Floods and Reservoir Safety Fourth Edition

Contents Preface vii
1 Introduction 1
Background 1
Changes 1
Scope of the guide 2
References 2
2 Floods and waves protection standards 3
General 3
The main factors 4
Standards-based approach 4
Risk-based approach 8
Other criteria 9
Other aspects 11
References 13
3 Derivation of reservoir flood inflow 15
Objective 15
Flood Studies Report and Flood Estimation Handbook 15
Revitalised flood hydrograph rainfall-runoff method 16
Clarification of appropriate models and design rainfall inputs 16
Summary of the FSR/FEH rainfall-runoff method for the T-year event 16
Summary of the methodology for estimating the PMF event 17
Summary of the rainfall DDF and the rainfall-runoff models 17
Use of local data 17
The contribution of extreme snowmelt 17
Climate change 19
Rapid method of assessment based on FSR procedures 19
Software 20
References 20
4 Reservoir flood routing 21
Objective 21
Recommended stages in routing calculation 21
Gated spillways 23
Siphon spillways, automatic toppling weirs and fuse plugs 23
Auxiliary spillways 24
Temporary upstream storage 24
References 24
5 Waves, wave overtopping and dam freeboard 25
Scope 25
Water surface and fetches 25
Wind speed, duration and direction 25
Wave height and period prediction 28
Wave overtopping 30
References 33
6 The overflowing and overtopping of embankment dams 35
Introduction 35
Classification 35
Physical factors affecting erodibility 35
Overflowing: assessment 36
Overflowing: remedial measures 38
Overtopping: assessment 40
Overtopping: remedial measures 41
References 41
7 Floods during dam construction and dam improvement works 43
Flood risks during new dam construction 43
Diversion structures 44
Flood risks during improvement and/or dam removal works 44
Health and safety requirements 44
References 45
Appendix 1 Rapid assessment of flood capacity and freeboard at existing dams 47
Purpose 47
Procedure 47
References 47
Appendix 2 Detailed advice on applying on FSR/FEH rainfall-runoff method to reservoir safety 55
Introduction 55
FEH rainfall DDF model 55
FEH13 rainfall DDF model 55
ReFH method 56
Advice on detailed aspects of the FSR/FEH rainfall-runoff method 56
Linking the flood frequency curve to the PMF estimate 60
References 60
Appendix 3 Process diagrams 61
Embankment dam 61
Concrete/masonry dam 62
Glossary 63
Bibliography 67
General 67
Hydrological 68
Overtopping of embankment, concrete and masonry dams 70
Dam breach analysis 71
Risk assessment 71