Arakawa River Sabo Dams

What the Arakawa River Sabo Dams Are

The Arakawa River Sabo Dams (荒川砂防堰堤群, Arakawa Sabō Enteigun) are 15 erosion-control structures built between 1925 and 1957 in the basin of the Arakawa River in Fukushima City, Fukushima Prefecture, and registered as Registered Tangible Cultural Properties (structures) of Japan in 2008. Fukushima Prefecture presents them under this collective name, and the city's list of cultural properties gives the owner of each one as the Ministry of Land, Infrastructure, Transport and Tourism (MLIT).

Ten of the 15 stand on the main river: the Arakawa First, Second, Third, Fifth, Sixth, Seventh and Eighth Dams, the Arakawa Fourth Groundsill, Jizohara Dam and Kawakami First Dam. The other five are on two tributaries: Shionokawa First and Fourth Dams on the Shionokawa, and the First, Third and Fourth Dams on the Higashi Karasu River. All except the groundsill are Erosion-control dam, which in Japan means a dam built to trap sediment and debris flows rather than to store water. Every one has a gravity-type concrete core faced with stone.

The registration came in two rounds. Jizohara Dam and eight structures on the main river were registered on March 7, 2008 (registration numbers 07-0084 to 07-0092), and the groundsill and the five tributary dams followed on July 8, 2008 (07-0102 to 07-0107). All 15 were listed under the same criterion: structures that contribute to the historic landscape of the country.

A Wild River and the Start of the Arakawa River Sabo Dams

According to MLIT's Fukushima River and National Highway Office, the Arakawa rises on Higashi-Azuma (1,975 meters), Issaikyo (1,949 meters) and Tetsuzan (1,710 meters), cuts deep into the hills, and gathers small tributaries such as the Nishi Karasu, Higashi Karasu and Shionokawa before reaching Jizohara Dam. Below that point it spreads across an alluvial fan with a radius of about 8 kilometers and joins the Abukuma River south of central Fukushima. The river is 26.6 kilometers long and drains 178.1 square kilometers.

The name means "rough river," and Fukushima Prefecture describes it as one of the steepest rivers in Japan. Erosion control began in 1900, when the prefecture started hillside works in the basin. Those works continued through three imperial eras, yet every heavy rain still flushed out enough sediment to choke the channel and flood the plain.

Jizohara Dam, the oldest of the 15, was begun in 1921 and finished in 1925. The Agency for Cultural Affairs calls it the first core structure built as part of the Abukuma River improvement scheme. It was rebuilt and reinforced several times and, according to the prefecture, reached roughly its present form in 1953.

The turning point came in 1936, when the national government took direct charge of sabo work in the basin. The Arakawa First Dam was completed the following year. A debris flow on the Higashi Karasu River in 1938 pushed construction into the tributaries as well. The prefecture says the basic framework of flood and sediment control on the Arakawa was largely in place by 1945, though building went on after the war: the youngest of the 15, Higashi Karasu River Fourth Dam, dates from 1957.

The Arakawa River Sabo Dams in Order Along the River

The numbers roughly follow the sequence of construction, not the order along the river. Using the positions given in the Agency for Cultural Affairs descriptions, the main-river structures run as follows from downstream to upstream. Figures in brackets are the construction years and dimensions in the Agency's database.

• Arakawa Fourth Groundsill (1954; 184 meters long, 2.7 meters high), in the middle reaches at Kaminagura and the lowest of the 15
• Jizohara Dam (1925, altered 1953; crest length 74 meters, height 8.7 meters), at the apex of the alluvial fan
• Arakawa Fifth Dam (1954, extended 1973; 150 meters, 12 meters), just below the Shionokawa confluence
• Arakawa First Dam (1937; 57 meters, 10 meters), about 300 meters above the Fifth
• Arakawa Sixth Dam (1950; 54 meters, 12 meters), about 900 meters above the First
• Arakawa Second Dam (1938, extended 1941; 54 meters, 13 meters), about 1,600 meters above the Sixth and just upstream of Tsuchiyu Onsen
• Kawakami First Dam (1946; 70 meters, 9.0 meters), about 570 meters above the Second
• Arakawa Seventh Dam (1951; 69 meters, 12 meters), about 200 meters above Kawakami First
• Arakawa Eighth Dam (1952; 60 meters, 12 meters), about 400 meters above the Seventh
• Arakawa Third Dam (1940; 47 meters, 15 meters), about 1,200 meters above the Eighth and the farthest upstream of the series on the main river

On the Shionokawa, a left-bank tributary, Shionokawa Fourth Dam (1956) sits near the confluence and Shionokawa First Dam (1954) about 1 kilometer upstream. On the Higashi Karasu River, which joins from the right bank, the First Dam (1948) stands inside the hot-spring town of Tsuchiyu, the Third (1951) 475 meters upstream, and the Fourth (1957) another 3.2 kilometers beyond.

Adding up the distances in the Agency's descriptions, the main-river dams between the Fifth and the Third span roughly 5.2 kilometers. The valley narrows as you climb. Downstream, the Fifth Dam stretches 150 meters across a broad bed; at the top, the Third Dam is only 47 meters long but 15 meters tall.

Shared Construction and Recognition

Each of the Arakawa River Sabo Dams pairs a concrete gravity body with a stone face. Most have an upstream face sloping 1 to 0.45 and a downstream face of 1 to 0.2, meaning the downstream side is close to vertical. The stonework changes from dam to dam: coursed Nunozumi with continuous horizontal joints, diagonally set Tanizumi, and rounded river cobbles.

Some details are specific to single structures. On the Arakawa Fifth Dam and the Arakawa Fourth Groundsill, the corner stones on the downstream edge of the crest are laid at an angle to the current so they will not be plucked out, an arrangement the Agency calls unusual. The Arakawa Seventh Dam carries an inset plaque recording its name, builder and year, and Kawakami First Dam is described as the only dam on the Arakawa whose construction ran through the war years into the postwar period. Each structure has its own page.

In 2007 the Japan Society of Civil Engineers named "Arakawa Basin Flood Control and Sabo Works" a Civil Engineering Heritage site, citing the way Edo-period open levees and flood-defense woods work together with the sabo dams built by the national government in the 1920s to 1950s. The cultural property registration followed a year later. All 15 structures still function. MLIT counts 30 sabo dams completed on the main river, the Higashi Karasu and the Shionokawa by the end of 2004, and the registered 15 belong to the older generation among them.

Visiting the Arakawa River Sabo Dams

The Arakawa River Sabo Dams are working flood-control structures in the open. There is no reception, no opening hours and no fee. You view them from nearby ground and cannot walk on the dam bodies. Fukushima Prefecture notes that, depending on the structure, a visit involves a round-trip walk of two hours or more or a light mountain hike. Guided walking tours along the river are also offered.

A good starting point is Fukushima City's Arakawa Archive Room (荒川資料室) near Jizohara Dam, which explains the river and its sabo works with photographs, panels and a relief model of the basin. It is open from 10:00 a.m. to 4:00 p.m., closed from December 29 to January 3, and free to enter, with parking for about 30 cars.

By public transport, take a Fukushima Kotsu bus bound for Tsuchiyu Onsen from the east exit of JR Fukushima Station. Get off at Jichi Kenshu Center after about 30 minutes and walk about 10 minutes to the Archive Room. For the upper main-river dams and the Higashi Karasu dams, ride the same line to its terminus at Tsuchiyu Onsen. By car, the area is about 20 minutes from the Fukushima-nishi Interchange on the Tohoku Expressway.

Water in these valleys rises quickly after rain, so stay away from the riverbed and banks in wet weather. Paths to the upper dams are narrow, and hiking footwear is advisable.