What the Kamakurazawa River No. 23 Ground Sill Is
The Kamakurazawa River No. 23 Ground Sill is a stone bed-control weir on the Kamakurazawa River in Yoshizato, Minamiuonuma City, Niigata Prefecture, completed in 1935 and entered on the national register as a Registered Tangible Cultural Property structure on 4 August 2015.
A ground sill, or tokodome in Japanese, is a low weir laid across a stream to stop the bed from cutting downward. It is not built to hold water back, and not built to trap large volumes of sediment either. Its job is to fix the level of the streambed at one point and ease the gradient above it. This one stands 1.4 meters high and runs 17 meters across, making the Kamakurazawa River No. 23 Ground Sill both the lowest and the shortest of the eight registered structures on the stream.
Where it sits explains what it does. The Agency for Cultural Affairs describes it as one of the ground sills built at the junction with the lower reach of the Kamakurazawa River, a stretch that had already been rechannelled before the sabo project began. It marks the point where mountain torrent engineering met ordinary river improvement on the valley floor. An incised plaque reading 床止２３ is set into the upper right wing.
Why It Was Registered, and What the Number Means
The structure met the registration criterion of contributing to the historic landscape of the country. The Council for Cultural Affairs recommended it on 13 March 2015 and the entry was made on 4 August of the same year, under registration number 15-0410.
Taken alone, it is a low stone weir across a shallow stream. Its interest lies in the sequence it belongs to. Placing dams and sills along the whole length of a torrent was still an early experiment in Japan when this work was carried out, and the Kamakurazawa River No. 23 Ground Sill holds down the bottom end of that sequence, joining nine years of upstream construction to the improved channel already in place below. It was also the last of the eight to be finished.
The number in the name is a construction serial from the original project, not a count from the river mouth. The plaque on the wing carries the same number.
Looking at a Low Weir
The masonry is nerizumi, mortared work in which the joints between stones are packed with a bonding material rather than left dry. Dry stonework, called Karazumi, relies on the stones locking against each other alone and looks quite different at close range. Here the joint lines run thin and continuous, so the pattern in which the stones were set can be read straight off the face.
A height of 1.4 meters is low enough for an adult to look down onto the crest. With so little drop, the water spreads instead of plunging, laying a thin sheet across the full 17 meters. That ratio of length to fall states the purpose plainly: this is less a container for sediment than a ruler setting the height of the bed.
The Kamakurazawa River No. 1 Ground Sill stands a short distance upstream, and the water surface steps down between the two. Standing between them is the clearest way to see how a run of sills quiets a stream by breaking its fall into stages.
Visiting the Kamakurazawa River No. 23 Ground Sill
This is a working outdoor structure with no interior. Visiting means looking at it from the bank. There is no admission charge, no reception desk and no restriction on photography.
Because the Kamakurazawa River No. 23 Ground Sill is the lowest of the eight, it makes a natural starting point for anyone working upstream. The No. 1 Ground Sill, about 20 meters above it, can be seen from the same spot. The structure is low, so a slightly raised position on the upstream side gives the best view of the crest and the overflow notch.
Stay out of the streambed. Water and debris collect here in heavy rain, and snow closes the valley in winter. For a clear look at the joints, come between about May and November. Directions to the valley and the parking situation are set out on the Kamakurazawa River Sabo Facilities page.
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Q&A
- Can I visit the Kamakurazawa River No. 23 Ground Sill, and is there an admission fee?
- It stands beside a public stream and can be viewed from the bank at any time, free of charge. No visitor car park or footpath has been provided, and entering the streambed is dangerous.
- When was the Kamakurazawa River No. 23 Ground Sill built and registered?
- It was completed in 1935 and registered as a Registered Tangible Cultural Property (structure) on 4 August 2015, under registration number 15-0410.
- What is the difference between a ground sill and a sabo dam, and which is the Kamakurazawa River No. 23 Ground Sill?
- A sabo dam holds sediment behind it and slows its movement downstream; a ground sill keeps the bed of the stream from cutting down. This structure is a ground sill, which is why it is only 1.4 meters high.
- Does the number 23 in Kamakurazawa River No. 23 Ground Sill mean anything?
- It is a serial number from the original 1920s and 1930s project rather than a position counted from downstream. The plaque cut into the upper right wing carries the same number.
- What is the best season to see the Kamakurazawa River No. 23 Ground Sill?
- Roughly May to November, once the snow has melted. Minamiuonuma receives very heavy snowfall and the valley cannot be reached in winter. Avoid the site in rain and immediately after rain.
Basic Information
| Name | Kamakurazawa River No. 23 Ground Sill (鎌倉沢川第二十三号床止) |
|---|---|
| Location | Yoshizato, Minamiuonuma City, Niigata Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | Registered 2015/8/4 (Heisei 27) |
| Quantity | 1 site |
| Dimensions | 17 meters long, 1.4 meters high |
| Owner | Niigata Prefecture |
| Public Access | Working outdoor structure; exterior visible from the bank at any time, no interior access |
References
- National Cultural Properties Database: Kamakurazawa River No. 23 Ground Sill (Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/heritage/detail/101/00010575
- Sabo Facilities on the Kamakurazawa River Entered on the National Register (Niigata Prefecture, Minamiuonuma Regional Promotion Bureau)
- https://www.pref.niigata.lg.jp/sec/minamiuonuma_seibi/1356827806289.html
- Registered Cultural Properties of Minamiuonuma City (Minamiuonuma City Board of Education)
- https://www.city.minamiuonuma.niigata.jp/docs/890.html
Last verified: 2026.09.12
