Higashi Karasu River Fourth Dam

The Highest and the Last of the Higashi-Karasu Dams

Higashi Karasu River Fourth Dam (東鴉川第四堰堤, Higashi-Karasugawa Daiyon Entei) is a gravity concrete erosion-control dam at Inokurayama in Tsuchiyu Onsen-machi, Fukushima City, Fukushima Prefecture, completed in 1957 and entered on the national register of Tangible Cultural Properties (Structures) on 8 July 2008.

It stands 3.2 kilometres above the Third Dam, further up the valley than any other registered structure on this river. The crest runs 67 metres from bank to bank and the dam rises 12 metres. A stone revetment armours the right bank immediately upstream, holding the slope where the current would otherwise bite into it.

The distance matters. Three point two kilometres of mountain stream separates this dam from the next one down, which means that everything the slopes above shed in a storm arrives here first, with nothing between it and the volcanic ground of the Azuma range. The Higashi-Karasu River is a right-bank tributary of the Arakawa, and the Arakawa drains the eastern flank of Higashi-Azumayama (1,975 m) and Issaikyozan (1,949 m) before running 26.6 kilometres to the Abukuma River.

A Detail That Most Visitors Walk Past

A sabo dam of this generation has three parts you can see from below: a central overflow notch where the water crosses, and two flanking wing sections, called sode in Japanese, that carry the structure into the valley walls on either side.

On most dams of the period the downstream face of those wings is built in two stages. The lower portion slopes back, and above a certain height it stands vertical. That is quicker to form and uses less concrete, and it leaves a visible break in the elevation where the two treatments meet.

The Fourth Dam was not built that way. Its wings carry the same 2 bu batter, about 0.2 metres of horizontal run for every metre of rise, continuously from base to top, with no vertical upper section at all. The whole downstream elevation therefore reads as a single unbroken plane sweeping from one abutment to the other. The Agency for Cultural Affairs singles out this treatment in its record of the structure, which suggests the choice was noticed by the people who assessed it as well.

Stand at the foot of the dam and the effect is subtle rather than dramatic. Nothing steps back. Nothing interrupts. The eye runs along the face without stopping.

Tani-zumi: Stones Set on the Diagonal

These dams are cyclopean concrete faced with stone, and the Fourth Dam is faced in tani-zumi, valley coursing. Each block is set with a corner pointing down, so the joints form a diagonal lattice of diamonds instead of level horizontal lines. Anyone who has looked at a Japanese castle base or an old river revetment has seen the pattern.

The contrast with the Third Dam downstream is worth walking for. That structure is faced in nuno-zumi, cloth coursing, with joints running level and unbroken across the face. Same river, same national programme, five years apart, and the masons went opposite ways. Both patterns are said to have their place in Japanese stonework, tani-zumi where a face has to accommodate settlement and nuno-zumi where a level, formal surface is wanted, though the record does not explain why this particular dam got this particular treatment.

The upstream face leans back much further than the downstream one, at a batter of 4.5 bu, or roughly 0.45 metres per metre of height. The sloping upstream face is what lets accumulated sediment press down into the dam rather than simply push against it.

Where It Falls in the Sequence

The upper Arakawa came under direct national erosion-control administration in 1936, and the Home Ministry set up a works depot in the village of Tsuchiyu that same year. The Arakawa First Dam followed in 1937. In 1938 a debris flow ran down the Higashi-Karasu River, and this tributary moved up the list of priorities.

Dams then went in through the postwar decades, and the Fourth Dam of 1957 closed that phase. From 1960 the emphasis on this river shifted to bed-consolidation structures, beginning with the First Bed Consolidation Dam, followed by others through the 1960s, and by stepped channel works in the late 1970s. The tall freestanding stone-faced dam belongs to the earlier chapter, and this is its last example on the Higashi-Karasu.

By the end of 2004 the Higashi-Karasu alone carried thirteen structures counting bed-consolidation dams, alongside thirteen on the Arakawa main stem and five on the Shio-no-kawa, thirty in all. Only a few of them were built to be looked at as well as to work.

Registration number 07-0107 was granted at the 60th session of the register and gazetted on 23 July 2008, under the criterion covering structures that contribute to the historic landscape of the country. The year before, the Japan Society of Civil Engineers had recognised the Arakawa flood-control and sabo programme as a Civil Engineering Heritage; fifteen structures in the basin were then registered together, three of them on the Higashi-Karasu.

Getting There, and Whether You Should

An honest answer first: this is the hardest of the three registered Higashi-Karasu dams to reach. There is no gate, no ticket, no opening hours and no visitor facility, but there is also no published visitor route to the dam itself. Getting to it means walking a long way up a mountain valley, and casual visitors are better served by the First Dam, which stands near the confluence with the Arakawa inside the Tsuchiyu Onsen district and can be seen from the town.

Tsuchiyu Onsen is the base either way: about 40 to 45 minutes by Fukushima Kotsu bus from the east exit of Fukushima Station, or around 15 minutes by car from the Fukushima-nishi interchange along Route 115. The town has three free common car parks for day visitors.

Two warnings apply to anyone heading upstream. Bear sightings have been reported along the Arakawa since about 2016, and Fukushima Prefecture advises carrying a noise-maker and travelling with others. Snow closes the upper valley for a good part of the year; footpaths in this area are generally walkable from early April to mid-November.

Photography is unrestricted. For visitors who want the wider picture without the walk, the Arakawa Reference Room in Fukushima City displays a relief model of the basin and panels on the sabo dams and the older discontinuous levees, open 10:00 to 16:00, closed over the New Year, with parking for about 30 cars.