Interim Guide to Quantitative Risk Assessment for UK Reservoirs

Table Of Contents

Contents

Preface xi

Disclaimer xii

Acknowledgements xii

Feedback sheet on the use of the Guide xiii

Part A: Overview of the Guide 1

Scope of the Guide 3

Intended application and standing of the Guide 4

Implications for existing Guides 5

Key terms and concepts adopted in the Guide 5

Process for carrying out QRA 6

Facilities included in Excel workbook and password 10

Intended users and quality control 10

Input data required 11

Programme for review and updating of Guide 11

Part B: Application of the Interim Guide to QRA (Excel workbook) 13

0 Document control 15

1 Site inspection 17

1.1 General 17

1.2 Subject reservoir (sheets 1.1-1.3) 17

1.3 Upstream and downstream reservoirs (sheets 1.4 and 1.5) 18

1.4 Downstream installations (sheet 1.6) 19

2 Annual probability of failure due to extreme rainfall 21

2.1 General 21

2.2 Review of criticality of mechanisms of deterioration (sheet 2.2) 21

2.3 Dam Critical Flood (sheet 2.3) 23

2.4 Wind-generated waves (sheet 2.4) 26

2.5 Assessment of peak reservoir inflow vs annual probability (sheet 2.5) 26

2.6 Estimating the annual probability of failure due to extreme rainfall (sheet 2.6) 26

2.7 Background 26

3 Annual probability of failure due to upstream reservoir 31

3.1 General 31

3.2 Review of criticality of mechanisms of deterioration (sheet 3.2) 31

3.3 Annual probability of failure due to failure of an upstream dam (sheet 3.3) 32

3.4 Background 34

4 Annual probability of failure due to internal stability (embankment) 35

4.1 General 35

4.2 Event train (sheet 4.2) 36

4.3 Evaluation of anchor point(s) (sheet 4.3) 36

4.4 Current Condition Score (sheet 4.4) 37

4.5 Estimating the annual probability of failure (sheet 4-5) 39

4.6 Background 39

5 Annual probability of failure due to internal stability (appurtenant works) 45

5.1 General 45

5.2 Event train (sheet 5.2) 46

5.3 Evaluation of anchor points (sheet 5.3) 47

5.4 Current Condition Score (sheets 5.4 and 5.5) 47

5.5 Estimating the annual probability of failure (sheet 5.6) 48

6 Annual probability of failure due to other threats 49

6.1 General 49

6.2 Non-core external threats that may be significant at a particular reservoir (sheet 6.1) 49

6.3 Seismic events (sheet 6.2) 50

6.4 Wind (sheet 6.3) 51

6.5 Background: quantifying annual probability of failure 51

7 Overall annual probability of failure 53

7.1 General 53

7.2 Overall annual probability of failure 53

7.3 Background 53

8 Dambreak analysis 55

8.1 Introduction 55

8.2 Dam breach hydrograph (sheet 8.2) 56

8.3 Setting up the routing (sheet 8.3) 57

8.4 Rapid method for estimating 100-year flood at confluence (sheet 8.4) 58

8.5 Routing the dambreak flood down the valley (sheet 8.5) 58

8.6 Background 59

9 Likely loss of life 65

9.1 General 65

9.2 Estimating population at risk and likely loss of life (sheet 9) 65

9.3 Background 66

10 Cost of flood damage 71

10.1 General 71

10.2 Estimating cost of direct third-party damage (sheet 10) 72

10.3 Background: approach to quantifying damage 73

11 Consequence class and tolerability of risk 77

11.1 General 77

11.2 Consequence class (sheet 11.2) 77

11.3 Risk analysis and assessment (sheet 11.3) 78

11.4 Risk assessment: ALARP calculation (sheet 11.4) 78

11.5 Background 79

12 Review of output 83

12.1 General 83

12.2 Review of output from interim Guide to QRA (sheets 12.1 and 12.2) 83

References 85

Appendix A: Terminology 89

Acronyms 89

Definitions 89

Appendix B: Introduction to quantitative risk assessment 93

Background 93

Use of quantitative risk assessment 93

Probability and uncertainty 94

Consequences of failure 95

Appendix C: Completed example of quantitative risk assessment 97

Index 157