Development of an Efficient Modelling Approach to Support Economically and Socially Acceptable Flood Risk Reduction in Coastal Cities; Can Tho City, Meking Delta, Vietnam

Description

Flooding is one of the most frequently occurring and damaging natural disasters worldwide. Quantitative flood risk management (FRM) in the modern context demands statistically robust approaches (e.g. probabilistic) due to the need to deal with complex uncertainties. However, probabilistic estimates often involve ensemble 2D model runs resulting in large computational costs.Additionally, modern FRM necessitates the involvement of a broad range of stakeholders via co-design sessions. This makes it necessary for the flood models, at least at a simplified level, to be understood by and accessible to non-specialists. This study was undertaken to develop a flood modelling system that can provide rapid and sufficiently accurate estimates of flood risk within a methodology that is accessible to a wider range of stakeholders for a coastal city – Can Tho city, Mekong Delta, Vietnam. A web-based hydraulic tool, Inform, was developed based on a simplified 1D model for the entire Mekong Delta, flood hazard and damage maps, and estimated flood damages for the urban centre of Can Tho city (Ninh Kieu district), containing the must-have features of a co-design tool (e.g. inbuilt input library, flexible options, easy to use, quick results, user-friendly interface). Inform provides rapid flood risk assessments with quantitative information (e.g. flood levels, flood hazard and damage maps, estimated damages) required for co-designing efforts aimed at flood risk reduction for Ninh Kieu district in the future. Cover Title Page Copyright Page Contents Acknowledgements Summary Samenvatting Contents 1 Introduction 1.1 Background and motivation 1.2 Study area 1.2.1 The Mekong Delta 1.2.2 Can Tho City 1.3 Hydraulic models and applications 1.3.1 Hydraulic models for rivers 1.3.2 Previous applications of hydraulic river models for the Mekong Delta 1.4 Main drivers that affect the flooding situation in the Mekong Delta and Can Tho 1.4.1 Future projections of climate change driven variations in main drivers of flooding in the Mekong Delta. 1.4.2 Projected change in river flow due to dam construction in the upstream part of the Mekong Delta. 1.4.3 Land subsidence in the Mekong Delta 1.5 Previous flood risk assessments studies. 1.6 Socially and economically acceptable flood risk reduction measures 1.7 Interactive tools used in FRM 1.8 Research objective and questions 1.9 Thesis outline 2 Development of an effective modelling approach to support probabilistic flood forecasting in Can Tho city, Mekong Delta, Vietnam 2.1 Introduction 2.2 Methodology 2.2.1 Data 2.2.2 Model selection 2.2.3 Model application 2.3 Results and Discussion 2.3.1 Calibration of the Simplified SWMM Model 2.3.2 Model validation 2.3.3 Performance comparison between the previous models and the simplified SWMM model for the entire Mekong Delta 2.4 Conclusions 3 Developing probabilistic flood hazard maps for the urban centre of Can Tho city for present-day and future 3.1 Introduction 3.2 Study area 3.3 Methodology 3.3.1 1D hydrodynamic model simulations 3.3.2 Reduction of the number of 1D/2D model runs 3.3.3 Derivation of probabilistic flood hazard quantification 3.4 Results 3.5 Discussion 3.5.1 Difference in using flood probabilities to develop probabilistic fluvial flood hazard maps 3.5.2 The difference in water level and flood extent between two studies 3.6 Conclusions 4 Assessment of present and future fluvial flood damages and risk for Ninh Kieu district 4.1 Introduction 4.2 Methodology 4.2.1 Data 4.2.2 Flood risk analysis 4.3 Results 4.3.1 Flood damage maps and the EADs corresponding to the baseline and future scenarios 4.3.2 Flood hazard and damage maps by linear interpolation 4.4 Discussion 4.5 Conclusions 5 Developing and testing an interactive, web-based flood risk management tool for co-design with stakeholders 5.1 Introduction 5.2 Challenges in creating interactive tools to support FRM 5.3 A new co-designing interactive tool to address flooding related challenges in Can Tho 5.4 Pilot testing and evaluation of Inform 5.5 Discussion 5.5.1 Comparison with the recent study on the probabilistic flood risk calculation approach 5.5.2 Scope for improving Inform tool 5.6 Conclusions 6 General Conclusions 6.1 Introduction 6.2 General conclusions 6.3 Limitations of the study and possible future research initiatives Appendix Appendix A Appendix B Appendix C References List of acronyms List of Tables List of Figures About the author