Nunobiki Water Source Waterworks Facility

A Working Dam from 1900

Walk about thirty minutes up the valley behind Shin-Kobe Station and you reach a gray masonry wall curving across a wooded gorge. This is the Gohonmatsu Dam, finished in 1900 and still sending water to households in central Kobe more than a century and a quarter later. It was the first gravity concrete dam built for a water supply in Japan, and it remains the centerpiece of the Nunobiki Water Source Facilities, a group of nine structures designated an Important Cultural Property in 2006.

The dam stands 33.3 meters high and 110.3 meters long. Its face is clad in cut granite laid in a running-bond pattern, stone that first served as the formwork for the concrete behind it. Along the crest runs a row of small projecting blocks, a dentil course borrowed from European classical architecture. Seen from below, the wall has the bearing of an old fortress.

Why Kobe Needed a Dam

Kobe opened to foreign trade in 1868, and its population climbed fast. Residents still drew drinking water from wells, which ran short in summer and carried disease. A cholera outbreak in 1890 killed many and made the case for a filtered, modern supply impossible to set aside. Yokohama had begun Japan's first such system a few years earlier, and Kobe followed.

The basic plan came from William Kinninmond Burton, a Scottish sanitary engineer employed by the Home Ministry who advised on waterworks across Meiji Japan. Japanese engineers then reworked and enlarged the design to meet the city's growing demand. Yoshimura Chosaku served as consulting engineer, Sano Tojiro as chief engineer, and Asami Chuji as supervising engineer. Their three names are cut in English into a stone tablet on the dam's parapet.

When water began flowing in 1900, Kobe became the seventh city in Japan to gain a modern water supply. Ships calling at the port took on Nunobiki water for long voyages because it kept fresh, and sailors are said to have prized a "Kobe Water" that stayed drinkable even after crossing the equator.

What Makes It Important

Building a concrete dam of this size in mountainous terrain had no domestic precedent. Materials were hauled in largely by hand, and the engineers worked out construction methods with few models to follow. The Gohonmatsu Dam is now regarded as the starting point for gravity concrete dam construction in Japan, which is the heart of its value in the history of civil engineering.

One problem the designers had to solve was uplift, the upward pressure of water seeping beneath and through a dam, a known cause of failures abroad. To relieve it they ran 157 wrought-iron pipes, each about an inch and a half across, through the body of the dam to drain the seepage. The structure had already been listed as a Registered Tangible Cultural Property in 1998 before its promotion to Important Cultural Property in 2006.

The Wider Site

The designation covers far more than the dam itself. Six dams and tunnels and three bridges make up the listed group, set along the Ikuta River from the diversion works upstream down to the Sunago Bridge. At the foot of Medaki, the lowest of the Nunobiki Falls, a stone arch weir still takes in water that travels by pipe and across the Sunago Bridge to the Okunohira purification plant, which today supplies the western part of Chuo Ward and Hyogo Ward. The small reinforced-concrete Tanigawa Bridge, added around 1913, is the youngest member of the group.

Visiting

The approach is a walk rather than a drive. From Shin-Kobe Station a well-kept trail climbs past the Nunobiki Falls, praised in poetry since the Heian period and named in the Tales of Ise, before reaching the dam in roughly half an hour. A loop path lets you see the reservoir side and part of the downstream face, though the crest itself is closed to visitors. Benches and a bird-watching shelter sit along the way, and mandarin ducks are among the species seen on the water.

Higher up, the Nunobiki Herb Gardens and the ropeway that serves them open onto views over the city and harbor. In autumn the slopes around the reservoir turn color, and the dam is lit after dark.