| Dam safety
irrigation to support agricultural production. Hydropower dams expanded rapidly in the 1950s and 1960s to meet rising electricity demand during postwar industrialisation. From the 1960s onwards, multipurpose dams became more common, combining flood control, water supply, and hydropower generation. The report documents how the number of concrete dams increased significantly during this period, reflecting a policy preference for structures perceived as more robust against overtopping and variable river flows. Many of these developments were led by national government agencies, with later participation by prefectural governments and private hydropower operators. Flood control has been a central driver of dam development in Japan. The report presents historical data showing a substantial reduction in flood- related casualties and economic losses from the 1960s onwards, coinciding with the expansion of multipurpose dams and river improvement works. Dams have also become increasingly important for domestic and industrial water supply. According to the report, the share of domestic water supplied by dams increased from 11% in 1965 to 48% in 2020. This reflects both rising demand and the need to buffer seasonal variability in river flows. In major metropolitan regions such as the Tokyo area, extensive systems of dams and bulk water conveyance infrastructure have been developed to ensure reliable supply Hydropower is a significant component of Japan’s
energy system. As of 2024, total installed hydropower capacity, including pumped storage, was 49.66GW. Japan has 650 hydropower dams, including both single-purpose and multipurpose facilities. The country also has the second-largest pumped storage capacity in the world, with 42 pumped storage plants capable of absorbing and discharging approximately 27GW of power. The report notes that Japan has been a technology leader in variable-speed pumped storage systems since the 1990s, enabling flexible integration of variable electricity demand and supply. Hydropower dams are owned and operated by private electric power companies, including regional utilities and wholesale generators. While ownership is private, dam safety obligations are governed by national laws and regulations.
Legal and institutional frameworks The legal foundation for dam safety in Japan is anchored
in the River Act, which establishes responsibilities for river administration, dam operation, and flood control. The report details how different dam purposes are governed by specific laws and administrative arrangements, while remaining integrated within a national framework. Multiple ministries are involved in water resources and dam management. The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) plays a central coordinating role, particularly for river management, flood control, and multipurpose dams. The Ministry of Agriculture, Forestry and Fisheries oversees irrigation dams and ponds, while the Ministry of Economy, Trade and Industry is responsible for hydropower. Environmental aspects fall under the Ministry of the Environment. Institutional arrangements vary depending on dam purpose and river classification, but the report highlights the importance of clear allocation of responsibilities among dam owners, regulators, and operators. Legal accountability for dam safety rests with dam owners, regardless of ownership structure.
Design standards, O&M Japan applies detailed technical standards for dam
design, construction, and operation. These standards include rigorous seismic design requirements, reflecting the country’s high earthquake risk. The report describes how seismic performance has been evaluated and upgraded following major events, including the Great East Japan Earthquake of 2011 and the Noto Peninsula Earthquake of 2024. Operation and maintenance requirements are formalised through dam operation rules and manuals, which define normal, flood, and emergency operating conditions. These rules are legally binding and subject to regulatory oversight. The report also describes systematic dam inspection and monitoring practices, supported by dense hydrometeorological and seismic monitoring networks and advanced data management systems. A significant portion of the report focuses on the safety of existing dams, particularly older structures built before modern standards were introduced. While failures of large dams in Japan have been rare, the report documents a small number of historical incidents, most of which occurred prior to the establishment of the current regulatory framework. Irrigation ponds present a distinct challenge due to their age, number, and dispersed ownership. The report notes that many ponds were constructed using older techniques and are located upstream of communities that have since urbanised. Following the failure of the Fujinuma-Ike irrigation pond during the 2011 earthquake, national and prefectural governments strengthened inspection, rehabilitation, and prioritisation programmes for irrigation ponds deemed to pose higher risks. Emergency preparedness is a core element of Japan’s dam safety system. The report outlines procedures for emergency dam operation during extraordinary floods, including pre-flood reservoir drawdown where appropriate. These operations are coordinated with downstream river management and disaster response agencies. Public safety measures include flood warning systems, notification protocols for dam discharge, and the use of flood hazard maps.
Funding mechanisms
Funding for dam safety assurance varies by dam purpose and ownership. Multipurpose dams are typically funded through national and prefectural budgets, while hydropower dams are financed by private operators. The report also describes the use of contingency budgets for emergency repairs and rehabilitation, as well as financing mechanisms employed by the Japan Water Agency for large-scale water infrastructure.
Report conclusions The World Bank report concludes that Japan’s dam
safety management system has evolved through long-term investment in legal frameworks, technical standards, institutional capacity, and operational practice. The system reflects the country’s exposure to floods, earthquakes, and climate variability, as well as the high consequences of dam failure in densely populated downstream areas. Rather than presenting a single transferable model, the report documents how dam safety assurance in Japan is embedded within broader water resources management and disaster risk reduction policies. It provides detailed descriptions intended to inform further study and reflection by practitioners and policymakers in other national contexts.
References
Tiwari, A. & Aadhar, S. (2025). A national-scale dataset for dam catchment characterisation in India. Scientific Data, Nature Portfolio.
World Bank (2025). Dam Safety Management in Japan: Legal, Institutional, and Operational Frameworks. Washington, DC: World Bank.
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Above: Kurobe Dam in Nagano Prefecture, Toyama Prefecture, Japan
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