Kuyamada Reservoir Dam

Kuyamada Reservoir Dam: A Living Monument of Taisho-Era Engineering in Onomichi

Tucked away in the forested hills southwest of Onomichi's historic port district, Kuyamada Reservoir Dam stands as a quietly magnificent testament to early twentieth-century Japanese civil engineering. Completed in 1924 during the Taisho period, this elegant stone-clad dam has been supplying drinking water to the people of Onomichi for over a century — and it continues to do so to this day. Designated as a Registered Tangible Cultural Property in 2004 and recognized as a significant modern civil engineering heritage site by the Japan Society of Civil Engineers, Kuyamada Reservoir Dam offers visitors a rare opportunity to witness a living piece of industrial history set amidst the tranquil beauty of the Hiroshima countryside.

A City's Thirst: The Story Behind the Dam

To understand the significance of Kuyamada Reservoir Dam, one must first appreciate the water challenges that Onomichi faced in the early twentieth century. Onomichi, a thriving port city built largely on reclaimed land along the Seto Inland Sea, lacked a major river. Groundwater was often brackish due to the city's coastal geography, and as the population grew during the Meiji and Taisho periods, the chronic water shortage became increasingly severe. Historical accounts tell of water vendors roaming the streets selling drinking water — a luxury that many residents could barely afford.

Initial plans to source water from wells proved unsuccessful when no suitable wells could be found. In 1920, the city appointed Dr. Tojiro Sano, a renowned engineering scholar who had designed the Kobe municipal waterworks, as an advisor, along with Hironoshin Mizuno, a former chief engineer of the Kobe waterworks department, as lead engineer. Together, they identified the Kuyamada valley along the Kadota River as the ideal site for a reservoir. The Onomichi City Council formally approved the waterworks construction plan in September 1921, and national authorization was granted in March 1922.

The Generosity of Gendo Yamaguchi

Perhaps the most remarkable aspect of the dam's creation story is the extraordinary philanthropy that made it possible. The total construction cost for the entire waterworks system, including the dam and the Nagae Water Purification Plant, amounted to approximately 1.39 million yen — an enormous sum at a time when a university graduate's starting salary was around 60 yen per month. The city's finances could scarcely bear such an expenditure.

Enter Gendo Yamaguchi, an Onomichi native who had left for Osaka at the age of sixteen and built a successful trading business through tireless effort. Upon learning of his hometown's desperate need for clean water, Yamaguchi donated approximately 1,035,000 yen — roughly three-quarters of the total project cost, equivalent to hundreds of millions of dollars in today's currency. When the city offered to erect a bronze bust in his honor after the dam's completion in 1925, Yamaguchi reportedly dismissed the idea, saying he had not made the donation for such recognition. His only request was that Onomichi's water rates be kept as low as possible. In 1967, the city honored him as an Honorary Citizen of Onomichi, and a memorial stone stands on the grounds of Saikokuji Temple where he is buried.

Engineering Marvel: The Structure of the Dam

What makes the Kuyamada Reservoir Dam architecturally distinctive is its hybrid structural design. The dam combines elements of both gravity-type and arch-type construction — a relatively uncommon approach that reflects the sophisticated engineering thinking of its designers. The dam wall follows an elegant curved arc rather than a straight line, sharing the same center of curvature as its subsidiary dam downstream. This curved form allows the structure to distribute water pressure more efficiently, while the massive weight of the dam body provides the gravitational stability needed to resist that pressure.

The construction material is equally noteworthy. Rather than poured concrete, the dam body is built using a technique known as "rough stone mortar masonry with stone cladding." Rough stones were packed together with mortar filling the gaps between them, and the exterior surfaces were then faced with carefully dressed granite ashlar blocks laid in a regular coursing pattern. The result is a dam that possesses both the structural strength of concrete and the handsome, almost castle-like appearance of fine stonework — a quality that has led some observers to compare it to a medieval fortress.

The dam stands 22 meters high with a crest length of 75 meters. A central overflow spillway allows excess water to cascade over the top during heavy rains, while a distinctive semicircular water intake tower projects from the right bank side of the dam wall. The subsidiary dam downstream echoes the main dam's curved form, creating a harmonious visual composition when viewed from below.

Why It Was Designated a Cultural Property

Kuyamada Reservoir Dam was registered as a national Tangible Cultural Property (architectural structure) on November 8, 2004. Several factors contributed to this recognition. The dam's hybrid gravity-arch structural form is an uncommon and technically significant approach in Japanese dam engineering of the Taisho period. The rough stone mortar masonry construction technique, combined with the finely dressed stone cladding, represents a craftsmanship tradition that has largely disappeared from modern construction practice. Additionally, the dam is a key component of the Onomichi municipal waterworks, one of the few public water systems in Japan whose creation was primarily funded by a single private donor — making it a unique piece of social and civic history as well as engineering heritage.

The Japan Society of Civil Engineers has also recognized the dam by including it in its selection of important modern civil engineering heritage sites (ranked C-class), further affirming its value as a physical record of Japan's modernization-era infrastructure development.

Highlights and What to See

Visitors approaching the dam will first notice its graceful curved profile emerging from the surrounding forest. The stone-clad surface of the dam wall, weathered to a soft gray-brown patina over its century of existence, presents a striking contrast against the verdant hillsides. Walking along the crest of the dam offers views of the reservoir lake on one side and the downstream valley on the other. The semicircular water intake tower is a particularly photogenic feature, projecting outward from the dam face like a turret on a castle wall.

The reservoir itself, known as Kuyamada Reservoir, is a peaceful body of water surrounded by forested hills. A walking path encircles the lake, providing a pleasant route for strolling or light exercise. The campus of Onomichi City University is visible on the far shore, adding a contemporary element to the otherwise timeless landscape. During spring, cherry blossoms frame the reservoir, while autumn brings vivid foliage to the surrounding slopes. Each year before the rainy season, a water deity festival (Suijin-sai) is held at the Ame-no-Mikumari Shrine near the reservoir to pray for sufficient rainfall and express gratitude for the water blessings — a tradition that has continued since the dam's completion in 1925.

Surrounding Area and Nearby Attractions

Kuyamada Reservoir Dam is situated in the southwestern hills of Onomichi, about 15 minutes by car from JR Onomichi Station. The nearby Bingo Sports Park offers athletic facilities including a track and baseball field, making the area popular with local residents for recreation. From the dam, visitors can easily continue into central Onomichi to explore the city's many other attractions.

Onomichi itself is a treasure trove for cultural tourism. The famous Temple Walk connects 25 historic temples along the hillside slopes, winding through atmospheric narrow lanes and residential neighborhoods. Senkoji Temple and its mountaintop park offer panoramic views of the Onomichi Strait and the islands of the Seto Inland Sea — accessible by a scenic ropeway ride. The city's retro Hondori Shopping Street stretches 1.6 kilometers along the waterfront, lined with cafés, ramen shops, and artisan boutiques.

For cycling enthusiasts, Onomichi serves as the starting point of the world-famous Shimanami Kaido, a 60-kilometer cycling route that crosses six islands via spectacular bridges to reach Imabari in Ehime Prefecture. The route is widely considered one of the finest cycling experiences in the world, offering breathtaking views of the Seto Inland Sea at every turn.

Additionally, the Onomichi Waterworks Memorial Museum, opened in May 2025 at the Nagae Water Purification Plant to commemorate the centennial of the city's waterworks, features exhibits on the history of Onomichi's water supply, including an animated presentation about the life of benefactor Gendo Yamaguchi. Visiting this museum before or after seeing the dam provides excellent context for understanding the full story of Onomichi's water heritage.