Watarase Keikoku Railway Konakagawa Bridge

Konakagawa Bridge on the Watarase Keikoku Railway: A Taisho-Era Steel Bridge over a Mountain Stream

Deep in the mountains of Gunma Prefecture, where the Watarase Keikoku Railway traces a winding path along the Watarase River gorge, a steel bridge built over a century ago still carries trains across the Konaka River. The Watarase Keikoku Railway Konakagawa Bridge (わたらせ渓谷鐵道小中川橋梁) is a registered tangible cultural property of Japan, recognized for its historical and engineering significance as a surviving example of Taisho-era railway infrastructure. Visitors riding the scenic train between Kiryu and Mato stations pass over this elegant bridge, often without realizing they are crossing a piece of living industrial heritage.

A Bridge Born from the Ashio Copper Mine

The Konakagawa Bridge was constructed in 1912 (Taisho 1), when the original Ashio Railway was being extended to serve the Ashio Copper Mine—once one of Japan's most productive copper mines. The Ashio Copper Mine, operated by the Furukawa zaibatsu, required a reliable means of transporting copper ore from the remote mountain town of Ashio to the city of Kiryu and beyond. Until the railway was built, ore had to be carried by horse and cart along treacherous mountain roads. The construction of the Ashio Railway, which began in 1911 and reached Ashio Station by the end of 1912, transformed the logistics of copper transport and opened the Watarase River valley to the wider world.

The Konakagawa Bridge was built as part of this ambitious railway project, spanning the Konaka River—a tributary of the Watarase River—in what is now the Higashimachi area of Midori City. It stands approximately 1,400 meters west of the Kando First Tunnel, in a stretch of the line where the railway threads through narrow mountain valleys alongside clear mountain streams.

Engineering and Construction

The Konakagawa Bridge is a steel two-span girder bridge with a total length of 40 meters, designed for single-track railway use. Each span consists of a 60-foot (approximately 18-meter) plate girder, a structural form that was widely used for railway bridges during the Meiji and Taisho periods. What makes this bridge particularly noteworthy is that its girders were fabricated using steel produced by Dorman Long & Co., a renowned British steelmaker based in Middlesbrough, England. Dorman Long was one of the world's leading steel manufacturers during this era, later famous for constructing the Sydney Harbour Bridge and the Tyne Bridge. The use of imported British steel reflects the international nature of Japan's rapid modernization during the early twentieth century, when the country eagerly adopted Western engineering technologies.

The bridge's abutments and central pier are constructed of precisely cut granite blocks laid in a French bond pattern—a masonry technique that alternates headers and stretchers for both structural strength and visual elegance. The pier features a distinctive spindle-shaped plan, designed to minimize resistance to river flow while providing a stable foundation for the steel superstructure. These stone elements remain in excellent condition, testifying to the skill of the masons who built them more than a century ago.

Why It Was Designated as a Registered Tangible Cultural Property

The Konakagawa Bridge was registered as a tangible cultural property on November 2, 2009, as part of a group of 37 railway structures along the Watarase Keikoku Railway that received designation on the same date. Together with the Kamikami Station building, which had been registered in 2008, these 38 structures make the Watarase Keikoku Railway one of the most extensively designated heritage railways in Japan. It was the first time in the nation's history that railway facilities spanning two prefectures—Gunma and Tochigi—were collectively registered as cultural properties.

The bridge's designation recognizes several important values. First, it is a well-preserved example of early Taisho-era railway bridge engineering, retaining its original steel girders with Dorman Long steel and its granite masonry substructure. Second, it embodies the technological exchange between Japan and Britain during the modernization period. Third, it continues to function as an active railway bridge, carrying passengers daily—a remarkable testament to the durability and quality of its original construction. The entire Watarase Keikoku Railway facility group was also recognized as a JSCE (Japan Society of Civil Engineers) Civil Engineering Heritage in 2016, further underscoring its importance in Japan's civil engineering history.

Highlights and Attractions

Riding the Watarase Keikoku Railway itself is one of the most memorable ways to experience the Konakagawa Bridge. The railway operates both regular diesel trains and seasonal open-air trolley trains (torokko ressha), which allow passengers to feel the breeze and hear the sounds of the gorge as they cross the bridge. From the train window, you can look down at the clear waters of the Konaka River flowing beneath the century-old steel girders, framed by the lush green mountains that characterize this region.

For those who wish to see the bridge from below, the area around the Konaka River offers walking paths where visitors can appreciate the granite piers and the overall proportions of the structure set against the mountain landscape. The spindle-shaped pier and the French bond stonework are best seen from the riverbank, where the craftsmanship of the original builders is clearly visible.

The surrounding area changes dramatically with the seasons: cherry blossoms and fresh green leaves in spring, deep green forests in summer, brilliant red and gold foliage in autumn, and a quiet snow-dusted landscape in winter. Each season provides a different backdrop for this historic bridge, making any time of year a worthwhile visit.

The Watarase Keikoku Railway: A Journey through History

The Watarase Keikoku Railway runs 44.1 kilometers from Kiryu Station in Gunma Prefecture to Mato Station in Nikko City, Tochigi Prefecture. Originally built as the Ashio Railway in 1911–1914 to transport copper ore, the line was nationalized in 1918 and became the JNR Ashio Line. After the Ashio Copper Mine closed in 1973 and the line was designated for closure as an unprofitable route, it was transferred to the third-sector Watarase Keikoku Railway in 1989.

Today, the railway has reinvented itself as a beloved scenic and heritage line. The trolley train services, which run primarily from April through November, are particularly popular with tourists. The line passes through a total of 38 registered tangible cultural properties, including stations, tunnels, and bridges, making each journey a rolling museum of Taisho-era railway engineering.

Nearby Attractions

The Konakagawa Bridge is located between Hanawa Station and Konaka Station on the Watarase Keikoku Railway. The surrounding area in Midori City offers several worthwhile destinations for visitors.

• Kusaki Lake and Kusaki Dam: A scenic reservoir created by the Kusaki Dam on the Watarase River. The 12.4-kilometer lakeside path is popular for walking, and seasonal activities include canoeing and stand-up paddleboarding. Cherry blossoms and autumn foliage make the lake particularly beautiful in spring and fall.
• Tomihiro Art Museum: Located on the shores of Kusaki Lake, this museum exhibits the watercolor paintings and poems of Hoshino Tomihiro, a local artist who lost the use of his limbs in an accident and learned to paint by holding a brush in his mouth. The museum building, designed by Yokomizo Makoto, won the Architectural Institute of Japan Prize in 2006. Note: the museum is undergoing renovation from December 2025.
• Konaka Great Waterfall (小中大滝): A dramatic 96-meter waterfall accessible via a mountain road from the Konaka area. The approach includes crossing the steep Kesakake Bridge, which has a maximum gradient of 44 percent.
• Former Hanawa Elementary School Memorial Museum (旧花輪小学校記念館): A repurposed former elementary school that now serves as a local history museum with exhibits about the region and the Watarase Keikoku Railway.
• Godo Station (神戸駅): A few stops up the line, this station features a unique restaurant housed in retired Tobu Railway romance cars, as well as beautiful peach blossom displays in spring.