NB/T 10882-2021Guidelines for risk prevention and control of cascade reservoirs safety (English PDF)

Foreword

This document was issued on 22 December 2021 by the National Energy Administration of the PRC and takes effect on 22 June 2022.

It is a NB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

It is classified under ICS 27.140, Chinese classification P 59.

In accordance with the requirements of the Notice of the National Energy Administration on Issuing the Second Batch of the 2014 Plan for the Formulation (Revision) of Energy Industry Standards (Guo Neng Ke Ji [2015] No. 12), the drafting group of this guideline carried out extensive investigation and research, conscientiously summarized practical experience and, on the basis of widely soliciting opinions, formulated this guideline.

The main technical contents of this guideline are: general provisions, terms, basic requirements, risk prevention and control of cascade reservoirs in the planning stage, risk prevention and control of cascade projects in the design stage, risk prevention and control of cascade projects in the construction stage, risk prevention and control of cascade reservoirs in the operational stage, risk prevention and control of cascade projects in the decommissioning stage, and preparation of the risk assessment and prevention and control report.

This guideline is under the administration of the National Energy Administration, is proposed by and under the routine management of China Renewable Energy Engineering Institute, and the specific technical contents are interpreted by the Energy Industry Standardization Technical Committee of Hydropower Survey and Design (NEA/TC 15).

Any comments or suggestions arising during the implementation of this guideline should be sent to China Renewable Energy Engineering Institute (Address: No. 2 Liupukang Beixiaojie, Xicheng District, Beijing; Postal code: 100120).

Chief development organization of this guideline: China Renewable Energy Engineering Institute.

Participating development organizations of this guideline: China Institute of Water Resources and Hydropower Research; PowerChina Chengdu Engineering Corporation Limited; PowerChina Northwest Engineering Corporation Limited; PowerChina Zhongnan Engineering Corporation Limited; Yalong River Hydropower Development Company, Ltd.; Yellow River Upstream Hydropower Development Co., Ltd.; Guoneng Dadu River Basin Hydropower Development Co., Ltd.; Huaneng Lancang River Hydropower Inc.; Wuling Power Corporation Ltd.; Xi'an University of Technology.

The foreword lists the principal drafting staff of this guideline, 31 persons in total, headed by Zhou Jianping.

The foreword also lists the principal reviewers of this guideline, 28 persons in total.

Publication Information

NB/T 10882-2021 is an Energy Industry Standard of the People's Republic of China, Guidelines for Risk Prevention and Control of Cascade Reservoirs Safety (Chinese title: 梯级水库群安全风险防控导则). ICS 27.140, CCS P 59. Issued on 2021-12-22 and implemented on 2022-06-22 by the National Energy Administration.

Chief development department: China Renewable Energy Engineering Institute. Approval department: National Energy Administration. Implementation date: 22 June 2022. Published by China Water and Power Press, Beijing, 2022.

The standard was released by Announcement No. 6 of 2021 of the National Energy Administration, dated 22 December 2021, which, in accordance with the Standardization Law of the People's Republic of China and the Administrative Measures for Energy Standardization, approved 356 energy industry standards (Attachment 1), including the Code for Design of Forced Grouting Engineering in Underground Coal Mines, and 25 foreign-language editions of energy industry standards (Attachment 2), including the Technical Code for Design and Calculation of Combustion System of Fossil-fired Power Plant.

In the catalogue of industry standards attached to the announcement, NB/T 10882-2021 appears as serial No. 33, with no standard superseded and no adopted international standard, approval date 2021-12-22 and implementation date 2022-06-22.

Structure of the Standard

Chapter 3 is completed by Section 3.5 Risk Prevention and Control, starting on page 9.

Chapter 4 Risk Prevention and Control of Cascade Reservoirs in Planning Stage (page 11) comprises 4.1 General Requirements, 4.2 Risk Identification in Planning Stage, 4.3 Risk Analysis and Assessment in Planning Stage and 4.4 Risk Control in Planning Stage.

Chapter 5 Risk Prevention and Control of Cascade Projects in Design Stage (page 14) comprises 5.1 General Requirements, 5.2 Risk Identification in Design Stage, 5.3 Risk Analysis and Assessment in Design Stage and 5.4 Risk Control in Design Stage.

Chapter 6 Risk Prevention and Control of Cascade Projects in Construction Stage (page 18) comprises 6.1 General Requirements, 6.2 Risk Identification in Construction Stage, 6.3 Risk Analysis and Assessment in Construction Stage and 6.4 Risk Control in Construction Stage.

Chapter 7 Risk Prevention and Control of Cascade Reservoirs in Operational Stage (page 21) comprises 7.1 General Requirements, 7.2 Risk Identification in Operational Stage, 7.3 Risk Analysis and Assessment in Operational Stage and 7.4 Risk Control in Operational Stage.

Chapter 8 Risk Prevention and Control of Cascade Projects in Decommissioning Stage (page 25) comprises 8.1 General Requirements, 8.2 Risk Identification in Decommissioning Stage, 8.3 Risk Analysis and Assessment in Decommissioning Stage and 8.4 Risk Control in Decommissioning Stage.

Chapter 9 Preparation of Risk Assessment and Prevention and Control Report starts on page 27.

Appendix A Basic Information Requirements for Risk Prevention and Control of Cascade Reservoirs starts on page 29.

Appendix B Probability Analysis Method starts on page 31.

Appendix C Dam Break Flood Analysis Method for Cascade Reservoirs starts on page 34.

Appendix D Risk Loss Estimation Method starts on page 40.

The back matter comprises the Explanation of Wording in This Guideline (page 45) and the List of Quoted Standards (page 46).

The document closes with the Addition: Explanation of Provision, starting on page 47.

1 Scope

NB/T 10882-2021 is the Chinese guide for assessing and controlling the safety risk of cascade reservoirs - a series of dams built one below another on the same river. A cascade changes the nature of dam safety: the failure of one dam releases a flood into the reservoir of the next, and if that dam cannot pass or contain it, the failure propagates down the river. The guide addresses that chain across the whole life of the cascade, from planning and design through construction and operation to decommissioning. It sets the general provisions and a full set of defined terms, then the basic requirements on the organisation of risk management across what are often several owners on one river, and the acceptable risk levels expressed as annual probabilities of loss of life. It covers risk identification for each dam and for the cascade as a system - extreme floods, earthquakes, landslides into reservoirs, structural failure, gate malfunction and operational error - the analysis of dam break scenarios and their cascading consequences downstream, and the evaluation of risk against the acceptance criteria. Risk control follows: the engineering measures on the structures, the joint operation of the reservoirs for flood control, the shared monitoring and early warning systems, emergency planning and evacuation, and the information exchange between the operators of successive dams. Periodic reassessment and the documentation of the risk management system close the guide.

1.0.1 This guideline is formulated with a view to standardizing the whole-lifecycle safety risk assessment and prevention and control work for cascade reservoirs in a river basin, guarding against the risks of dam break and cascading dam break of cascade reservoirs, and raising the level of basin risk prevention and control.

1.0.2 This guideline is applicable to the safety risk assessment and prevention and control of cascade reservoir projects at every stage of their whole lifecycle, namely planning, design, construction, operation and decommissioning.

1.0.3 The safety risk prevention and control of cascade reservoirs shall follow the basic principles of "people first, overall coordination, scientific assessment, systematic prevention and graded management and control".

1.0.4 In addition to this guideline, the safety risk assessment and prevention and control of cascade reservoirs shall also comply with the requirements of the current relevant national standards.

2 Terms

2.0.1 cascade reservoirs: A group of reservoirs consisting of two or more cascade reservoirs. According to the mode of hydraulic connection, they are divided into series reservoir groups and mixed reservoir groups.

2.0.2 lifecycle of cascade reservoirs: The whole process of a cascade reservoir project from planning, design, construction and operation to decommissioning.

2.0.3 risk probability: The likelihood that a risk event turns into a hazardous accident.

2.0.4 risk loss: The losses or impacts caused by a hazardous accident, including loss of life, economic loss, environmental impact and social impact.

2.0.5 risk factor: Energy or an element that potentially may cause harm or damage in any form.

2.0.6 risk portfolio: The combination of conditions of different types of risk factors.

2.0.7 risk criterion: The limit values for risk acceptance and tolerance, covering acceptable risk, tolerable risk and unacceptable risk.

2.0.8 acceptable risk: The risk that those affected are able to accept under defined risk control conditions in order to obtain expected benefits or achieve a certain purpose.

2.0.9 tolerable risk: The risk that those affected are able to bear in order to obtain certain benefits or achieve a certain purpose.

2.0.10 ALARP principle (as low as reasonably practicable principle): The principle that risk shall be as low as reasonably practicable.

2.0.11 annual failure probability: The likelihood that a dam break of a cascade reservoir occurs in any single year within the actual service life.

2.0.12 extreme condition: A condition in which a low-probability event, such as a flood exceeding the design standard or an earthquake, is combined with usual loads.

2.0.13 dam break flood: A flood released suddenly or discharged downstream out of control as a result of the breach of a dam or other water-retaining structure.

2.0.14 dams break in cascade: An event in which the dams of two or more cascade reservoirs break in succession.

2.0.15 special freeboard: The dam height additionally added on top of the dam crest elevation determined in accordance with the current codes, in order to cope with basin system risk and increase the surcharge storage capacity of the project.

2.0.16 control cascade reservoir: A cascade that has sufficient flood regulation capacity to intercept or attenuate the propagation of basin risk to a certain extent, and whose own breach would lead to systemic risk in the basin.

2.0.17 key cascade reservoir: A cascade that has a certain flood regulation capacity, can ensure its own safety when a dam break occurs upstream, and does not amplify the risk passed downstream.

2.0.18 general cascade reservoir: A cascade that has no flood regulation capacity or only a small one, and cannot ensure its own safety when a dam break occurs upstream.

2.0.19 individual risk: In a basin cascade system, the likelihood that an individual without any protection and not evacuated dies as a result of a dam break flood.

2.0.20 societal risk: In a basin cascade system, the relationship between the number of deaths of a population group along the river banks inundated by a dam break flood and the frequency of dam break events, generally represented by an F-N curve, in which F is the cumulative frequency of N deaths.

3 Basic Requirements

3.1.1 The safety risk assessment and prevention and control of cascade reservoirs shall be supported by a sound management system, established rules and regulations, clearly defined boundaries of responsibility, strengthened communication and coordination and implemented control measures, so as to continuously raise the level of safety risk prevention of the basin system.

3.1.2 The safety risk assessment and prevention and control of cascade reservoirs shall, on the basis of engineering safety and in accordance with public safety requirements, establish a sound technical system for safety risk assessment and prevention and control.

3.1.3 The safety risk assessment and prevention and control of cascade reservoirs shall follow the working procedure of "comprehensively carrying out risk identification, scientifically analysing risk characteristics, objectively determining risk grades, formulating control plans by category, effectively controlling risk sources, monitoring risk information in real time, and preventing and defusing dam break risk", so as to ensure the safety of the cascade reservoirs in the basin.

3.1.4 The safety risk assessment and prevention and control of cascade reservoirs shall, in accordance with the characteristics and evolution patterns of basin risk, adhere to control of risk at its source, moving control checkpoints forward and closed-loop management, and shall adopt standardized, procedural and information-based methods to implement graded, categorized and dynamic risk management.

3.1.5 At different stages of the project, the safety risk assessment and prevention and control work for cascade reservoirs shall each have its own emphasis. In the planning stage, risk identification shall be strengthened, with the focus on avoidance; in the design stage, defences shall be strengthened and margins retained; in the construction stage, quality shall be ensured and no hidden hazards left; in the operation stage, risk monitoring shall be strengthened for prevention and early warning.

3.1.6 For relatively major and major risks identified at each stage of the lifecycle of cascade reservoirs, disposal measures shall be studied and proposed, or disposal completed, within the corresponding stage. Where disposal is carried over to the next stage, it shall be treated as a key point of risk prevention and control, and countermeasures shall be implemented to further reduce the risk or eliminate the hidden hazard.

3.1.7 The safety risk prevention and control of cascade reservoirs shall adhere to the principle of on-site disposal. For risks which, upon assessment, exceed the disposal capacity of the cascade reservoir itself and need to be passed downstream, their impact on the downstream cascades shall be assessed and corresponding countermeasures studied.

3.1.8 Where a cascade reservoir shows signs of dam overtopping or dam breach, effective measures shall be taken immediately to prevent the situation from worsening, the relevant authorities shall be notified immediately and the emergency plan shall be activated. Action shall not be delayed or refused on account of uncertainty, thereby missing the best time for disposal.

3.1.9 The safety risk assessment of cascade reservoirs in a basin should be carried out once every five years. A comprehensive assessment or a special assessment may be carried out according to actual needs, in order to review and update the list of risk factors of the cascade reservoirs, assess the risk grade of the cascade reservoir projects, propose the key points of risk prevention and control, formulate graded control measures and implementation plans, and produce a safety risk assessment report.

3.1.10 For cascade reservoir projects whose risk grade is high risk (Grade I) or relatively high risk (Grade II), special inspection and analysis shall be further carried out in depth, and measures to reduce the risk shall be studied and proposed.

3.1.11 The basic information requirements for safety risk prevention and control of cascade reservoirs shall comply with Appendix A of this guideline.

3.2.1 In view of the cascade development of the basin and the operation and management characteristics of the power stations, the safety risk assessment of cascade reservoirs shall include the identification of disaster-causing risk factors such as natural risks, engineering risks and management risks.

3.2.2 Safety risk identification of cascade reservoirs shall be carried out stage by stage, covering planning, design, construction, operation and decommissioning, and new risk factors shall be identified as early as possible, taking into account the cascade development of the basin and changes in conditions and environment.

3.2.3 Risk identification shall focus on the natural risks, engineering risks and management risks affecting the safety of the dams of cascade reservoirs; the identified risk factors shall be graded and categorized, and the list of risk factors shall be updated in a timely manner.

3.2.4 Risk identification shall combine multiple methods and should establish the identification list of risk factors of the cascade reservoirs level by level, in the order "cascade reservoirs - cascade reservoir project - main structures - key units".

3.3.1 Risk analysis shall comprise risk probability analysis and risk loss estimation. The identified risk factors should be categorized and graded, and the possible risk portfolios, risk triggering conditions, chain effects and failure modes should be analysed.

3.3.2 Risk probability analysis should adopt expert experience methods or reliability analysis methods, according to the characteristics of the cascade reservoir projects and the assessment requirements. Risk probability analysis methods may be applied in accordance with Appendix B of this guideline.

3.3.3 Risk loss estimation shall include the analysis and estimation of loss of life, economic loss, social impact and environmental impact, and shall be carried out on the basis of the risk analysis of the objects possibly affected by the dam break flood of the cascade reservoirs.

3.3.4 The dam break flood and the extent of possible inundation shall be determined through analysis of possible dam break modes, dam break flood calculation and flood routing analysis, establishing the inundated area, inundation depth, duration and the like. The dam break flood analysis methods for cascade reservoirs may be applied in accordance with Appendix C of this guideline. Risk loss estimation methods should be applied in accordance with Appendix D of this guideline.

3.3.5 The analysis of the objects possibly affected by cascade reservoirs should analyse engineering impact, social impact and environmental impact level by level, in the order "key units - main structures - cascade reservoir project - cascade reservoirs".

3.4.1 The individual risk of the dams of cascade reservoirs shall not be higher than the tolerable risk criterion of 1 x 10^-4 per year and should be lower than the acceptable risk criterion of 1 x 10^-6 per year. Group risk shall comply with the societal risk criterion given in Figure 3.4.1.

3.4.2 The classification of risk probability grades shall comply with Table 3.4.2. From low to high, risk probability is divided into five grades, "almost impossible", "unlikely", "possible", "very likely" and "highly likely", corresponding to Grades 1 to 5 respectively.