushu Electric Power Myoken Power Station Unit 1 Head Tank
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00008606
- Cultural Heritage Online: Kyushu Electric Power Myoken Power Station Unit 1 Head Tank
- https://bunka.nii.ac.jp/heritages/detail/199322
- Kagoshima Cultural Properties Encyclopedia Plus: Myoken Power Station Unit 1 Head Tank
- https://k-bunkazai.com/cultural/f-q-60091/
- National Database of Cultural Properties, Agency for Cultural Affairs: Myoken Power Station Main Building
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00008605
- Kagoshima Prefecture Tourism Site: Myoken Onsen
- https://www.kagoshima-kankou.com/guide/10128
Last verified: 2026.07.30