Hidden deep in the mountains of Nakatsugawa, Japan, the Yandani Erosion Control Dam Complex is a remarkable example of early modern erosion-control engineering. Located in the active Atera Fault Zone, an area historically affected by landslides and severe sediment flows, the complex represents an important chapter in the development of Japanese water and land management.

• More than 300 metres long, the complex consists of 13 stone in-stream structures, complemented by belt structures and channel works.
• The works were constructed under the supervision of Dutch water engineer Johannis de Rijke, who introduced Dutch approaches to erosion and sediment control in Japan.
• De Rijke recognised that severe flooding in the Kiso River delta was closely connected to sediment generated in the mountainous upper reaches. His approach therefore addressed the river system as a whole, rather than treating flooding as an isolated downstream problem.
• In the 1870s and 1880s, De Rijke and his colleagues promoted forest protection, soil-erosion prevention and sediment control. These methods became known as the “Dutch method” and were incorporated into Japanese civil-engineering guidance.
• During his 1880 inspection of the Kiso River basin, De Rijke personally surveyed vulnerable mountain areas and prescribed erosion-control measures for several locations, including the Shiradani area near Yandani.
• The project also illustrates the importance of local knowledge and community involvement. Historical evidence suggests that local residents contributed to erosion-control works and forest restoration, working alongside officials and following the methods promoted by De Rijke.
• The Yandani complex helped protect the downstream area and created conditions for further development, including the construction of the Meiji-za theatre, an important part of Kashimo's history.

Why Yandani matters today

The Yandani Erosion Control Dam Complex is more than a historic engineering structure. It demonstrates De Rijke's integrated approach to water management: understanding the relationship between mountains, sediment, rivers, flooding, forests and human settlements.

It is a powerful example of how knowledge can cross borders, how engineering can be adapted to local conditions, and how long-term solutions can emerge from cooperation between experts, government and local communities.

Yandani therefore offers a valuable source of inspiration for today's and tomorrow's Water Masters.