What the Kamakurazawa River No. 1 Ground Sill Is
The Kamakurazawa River No. 1 Ground Sill is a stone bed-control weir on the Kamakurazawa River in Yoshizato, Minamiuonuma City, Niigata Prefecture, completed in 1927 and entered on the national register as a Registered Tangible Cultural Property structure on 4 August 2015.
It measures 26 meters across and 1.5 meters high, and stands about 20 meters above the No. 23 Ground Sill. The two work as a pair over the lower part of the sabo project. According to the Agency for Cultural Affairs, their task is to prevent downcutting and stabilise the bed of the stream. When a torrent scours its own bed, the slopes on either side lose their footing and begin to slide, so the height of the bed had to be secured before any dams could be built above.
The year matters. 1927 was the first year of construction in this valley, and the Kamakurazawa River No. 1 Ground Sill went up alongside the No. 1 Sabo Dam upstream. The opening move of a nine-year project was made not with a dam alone but with a dam and a sill together.
The First Year of the Works
Registration came under the criterion of contributing to the historic landscape of the country. The Council for Cultural Affairs made its recommendation on 13 March 2015 and the entry followed on 4 August, under registration number 15-0411.
Laying dams and sills along an entire torrent was still an unusual approach in Japan at the time. The Kamakurazawa River No. 1 Ground Sill is where that approach starts on this stream: it sets, in the form of a fixed bed level, the datum from which the six dams above it were designed. A structure a metre and a half tall governed everything built higher up the valley.
A Wide Notch and a Diagonal Face
The width of the overflow section is the first thing to notice. Across 26 meters of crest, the spilling zone has been kept broad, so the water divides and falls over a wide stretch instead of concentrating at one point. Spreading the force across a face rather than a line matters especially on a low sill.
The face of the dam body is laid in tanizumi, a bond in which the stones are set on the diagonal and lean against each other, so that the joints cross at an angle rather than running level. Compared with coursed masonry such as Nunozumi, a diagonal bond makes it harder for a whole line of stones to be pulled out together under overflow. Standing just below the crest and looking up, the raking joints show clearly in the way the shadows fall.
The water surface changes level here. Between the Kamakurazawa River No. 1 Ground Sill and the No. 23 Ground Sill twenty meters below, the stream drops in two stages, and the pairing of the two structures can be read directly from the shape of the water.
Visiting the Kamakurazawa River No. 1 Ground Sill
This is a working outdoor structure and has no interior. Visiting means looking at the exterior from the bank, free of charge, with no reception and no restriction on photography.
Because it is low, a slightly raised position on the upstream side gives a better view than standing square in front of it: from there both the width of the notch and the diagonal bond of the masonry are legible. Seen together with the No. 23 Ground Sill downstream, the two-stage drop shows how a run of sills holds a streambed in place. The No. 1 Sabo Dam lies about 50 meters upstream, and the change from sill to dam happens within that short stretch.
Keep out of the streambed. The site is dangerous when the water rises, and snow closes the valley through the winter, so plan for roughly May to November. Directions and the parking situation are covered on the Kamakurazawa River Sabo Facilities page.
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Q&A
- Can the Kamakurazawa River No. 1 Ground Sill be visited, and is there a fee?
- It stands in the open beside the stream and can be seen from the bank at any time without charge. No car park or footpath has been laid out, so give some thought to where you leave a vehicle.
- When was the Kamakurazawa River No. 1 Ground Sill built?
- In 1927, the first year of sabo construction in this valley; the No. 1 Sabo Dam was completed the same year. It was registered as a Registered Tangible Cultural Property (structure) on 4 August 2015, under registration number 15-0411.
- What is the diagonal stonework on the Kamakurazawa River No. 1 Ground Sill called?
- Tanizumi, a bond in which stones are set on the slant so the joints cross at an angle. It was favoured on weirs and revetments because water passing over the crest is less likely to draw out a whole course of stone.
- What is the purpose of the Kamakurazawa River No. 1 Ground Sill?
- To stop the stream cutting down into its own bed and to hold the bed at a stable height. Together with the No. 23 Ground Sill it covers the lower part of the sabo section and fixes the level on which the dams upstream depend.
- Is there anything else to see near the Kamakurazawa River No. 1 Ground Sill?
- The No. 23 Ground Sill is 20 meters downstream and the No. 1 Sabo Dam about 50 meters upstream. All three are registered, and the difference between a sill and a dam can be compared over a very short walk.
Basic Information
| Name | Kamakurazawa River No. 1 Ground Sill (鎌倉沢川第一号床止) |
|---|---|
| Location | Yoshizato, Minamiuonuma City, Niigata Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | Registered 2015/8/4 (Heisei 27) |
| Quantity | 1 site |
| Dimensions | 26 meters long, 1.5 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. 1 Ground Sill (Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/heritage/detail/101/00010576
- 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
