Arakawa Fifth Dam

What the Arakawa Fifth Dam Is

The Arakawa Fifth Dam (荒川第五堰堤, Arakawa Dai-go Entei) is a gravity-type concrete sabo dam built in 1954 and extended in 1973 on the Arakawa River at Amanuma, Tsuchiyu Onsen-cho, in Fukushima City, Fukushima Prefecture, and registered as a Registered Tangible Cultural Property (structure) of Japan on March 7, 2008. It is 150 meters long and 12 meters high, with a revetment on the left bank, and Fukushima City lists the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) as the owner.

Part of the 15 registered Arakawa River Sabo Dams, it lies upstream of Jizohara Dam and just below the point where the Shionokawa tributary joins the main river. The Arakawa First Dam is about 300 meters farther up. It was registered as a Registered Tangible Cultural Property in 2008 under number 07-0085.

The Longest Dam in the Group

At 150 meters, the Arakawa Fifth Dam is the longest dam among the registered structures. Jizohara Dam comes next at 74 meters, and the other main-river dams measure 47 meters at the shortest and 70 meters at the longest, so the Fifth spans the valley at roughly twice the width of any of them. The Arakawa Fourth Groundsill is longer still at 184 meters, but it is a low bed-stabilizing structure only 2.7 meters high and does a different job.

Its site also sets it apart. Below the Shionokawa confluence the main river and its tributary have just merged, and the dam stands where it can catch sediment arriving from both streams at once.

Despite the number, the Arakawa Fifth Dam is younger than the Sixth (1950), Seventh (1951) and Eighth (1952). The Agency for Cultural Affairs records an extension in 1973 without saying which part was added.

Corner Stones Set at an Angle

The feature the Agency singles out is on the downstream edge of the crest. There the corner stones are laid at an angle to the current so that they will not be torn loose, an arrangement the Agency describes as unusual.

That edge takes the full force of water and stones pouring over the dam. The same detail appears on the Arakawa Fourth Groundsill in the middle reaches, which was also completed in 1954.

In section the dam follows the standard profile of the group, with an upstream face sloping 1 to 0.45 and a downstream face of 1 to 0.2. The surface is faced with stone.

Seeing the Arakawa Fifth Dam

The Arakawa Fifth Dam is a working sabo structure. Viewing is free from nearby ground; you cannot walk on the dam or go down into the riverbed.

Start with the length. A low wall running 150 meters from bank to bank gives a very different impression from the tall, narrow dams upstream. Then look along the downstream edge of the crest, where the corner stones sit askew to the flow.

The Arakawa First Dam of 1937 is about 300 meters upstream, so Amanuma lets you see a prewar and a postwar dam in one short walk. Stay off the banks after rain, when the river rises quickly. Directions are on the Arakawa River Sabo Dams page.