Published on The Water Blog

Enhancing the safety and resilience of dams and downstream communities

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Metolong water supply dam (Lesotho). © Marcus Wishart/World Bank. Metolong water supply dam (Lesotho). © Marcus Wishart/World Bank.

The challenge: delivering water storage services safely 

The world has a plethora of dams, including the more than 58,000 large dams registered with the International Commission on Large Dams, as well as several million small dams. These structures play an important role in the provision of water services, including the supply of water for drinking, agriculture, electricity generation and industrial processes. Many dams also support recreational activities, and the lakes they create are appreciated for their scenic beauty. Dams are also critically important in mitigating the impacts of extreme weather, as they hold reserves of water for when there is a drought or buffer against the devastation caused by extreme floods. 

With so many people and economic sectors depending on well-functioning dams, it is more important than ever to ensure that they are structurally sound and have fundamental dam safety management measures in place. 

Dam safety has long been a priority for the World Bank given its robust portfolio of projects involving dams. As early as 1977, the Bank issued Operational Manual Statement (OMS) 3.80, “Safety of Dams,” which underscored the importance of dam safety and made it clear that the malfunction or failure of a dam can have serious  consequences. This OMS was revised and reissued twice to reflect the evolving thinking on dam safety issues, eventually leading to the October 2001 release of Operational Policy (OP) 4.37, together with Bank Procedure (BP) 4.37, which went beyond water storage dams and extended the policy to cover tailings and ash dams. 

The World Bank’s new Environmental and Social Framework (ESF), which was launched in October 2018, addresses dam safety under the Environmental and Social Standard 4, Community Health and Safety, which stipulates, “Where the project involves a new or existing dam, the Borrower will provide sufficient resources to apply the requirements on safety of dams, as set out in Annex 1.” ESS4 Annex 1 intends to address dam safety risks and impacts on project-affected communities in a way that is consistent with the mitigation hierarchy that underpins the ESF. 

The solution: understanding and managing safety risks through the whole life cycle 

ESS4 applies to new dams or dams under construction; the rehabilitation of existing dams; and projects that rely or may rely on existing dams or dams under construction.  

ESS4 recognizes that risks associated with the safety of dams are design- and situation-specific and has introduced three major modifications under its provisions. These include: (a) lowering the threshold for large dams with a reservoir capacity greater than 3 million cubic meters from 10 meters to 5 meters in height; (b) including all other dams, regardless of size or retention capacity (referred to as small dams) that could cause safety risks; and (c) explicitly introducing a proportional risk management approach to the application of the dam safety requirements considering a dam’s size, complexity, and potential risk. 

Risk management approaches to dam safety assurance typically follow four steps: (a) risk analysis, (b) risk assessments, (c) decision making for risk control and reduction measures, and (d) monitoring and evaluation. It is important that this approach be used throughout the life cycle of a dam.

Good Practice Note On Dam Safety

Introducing the new Good Practice Note on Dam Safety

To provide additional guidance on the application of these requirements under the ESF, the World Bank’s Water Practice has developed a Good Practice Note (GPN) on Dam Safety in coordination with OPCS, which equips Bank task teams and counterparts with a risk management approach to dam safety in the context of World Bank projects. This guidance is meant to enhance the quality of practice without creating new requirements for the application of the ESF and are, thus, complementary to the compliance requirements contained in the ESF and the Guidance Notes for Borrowers

The Good Practice Note on Dam Safety includes sample frameworks for the four dam safety plans as well as sample terms of reference for an independent dam safety review and useful examples and references. The Good Practice Note is also accompanied by seven Technical Notes that provide more detailed explanation and guidance on hydrological, geotechnical and seismic risk, small dam safety, potential failure modes analysis, portfolio risk assessment using a risk index, and tailings storage facilities.

Why should you read it? 

These resources bring together a wealth of global experience reflecting good international industry practice to support the Bank’s more than $30 billion in active investments related to dams. These range from the construction of new dams and rehabilitation and upgrading of existing dams, to preparatory studies and safety assessments of existing dams on which Bank-funded projects rely.  

From Bank staff to borrowers and interested practitioners in the sector, the Good Practice Note and associated materials provide a comprehensive overview of risk management approaches to dam safety. Its appendices and accompanying Technical Notes can be downloaded separately so readers can easily find the guidance they need. 

Read More: 

These resources complement other recent analytic work produced by the Water Global Practice around dams and dam safety, including Laying the Foundations : A Global Analysis of Regulatory Frameworks for the Safety of Dams and Downstream Communities and Using the Hydropower Sustainability Tools in World Bank Group Client Countries : Lessons Learned and Recommendations

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