Arakawa First Dam

What the Arakawa First Dam Is

The Arakawa First Dam (荒川第一堰堤, Arakawa Dai-ichi Entei) is a gravity-type concrete sabo dam built in 1937 across 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 57 meters long at the crest and 10 meters high, and Fukushima City lists the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) as its owner.

A sabo dam is built to catch sediment and debris flows rather than to hold back a reservoir. This one is among the 15 registered Arakawa River Sabo Dams and stands about 300 meters upstream of the Arakawa Fifth Dam. Its registration number is 07-0086.

The First Dam Built by the National Government

The Agency for Cultural Affairs describes the Arakawa First Dam as the first sabo dam built after the former village of Tsuchiyu was declared a sabo zone in 1936. MLIT's own history records the same step: in 1936 the Arakawa basin came under direct national control, and work began on the Arakawa No. 1 Sabo Dam. The number on the dam reflects that sequence, not its position on the river.

Until then, erosion control on the Arakawa had been a prefectural job. Hillside works started in 1900, and Jizohara Dam had been finished at the head of the alluvial fan in 1925. Floods kept carrying sediment down regardless, and the national government stepped in. The Arakawa Second Dam followed in 1938 and the Arakawa Third Dam in 1940. Among the registered dams on the main river, these three are the only prewar works built under national control.

How the Arakawa First Dam Is Built

As a gravity dam, the structure resists the push of water and sediment by its own weight. The Agency gives the upstream face a slope of 1 to 0.45 and the downstream face 1 to 0.2, which leaves the downstream side standing almost upright.

That downstream face is finished in Nunozumi, coursed stonework in which the stones are cut to a uniform height and laid so the horizontal joints run straight across. Later dams in the series introduce diagonally set Tanizumi and rounded river cobbles, but the Arakawa First Dam keeps to calm, level lines.

At 10 meters it is one of the lower dams on the main river. The Arakawa Fifth Dam, just downstream, was completed 17 years later in 1954 and is 150 meters long and 12 meters high, so the short reach at Amanuma holds one prewar and one postwar dam side by side.

Seeing the Arakawa First Dam

The Arakawa First Dam is a working flood-control structure. There is no fee, and visitors view it from the surrounding ground; walking on the dam or climbing down to the riverbed is not possible.

The thing to look at is the stonework on the downstream face. Seen head-on, the coursed rows rise in steady steps, and the near-vertical slope makes the horizontal joints read as a set of ruled lines. With the Arakawa Fifth Dam only about 300 meters away, you can compare a 1937 dam and a 1954 dam within a few minutes of each other.

The river rises quickly after rain, so keep away from the banks in wet weather. Directions to the dams and the opening hours of the Arakawa Archive Room are on the Arakawa River Sabo Dams page.