Ishioka Daiichi Power Plant Facilities

What the Ishioka Daiichi Power Plant Facilities Are

The Ishioka Daiichi Power Plant Facilities (石岡第一発電所施設) are a run-of-river hydroelectric complex completed in 1911 and strung out between Yokokawa in Takahagi City and Ishioka in Kitaibaraki City, Ibaraki Prefecture, designated an Important Cultural Property on 2 December 2008. The designation covers 9 items: the main generator hall, the former transformer room, the substation room, the surge tank, the tank spillway, the No. 2 aqueduct bridge, the No. 1 aqueduct bridge, the settling basin and the intake weir, counted as 3 buildings, 3 units and 3 sites.

The complex runs east to west, roughly parallel to the Ōkita River. Water is drawn off upstream, carried along the hillside in a channel, and dropped through a head onto the turbines. There is no dam and no reservoir; the river's own flow does the work.

What sets this place apart is that it was never turned into a museum. Under its owner, Tokyo Hatsuden Co., Ltd., the plant is still generating electricity.

Built to Power a Copper Mine

The reason for building was specific. Expansion at the Hitachi Mine had pushed electricity demand beyond what could be bought in, and the mine decided to generate its own. The Ibaraki Prefectural Board of Education records that the project was led by Kodaira Namihei, head of the engineering section at the Kuhara Mining Company's Hitachi Mine, together with a section engineer named Miyanaga Heisaku. Work began in October 1909 and the plant was completed in October 1911, reaching its present configuration after further construction during the Taishō era.

A mining company designing and building an entire power station with its own staff sounds audacious now. In the Japan of 1909 there was simply no mature market to buy power from. The Ishioka Daiichi Power Plant Facilities are the answer a mine arrived at when it had to solve civil engineering, architecture and electrical work all at once, in house.

Japan's First Reinforced Concrete Power Station

The Ishioka Daiichi Power Plant Facilities were designated for their material and their method. The Agency for Cultural Affairs describes the complex as the first power station in Japan to use reinforced concrete technology across the facility as a whole, and singles out the main building as one of the oldest surviving reinforced concrete structures in the country.

The claim is worth unpacking. Buildings using reinforced concrete in part were not unknown by this date. What distinguishes the Ishioka Daiichi Power Plant Facilities is that structures of completely different kinds, a building, a bridge, a tank, a weir, were all built from the same material to a single technical programme, in 1911, on a mountain site. Of the 9 designated items, 8 were listed under the criterion of high historical value; the settling basin alone was listed for technical excellence.

A tenth element, the forebay tank, was part of the original designation. It was destroyed in the 2011 Tōhoku earthquake, and according to the owner's records its Important Cultural Property status was revoked in October of that year. The present count of 9 is the result.

Following the Water

The clearest way to grasp the 9 items is to take them in the order the water does.

Everything starts at the intake weir: a gravity concrete structure 30.0 metres long and 6.2 metres high, fitted with sluice and sand-flushing gates, with stone-faced revetment and the No. 1 open channel attached. This is the one element built during the Taishō era, between 1912 and 1925, and it marks where the later construction campaign left its trace.

The water then enters the settling basin, 53.5 metres of reinforced concrete with control gates at both ends. Its job is to drop suspended sand out of the flow before it reaches the turbines. Unglamorous, and decisive for the life of the machinery. It is the only one of the 9 items listed for technical excellence rather than historical value.

Beyond it the channel has to cross two ravines. The No. 1 aqueduct bridge spans 12.2 metres and the No. 2 spans 20.0 metres, both single-arch structures in reinforced concrete. Small as bridges go, they are early Japanese examples of the concrete arch, and they were carrying water in 1911.

Further along the hillside the flow reaches the surge tank, a reinforced concrete cylinder 8.2 metres across and 11.0 metres tall, which absorbs the pressure shock when load changes suddenly. Alongside it the tank spillway combines masonry with reinforced concrete over a length of 212.7 metres, carrying surplus water away safely along with sand-flushing channels and a stilling basin.

Then the main building. The generator hall dates from 1911: reinforced concrete, 264.99 square metres in footprint, roofed in sheet metal. Tokyo Hatsuden describes a run of tall windows with segmental arched heads, put there to bring daylight deep into the hall. For a small mountain station the presence of the building is considerable.

The former transformer room adjoins the generator hall on its east side, also from 1911, with a footprint of 139.25 square metres. East again is the substation room of 1916, 149.06 square metres over 2 storeys, with a high-tension cable entry. The 3 volumes stand in a row, and the gap in construction dates shows plainly in the handling of the wall surfaces.

Visiting the Ishioka Daiichi Power Plant Facilities

One thing needs saying first. The Ishioka Daiichi Power Plant Facilities form a working power station managed by Tokyo Hatsuden Co., Ltd. There is no public access to the interior and the grounds are closed to entry. A visit means viewing the exteriors from the public road and other land outside the site.

There is still something to see. The main building sits in the valley bottom and its roof and part of its walls can be picked out from the riverside road. The aqueduct bridges are up on the hillside, and from certain points you can look up at an arch. This is live high-voltage plant, so do not pass any fence or sign. Doing so is dangerous, and it puts at risk the informal exterior viewing that the owner currently tolerates.

Photography follows the same rule: from outside the site, no problem. Systematically documenting equipment details or anything security-related is not appropriate.

Takahagi Station on the JR Jōban Line is the nearest railway station. The plant, however, lies up the Ōkita River valley well away from the town, and no bus route serves it. Allow about 25 minutes by car from Takahagi Station. Parts of the road are narrow and the surface ices over in winter. No visitor parking exists, so choose somewhere that does not obstruct the road.