What Aoshita No. 3 Dam Is
Aoshita No. 3 Dam (青下第３ダム) is a water-supply barrage on the upper Aoshita River at Ōkura, Aoba Ward, Sendai City, Miyagi Prefecture, completed in 1934 and listed as a Registered Tangible Cultural Property (Structures) on 7 June 1999. It stands furthest upstream of the three dams in the valley and is the first structure the river meets on its way down.
The main barrage measures 15.2 m high and 60.4 m long, the longest crest of the three. It was built where the valley opens out, so its profile stretches sideways in a way the two lower dams do not. A subsidiary weir 2.4 m high and 27.7 m long lies below it, and a maintenance bridge 1.2 m wide crosses the crest. The finish matches its neighbours: concrete faced with river cobbles.
Full water level here stands roughly 18 m above the second reservoir, the largest step in the chain. Water impounded at Aoshita No. 3 Dam passes down through the two lower pools before being drawn off at the first dam and sent to the Nakahara Purification Plant.
The Sediment Outlet
One feature sets Aoshita No. 3 Dam apart from the other two: a sediment outlet placed below the subsidiary weir. A barrage at the head of a catchment receives the silt and gravel washing off the slopes before anything else does. Left alone, that material settles on the reservoir floor, reduces capacity year by year and eventually interferes with the intake. Building an opening to flush it out was a design response to the particular job this dam had to do.
The stepped arrangement of the three dams serves more than storage. If the uppermost reservoir traps sediment, the pools below stay comparatively clean. Aoshita No. 3 Dam therefore acts as a filter at the entrance to the whole system as well as a place to keep water, and the sediment outlet is what allows it to keep playing that role.
The listing criterion is contribution to the historic landscape of the nation. The facilities built during Sendai's first waterworks expansion, begun in 1931, were registered together as eight items in 1999. Aoshita No. 3 Dam is the deepest into the valley of the group.
What Makes It Distinctive
The 60.4 m crest is the immediate difference. Where the two lower barrages are wedged into narrow points in the valley, Aoshita No. 3 Dam crosses the water broadly, and the cobbled face reads as one wide wall rather than a compressed panel.
The forest around it matters just as much. The woodland of the Aoshita catchment is managed as a water source conservation forest, certified by the Ministry of the Environment as a Nature Coexistence Site in March 2024, with part of it entered on the international OECM database that August. Trees are grown to protect the reservoirs, and growing them turns out to protect biodiversity too. The landscape around this dam is the product of that management rather than an accident of remoteness.
Access is the catch. The walking routes published by the Sendai City Waterworks Bureau reach only as far as Aoshita No. 2 Dam, and everything upstream falls inside the managed conservation forest. Visitors curious about this structure will get more out of the exhibits at the Sendai City Waterworks Memorial Hall, which explain how the three dams work as one system.
Visiting Aoshita No. 3 Dam
No public route leads to Aoshita No. 3 Dam. The four walking courses published by the waterworks bureau, A through D, extend only to the second dam; the third lies further upstream inside the water source conservation forest. Anyone planning a visit should contact the Sendai City Waterworks Memorial Hall on 022-393-2188 to ask whether access is possible.
The water source grounds themselves are open to anyone, from 9:30 a.m. to 4 p.m., free of charge. The other structures registered on the same day, including the first dam and the former management office, can all be seen from the paths, so a visit still explains how the system fits together.
Nothing on site restricts photography, and shooting from the paths is unrestricted. For tripod work or commercial photography, contact the Memorial Hall in advance.
To reach the grounds, take a Sendai City bus for Jōgi from Sendai Station, alight at Ōtemon-iriguchi and walk 8 minutes, or walk 20 minutes from Kumagane Station on the JR Senzan Line. Driving takes about 40 minutes from Sendai Station or about 30 minutes from the Sendai-Miyagi interchange. The Memorial Hall closes from 1 December to 31 March.
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Q&A
- Can visitors see Aoshita No. 3 Dam?
- There is no public viewing route. The published walking paths stop at Aoshita No. 2 Dam, and the area upstream is managed conservation forest. Ask the Sendai City Waterworks Memorial Hall about access.
- How large is Aoshita No. 3 Dam?
- The main barrage is 15.2 m high and 60.4 m long, the longest of the three. Below it sits a subsidiary weir 2.4 m high and 27.7 m long, with a maintenance bridge 1.2 m wide across the crest.
- What is the sediment outlet at Aoshita No. 3 Dam for?
- It is an opening below the subsidiary weir that lets accumulated silt and gravel be flushed away. As the uppermost barrage, this dam receives material washing off the slopes first, so the outlet protects its storage capacity.
- How far above the next reservoir is Aoshita No. 3 Dam?
- Its full water level stands roughly 18 m above the second reservoir, the biggest step in the sequence. Water moves down the chain on that gradient without pumping.
- When was Aoshita No. 3 Dam registered?
- On 7 June 1999. The criterion applied to this barrage is contribution to the historic landscape of the nation, and eight structures in the Aoshita water source area were listed on the same date.
Basic Information
| Name | Aoshita No. 3 Dam (青下第３ダム, Aoshita Dai-san Damu) |
|---|---|
| Location | 1-2 Maehara, Ōkura, Aoba Ward, Sendai City, Miyagi Prefecture |
| Designation | Registered Tangible Cultural Property (Structures) |
| Year Designated | Registered on 7 June 1999 |
| Quantity | 1 unit |
| Dimensions | Main barrage 15.2 m high, 60.4 m long; subsidiary weir 2.4 m high, 27.7 m long; maintenance bridge 15.5 m long, 1.2 m wide |
| Owner | Sendai City Water Supply Business Manager |
| Public Access | No public viewing route. Located inside the managed water source conservation forest |
References
- Agency for Cultural Affairs, National Cultural Properties Database: Aoshita No. 3 Dam
- https://kunishitei.bunka.go.jp/heritage/detail/101/00001090
- Sendai City Waterworks Bureau: Aoshita Water Source Walking Map
- https://www.suidou.city.sendai.jp/soshiki/somu-eigyo/koho/7/405.html
- Sendai City Waterworks Bureau: Visitor Information for the Aoshita Water Source Area and Memorial Hall
- https://www.suidou.city.sendai.jp/soshiki/somu-eigyo/koho/7/403.html
- Sendai City Waterworks Bureau: Aoshita Water Source Conservation Forest Entered on the World OECM Database
- https://www.suidou.city.sendai.jp/jigyo/suigen-shisetsu-suishistsu/syuyoshisetsu/655.html
Last verified: 2026.09.08