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Marunuma Dam, located in Katashina Village, Gunma Prefecture, is a remarkable example of a buttress-style dam. Built in the early Showa era, its rarity and historical significance led to its designation as Japan's first power-generating dam to be named an Important Cultural Property (Structure). The buttress design is quite rare, and Marunuma Dam stands as the largest existing dam of this specific type. The structure, supported by vertical beams, offers a striking visual of modern civil engineering history.
Completed in 1931, the dam showcases the advanced design and construction techniques of the Jomo Electric Power Company of that era. It has been selected as a "Selected Civil Engineering Heritage" by the Japan Society of Civil Engineers. Even after more than 70 years, the dam continues to function while maintaining its original appearance. Its designation as an Important Cultural Property reflects not just its utility, but the preservation of the design philosophy and engineering prowess that supported Japan's modernization.
The dam's body features a unique grid-like pattern of massive concrete beams and pillars, which can be viewed from a breathtaking perspective. The surrounding Marunuma Lake offers a scenic landscape where man-made engineering meets natural beauty. A popular activity for visitors is collecting the