Higashi Karasu River Third Dam

One Registered Property, Two Campaigns of Construction

Higashi Karasu River Third Dam (東鴉川第三堰堤, Higashi-Karasugawa Daisan Entei) is a gravity concrete erosion-control dam on the Higashi-Karasu River at Tatekoshi in Tsuchiyu Onsen-machi, Fukushima City, Fukushima Prefecture, dating from 1951 with an enlargement of 1954, and it was entered on the national register of Tangible Cultural Properties (Structures) on 8 July 2008.

The register counts it as a single unit. Stand below it and you are looking at the work of two different builders. Fukushima Prefecture put up a gravity concrete dam on this spot in 1951, roughly 4.4 metres from base to crest. Three years later the national government added a far heavier structure, 66 metres across the crest and 15 metres tall, and the register files that second campaign as an enlargement of the first.

The difference in scale is the whole story. A 4.4-metre dam holds back gravel. A 15-metre dam holds back a hillside.

The Higashi-Karasu River is a short right-bank tributary of the Arakawa, which drains the eastern flank of the Azuma range below Higashi-Azumayama (1,975 m) and Issaikyozan (1,949 m). The Arakawa itself runs only 26.6 kilometres before meeting the Abukuma River in the southern part of Fukushima City, gathering a catchment of 178.1 square kilometres on the way. Short, steep, and fed by volcanic slopes where hot ground and landslip keep vegetation thin, it has always deserved its name: arakawa, the rough river.

The Third Dam sits 475 metres above the First Dam, which stands near the confluence with the Arakawa in the hot spring district itself.

Why This Dam Went on the Register

Registration number 07-0106 was granted at the 60th session of the register and gazetted on 23 July 2008. The criterion applied was the one covering structures that contribute to the historic landscape of the country, and the dam is classified under erosion and flood control works and civil engineering structures.

Sabo work in this valley is older than the dam by half a century. Fukushima Prefecture began slope stabilisation in the Arakawa basin in 1900, three years after Japan passed its first Erosion Control Act. The techniques of the day were no match for the river. Typhoon rains washed out the works, crews rebuilt them, and the cycle repeated for decades.

The turning point came in 1936, when the upper Arakawa was brought under direct national administration. The Home Ministry opened a sabo works depot in what was then the village of Tsuchiyu and began the Arakawa First Dam, finished in 1937. Two years later a debris flow came down the Higashi-Karasu River, and this tributary became a target in its own right rather than a footnote to the main stem.

A note on dates for anyone comparing sources. The Fukushima Office of River and National Highway lists the Third Dam as completed in 1952, while the national register records 1951 with an enlargement in 1954. The gap most likely reflects what each record treats as the finishing point, but the two sets of figures do not line up exactly.

In 2007 the Japan Society of Civil Engineers recognised the Arakawa flood-control and sabo programme as a Civil Engineering Heritage. The following year fifteen structures in the basin went onto the national register, this dam among them. Of the sabo dams on the Higashi-Karasu, three carry that status: the First, the Third and the Fourth.

Reading the Face of the Dam

The Arakawa sabo dams are cyclopean concrete with stone facing, and the pattern of that facing rewards a close look. On the Third Dam it is nuno-zumi, cloth coursing: blocks laid in continuous horizontal rows so that the joints run level and unbroken from one bank to the other, like the weft of woven cloth. Walk 3.2 kilometres upstream to the Fourth Dam and the pattern changes to tani-zumi, stones set on the diagonal. Five years separate the two structures, and the masons chose differently.

The profile repays attention too. The upstream face leans back at a batter of 4.5 bu, about 0.45 metres of horizontal run for every metre of height. The downstream face is far steeper at 2 bu, roughly 0.2 metres per metre. That steep downstream slope is deliberate: water clearing the crest falls away from the concrete rather than running down it, which keeps the abrasive load of sand and gravel off the face.

At 15 metres this is the tallest of the three registered Higashi-Karasu dams. The First reaches 7.5 metres, the Fourth 12. When the pool behind the crest is full of accumulated sediment, as it usually is, the dam reads as a stone step in the riverbed rather than a wall, which is precisely how a sabo dam is meant to work. It fills up, the gradient above it flattens, and the flattened reach stops feeding the flood.

Seeing It for Yourself

The practical facts are simple. There is no gate, no ticket office and no opening hours. This is working national infrastructure sitting in a river valley, viewed from outside, and photography is not restricted. The nearest base is Tsuchiyu Onsen, about 40 to 45 minutes by Fukushima Kotsu bus from the east exit of Fukushima Station, or a quarter of an hour by car from the Fukushima-nishi interchange along Route 115.

Two cautions for anyone walking up the valley. Bear sightings have been reported along the Arakawa since around 2016, and Fukushima Prefecture advises carrying something that makes noise and travelling in company. Snow also shuts the upper valley for much of the winter; mountain footpaths in this area generally open from early April to mid-November.

Visitors who would rather understand the system before looking at one piece of it can call at the Arakawa Reference Room in Fukushima City, which holds a relief model of the whole basin along with panels on the sabo dams and the older kasumi-tei discontinuous levees. It opens 10:00 to 16:00, closes over the New Year period, and has parking for about 30 cars, roughly ten minutes on foot from the Jichi Kenshu Center stop on the same Tsuchiyu bus line.