SAFETY OF DAMS AND DOWNSTREAM COMMUNITIES T E C H N I C A L N OT E 6 PORTFOLIO RISK ASSESSMENT USING RISK INDEX GOOD PRACTICE NOTE ON DAM SAFETY About the Water Global Practice Launched in 2014, the World Bank Group’s Water Global Practice 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 Twitter at @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 Water Global Practice and supported by Austria’s Federal Ministry of Finance, the Bill & Melinda Gates Foundation, Denmark’s Ministry of Foreign Affairs, the Netherlands’ Ministry of Foreign Affairs, the Swedish International Development Cooperation Agency, Switzerland’s State Secretariat for Economic Affairs, the Swiss Agency for Development and Cooperation, and the U.S. Agency for International Development. Please visit us at www.worldbank.org/gwsp or follow us on Twitter #gwsp. GOOD PRACTICE NOTE ON DAM SAFETY T E C H N I C A L N OT E 6 PORTFOLIO RISK ASSESSMENT USING RISK INDEX © 2021 International Bank for Reconstruction and Development / The World Bank 1818 H Street NW, Washington, DC 20433 Telephone: 202-473-1000; Internet: www.worldbank.org 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 of the data included in this work. The boundaries, colors, denominations, and other information shown on any map 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. 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 noncommercial purposes as long as full attribution to this work is given. This Technical Note on Portfolio Risk Assessment Using Risk Index is a supplementary document to the Good Practice Note on Dam Safety. Please cite the work as follows: World Bank. 2021. “Good Practice Note on Dam Safety – Technical Note 6: Portfolio Risk Assessment Using Risk Index.” World Bank, Washington, DC. 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; fax: 202-522-2625; e-mail: pubrights​ @­worldbank.org. Cover photo: Metolong water supply dam (Lesotho) © Marcus Wishart/World Bank. Cover design: Bill Pragluski, Critical Stages LLC. Technical Note 6: Portfolio Risk Assessment Using Risk Index Contents Introduction 1 Risk Index Method in Three Steps 3 Step One: Classify Dam Risk 3 Step Two: Select Relevant Measures for Indexing Risk 3 Step Three: Assign Weights to Risk Indexes 5 Risk Assessment for a Portfolio of Dams 9 Risk Assessment for an Individual Dam 9 Required Cautions for Using Risk Index Approach 9 Annex A: Dam Classification System Using Risk Index by Quebec Province of Canada 11 Annex B: India’s Risk Index Scheme under World Bank Financing 14 Annex C: Fatality Rates with and without Adequate Warning 17 References 19 Introduction Before the mid 1990s, a few organizations in International Commission on Large Dams (ICOLD) member countries started to practice risk analysis in the context of dam safety programs. Since that time, several methods and frameworks have been introduced into dam safety and risk analysis. The Risk-Based Profiling System (U.S. Bureau of Reclamation 2000) is one of the qualitative approaches, which is based on the “failure index” concept, that is, load x response associated with hydraulic, seismic, and static (normal) conditions. The failure index is multiplied by a hydrological-­ loss-of-life factor to characterize the consequences associated with a failure and is called the risk index (RI). RI methods provide a useful way of characterizing dam safety risks in a systematic, qualitative, and relatively simple manner to help evaluate and prioritize safety issues for individual dams and portfolios of dams. The approach strives to describe and communicate the significance of risk by using numbers or categorical values for the purpose of identifying and comparing risks using: •• Color-coded risk matrices •• Additive scoring methods for characterization of failure likelihood. The RI allows the user to assign points reflecting the significance of risk by following a defined process or series of matrices characterizing some specific aspects of the dam structure, but it does not relate the resulting index to an actual probability of failure. Thus, the process is typically easy to roll out and can Technical Note 6: Portfolio Risk Assessment Using Risk Index 1 also be implemented by individuals with limited understanding of the potential failure modes or risks associated with the dam structure. The approach presented herein is called a risk index because it provides an indication of potential levels of risk that might be associated with a dam failure. This tool is not a measure of risk estimating failure probability, but it provides a relative indication of potential levels of risk. These potential risks are quan- tified as deficiencies in the current physical state or condition of the dam and are weighted by their overall importance to the safety of the dam and the vulnerability and downstream hazard/consequence potential of the dam. Several countries have developed similar tools, including Australia, Canada, Czech Republic, New Zealand, Poland, Republic of Korea, South Africa, Sweden, the United Kingdom, and the United States (ICOLD 2005 and Wishart et al 2020). The World Bank has applied such methods in several national or subnational dam safety projects, such as in Armenia, Indonesia, Sri Lanka, and Vietnam. In these projects, RI was found to be a useful tool to assess the potential risk of portfolios of dams, enabling prioritization of riskier dams and their remedial works by means of both structural and nonstructural measures and comparing pre- and post-project interventions in a programmatic manner. The World Bank also recently assisted the Central Water Commission (CWC) in India for developing an RI scheme, building on the Brazilian system but adapting it to India’s context through a series of expert consultations with CWC and state-level officials. The Excel spreadsheet indexing tool and user manual has been prepared and validated using a series of case studies and examples by multiple groups (Zielinski, et al 2021). This Technical Note provides detailed information on the Brazilian risk classification system using the RI approach and the Indian RI system for the initial risk screening of a large portfolio of existing dams. Annex A provides basic information about the RI approach used in Quebec, Canada, for its dam classifi- cation system.1 These RIs are used for prioritization of required remedial works and other safety requirements. It should be noted, however, that RI is also a basic tool for preliminary level risk analyses for portfolios of dams and initial screening of risky dams, which may need to be supplemented by more advanced methods, depending on the type and potential risk of the dams. Because RI largely relies on visual inspection of the dams’ conditions, some critical failure modes could be missed. underestimated, or overestimated. In the higher risk cases, or whenever deemed appropriate, more detailed risk analyses, such as potential failure mode analysis (PFMA), can fill some of the gaps. RI methods should be tailor-made with due consideration to the local context, including the size and  makeup of a country’s portfolio of dams. A recommended approach is to go through the following three steps: 1 Mozambique has also developed a similar type of existing dam classification system to that of Brazil (Pinheiro et al. 2015). 2 Technical Note 6: Portfolio Risk Assessment Using Risk Index 1. Assign simple preliminary classification, using readily available information 2. Assign scores to a set of appropriate indexes for the specific dam or portfolio of dams 3. Assign weights to each index Risk Index Method in Three Steps Step One: Classify Dam Risk The method described in ICOLD (1989) is based on four parameters of simple quantification even at the early stage of dam safety assessment. It is recommended that such a method be used as the initial step of dam safety risk assessment, as introduced in the main Good Practice Note (GPN). The method ­described in table 1 allows dams to be assigned a risk class out of four categories: low, moderate, high, and extreme. For estimating the number of people for evacuation requirements, the number of population at risk (PAR) is estimated by assessing the number of households or people in the inundation areas in the case of dam failure. Then, the PAR can be converted into the potential loss of life by considering the fatality rate. Annex C provides diagrams used by the USBR on fatality rates with and without adequate warning under the Reclamation Consequence Estimating Technology (USBR, 2014). Fatality rates are based on warning time for each group of people at risk and flood severity. The flood severity is calculated as the product of inundation depth and flow velocity, which should be estimated using dam break and flood- ing simulation. Step Two: Select Relevant Measures for Indexing Risk RI methods have evolved since the earliest USBR application, with different entities with dam safety responsibility having adopted their own versions. TABLE 1. Assigning a Risk Class to Dams Potential hydraulic force in Reservoir capacity <0.1 0.1 to 1 1 to 120 >120 case of dam failure (million cubic meters) Points 0 2 4 6 Dam height (meters) <15 15 to 30 30 to 45 >45 Points 0 2 4 6 Potential downstream Evacuation requirements None 1 to 100 100 to 1,000 >1,000 consequence in case of (number of people) dam failure Points 0 4 8 12 Potential damage downstream None Low Moderate High Points 0 4 8 12 Total risk points (summation of the four factors’ points) <6 7 to 18 19 to 30 31 to 36 Class I (low) II (moderate) III (significant) IV (high) Source: Adapted from ICOLD 1989. Technical Note 6: Portfolio Risk Assessment Using Risk Index 3 Brazil’s risk classification system using risk index Among such specific country adaptations is the framework developed in Brazil (Brazil CNRH 2012). The Brazilian risk classification system has a good structure and has proved to be manageable. In the Brazilian system, the risk (R) is defined as the product of risk category/vulnerability (RC) and potential hazard (PH). R = RC * PH. RC is subdivided into three elements: •• Technical characteristics (TC), calculated by summation of respective points for dam height, length, construction material, foundation type, age, design flood return period, and so on •• Existing condition of dams (EC), calculated by points for reliability of spillway, reliability of outlet structures, seepage, deformation/settlement, slope deterioration, sluice gate/hydromechanical main- tenance, and so on •• Dam safety plan (SP), calculated by points for existence of project documentation, organization struc- ture/dam safety staff qualification, dam safety inspection/monitoring procedure, operational rules, dam safety reports with analysis and interpretation, and so on RC score is the sum of three subdivision scores. RC = TC + EC + SP Table 2, 3, and 4 provide a list of sub-parameters under TC, EC, and SP respectively under RC. The RC index can be regarded as a proxy of the likelihood of failure reflecting three aspects relevant to dam safety. PH is defined based on the points of four elements: (a) storage capacity; (b) potential loss of life; (c) socioeconomic impact; and (d) environmental impacts in case of dam failure, and the PH score is the sum of these three subdivision scores as shown in Table 5. As previously mentioned, R is defined as the product of RC and PH. Although this risk is not a formal risk metric (no probabilities are assigned), it can be used as a proxy for comparing the level of risk of individ- ual dams within a portfolio and meaningfully adapted to a country’s context. India’s Risk Index Scheme India’s RI scheme is based on Brazil’s system but modified for India’s dam safety context. Although the overall RI framework as the product of fragility (or vulnerability) and potential hazard/consequence is like that of Brazil, various key parameters and indicators have been selected based on the ICOLD general risk analysis framework (ICOLD 2017) and fault tree method. The simplification from a comprehensive probabilistic approach to RI was demonstrated to show the backward links and logic in constructing the indexing scheme. Further detailed mythology is provided in Annex B. 4 Technical Note 6: Portfolio Risk Assessment Using Risk Index TABLE 2. Score for Technical Characteristics Technical Characteristics Criteria (TC) Height (H), Age, m (a) Length (L), m and L/H (b) Type (c) Foundation (d) yrs (e) Design Flood (f) ≤ 15(1) Embankment: L ≤ 200 and L/H > 3 Concrete arch Very good 2 30 to 50 PMF concrete/masonry stone/cyclopean (1) (0) (1) (1) concrete/concrete gravity: L ≤ 200 (1) 15 < H < 30 Embankment: 200 < L < 500 and Concrete gravity Good3 10 to 30 5,000 years (2) L/H > 3 concrete/masonry stone/ (2) (2) (2) (2) cyclopean concrete/concrete gravity: 200 < L < 500 (2) 30 ≤ H ≤ 60 Embankment: 200 < L < 500 and Masonry Acceptable4 5 to 10 (3) 1,000 years (3) L/H ≤ 3 or 500 ≤ 2,000 and L/H > 3 stone/cyclopean (3) (5) concrete/masonry stone/cyclopean concrete/ concrete/concrete gravity: 500 ≤ L ≤ concrete gravity 2.000 (3) (3) 60 < H ≤ 100 Embankment: 500 ≤ L ≤ 2,000 and Zoned earth- Poor5 < 5 or > 50 500 years (4) L/H ≤ 3; or L > 2,000 fill and earth/ (8) or without (8) concrete/masonry stone/cyclopean rock-fill1 information concrete/concrete gravity: L > 2,000 (4) (4) (4) > 100 Homogeneous1 Very poor6 < 500 years or (5) (5) (10) unknown (10) TC = Σ (a - f) Source: Adapted from Resolution No. 143 of the Conselho Nacional De Recursos Hídricos (CNRH) or National Council of Water Resources, July 10, 2012, Ministry of Environment, Brazil Note: TC = technical characteristics; m = meters; PMF = probable maximum flood  Add (1) to the weight when any conduit is in direct contact with or penetrates the embankment. 1 2  Very good: Adequate mechanical and hydraulic characteristics of the foundation according to the dam type (no treatment required) 3  Good: Adequate mechanical characteristics and adequate hydraulic treatment of the foundation according to the dam type 4  Acceptable: Adequate mechanical and hydraulic treatment of the foundation according to the dam type 5  Poor: Non-existent or inadequate mechanical or hydraulic treatment of the foundation according to the dam type 6  Very poor: Problematic soil or rock foundation Step Three: Assign Weights to Risk Indexes The final step in the methodology is to combine the results of the dam safety review including onsite inspection with the results of the relative importance determination to generate a set of risk indexes, or ‘‘weighted’’ risk scores, for the current condition of existing dams. Although weights are project-specific and best assigned by expert elicitation, it is important to optimize the balance of weights between different indexes pertaining to each group, that is, TC, EC, and SP. In India’s RI scheme, for example, it deviates from Brazil’s system by appropriately adapting the sub-­ elements of the RI under the categories of TC, EC, SP, and PH. Technical Note 6: Portfolio Risk Assessment Using Risk Index 5 6 TABLE 3. Score for Existing Conditions Existing Conditions Criteria (EC) Outlet Works Intake Deformations and Slope Spillway Reliability Structure Reliability Seepage Settlements Deterioration Locks (g) (h) (i) ( j) (k) (l) Civil and hydro-electromechanical structures in full Civil and hydro- Totally controlled by None None None working conditions/unobstructed approach channel electromechanical structures drainage system (0) (0) (0) or uncontrolled spillway (including morning glory) in adequate conditions, (0) (0) maintained and functioning (0) Civil and hydro-electromechanical structures in Civil and hydro- Stabilized and Presence of some lack of maintenance Civil and hydro- operating conditions but without an emergency electromechanical structures monitored wet areas cracks and depressions in slope protection, electromechanical plant/approach channel or uncontrolled spillway with identified problems, with in downstream areas, without adverse effect presence of some small structures, well (including morning glory) with erosion or reduction in flow capacity and slopes, or abutments (1) bushes without adverse maintained and obstructions but without risk to spillway structure corrective actions underway (3) effect functioning (4) (2) (1) (1) Civil and hydro-electromechanical structures Civil and hydro- Wet areas in Significant presence of Surface erosion, exposed Civil and hydro- Technical Note 6: Portfolio Risk Assessment Using Risk Index with identified problems, with corrective actions electromechanical and downstream areas, cracks and depressions steel, generalized electromechanical underway for reduction in flow capacity/approach uncontrolled structures with slopes, or abutments that may lead to vegetation growth, and structures with channel of uncontrolled spillway (including morning identified problems, with without treatment or sinkholes, requiring animal burrows requiring identified problems glory) with erosion and/or partially obstructed, with reduction in flow capacity, under investigation additional studies or monitoring or corrective and corrective actions risk of compromising spillway structure and without corrective (5) monitoring action underway (7) actions (5) (5) (2) (4) Civil and hydro-electromechanical structures with Uncontrolled structures Emerging in Significant presence Significant erosion Civil and hydro- identified problems, reduction in flow capacity with identified problems downstream areas, of cracks, sinkholes or and deep gullies, with electromechanical without corrective actions/approach channel of or conduit with seepage slopes, or abutments slides, with potentially potentially compromised structures with uncontrolled spillway (including morning glory), emerging downstream with soil migration or compromised slope stability and safety identified problems obstructed or with damaged structures without corrective actions increasing flow structural safety (7) and without corrective (10) (8) (8) (8) actions underway (4) EC = Σ (g-l) Source: adapted from Resolution No. 143 of the Conselho Nacional De Recursos Hídricos (CNRH) or National Council of Water Resources, July 10, 2012, Ministry of Environment, Brazil Note: EC = existing condition. TABLE 4. Score for Dam Safety Plan Dam Safety Plan Criteria (SP) Organizational Structure Operational Dam Safety and Technical Qualifications Regulations Reports with Existing Design of Dam Safety Professional Safety Inspection Report and of Discharge Analysis and Documentation Team Members Monitoring Procedures Facilities Interpretation (n) (o) (p) (q) (r) Plans/specs, as-built, Have organizational structure Have and use inspection yes or have Submit report and construction with dam safety technician and monitoring procedures uncontrolled periodically in records (0) in accordance with the spillway or accordance with the (0) regulations other discharge regulations (0) structures (0) (0) Plans/specs, as-built, Have dam safety technician Have and seldom use None Submit report and construction (4) inspection procedures (6) irregularly in records in accordance with the accordance with the (2) regulations regulations (3) (3) Basic design Does not have organizational Have and does not use Does not submit (4) structure nor dam safety Inspection and monitoring reports in technician procedures in accordance with accordance with the (8) the regulations regulations (5) (5) Feasibility or Does not have nor use conceptual design inspection and monitoring (6) procedures in accordance with the regulations (6) None (8) SP = Σ (n - r) Source: Adapted from Resolution No. 143 of the Conselho Nacional De Recursos Hídricos (CNRH) or National Council of Water Resources, July 10, 2012, Ministry of Environment, Brazil. Note: SP = Dam Safety Plan. The process of allocating weighting scores was guided by the approach founded on the Analytical Hierarchy Process that uses a Saaty’s Scale of Relative Importance (Saaty 1987) via pairwise comparisons of all fragility factors. The knowledge (experts’) elicitation process involved a team of international experts, staff, and engineers from the Central Water Commission, State Dam Safety Organizations, and other dam management agencies. Based on the World Bank’s experience of various dams’ safety and rehabilitation projects and the recent discussions with the international and national experts for a project in India, the weighting factor (WF) for India can be used as an initial reference in the case of existing dams, which represents the prevalent application in World Bank–supported operations. However, it may occasionally be necessary to deal with a program of new dams, in which screening and ranking of investment options needs to be done. In that case, the WFs should be different, at least because EC and SP are expected to be satisfactory for new dams. Table 6 reflects such considerations Technical Note 6: Portfolio Risk Assessment Using Risk Index 7 TABLE 5. Score for Potential Hazard Reservior Total Volume, hm3 Loss of Life Potential Environmental Impact Socio-Economic Impact (a) (b) (c) (d) Small NON-EXISTING SIGNIFICANT NON-EXISTING ≤5 (no persons permanently or (affected area of dam is not (infrastructure and navigational (1) temporarily occupy nor drive in/ environmentally relevant services do not exist in area affected by through affected area downstream protected under specific potential failure of dam) of dam) legislation, or lacking its (0) (0) natural conditions) (3) Medium LITTLE FREQUENT VERY SIGNIFICANT LOW 5 to 75 (2) (no persons permanently occupy (affected area of dam is (small concentration of residential affected area downstream of dam envionmentally relevant commercial agricultural industrial areas but a locally used road exists) protected under specific and infrastructure in area affected by (4) legislation) dam or ports navigational services) (5) (4) Large FREQUENT HIGH 75 to 200 (persons permanently occupy (large concentration of residential, (3) affected area downstream of dam commercial, agricultural industrial plus municipal stale federal highway areas and infrastructure and tourist and or a possibly permanent place leisure services in area affected by dam with people that may be impacted) or ports & navigational services) (8) (8) Very large >200 EXISTING (5) (persons permanently occupy affected area downstream of dam and lives may be impacted) (12) PH-Σ (a - d) Source: Adapted from Resolution No. 143 of the Conselho Nacional De Recursos Hídricos (CNRH) or National Council of Water Resources, July 10, 2012, Ministry of Environment, Brazil. Notes: PH = potential hazard. TABLE 6. A Sample of the Weighting Factors Distribution for Existing and New Dams Weighting Factors (WFs) Classification element (Brazil and India) WFs for existing dams WFs for new dams Technical characteristics 0.10 0.40 Existing conditions 0.35 0.00 Dam safety plan 0.05 0.10 Potential hazard 0.50 0.50 Source: Original compilation. and provides a sample of the WFs considering the Indian RI scheme, which builds on the Brazilian risk classification system. It must be reiterated that the proposed WFs are for initial reference only. Actual WFs should reflect spec- ificity of each project, adapting to local conditions, and they are best assigned by expert elicitation. It is 8 Technical Note 6: Portfolio Risk Assessment Using Risk Index important to test the RI system for some sample dams and ensure that the ranking results by RI are generally consistent with the overall understanding of the dam owners and regulators regarding the safety condition of the portfolio of dams and their priority of rehabilitation needs. Risk Assessment for a Portfolio of Dams The typical application of RI methods is in portfolio risk assessment (PRA) or portfolio risk management (PRM). They are useful in assessing the risk profiles of a portfolio of dams and prioritizing higher-risk dams and risk-reduction measures including structural and nonstructural measures in an optimized and programmatic manner. The results typically include: •• Assessment of risk profile of portfolio of dams as baseline conditions •• Prioritization of risky dams and required remedial measures covering both short- and long-term ones •• Improvement of overall dam safety management program along with intensified monitoring and sur- veillance for higher-risk dams •• Confirmation of project impacts comparing the risk profile before and after the project interventions •• Development of a short- and long-term business and budget plan Risk Assessment for an Individual Dam RI methods do not provide a quantified risk assessment; therefore, it is not possible to compare dam conditions with any tolerable risk level. Nevertheless, RI methods can still offer value when applied to an individual case; for example: •• They prompt the users to focus on key safety-related issues. •• They help in identifying gaps of knowledge (for example, dam records, hydrological data, instrumen- tation adequacy, and so on) and to address them on a priority basis. •• Using another dam with quantified risk level as a benchmark can assist in empirical quantification of risk. •• They can help evaluate the effects of risk reduction and dam safety enhancement measures on the risk score. Required Cautions for Using Risk Index Approach It is noted that the RI method is suitable for periodic re-evaluation of dam safety aspects during proj- ect implementation as more information and resources become available. When significant changes are anticipated, it could be advisable to include such a provision and appropriate budget under the project. Technical Note 6: Portfolio Risk Assessment Using Risk Index 9 Recognizing the benefits from applying RI approaches, it is also necessary to keep in mind their limita- tions. The most important among these are: •• Poor classification of risk levels in characterizing failure likelihood and adverse consequences or improper size of intervals (either too narrow or too wide) for each level of risk class. It can result in assignment of identical ratings to very different level of risks. •• Incorrect assigning of higher qualitative ratings to quantitatively smaller risks. For risks with nega- tively correlated reliabilities or likelihoods of failure and adverse consequences, it can lead to serious mischaracterization of risk. •• Ambiguity and subjectivity in characterization of risk index parameters. It can cause different users to arrive at different ratings of the same quantitative risks. Categorizing parameters used for the index requires subjective judgments and arbitrary decisions about aggregation of multiple small and fre- quent events as opposed to fewer and less frequent but more severe events.2 •• Need to adjust the structure of the RI depending on the national economic, social, and cultural reali- ties and traditions. Risk aversion or risk tolerance differs from country to country, and these differ- ences must be reflected in the RI. These limitations suggest that RIs should always be used with caution and only with detailed explana- tions of judgments applied to the development of RIs/matrices and the calculations of outcomes. Although the information obtained with the help of RI can be extremely useful for preliminary screening or ranking of riskier dams, especially for a large portfolio of dams, it is recommended that those identified higher risk dams should be subject to further detailed risk assessment, using PFMA or other qualitative or quantitative risk analysis. This will inform decision making on priority remedial works at the next stage. 2 Ambiguity can be reduced by a better description of risk index parameters and arbitrariness by a detailed guidance on interpretation and selection. Consistency across the portfolio of dams and consistency in applications by different analysts or teams can be improved by a comprehensive training. 10 Technical Note 6: Portfolio Risk Assessment Using Risk Index Annex A: Dam Classification System Using Risk Index by Quebec Province of Canada The classification of dams in Quebec, Canada, is derived from an RI based on characterization of dam’s vulnerability and potential consequences if the dam fails. The regulation provides detailed instructions on how the RI should be applied. The Provincial government of Quebec, Canada, passed the Dam Safety Act and its regulation in 2002. The act defines two types of dams: (a) high-capacity dams and (b) low-capacity Dams. High-capacity dams are defined and categorized as: •• I-a. Dams one meter or more in height having an impounding capacity greater than 1 million cubic meters •• I-b. Dams 2.5 meters or more in height having an impounding capacity greater than 30,000 cubic meters •• I-c. Dams 7.5 meters or more in height, regardless of impounding capacity The main dam safety provisions apply to high-capacity dams. Low capacity dams are defined as dams with 2 meters or more in height that are not high capacity dams. The Act requires that a dam be classified by the minister before authorization for the construction of the dam. A dam owner may apply for a review of the classification of the structure if a supporting report or study made under the responsibility of an engineer is submitted with the application. The Act also pro- vides for the establishment of a register for all dams one meter or more in height. The dam owners are required to submit information, including documents for dam registration, and offense against the pro- vision renders the owner liable for a fine of not less than US$2,000 and not more than US$200,000. The Act provides details of the dam classification system based on the degree of risk, which has five categories from A to E, with the formula of P (degree of risk) = V (vulnerability) * C (consequences). The V of a dam is measured by multiplying the arithmetic mean value of “constant physical parameters” by the arithmetic mean value of “variable parameters.” The constant physical parameters to be considered are: (a) dam height, (b) dam types, (c) impounding capacity, and (d) foundation types. The variable parameters to be considered are: (a) dam age as per dam type, (b) seismicity (seismic zone), (c) dam condition, and (d) reliability of the discharge facilities. The dam condition is assessed considering the physical state and structural condition of the dam, the quality and effectiveness of maintenance, aging, possible effects of external factors, and any dam design or structural defects. The dam failure consequence (C) category is classified into six categories from very low to severe, with 1 to 10 points based on the characteristics of the downstream area that would be affected by the dam failure in terms of population density and the extent of downstream infrastructure and services that would be destroyed or severely damaged in the event of a dam failure. A detailed description of each category is provided, including the number of people and size of enterprises, and so on in downstream flooding areas. The dam classification system using these indexes is summarized as below. Technical Note 6: Portfolio Risk Assessment Using Risk Index 11 Dam Classification System Using Risk Index in Quebec 1. Dam’s Vulnerability a. Constant physical parameters i. Dam height ii. Dam types iii. Impounding capacity iv. Foundation types b. Variable parameters i. Dam age as per dam type ii. Seismicity (seismic zone) iii. Dam Condition iv. Reliability of discharge facilities 2. Consequence The Act also defines the required level of consequence assessment depending on the consequence ­ category. For example, The delineation of the area that would be affected by a dam failure and identification of the charac- teristics of the area are based on a dam failure analysis that includes inundation maps. That anal- ysis, using recognized methods, consists of a detailed evaluation of the consequences of a dam failure by means of an accurate delineation of the affected area and identification of the character- istics of the area. The analysis involves an examination of various dam failure scenarios under normal conditions and in flood conditions. It includes a description of the assumptions and proce- dures that were used to select the scenarios examined and to determine the dam break flood wave, flood wave arrival times and the extent of the affected area. For scenarios in which the dam fails during a flood, the affected area would be the area that would be inundated due entirely to the dam failure. If, in the opinion of the engineer in charge, the dam failure consequence category is “moderate”, only rough inundation maps showing the area that would be affected by a dam failure are required. This mapping consists of a rough assessment of the consequences of a dam failure by means of a delinea- tion of the affected area on topographical maps and identification of the characteristics of the area. calculations, such as flood flows and The mapping is established on basic hydrologic and hydraulic ­ breach flows, as well as on a rough analysis of the downstream watercourse profile and cross-sections. For the purposes of the mapping, the extent of the affected area is determined by adding the breach flow to the 1000-year flood flow to a point of attenuation or restriction, such as confluence with a large lake or river or another dam. 12 Technical Note 6: Portfolio Risk Assessment Using Risk Index If, in the opinion of the engineer in charge, the dam failure consequence category is “very low” or “low”, only a characterization of the area that would be affected by the dam failure is required.” That characterization consists of a conservative estimate of the consequences of a dam failure by means of a rough delineation of the affected area and a general description of the characteristics of the area. For the purposes of the characterization, the extent of the affected area is established by adding the reservoir depth to the 100-year flood level to a point of attenuation or restriction, such as confluence with a large lake or river or another dam. Every dam must, according to its class, be the subject of the minimum number of inspections in accor- dance with the required frequency as per dam classification. On the other hand, it should be noted that design flood is determined solely by consequence category. Technical Note 6: Portfolio Risk Assessment Using Risk Index 13 Annex B: India’s Risk Index Scheme under World Bank Financing Table B.1 indicates India’s RI scheme for a recently approved Bank-funded project. The risk of a dam is defined as the product of the fragility (or vulnerability) of the dam and the potential hazard associated with the dam. The fragility score is calculated as the sum of scores for the following three subcategories: (a) TC largely related to the design of the dam, (b) EC relating to the current condition of the dam, and (c) SP for dam safety. Each of these three categories is subdivided into more-detailed risk factors. TABLE B.1. India’s Risk Index Scheme – Fragility Categories and Factors Technical characteristics Existing conditions Safety plan 1 Dam age 1 Seismic design 1 Design documentation 2 Inflow design flood 2 Installed flow control equipment 2 Operation and maintenance manual 3 Seismic zone 3 Flow control equipment condition 3 Emergency Preparedness Plan 4 Landslide, glacier lake 4 Presence of back-up power 4 Organization, staff number, capacity, outburst flow, landslide dam qualification outburst flow, debris flow 5 Length 5 Access to site 5 Safety inspection, monitoring, and reporting 6 Conduits 6 System operation 6 Dam safety reports, analysis, and interpretation 7 Filters 7 Concrete gravity structure 7 Follow-up actions 8 Foundation and abutments 8 Spillway structure 9 Masonry structure 10 Embankment, foundation and abutments The potential hazard is also subdivided into three factors: (a) threat to life safety characterized by pop- ulation at risk (PAR), (b) environmental impacts, and (c) socioeconomic impacts. The Indian National Dam Inventory Assessment (INDIA) includes the user manual and Excel spread- sheet indexing tool (Zielinski, et al 2021) provides detailed guidance on how to assess and assign scores for each of fragility and hazard potential indicators. Figure B.1 shows the fault tree model as the foundation of India’s RI system based on the general risk analysis framework as recommended by ICOLD (2017). The model provides the logical framework for the characterization of possible dam failure scenarios in terms of both sequence of events leading to the dam failure as well as probabilities involved. As such, the model is of a general nature and is capable to fully characterize the risk of dam failure if numerical values of all relevant probabilities are available. For the screening purposes of portfolios of dams, especially when the portfolio is large, full numerical characterization of probabilities is either not feasible or simply cost ineffective. In such cases, a simpli- fied process can be applied, and the simplification replaces the numerical values of probabilities by scoring indexes which are therefore the proxies for unknown probabilities. 14 Technical Note 6: Portfolio Risk Assessment Using Risk Index FIGURE B.1. Fault Tree Model for Risk Indexing Scheme Dam failure Loss of strength Overtopping Discharge equipment Inadequate discharge Inadequate stability Inadequate durability failure capacity Inadequate water tightness Global failure mode Specific failure mode OR gate Furthermore, table B.2 shows the relationship between global/specific potential failure modes and fra- gility factors based on the fault tree model in figure B.1. The cells with x means that potential failure modes on the horizontal axis can be triggered by fragility factors in TC, EC, and SP on the vertical axis. For example, x in the cells of the fourth column indicate which of the fragility factors can increase the likelihood of mass movement occurring. Increasing the scores for the factors serve as proxies for increas- ing probabilities of occurrence. Technical Note 6: Portfolio Risk Assessment Using Risk Index 15 TABLE B.2. Relationship between Fragility Factors and Potential Failure Modes Inadequate Inadequate water Inadequate stability durability tightness Overtopping Inadequate Discharge Instant. Seepage Seepage discharge capacity capacity Mass Loss of change Structural through around not movement support of state weakening the dam the dam design installed available TC-1 Dam age x x x x x x x TC-2 Inflow design flood x Technical Characteristics (TC) TC-3 Seismic zone x x x x x x x x TC-4 Landslides, GLOFs, x x x x x x x LDOFs and debris flow TC-5 Dam length x x TC-6 Conduits x x TC-7 Filters x x x x x x TC-8 Foundation and x x x x x abutments EC-1 Seismic design x x x x x x x EC-2 Installed flow control x equipment EC-3 Flow control equipment x Existing Conditions (EC) condition EC-4 Backup power x EC-5 Access to site x EC-6 System operation x EC-7 Concrete gravity structure x x x EC-8 Spillway structure x x x x x x EC-9 Masonry structure x x x x EC-10 Embankment, abutments x x x x x x and foundation SP-1 Documentation x x x x x x x x x SP-2 Operation & maintenance x x x x x x x manual SP-3 Emergency Preparedness Safety Plans (SP) Plans SP-4 Organization, manpower x x x x x x x x x and qualifications SP-5 Safety inspections, x x x x x x x monitoring, and reporting SP-6 Dam safety reports, x x x x x x x x analysis and interpretation SP-7 Follow and up actions x x x x x x x x x Source: Zielinski, et al (2021) Note: GLOF = glacial lake outburst flood; LDOF = landslide dam outburst flood. 16 Technical Note 6: Portfolio Risk Assessment Using Risk Index Annex C: Fatality Rates with and without Adequate Warning Figures C.1 and C.2 (USBR 2014) give some ideas on the fatality rate along the y axis corresponding to the hydraulic force, which is the product of inundation depth and flow velocity, in the x axis. The inunda- tion depth and flow velocity should be estimated using dam break and flooding simulation. The dots in the two figures generally indicate the anticipated fatality rate in the case of little or no warning versus adequate warning. These figures are useful in estimating the number of potential loss of life depending on the Emergency Preparedness Plan availability and deployment of the emergency notification/warn- ing system. The fatality rates should however be referred to only for general reference but be adapted to different countries’ contexts considering their societal, cultural and economic conditions. FIGURE C .1. Fatality Rate—Flood Severity with Little or No Warning 1.0 0.1 0.01 Fatality rate 0.001 0.0001 0 10 100 1,000 10,000 DV (depth velocity, ft2/sec) Overall limit Cases with little or no warning Suggested limit Cases with partial warning Source: USBR 2015. Note: This chart is part of USBR’s consequence estimating methodology (RCEM, 2014). It is intended to be used only in conjunction with the entire methodology (revised June 2015 to reflect revised case data). DV = the product of maximum depth of flooding and maximum flood velocity; ft2/sec = square feet per second. Technical Note 6: Portfolio Risk Assessment Using Risk Index 17 FIGURE C .2. Fatality Rate—Flood Severity with Adequate Warning 1.0 0.1 0.01 Fatality rate 0.001 0.0001 0 10 100 1,000 10,000 DV (depth velocity, ft2/sec) Overall limit Cases with adequate warning Suggested limit Cases with partial warning Source: USBR 2015. Note: This chart is part of USBR’s consequence estimating methodology (RCEM, 2014). It is intended to be used only in conjunction with the entire methodology (revised June 2015 to reflect revised case data). DV = the product of maximum depth of flooding and maximum flood velocity; ft2/sec = square feet per second. Note: ft3 = cubic feet. 18 Technical Note 6: Portfolio Risk Assessment Using Risk Index References Brazil. Conselho Nacional De Recursos Hídricos (CNRH) or National Water Resources Council, Ministry of Environment. Resolution No. 143. 2012. “It lays down general classification criteria for dams by risk category, potential damage associated with the volume of the reservoir in attention to article 7 of Law 12344 of September 2010.” ICOLD. 1989. Bulletin 72: Selecting Seismic Parameters for Large Dams. Paris: ICOLD. ———. 2017. Bulletin 154: Dam Safety Management: Operational Phase of the Dam Life Cycle. Paris: ICOLD. ———. 2005. Bulletin 130: Risk Assessment in Dam Safety Management: A Reconnaissance of Benefits. Paris: ICOLD. Pinheiro, A., J. Mora Ramos, L. Caldeira, E. Jossefa, and A. Boavida. 2015. Proposal for the Dam Safety Regulation of Mozambique. Paper presented at the Dam World Conference, Lisbon, Portugal. Saaty, R. W. 1987. “The Analytic Hierarchy Process: What It Is and How It Is Used,” Mathematical Modelling 9(3–5), 161–176. USBR (U.S. Bureau of Reclamation). 2000. “Risk Based Profiling System.” Denver, Colorado. USBR (US Bureau of Reclamation). 2015. “Reclamation Consequence Estimating Methodology (RECM): Interim Guidelines for Estimating Life Loss for Dam Safety Risk Analysis.” Denver, Colorado. Wishart, Marcus J., Satoru Ueda, John D. Pisaniello, Joanne L. Tingey-Holyoak, Kimberly N. Lyon, and Esteban Boj Garcia. 2020. “Laying the Foundations: A Global Analysis of Regulatory Frameworks for the Safety of Dams and Downstream Communities.” Sustainable Infrastructure Series, Washington, D.C.: World Bank. Zielinski, A. Przemyslaw, Pramod Narayan, C. Richard Donnelly, Eric Halpin, Jonathan Quebbeman, Halla Maher Qaddumi, Chabungbam Rajagopal Singh, Satoru Ueda, and Marcus Wishart. 2021. “Risk screening tool in dam safety assessment.” manuscript for Hydropower & Dams: Aqua-Media International Ltd. Surrey, UK. Technical Note 6: Portfolio Risk Assessment Using Risk Index 19 SKU W20086