# Risk and Uncertainty in Dam Safety

## Table Of Contents

Contents

Dedication vi

CEA Technologies Dam Safety Interest Group vii

Acknowledgements ix

The Sponsors' Working Group X

Foreword xii

Preface XV

List of figures xix

List of tables XXV

Part I Guiding principles

1 Dam risk management 3

1.1 Dam risk management process 4

1.2 Potential benefits of integrated risk management 9

2 Guiding principles for risk analysis 11

2.1 Risk analysis methods 11

2.2 Risk analysis process 16

2.3 Iteration 19

2.4 Uncertainty and sensitivity analysis 20

2.5 Issues of good practice 20

3 Risk in decision-making 22

3.1 Significance of risk 22

3.2 Risk assessment 25

3.3 The value of risk information in decision-making 26

Part II Commentary on risk analysis

4 Reliability analysis 33

4.1 Failure modes, effects and criticality analysis 33

4.2 Event tree analysis 47

4.3 Fault tree analysis 67

Endnote 80

5 Consequence analysis 81

5.1 General considerations 82

5.2 General modelling considerations 84

5.3 Specific modelling considerations 90

5.4 Category considerations 94

5.5 Life safety analysis 97

6 Probability assignment 106

6.1 Philosophical preliminaries 106

6.2 Probability construct 114

6.3 Data 117

6.4 Phenomenological models 119

6.5 Experts and judgement 120

Endnote 123

Part III Theoretical considerations

7 Essential elements of probability theory 127

7.1 Uncertainty 127

7.2 Probability 134

7.3 The strength of evidence 140

7.4 Expert opinion 149

7.5 Appendix: mathematics of probability theory 166

Endnotes 175

8 Event tree analysis 176

8.1 Background 177

8.2 Concepts 184

8.3 Influence diagrams 191

8.4 Event trees 198

8.5 Branch probabilities 214

8.6 Calculations on event trees 228

Endnotes 233

9 Fault tree analysis 234

9.1 Mathematics of fault tree analysis 234

9.2 Fault tree evaluation 240

9.3 Quantitative evaluation 242

9.4 Component considerations 244

9.5 Operator actions 246

9.6 Probability 247

10 Consequence assessment 251

10.1 Importance of consequence analysis to risk 252

10.2 Modelling consequences 260

10.3 Measuring consequences 267

10.4 Public safety modelling and assessment 275

10.5 Economic modelling and assessment 282

10.6 Environmental modelling and assessment 288

Endnote 296

11 Methods for probability assignment 297

11.1 Quantifying probabilities 298

11.2 What do assigned probabilities mean? 302

11.3 Reasoning with probabilities 306

11.4 Quantified probability assignments 318

11.5 Judgement and probability 348

Endnotes 356

References 357

Glossary 370

Index 377