Azukisawa No. 1 Sabo Dam

The Lowest Dam in the Azukisawa Valley

The Azukisawa No. 1 Sabo Dam (小豆沢第一号砂防堰堤, Azukisawa Daiichigō Sabō Entei) is a dry-stone erosion control dam built in 1919 at Azukisawa, Miyagawa-cho, Hida City, Gifu Prefecture, and was registered as a Registered Tangible Cultural Property of Japan on March 29, 2019. It is the lowest of the three registered dams on this small Miyagawa tributary and, at 36 meters long and 5.5 meters high, the longest of them.

The date matters. 1919 was the year the national government began its directly managed sabo program on the Miyagawa, five years after the debris floods of August 1914. The Agency for Cultural Affairs describes this dam as the first sabo facility installed anywhere in the Jinzu River system, the river that eventually runs out through Toyama into the Sea of Japan. In other words, the first of many barriers built to hold back that watershed's sediment was placed at the mouth of this modest side valley.

Why the No. 1 Dam Was Registered

The Azukisawa No. 1 Sabo Dam was registered under the criterion of contributing to the historic landscape of the country, with registration number 21-270, the first of the three consecutive numbers given to the Azukisawa dams.

What the listing values most is how it was built. The body is dry-stone masonry: no mortar, just the weight of each stone and the way it locks against its neighbors. Gifu Prefecture's Sabo Division points out that every stone was set by hand, a method that would be difficult to reproduce today. Before machines reached these valleys, the stone was split, carried and bedded by crews working on the stream itself, and the dam's size is a direct measure of that labor.

The other point is its place at the start of sabo work in the Jinzu basin. More than a century on, Azukisawa No. 1 still catches sediment at the valley mouth. It is a heritage structure and a working one at the same time.

What to Look For at Azukisawa No. 1

Start with the slope. The national database records that the Azukisawa No. 1 Sabo Dam was raised at a gradient of 1:1.5, meaning the stonework moves 1.5 units sideways for every unit it rises, a little over 30 degrees. Applied to a height of 5.5 meters, that works out to more than 8 meters of stone measured horizontally from top to toe. It reads less like a wall than a steep, paved bank. With no mortar holding the stones, that gentle angle spreads their weight across the whole face and keeps the structure stable.

Then look at the notch in the crest and the floor below it. The notch, called the mizutōshi, is the spillway that lets water pass over the dam; the apron beneath it, the mizutataki, takes the force of the falling water so it cannot dig out the foot of the dam. At Azukisawa No. 1 both have been reinforced with concrete. Only the parts that take the hardest pounding from water and gravel were hardened, and the rest was left as Taishō-era stonework, so you can read the original masons' work and the later reinforcement side by side on one structure.

The photo of the dam on the prefecture's signboard, taken in autumn color, shows a white band of water running down the stone face, with a stone wall and a railed path alongside. It also makes clear how close the valley mouth is to the houses and garden walls of the hamlet.

Seeing Azukisawa No. 1 in Person

The Azukisawa No. 1 Sabo Dam is an outdoor flood-control structure with no reception desk and no admission fee; you can see its exterior only. Of the three Azukisawa dams it is the one nearest the hamlet, a short way up the valley from the roadside information board. Do not climb onto the crest or step down onto the apron.

No specific photography rules are published. The dam sits close to houses and fields, though, so stay off private ground and keep your camera off people's homes. Avoid the valley during or after rain, when the stream can rise quickly. Directions to Azukisawa are on the Azukisawa Sabo Dams page.