Izawa River No. 7 Stone Check Dam

The Number Seven and What It Implies

Izawagawa Dai-nanago Ishi-entei (荏沢川第七号石堰堤, also written Izawa-gawa Dai-nanagō Ishi-entei, the No. 7 Stone Check Dam on the Izawa River) is a dry-stone erosion-control dam in Kuwabara, Chikuma City, Nagano Prefecture, built around 1884 in the Meiji era and listed as a Registered Tangible Cultural Property of Japan on 8 January 2009.

Four dams on this stream carry cultural property status, and they are numbered 1, 2, 3 and 7. Nothing fills the gap. The absence of Nos. 4, 5 and 6 from the register suggests that the original scheme ran to at least seven structures and that the sequence has thinned over the intervening century, though the sources consulted here do not record what became of the missing ones.

No. 7 is the lowest of the survivors, about 80 metres below No. 3, and the first that a visitor walking up from the trailhead meets. It is also the smallest: 12 metres across the crest, 3.2 metres high, with an apron running 5.6 metres downstream from the toe of the dam body. Small, in this case, does not mean incidental. Standing at the downstream end of the chain, it takes whatever the three dams above have let through.

Before There Was a Law

Japan had no statutory framework for erosion control when this dam was built. The Sabo Act came into force in 1897; the Izawa River works were carried out between 1882 and 1884 according to prefectural records, under the direct administration of the Home Ministry. The Agency for Cultural Affairs describes No. 7 as one of the country's early erosion-control facilities built under that direct administration, and the phrasing is not decorative. Structures of this generation are the physical record of how Japanese engineers first approached mountain sediment before methods hardened into standards.

What they arrived at here is visible in the crest. The top of the dam does not run level. It dips through a shallow curve, the shape Japanese engineers call nawadarumi after the sag of a slack rope, and every dam in this group shares it. The curve pulls flow toward the middle of the channel, keeping water off the shoulders where a straight lip would let it spill and undercut the ends.

The construction is dry masonry throughout, karaishizumi, with large stones fitted against one another and small ones driven into the gaps. Nothing is bonded. A wall built this way drains rather than dams, so groundwater passes through instead of accumulating behind the face, and individual blocks can settle without cracking the whole.

A completion drawing said to have been preserved in the old village of Kuwabara, recording the finished work sites of the sediment-control project along the Sano River, is reported to correspond to the structures still standing. Documentary evidence of that kind rarely survives alongside civil engineering of the early 1880s.

The registration criterion cited for No. 7 is contribution to the historical landscape of the nation, under number 20-0339.

Starting Here

The footpath along the Izawa River runs about one kilometre and takes in all four dams, with a car park and an explanatory board at the entrance. Nagano Prefecture built and maintains it, and there is no admission fee, no gate and no closing time; photography is unrestricted. Spring through autumn is the season the prefecture recommends, and there are no toilets on the route. Chikuma City Hall is roughly twenty minutes away by car via the prefectural Komine-Inariyama road, and the Nagano Expressway passes directly overhead near the entrance.

Begin at No. 7 and the walk builds. This dam sets the vocabulary: dry joints, sagging crest, paved apron below. Each structure upstream then plays a variation on it, and the differences become the interest. No. 3 stretches to 35 metres. No. 2 rises in two tiers to eight metres. No. 1 leans back at the gentlest slope of all.

The stream here is modest and the atmosphere domestic rather than remote. Houses are close, the grade is easy, and volunteers from the Kuwabara district clear the vegetation each year in partnership with the prefecture, which is why the masonry stays visible at all. A century and a half after they were built, these dams still hold back sediment for the people living below them.

Chikuma City offers two further stops within a short drive: Inariyama, a former post town on the Hokkoku Nishi Kaido designated an Important Preservation District for Groups of Traditional Buildings in 2014, and the terraced rice fields of Obasute.