UNU-INWEH REPORT SERIES 11 Ageing Water Storage Infrastructure: An Emerging Global Risk Duminda Perera, Vladimir Smakhtin, Spencer Williams, Taylor North, Allen Curry www.inweh.unu.edu About UNU-INWEH UNU-INWEH’s mission is to help resolve pressing water challenges that are of concern to the United Nations, its Member States, and their people, through critical analysis and synthesis of existing bodies of scientific discovery; targeted research that identifies emerging policy issues; application of on-the-ground scalable science-based solutions to water issues; and global outreach. UNU-INWEH carries out its work in cooperation with the network of other research institutions, international organisations and individual scholars throughout the world. UNU-INWEH is an integral part of the United Nations University (UNU) – an academic arm of the UN, which includes 13 institutes and programmes located in 12 countries around the world, and dealing with various issues of development. UNU-INWEH was established, as a public service agency and a subsidiary body of the UNU, in 1996. Its operations are secured through long-term host-country and core-funding agreements with the Government of Canada. The Institute is located in Hamilton, Canada, and its facilities are supported by McMaster University. About UNU-INWEH Report Series UNU-INWEH Reports normally address global water issues, gaps and challenges, and range from original research on specific subject to synthesis or critical review and analysis of a problem of global nature and significance. Reports are published by UNU-INWEH staff, in collaboration with partners, as / when applicable. Each report is internally and externally peer-reviewed. UNU-INWEH Reports are an open access publication series, available from the Institute’s web site and in hard copies. © United Nations University Institute for Water, Environment and Health (UNU-INWEH), 2021 Suggested Reference: Perera, D., Smakhtin, V., Williams, S., North, T., Curry, A., 2021. Ageing Water Storage Infrastructure: An Emerging Global Risk.UNU-INWEH Report Series, Issue 11. United Nations University Institute for Water, Environment and Health, Hamilton, Canada. Cover image: Ben Cody, CC BY-SA 3.0, via Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Elwha_Dam_under_ deconstruction.jpg Design: Kelsey Anderson (UNU-INWEH) Download at: http://inweh.unu.edu/publications/ ISBN: 978-92-808-6105-1 UNU-INWEH is supported by the Government of Canada through Global Affairs Canada. UNU-INWEH Report Series Issue 11 Ageing Water Storage Infrastructure: An Emerging Global Risk Duminda Perera United Nations University Institute for Water, Environment and Health, Hamilton, Canada University of Ottawa, Ottawa, ON, Canada McMaster University, Hamilton, ON, Canada Vladimir Smakhtin United Nations University Institute for Water, Environment and Health, Hamilton, Canada Spencer Williams The Graduate Institute of International and Development Studies, Geneva, Switzerland Taylor North McMaster University, Hamilton, ON, Canada Allen Curry Canadian Rivers Institute, University of New Brunswick, NB, Canada United Nations University Institute for Water, Environment, and Health, Hamilton, ON, Canada CONTENTS EXECUTIVE SUMMARY 4 INTRODUCTION 5 GLOBAL DATASETS ON DAM CHARACTERISTICS 6 GLOBAL TRENDS IN LARGE DAM CONSTRUCTION AND AGEING 7 OVERVIEW OF DAM AGEING BY REGION AND DAM FUNCTION 10 Africa 10 Asia 10 Australia 11 Europe 11 North America 11 South America 12 DAM DECOMMISSIONING: REASONS, IMPACTS, AND TRENDS 12 Public safety: increasing risk 12 Maintenance: rising expense 14 Sedimentation: declining effectiveness of functions 15 Environment: restoring or redesigning natural environments 15 Societal impacts of dam decommissioning 15 Emerging trends 16 CASE STUDIES OF DAM AGEING AND DECOMMISSIONING 17 The Glines Canyon and Elwha dams, USA 17 The Poutès Dam, France 18 Mactaquac Dam, Canada 18 Mullaperiyar Dam, India 19 Kariba Dam, Zambia & Zimbabwe 20 Arase Dam, Japan 21 CONCLUSIONS 22 ACKNOWLEDGEMENTS 24 REFERENCES 24 EXECUTIVE SUMMARY The Report provides an overview of the current state of knowledge on the ageing of large dams –an emerging global development issue as tens of thousands of existing large dams have reached or exceeded an "alert" age threshold of 50 years, and many others will soon approach 100 years. These aged structures incur rapidly rising maintenance needs and costs while simultaneously declining their effectiveness and posing potential threats to human safety and the environment. The Report analyzes large dam construction trends across major geographical regions and primary dam functions, such as water supply, irrigation, flood control, hydropower, and recreation. Analysis of existing global datasets indicates that despite plans in some regions and countries to build more water storage dams, particularly for hydropower generation, there will not be another "dam revolution" to match the scale of the high-intensity dam construction experienced in the early to middle, 20th century. At the same time, many of the large dams constructed then are aging, and hence we are already experiencing a "mass ageing" of water storage infrastructure. The Report further explores the emerging practice of decommissioning ageing dams, which can be removal or re-operation, to address issues of ensuring public safety, escalating maintenance costs, reservoir sedimentation, and restoration of a natural river ecosystem. Decommissioning becomes the option if economic and practical limitations prevent a dam from being upgraded or if its original use has become obsolete. The cost of dam removal is estimated to be an order of magnitude less than that of repairing. The Report also gives an overview of dam decommissioning's socio-economic impacts, including those on local livelihoods, heritage, property value, recreation, and aesthetics. Notably, the nature of these impacts varies significantly between low- and high-income countries. The Report shows that while dam decommissioning is a relatively recent phenomenon, it is gaining pace in the USA and Europe, where many dams are older. However, it is primarily small dams that have been removed to date, and the decommissioning of large dams is still in its infancy, with only a few known cases in the last decade. A few case studies of ageing and decommissioned large dams illustrate the complexity and length of the process that is often necessary to orchestrate the dam removal safely. Even removing a small dam requires years (often decades), continuous expert and public involvement, and lengthy regulatory reviews. With the mass ageing of dams well underway, it is important to develop a framework of protocols that will guide and accelerate the process of dam removal. Overall, the Report aims to attract global attention to the creeping issue of ageing water storage infrastructure and stimulate international efforts to deal with this emerging water risk. This Report's primary target audiences are governments and their partners responsible for planning and implementing water infrastructure development and management, emphasizing adaptation to a changing climate and sustainable development. Keywords: dams, large dams, dam ageing, dam decommissioning, dam re-operation, dam removal, dam failure, reservoirs, sedimentation, public safety, river restoration, water storage, water infrastructure. 4 Ageing Water Storage Infrastructure: An Emerging Global Risk INTRODUCTION dams were built) have a design life of approximately 50-100 years (Mahmood, 1987; Ho et al., 2017). Water storage infrastructure, particularly large dams Others suggest the service life of well-designed, in the last 100 years, has traditionally been used to well-constructed, and well-maintained and regulate river flow worldwide. "Large dams" are monitored dams can easily reach 100 years, while defined by International Commission on Large some dam elements (gates, motors) may need Dams (ICOLD) as having a "height of 15 metres or to be replaced after 30 to 50 years (Wieland and greater from lowest foundation to crest, or a dam Mueller, 2009). According to Wan-Wendner (2018), between 5 metres and 15 metres impounding more all modern dams must meet safety regulations that than 3 million cubic metres". ICOLD's current World typically model and examine scenarios of failure up Register of Dams (WRD) comprises over 58,700 large to 100 years. In this Report, and similarly to Wan- dams that satisfy these criteria, although this list Wendner (2018), an arbitrary age of 50 years is used may be incomplete (ICOLD WRD, 2020). Together, as the point when "a human-built, large concrete these dams can store approximately between 7,000 structure such as a dam that controls water would and 8,300 km³ (Vörösmarty et al., 2003; Chao et al., most probably begin to express signs of aging." 2008, Zhou et al., 2015), or approximately 16% of all global annual river discharge, ~ 40,000 km³yr-1 These ageing signs may include increasing cases (Hanasaki et al., 2006). of dam failures, progressively increasing costs of dam repair and maintenance, increasing reservoir Dams exist in various designs and types that sedimentation, and loss of a dam's functionality and depend on several context-specific factors, effectiveness. These manifestations are strongly including geology, reservoir storage capacity, interconnected. Therefore, age per se is not a intended dam function(s), availability of materials, decisive variable for action. Two dams constructed and funds (USSD, 2015). The main functions