What Aoshita Gauging Weir Is
Aoshita Gauging Weir (青下量水堰) is a small flow-measuring weir on the Aoshita River at Ōkura, Aoba Ward, Sendai City, Miyagi Prefecture, built in 1933 and listed as a Registered Tangible Cultural Property (Structures) on 7 June 1999. It stands 518 m upstream of Aoshita No. 3 Dam, making it the most remote of the eight structures registered in the Aoshita water source area.
The weir is 2.0 m high and 20.0 m long. Its section tapers from a base 3.4 m wide to a crest just 0.6 m across. The fabric is concrete faced with river cobbles, matching the three dams downstream. As barriers go it is small, standing barely above head height.
Aoshita Gauging Weir was never meant to store water. A rectangular notch 1.37 m wide and 0.5 m deep is cut into the crest near the right bank, and ordinary flow passes over that notch. Read the depth of water crossing it and you have the discharge of the river at that moment. This is a device for turning a stream into a number before it ever reaches a reservoir.
Measurement Came First
The weir was finished in 1933, a year ahead of the three dams below it. The instrument for measuring water was in place before the works for holding it. That order makes sense once you consider the question the engineers faced: how much water does the Aoshita actually deliver, and how far does it swing between seasons? No reservoir can be sized without an answer. Sendai's first waterworks expansion had begun in 1931, and this weir supplied the figures on which decisions rested.
The dimensions are specified tightly. The notch is 1.37 m wide and 0.5 m deep; the section narrows from a 3.4 m base to a 0.6 m crest, so the edge the water crosses is thin. For a structure whose purpose is to be read rather than to resist, the measurements are the working parts.
The listing criterion is contribution to the historic landscape of the nation. Aoshita Gauging Weir carries no ornament and very little scale. It earned its place because it preserves, in built form, the fact that this water system began with counting rather than with damming.
What Makes It Distinctive
Everything interesting about this weir gathers at the notch. The straight line of the crest breaks near the right bank for a rectangular cut 1.37 m across. In normal conditions water runs only through that cut while the crest on either side stays dry. High water spills across the whole length, but routine gauging happens at that single point.
The cobble facing also reads differently here than on the dams. At 2.0 m there is room for only a few courses of stone, so individual cobbles hold their shape instead of merging into texture. Seeing the same technique applied at two very different scales is instructive in a way photographs of the big dams alone are not.
The forest around Aoshita Gauging Weir is managed as a water source conservation forest. In March 2024 the Ministry of the Environment certified it as a Nature Coexistence Site, and part of it was entered on the international OECM database that August. Weir and woodland belong to one scheme: measure the water, store it, and grow the trees that keep producing it.
Visiting Aoshita Gauging Weir
No public route leads to Aoshita Gauging Weir. The four walking courses published by the Sendai City Waterworks Bureau end at Aoshita No. 2 Dam, and this weir lies well beyond that, 518 m above the third dam inside the managed conservation forest. A normal visit will not bring it into view. To ask whether access is possible, contact the Sendai City Waterworks Memorial Hall on 022-393-2188.
The water source grounds themselves are open to all, from 9:30 a.m. to 4 p.m., with no admission charge. The Memorial Hall, also free, explains how the whole catchment works, which is where the gauging role of this weir makes sense in context.
No published notice restricts photography, and shooting from the walking paths is unrestricted. For tripod work or commercial photography, speak to the Memorial Hall in advance.
Reaching the grounds: take a Sendai City bus bound 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. By car, 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
- What is Aoshita Gauging Weir for?
- It measures the flow of the Aoshita River. A notch 1.37 m wide and 0.5 m deep near the right bank lets the depth of passing water be read and converted into a discharge figure.
- Can visitors see Aoshita Gauging Weir?
- No public viewing route exists. The published walking paths stop at Aoshita No. 2 Dam, and the weir lies inside the managed water source conservation forest upstream.
- Where is Aoshita Gauging Weir located?
- At Nishihara, Ōkura, Aoba Ward, Sendai City, 518 m upstream of Aoshita No. 3 Dam. It is the furthest of the eight registered structures in the water source area.
- How big is Aoshita Gauging Weir?
- It stands 2.0 m high and 20.0 m long, with a base 3.4 m wide narrowing to a crest 0.6 m across. The construction is concrete faced with river cobbles.
- When was Aoshita Gauging Weir built and registered?
- Built in 1933 and registered on 7 June 1999. It was completed a year before the three dams downstream, so the means of measuring the river preceded the means of storing it.
Basic Information
| Name | Aoshita Gauging Weir (青下量水堰, Aoshita Ryōsui Zeki) |
|---|---|
| Location | 38 Nishihara, Ōkura, Aoba Ward, Sendai City, Miyagi Prefecture |
| Designation | Registered Tangible Cultural Property (Structures) |
| Year Designated | Registered on 7 June 1999 |
| Quantity | 1 unit |
| Dimensions | Concrete faced with cobbles; 2.0 m high, 20.0 m long, base width 3.4 m, crest width 0.6 m; notch 1.37 m wide and 0.5 m deep |
| 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 Gauging Weir
- https://kunishitei.bunka.go.jp/heritage/detail/101/00001091
- 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