SAFETY OF DAMS AND DOWNSTREAM COMMUNITIES Dam Safety Management in Japan About the Global Department for Water The World Bank Group’s Global Department for Water brings together financing, knowledge, and implementation in one platform. By combining the Bank’s global knowledge with country investments, this model generates more firepower for transformational solutions to help countries grow sustainably. Please visit us at www.worldbank.org/water or follow us on : @WorldBankWater. About GWSP This publication received the support of the Global Water Security & Sanitation Partnership (GWSP). GWSP is a multidonor trust fund administered by the World Bank’s Global Department for Water and supported by Australia’s Department of Foreign Affairs and Trade; Austria’s Federal Ministry of Finance; Denmark’s Ministry of Foreign Affairs; the Netherlands’ Ministry of Foreign Affairs, the Gates Foundation; Spain’s Ministry of Economic Affairs and Digital Transformation; the Swedish International Development Cooperation Agency, Switzerland’s State Secretariat for Economic Affairs; the Swiss Agency for Development and Cooperation; and the United Kingdom Foreign, Commonwealth and Development Office. Please visit us at www.worldbank.org/gwsp or follow us on : @TheGwsp About World Bank Tokyo DRM Hub The World Bank Tokyo Disaster Risk Management (DRM) Hub supports developing countries to mainstream DRM in national development planning and investment programs. As part of the Global Facility for Disaster Reduction and Recovery, the DRM Hub provides technical assistance grants and connects Japanese and global DRM expertise and solutions with World Bank teams and government officials. The DRM Hub was established in 2014 through the Japan-World Bank Program for Mainstreaming DRM in Developing Countries—a partnership between Japan’s Ministry of Finance and the World Bank. Please visit us at https://www.worldbank.org/en/programs/tokyo-drm-hub. About GFDRR The Global Facility for Disaster Reduction and Recovery (GFDRR) is a global partnership that helps developing countries better understand and reduce their vulnerabilities to natural hazards and adapt to climate change. Working with over 400 local, national, regional, and international partners, GFDRR provides grant financing, technical assistance, training, and knowledge sharing activities to mainstream disaster and climate risk management in policies and strategies. Managed by the World Bank, GFDRR is supported by 36 countries and 10 international organizations. Please visit us at https://www.gfdrr.org/en. Dam Safety Management in Japan © 2025 International Bank for Reconstruction and Development/The World Bank 1818 H Street NW, Washington, DC 20433 Telephone: 202-473-1000; Internet: www.worldbank.org Disclaimer This work is a product of the staff of The World Bank with external contributions. The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent. The World Bank does not guarantee the accuracy, completeness, or currency of the data included in this work and does not assume responsibility for any errors, omissions, or discrepancies in the information, or liability with respect to the use of or failure to use the information, methods, processes, or conclusions set forth. The boundaries, colors, denominations, links/ footnotes and other information shown in this work do not imply any judgment on the part of The World Bank concerning the legal status of any territory or the endorsement or acceptance of such boundaries. The citation of works authored by others does not mean The World Bank endorses the views expressed by those authors or the content of their works. Nothing herein shall constitute or be construed or considered to be a limitation upon or waiver of the privileges and immunities of The World Bank, all of which are specifically reserved. The report reflects information available up to November 2024. Rights and Permissions The material in this work is subject to copyright. Because The World Bank encourages dissemination of its knowledge, this work may be reproduced, in whole or in part, for non-commercial purposes as long as full attribution to this work is given. Any queries on rights and licenses, including subsidiary rights, should be addressed to World Bank Publications, The World Bank Group, 1818 H Street NW, Washington, DC 20433, USA; e-mail: pubrights@worldbank.org. Citation Please cite the report as follows: World Bank. 2025. “Dam Safety Management in Japan.” World Bank, Washington, DC. Cover photo: Kawamata Dam. © Japan Ministry of Land, Infrastructure, Transport and Tourism. Reproduced with permission from MLIT. Further permission required for reuse. Cover design: Bill Pragluski, Critical Stages, LLC. Contents Acknowledgments..........................................................................................................................................vii Abbreviations...................................................................................................................................................ix Chapter 1 Introduction............................................................................................................................... 1 Objective................................................................................................................................................................................1 Overview................................................................................................................................................................................1 Notes......................................................................................................................................................................................2 Chapter 2 Historical and Present Water Resources Development and Management.......................3 Overview...............................................................................................................................................................................3 Characteristics of Japan..................................................................................................................................................3 Historical Development of Dams.................................................................................................................................5 Multipurpose Dams.....................................................................................................................................................6 Flood Control...............................................................................................................................................................10 Hydropower.................................................................................................................................................................. 11 Agriculture and Irrigation....................................................................................................................................... 15 Failures and Incidents of Dams and Ponds in Japan.................................................................................... 16 Evolving Water Resources Management Framework........................................................................................ 18 Increasing Climate Risks............................................................................................................................................... 19 Climate Change Impact Assessment on Floods...........................................................................................20 Basinwide Concerted Measures for Flood Risk Reduction and Resilience Enhancement............ 22 Notes................................................................................................................................................................................... 23 Chapter 3 Legal Foundations and Institutional Arrangements......................................................... 24 Overview............................................................................................................................................................................ 24 River Act as the Foundation for Dam Safety Assurance................................................................................. 25 Legal Foundation...................................................................................................................................................... 25 Institutional Arrangements .................................................................................................................................. 28 Multipurpose Dams........................................................................................................................................................ 33 Legal Foundation...................................................................................................................................................... 33 Institutional Arrangements...................................................................................................................................34 Irrigation ............................................................................................................................................................................ 35 Law on Management and Protection of Irrigation Dams ......................................................................... 35 Water Supply.................................................................................................................................................................... 36 Hydropower...................................................................................................................................................................... 37 Institutional Arrangements for Dam Safety Assurance and Capacity Building...................................... 38 Dam Safety Review Mechanism ......................................................................................................................... 38 Role of In-House Engineers, Consultants, and Contractors..................................................................... 38 Notes.................................................................................................................................................................................. 40 Chapter 4 Regulatory Regime for Design, Construction, and O&M................................................... 41 Overview............................................................................................................................................................................. 41 River Basin-Scale Planning........................................................................................................................................... 41 Key Design Standards...................................................................................................................................................43 iii iv Dam Safety Management in Japan Seismic Design Standards...........................................................................................................................................43 Requirements for Operation and Maintenance................................................................................................... 47 Dam Operation Rules and Manuals.................................................................................................................... 47 Environmental Flow Management ....................................................................................................................49 Sediment Management...........................................................................................................................................50 State-of-the-Art Hydrometeorological and Seismic Information Networks and IT-Based Analysis Systems.............................................................................................................................................................54 Integrated Dam Operation Systems .......................................................................................................................54 Systematic Dam Monitoring, Inspection, and Maintenance........................................................................... 55 Recordkeeping Requirements.............................................................................................................................. 55 Enforcement and Arbitration............................................................................................................................... 56 Notes................................................................................................................................................................................... 56 Chapter 5 Safety Assurance of Existing Dams and Ponds..................................................................58 Overview............................................................................................................................................................................ 58 Safety Assurance of Existing Dams and Ponds.................................................................................................. 58 Periodic Rehabilitation Based on Systematic Dam Inspection............................................................... 58 Hydropower Dam Safety Assessment..............................................................................................................60 Safety Assurance of Irrigation Ponds................................................................................................................60 Notes.................................................................................................................................................................................... 61 Chapter 6 Emergency Preparedness and Public Safety..................................................................... 62 Overview............................................................................................................................................................................ 62 Emergency Dam Operation During Extraordinary Floods............................................................................. 62 Emergency Operation for Dam Safety............................................................................................................. 62 Preflood Reservoir Drawdown Operations .................................................................................................... 65 Public Safety and Risk Communication ................................................................................................................ 67 Notification of Flood Discharge ......................................................................................................................... 67 Downstream Flood Warning Procedures......................................................................................................... 67 Flood Disaster Management and Hazard Maps............................................................................................68 Notes...................................................................................................................................................................................68 Chapter 7 Funding Mechanisms for Dam Safety Assurance.............................................................. 70 Overview............................................................................................................................................................................70 Funding Mechanisms.....................................................................................................................................................70 Multipurpose Dams..................................................................................................................................................70 Hydropower................................................................................................................................................................70 Water Supply.............................................................................................................................................................. 72 Irrigation....................................................................................................................................................................... 72 Contingency Budget................................................................................................................................................ 73 Notes................................................................................................................................................................................... 74 Chapter 8 Key Takeaways on the Japanese Experience on Dams Development and Management.....................................................................................................................75 References.......................................................................................................................................................79 Appendix A Chronology of Legislation for Water Resources Development and Historical Background............................................................................................................82 Contents v Boxes 2.1 Aichi Irrigation Project..............................................................................................................................................7 2.2 Hydropower Development on the Kurobe River.......................................................................................... 12 2.3 World Bank–Funded Hydropower Projects ...................................................................................................14 2.4 Sayama-Ike Rehabilitation and Repurposing Project................................................................................. 15 2.5 Failure of Fujinuma-Ike—Lessons Learned From the Great East Japan Earthquake..................... 18 3.1 Environmental and Social Impact Management........................................................................................... 31 3.2 The Development of the Japanese Roller-Compacted Dam by MOC In-House Engineers............39 4.1 The Great East Japan Earthquake ...................................................................................................................44 4.2 Continued Seismic Changes—Noto Peninsular Earthquake (January 2024)...................................46 4.3 Sediment Flushing by Dashidaira Dam (KEPCO) and Unazuki Dam (MLIT).................................... 52 6.1 Special Operation for Disaster Prevention in Hiyoshi Dam (2013)....................................................... 63 6.2 Preflood Reservoir Drawdown Operations in the Kiso River System (2021)....................................66 7.1 JWA’s Financing Mechanism, including Water Resources Bonds ........................................................ 71 7.2 Management of Small Irrigation Off-Stream Dam by the LID in Gunma Prefecture (Sanna-Gawa Dam of the Fujioka LID)............................................................................................................ 72 Figures 1.1 Large Dams in Japan, by Purpose and Type, 2022.......................................................................................2 2.1 Comparison of Longitudinal Profile of Typical Rivers in Japan and Other Countries.................... 4 2.2 Number of Large Dams Constructed in Japan, by Purpose and Structural Type, 1900–2022........5 2.3 Annual Domestic Water Intake by Water Sources, 1965–2020................................................................6 B2.1.1 Historical Changes of Sectoral Water Supply Volume by Aichi Canal System.................................10 2.4 Annual Human and Economic Losses in Japan by Water-Related Disasters, 1946–2021.............. 11 B2.4.1 Historical Rehabilitation of Sayama-Ike (Cross-Section of the Embankment)................................. 16 2.5 Historical Deviation From Average Temperature (°C) In Japan, 1898–2023..................................... 19 2.6 Trend of Heavy Rainfall Events in Japan, 1976–2023.................................................................................20 2.7 Conceptual Diagram of River Basin Disaster Resilience and Sustainability by All......................... 22 3.1 Classification of River Systems in Japan........................................................................................................ 27 3.2 Coordination Mechanism for JWA’s Dam Development and Management ..................................... 35 B4.3.1 Integrated Sediment Flushing on the Kurobe River................................................................................... 52 B6.1.1 Flood Control Operation in Hiyoshi Dam....................................................................................................... 63 6.1 Concept of Preflood Reservoir Drawdown Operation.............................................................................. 65 Maps 2.1 Dams and Extended Bulk-Water Conveyance Systems for Tokyo Metropolitan Area.....................7 B2.1.1 Areas of the Aichi Irrigation Project....................................................................................................................8 B2.2.1 Dams on the Kurobe River.................................................................................................................................... 13 2.2 Regional Classification of Japan......................................................................................................................... 21 4.1 Seven Important River Systems Designated Under the Water Resources Development Promotion Act.......................................................................................................................................................... 42 B4.1.1 Peak Ground Acceleration (cm/s2) During the Great East Japan Earthquake................................44 B4.2.1 Seismic Intensity Distribution and Location of Three Dams Subject to 300-Gallon Seismic Motion..........................................................................................................................................................................46 4.2 Basin-Level Erosion Rate Potential Map.......................................................................................................... 51 B6.2.1 Preflood Emergency Reservoir Drawdown Operation on the Otaki River (2021).......................... 67 Photos B2.1.1 Makio Dam....................................................................................................................................................................9 B2.1.2 Aichi Canal....................................................................................................................................................................9 B2.2.1 Kurobe Dam................................................................................................................................................................ 12 B2.4.1 Sayama-Ike and Surrounding Areas.................................................................................................................. 15 B2.5.1 Fujinuma-Ike After Breach.................................................................................................................................... 18 B4.3.1 Unazuki Dam Sediment Flushing ..................................................................................................................... 53 B6.1.1 Peak Flood at Togetsukyo Bridge In Kyoto...................................................................................................64 B6.1.2 Flood Storage at Hiyoshi Dam Over Katsura River a Tributary of the Yodo River.........................64 B7.2.1 Sanna Lake/Sanna-Gawa Dam........................................................................................................................... 73 vi Dam Safety Management in Japan Tables B2.3.1 List of World Bank–Funded Hydropower Projects in Japan....................................................................14 2.1 Failures and Incidents of Dams and Ponds in Japan.................................................................................. 16 2.2 Estimated Increase Rate In Rainfall With 100-Year Return Period In Japan...................................... 21 2.3 Estimated Average Increase Rates in Flood Discharge and Frequency of Floods........................ 22 3.1 Key Laws and Regulations Relating to Dam Safety in Japan................................................................. 24 3.2 Definition of River Classes................................................................................................................................... 26 3.3 Roles and Responsibilities of River Administrators and Other Entities............................................. 29 3.4 Institutional Arrangements for Dams In Japan, by Purpose and River Class................................... 29 3.5 Legal Responsibility of Dam Owners................................................................................................................ 31 3.6 Permits to be Obtained by Dam Owners....................................................................................................... 33 B4.1.1 Dams in the Areas Affected by the Great East Japan Earthquake......................................................45 B4.2.1 Three Dams’ Seismic Impacts and Damages................................................................................................ 47 4.1 Extracted Articles of the River Act Regarding Dam O&M Requirements.........................................48 4.2 Legal Basis of Operation Rules for Dams for Different Purposes and Owners...............................49 5.1 Prioritization for Remedial Work....................................................................................................................... 59 6.1 Number of Rivers and Dams That Have Participated in Flood Control Agreements....................66 6.2 Implementation of Preflood Reservoir Drawdown Operations.............................................................66 B7.1.1 Financing Sources of JWA.................................................................................................................................... 71 Acknowledgments This report was prepared by the World Bank Water Global Department with contributions from numerous individual experts and organizations, without whom this work would not have been possible. The team gratefully acknowledges their contributions to this report. However, the opinions expressed in this report and any errors herein are the sole responsibility of the authors and should not be attributed to the individuals or institutions acknowledged herein. The team was led by Satoru Ueda (Lead Dam Specialist) and Naho Shibuya (Senior Disaster Risk Management Specialist) and included Marcus J. Wishart (Lead Water Resources Management Specialist), Kimberly N. Lyon (Senior Water Resources Management Specialist), Hisashi Mitsuhashi (Senior Water Resources Specialist), Yong Nyam (Consultant), and Ayelen Becker (Consultant). Eileen Burke (Global Lead for Water Resources Management) and Maria Guell Pons (former Dam Specialist) provided review and feedback. Kenzo Hiroki (Advisor, Japan Water Forum and Professor, National Graduate Institute for Policy Studies) provided critical inputs and guidance for the report. The team also acknowledges the strategic direction provided by Saroj Kumar Jha (Global Water Director, World Bank), Yogita Mumssen (Practice Manager, Global Solutions, Water), and Soma Ghosh Moulik (Practice Manager for the Heart of Africa, Water and former Practice Manager for Global Solutions, Water). The report was prepared building on a consultancy report on the legal and institutional frameworks for dam safety assurance in Japan by Nippon Koei, including Tomonori Abe (Managing Director), Ichiro Araki (Chief Dam and Hydropower Engineer), Junichi Fukuwatari (Acting General Manager, Water Resources and Energy Department), Takuji Kataoka (Chief Engineer), Shintaro Suzuki (Consultant), and Naoki Yamashita (Consultant). The report benefited from technical inputs on seismic standards and designs by Norihisa Matsumoto (former Japan Dam Engineering Center (JDEC) and former Japan Commission on Large Dams (JCOLD)). Professor Toshio Koike (Executive Director, International Centre for Water Hazard and Risk Management under the auspices of UNESCO and Professor Emeritus of the University of Tokyo) provided valuable feedback to flood forecasting and other relevant aspects. Professor Tetsuya Sumi (Kyoto University, Vice President of the International Commission on Large Dams) also provided valuable feedback including sediment management aspects. vii viii Dam Safety Management in Japan This report builds on an earlier set of country case studies compiled for “Laying the Foundations: A Global Analysis of Regulatory Frameworks for the Safety of Dams and Downstream Communities,” authored by Marcus J. Wishart (Lead Water Resources Specialist), Satoru Ueda (Lead Dam Specialist), John D. Pisaniello (Research Professor of Engineering Law, University of South Australia), Joanne L. Tingey-Holyoak (Associate Professor of Accounting, University of South Australia), Kimberly N. Lyon (Senior Water Resources Management Specialist), and Esteban Boj García (Water Analyst, World Bank, during preparation of the book, now Head of Water Resources Management, Deutsche Gesellschaft für Internationale Zusammenarbeit [GIZ], Tajikistan), with contributions from Naho Shibuya (Senior Disaster Risk Management Specialist), Priyali Sur (Communications Specialist), and Yue Chen (Analyst). The report also benefited from peer reviews and inputs from Japanese experts (all affiliations are as of that time): Hirotada Matsuki, Ryoichi Suga, Daisaku Saito, Shinji Takahashi, Hiroyuki Murata, Takahiro Konami, and Kiichi Ikehara from the Water and Disaster Management Bureau of the Ministry of Land, Infrastructure, Transport, and Tourism (MLIT); Satoru Fujita and Yasuaki Nakamura from the Ministry of Agriculture, Forestry, and Fisheries (MAFF); Takehisa Sato from the Ministry of Economy, Trade, and Industry (METI); Mikio Ishiwatari from the Japan International Cooperation Agency (JICA); Masayuki Kashiwayanagi (JCOLD); Hideshi Sasahara, Tatsuo Kunieda, Nobuyuki Ichihara, Takaaki Kusakabe, and Atsushi Suzuki from the Japan Water Agency (JWA); Professor Emeritus Tsuneaki Yoshida from the University of Tokyo; and Jun Matsumoto and Toshihiro Sonoda from the World Bank. The team wishes to extend thanks to the following intervewees (all affiliations are as of that time): Yoshiro Hori from the Water and Disaster Management Bureau, MLIT; Masahiro Mukai and Kazuhiro Nakajima from the Kantō Regional Development Bureau, MLIT; Hisashi Ota, Hisakazu Kuroiwa, and Kimihide Hoshino from the Tone River Integrated Dam Operation Office, MLIT; Yoshimitsu Mizuno from the Kantō Regional Agricultural Administration Office, MAFF; Shin-ichi Shibuya and Masaki Kinoshita from JWA; Tadayoshi Nakahara and Yusaku Yamamoto from the JWA Numata Comprehensive Management Office; Takayuki Shinohara, Shizuo Nakabayashi, and Toshiyuki Nakano from Gunma Prefecture; Hideaki Sugawa and Makoto Horiguchi from the Fujioka Land Improvement District; Shigeru Tsuruta, Akira Takahashi, and Muneharu Ashizawa from Tokyo Electric Power Company (TEPCO); and Tomotoshi Shinozaki and Hiroyuki Hayakawa from Electric Power Development Co., Ltd. (J-POWER). The team also extends special thanks to Erin Ann Barrett for coordination of editing and layout design; David Gray and Ayse Boybeyi for overall publication support; Saengkeo Touttavong for the graphic design; Susi Victor, Selvaraj Ranganathan, and Mary Anderson for editorial works; and Haruko Nakamatsu and Shoko Takemoto of the World Bank and Chihiro Sudo of MLIT for their support. The team also thanks Nagaraja Rao Harshadeep, Aminul Islam, and Hrishikesh Prakash Patel for developing a river profile figure based on geographic information system (GIS) data. This report was made possible with financial support from the Japan-World Bank Program for Mainstreaming Disaster Risk Management in Developing Countries, which is financed by the Ministry of Finance, Japan, and the Global Water Security and Sanitation Partnership of the World Bank Global Water Department. Abbreviations AIPC Aichi Irrigation Public Corporation DBDC dam basic design committee DFL design flood level EIA environmental impact assessment g gravitational acceleration ICOLD International Commission on Large Dams IPCC Intergovernmental Panel on Climate Change JCOLD Japan Commission on Large Dams JDEC Japan Dam Engineering Center JICA Japan International Cooperation Agency JMA Japan Meteorological Agency J-POWER Electric Power Development Co., Ltd. JWA Japan Water Agency KEPCO Kansai Electric Power Co., Inc. LID land improvement district MAFF Ministry of Agriculture, Forestry and Fisheries METI Ministry of Economy, Trade and Industry MHLW Ministry of Health, Labor and Welfare MLIT Ministry of Land, Infrastructure, Transport and Tourism MOC Ministry of Construction MOE Ministry of the Environment NWL normal maximum water level O&M operation and maintenance PGA peak ground acceleration RCC roller-compacted concrete RCD roller-compacted dam RCP Representative Concentration Pathway R&D research and development SWL surcharge water level TEPCO Tokyo Electric Power Corporation WARDEC Water Resources Development Public Corporation ix CHAPTER 1 Introduction OBJECTIVE This report provides an overview of the legal, regulatory, and institutional frame- works of dam safety in Japan. The key objective is to share good practices and lessons learned from Japan with practitioners and governments working on establishing or enhancing a dam safety assurance system for further study and reflection in line with their national contexts. It was built on an earlier set of fifty-one country case studies compiled for the World Bank global comparative analysis of regulatory frameworks for the safety of dams and downstream commu- nities (Wishart et al. 2020). OVERVIEW Japan has developed a holistic system of dam safety management and standards. Water resources development played a central role in Japan’s socioeconomic development by controlling floods; providing irrigation, domestic, and industrial water supply; and generating hydroelectric power. Yet planning, design, construction, operation, maintenance, and management of dams have always been a challenge because of natural conditions, such as steep mountains, narrow valleys, fragile foundations, frequent earthquakes, and floods, as well as socioeconomic condi- tions, such as densely populated industrial and residential areas downstream of dams. Japan has overcome these challenges by developing and iteratively improving solutions for integrated water resources management and dam safety. Japan’s legal and institutional frameworks for dam safety assurance are thus underpinned by systematic research and development (R&D) on advanced technology to operate dams safely under extremely challenging conditions, including frequent natural hazards. There are more than 3,100 large dams with a height of 15 m or greater in Japan, which is ranked fourth in the world in terms of the number of dams, following China, the United States, and India.1 The majority of dams are irrigation and multipurpose dams, includ- ing flood control, followed by hydropower dams (figure 1.1). Regarding dam types, concrete gravity and earthfill dams (largely for irrigation) are the majority followed by rockfill dams. 1 2 Dam Safety Management in Japan FIGURE 1.1 Large Dams in Japan, by Purpose and Type, 2022 a. Large dam by purpose b. Large dam by type 5% 2% 2% 6% 13% 42% 42% 56% 20% 12% Irrigation Multipurpose Hydropower Earthfill Rockfill Concrete gravity Flood control Water supply Concrete arch Others Source: Original for this publication based on JCOLD survey. Note: All dams included are at least 15 m in height. Water supply is the sum of domestic water and industrial water. In addition, there are more than 150,000 irrigation ponds.2 Approximately 61,000 have irrigation areas larger than 2 ha, of which 70 percent were constructed during the Edo period (1603–1868) or before (MAFF 2016, 2023). Irrigation ponds are managed by farmer associations called land improvement districts (LIDs). Because the majority of irrigation ponds were constructed before the present legal and institutional system, their safety inspections, rehabilitation/safety improvement, and emergency preparedness need to be enhanced. NOTES 1. A dam with a height of 15 m or greater from the lowest foundation to the crest or a dam between 5 m and 15 m impounding more than 3 million m3 of water is considered a large dam. China, the United States, and India have more large dams with 24,089, 10,158, and 4,540, respectively. Japan is followed by Canada and South Africa with 1,440 and 1,428 large dams, respectively. Source: International Commission on Large Dams (ICOLD). https://www.icold-cigb.org/article/GB/world​_register/general_ synthesis/number-of-dams-by-country Accessed on August 30, 2024. 2. Irrigation ponds are generally off-stream irrigation storage structures outside of designated Class A or Class B river areas (see table 3.2 and figure 3.1 in chapter 3) and/or very old ones built before the River Act was enacted in 1896 and not subject to its regulation in Japan. Irrigation ponds are often called ike or tameike as in Japanese. CHAPTER 2 Historical and Present Water Resources Development and Management OVERVIEW Historically, water resources development played a critical role in Japan’s socioeco- nomic development through the formulation of respective laws, regulations, and guidelines to meet the changing socioeconomic conditions. Japan has been constructing modern dams from the rapid growth period that started in the late 1950s to date in response to public demand. Dams have been constructed to control floods; provide irrigation, domestic, and industrial water supply; and generate hydroelectric power considering hydrometeorological, topographic, and geological characteristics of the nation. Chronological development of legisla- tion and historical background are provided in appendix A. CHARACTERISTICS OF JAPAN Japan lies at the northeast tip of the Asian monsoon zone. The country’s four distinct sea- sons feature three periods of heavy precipitation: heavy snowfalls, blanketing the Sea of Japan side in the winter; continuous heavy rains in June and July; and typhoons that originate in the Southern Pacific in September and October. Heavy annual precipitation (including snowfall) supports hydropower generation; conversely, Japan suffers from frequent floods. Japan has been experiencing climate variability and extreme events, such as record-​ breaking heavy rainfall and drought. Rainfall episodes exceeding 50 mm per hour are approximately 1.5 times more frequent than 30 years ago. The number of daily rainfalls exceed- ing 100–200 mm has increased, while the number of days without any rainfall is also increasing. The national average yearly temperature has increased by approximately 1.35°C, whereas while it has increased by approximately 2°C–3°C in major cities over the past 100 years (JMA 2024). In terms of topography, Japan has a total area of 377,727 km2, of which about 70 percent is covered by mountainous and hilly areas. The long mountain ranges, with 3,000-meter peaks, form the backbone of the archipelago and bisect the central portion of Honshu, the main island. This mountainous setting creates rivers that generally are short with steep channel slopes. The rivers carry sediments to the downstream areas to form medium and moderate-size alluvial floodplains. The rivers are prone to flooding because of the rapid flow caused by their steep slopes and relatively short lengths (figure 2.1). The river regime coefficient1 is between 200 and 400, which is ten times larger than that of continental-scale rivers. Large metropolitan areas, 3 4 Dam Safety Management in Japan FIGURE 2.1 Comparison of Longitudinal Profile of Typical Rivers in Japan and Other Countries Altitude (m) 3,000 2,500 2,000 1,500 1,000 500 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 Distance from estuary (km) Chikugo Joganji Kiso Kitakami Shinano Tone Yodo Yoshino Amazon Colorado Ganges Loire Mekong Mississippi Nile (Blue) Nile (White) Rhine Source: Original for this publication by the World Bank Disruptive KIDS (Knowledge, Information & Data Services) Helpdesk. such as Tokyo (population over of more than 30 million), Osaka (population over of more than 17 million), Nagoya, and Fukuoka are located in floodplains or alluvial plains, which account for about 10 percent of the national land area, 50 percent of the total population, and 75 percent of the national fixed assets. Therefore, flood control measures have been central to Japan’s water resources management. Japan receives a lot of rainfall annually but relies on storage to meet the needs of its pop- ulation. Although annual precipitation in Japan is about 1.4 times the world average,2 because of Japan’s dense population, its annual per capita precipitation volume is only about one-fourth of the world average.3 A relatively small amount of water is available for use because of small basins and steep channels. Therefore, dam reservoirs play a vital role in utilizing the rivers to ensure stable supplies of water for agricultural users and, domestic potable and industrial water supply, while providing effective flood discharge control functions. Also, the concentration of productive irrigated rice agriculture and the population on floodplains has required Japan to build and operate many dams in mountainous regions in upstream of the floodplains (JCOLD 2017). Because of the seismic risk and densely populated urban and industrial areas in the downstream of dams, Japan has developed rigorous dam safety standards and prac- tices. The Japanese archipelago is on the Ring of Fire, or Circum-Pacific Orogenic Belt, where Historical and Present Water Resources Development and Management 5 earthquakes frequently occur, and grounds are geologically fragile. Approximately 20 percent of earthquakes exceeding magnitude 6 in the world have occurred around Japan (MLIT 2023b, c). Various types of dams, including concrete gravity, arch, and rockfill types, have been constructed so that the dams are to fit to diverse geological and seismic conditions. HISTORICAL DEVELOPMENT OF DAMS The history of dams in Japan, including irrigation ponds and embankment dams, dates back more than 2,000 years. River development has been historically promoted to meet the needs of changing socioeconomic and demographic conditions as described in the subsequent sections. The historical development of dams by purpose and by structural type are shown in figure 2.2. Dams were historically built for irrigation to secure agriculture production and food supply. Then hydropower dams were rapidly built to supply much-needed energy for the rapidly developing economy and industries in the 1950s and 1960s. Since then, the construction of multipurpose dams, including domestic water supply and flood control, have rapidly increased to address severe water shortages and flood disasters in large metropolitan areas. The quick increase in the number of concrete dams, as shown in figure 2.2, also reflects the increase of multipurpose/flood control dams promoted by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT; then the Ministry of Construction) for enhanced safety against potential overtopping failure risk because of high variabilities of river flows. FIGURE 2.2 Number of Large Dams Constructed in Japan, By Purpose and Structural Type, 1900–2022 a. Large dam by purpose b. Large dam by type Number of dams Number of dams 2,500 2,500 2,000 2,000 1,500 1,500 1,000 1,000 500 500 0 0 19 10 19 20 19 –30 19 –40 19 –60 19 –70 19 –80 –2 0 20 000 20 –10 22 19 10 19 20 19 –30 19 –40 19 –60 19 –70 19 81– 0 –2 0 20 000 20 –10 22 19 –50 19 –50 91 9 19 –8 91 9 – – 11– 11– 11– 19 1– 11– 00 01 00 01 21 31 51 61 71 21 31 51 61 71 41 41 8 19 19 Year Year Water supply Flood control Combined Multiple arch Buttress Multipurpose Hydropower Arch Gravity Earthfill Irrigation Rockfill Source: Original for this publication based on JCOLD survey. Note: In addition, 662 dams were constructed before the year 1900 mainly for irrigation. All dams included are at least 15 m in height. Water supply is the sum of domestic water and industrial water. 6 Dam Safety Management in Japan The annual amount of domestic water provided by dams increased from 11 percent in 1965 to 48 percent in 2020 (figure 2.3). This trend can be attributed to the increasing dependence on dams as a water source to ensure its stable supply given high seasonal variability of natural river flows. FIGURE 2.3 Annual Domestic Water Intake by Water Sources, 1965–2020 Annual supply volume (100 million m3) 180 160 140 120 100 80 60 40 20 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 Fiscal year Dam River Lake Riverbed undersurface flow Well Others Sources: Created based on Japan Water Works Association 1965, 1970, 1975, 1980, 1985, 1990, 1995, 2000, 2005, 2010, 2015, 2020. In particular, about twenty dams and extended bulk-water conveyance systems have been developed and managed in the Tone and Arakawa Rivers (map 2.1) to increase the water stor- age to supply domestic and industrial water to megalopolis for the Tokyo metropolitan areas with a total population of more than 30 million. The regions suffered from serious water short- age in the 1960s because of rapidly increased gaps between water supply and demand. Also, as Tokyo and other large metropolitan areas suffered from major land subsidence because of rapidly increased groundwater pumping, local governments imposed restriction of groundwater use and, in parallel, water resource development projects to secure surface water regulated by dams. Multipurpose Dams Since the 1960s, the number of dams has risen, mainly because of the construction of multipurpose dams through comprehensive land development projects led by the national government. The construction of dams has expanded the capacity for waterworks, supporting the rise in the population with access to clean water. From approximately 1970, the prefectural governments also started constructing multipurpose dams on the rivers under their jurisdiction, with subsidies from the national government. Historical and Present Water Resources Development and Management 7 MAP 2.1 Dams and Extended Bulk-Water Conveyance Systems for Tokyo Metropolitan Area Yagisawa Dam Naramata Dam Kusaki Dam Yanba Dam Shimokubo Dam Tone River Takizawa Dam Arakawa River Urayama Dam Ogochi Dam Ozaku Murayama-Shimo Reservoir Tama River Purification plant Channel Sagami River Intake weir Dam Source: Based on Matsumoto 2012. BOX 2.1 Aichi Irrigation Project The Aichi Irrigation Project (1955–61) was initiated by Shotaro Kuno, an engi- neer, and Tatsuo Hamajima, a teacher at the local agricultural school, in the Chita Peninsula, where the water shortage was very severe because of low rain- fall amount without any particular surface water and groundwater resources. They developed a basin plan to build an irrigation canal diverting water from the Kiso River and presented it to the government in 1948. The government adopted the plan and, under the Comprehensive National Land Development Act (1950), established the Aichi Irrigation Public Corporation (AIPC) as the implementation agency to design, construct, and operate the multipurpose project, comprising irrigation, domestic, and industrial water supply, and hydropower generation for Aichi Prefecture. The World Bank and AIPC signed a loan agreement in 1957 and assisted the engineering designs and construction.a (box continues next page ) 8 Dam Safety Management in Japan BOX 2.1 Aichi Irrigation Project (Continued) Makio Dam (center core rockfill dam with 105 m in height, 264 m in crest length, and 75 million m3 in reservoir capacity) in Nagano Prefecture was constructed in 1961 along with a 112-km-long main canal and approximately 1,000-km-long irriga- tion canals. The purpose of the dam was irrigation, domestic, and industrial water supply. Mio hydropower plant (35 megawatts, later increased to 37  megawatts with pumped storage function) was also built as a supplementary project by the Kansai Electric Power Co., Inc. (KEPCO). In 1968, AIPC merged with the Water Resources Development Public Corporation (WARDEC), which later became the Japan Water Agency (JWA) in 2003. MAP B2.1.1 Areas of the Aichi Irrigation Project FUKUI IBRD | 48653 FEBRUARY 2025 Mino GIFU iso Riv er K Yamagata Seki Kiso River Nakatsugawa Nagahama Motosu Kaneyama Intake Kani Channel Ena Gifu NAGANO Mizuho Ogaki Inuyama Makio Dam Toki Lake Biwa Konan Iruka Reservoir GIFU Maibara Hashima Ichinomiya Komaki Hikone Iwakura NAGANO p Kasugai Area of ma Inazawa Kitanagoya Seto Kaizu Kiyosu SHIGA Owariasahi Ama Nagoya AICHI Tsushima Nagakute AICHI Inabe Aisai Nisshin Main Canal Higashiomi Togo Balancing Reservoir Yatomi Miyoshi Toyota Kuwana Toyoake Tokai Obu Chiryu Koka Chita Kariya Yokkaichi Ise Bay Okazaki CHINA RUSSIAN Tokoname Takahama FEDERATION Handa Shinshiro Suzuka Maeyama Reservoir Kameyama Hekinan Gamagori D. P. R. OF Toyokawa JAPAN Nishio KOREA SHIZUOKA M I E FACILITIES JWA’S ADMINISTRATIVE Toyohashi Iga DOMESTIC WATER Tsu Mihama Balancing Reservoir REP. INDUSTRIAL WATER OF KOREA Kosai Mikawa Bay Hamamatsu AGRICULTURAL WATER MAIN ROADS Tahara PREFECTURE BOUNDARIES INTERNATIONAL BOUNDARIES Matsusaka Source: Adapted from JWA 2023. (box continues next page ) Historical and Present Water Resources Development and Management 9 BOX 2.1 Aichi Irrigation Project (Continued) PHOTO B2.1.1 Makio Dam Source: JWA. Used with permission. Further permission required for reuse. PHOTO B2.1.2 Aichi Canal Source: JWA. Used with permission. Further permission required for reuse. (box continues next page ) 10 Dam Safety Management in Japan BOX 2.1 Aichi Irrigation Project (Continued) The project has continued scaling up the water storage and supply capacity by building additional two dams in the upstream of the Kiso River—that is, Misogawa Dam and Agigawa Dam—and optimized the water allocation in an adaptive manner to changing patterns of water demands as the surrounding areas have dramati- cally changed from rural agriculture lands to urban and industrial areas. The origi- nal water supply volume increased from 143 million m3/year in 1963 to 442 million m3/year in 2022. Although 65 percent of water was used for agriculture, 26 percent for industrial water, and 9 percent for domestic water in 1963, 53 percent of the water is used for industrial purposes, 27 percent for domestic water, and 20 percent for agriculture in 2022 (figure B2.1.1). FIGURE B2.1.1 Historical Changes of Sectoral Water Supply Volume by Aichi Canal System a. FY 1963 b. FY 1981 c. FY 2022 20% 26% 26% Annual Annual Annual volume used volume used volume used 143 million m3 58% 399 million m3 53% 442 million m3 9% 65% 65% 16% 27% Agricultural water Domestic water Industrial water Source: Adapted from JWA 2008. a. To see the loan agreement, visit https://documents1.worldbank.org/curated​ /­en/233351468253208569/pdf/Loan-0173-Japan-Aichi-Project-Loan-Agreement.pdf. Flood Control The development of multipurpose/flood control dams greatly contributed to the reduction in the number of casualties and economic impacts by flooding disasters. Figure 2.4 shows drastic reduction of dead and missing people and economic damages in the 1960s thanks to the rapid development of multipurpose/flood control dams in addition to dikes/levees along rivers and coasts. In the 1940s and 1950s, the country was devastated by a series of catastrophic flooding disasters. Typhoon Kathleen breached the Tone River and caused flood disasters in the Tokyo metropolitan areas, with 1,930 dead and missing people in 1947. Other major disasters included Historical and Present Water Resources Development and Management 11 Makurazaki (Ida) Typhoon (3,756 dead and missing in 1945), Ione Typhoon (838 dead and miss- ing in 1948), Tōya Maru (Marie) Typhoon (1,761 dead and missing in 1954), Kano River (Ida) Typhoon (1,189 dead and missing in 1958), Ise-Bay (Vera) Typhoon (5,098 dead and missing in 1959), and so on. FIGURE 2.4 Annual Human and Economic Losses in Japan by Water-Related Disasters, 1946–2021 a. Historical changes in the number b. Historical changes in economic damages of dead and missing people by ratio (%) compared with national income water-related disasters by water-related disasters People Percent (%) 6,000 12 5,000 10 4,000 8 3,000 6 2,000 4 1,000 2 0 0 46 56 66 76 86 96 06 16 46 56 66 76 86 96 06 16 20 20 19 19 19 19 19 19 19 19 19 19 19 19 20 20 Year Year Source: MLIT 2024a. Hydropower At present, the total installed capacity of hydropower generation including pumped storage is 49.6 gigawatts (IHA 2024).4 The total number of hydropower dams is 650, including single-purpose (420) and multipurpose (230) dams (JCOLD 2020). As of 2022, the amount of hydropower generation was 85.0 terawatthours, accounting for 9.1 percent of the country’s total power generation of 937.6 terawatthours (JEPIC 2024). There are ten regional electric power companies and two wholesale electric power companies, called Electric Power Development Co., Ltd. (J-POWER) and the Japan Atomic Power Company. All of them are pri- vate companies.5 Japan has the second-largest installed capacity of pumped storage plants in the world after China, capable of absorbing and discharging about 27.0 gigawatts of power by forty-two plants, corresponding to 54 percent of the total installed capacity. The plants are also technology leaders with variable-speed pump technology developed since the 1990s and are uniquely designed to integrate variable power demand and generation. 12 Dam Safety Management in Japan BOX 2.2 Hydropower Development on the Kurobe River In 1949, after the end of World War II, a hydropower development plan was approved for thirty-three locations with an intended production of 1,180 mega- watts to meet the rapidly increasing electricity demands. In 1951, the Japan Electric Generation and Transmission Company was dismantled and broken into the nine regional electric power companies. Coupled with a severe drought in 1951 that resulted in an unprecedented electric power crisis, Japan accelerated the devel- opment of large-scale hydroelectric sources, including the Kurobe Dam (JCOLD 2017). The Kurobe Dam (arch type) is the tallest dam in Japan with the height of 186 m, reservoir capacity of about 200 million m3, and installed capacity of 337 mega- watts by its No. 4 plant. The dam was built between 1956 and 1963 on the Kurobe River in Toyama Prefecture and is operated by the Kansai Electric Power Co., Inc. (KEPCO). KEPCO has installed ten cascade hydropower plants, with a total maxi- mum capacity of 899 megawatts, using the head drop of nearly 1,400 m from the Kurobe Dam (KEPCO n.d.). Construction of the dam at the narrow gorge in the nonaccessible high mountain area was regarded as a civil engineering monument. PHOTO B2.2.1 Kurobe Dam Source: KEPCO, https://www.kepco.co.jp/corporate/profile/community/pr/kurobe/guide/en/pwr​ _gen_eqp.html. (box continues next page ) Historical and Present Water Resources Development and Management 13 BOX 2.2 Hydropower Development on the Kurobe River (Continued) MAP B2.2.1 Dams on the Kurobe River Japan Sea Ku Asahi Town rob eR Niigata N ive r Pref. 14 km Kitamata Dam y Ba Unazuki Dam ma 5k ya To m Dashidaira Dam 7k m Koyadaira Dam Ku ro be Sennindani Dam Riv Toyama Prefecture er Kurobe Dam Kurobe Reservoir Kurobe River Nagano Prefecture Gifu Prefecture  Source: Kantoush, Sumi, Suzuki, and Murasaki. 2010. 14 Dam Safety Management in Japan BOX 2.3 World Bank–Funded Hydropower Projects The World Bank provided loans for developing hydropower projects in Japan from 1958 to 1965. Those funds were dedicated for hydropower plants but did not cover the construction of dams. Additional capacity and function were provided in par- allel or at a subsequent phase with their own/other funds. Although all power companies are private, the Electric Power Development Co., Ltd. (J-POWER) was established as a semipublic company in 1952 but became fully private in 2004. TABLE B2.3.1 List of World Bank–Funded Hydropower Projects in Japan Installed Loan capacity Name of Loan amount (MW) Reservoir Installed hydropower signed (US$ under Dam Dam capacity capacity plant Owner year million) loan name type Height (MCM) (MW) Kurobe KEPCO 1958 37 258 Kurobe Arch 186 199 337 No. 4 Arimine Hokuriku 1958 25 261 Arimine Concrete 140 222 265 Electric gravity Power Company Hatanagi Chubu 1958 29 170 Hatanagi Hollow 125 107 137 No. 1 Electric No. 1 gravity including Power pumped storage Hatanagi Hatanagi Hollow 69 11 85 No. 2 No. 2 Miboro J-POWER 1959 10 215 Miboro Rockfill 131 370 215 Kuzuryu- J-POWER 1965 25 113 Kuzuryu Rockfill 128 353 220 Nagano including (including pumped pumped storage storage) Kuzuryu- Washi Arch 44 1 54 Yuage Note: Kuzuryu Dam is a multiple dam managed by MLIT. The effective storage for hydropower generation is 180 MCM out of 353 MCM total storage. J-POWER = Electric Power Development Co., Ltd.; KEPCO = Kansai Electric Power Co., Inc.; MCM = million cubic meters; MLIT = Ministry of Land, Infrastructure, Transport and Tourism; MW = megawatt. Historical and Present Water Resources Development and Management 15 Agriculture and Irrigation Many irrigation dams and ponds were constructed during and before the Edo period (1603–1868) and after World War II to address food security. Irrigation ponds are reservoirs formed by earthfill dams with a storage capacity between a few thousand and 10,000 m3 of water. The major irrigation ponds were constructed from the seventh century to the early twentieth cen- tury. The old irrigation ponds, such as Sayama-Ike and Manno-Ike, built in 616 and 704, respec- tively, are still operational, with improvement in response to the demands of the times. To increase food production and expand agricultural land, postwar land reform was implemented, including the 1949 Land Improvement Act and other related acts, as the basis for large-scale irrigation and drainage projects. In 1961, the Basic Act on Agriculture6 was enacted to improve agricultural productivity, which promoted farmland expansion, rural roads development, and improvement in quality of agricultural land. As a result, about 1.1 billion m3 of water was developed for irrigation, which supported an increase in the gross agricultural output (JWA 2015b). BOX 2.4 Sayama-Ike Rehabilitation and Repurposing Project The Sayama-Ike (pond), originally built in 616 for irrigation, was rehabilitated and repurposed to flood control for the downstream river and surrounding areas by Osaka Prefecture in 2001. The project involved excavation of the reservoir floor by 3 m and raising of the embankment crest elevation by 1 m for increasing the res- ervoir capacity to 2.8 million m3. As shown in photo B2.4.1, the surrounding areas of the dam have completely changed from rural irrigation areas to densely pop- ulated urban areas, with the repurposing conducted to adapt to changing needs. The survey of the embankment body cross-section showed the historical buildup of the dam over 1,400 years, as shown in figure B2.4.1. PHOTO B2.4.1 Sayama-Ike and Surrounding Areas Source: Osakasayama City, https://www.city.osakasayama.osaka.jp/sosiki/siminseikatsubu​ /­sangyounigiwaizukuri/citypromotion/6003.html. (box continues next page ) 16 Dam Safety Management in Japan BOX 2.4 Sayama-Ike Rehabilitation and Repurposing Project (Continued) FIGURE B2.4.1 Historical Rehabilitation of Sayama-Ike (Cross-Section of the Embankment) 1 1926–31 1962–64 2 1620-21 1693–94 4 –2 1452 1857–59 8 –2 1 2 3 1608 4 –1 1202 3 4 –2 5 762 4 –1 8 –2 8 –2 1596 (Earthquake) 6 731 5 6 7 616 7 8 –1 8 –1 734 (Earthquake) Source: Based on Osaka Prefectural Sayamaike Museum, https://sayamaikehaku.osakasayama​.osaka.jp/. Failures and Incidents of Dams and Ponds in Japan Table 2.1 provides a list of failures and incidents of dams and ponds from the end of the nine- teenth century. Despite the number of large dams in Japan, only eight caused casualties. All failures occurred to dams that were constructed before the modern technical design standards and regulatory framework were established under the amended River Act in 1964 and its Order for Structural Standards for River Administration Facilities, and so on, in 1976. The regulatory framework and standards are generally considered as adequate to ensure the safety of modern dams. At the same time, it is critical to pay attention to those dams and ponds that were not subject to modern design standards and regulations. TABLE 2.1 Failures and Incidents of Dams and Ponds in Japan Year of Type and Name of dam/ Year of failure/ purpose of Description of failure/ pond completion incident dam/pond incident of dam/pond Casualties Iruka-Ike 1633 1868 Earthfill Overtopping failure because 941 people dam for of heavy rainfall. dead and irrigation numerous missing Komoro 1927 1928 Buttress Inadequate foundation 5 people dead Hydropower concrete treatment caused seepage Station, No. 1 dam for erosion and piping, resulting regulating hydropower in dam failure. The dam pond was constructed without regulatory permission. (table continues next page ) Historical and Present Water Resources Development and Management 17 TABLE 2.1 Failures and Incidents of Dams and Ponds in Japan (Continued) Year of Type and Name of dam/ Year of failure/ purpose of Description of failure/ pond completion incident dam/pond incident of dam/pond Casualties Horonai Dam 1939 1941 Concrete Inoperable closed gates 60 people gravity because of clogging with dead dam for floating wood during a flood hydropower resulted in overtopping of the dam. The failure was also attributed to poor construction works not removing sand and gravel layers in the foundation. Heiwa-Ike 1949 1951 Earthfill Overtopping failure because 75 people dam for of heavy rainfall. dead irrigation Yoake Dam 1954 1953 Concrete Flood water because severe No casualties (during gravity rains heavily eroded both construction) dam for abutments. A possibility hydropower that some gates could not be fully opened because of power loss was also raised. Taisho-Ike 1914 1953 Earthfill Overtopping failure together 105 people dam for with failure of another dead irrigation reservoir pond downstream. Wachi Dam 1968 1967 Concrete A tainter gate failure (No. 1 person dead gravity 3) because of its vibration dam for phenomena during the initial hydropower impoundment, discharging a large amount of water and drowning a fishing person downstream of the river. Fujinuma-Ike 1949 2011 Earthfill The dam collapsed because 8 people dead dam for of the Great East Japan or missing irrigation Earthquake in March 2011. The construction of the original dam began in 1937 but was suspended because of World War II. Source: Adapted from Expert Panel Meeting on the Future Flood Management Policy 2011. Note: Ike means irrigation ponds. 18 Dam Safety Management in Japan BOX 2.5 Failure of Fujinuma-Ike—Lessons Learned From the Great East Japan Earthquake Fujinuma-Ike, an irrigation off-stream pond—an earthfill dam with height of 18.5 m, crest length of 133 m, and the reservoir capacity of 1.5 million m3, constructed in 1949 in Fukushima Prefecture—failed by the Great East Japan Earthquake (magni- tude 9.0) in 2011. A large amount of released water reached the downstream com- munity, causing seven to lose their lives and one person to go missing. Fukushima Prefecture set up an inspection panel of external experts to evaluate the seis- mic stability of the ponds in the area that were built for agricultural purposes. The panel concluded that the main causes of the breach were (a) the extremely intense and long seismic motion (which continued more than 100 seconds with the maximum 442 gal peak ground acceleration by the analysis) and (b) the lower technical standard applied, such as low embankment compaction, compared with the current design and construction standard (Fukushima Prefectural Committee for Verification of Seismic Resistance of Agricultural Dams and Ponds 2012). PHOTO B2.5.1 Fujinuma-Ike after Breach a. Breached embankment b. Aerial view of the reservoir Sources: Matsumoto, Sasaki, and Ohmachi 2011; National Institute of Land and Infrastructure Management 2011. EVOLVING WATER RESOURCES MANAGEMENT FRAMEWORK The majority of large dams in Japan are irrigation and multipurpose dams, followed by hydropower dams. For domestic water supply, municipalities or regional water supply entities have built dedicated water supply dams and/or joined multipurpose dam projects. The latter has increased over the years because of its cost efficiency. Most multipurpose dams include flood control functions. Japan’s piped water supply coverage increased from 26 percent in 1950 to approximately 98 percent in 2021, and access to electricity has been staying 100 percent. With a declining population and aging infrastructure, Japan prioritizes maintenance and reha- bilitation to ensure the safety of and extend the lifetime of dams. Integrated water resources Historical and Present Water Resources Development and Management 19 management is increasingly essential to minimize the effects of extreme hydrometeorological events, such as floods and droughts, and to develop and manage sustainable water resources. The water-related policies demarcation and relationships among relevant ministries in Japan can be described as follows: MLIT is in charge of overall coordination for water resources manage- ment, flood control, riverine environment management, water rights provision, domestic water supply,7 and sewage treatment; the Ministry of Agriculture, Forestry and Fisheries (MAFF) is responsible for irrigation water; the Ministry of Economy, Trade and Industry (METI) is respon- sible for industrial water and hydropower generation; and the Ministry of the Environment (MOE) is responsible for the environment and water quality management in rivers and lakes. In particular, the Water Resources Department of MLIT is responsible for preparing and imple- menting the basic water resources development plans and coordination of comprehensive water demand and supply management. INCREASING CLIMATE RISKS Per the Japan Meteorological Agency (JMA), the global average temperature has risen by 0.74°C per 100 years since the end of the nineteenth century. However, the average temperature in Japan has risen 1.35°C per 100 years based on the records between 1898 and 2023, as shown in figure 2.5. FIGURE 2.5 Historical Deviation from Average Temperature (°C) In Japan, 1898–2023 Temperature anomaly (°C) 1.5 Trend = 1.35 (°C/century) 1.0 Base line: 1991–2020 average 0.5 0 –0.5 –1.0 –1.5 –2.0 90 0 10 20 30 40 0 60 70 80 90 00 10 20 0 5 19 20 19 19 20 19 19 19 18 19 19 19 19 20 Year Source: Based on JMA. https://www.data.jma.go.jp/cpdinfo/temp/an_jpn.html. Note: The thirty-year average for the period 1991–2020 is used as the base value. The straight line indicates the long-term change trend. Extreme meteorological events, such as heavy rains and droughts, have increased in Japan. Figure 2.6, panel a indicates the number of rainfall events exceeding 50 mm/hour/year recorded in 1,300 rain gauges between 1976 and 2023. The number of rainfall events exceeding 50 mm/hour during the past ten years between 2014 and 2023 is about 1.5 times compared with 20 Dam Safety Management in Japan that during the first ten years between 1976 and 1985. Figure 2.6, panel b indicates the average number of days with daily rainfall greater than 200 mm/day based on 1,300 rain gauges at the same period. The number of days exceeding 200 mm/day during the past ten years between 2014 and 2023 is about 1.6 times compared with that during the first ten years between 1976 and 1985. FIGURE 2.6 Trend of Heavy Rainfall Events in Japan, 1976–2023 a. Historical trend of annual frequency of b. Rainfall events greater rainfall events greater than 50 mm per hour than 200 mm per day Number of events per year Number of events per year 500 500 400 400 300 300 200 200 100 100 0 0 76 80 84 88 92 20 6 00 04 08 12 16 20 76 80 84 88 92 96 20 0 20 4 08 12 16 20 9 0 0 20 20 20 20 19 19 19 19 19 19 19 19 19 19 20 20 19 20 19 20 20 Year Year Source: Based on JMA, https://www.data.jma.go.jp/cpdinfo/extreme/extreme_p.html. Note: Bars indicate the annual number of occurrences for each year (values converted from nationwide rain gauge observations per 1,300 locations). The straight line indicates the average trend from 1976 to 2023. Climate Change Impact Assessment on Floods To assess the climate change impact on floods, the national government has devel- oped a new flood management policy based on the general circulation models’ out- puts using two climate warning scenarios for 4°C and 2°C by the Intergovernmental Panel on Climate Change (IPCC)8 and set up the increased ratio of storm rainfall intensity and peak flood discharge volume for different regions of Japan, which needs to be incorporated into the river flood management and dams planning (map  2.2). Considering uncertainty in the future, MLIT set the 2°C warming case corresponding to the Representative Concentration Pathway (RCP) 2.6 to be the main case used for dam and river planning and the 4°C warming case corresponding to the RCP 8.5 as a reference case for unmodifiable structures with long- range service duration. Table 2.2 shows the estimated increase rate in rainfall with 100-year return period, and table 2.3 shows the estimated average increase rates in flood discharge and Historical and Present Water Resources Development and Management 21 frequency of floods by applying the results of table 2.2 to class A river systems in Japan. Table 2.3 shows that, for example, at a 2°C rise, the flood discharge targeted by the flood control plan (100-year return period) would increase by about 1.2 times, and the frequency of floods of the magnitude targeted by the current flood control plan would approximately double, indicating that the impacts of climate change would be very severe (MLIT 2021c). MAP 2.2 Regional Classification of Japan Northern Hokkaido Southern Hokkaido Western Tohoku San’in Hokuriku Setouchi Eastern Tohoku Western Chugoku Northwestern Kanto Kyushu Chubu Okinawa Kinki Southern Kii Southern Shikoku Southeastern Kyushu TABLE 2.2 Estimated Increase Rate In Rainfall with 100-Year Return Period In Japan +2°C +4°C +4°C(SR) Nationwide average 1.1 1.3 1.4 Hokkaido 1.15 1.4 1.5 Northwestern Kyushu 1.1 1.4 1.5 Other areas 1.1 1.2 1.3 Source: Adapted from MLIT 2021c. Notes: Short-range (SR) means rainfall duration of more than three hours but less than 12 hours. Applicable to flood control plans for floods less than or equal to 200-year return period in the catchment area greater than or equal to 100 km2. Colors of areas correspond to map 2.2. 22 Dam Safety Management in Japan TABLE 2.3 Estimated Average Increase Rates in Flood Discharge and Frequency of Floods Scenario Rainfall Flood discharge Frequency of floods +2°C 1.1 ≈1.2 ≈2 +4°C 1.3 ≈1.4 ≈4 Source: Adapted from MLIT 2021c. Basinwide Concerted Measures for Flood Risk Reduction and Resilience Enhancement For addressing this intensified challenge, the national government established a policy of basinwide concerted measures for flood risk reduction and resilience enhancement, under which all stakeholders related to flood damage reduction are encouraged to work together to reduce flood disaster risks (MLIT 2020). The taskforce to promote this policy, including mem- bers from sixteen ministries and agencies, was established at the national government level in 2020 and drew up the Action Plan to Promote River Basin Disaster Resilience and Sustainability by All in 2021. It comprises various flood management measures, such as enhanced flood opera- tion of dams, levees, retarding basins, “paddy fields dams” (meaning floodwater storage in paddy fields), flood hazard maps, relocation/evacuation to low-risk areas, other flood defense measures for key infrastructure, and so forth (figure 2.7). One of the important measures is preflood dis- charge/reservoir drawdown by dams on a basin scale, which is explained more in chapter 6. The cabinet approved a special budget in the amount of about US$140 billion for five years, and the National Diet (national legislature of Japan) passed the bill for the amendment of nine related acts (Koike 2021; MLIT 2021b). FIGURE 2.7 Conceptual Diagram of River Basin Disaster Resilience and Sustainability by All 1. Flood prevention 2. Exposure reduction 3. Disaster resilience Basins • Guide residents to Floodplains Floodplains • Improve rainwater lower risk areas • Localize • Improve land risk storage functions • Promote safer way to inundation information living areas • Reinforce evacuation River areas Basins systems • Store flowing water Effective use of Construction / Use of agricultural • Minimize economic through construction / water utilization upgrade of flood reservoirs for flood damages upgrades / effective dams control dams control use of dams, and so on • Promote safer ways of Relocation living • Ensure and improve the discharge capacity • Improve support of river channels Floodplains systems for affected Retarding basin improvement local governments • Reduce overflow • Eliminate inundation Levee development promptly Storage facility improvement River areas Source: Based on Ikeuchi 2024. Historical and Present Water Resources Development and Management 23 NOTES 1. The ratio of the maximum discharge to minimum discharge. 2. Annual precipitation in Japan and in the world is approximately 1,668 mm and approximately 1,171 mm, respectively. For more information, see MLIT (2024a). 3. Annual precipitation per capita in Japan and in the world is approximately 5,000 m3 and approximately 20,000 m3, respectively. For more information, see MLIT (2024a). 4. As of 2023. The installed capacity of 49.6 gigawatts is ranked as the seventh in the world, following China, Brazil, the United States, Canada, Russia, and India. 5. The ten regional electric power companies comprise the nine regional electric power companies that originated from the Japan Electric Generation and Transmission Company and the Okinawa Electric Power Company, Incorporated, which was privatized in 1988. 6. The Basic Act on Agriculture was succeeded by the Basic Act on Food, Agriculture and Rural Areas of 1999. 7. Water supply, including the approval function of the dam construction for domestic water supply utilities and municipalities, used to be under the jurisdiction of the Ministry of Health, Labor and Welfare (MHLW) but has been transferred to MLIT since April 2024. Article 6 of the Water Supply Act was amended in April 2024, stating that the Minister of Land, Infrastructure, Transport and Tourism is responsible for licensing water supply projects. 8. A rainfall dataset created by dynamic downscaling produced 5 km gridded model output for Japan and its surrounding area, dividing into fifteen climate zones enabled to compare the probabilities of extreme events under the present and future climate conditions for each zone. Although the 4°C global warming scenario provides the peak rainfall and flood in approximately 2090 under the IPCC RCP 8.5 scenario, the 2°C global warming scenario provides their projections in approximately 2040 under RCP 2.6. CHAPTER 3 Legal Foundations and Institutional Arrangements OVERVIEW In Japan, river management and dam safety are governed by the River Act and reg- ulated by the Act on Specified Multipurpose Dams, the Erosion Control Act, and the Coast Act (table 3.1). Among several other primary acts and regulations governing dam safety and disaster resilience, the Basic Act on Disaster Management, enacted in 1961, is the funda- mental act for disaster risk management. Although it is not applied to dam operations itself, it relates to disaster risk management in the river basins. Engineering designs, construction, and operation and maintenance (O&M) of river structures are covered by the River Act and underpinned by a strong institutional foundation for human resources, technological development, and quality assurance systems. In particular, in-house engineers of the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), the Ministry of Agriculture, Forestry and Fisheries (MAFF), electric power companies, and dam owners play an important role in securing dam safety. Technological devel- opment, capacity building, and the transfer of technical knowledge and experiences are led by various research and development (R&D) institutions. TABLE 3.1 Key Laws and Regulations Relating to Dam Safety in Japan Law or regulation Description River Act of 1896 (substantially Fundamental act for river management, including water-related amended in 1964 and 1997) along disaster reduction, water resources management, conservation, and with the following: creation of river environment, using the river basin management • Order for Enforcement of the approach. The act was also amended in 2013 to formerly establish River Act the technical standards on the maintenance, rehabilitation, and • Regulation for Enforcement of inspections to maintain dams and other river management and the River Act permitted facilities in good condition. Erosion Control Act of 1897 Act for prevention and mitigation of damage from floods by designating erosion control areas and installing erosion control facilities. Coast Act of 1956 Act for protection of coasts from damage caused by tsunamis, storm surges, waves, and so on and for improvement and preservation of the coastal environment. Act on Specified Multipurpose Act on administrative procedure, ownership, and cost allocation for Dams of 1957 construction of multipurpose dams. (table continues next page) 24 Legal Foundations and Institutional Arrangements 25 TABLE 3.1 Key Laws and Regulations Relating to Dam Safety in Japan (Continued) Law or regulation Description Water Resources Development Act for water resources development and conservation for the Promotion Act of 1961 designated seven important river systems where basin-scale water resources management was required because of the rapid increase of population and industrial development. Order for Structural Standard for General technical criteria and standards for river structures River Administration Facilities of constructed under the River Act. 1976 Technical Standard for River Technical criteria and standards for investigation, survey, planning, Works of 1958 design, and O&M of river structures, which has been periodically upgraded to date. Act on the Japan Water Agency, Act on objectives and tasks of JWA, including its creation. Independent Administrative Agency of 2002 Land Improvement Act of 1949 Act on agricultural land development, agricultural land conservation, organization for O&M of agricultural land and related infrastructures, and so on. Technical Criteria for Planning Technical criteria and standards for investigation, planning, design, and Design of Agricultural Land and O&M of agriculture-related infrastructures, including irrigation Improvement Project (MAFF) ponds. of 1952 Basic Act on Disaster Basic policy on institutional arrangements, responsibilities, and Management of 1961 budgetary and financial arrangements for disaster prevention. Act on Special Financial Aid Act on the administrative procedures for special budget support to Cope with Severe Natural to local governments by the national government for damages by Disaster of 1962 extremely severe disasters. Note: This note conducted the translation of act/law names and others from Japanese to English with a primary focus on international readers better understanding the meaning, not necessarily following the most commonly used translation in Japan. JWA = Japan Water Agency; MAFF = Ministry of Agriculture, Forestry and Fisheries; O&M = operation and maintenance. RIVER ACT AS THE FOUNDATION FOR DAM SAFETY ASSURANCE Legal Foundation The River Act, enacted in 1896 and substantially amended in 1964 and 1997, is the fundamental act for river management in Japan underpinned by the concept of inte- grated river basin management approach. Its primary objectives are water-related disas- ter risk reduction, water resources development, and conservation of river environment. In response to the frequent and large floods that occurred in the late 1880s throughout Japan, the River Act was meant to promote flood controls and to specify the roles and responsibility for 26 Dam Safety Management in Japan river management. Initially, river administrators were prefectural governors or mayors of cities, towns, or villages, whereas the national government implemented strategically important or large-scale projects directly. To meet the increasing demands for water and electricity after World War II and to establish an integrated river basin management system, the River Act was amended in 1964, with the following key features: • Establishment of classification system of rivers and river administrators • Requirements to prepare an integrated basic plan for the river improvement works for flood controls and other waterworks in a river basin • Authorization of water rights by river administrators • Establishment of a river council comprising academics and dam experts for making recommen- dations to the Minister of Construction (Minister of Land, Infrastructure, Transport and Tourism since 2001) • Establishment of dam-operating regulations, including instructions for action during floods and intake regulation for droughts under the river administrators Classification of Rivers and River Systems Under the River Act, rivers and river systems are classified into Class A, Class B, and so on, according to their importance, as summarized in table 3.2 and shown in figure 3.1. TABLE 3.2 Definition of River Classes Classificationa Definition Designation River management Class A river Rivers that are part of river systems Minister • MLIT for the river segments (14,083) considered to be particularly of Land, with a particularly high level important for the maintenance of Infrastructure, of importance (presently 7 the land or national economyb Transport and percent of the total length Tourism of all rivers) • Prefectural governors for the other segments designated by MLIT Class B river Rivers that are part of river Prefectural governors (7,086) systems, not part of Class A rivers, but considered to be particularly important for the interests of the public Locally Rivers designated by the mayors of Mayors of municipal governments designated riverc municipal governments that are not Class A or Class B rivers Souce: MLIT 2023c. Note: MLIT = Ministry of Land, Infrastructure, Transport and Tourism. a. Numbers in parentheses indicate the number of rivers. b. Class A river includes all the prefectural transboundary rivers. c. Managed in accordance with the rules and regulations for Class B river. Legal Foundations and Institutional Arrangements 27 FIGURE 3.1 Classification of River Systems in Japan Specific section designated by the Minister of Land, Infrastructure, Transport and Tourism to be administrated partially by related prefectural governors Boundary between prefectures Managed by the Minister of Land, Managed by mayors of Managed by prefectural Infrastructure, governors or mayors of municipal governments Transport and government ordinance Tourism designated cities Class A river system Class B river system Other river system (109) (2,710) Class A river (directly managed segment) Class A river (designated segment) Class B river Locally designated river Nonclassified river (rivers outside the scope of the River Act) Source: Based on MLIT 2023c. Note: Numbers in parentheses indicate the number of river systems. Definition of Dams and Dam Safety Dam owners are responsible for dam safety, as the River Act clearly states that the technical standards of dams, levees, and other important river management facilities1 are stipulated by its ordinance in article 13. In article 44, a dam is defined as a river structure that is constructed with approval, as stipulated in article 26, paragraph 1, to store or intake the flowing water of the river and has a height of at least 15 m from the foundation to the crest.2 The 1997 Amendments In 1997, the River Act was amended to maintain and conserve the river environment in response to the needs for environmental conservation,3 including water quality and biodiversity.4 Under the amended River Act, public consultation of a river improvement plan is required to obtain and incorporate public opinions. The act also stipulates riparian forest zones around reservoirs and along levees to avoid contamination of reservoir water and inflow of sed- iments into the reservoirs and to improve the safety of the levees in the event of overtopping or breaching of the levees.5 As a lesson learned from frequent drought events that required water rationing in 1990s, amendments to the River Act promote drought management through coordination between river administrators and water users. In particular, article 53 of the amended River Act requires consultation and conciliation among the river administrator, water users, and other concerned agencies to reduce negative effects from extreme drought. To facilitate concerted water intake volume reduction at times of drought, the amended River Act provides a provision on exceptional arrangements for water utilization during droughts. 28 Dam Safety Management in Japan The amendments in 1997 also required river administrators to prepare the master plan for river improvement in two steps: (a) fundamental river management policy (article 16)6 and (b) river improvement plan (article 16-2) for each specific river system, covering dams, levees, and other river management facilities, in consultation with relevant stakeholders, as explained more in the next section. Institutional Arrangements River Management Authorities MLIT and prefectural governments are designated as river administrators pursuant to the River Act. They are responsible for managing rivers in terms of flood controls, water resources development, and river environment conservation in accordance with a fundamental river management policy and a river improvement plan formulated for each major river system in Japan. The former stipulates a comprehensive approach to river conservation and utilization of the river system. The latter sets forth concrete measures for construction and operation to be undertaken in accordance with the former. The river administrators are the prime regulator of dam design, construction, and O&M. Roles and responsibilities of the designated administrators and relationships with other entities for different purposes of dams are summarized in table 3.3. They regulate and must approve dam construction in the designated rivers under the River Act. In the case of multipur- pose dam projects, including flood control, developed by the river administrators, the dams are considered “river management facilities,” and hence there is no need to obtain specific approval, unlike single-purpose dams for hydropower and water supply. Although this is a sort of self-reg- ulation approach, MLIT conducts a semi-independent dam safety review with a dam basic design committee (DBDC). In addition, single-purpose dams for domestic water supply, irrigation, and power generation are subject to a business license scheme of the respective sectoral ministries, such as MLIT,7 MAFF, and the Ministry of Economy, Trade and Industry (METI). Dam design and construction should follow the technical codes, standards, and guidelines developed under the River Act, as discussed in chapter 4. Although ownership, licensers, regulators, and approvers of dams are determined based on the purpose of dams and river classification, MLIT is the supreme regulatory body for dams. Table 3.4 summarizes the responsibility of various organizations for different dam purposes. Even in the specific sections designated to be administered by prefectural gover- nors, MLIT still establishes all the regulations, guidelines, and manuals for dam safety and gives licenses or approvals for dam construction and operation. When a dam owner desires to start construction in a river covered by the River Act (that is, a Class A or Class B river), they must prepare a plan in compliance with the river improvement plan, formulated for most of the riv- ers in Japan and based on article 16-2 of the River Act. Also complying with the River Act, the owner must obtain permission from MLIT to use river water (article 23), occupy land in the river (article 24), and construct the dam (article 26-1). Prefectural governors who manage Class B rivers are still required to obtain approval from MLIT when they intend to (a) prepare or revise the fundamental river management policy and the river improvement plan, (b) grant use to river areas for any projects, or (c) grant water rights in accordance with the River Act. Legal Foundations and Institutional Arrangements 29 TABLE 3.3 Roles and Responsibilities of River Administrators and Other Entities Regulators/entities Responsibilities MLIT (for Class A • Preparation of a basic plana for dam construction river systems) • Approval of dam construction in coordination with related agencies and stakeholders • Approval of water rights for water users • Dam safety assurance throughout the project cycle Prefectural • Preparation of overall planb for dam construction government • Approval of dam construction in coordination with related agencies and (for Class B river stakeholders systems) • Approval of water rights for water users • Dam safety assurance throughout the project cycle JWA • Construction of dams in designated seven rivers as approved by MLIT and other relevant ministries • Coordination among various water users and stakeholders • Dam safety assurance throughout the project cycle MAFF or • Permission for water rights from MLIT prefectural • Approval of dam construction from MAFF government AFF • Dam safety assurance throughout the project cycle with the river administrators (irrigation) examination for some particular aspects Electric power • Permission for water rights from MLIT companies • Approval of dam construction from METI (private) • Dam safety assurance throughout the project cycle with the river administrators examination for some particular aspects Domestic water • Permission for water rights from MLIT supply utilities or • Approval of dam construction from MLITc municipalities • Dam safety assurance throughout the project cycle with the river administrators examination for some particular aspects Note: AFF = Agriculture, Forestry and Fisheries; JWA = Japan Water Agency; MAFF = Ministry of Agriculture, Forestry and Fisheries; METI = Ministry of Economy, Trade and Industry; MHLW = Ministry of Health, Labor and Welfare; MLIT = Ministry of Land, Infrastructure, Transport and Tourism. a. The basic plan contains (a) purpose of the development, (b) location and name of the project, (c) scale and type of the structure, (d) water storage capacity and reservoir volume allocation for each purpose, (e) licenses to be given for dam users, (f) construction cost for the project and cost allocation, (g) construction period, and (h) other considerations as necessary. The basic plan is prepared based on geotechnical investigation reports and detailed design of dams. b. The contents of the overall plan are similar to the basic plans prepared by MLIT. This is also prepared based on geotechnical investigation reports and detailed design of dams. c. As aforementioned, this has changed from MHLW to MLIT since April 2024. TABLE 3.4 Institutional Arrangements for Dams In Japan, by Purpose and River Class River Dam purpose classification Dam owner Licenser Regulatora Approverb Multipurpose including flood Class A MLIT n/ac MLIT MLIT control JWA MLIT MLIT MLIT Prefectural MLIT MLIT MLIT governmentd Class B Prefectural Prefectural Prefectural MLIT government government government (table continues next page) 30 Dam Safety Management in Japan TABLE 3.4 Institutional Arrangements for Dams in Japan, by Purpose and River Class (Continued) River Dam purpose classification Dam owner Licenser Regulatora Approverb Single- Irrigation Class A or MAFF, JWA, MAFF MLIT MLIT, MAFF purpose Class B prefectural government Hydropower Class A or Electric METI MLIT MLIT, METI Class B power company Industrial Class A or Local public METI MLIT MLIT, METI water Class B body Domestic Class A or JWA, MLIT MLIT MLIT water Class B domestic water supply utility, local public body Sources: Act on Specified Multipurpose Dams; River Act. Note: JWA = Japan Water Agency; MAFF = Ministry of Agriculture, Forestry and Fisheries; METI = Ministry of Economy, Trade and Industry; MLIT = Ministry of Land, Infrastructure, Transport and Tourism; O&M = operation and maintenance. a. River administrators permit river water use (granting water rights; article 23), river area occupation (article 24), and construction of new facilities within river zones (article 26). b. Approval is given for plan, design, construction, O&M manual, and so on per the Order for Enforcement of the River Act and for single-purpose dams per the respective sector acts, depending on their purposes. c. Because MLIT builds single-purpose and multipurpose dams, including flood control, as the river management facilities for its mandates, it does not need specific approval from itself. MLIT has established its own internal review/clearance mechanism using DBDC. d. Prefectural government refers to forty-seven local public bodies under the Local Autonomy Act comprising cities, towns, and villages. Under the River Act, prefectural governors are designated as the river administrators for Class B rivers. Dam Owners Dam owners are responsible for the safety management of their dams under the supervision of river administrators. The River Act stipulates the legal responsibility of dam owners, as described in table 3.5, to maintain the original function of the river, carry out meteo- rological and hydrological monitoring, record and report the status of dam operation to the river administrator, establish dam O&M rules, and so on. Legal Foundations and Institutional Arrangements 31 TABLE 3.5 Legal Responsibility of Dam Owners Provisions Description Maintenance of original If the condition of a river changes because of the construction of a dam, and function of a river the original functions of the river during floods are reduced, the dam owner (River Act art. 44) shall establish facilities necessary to maintain said functions or take alternative measures in accordance with the directions of the river administrator.a Monitoring of hydrological A dam owner shall construct observation facilities and observe reservoir situation water level, outflow and inflow discharges, and precipitation. (River Act art. 45) Report on the dam operation When a flood occurs or when it is apprehended that a flood may occur, a (River Act art. 46) dam owner shall report the results of observation under article 45 and the operational condition of the dam to the river administrator and the related prefectural governors. Establishment of dam When a dam owner intends to use the dam for storing or taking river water, operation rules he/she shall establish regulations for operating it and obtain the approval (River Act art. 47) of the river administrator. Preventive measures for Whenever a dam owner deems that the operation of the dam will cause damage a considerable change in the condition of the river water and that it is (River Act art. 48) necessary for prevention of the resulting harm, he/she shall in advance report the fact to the prefectural governor concerned; the mayors of the cities, towns, and villages concerned; and the heads of the police stations concerned and take necessary steps to make it known to the public. Preparation and custody of A dam owner shall prepare a record of the operation of the dam whenever operation record a flood occurs, keep it, and, when requested, submit it without delay to the (River Act art. 49) river administrator. Arrangement of a Chief In case a dam owner uses the dam for storing or taking river water, he/she Superintendent shall appoint, as chief superintendent for dam operation, an engineer with (River Act art. 50) the required qualifications by the Regulation for Enforcement of the River Act for proper execution of the O&M and other administration of the dam. Source: Omachi 1999. Note: O&M = operation and maintenance. a. For example, if the upstream water level during floods is raised, possibly causing disasters, required safety measures, such as building/raising the embankment structures, need to be implemented. Also, if the upstream flood discharge increases by the dam, necessary measures need to be incorporated into the design, such as including surcharge water level/volume for flood control, operation procedures, and so on. BOX 3.1 Environmental and Social Impact Management The environmental impact assessment (EIA) was introduced in 1972 “concerning the environmental conservation measures in relation to public works” by approval of the Cabinet. Subsequently, the EIA Act was enacted in 1997 and has been imple- mented since 1999. It defines two types of projects based on their scale. Whereas Class 1 projects always require EIA, Class 2 projects are individually assessed whether or not the authorizing agency requires an EIA. Dams with reservoir area of 100 ha or greater are categorized as Class 1. (box continues next page) 32 Dam Safety Management in Japan BOX 3.1 Environmental and Social Impact Management (Continued) The project proponent prepares the EIA in line with the procedure and steps defined by the EIA Act. During the screening, scoping, and preparation stages, the project proponent seeks opinions from the authorizing agency, such as the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), Ministry of Agriculture, Forestry and Fisheries (MAFF), and Ministry of Economy, Trade and Industry (METI), as well as the heads of relevant local governments and public. Also, the Minister of the Environment, who takes responsibility for the environ- mental protection, expresses its opinion on the EIAs, if necessary, to the authoriz- ing agency of the project. To mitigate social impact by the dam and its reservoir, the Act on Special Measures Related to Watershed Areas enacted in 1973 defines the provision of special sup- port measures for local governments, communities, and residents in areas directly affected by reservoir impoundment. Local governments prepare and the national government approves the development plan for the affected areas. The support measures include the construction of roads, water supply and sewerage systems, hospitals, schools, public houses, recreation facilities, and so on, which the national government subsidizes. Permits and Water Rights The River Act stipulates that any utilization of land and river water within the sec- tions defined by the River Act must obtain approval from the designated river admin- istrator. The rivers in Japan are public property, and their conservation, utilization, and other forms of administration shall be properly performed to attain the purposes stated earlier and that the water of rivers cannot be made the subject of private rights. Permits are issued as a regulatory tool to ensure the consistency of new water rights provision with the overall water availability and safety of the newly built struc- tures. The River Act stipulates that those who use river water or build hydraulic structures in river zones must obtain permission for the items listed in table 3.6 from river administrators. Applicants have to ensure dam safety to obtain a water right. For water allocation and permit issuance procedures, a water right is classified into the permitted water right and the customary water right in the River Act. The latter has been socially acknowledged based on a long-term irrigation water use that has continued before the establishment of a legal framework on water permits under the River Act. In river zones, a safety review of dam structures by the river administrator is required to obtain the former. Legal Foundations and Institutional Arrangements 33 TABLE 3.6 Permits to be Obtained by Dam Owners Provisions Description Permission for exclusive Any person who intends to use the water of a river shall obtain the use of river water permission of the river administrator as may be provided for in detail by the (River Act art. 23) Regulation for Enforcement of the River Act. Permission for land Any person who intends to occupy land within a river zone (excluding land occupancy administered by a person other than the river administrator on the basis of (River Act art. 24) his/her title) shall obtain the permission of the river administrator. Permission for construction Any person who intends to construct, reconstruct, or remove a structure of structures on the land within a river zone shall obtain the permission of the river (River Act art. 26-1) administrator. The same shall apply to any person who intends to construct, reconstruct, or remove a structure for storing or making stagnated the water of a river in the sea, near the estuary. Permission for excavation Any person who intends to perform excavation, cutting slope, embankment, works or other modification of the land, or cut or plant trees within a river zone (River Act art. 27-1) shall obtain the permission of the river administrator. Source: Omachi 1999. MULTIPURPOSE DAMS Legal Foundation The Comprehensive National Development Act was enacted in 1950 (later succeeded by the National Spatial Planning Act of 2005) to restore the national economy and lands that were devastated during World War II and catastrophic flooding disasters. As the first basic act for land planning in Japan, the objectives of the act were to comprehensively utilize, develop, and conserve land from economic, social, and environmental perspectives. The act spurred the rapid development of the nation, which led to a drastic rise in water demand. The following were enacted to support the high economic growth period (1950–73) by effectively developing and using water resources while ensuring flood controls: (a) Act on Specified Multipurpose Dams (1957), (b) Water Resources Development Promotion Act (1961), and (c) Water Resources Development Public Corporation Act (1961). The Act on Specified Multipurpose Dams enabled the Ministry of Construction (MLIT since 2001) to (a) administer the construction and administration of dams, (b) uniformly plan and manage multipurpose dams by developing a basic plan and operating protocols related to construction of a multipurpose dam, and (c) allocate a storage capacity for water users according to their application and to provide a property right to users (for example, domestic and industrial water supply or electric power). The Water Resources Development Promotion Act and Water Resources Development Public Corporation Act were enacted in 1961 by the Economic Planning Agency under the Prime Minister’s Office (which was transferred to MLIT in 2001). The water resources development basic plans (so-called ”full plans”) have been prepared with periodic reviews based on the former act for seven major Class A river systems,8 where basinwide integrated water 34 Dam Safety Management in Japan resources management is required to meet the increasing population and industrial develop- ment. Further, Water Resources Development Public Corporation (WARDEC; converted to Japan Water Agency [JWA] in 2003) was established in 1962, based on the latter act, and has been developing and managing water resources infrastructures, such as dams and water canals, in accordance with the full plan for the seven important river systems. Multipurpose dams provide flood control and regulate water use for irrigation, domestic water supply, and hydropower. Reservoir capacity is allocated for each purpose. Multipurpose dams are supposed to be operated such that reservoirs are full at the end of the flood season and the stored water can be released for domestic water supply and irrigation during the nonflood season, when downstream flow decreases. Each dam establishes its own reservoir operation rule but in a coordinated manner with others in the same basin. Institutional Arrangements Multipurpose/Flood Control Dams Administered by MLIT MLIT, including its regional bureaus and dam management offices, are responsible for planning, design, construction supervision, and O&M of multipurpose/flood control dams in coordination with the relevant ministries and prefectural governments based on the fundamental river management policies and plans. These are formulated in accordance with the River Act, the Act on Specified Multipurpose Dams, and related ordinances. DBDCs comprising leading dam experts in respective technical fields, such as hydrology, geology, seismicity, con- crete, soil mechanics, hydraulics, and so on—mainly from the Public Works Research Institute, the National Institute for Land and Infrastructure Management, and Japan Dam Engineering Center—provide technical support for reviewing the engineering designs and construction plans. Multipurpose Dams Administered by JWA JWA, which succeeded WARDEC in 2003, is responsible for water resources develop- ment and management in the seven designated major river basins based on the Water Resources Development Promotion Act (enacted in 1961) and Act on the Japan Water Agency, Independent Administrative Agency (enacted in 2002). The total basin area of these rivers accounts for approximately 17 percent of the national land and hosted approximately 53 percent of the national population in 2021. JWA mainly constructs and operates multipurpose dams, including flood control licensed by MLIT; however, it also develops and operates other purposes dams licensed by MAFF for irrigation and MLIT for domestic water supply. These dams need to be registered in the water resources development plan under the Water Resources Development Act for their corresponding basins, administered by MLIT in coordination with other relevant ministries and with the approval of the Prime Minister’s Cabinet Office. JWA prepares proj- ect implementation plans in coordination with relevant prefectural governments and with the approval of respective sectoral ministries, including cost allocation for construction and opera- tion, in line with the basin water resources development plan (figure 3.2). Legal Foundations and Institutional Arrangements 35 FIGURE 3.2 Coordination Mechanism for JWA’s Dam Development and Management Competent authorities MLIT MAFF METI Municipalities Inhabitant around Supervision facility Coordination Fishermens association JWA and so on Activity Other stakeholders Service Water resources development facilities Service Operation and Construction Water supply maintenance Waterworks bureau Irrigators association Flood control and discharge for maintenance flow Purification plant Irrigation Domestic Industrial Houses Factories Farmlands Source: Created by JWA for this publication. Note: Until March 2024, MHLW also supervised JWA as one of the competent authorities for water supply. JWA = Japan Water Agency; MAFF = Ministry of Agriculture, Forestry and Fisheries; METI = Ministry of Economy, Trade and Industry; MHLW = Ministry of Health, Labor and Welfare; MLIT = Ministry of Land, Infrastructure, Transport and Tourism. Multipurpose/Flood Control Dams Administered by Prefecture9 Prefectural governments are responsible for developing multipurpose/flood control dams in Class B rivers. The prefectural government prepares and submits an overall plan for dam development to MLIT for approval. The overall plan has to be in accordance with the fundamental river management policy and the river improvement plan. The prefectural govern- ment can request subsidies from MLIT for developing such dams and coordinates with MLIT for the design of dams and other associated facilities at various stages, including feasibility design, detailed design, first reservoir filling, and so on. The prefectural government also coordinates with other relevant agencies as required. IRRIGATION Law on Management and Protection of Irrigation Dams The Land Improvement Act, enacted in 1949 and amended multiple times through 2022, defines the design, construction, and O&M of the irrigation and other associated facilities, including dams and headworks under the jurisdiction of MAFF, involving agricultural department of local governments (that is, prefectures and municipalities), and land improvement districts (LIDs). 36 Dam Safety Management in Japan LIDs are agricultural farmers organizations founded under the act and have the role of farmland and related infrastructure development and management. There are 4,095 in 2024, with an average of about 590 ha and 820 members per district (MAFF 2024). LIDs are the core organi- zations in ensuring dam safety as they are responsible for the sustainability and maintenance of the irrigation dams and other facilities. Farmers under LIDs are legally obligated to participate in the O&M works and cover the costs for securing their functions. In 2023, LIDs operated and maintained about 60 percent of irrigation dams and canals. Municipality and prefectural govern- ments covered most of the remaining infrastructure; the national government—that is, MAFF— operated few irrigation infrastructures. In addition to irrigation dams regulated by the River Act, there were more than 150,000 irrigation ponds in 2023; of those irrigating more than 2 ha, 70 percent were built in the nineteenth century or well before. Because almost all of them were not constructed per the modern design and quality management, managing their safety has been a challenge. Considering the fatal consequences (eight people dead or missing) of the failure of an irrigation pond (Fujinuma-Ike) by the Great East Japan Earthquake in 2011 and in response to thirty-two irrigation ponds failing because of heavy rains in western part of Japan in July 2018, MAFF conducted a nationwide survey inspecting 88,130 irrigation ponds and identified 1,504 risky ponds that required temporary remedial measures (including reser- voir drawdown) against severe storms (MAFF 2018a). Considering the risks associated with irrigation ponds, the Act on Management and Conservation of Irrigation Ponds was enacted under the jurisdiction of MAFF to ensure the proper management and con- servation of irrigation ponds for securing irrigation water and reducing risks by ponds failure in 2019. It introduced key measures, such as (a) owners’ requirement of submitting information on irrigation ponds to prefectural governments; (b) preparation and disclosure of irrigation ponds database by prefectures; (c) prefecture governments’ designation of specified irrigation ponds that would cause downstream consequence in case of failures; and so forth. Moreover, designated specified irrigation ponds require additional measures, including munici- palities’ preparation and dissemination of hazard maps, indicating flooding areas/depth in case of pond failure for local residents‘ safe evacuation.10 WATER SUPPLY The domestic and industrial waterworks are also subject to the River Act if water is drawn from a designated river. The project proponents must obtain the required permission and approval from the river administrator if any river structure is constructed in a river desig- nated by the River Act. In principle, the relevant river administrator grants permission for ten years if the proposed intake is not deemed to pose a threat to existing water users. In the event of extreme drought, water users in the relevant river system must cooperate and participate in stakeholder consultations to adjust the intake amounts as facilitated and mediated by the river administrator in accordance with the River Act. Local governments, including prefectures, cities, towns, as well as domestic water utilities and industrial water supply entities, can construct and operate dams for domestic and/or industrial water supply. The project-promoting and operating entities are Legal Foundations and Institutional Arrangements 37 required to obtain permission for water rights and dam construction by river administrators and accommodate their periodic safety inspection in accordance with the River Act. In addition, the domestic water supply projects are licensed and regulated by MLIT and the industrial water supply projects by METI. MLIT also carries out regular inspection for the water supply dams operated by prefectural governments. HYDROPOWER In 1952, the Electric Power Development Promotion Act was enacted, and the Electric Power Development Co., Ltd. (J-POWER) was established to directly invest govern- ment funds in regions where power development was difficult.11 The act established the Electric Power Development Coordination Council to centrally develop, approve, and imple- ment a long-term electricity supply plan and prepare an annual implementation plan. Electric power generation is regulated by METI under the Electricity Business Act of 1964. To diversify energy sources in the wake of the oil crisis in 1973 and to obtain stakeholder consensus for further hydropower development, three basic acts were enacted in 1974.12 Per the 1997 Act on Special Measures Concerning the Promotion of New Energy Usage, small, mini, and micro hydroelectric power of less than 1,000 kW is considered “new energy” and regulated by the 2011 Act on Special Measures Concerning Procurement of Electricity from Renewable Energy Sources by Electricity Utilities. When an electric power company intends to build a hydropower plant, the company must submit an electricity generation application and get permission from METI and from the relevant river administrator when the river structure is built in a river des- ignated by the River Act. The structural standards for hydroelectric power plants and the daily, annual, and maximum intake of river water are regulated by the River Act. In principle, the relevant river administrator grants an intake permission for hydroelectric power generation for twenty years. They also carry out regular inspection for the hydropower dams operated by the electric power companies. In the event of a natural hazard such as flooding, the hydropower dam owners must cooperate with the relevant river administrator and carry out emergency operations per their instruction. Electric power companies have also developed safety assurance systems and proce- dures to address specific safety needs related to the hydropower sector in line with the dam safety framework under the River Act. For example, J-POWER has established a dam safety management system supervised by the Advisory Committee on Safety Evaluation of Hydropower Facilities that includes external technical experts to independently evaluate dam safety. Based on information from regular inspections, surveillance, as well as monitoring data, such as deformation and leakage and facility deterioration checks, potential risks are identified using failure mode analysis. 38 Dam Safety Management in Japan INSTITUTIONAL ARRANGEMENTS FOR DAM SAFETY ASSURANCE AND CAPACITY BUILDING Dam Safety Review Mechanism DBDC has been established to review all multipurpose/flood control dam projects under MLIT and prefectural governments and thus plays a pivotal role in providing semi-independent technical oversight and ensuring dam safety. It comprises representa- tives of the supervising authority and a group of leading dam experts in key technical subjects, such as geology, seismicity, hydrology, design of concrete dams, rockfill dams, and so on. A DBDC meeting is held at critical milestones in a dam project, such as when the decision on the dam axis is made, commencement of detailed dam design, approval for dam construction, and initiation of reservoir impounding. The committee closely examines the geological conditions of the dam foundation, compliance of the dam design to standards, investigation results of dam sites, and other key items on dam safety. The project may not proceed to the next implementa- tion stage, including any budgetary arrangement, without committee approval. Therefore, dam project officials diligently prepare documents, check the quality of site investigation works, and so on. A similar technical oversight arrangement is made for hydropower dams under electric power companies. Role of In-House Engineers, Consultants, and Contractors In-house engineers of the dam owners and promoting entities, such as MLIT, MAFF, JWA, and electric power companies, are primarily responsible for project manage- ment, designing, construction supervision, and O&M of dams at their construction and management offices. Many of those entities have their own research institutes for tech- nological development and practical application to operational projects as well as educational/ training institutes for in-house engineers’ capacity enhancement and learning. Those ministries, agencies, and companies also work with private consulting companies that have experience and skills in geology, hydrology, structural analysis, design, and so forth at plan- ning, design, and construction phases. Civil contractors carry out construction works under the supervision and instruction of the dam construction office, where quite a number of in-house engineers are assigned. These three parties maintain daily communication, coordination, and cooperation to ensure smooth and expeditious project implementation as well as dam safety. The in-house engineers of the river administrators under MLIT are responsible for reviewing and clearing owners’ dam safety works, including designs, excavated foundation quality, O&M plan, and so on. Education and Training Because the quality of dam safety depends on the capacities and capabilities of engi- neers, training programs and a qualification system have been established and main- tained for both the public and private sectors. As aforementioned, MLIT, MAFF, JWA, and electric power companies have their research and educational institutes or groups in which a number of top-notch experts are designated for their respective fields and provide training for younger staff. The training of in-house engineers from different entities, such as prefectural gov- ernments, also establishes a network among them, which can be instrumental for their careers as they can call on one another during various projects. Legal Foundations and Institutional Arrangements 39 Civil contractors are required to place certified chief managing engineers for dam construction at dam construction offices. The dam owners also have experienced in-house engineers for con- struction supervision and quality control in place. BOX 3.2 The Development of the Japanese Roller-Compacted Dam by MOC In-House Engineers The Ministry of Construction (MOC)—Ministry of Land, Infrastructure, Transport and Tourism (MLIT) since 2001—developed the design and construction method of the roller-compacted dam (RCD) for building concrete gravity dams in a much faster and cost-effective manner, maintaining the same functional and safety requirements as conventional concrete gravity dams. After a full-scale test con- ducted at the cofferdam of Okawa Dam in 1976, MOC constructed the main RCD— the 89-m-high Shimajigawa Dam—from 1978 to 1980. It was the world’s first major dam using roller-compacted concrete (RCC).a The in-house engineers of MOC at headquarters, dam construction offices, research institutes, and others played a central role for developing the technical standard and guidelines for RCDs in collaboration with consulting firms, suppliers, and con- tractors. Various kinds of advanced machinery and equipment were developed for concrete mixing, transportation, spreading, compacting, cutting of joints, and so on. New quality control methods were also established using advanced moni- toring equipment, such as a nuclear density gauge for checking concrete density and compaction. The MOC engineers continued advancing the RCD construction technology for building higher dams, including the Tamagawa Dam (100 m high, 1987), Miyagase Dam (156 m high, 1996), and Urayama dam (156 m high, 1998), in collaboration with consulting companies and civil contractors. They also devel- oped the technical standard and constructed trapezoidal cemented sand and gravel dams for enhanced safety and economic efficiency since the 1990s, includ- ing some 100-m-high class dams. These projects helped engineers advance their skills and experiences through actual design and construction supervision, which also contributed to enhancing the quality of design and construction works.b Note: a. The ICOLD Bulletin 126 in 2003 and Bulletin 177 in 2018 on RCCs notes, “After the extensive use of RCC for repair work and coffer dams at Tarbela Dam (Pakistan) in 1975, the first significant RCD dam, Shimajigawa Dam (89 m in height) was completed in Japan in 1980, and the first significant RCC dam, Willow Creek was completed (52 m in height) in the USA in 1982. b. The Guanyinge (Kwan-in-Temple) Multipurpose Dam in Liaoning Province, China, was constructed under Japanese Official Development Assistance (ODA) loan using the Japanese RCD construction method. The dam is 82 m in height, 1,040 m in crest length, and 2.2 billion m3 in reservoir capacity. The dam’s purpose was flood control; domestic, industrial, and irrigation water supply; and hydropower generation. The volume of the concrete body was 1.97 million m3. The project implementation period was between 1988 and 1997. The implementing agency was Liaoning Provincial Water Resources and Electricity Department. Japanese RCD experts provided technical advisory and construction supervision service. For more information, see https://www.jica.go.jp​/­Resource/english/our_work/evaluation/oda​ _loan/post/2000/pdf/02-01.pdf. 40 Dam Safety Management in Japan NOTES 1. The river management facilities include not only dams, barrages, levees, and dikes but also gates, river- bed protection works, and riparian forest zones along rivers and dam reservoirs. 2. Ponds built in other river systems (non–Class A or non–Class B river systems) are not subject to the dam safety regulation under the River Act, even if the height of the pond is higher than 15 m. 3. For the overarching environmental management, the Basic Act of the Environment and the Environmental Impact Assessment Act were enacted in 1993 and 1997, respectively, under the juris- diction of the Environmental Agency and, since 2001, under the Ministry of the Environment (MOE). 4. Guidelines for fishway design were developed for promoting the installation of fishways to dams and barrages considering various types of fish and riverine conditions (Nakamura 1995; MLIT 2005b). 5. Article 1 of the Regulation for Enforcement of the River Act stipulates that the riparian forest zones around reservoirs are located within approximately 50 m from the line at surcharge flood water level of the reservoir. 6. The direct translation is basic principles for river improvement for long-term policies. 7. As aforementioned, MLIT has assumed the jurisdiction for domestic water supply from the Ministry of Health, Labor and Welfare (MHLW) since 2024. 8. Tone, Ara, Toyo, Kiso, Yodo, Yoshino, and Chikugo River systems. The location of each river system is shown in figure 4.1. 9. Prefectures of Japan are the country’s first level of jurisdiction and administrative division larger than cities, towns, and villages. There are forty-seven prefectures of the island nation. Each prefecture’s chief executive is a directly elected governor. Ordinances and budgets are enacted by an assembly whose members are elected for four-year terms. 10. Furthermore, the Act on Special Measures for the Promotion of Disaster Prevention Works for Disaster- Prone Irrigation Ponds was enacted in 2020 to provide adequate financial and technical support for accelerating required risk mitigation measures for irrigation ponds prioritized for disaster prevention. In line with the basic guideline by MAFF, prefectures prepare plans for promoting the execution of required remedial works, for which MAFF will provide necessary financial support for prefectures. 11. The Electric Power Development Promotion Act was repealed in 2003, and J-POWER was fully privat- ized in 2004. 12. The Act on Tax for Promotion of Power-Resources Development, the Act on Special Account for Electric Power Development Promotion, and the Act on the Development of Areas Adjacent to Electric Power Generating Facilities. CHAPTER 4 Regulatory Regime for Design, Construction, and O&M OVERVIEW A holistic set of technical standards and their application system have been developed in Japan to build and operate about 2,000 dams safely, economically, and efficiently, considering the diverse natural and socioeconomic conditions. The system comprises (a) a set of technical stan- dards closely connected with acts and regulations, (b) a procedural framework to examine the compliance of dam design and works to the standards, (c) organizational structures and a capacity-​building system through which the standards are thoroughly reflected on the works, (d) an effective and economical monitoring and inspection system to ensure safety and smooth operation of completed dams, and (e) a research and development (R&D) system that develops advanced technology for dam safety. The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) and its minister, as the river administrator, issue various ordinances, technical standards, guidelines, and so on to guide the safety assurance and management of the dam. MLIT is the authority over dam safety and reviews the safety aspects of all dams higher than 15 m. No particular dam classification system is used given that virtually all dams are considered as potentially high-consequence dams; most cities, towns, and communities have been developed along the downstream of steep rivers that are vulnerable to flooding disasters. The dam owners must prepare dam operation and mainte- nance (O&M) rules in compliance with the River Act and related guidelines and receive approval from MLIT. RIVER BASIN-SCALE PLANNING Multipurpose dam project plans are based on the fundamental river management policy and river improvement plan of specific river systems, formulated for most rivers in Japan. The former is the foundational plan of flood control, water use, and river environment, which should be formulated under the River Act for each river basin—defining flood discharge to be controlled, flood water level, river flow rate to be maintained in the river to conserve the river environment and water use, and so on. The latter is formulated for each river basin to determine purposes, types, locations, and scales of river management facilities to be constructed and maintained in the river for achieving the targets defined by the former. 41 42 Dam Safety Management in Japan The river basins of the seven important river systems (Tone, Ara, Toyo, Kiso, Yodo, Yoshino, and Chikugo River systems) designated under the Water Resources Development Promotion Act of 1961 cover major urban areas with a significant concentration of population and industry, as in map 4.1. The multipurpose dams constructed by the Japan Water Agency (JWA) in the river systems designated by the Water Resources Development Promotion Act need to be authorized by the water resources development basic plans, considering basin-scale water resources management. JWA is required to obtain necessary permissions from the river admin- istrators, according to the River Act, for dam development. The basic plans should be formulated for the seven river systems for basin-scale water resources management. MAP 4.1 Seven Important River Systems Designated Under the Water Resources Development Promotion Act TONE and ARA river systems KISO river system YODO river system TOYO river system YOSHINO river system CHIKUGO river system Source: Adapted from MLIT 2023a. Regulatory Regime for Design, Construction, and O&M 43 KEY DESIGN STANDARDS To design and construct the defined dams properly, a number of standards and guide- lines have been established. Among them, the principal code for dam design in Japan is the Order for Structural Standard for River Administration Facilities1 under the River Act. The order actually covers the design standard of both river management facilities and permitted facilities, including dams, barrages, levees/dikes, intake structures, spillway/sluice gates, protec- tion works, and riparian forest zones around reservoirs and so on, specifying basic design loads, methods, and criteria. A detailed explanation of design methodology is developed using various design standards and criteria, such as Technical Standard for River Works, developed by MLIT, and Technical Standard for Planning and Design of Agricultural Land Improvement Project, developed by the Ministry of Agriculture, Forestry and Fisheries (MAFF).2 These standards and criteria are required to be applied with due consideration to actual site conditions, and they are adequately detailed not to be applied arbitrarily. SEISMIC DESIGN STANDARDS Distinctive features of Japanese dam standards include a systematic and detailed dam design system for natural hazards, in particular for seismic resilience. The seismic design concept was already considered in one of the earliest modern dams of Japan in 1930 as the country had been frequently hit by severe earthquakes throughout its history. Experiences and lessons since then have been reflected to form the current advanced dam design standards for seismic resilience. These are applied, covering planning, design, and construction, and O&M stages, including emergency dam inspection and rehabilitation after earthquakes. The standards ensure that a dam does not incur damage by a generally foreseeable earthquake motion (which is called Level 1 class earthquake motion) nor major (irreparable) damage that may affect the storage function of the dam by a probable maximum earthquake motion (which is called Level 2 class earthquake motion) through dynamic stability analyses.3 Also, for dam sites selection, a detailed seismic hazard assessment, including an analysis of the dis- tribution and direction of probable active faults and lineaments around the dam site and reservoir areas, has identified approximately 2,000 active faults in Japan. The faults can be verified based on literature review, aerial photo analysis for lineaments, and detailed field surveys. It is a standard requirement to avoid such sites. A number of database, digital maps, and inventories have been compiled, covering all identified active faults in Japan by the Geospatial Information Authority of Japan/MLIT, the University of Tokyo, and so on. The potential active faults are also carefully examined for each dam site. The seismic safety records of modern dams have proved the robust- ness of Japan’s dam design system and quality construction and O&M works. Although about fifty earthquakes with a magnitude of 7.0 or higher have occurred in Japan over the past 100 years, dams have not been seriously damaged to the extent of affecting their safety, except for minor ones. The safety records of modern dams against earthquakes also prove the effectiveness of the dam safety assurance system in Japan thanks to rigorous standards for seismic hazard assessment and design. The required monitoring instrumentation and warning system help owners identify critical dams and undertake immediate post-earthquake inspection. A large set of seismogram data on dams’ crest and foundation has been accumulated, analyzed, and globally disseminated, including earthquake acceleration records and dams’ structural responses, which also contributed to seismic safety of dams.4 44 Dam Safety Management in Japan BOX 4.1 The Great East Japan Earthquake The Great East Japan Earthquake—also known as the 2011 off the Pacific coast of Tohoku Earthquake—occurred in northeastern Japan on March 11, 2011, with a 9.0 magnitude that caused widespread damage to the eastern coastal area of Honshu Island. The National Research Institute for Earth Science and Disaster Resilience recorded strong motions at more than 1,200 locations, indicating the peak ground acceleration (PGA) in excess of 1.0 g at twenty locations. Strong motion recorded at more than seventy dams indicated the PGA between 0.1 and 0.5 g. The duration of the motion was from 150 to 300 seconds, which is extraordinarily long, because of the consecutive rupture of two plates of north and south. The distribution of PGA is indicated in map B4.1.1, showing that quite large areas along the Pacific Sea for more than 300 km experienced PGA of about 0.2 to 1.0 g. MAP B4.1.1 Peak Ground Acceleration (cm/s2) During the Great East Japan Earthquake 45' PGA [gal] 2000.0 40' 1000.0 500.0 200.0 100.0 50.0 20.0 35' 10.0 5.0 2.0 1.0 0.5 30' 0.2 130' 135' 140' 145' Source: National Research Institute for Earth Science and Disaster Resilience 2023. Note: PGA = peak ground acceleration. (box continues next page) Regulatory Regime for Design, Construction, and O&M 45 BOX 4.1 The Great East Japan Earthquake (Continued) The number of dams in the affected areas for respective owners is indicated in table B4.1.1. Dam owners carried out emergency visual inspection for about 400 dams immediately after the earthquake. There were no reports of damages that may have caused serious compromises to dam safety. Only small incidents, such as minor or moderate cracks on dam crests and spillway concrete and temporary increases of leakage, were noted from some dams. A survey team from the Public Works Research Institute and the National Institute for Land and Infrastructure Management with MLIT was dispatched to investigate and evaluate safety for five dams in which relatively large cracks and increase of leakage were reported. The survey and evaluation concluded that urgent remedial measures were not nec- essary, but continuous monitoring by instrumentation was recommended. These results show that the dams under the current River Act have sufficient safety for large-scale earthquakes such as the Great East Japan Earthquake. TABLE B4.1.1 Dams in the Areas Affected by the Great East Japan Earthquake Number of dams Jurisdiction (Number of Suffered unusual behaviora dams) Owner Inspected or damage (falure) MLIT Central government 46 11 (150) Local government 104 8 MAFF Central government 51 4 (172) Local government 121 23(lb) Electric power Hokkaido Electric Power Co., Inc. 8 0 companies (69) Tohoku Electric Power Co., Inc. 24 0 TEPCO 29 1 J-POWER 7 1 KEPCO 1 0 Total 391 48(1) Source: Matsumoto, Sasaki, and Ohmachi 2011. Note: TEPCO = Tokyo Electric Power Corporation; J-POWER = Electric Power Development Co., Ltd.; KEPCO = Kansai Electric Power Co., Inc. a. Unusual behavior: Small increase of leakage and uplift, nominal settlement, and others. b. The failed one was on a nonregulated river. 46 Dam Safety Management in Japan BOX 4.2 Continued Seismic Changes—Noto Peninsular Earthquake (January 2024) The Noto Peninsular Earthquake occurred on January 1, 2024, affected a total of ninety-six dams, including one barrage, in Ishikawa, Toyoma, Niigata, and Fukui prefectures. The magnitude was 7.6 (Japan Meteorological Agency [JMA] scale), and the Japanese seismic intensive was 7 (maximum). Although ninety-four dams reported no damages through the primary and secondary aftershock inspections, two dams—Oya and Kitakawachi Dams—were reported as partially damaged, and temporary rehabilitation measures were quickly undertaken. Hakkagawa Dam also observed strong ground motion of more than 300 gal. MAP B4.2.1 Seismic Intensity Distribution and Location of Three Dams Subject to 300-Gallon Seismic Motion Oya Dam Suzu Kitakawachi Dam Wajima Noto Hakkagawa Dam Strong ground motion observed but no damage reported Anamizu Epicenter 7 Shika 6+ Nanao 6– Nakanoto 5+ 5– Hakui 4 (box continues next page) Regulatory Regime for Design, Construction, and O&M 47 BOX 4.2 Continued Seismic Changes—Noto Peninsular Earthquake (January 2024) (Continued) TABLE B4.2.1 Three Dams’ Seismic Impacts and Damages Horizontal maximum Distance Seismic intensity acceleration Dam name from at nearest (gal) [type] Height epicentera observatory (name Reported damage to (completed) (m) (km) of observatory) Base Top dam body Oya 56.5 9.4 6+ 528 648 Cracks at the dam [Rockfill] (Matsunami, Noto) crest road pavement. (1993) Partial deformation of the surface coating on the dam body. Dam body subsidence (maximum 36 cm at the top). Damage to the retaining wall at the plaza next to the administration building. Kitakawachi 47.0 5.7 6− 487 1,087 No reported damage [Concrete (Yanagida, Noto) on the dam body. gravity] Drain pump failure (2011) because of partial inundation in gallery. Hakkagawa 52.0 7.8 7 310 1,603 No reported damage. [Concrete (Hashiride, Wajima) gravity] (1995) Source: Based on MLIT 2024c. a. Minimum distance from epicenter fault (Geospatial Information Authority model). REQUIREMENTS FOR OPERATION AND MAINTENANCE Dam Operation Rules and Manuals The O&M rules and manuals for dams, including for spillway gates and valves, must be approved by river administrators or MLIT before the commencement of operation. After issuance of the approval, the operation rules shall be effective. These dam operation rules and regulations are usually established with unified articles, although details are changed sub- ject to the conditions of each dam. A set of laws, rules and regulations, and manuals have been developed to ensure a high safety level, which allows resilience in O&M practices for dams under various social and natural conditions. The River Act stipulated the O&M responsibility of dam owners (table 4.1). 48 Dam Safety Management in Japan TABLE 4.1 Extracted Articles of the River Act Regarding Dam O&M Requirements Article Provision Monitoring of A dam owner shall construct observation facilities and observe reservoir water hydrological situation level, outflow and inflow discharges, and precipitation in accordance with the (River Act art. 45) standards that may be fixed by the Order for Enforcement of the River Act. Report on the dam When a flood occurs or when it is apprehended that a flood may occur, a operation dam owner shall report the results of observation under article 45 and the (River Act art. 46) operational condition of the dam to the river administrator and the related prefectural governors, as may be provided for in detail by the Order for Enforcement of the River Act. Establishment of dam When a dam owner intends to use the dam for storing or taking river water, operation rules he/she shall establish regulations for operating it and obtain the approval of the (River Act art. 47) river administrator concerning the regulations, as may be provided for in detail by the Order for Enforcement of the River Act. The same shall apply in case he/she intends to revise the regulations. Preventive Whenever a dam owner deems that the operation of the dam will cause a measures for damage considerable change in the condition of the river water and that it is necessary (River Act art. 48) for prevention of the resulting harm, he/she shall in advance report the fact to the prefectural governor concerned; the mayors of the cities, towns, and villages concerned; and the heads of the police stations concerned and take necessary steps to make it known to the public, as may be provided for in detail by the Order for Enforcement of the River Act. Preparation and A dam owner shall prepare a record of the operation of the dam whenever custody of operation a flood occurs, keep it, and, when requested submit it without delay to the record river administrator, as may be provided for in detail by the Regulation for (River Act art. 49) Enforcement of the River Act. Instructions for flood In case a disaster has been caused or there is a strong probability that a disaster control will be caused by floods, if the river administrator deems it of urgent necessity (River Act art. 52) for preventing or minimizing the disaster, he/she may instruct a dam owner that he/she should, on the basis of overall consideration of the conditions of the rivers belonging to the water system, take necessary action in connection with the operation of the dam to prevent or minimize the disaster. Water uses In case an unusual drought makes it difficult to adequately use the river water conciliation during for the permitted utilization or when such a situation is expected, the people droughts who have obtained permissions to use the water (hereinafter “permitted water (River Act art. 53) users”) shall make efforts to consult with one another. In this case, the river administrator shall exert himself/herself to provide necessary information for water use conciliation to achieve a smooth consultation. Source: Omachi 1999. Note: O&M = operation and maintenance. Article 14 of the River Act notes that a river administrator must formulate an oper- ation rule that complies with a related ordinance for each river management facility operated by the river administrator (table 4.2). Article 47 of the River Act mentions that a dam owner who intends to use the dam to store and withdraw water from intake facilities must formulate an operation rule and obtain approval for it. Further, article 16 of the Act on the Japan Water Agency, Independent Administrative Agency mentions that JWA must formulate a “management rule of structure” for a structure built by JWA based on the water resources development basic plan. Regulatory Regime for Design, Construction, and O&M 49 TABLE 4.2 Legal Basis of Operation Rules for Dams for Different Purposes and Ownersa Dam purpose Responsibility (dam owner) O&M plan and manual Base law Multipurpose and flood Minister of Land, Infrastructure, Operation rule River Act art. 14 control Transport and Tourism, prefectural governor (the river administrators) JWAb Management rule of Act on the Japan Water structure Agency, Independent Administrative Agency art. 16 Single-purpose MAFF, local government, electric Operation rule River Act art. 47 (irrigation, hydropower, power company, and so forth domestic, and industrial) Sources: Act on the Japan Water Agency, Independent Administrative Agency; River Act. Note: JWA = Japan Water Agency; MAFF = Ministry of Agriculture, Forestry and Fisheries; O&M = operation and maintenance. a. The need for the environment impact assessment (EIA) under the EIA Act for the operational rule changes by existing dams’ upgrading/restoration will be determined based on its criteria. However, an adequate level of the environmental assessment is required to protect the riverine and reservoir environment and to incorporate required mitigation measures, such as the conservation of ecosystems by biotopes, fishways, and water quality to prevent turbid and cold water and reservoir eutrophication, regardless of whether EIA Act procedures are required (MLIT 2018a). b. JWA operates both multipurpose and single-purpose dams. Good practices and examples of dam operation rules are presented in the Dam Management Rule Book, prepared by MLIT. The operation rules regarding flood control, allocated storage volumes, and water supply amounts should be consistent with the concerned dam basic plan, the river improvement plan, and the water resources development basic plan. In addition to the general operation rules, the dam owner must establish the operation manual for extraordinary floods that exceed the planned flood discharge for flood control, which is related to dam safety. Operation Rules for Single-purpose Dams Dam owners conduct reservoir operations for water supply and hydroelectric gener- ation based on the operation rule that the river administrator has approved (River Act art. 47). Water supply operations are conducted according to water rights permits. Dam owners observe river discharge at downstream control points to determine how much water should be released from the dam. Water supply operations should be conducted within the storage volume allocated for water supply and flow rate, which are stipulated in the reservoir operation rules for each dam, because the amounts that users can take are stipulated in the permissions issued during dam development. Environmental Flow Management The principal purpose of the river in-stream flow is stipulated as “maintenance and environ- mental flow” by article 1 of the River Act as “The purpose of this Act is to contribute to land 50 Dam Safety Management in Japan conservation and development of the country and thereby maintain public security and promote public welfare by administering rivers comprehensively to prevent damage due to floods, high tides, etc.; use rivers properly; and maintain the normal functions of the river by maintaining and conserving the fluvial environment.” MLIT issued a guideline in 2007 on how to determine the required volume of in-stream flow for different river sections and season/timing considering the earlier items (MLIT 2007). This is reviewed and defined in the river improvement basic principle and plan for each river. The in-stream flow requirement is also reflected in the dam basic plan and design, as well as the reservoir operation rules, in addition to its environmental impact assessment consultation and certification process.5 It also issued a guideline for fishway design to dams and barrages, including selection of suitable types of fishways considering the fish species, size, swimming capacity, reservoir operation, and so on (MLIT 2005b). MLIT also has introduced dynamic reservoir operation procedures allowing dam oper- ators to store some flood discharge water in the reservoirs toward the end of floods to its end with its safety confirmation. The stored water will be used for subsequent and intermittent flush discharge operations to mimic the natural river flow regime and contribute to reviving the natural riverine ecosystem and water quality through removing adhesive algae from riverbed rocks, and so on. Sediment Management Although most dam catchments are generally well protected by forest conservation (under the Forestry Agency, MAFF), some along the Fossa Magna, a great rift or tectonic line that traverses the widest portion of Honshu in the north-south direction, have high soil erosion and sediment deposit in reservoirs because of the fragile geological condition of the area (map 4.2). Thus, sed- iment management is an important subject not only for water storage but also for dam safety because it possibly reduces flood attenuation capacity of the reservoir, outlet works of the dam, and so on. The dead storage volume of dams is based on the estimated sediment deposits in reservoirs for 100 years per the Technical Standards for River Works under the River Act.6 Sediment deposit volume in most dam reservoirs is annually checked by bathymetric survey for updating the live storage volume for flood control and water supply. For the reservoirs with high sediment deposits, suitable sediment management measures are incorporated, reflecting the dam/reservoir profiles and sediments characteristic, either in the original designs or in a retrospective manner. The options include the construction of check dams; dredging and excavations of sediment deposits; bypass tunnel to transport water with a high concentration of sediment to downstream river; turbidity current venting; periodic sediment sluicing (with res- ervoir drawdown); and flushing, including coordinated cascade dam operation with due consid- eration to the environmental aspects. Other methods include sediment replenishment to rivers below dams: Sediment from dam reservoirs or check dams is excavated, transported, and depos- ited in the river channel downstream of the dam, which then gets washed to downstream rivers using the natural hydraulic force of flood discharge. Although this method does not provide a fundamental solution for dams with a significant volume of sedimentation, it is economically Regulatory Regime for Design, Construction, and O&M 51 and technically feasible without large-scale facilities. Therefore, it has been implemented in many dams, mainly in small and medium-sized rivers, to reduce sedimentation in reservoirs and improve downstream river environments (MLIT 2011b; Ock, Sumi, and Takemon 2013). MLIT aims to manage sediment issues on a basin scale in an integrated manner, includ- ing upstream erosion control (Sabo in Japanese) and coastal management works (under the Erosion Control Act and the Coast Act, respectively) together with dams and rivers. It issued a guideline for reservoir sediment management in 2018, which summarizes the basic concept of an integrated sediment management from sediment survey and monitor- ing to decision-making steps for assessing and prioritizing management and remedial measures including construction and O&M cost implications (MLIT 2018b). MAP 4.2 Basin-Level Erosion Rate Potential Map Specific sediment Volume (103m3/km2/year) 1.6–4.6 0.8–1.6 0.5–0.8 0.3–0.5 0.2–0.3 0.1–0.2 0–0.1 0 250 500 Kilometers Source: Adapted from Hasegawa, Wakamatsu, and Matsuoka 2005. 52 Dam Safety Management in Japan BOX 4.3 Sediment Flushing by Dashidaira Dam (KEPCO) and Unazuki Dam (MLIT) The Dashidaira Dam (124 megawatts), managed by the Kansai Electric Power Co., Inc. (KEPCO), and the multipurpose Unazuki Dam, managed by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), are located on the Kurobe River—a steep river with severe erosion and sediment deposit (the specific sedi- ment yield is estimated at about 3,300 m3/km2/year). They have flushed sediment cooperatively to maintain the capacity of the dam reservoir for flood control and power generation on the Kurobe River and Toyama Bay coast. After a decade, sedimentation reduced half of the storage capacity of Dashidaira, causing a problem of the intake facility and a reduction in water storage capac- ity. A combination of sluicing and flushing techniques has successfully resulted in maintaining the reservoir storage capacity. This operation is implemented once per year in coordination with the downstream Unazuki Dam in three steps: the rapid drawdown of the reservoir, flushing and sluicing, and filling the reservoir again (figure B4.3.1; photo B4.3.1). FIGURE B4.3.1 Integrated Sediment Flushing on the Kurobe River a. Drawdown Dashidaira Dam Drawdown Unazuki Dam Drawdown b. Flushing Dashidaira Dam Unazuki Dam Flushing (sluicing) Flushing (sluicing) (box continues next page) Regulatory Regime for Design, Construction, and O&M 53 BOX 4.3 Sediment Flushing by Dashidaira Dam (KEPCO) and Unazuki Dam (MLIT) (Continued) FIGURE B4.3.1 Integrated Sediment Flushing on the Kurobe River (Continued) c. Refill Dashidaira Dam Refill Unazuki Dam Refill Source: MLIT 2002. PHOTO B4.3.1 Unazuki Dam Sediment Flushing Source: MLIT 2002. Because the first sediment flushing from the Dashidaira Dam in 1991 damaged the environment of the river and the seacoast, KEPCO has carefully assessed and gradually made improvements. In particular, after the Unazuki Dam was built, MLIT and KEPCO jointly organized sediment flushing operations with detailed environ- mental impact assessments and monitoring. Thanks to improvements in flushing methods using hydrological conditions similar to those of natural floods at dam sites, the effects are manageable (JCOLD 2006). 54 Dam Safety Management in Japan STATE-OF-THE-ART HYDROMETEOROLOGICAL AND SEISMIC INFORMATION NETWORKS AND IT-BASED ANALYSIS SYSTEMS Highly advanced dam operation and management systems have been developed to cope with the increased hydrological/meteorological variabilities and climatic effects, which enabled resilient and effective dam operation under extreme weather events. A series of multipurpose dams are interconnected through advanced information technology networks so that they are efficiently operated on time. The systems include subsystems of state-of-the-art hydrometeorological monitoring and analysis, data and knowledge base of dam operation, and regulation and operational rules developed through trials and adjustments. An extensive hydrometeorological and seismic monitoring network has been installed by river administrators and the Japan Meteorological Agency (JMA). There are 1,300 weather observation stations, twenty doppler radars, about 3,000 rainfall observation stations, sixty radars, and about 15,000 water-level gauging stations.7 They collect and transmit data every thirty minutes, which are analyzed and sent to the central ministries and related offices through the Integrated River Information System. About 10,700 cameras are equipped to pro- vide real-time images for managing their facilities. Doppler radars are quite effective in obtaining rainfall information on a real-time basis. About 6,000 seismic monitoring stations are managed by JMA, the National Research Institute for Earth Science and Disaster Resilience, and others. JWA collects and analyzes data on a real- time basis and issues seismic/tsunami warnings to relevant agencies and media in three to four seconds to urge caution and emergency actions. In addition, about 700 seismological observation stations are embedded in major infrastructures and facilities. Magnitude, acceleration, and seis- mic intensity are recorded during the earthquake and transmitted three minutes after for owners to undertake emergency post-earthquake damage assessment and any other required measures. A large amount of data on precipitation, water levels, earthquakes, and other environ- mental factors is collected and analyzed on a real-time basis by MLIT, including JMA and Water and Disaster Management Bureau, and distributed to relevant national and local government offices, including disaster management units, utilities, mass media, and the public. In particular, rainfall data are collected and integrated with the Automated Meteorological Data Acquisition System of JMA, connected with 1,300 weather observation stations, and shared with the public through the Disaster Prevention Portal.8 Other information related to rivers and floods is shared with the public through the River Disaster Management Information Portal.9 Radar data are directly provided to the national broadcasting system. INTEGRATED DAM OPERATION SYSTEMS In addition to the highly advanced hydrometeorological information system, inte- grated dam operation systems have been developed in Japan to manage flow and quality of water in major rivers. Because mountains are steep and valleys are narrow in Japan, storage capacities of dams in the country are smaller than those of dams with similar heights in other regions or countries. Integrated operation has been implemented to maximize their storage capacities, optimize flood management, and secure the required minimum amount Regulatory Regime for Design, Construction, and O&M 55 of flow discharge in rivers. Experience and know-how obtained through years of operation as well as the advancement of automated data acquisition and management system helped develop an efficient management mechanism. Integrated dam operation is carried out in major river systems in Japan, such as the Tone, Kinu, Tenryu, Kiso, Yodo, Yoshino, and Chikugo Rivers and the Northern Okinawa Region. The Integrated Dam Operation Office for each of such major rivers monitors the reser- voir volume and guides water releases of all dams continuously, ensuring an efficient water supply operation. For low water management, the office provides forecasting informa- tion on discharge into the reservoirs and reservoir water levels based on the long-term weather forecast and expected water demand at downstream critical points and develops policies for mid- term (two to three months) reservoir operation of multiple dams based on forecasted river flow discharge. It guides flood operation to all dam offices considering rainfall data, flood forecasting information, remaining reservoir capacity and operating rules of those dams, and downstream river flooding situation. SYSTEMATIC DAM MONITORING, INSPECTION, AND MAINTENANCE Monitoring and maintaining dams after their completion are of utmost importance in terms of safety, extending structural life span, and economizing the life cycle cost of dams. Dam owners are obligated to conduct short-term (regular surveillance, daily or weekly), long-term (periodic audit, once in a few years), and comprehensive (comprehensive dam safety review and inspection, once in thirty years) inspections. Automatic monitoring equipment, which is rationally installed in and around a dam, helps enhanced quality and timely data acqui- sition and detection of anomalies and optimize the O&M arrangements though visual inspection of dams and is an integral part of dam safety management. Frequent and diligent safety checks lead to safe and reliable operation. Daily surveillance of the main dam structure and facilities is prioritized as it facilitates site staff members to be aware of dam safety status on a 24/7 basis and enables them to respond quickly when anomalies are detected. Dam owners are also required to undertake emergency inspections immediately after large floods and earthquakes based on an emergency operation manual developed for indi- vidual dams. The inspection items and rules are determined in advance in the operation rules but generally include deformation and cracks within three hours and water leakage and par- ticular deformation within twenty-four hours, and so forth. Measured inspection data are ana- lyzed and accumulated to develop an investment plan for rehabilitation and upgrading works to extend the dam’s life span (JSCE 2001, MLIT 2005a). Recordkeeping Requirements As one of the legal responsibilities defined in the River Act, dam owners must prepare and submit to their respective river administrators (a) an annual O&M report on the dam, reservoir, and river flow; (b) a report on dam operations whenever a flood occurs; and (c) monitoring and inspection records. These are regularly reviewed to enhance safety management, improve operations, and revisit the design criteria at the time of future rehabilitation or upgrades (JDEC 2005). 56 Dam Safety Management in Japan Enforcement and Arbitration Dam owners who do not comply with the dam safety requirements under the River Act can be subject to penalties by river administrators, including revoking permission for river land use and the water use rights. Article 75 of the River Act stipulates the enforcement capacity of the river administrator—that is, enabling them to exercise supervisory disposition and orders over per- mitted water users/private dam owners. When the river administrator find significant incompli- ance by dam owners, such as execution of major rehabilitation/upgrading works without prior permission, nonreporting of major incidents, serious safety deficiencies (such as a large amount of leakage), excessive water abstraction beyond permitted amount over a long period, and so on, they can impose sanctions, such as revocation of permitted water use rights, reduction of permitted water abstraction volume, suspension of utility operation, instruction of undertaking safety improvement/remedial works (such as additional grouting), removal/reconstruction of unsafe structures, safety inspection by third party, and so on. If the dam owners do not follow these instructions, the river administrators can execute subrogation of administrative acts. NOTES 1. Its direct translation is the Order for Structural Standard for River Administration and Other Facilities. 2. Agricultural land improvement covers irrigation dams/ponds and irrigation and drainage facilities. 3. The Great Hanshin Awaji Earthquake with the magnitude of 7.3 in 1995 triggered a nationwide review of the seismic design of civil engineering structures. As a result, the Japan Society of Civil Engineers proposed the establishment of Level 1 and Level 2 earthquake classifications, designating Level 2 as the possible maximum earthquake for seismic design. Also, MLIT established guidelines for seismic perfor- mance evaluation of dams during large earthquakes in 2005 (MLIT 2005a). 4. For example, the Japan and the French commissions on large dams (Japan Commission on Large Dams [JCOLD] and CFBR [Comité Français des Barrages et Réservoirs]) jointly implemented a three-year technical exchange program on seismic assessment, analysis, and regulation from 2013 to 2017. The program interpreted the dynamic behavior of concrete and embankment dams from the recorded accel- eration database of JCOLD. The analytical methods for seismic response of concrete and embankment dams are presented with the comparison of measured behavior. The program also reviewed qualifi- cation of equipment, such as comparison of design criteria for gates between Japan and France, and analyzed gates compared with the field measurements (Fry and Matsumoto 2018). 5. Many water rights for hydropower generation were granted before the current River Act was passed, without consideration of conservation of the river environment. Water is abstracted at dam reservoirs for power generation and returned downstream from power stations. In many cases, power stations are located a few kilometers downstream of dams. River flow between the dam reservoir and the power station may decrease and not meet the required maintenance flow of the river, especially during the dry season. To address these issues, in 1988, the Ministry of Construction (MLIT since 2001) and the Ministry of  Economy, Trade  and  Industry (METI) came to an agreement that a limitation of water abstraction for maintaining the necessary in-stream flow in the section between an intake and a tail- race must be stipulated in conditions for renewal of water rights for hydropower generation, setting up a specific set of criterial and recommending the maintenance flow of about 0.1 to 0.3 m3/s/100 km2 catchment area. 6. The horizontal deposits of 100-year sediment are also reflected in the structural design of dams. The amended River Act and Order for Enforcement of the River Act in 2013, as well as the updated Technical Standard for River Works in 2021, provide technical guidance on dam operation and maintenance. Regulatory Regime for Design, Construction, and O&M 57 7. Out of 15,000 water-level gauging stations, 8,000 stations are equipped with “low cost, long life, and localized water-level gauge (3L water-level gauge),” which measures river water level only during floods. Because it has advantages of lower costs for installation and O&M, it has become popular mainly in small and medium-sized rivers. 8. For more information about the Disaster Prevention Portal, see its website at https://www.mlit.go.jp​ /­river/bousai/bousai-portal/en/index.html. 9. For more information about the River Disaster Management Information Portal, see its website [in Japanese] at https://www.river.go.jp/index. CHAPTER 5 Safety Assurance of Existing Dams and Ponds1 OVERVIEW Japan has continued applying a standards-based approach for designing new dams. As the downstream consequences of almost all dams are very high or extremely high because of densely populated flood plain areas along river courses there, the national government does not see the merits of introducing different levels of safety criteria for individual dams but rather has been making efforts to ensure the safety of all dams and to develop and maintain the required human and financial capacity of dam own- ers and regulator.2 For existing dams and ponds, the national government and owners have gradually introduced a risk management approach for their safety assurance by identifying risky dams and ponds through systematic safety inspection and assessment and prioritiz- ing critical rehabilitation and safety improvement measures. For example, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has introduced a prioritization or clas- sification system for implementing remedial works for existing dams, and the Electric Power Development Co., Ltd. (J-POWER) has also established and practiced a dam safety evaluation system including risk analysis. The Ministry of Agriculture, Forestry and Fisheries (MAFF) has introduced a system for designating irrigation ponds with negative consequence in case of their failure under the 2019 act. SAFETY ASSURANCE OF EXISTING DAMS AND PONDS Periodic Rehabilitation Based on Systematic Dam Inspection Periodic rehabilitation is executed based on the results of daily inspections and peri- odic inspections, the degree of necessity and priority of improvement and repair, and the availability of a budget across concerned ministries or local governments. Long- term maintenance, rehabilitation, and monitoring plans shall be established for the dam and the appurtenant structures, based on the analysis of the results of the comprehensive inspection. In the periodic inspection, risk reduction investments for dam safety are grouped into four pri- oritization grades—namely, A, B1, B2, and C, as shown in table 5.1—considering the degree of deterioration and damage identified. The priority is based on the result of a periodic inspection 58 Safety Assurance of Existing Dams and Ponds 59 TABLE 5.1 Prioritization for Remedial Work Prioritization grade Condition of facilities Aa Serious damage and deterioration that affect the safety and function of the dam are identified, and urgent remedial works are required. (There are elements that are assessed as A.) B1b Although the safety and function of the dam are considered to be maintained, remedial works are required in an expeditious manner. (Although there are no elements assessed as A, there are elements that are assessed as B1.) B2b The safety and function of the dam are maintained. Remedial work is required as needed. (Although there are no elements assessed as A or B1, there are elements assessed as B2.) Cc No particular issues are observed that would affect the safety and function of dam. Continuous surveillance is required. (All elements are assessed as C.) Source: MLIT 2016a. Note: a. Conditions recognized to have an effect on the safety and function of the dam and require immediate action. b. Condition of the safety and function of the dam judged to be maintained, but actions need to be taken promptly (B1) and actions need to be taken as necessary (B2). c. Condition in which no deterioration or damage is observed, or minor deterioration or damage has occurred but there is no risk of affecting the safety and function of the dam and continued condition monitoring is sufficient. covering all dam safety related elements in the following: (a)  civil  structures, (b)  mechanical equipment, (c) electrical equipment and telecommunication facilities, (d) reservoir bank slope, (e) observation and monitoring equipment, (f) reservoir sedimentation, and (g) other manage- ment facilities. The Guideline for Comprehensive Inspection of Dams of 2013 also provides recommendations on dam safety management systems considering potential risks and impacts. It guides how to categorize the required management level of various dam safety–related elements based on their potential effects on the dam’s key functions, including water storage, flood control, and water supply. The guideline further recommends the required type/timing of interventions and remedial measures and their conditions per the inspection result (MLIT 2013). MLIT also issued a guideline for existing dams’ restoration, covering key elements that should be considered for dam rehabilitation, retrofitting, and reoperation for safety and functional capacity enhancement. Major retrofitting works, such as raising of existing dams’ height for increased storage capacity, drilling/installation of bottom outlets installation for existing con- crete dams, installation of new tunnel spillways through dam abutments, and so on, have been carried out without interfering with dam operations. This has been achieved by advanced construction technologies, such as works under deep water, by various coffering techniques. Safety inspection of existing dams has also been advanced using satellite images for geodetic survey and so forth. 60 Dam Safety Management in Japan Hydropower Dam Safety Assessment Electric power companies develop safety assurance systems and procedures to address safety needs arising from specific construction and usage conditions of hydro- power dams. For example, J-POWER3 has a dam safety management system supervised by the Advisory Committee on Safety Evaluation of Hydropower Facilities, which includes external technical experts to independently evaluate dam safety. The Advisory Committee holds one technical meeting and two site inspection meetings annually. Working groups are organized in J-POWER’s three regional offices to analyze, evaluate, and report on dam safety in consultation with the committee. Based on information from regular inspections, patrols, measured data, such as defor- mation and leakage, and facility deterioration checks, potential risks are identified using failure mode analysis, a type of tree analysis for risk analysis and assessment. Engineers with expertise in dam safety management participate in risk communication activities to share information about potential risks and discuss and agree on required remedial measures. Safety Assurance of Irrigation Ponds More than 150,000 small and old irrigation ponds (ike or tameike in Japanese) have been built over centuries, but most of them were not designed and constructed in compliance with the dam safety regulations and criteria under the River Act. Seventy percent of about 61,000 irrigation ponds which irrigate larger than 2 ha were built during the Edo period (1603–1868) or before.4 Some of these ponds were built centuries ago, as described in chapter 2, and their design criteria, physical properties of the foundation, and embankment material are unknown. Accordingly, such small and old irrigation ponds face seri- ous risks of settlement, leakage, and possibility of failure caused by heavy rain and earthquakes. Also, many of them are managed by local land improvement districts (LIDs) or private farmers without technical experts on-site. In response to the Fujinuma-Ike failure by the Great East Japan Earthquake in March  2011 and thirty-two irrigation ponds’ failure because of heavy storms in July 2018, the Act on Management and Conservation of Irrigation Ponds was enacted in July 2019 under the jurisdiction of MAFF. A new system has been established for desig- nating risky irrigation ponds as “specified” irrigation ponds by prefectural governments in con- sultation with municipalities. The selection criteria of the specified irrigation ponds has been established, including the following: (a)  houses, public facilities, and so on are built within 100 m downstream from ponds; (b) same as before but built within 100 to 500 m if the reservoir capacity is greater than 1,000 m3; (c) same as before but built downstream of 500 m or more if the reservoir capacity is greater than 5,000 m3, and (d) special case based on prefectural gov- ernment and municipality decision based on topographic condition, location of houses, pond’s maintenance condition, and so on (MAFF 2018b, 2020). To promote required remedial works for irrigation ponds prioritized for disaster prevention, the Act on Special Measures for the Promotion of Disaster Prevention Works for Disaster-prone Irrigation Ponds was enacted in 2020. For identified and prioritized risky irrigation ponds, MAFF and local governments have taken remedial measures, such as structural reinforcement, establishment of emergency response system, preparation of flood hazard maps in case of pond Safety Assurance of Existing Dams and Ponds 61 failure (called hazard maps) and their dissemination to downstream communities, and so on. In addition, MAFF issued guidance for providing detailed implementation procedures of required actions under the laws and conducting risk assessment and preparing an emergency prepared- ness and response plan under the guidance of agriculture departments of local governments (MAFF 2021). NOTES 1. The International Commission on Large Dams defines standards-based or deterministic approaches as “the traditional approach to dams engineering, in which risks are controlled by following estab- lished rules as to design events and loads, structural capacity, safety coefficients, and defensive design measures” (ICOLD 2005). Risk-informed approaches are increasingly being used to inform dam safety assurance, recognizing that there are a number of dam safety incidents caused by nonstructural ele- ments and that there is a need to prioritize remedial action to reduce risks to acceptable levels (World Bank 2020). 2. Chapter 6: Risk-Informed Decision Making of “Laying the Foundations: A Global Analysis of Regulatory Frameworks for the Safety of Dams and Downstream Communities” (Wishart et al. 2020) provides comprehensive analysis of standards-based and risk-informed approach to dam safety. 3. Of the sixty-one hydropower plants operated by J-POWER, forty-two hydropower plants were built more than fifty years ago. For more information, see https://www.jpower.co.jp/bs/renewable_energy​ /­hydro/ichiran​.html. Accessed April 9, 2025. 4. Dams and ponds built in “other” small rivers and off-stream ponds built outside of the designated zones/areas of Class A or Class B rivers are not subject to the River Act. CHAPTER 6 Emergency Preparedness and Public Safety OVERVIEW Japan’s disaster management policy is underpinned by the Basic Act on Disaster Management of 1961. The Basic Disaster Management Plan forms the foundation for the disas- ter management operation plans of the national government agencies and designated institu- tions, as well as local plans of municipalities. It defines the responsibilities of each entity, such as the national and local governments, public corporations, and others. It consists of various plans for each type of disaster, describing specific countermeasures for each entity to take according to the disaster management phases of prevention, preparedness, emergency response, and recov- ery and reconstruction (Cabinet Office 2023). The plans are regularly updated to incorporate lessons learned from natural disasters. Flood hazard maps, emergency communication regimens, and joint action plans between the national and local governments, including the mobilization of the Japan Self-Defense Forces, are established and reflected in municipal disaster management plans. It also includes consideration of downstream embankment breaches because the probabil- ity of embankment failure is much higher than dam failure. Mock drills for emergencies are carried out for major rivers every year. Although dam break scenarios are not specifically mentioned, the disaster management plans are applicable for emergency actions associated with dam failure. EMERGENCY DAM OPERATION DURING EXTRAORDINARY FLOODS Emergency Operation for Dam Safety Dams with flood control functions operate to cut peak flood flows at the dam as much as possi- ble to minimize flood damage in downstream areas (box 6.1). However, in case of large floods exceeding the planned magnitude, the water level for initiating the emergency reservoir oper- ation is defined to allow the dam operator to begin increasing flood discharge, possibly to the extent of discharging all incoming flow, when the reservoir water level may reach and exceed surcharge water level (SWL)1—in general, when the reservoir water level reaches 70 percent to 80 percent of flood control capacity and continues increasing. This operation is called an emer- gency discharge operation because it is usually stipulated as an exceptional emergency opera- tion vis-à-vis normal flood control operation in the dam’s operation rule. The spillway/conduit gates may need to be fully opened to release the total amount of the flood inflow to prevent the reservoir from rising above the SWL. The dam operator is required to decide whether it should initiate the emergency discharge operation, considering the hydrometeorological data and flood forecast information. 62 Emergency Preparedness and Public Safety 63 BOX 6.1 Special Operation for Disaster Prevention in Hiyoshi Dam (2013) Typhoon Man-yi in September 2013 brought heavy rain to west Japan, with 345  mm of total rainfall in about a day, with its hourly maximum of 34.5 mm. Peak inflow into the Hiyoshi Dam reservoir, managed by the Japan Water Agency (JWA), was 1,690 m3/s and discharge at peak inflow was 140 m3/s, meaning that the reservoir retained 1,550 m3/s (which is more than 90 percent of peak inflow). Operation of the Hiyoshi Dam during this time was an example of the special oper- ations for disaster prevention. The operator delayed the start of the special oper- ation by about ninety minutes, controlling the peak discharge to about 500 m3/s, which would have reached about 700 to 800 m3/s at an earlier time. This oper- ation resulted in allowing the maximum water level to elevation (EL) 201.87 m above the surcharge water level at EL 201.0 m (figure B6.1.1). The special opera- tion was coordinated with the Yodo River Integrated Dam Operation Office while checking the inflow forecasting data and ensuring the safety of the dam. FIGURE B6.1.1 Flood Control Operation in Hiyoshi Dam 0 0 10 100 20 200 30 300 40 400 Hourly rainfall (mm) Accumulated rainfall (mm) (m3/s) Reservoir water level (EL.m) 1 2 3 4 2,400 205 2,000 195 Peak inflow discharge 1,600 1,690m3/s 185 1,200 175 800 165 400 155 Actual operation 0 145 0 0 0 00 0 0 0 00 00 00 00 00 0 0 0 0 0 0 0 00 00 :0 :0 :0 :0 :0 :0 :0 :0 :0 :0 :0 :0 :0 : 0: 2: 4: 6: 8: 0: 2: 10 12 14 16 18 20 22 10 12 14 16 18 20 22 9/15 9/16 9/17 High water level (HWL EL 203.7 m); that is, Surcharge water level (SWL EL 201.0 m); that is, maximum water level by design flood maximum water level in flood control operation Controlled full water level during Emergency gate operation for flood season (EL 178.5 m) extreme flood based on operation rule Outflow: Actual operation during Inflow Water level September 15–17, 2013 Source: JWA 2015a. Note: EL = elevation. (box continues next page) 64 Dam Safety Management in Japan BOX 6.1 Special Operation for Disaster Prevention in Hiyoshi Dam (2013) (Continued) PHOTO B6.1.1 Peak Flood at Togetsukyo Bridge In Kyoto Source: MLIT 2014a. PHOTO B6.1.2 Flood Storage at Hiyoshi Dam Over Katsura River a Tributary of the Yodo River Source: MLIT 2014b. It is estimated that the maximum water level of the downstream river would have been higher by 1.5 m without this special operation, having prevented the embankment breach of the downstream river and protected about 13,000 house- holds from flooding disaster and damage of ¥1.2 trillion (US$11 billion). Emergency Preparedness and Public Safety 65 Preflood Reservoir Drawdown Operations As the number and intensity of severe rainfall and flood events have been sharply increas- ing, preflood reservoir drawdown operations are becoming very important for accommo- dating such floods and reducing flood disaster risks downstream of rivers. There are more than 700 single- and multipurpose dams, including flood control functions, but this needs to be extended to other private dams where large flood events are anticipated. In the wake of the extraordinarily severe floods and disasters in July 2018 and October 2019, the national government, through the Prime Minister’s Cabinet Office, issued basic policies for enhancing flood control function of existing dams in December 2019 to promote preflood reservoir drawdown operations for all possible dams. Under this, flood con- trol agreements are established between dam owners and river administrators on a river basin scale, based on which the preflood reservoir drawdown operations are conducted when an expected amount of rainfall in the upper catchments of a dam reaches a threshold, beyond which flooding is likely to cause damage downstream. MLIT also issued a guideline for pre- flood reservoir drawdown operations for all dams, including private dams for hydropower, irrigation, domestic water supply, and so on, in April 2020, significantly upgrading the 2005 version.2 The concept of the preflood reservoir drawdown operations is described in figure 6.1. The number of rivers and dams participating in the concerted preflood reservoir drawdown operations for flood control has been increasing. According to MLIT, flood control agreements between dam owners and river administrators have been established for the Class B river systems, managed by prefectural governors, in addition to the Class A river systems, managed by the national government through MLIT (MLIT 2021c). The total number of rivers and dams that have signed the agreements are summarized in table 6.1. Whereas all Class A river systems where dams are located (except off-stream irrigation ponds) have established flood control agreements, all Class B river systems except those where dams are located only close to the sea have established the agreements. FIGURE 6.1 Concept of Preflood Reservoir Drawdown Operation a. Multipurpose dam b. Water utilization dam Create more capacity Create capacity to store floods to store floods Emergency Spillway gate Lower water level spillway gate by predischarge Flood control capacity Lower water level Water use capacity by predischarge Water use capacity Flood control Power plant outlet Dead storage Dead storage capacity capacity Source: MLIT 2024b. 66 Dam Safety Management in Japan Table 6.2 shows the number of dams that conducted preflood reservoir drawdown operations in each fiscal year and the total secured capacity. When Typhoon Nanmadol swept across the Japanese archipelago in September 2022, the largest number of dams (129, including seventy-​ seven single-purpose dams) conducted preflood reservoir drawdown operations and secured a total capacity of approximately 420 million m3 (MLIT et al. 2023). TABLE 6.1 Number of Rivers and Dams That Have Participated in Flood Control Agreements River class Number of river systems Number of dams Class A 99 955 Class B 321 479 Total 420 1,434 Source: MLIT 2021d. TABLE 6.2 Implementation of Preflood Reservoir Drawdown Operations Number of dams Total secured capacity Year Multipurpose Water utilization Total (million m3) 2020 59 63 122 136 2021 48 46 94 101 2022 61 82 143 553 2023 72 73 145 741 Source: Based on MLIT n.d.-a. Note: Some dams listed in this table conducted the preflood reservoir drawdown operations multiple times within one year. BOX 6.2 Preflood Reservoir Drawdown Operations in the Kiso River System (2021) When heavy rains fell in the upper reaches of the Kiso River system in August 2021, the Japan Water Agency (JWA) and the Kansai Electric Power Co., Inc. (KEPCO)— dam owners of five water utilization dams on the Otaki River, one of the trib- utaries of the Kiso River—conducted preflood reservoir drawdown operations and temporarily secured a capacity of approximately 53.5 million m3 for storing floods. As a result, the peak flow of the main river just downstream of the con- fluence, Momoyama Observatory Station, was reduced by approximately 20 per- cent (approximately 730 m3/s; water level dropped by approximately 0.7 m), and flooding of roads and houses along the Kiso River (Morohara, Agematsu Town) was avoided (map B6.2.1; MLIT et al. 2023). (box continues next page) Emergency Preparedness and Public Safety 67 BOX 6.2 Preflood Reservoir Drawdown Operations in the Kiso River System (2021) (Continued) MAP B6.2.1 Preflood Emergency Reservoir Drawdown Operation on the Otaki River (2021) Tokiwa Dam Otaki River (KEPCO) Kiso town Kiso Dam (KEPCO) Otaki-gawa Dam (KEPCO) Miura Dam (KEPCO) Kiso River Makio Dam (JWA) Agematsu town Otaki village Secured capacity at the five dam reservoirs: approximately 53.5 million m3 Secured by pre-flood emergency reservoir drawdown Momoyama at Miura, Makio, Tokiwa, and Kiso: approximately 13.7 million m3 observatory Secured by water use operation station at Otaki-gawa: approximately 39.8 million m3 Morohara Source: Based on MLIT et al. 2023. Note: JWA = Japan Water Agency; KEPCO = Kansai Electric Power Co., Inc. PUBLIC SAFETY AND RISK COMMUNICATION Notification of Flood Discharge Before starting discharge from spillway gates, the dam owner or operator is required to check the needs and level of discharge based on hydrometeorological data and flood forecasting information per article 48 of the River Act. The owner or operator will then notify the commencement of discharge to the dam management branch office, integrated dam operation office, and director of the regional development bureau of MLIT. The owner or oper- ator is also required to issue warnings and sirens to downstream areas according to the warning guideline by MLIT (MLIT 2011a). Downstream Flood Warning Procedures For predesignated rivers, flood warning/information dissemination and communica- tion are carried out in collaboration with river administrators and JMA using moni- tored or analyzed hydrometeorological and flood information.3 This is delivered to the 68 Dam Safety Management in Japan related head of local governments, who are authorized to issue evacuation orders according to the Basic Act on Disaster Management, as well as to residents—via television, radio, Internet, and mobile phone—who are alerted to evacuate safely and appropriately before serious inun- dation occurs (Cabinet Office 2021). During normal times, the river administrator and local governments carry out flood awareness-raising efforts to make the flood early warning system effective. MLIT has issued guidelines on how to set river warning levels for appropriate flood control activities and evacuation actions (MLIT n.d.-b). Flood Disaster Management and Hazard Maps The Flood Control Act obligates MLIT to notify the public of potential flood inunda- tion areas and the possible inundation depth around designated rivers in vulnerable regions. Municipal governments must prepare and disclose hazard maps, developed in line with a manual prepared by MLIT, to reflect all relevant information on the river systems, including the condition of the entire river course, operation of dams/retarding ponds, condition of levees/ dikes, and so on. The maps enable municipalities to conduct effective evacuations in case of flood inundation, showing the assumed maximum inundation depth in grids and identifying evacuation routes and destinations. Periodic evacuation drills are conducted in these areas, led by municipalities under the local disaster management plans. MAFF issued the Irrigation Pond Management Manual in 2015 for local communities, such as land improvement districts or irrigation water user associations, who operate small earthfill irri- gation ponds to establish a communication network of disaster information with local commu- nities and local governments in case of ponds emergencies (MAFF 2015). It also published the Guidance for Preparation of Hazard Maps for Irrigation Ponds in 2013 for preparing hazard maps against possible breaches of small irrigation ponds, including possible flood areas as well as safety zones and evacuation routes to guide local people for safe evacuation (MAFF 2013). NOTES 1. All dams are required to prepare their reservoir operation rules and obtain approval from the river administrator for the specific river. Typically, reservoir water levels are specified for: (a) normal maxi- mum water level (NWL), (b) surcharge water level (SWL), and (c) design flood level (DFL). NWL is the elevation to which water is stored for water supply, hydropower, and so on. Some dams set different elevations of NWL, depending on wet and dry seasons. SWL is the maximum water elevation for flood control by which incoming flood water is stored to reduce flood discharge to downstream rivers. DFL is the maximum water elevation in case of design floods at which the full flood discharge capacity is attained to safely pass all incoming flows to prevent further water level rising. The DFL set the maxi- mum hydraulic load for the dam’s stability design and allowable maximum flood water level for ensur- ing the structural safety of the dam. 2. The guideline provides flood forecasting methods with ensemble scenarios using the Japan Meteorological Agency Global Spectral Model (GSM) (eighty-four hours) and the Meso-Scale Model (MSM) (thirty-nine hours) with 20 km2 resolution. In addition, it sets the procedures for reservoir operations and coordina- tion mechanisms among river administrators, water users, downstream municipalities, and so on. It also gives specific details on compensation measures for private dam owners/users in case the anticipated Emergency Preparedness and Public Safety 69 flood is not large enough to restore the reservoir water, including the calculation method of the financial compensation amount, budget source, submission procedure of such a request to the river administrators, and so on. The guideline was revised in July 2021 (MLIT 2021a). 3. This applies to rivers with a basin area technically feasible for flood forecasting among rivers where there is a risk of serious flood damage. For predesignated rivers with a basin area not large enough for flood forecasting, the river administrator announces a special warning water level. CHAPTER 7 Funding Mechanisms for Dam Safety Assurance OVERVIEW The national public financing scheme for flood management and water resources development has been instrumental in promoting multipurpose dam construction for the past five decades. The scheme has also facilitated the private sector to join multipur- pose projects, leading to the optimal use of limited suitable dam sites in a cost-effective manner. The budget for planning, design, construction, and operation and maintenance (O&M) of dams is covered by the national and local governments’ budgets as well as user tariffs for electricity, water services, and irrigation per the cost allocation formula based on the principle of benefi- ciary pays. The Japan Water Agency (JWA) can also finance the cost for building, operating, and maintaining its dams by issuing its water resources bonds (box 7.1, table B7.1.1). An integrated financing and funding mechanism of dams that comprises public budget, private investment, and loan programs was established at the early time of Japan’s rapid economic growth in the 1960s, which has significantly contributed to the acceleration of the social and economic growth of the country. The clear cost allocation method and the advantage of joining a multipurpose rather than building a single-purpose dam has significantly promoted the devel- opment of multipurpose dam projects. FUNDING MECHANISMS Multipurpose Dams The Act on Specific Multipurpose Dams of 1967 and its ordinances provided a formula and procedure for determining the cost allocation of multipurpose dam projects cov- ering investment and O&M costs between the river administrator in charge of flood control and in-stream flow provision and other water users.1 The allocated ratio for each dam user is described in the dam basic plan. Hydropower The nine regional electric power companies2 are private utilities financing their construction and operation of hydropower dams and plants by their utility service revenues in principle, though there are some government subsidies for sale price adjustments. 70 Funding Mechanisms for Dam Safety Assurance 71 BOX 7.1 JWA’s Financing Mechanism, including Water Resources Bonds The Japan Water Agency (JWA) receives a public budget allocation for the flood control function of multipurpose dams, as well as water users’ tariffs for domestic and irrigation water supply and hydropower functions. It is commissioned by the national government through, for example, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), the Ministry of Agriculture, Forestry and Fisheries (MAFF), and the Ministry of Economy, Trade and Industry (METI); by land improve- ment districts (LIDs); and by electric power companies, which shoulder its con- struction and administration costs. JWA’s dam construction and operational costs are financed largely by grants from the national government, subsidies from the concerned ministries, contributions and fees from water users, and loans, including the water resources bonds, as described in table B7.1.1. Water resources bonds are a unique system of JWA and are issued through stock brokerage firms. Through the loan system of JWA, the burden to water users for domestic use, industrial use, and irrigation use can be reduced. TABLE B7.1.1 Financing Sources of JWA Source Descriptions Grants MLIT provides grants to defray the cost of JWA’s construction and O&M works for flood control and environmental river flow provision. Subsidies MAFF, MLIT, and METI provide subsidies to JWA to mitigate the financial burden on water users (LID associations, domestic water users, and industrial water users). Beneficiary contributions Water users pay their contributions to finance facility construction (paid during the construction). Loans and bonds JWA receives long-term loans from government funds—that is, fiscal investment and loan program funds that allow water users to pay their contributions for facilities construction by installments. JWA also issues its own water resources bonds. Payment for commission Electric power companies pay a commission fee for construction and by electric power management related to hydropower generation in multipurposed dam companies projects. Source: Based on JWA 2017. Note: JWA = Japan Water Agency; LID = land improvement district; MAFF = Ministry of Agriculture, Forestry and Fisheries; METI = Ministry of Economy, Trade and Industry; MLIT = Ministry of Land, Infrastructure, Transport and Tourism; O&M = operation and maintenance. 72 Dam Safety Management in Japan Water Supply Because water supply is mainly managed by local governments and public water supply service organizations, they receive governmental subsidies for dam construction and operation, includ- ing their share of contribution to multipurpose dams. Irrigation As the financing for sustainable O&M of small irrigation dams/ponds is challenging in many parts of the world, this chapter introduces a community-based participatory irrigation manage- ment system, including dam/reservoir O&M by local user groups, which are called land improvement districts (LIDs) under the 1949 Land Improvement Act adminis- tered by the Ministry of Agriculture, Forestry and Fisheries (MAFF). LID members or irrigation water users are responsible for irrigation water management and O&M of facilities under the beneficiaries pay principle. More than two-thirds of farmers in an LID must agree on the implementation of new projects, and after they are constructed, most project facilities are operated and maintained by either the local government or the LID. The required O&M costs are covered by ordinary levies collected from LID members. On average, about two-thirds of total annual O&M cost is covered by the commissioning LID, and the remaining one-third is covered by members’ voluntary services. About 58 percent of irrigation dams and headworks devel- oped by MAFF have been transferred to and managed by LIDs, followed by local governments (41 percent) and the national government (1 percent) in 2024.3 BOX 7.2 Management of Small Irrigation Off-Stream Dam by the LID in Gunma Prefecture (Sanna-Gawa Dam of the Fujioka LID) Sanna Lake or Sanna-gawa Dam was completed in 1933 as a homogeneous earth dam as high as 19.7 m for irrigation purposes. Gunma Prefecture built the pond with a national subsidy, but ownership and management of the dam and related facilities have been handed over to the Fujioka land improvement district (LID) after the completion. Because it is an off-stream reservoir, water is withdrawn from the adjacent Ayu and Sanna Rivers through intake facilities and channels and stored in the reservoir. The dam distributes irrigation water to a designated area of the Fujioka LID that has 250 ha of irrigated area. The Ministry of Agriculture, Forestry and Fisheries (MAFF) subsidized development and construction of the dam, irrigation infrastructure, and land improvement, and the water users group paid for a small part of the project. The LID covers most of the cost of operation and maintenance (O&M), except for large repair and rehabilitation costs, which the national and local governments subsidize. The LID hired two staff for O&M tasks of the dam and associated irri- gation facilities in 2017. Regular management costs are covered by levies from LID members (farmers), including personnel expenses for the staff, cleaning of the facilities (three times in a year), excavation of sediment in irrigation channels, clearing grasses, maintenance of gate equipment, and so on. However, when it (box continues next page) Funding Mechanisms for Dam Safety Assurance 73 BOX 7.2 Management of Small Irrigation Off-Stream Dam by the LID in Gunma Prefecture (Sanna-Gawa Dam of the Fujioka LID) (Continued) comes to major rehabilitation and safety improvement works, the prefectural gov- ernment executes the project under the MAFF program with its subsidy. Because the dam did not meet the seismic design criteria, the safety improvement works have been implemented by Gunma Prefectural Office. PHOTO B7.2.1 Sanna Lake/Sanna-Gawa Dam Source: Gunma Prefectural Office. Sources: Based on materials distributed at the World Bank East Asia and Pacific and South Asia Regional Workshop and Exposure Visits for Dam Safety Management and Disaster Resilience, April 4, 2017, and Gunma Prefectural Office 2020. Contingency Budget Japan also allocates contingency budgets for reconstructing public infrastructure and facilities, including dams that are damaged by a natural disaster. The eligibility criteria for subsidies are based on the intensity of a natural hazard event. The Act on Special Financial Aid to Cope with Severe Natural Disaster of 1962 allows the designated technical officials to estimate and decide on the expenditure for the rehabilitation of a damaged public infrastructure without waiting for budgetary procedures. 74 Dam Safety Management in Japan NOTES 1. The cost allocation scheme of multipurpose dams is defined as follows: First, the total cost of the mul- tipurpose dam project is divided into (a) separable cost and (b) nonseparable cost. Separable cost is calculated for each participant based on the incremental cost when it participates in the project as the “last” participant. Nonseparable cost is a reminder of the total cost minus the total separable cost of all participants, which is also called remaining joint project cost. Nonseparable cost is allocated to all par- ticipants in proportion to the remaining benefit of each participant. Remaining benefit is calculated as follows: First, the substitute construction cost of each participant is calculated as the cost of construct- ing a hypothetical single-purpose “substitute” dam without participating in the joint project. Second, the feasible (or justifiable) investment costs of each participant are calculated based on its economic/ financial benefits. Third, the remaining benefit of each participant is calculated by deducting the cost of constructing its dedicated facility and separable cost from the lower cost of either substitute construc- tion cost or investment costs for each. Finally, the allocated share of the total cost for each participant is calculated as the sum of separable cost and remaining benefit. Each participant also covers the cost of a dedicated facility. 2. Of the ten regional electric power companies, the Okinawa Electric Power Company, Incorporated, does not have a hydropower plant. 3. For more information, see the MAFF website, “Management Status of Land Improvement Facilities Developed by the National Government” [in Japanese]. https://www.maff.go.jp/j/nousin/sekkei/nn/n​ _suiri/attach/pdf/index-16.pdf. CHAPTER 8 Key Takeaways on the Japanese Experience on Dams Development and Management Japan has developed a robust system of dam safety management and standards to address the challenging natural conditions of the country, such as steep mountains, narrow valleys, fragile geological conditions, frequent and intensive earthquakes, drought and floods, as well as socioeconomic conditions, such as densely populated industrial and residential areas downstream of dams. To meet the strong demands for natural river flow regulations and storage against floods and droughts, more than 3,100 large dams with a height of 15 m or greater have been built and operated in Japan, the number of which is ranked fourth in the world per the International Commission on Large Dams (ICOLD). The majority of large dams have been built for irrigation and multipurpose, including flood control, followed by hydropower genera- tion. These dams are subject to the safety regulation under the River Act, administered by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), which covers planning, design, construction, and operation and maintenance (O&M) of all hydraulic infrastructure in rivers, including dams, barrages, levees/dikes, and so forth. An integrated dam safety regulatory framework was needed, covering the entire proj- ect cycle from planning and design to construction to O&M, with close attention to institutional capacity building given the high rate of new dam construction (nearly 1,800 dams since the 1950s), aligning with rapid economic development, and potential high risk of dams because of intensive natural hazards and high downstream consequence. Indeed, this is in line with the case requiring the maximum dam safety assurance regulatory continuum per the decision support tool to assess the regulatory frameworks for dam safety assurance (Wishart et al. 2020). In addition, an integrated legal, institutional, and financial framework has been developed to enable rapid development of multi- and single-purpose dams for flood control, domestic and irrigation water supply, and hydropower generation in a sys- tematic manner. In particular, for seven major basins, including large metropolitan areas, the system requires development and agreement on basin-level integrated water resources plans, and the Japan Water Agency (JWA) was established as a professional entity for construction and O&M of large dams and other associated facilities. 75 76 Dam Safety Management in Japan Engineering designs, construction, and O&M of hydraulic infrastructure, including dams, barrages, and levees/dikes, are governed by the River Act and underpinned by a strong institutional framework coupled with human and financial resources and tech- nological development and a quality assurance system. The system comprises (a) a set of technical standards under the laws and regulations; (b) a procedural framework for compliance assurance with the design standards; (c) strong organizational structures and a capacity-building system; (d) an effective monitoring and inspection system to ensure safety and sustainable oper- ation; and (e) a research and development (R&D) system that develops advanced technology for dam safety. In-house engineers of the dam development, management, and regulatory entities, such as MLIT, the Ministry of Agriculture, Forestry and Fisheries (MAFF), and electric power companies, play an important role for securing dam safety in collaboration with the engineers of consulting firms and civil contractors throughout all stages of dam development and man- agement. Advanced technological development, capacity building, and the transfer of technical knowledge and experiences have been prioritized and promoted with their R&D and educational institutions by those entities. The capacity of local farmers groups—that is, land improvement districts (LIDs)—is also important for ensuring the safety of irrigation dams because about 60 percent of irrigation dams and headworks developed by MAFF have been transferred to them after completion. Although large-scale rehabilitation works needed after disasters and so on are subsidized by the government, the LIDs’ organization and regular O&M activities are managed by member fees. Prominent features of Japanese dam standards include a systematic and detailed dam design system for seismic resilience. The standards are applied from planning and design to construction to O&M stages, including emergency dam inspection and rehabilitation after earth- quakes. They ensure that a dam does not incur damage by a generally foreseeable earthquake motion (Level 1) or major/irreparable damage that may affect the storage function of the dam by a probable maximum earthquake motion (Level 2). The safety records of modern dams against earthquakes have proved the robustness of dam design, construction quality, and O&M systems in Japan. A semi-independent review system of dam basic design committee (DBDC) plays a pivotal role in ensuring safety design of multipurpose dams governed by MLIT, which is composed of representatives of a supervising authority and leading experts in their respective technical fields. A DBDC meeting is held at critical occasions of a dam project, such as deciding dam axis, commencing detailed dam design, starting construction works, and initiating reser- voir impounding. The project is not allowed to proceed to the next stage without committee approval. Electric power companies have also developed systems and procedures to address safety needs arising from specific construction and operational conditions of hydropower dams. In addition to highly advanced hydrological and meteorological information systems, integrated dam operation systems have been developed in Japan to manage river flow and quality of water in major Japanese rivers. Because Japan has steep mountains and narrow valleys, dams have less storage capacity than those of similar heights in other countries. Key Takeaways on the Japanese Experience on Dams Development and Management 77 Thus, they need to be operated in an integrated manner to make optimal use of their storage capacities. The systems include state-of-the-art hydrometeorological monitoring, data collection and analyses for dam reservoir operation, and regulation and operational rules developed over years for coping with extreme weather events that may drastically change in hours or less. For public safety, dam owners are legally required to warn the public before flood discharge by siren, electric display boards, patrol cars, and other means. The Flood Control Act also stipulates that river administrators are obligated to publicize areas and depth of river flooding in critical downstream areas. Municipalities prepare and disseminate flood hazard maps based on the inundation assessment by river administrators. Prefectural governments and municipalities prepare and publicize disaster response plans based on the hazard maps. Disaster response plans provide critical guidance for local governments and stakeholders to take con- certed actions in case of emergency operation of dams. Monitoring and maintaining dams after their completion are of utmost importance in terms of safety assurance, extending the life span and reducing the life cycle cost. Dam owners must conduct various types of inspections and safety assessments along with instrumen- tation monitoring. Daily surveillance is given priority as it facilitates field staff to be aware of dam safety status on a 24/7 basis. Emergency inspection is also conducted immediately after severe disasters, such as a large earthquake. Japan applies a risk management approach for safety assurance of existing dams by prioritizing rehabilitation and safety improvement of dams that warrant critical reme- dial measures based on comprehensive dam safety inspections and assessments. For example, MLIT has introduced and applied a prioritization or classification system for implementing reme- dial works for existing dams, and the Electric Power Development Co., Ltd. (J-POWER) has established and practiced a dam safety evaluation system, including failure mode risk analysis. Climate change has been clearly affecting hydrometeorological conditions in Japan. The average temperature in Japan has risen 1.35°C compared with the global average of 0.74°C over the past 100 years. The number of intensive rainfall events with greater than 50 mm/hour and 200 mm/day has increased more than 50 percent on average over the past fifty years. To assess the climate change impact on floods and enhance climate resilience, the national government has developed a new flood management policy based on the ensemble general circulation model’s dynamic downscaling outputs using two climate warning scenarios for 2°C and 4°C by the Intergovernmental Panel on Climate Change (IPCC) and set up the increased ratio of storm rainfall intensity and peak flood discharge vol- ume in Japan. For example, at a 2°C rise, the flood discharge targeted by the flood control plan (100-year return period) would increase by about 1.2 times, and the frequency of floods of the magnitude targeted by the current flood control plan would approximately double. It indicates that the impacts of climate change would be severe and needs to be incorporated into the river flood management and dams planning. For addressing this intensified challenge, the national government has established a policy of basinwide concerted measures for flood risk reduction and resilience enhancement and developed the Action Plan to Promote River Basin Disaster Resilience 78 Dam Safety Management in Japan and Sustainability by All in 2021. It comprises various flood management measures, such as enhanced flood operation of dams, levees, retarding basins, “paddy fields dams” (meaning flood- water storage in paddy fields), flood hazard maps, relocation/evacuation to low-risk areas, other flood defense measures for key infrastructure, and so on. Building on the advanced hydrometeorological monitoring and ensemble inflow/ flood forecasting system for basinwide reservoir operations, the national government has formalized a new integrated dam reservoirs operation system to allow for predis- charge in advance of floods, enabling predrawdown of reservoir water levels to increase their flood attenuation functions with the guideline for preflood reservoir drawdown operations by MLIT. Many privately owned dams, which do not include flood control functions, have signed agreements with river administrators for their contribution to flood control and demonstrated significant effects during some severe flood events. The strong institutional collaboration mech- anism among MLIT, the Japan Meteorological Agency (JMA), other dam owners, downstream municipalities, and so on, and their capacity plays a critical role. An emerging and increasing challenge is the safety assurance of irrigation ponds against intensified floods, which are often off-stream ponds outside of designated river areas by the River Act. More than 150,000 irrigation ponds have been identified. Some are managed by individual farmers or irrigation water user associations, but others are unknown. The major- ity of irrigation ponds were constructed prior to the present legal and regulatory framework. In response to increased irrigation ponds failure/incidents, the technical and financial support has been enhanced by two new acts for irrigation ponds administered by MAFF in coordina- tion with local governments and LIDs for enhancing safety inspections, rehabilitation/safety improvement, and emergency preparedness. Overall, Japan has developed a strong legal, institutional, and financial framework for rapidly building many dams to enhance the integrated water resources and flood management and ensuring dam safety in an integrated manner across the board. The case in Japan also illustrates the importance of institutional capacity building. Many of their systems and practices may serve as a good reference and could be adapted to other countries in which water storage development is critical. The World Bank is ready to provide required finan- cial and technical support for them in collaboration with Japan and other countries. REFERENCES Cabinet Office. 2021. “Guidelines for Evacuation Information” [in Japanese]. Cabinet Office, Tokyo. Available at: https://www.bousai.go.jp/oukyu/hinanjouhou/r3_hinanjouhou_guideline/pdf/hinan_guideline.pdf. Cabinet Office. 2023. “Basic Disaster Management Plan” [in Japanese]. Cabinet Office, Tokyo. Available at: https://www.bousai.go.jp/taisaku/keikaku/pdf/kihon_basicplan.pdf. Expert Panel Meeting on the Future Flood Management Policy. 2011. “Findings and Information Related to Future Flood Control Systems in Light of the 3.11 Disaster ” [in Japanese]. MLIT. Tokyo. Available at: https://www.mlit.go.jp/river/shinngikai_blog/tisuinoarikata/dai21kai/dai21kai_ref1.pdf. Fry, J.-J., and N. Matsumoto, eds. 2018. Validation of Dynamic Analyses of Dams and Their Equipment. Vol. 1, ICOLD Proceedings. Boca Raton, FL: CRC Press. Fukushima Prefectural Committee for Verification of Seismic Resistance of Agricultural Dams and Ponds. 2012. “Report of Investigation on Breach of Fujinuma Lake” [in Japanese]. Fukushima: Fukushima Prefectural Office. Available at: https://www.pref.fukushima.lg.jp/download/1/nosonkeikaku_kensyo_houkoku1-1.pdf. Gunma Prefectural Office. 2020. “Otani Ushimagusa District” (Prefectural Rural Area Disaster Prevention and Mitigation Project [Reservoir Group Maintenance Work]). Gunma Prefectural Office (last modified July 21). Available at: https://www.pref.gunma.jp.e.aag.hp.transer.com/page/18796.html. Hasegawa, K., K. Wakamatsu, and M. Matsuoka. 2005. “Mapping of Potential Erosion-rate Evaluated from Reservoir Sedimentation in Japan.” Journal of Japan Society for Natural Disaster Science 24 (3): 287–301. ICOLD (International Commission on Large Dams). 2003. Roller-Compacted Concrete Dams. Bulletin 126. Paris: ICOLD. ICOLD. 2005. Risk Assessment in Dam Safety Management. Bulletin 130. Paris: ICOLD. ICOLD. 2018. Roller-Compacted Concrete Dams. Bulletin 177. Paris: ICOLD International Hydropower Association (IHA). 2024. 2024 World Hydropower Outlook. IHA, London. Available at: https://www.hydropower.org/publications/2024-world-hydropower-outlook Ikeuchi, H. 2024. “Novel Approaches in Flood Management Policies in Japan: Integrating Sociocultural Wisdom in Climate Change Adaptation.” In Sociocultural Dimensions in Water Resources Management, edited by M. Ishiwatari and K. E. S. Ram, 97–112. Available at: https://www.adb.org/sites/default/files/publication/957621​/sociocultural​ -dimensions-water-resources-management-rev3.pdf. Japan Water Works Association. 1965, 1970, 1975, 1980, 1985, 1990, 1995, 2000, 2005, 2010, 2015, 2020. Water Supply Statistics [in Japanese]. Tokyo: Japan Water Works Association. JCOLD (Japan Commission on Large Dams). 2006. Current Activities on Dams in Japan. 91–97. Tokyo: JCOLD. JCOLD. 2017. Dams in Japan: Past, Present, and Future (1st ed.). AK Leiden, Netherlands: CRC Press. JDEC (Japan Dam Engineering Center). 2005. “Management.” In Construction of Multipurpose Dams, Volume VII. Tokyo: JDEC. JEPIC (Japan Electric Power Information Center). 2024. The Electric Power Industry in Japan 2024. JEPIC, Tokyo. Available at: https://www.jepic.or.jp/pub/pdf/epijJepic2024.pdf. JMA (Japan Meteorological Agency). 2024. Climate Change Monitoring Report 2023. JMA, Tokyo. Available at: https://www.jma.go.jp/jma/en/NMHS/ccmr/ccmr2023.pdf. JSCE (Japan Society of Civil Engineers), Seismic Standards Subcommittee of the Earthquake Engineering Committee. 2001. “Seismic Resistant Design of Civil Engineering Structures (Proposal) - Seismic Standard Preparation Manual – Seismic Standards Subcommittee Activity Report” [in Japanese]. JSCE, Tokyo. JWA (Japan Water Agency). 2008. Outline of the Aichi Irrigation Project. JWA, Aichi, Japan. Available at: https:// www.water.go.jp/chubu/­aityosui/a(jyouhou-sub)/06(english)/01.pdf. JWA. 2015a. “The Introduction for the Effective Flood Control by Dams of Japan Water Agency.” Kasen (River) 830: 19–22. Tokyo: Japan River Association. JWA. 2015b. “Japan’s Experience in Integrated Water Resources Management: Sharing the Lessons with the Monsoonal Asian Countries.” 7th World Water Forum, Daegu-Gyeongbuk, South Korea, April 12–17, 2015. JWA. 2017. “JWA’s Brief History on IWRM, Financial System and Emergency Preparedness.” JWA, Saitama, Japan. JWA. 2023. “Naturing Culture with Water” [in Japanese]. JWA, Aichi Canal Management Office, Aichi, Japan. Kantoush, S.A., T. Sumi, T. Suzuki, and M. Murasaki. 2010. “Impacts of sediment flushing on channel evolution and morphological processes: Case study of the Kurobe River, Japan.” In River Flow 2010, edited by A. Dittrich, Ka. Koll, J. Aberle, and P. Geisenhainer, pp. 1165–1173. 79 80 Dam Safety Management in Japan KEPCO (Kansai Electric Power Co., Inc.). n.d. “KEPCO’s Hydroelectric Power Plants: List of Hydroelectric Power Plants” [in Japanese]. Available at: https://www.kepco.co.jp/energy_supply/energy/newenergy/water/plant​ /list.html. Accessed on March 31, 2025. Koike, T. 2021. “Evolution of Japan’s Flood Control Planning and Policy in Response to Climate Change Risks and Social Changes.” Water Policy 23 (S1): 77–84. doi: 10.2166/wp.2021.287. MAFF (Ministry of Agriculture, Forestry and Fisheries). 2013. “Guidance for Preparation of Hazard Maps for Irrigation Ponds” [in Japanese]. MAFF, Tokyo. Available at: https://www.maff.go.jp/j/nousin/bousai/bousai​ _saigai/b_tameike/pdf/tameike_manual_1rev.pdf. MAFF. 2015. “Irrigation Pond Management Manual” [in Japanese]. MAFF, Tokyo. Available at: https://www​ .maff.go.jp/j/nousin/bousai/bousai_saigai/b_tameike/attach/pdf/index-102.pdf. MAFF. 2016. “History of Tameike” [in Japanese]. MAFF, Tokyo. Available at: https://www.maff.go.jp/j/nousin​ /­bousai/bousai_saigai/b_tameike/attach/pdf/index-116.pdf. MAFF. 2018a. “Result of the Emergency Nationwide Survey on Irrigation Ponds” [in Japanese]. MAFF, Tokyo. Available at: https://www.maff.go.jp/j/nousin/bousai/bousai_saigai/b_tameike/attach/pdf/index-93.pdf. MAFF. 2018b. “Future Plans for Countermeasures of Irrigation Ponds in light of the Heavy Rain in July 2008” [in  Japanese]. Press Release, November 13, 2018. Available at: https://www.maff.go.jp/j/nousin/bousai​ /bousai_saigai/b_tameike/attach/pdf/index-2.pdf. MAFF. 2020. “Manual for Maintenance of Irrigation Ponds” [in Japanese]. MAFF, Tokyo. Available at: https:// www.maff.go.jp/j/nousin/bousai/bousai_saigai/b_tameike/attach/pdf/index-102.pdf. MAFF. 2021. “Guidance for the Evaluation of Deterioration of Disaster-prone Irrigation Ponds” [in Japanese]. MAFF, Tokyo. Available at: https://www.maff.go.jp/j/nousin/bousai/bousai_saigai/b_tameike/attach/pdf​ /­index-77.pdf. MAFF. 2023. “About Tameike” [in Japanese]. MAFF, Tokyo. Available at: https://www.maff.go.jp/j/nousin​ /­bousai/bousai_saigai/b_tameike/attach/pdf/index-46.pdf. MAFF. 2024. “Status of LID” [in Japanese]. MAFF, Tokyo. https://www.maff.go.jp/j/nousin/kikaku/attach/pdf​ /­dantaisidou_riyouchousei-60.pdf. Matsumoto, N., T. Sasaki, and T. Ohmachi. 2011. “The 2011 Tohoku Earthquake and Dams.” ICOLD 79th Annual Meeting, Lucerne, Switzerland, May 29–June 3, 2011. Matsumoto, N. 2012. “Dams in Japan.” Memorial lecture at 24th ICOLD Congress, Kyoto, Japan, June 6, 2012. MEXT (Ministry of Education, Culture, Sports, Science and Technology). 2019. Program for Risk Information on Climate Change (SOUSEI). Database for Policy Decision Making for Future Climate Change (d4PDF). Available at: http://www.miroc-gcm.jp/-pub/d4PDF/. MLIT (Ministry of Land, Infrastructure, Transport and Tourism). 2002. “Integrated Sediment Flushing from Unazuki Dam and Dashidaira Dam on the Kurobe River” [in Japanese]. MLIT, Hokuriku Regional Development Bureau, Kurobe River Office, Kurobe, Japan. Available at: https://www.hrr.mlit.go.jp/kurobe​/­jigyo/panf​ /panf_dl/haisa.html. MLIT. 2005a. Guidelines for Seismic Performance Evaluation of Dams during Large Earthquakes. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river/shishin_guideline/bousai/daml2/pdf/daml2.pdf. MLIT. 2005b. “Guide to Creating a Fish-friendly River” [in Japanese]. MLIT, Tokyo. Available at: https://www​ .mlit.go.jp/river/shishin_guideline/kankyo/kankyou/sakana_tebiki/index.html. MLIT. 2007. “Draft Guideline for Examination of Required In-stream Flow Volume” [in Japanese]. MLIT, Tokyo​ . Available at: https://www.mlit.go.jp/river/shishin_guideline/ryuuryoukentou/tebiki.pdf. MLIT. 2011a. “Guidelines for Planning and Design of Warning System for Water Release of Dams” [in Japanese]. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river/shishin_guideline/dam3/pdf​/­houryuukeihou​ _kaisetsu.pdf MLIT. 2011b. “Manual for Sediment Replenishment to Downstream Reaches below Dams” [in Japanese]. MLIT, Tokyo. MLIT. 2013. “Guideline for Comprehensive Inspection of Dams” [in Japanese]. MLIT, Tokyo. Available at: https:// www.mlit.go.jp/river/shishin_guideline/dam/pdf3/02.pdf. MLIT. 2014a. Report of Water-related Disaster in 2013. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river​ /­pamphlet_jirei/pdf/suigai2013.pdf. MLIT. 2014b. Summary of Floods by September 2013 Typhoon No. 18. MLIT, Kinki Regional Development Bureau, Osaka. Available at: https://www-1.kkr.mlit.go.jp/news/river/disaster/ol9a8v000001ffu8-att​/­ol9a8v000001ffvr.pdf. MLIT. 2016a. “Guidelines for Periodical Inspection of Dams” [in Japanese]. MLIT, Tokyo. Available at: https://www​ .mlit.go.jp/river/shishin_guideline/dam/07.pdf. MLIT. 2016b. “Technical Standards for River Works in Japan, Volume for Operation and Maintenance (Dam)” [in Japanese]. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river/shishin_guideline/gijutsu​/­gijutsukijunn​ /ijikanri_dam/pdf/ijikanri_dam.pdf. MLIT. 2018a. “Existing Dams Restoration Guideline” [in Japanese]. MLIT, Tokyo. Available at: https://www​.mlit​ .go.jp/river/dam/pdf/guideline.pdf. References 81 MLIT. 2018b. “Guidelines for Sediment Management of Dam Reservoir” [in Japanese]. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river/shishin_guideline/dam7/pdf/damtyosuichidosyakanritebikiH30.pdf. MLIT. 2020. River Basin Disaster Resilience and Sustainability by All. MLIT, Tokyo. Available at: https://www.mlit​.go​ .jp/river/kokusai/pdf/pdf21.pdf. MLIT. 2021a. “Guideline for Pre-flood Reservoir Drawdown Operations” [in Japanese]. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river/shishin_guideline/dam/pdf4/02jizenhouryu_guideline_honbun.pdf. MLIT. 2021b. “Cabinet Decision on the Bill to Partially Amend the Act on Countermeasures against Flood Damage of Specified Rivers Running across Cities” [in Japanese]. Press Release, February 2, 2021. Available at: https:// www.mlit.go.jp/report/press/content/001385277.pdf. MLIT. 2021c. “Revision of the Suggestion for “Appropriate Flood Control Planning in light of Climate Change” [in Japanese]. Press Release, April 30, 2021. Available at: https://www.mlit.go.jp/report/press​/­mizukokudo03​ _hh_001060.html. MLIT. 2021d. “Status of Flood Control Agreements Regarding Implementation of Preflood Reservoir Drawdown Operations” [in Japanese]. Press Release, May 26, 2021. Available at: https://www.mlit.go.jp/report/press​ /­mizukokudo04_hh_000161.html. MLIT. 2023a. “Current Status of Water Resources in Japan 2023” [in Japanese]. MLIT, Tokyo. Available at: https:// www.mlit.go.jp/mizukokudo/mizsei/mizukokudo_mizsei_fr2_000050.html. MLIT. 2023b. “River Data Book 2023” [in Japanese]. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river​ /­toukei_chousa/kasen_db/. MLIT. 2023c. Rivers in Japan. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river/kokusai/pdf/pdf45.pdf. MLIT. 2024a. “Status of Water Resources in Japan FY 2023” [in Japanese]. MLIT, Tokyo. Available at: https://www​ .mlit.go.jp/mizukokudo/mizsei/content/001720098.pdf. MLIT. 2024b. “Outline of River Projects 2024” [in Japanese]. MLIT, Tokyo. Available at: https://www.mlit.go.jp​ /­river/pamphlet_jirei/kasen/gaiyou/panf/pdf/2024/kasengaiyou2024_all.pdf. MLIT. 2024c. “Dam Conditions After the 2024 Noto Peninsula Earthquake” [in Japanese]. MLIT, Tokyo. Available at: https://www.mlit.go.jp/river/bousai/240101_noto/pdf/damhigai_240401.pdf MLIT. n.d.-a. “Implementation of Pre-flood Reservoir Drawdown Operations” [in Japanese]. Available at: https:// www.mlit.go.jp/river/dam/dam_discharge.html. Accessed on March 31, 2025. MLIT. n.d.-b. “Guidelines for Establishment of Hazardous Water Level, Special Warning Water Level, and Evacuation Warning Water Level” [in Japanese]. Available at: https://www.mlit.go.jp/river/shishin_guideline​ /bousai/saigai/suii/. Accessed on March 31, 2025. MLIT, MAFF (Ministry of Agriculture, Forestry and Fisheries), MEXT (Ministry of Education, Culture, Sports, Science and Technology), and METI (Ministry of Economy, Trade and Industry). 2023. “Collection of Policies on ‘River Basin Disaster Resilience and Sustainability by All’” [in Japanese]. MLIT, Tokyo. Available at: https:// www.mlit.go.jp/river/pamphlet_jirei/kasen/gaiyou/panf/sesaku/pdf/r503_sesaku_01.pdf. Nakamura, S. 1995. “Fishway: Creating a Fish-friendly River, Guidelines for Fishway Design” [in Japanese]. Edited by Foundation for Riverfront Improvement and Restoration. Sankaido, Tokyo. NIED (National Research Institute for Earth Science and Disaster Resilience). 2023. “Strong Ground Motion Caused by the 2011 off the Pacific Coast of Tohoku Earthquake” [in Japanese]. NIED, Tsukuba, Japan. Available at: https://www.kyoshin.bosai.go.jp/kyoshin/topics/html20110311144626/main​_20110​311144626.html. NILIM (National Institute for Land and Infrastructure Management). 2011. “Helicopter Survey Report After GEJE” [in Japanese]. NILIM, Tsukuba, Japan. Available at: https://www.nilim.go.jp/lab/bbg/saigai​ /­h23tohoku/110314sabo.pdf. Ock, G., T. Sumi, and Y. Takemon. 2013. “Sediment Replenishment to Downstream Reaches below Dams: Implementation Perspectives.” Hydrological Research Letters 7 (3): 54–59. doi: 10.3178/hrl.7.54. Omachi, T. 1999. The River Law with Commentary by Article: Legal Framework for River and Water Management in Japan. Infrastructure Development Institute Water Series No. 4, Infrastructure Development Institute, Tokyo, Japan. Available at: http://www.idi.or.jp/wp/wp-content/uploads/2018/05/RIVERE.pdf. Wishart, M. J., S. Ueda, J. D. Pisaniello, J. L. Tingey-Holyoak, K. N. Lyon, and E. B. Garcia. 2020. Laying the Foundations: A Global Analysis of Regulatory Frameworks for the Safety of Dams and Downstream Communities. Sustainable Infrastructure Series, World Bank, Washington, DC. World Bank. 2020. Good Practice Note on Dam Safety. World Bank, Washington, DC. APPENDIX A Chronology of Legislation for Water Resources Development and Historical Background Year Relevant laws and regulation Key drivers 1890 Water Supply Act To address waterborne disease outbreaks in the late 1800s 1896 River Act Demands on flood control on relatively large-scale rivers 1897 Erosion Control Act, Forest Act Demands for disaster prevention by controlling sediment runoff from devastated mountains 1899 Agricultural Land Consolidation To reorganize agricultural lands Act 1905 Amendment of Agricultural To expand the development of irrigation and drainage Land Consolidation Act systems 1909 Amendment of Agricultural To establish the Agricultural Land Consolidation Land Consolidation Act Associations for implementing land improvement 1949 Land Improvement Act To address food shortage and improve farm production after severe damages and improve farm production after severe damages to land by World War II. Flood Control Act  1947 Typhoon Kathleen 1950 Comprehensive National Land To restore the national economy and lands that were Development Act devastated during World War II and as a lesson learned from Typhoon Kathleen, which flooded the Tone River basin in 1947 1952 Electric Power Development Rapidly increased demands of electricity, especially in Promotion Act metropolitan areas Technical Criteria for Planning To establish technical criteria and standards and Design of Agricultural for investigation, planning, design, and O&M of Land Improvement Project agriculture-related infrastructure 1956 Industrial Water Act To regulate excessive groundwater abstraction by heavy and chemical industries, which had caused land subsidence during the rapid economic growth period 82 Chronology of Legislation for Water Resources Development and Historical Background 83 Year Relevant laws and regulation Key drivers 1957 Act on Specified Multipurpose To meet the rapidly increased demands of water Dams resources and electricity especially in metropolitan areas To better coordinate the allocation of planning and costs among the river managers, electric power companies, waterworks operators, and industrial water users Amendment of Water Supply To regulate the supply and quality of drinking water Act sources during the rapid economic and population growth period after World War II 1958 Industrial Water Supply To secure industrial water resources development Business Act Technical Standard for River To establish technical criteria and standards for Works investigation, survey, planning, design, and O&M of river structures 1960 Act on Emergency Measures In response to a 1959 typhoon that ravaged Ise Bay for Forest Protection and Flood and claimed approximately 4,700 lives Control 1961 Water Resources Development To support the high economic growth period (1950–73) Promotion Act by effectively developing and using water resources Water Resources Development while ensuring flood controls Public Corporation Act Basic Act on Disaster The 1959 typhoon described earlier Management Basic Act on Agriculture To improve agricultural productivity 1962 Act on Special Financial Aid The 1959 typhoon described earlier to Cope with Severe Natural Disaster 1964 Amendment of the River Act Increasing demand on flood control and water use Electricity Business Act Population increases in urban areas Increase of industrial production 1974 Act on Tax for Promotion of To diversify energy sources in the wake of the oil crisis Power-Resources Development in 1973 and to obtain stakeholder consensus for further Act on Special Account for hydropower development Electric Power Development Promotion Act on the Development of Areas Adjacent to Electric Power Generating Facilities 1976 Order for Structural Standard To establish general technical standards for the for River Administration structure of dams, levees, and other major river Facilities and so on management facilities 1993 Basic Act of the Environment The 1992 United Nations Conference on Environment and Development 1995 Act on Special Measures 1995 Great Hanshin-Awaji Earthquake Concerning Earthquake Disaster Management 84 Dam Safety Management in Japan Year Relevant laws and regulation Key drivers 1997 Amendment of the River Act Environmental conservation and management To create riparian forest zones around reservoirs and along levees Environmental Impact To promote environmental impact assessment Assessment Act 1999 Basic Act on Food, Agriculture To promote measures for food, agriculture, and rural and Rural Areas areas in a comprehensive and systematic manner 2002 Act on the Japan Water Administrative reform Agency, Independent Administrative Agency 2005 Guidelines for Seismic 1995 Great Hanshin-Awaji Earthquake Performance Evaluation of Dams during Large Earthquakes 2013 Amendment of the River Act To establish standards on regular inspections to maintain dams and other river management facilities in good condition 2019 Act on Management and To prevent damage caused by collapsed irrigation Conservation of Irrigation ponds while ensuring their function for irrigation Ponds through their proper management and conservation 2021 Amendment of the Act on To implement the policy of River Basin Disaster Countermeasures against Resilience and Sustainability by All Flood Damage of Specified Rivers Running across Cities 2023 Amendment of the Water Change of jurisdiction from MHLW to MLIT Supply Act Sources: MLIT 2007 and relevant information. Note: MHLW = Ministry of Health, Labor and Welfare; MLIT = Ministry of Land, Infrastructure, Transport and Tourism; O&M = operation and maintenance. SKU W23015