Nakazawa River Higashiyama Dam

Where Yamagata's Erosion Control Began

The Nakazawa River Higashiyama Dam (中沢川東山堰堤, Nakazawa-gawa Higashiyama Entei) is a masonry erosion control dam on the upper Nakazawa River in Oshikiri, Obanazawa City, Yamagata Prefecture, built between 1916 and 1920 and registered as a Registered Tangible Cultural Property on 15 January 2010.

The Nakazawa is a tributary of the Nyu River in the Mogami River system. According to Yamagata Prefecture its catchment covers about 11.7 square kilometers and its channel runs about 8.2 kilometers, falling at an average gradient of about 1 in 10.6, which makes it a torrent. The Higashiyama Dam sits in a narrow gorge on its upper course, where the stream bends.

It is 12 meters long and 2.4 meters high, a gravity dam of mortared stone, with a dry-stone revetment on the right bank upstream.

Why It Was Registered

In 1913 heavy rain over the Nyu River basin, the Nakazawa included, set off widespread landslides on the mountain slopes and flooded the communities along the river. Yamagata's erosion control programme began in 1916 in response to that disaster and others. The Nakazawa River Higashiyama Dam is among the first modern sabo works built by the prefecture itself, and the Agency for Cultural Affairs describes it as the first modern erosion control facility in the prefecture built as a prefectural project.

Four dams on the Nakazawa were registered on the same day. Yamagata Prefecture notes that pairing mortared stone dams with dry-stone revetments to hold back sediment was an early example nationally, and that the dams still do their job more than 90 years after construction.

The registration number is 06-0115, under the criterion of contributing to the historic landscape of the country.

What to Look For

Placed on the Bend

The Nakazawa River Higashiyama Dam stands in a narrow valley where the river curves. Debris flows coming round the bend are met by the dam and by the revetment on the right bank upstream together. The defence is not the wall alone but the wall, the bend and the bank working as one.

Mortared Stone and Dry Stone

The body of the dam is mortared masonry, built as a gravity structure. The revetment is dry-laid, stones stacked without binder. The wall that takes water and debris head on is bonded solid; the bank that protects the slope is left as open stonework.

A Staircase of Dams Downstream

180 meters below the Higashiyama Dam is the Kuzure Upper Dam, 70 meters below that the Kuzure Lower Dam, and 420 meters further on the Kawarasawa Dam. All are Taisho-era mortared stone dams, low walls set in series to ease the steep riverbed in steps and steady the channel. At the bottom of the series stands the Miyazawa erosion control memorial, erected in 1920. The Higashiyama Dam is the highest of the four.

Visiting

The Nakazawa River Higashiyama Dam is a working erosion control structure on a mountain stream. Neither Yamagata Prefecture nor Obanazawa City publishes any visitor parking, footpath or viewing arrangement for it. The location is Yanagidaira, Oshikiri, Obanazawa City; anyone who goes should stay out of the riverbed and off the dam and look from the surroundings only.

Obanazawa is among the snowiest places in Japan; the prefecture notes that snow can lie more than 2 meters deep even on the plain. In winter the upper valley should be treated as out of reach.