Flood Inundation Modeling and Hazard Mapping under Uncertainty in the Sungai Johor Basin, Malaysia

"Flooding can have devastating impacts on peoples livelihood, economy and the environment. One way to minimize flood losses is using floodplain maps, which assist land planners and local authorities in identifying flood-prone areas, and provide useful information for rescue and relief agencies for their operations. Developing floodplain maps often involves flood inundation modeling. This typically requires precipitation and stream flow data, topographic information, the selection of a hydraulic model and the calibration of its parameters. A common representation of floodplain map is based on a single outcome without an explicit consideration of all the sources of uncertainty in the modeling process. The research presented in this thesis addresses the uncertainty in the flood inundation modeling, which may arise from input data and hydraulic modeling approach. The study area is the Sungai Johor basin in Johor, Malaysia, which is an agricultural dominated area. By using a set of sample data for Sungai Johor Basin, the case study show the uncertainties arising from an estimation of design flow, terrain data sets, geometric description in hydraulic models and different modeling approaches. The intent of the research in flood inundation maps is to emphasize the impact of uncertainties in flood inundation maps that not only provide useful results but also suggested further research and improvement of flood inundation mapping practices."--Provided by publisher Cover 1 Halftitle 2 Title 4 Copyright 5 Dedication 6 Summary 8 Samenvatting 10 Table of Contents 14 Chapter 1 Introduction 18 1.1 Background 18 1.2 Problem statement 19 1.3 Flood mapping 20 1.4 Uncertainty in flood hazard mapping 22 1.5 Research questions 23 1.6 Aims and research objectives 23 1.7 Dissertation structure 24 Chapter 2 Literature review 26 2.1 What is floods 26 2.2 Types of flood 26 2.3 Flood prone areas 28 2.4 Hazard and flood hazard 28 2.4.1 Definition 28 2.5 Flood modelling 30 2.5.1 Mathematical model application 31 2.5.2 GIS environment 34 2.5.3 Input data for flood modelling 35 2.6 Uncertainty in flood modelling and mapping 37 2.6.1 Definition of uncertainty 37 2.6.2 Types of uncertainty 38 2.6.3 Sources of uncertainty 39 2.7 Flood mapping 41 2.7.1 Types and content of flood mapping 41 2.7.2 Use of flood maps 44 2.7.3 Flood hazard map in Malaysia 46 Chapter 3 Study area and data availability 48 3.1 Study area 48 3.1.1 Administrative 48 3.1.2 River systems 50 3.1.3 Climate 52 3.1.4 Land use 52 3.1.5 Flood issues 54 3.2 Data Availability 56 3.2.1 Hydrological data 56 3.2.2 Topography data 57 Chapter 4 1-D hydraulic modelling: the role of cross-sections spacing 62 4.1 Introduction 62 4.2 Methodology 67 4.2.1 Hydraulic modelling 67 4.2.2 Cross-section spacing 68 4.3 Results and Discussion 71 4.3.1 Model performance 71 4.3.2 Comparing flood water profiles and inundation maps 73 4.3.3 Representation of bridge structures in the model 77 4.4 Concluding remarks 81 Chapter 5 2-D hydraulic modelling: the role of digital elevation models 82 5.1 Introduction 82 5.2 Differentiation of DEMs re-sampling technique 85 5.3 Results and discussion 88 5.3.1 Model calibration and validation 88 5.3.2 Flood simulation 91 5.4 Conclusions 93 Chapter 6 1-D hydraulic modelling: the role of digital elevation models 94 6.1 Introduction 94 6.2 Available data 99 6.2.1 Hydraulic modelling 99 6.2.2 Digital elevation model 99 6.3 Methodology 101 6.3.1 Evaluating the DEMs quality 101 6.3.2 Model calibration and validation 102 6.3.3 Quantifying the effect of the topographic data source on the watersurface elevation and inundation area (sensitivity analysis) 103 6.3.4 Uncertainty estimation – GLUE analysis 104 6.4 Results and discussion 105 6.4.1 Quality of DEMs compared with reference points 105 6.4.2 Model calibration and validation 108 6.4.3 Quantifying the effect of the topographic data source on the watersurface elevation and inundation area 112 6.5 Conclusions 117 Chapter 7 Uncertainty in simulating design flood profiles and inundation maps on the Johor River, Malaysia 120 7.1 Introduction 120 7.2 Methodology 123 7.2.1 Model calibration and validation 123 7.2.2 Estimation of design flood profile 124 7.2.3 Simulation of flood inundation maps 128 7.3 Results and discussion 129 7.3.1 Calibration and validation 129 7.3.2 Estimation of design flood profile 130 7.3.3 Simulation of flood inundation map 133 7.4 Conclusions 137 Chapter 8 Conclusions and recommendations 140 8.1 Conclusion 140 8.1.1 Summary of conclusions and contributions 142 8.1.2 Recommendations 147 References 150 Acknowledgements 168 About the author 172 Index of notation and abbreviations 176 Flooding can have devastating impacts on people's livelihood, economy and the environment. An important instrument in flood management is floodplain maps, which assist land planners and local authorities in identifying flood-prone areas, and provide useful information for rescue and relief agencies for their operations. Developing floodplain maps often involves flood inundation modeling. This typically requires precipitation and stream flow data, topographic information, building a hydraulic model and calibration of its parameters. Often however, floodplain maps are built on a single model outcome without an explicit consideration of all the sources of uncertainty in the modeling process. The research presented in this thesis addresses the uncertainty in flood inundation modeling, which may arise from input data and hydraulic modeling approach. The study area is the Sungai Johor basin in Johor, Malaysia, an agriculture-dominated area. The present study analyses the modelling uncertainties arising from estimations of design flow, terrain data sets, geometric description in hydraulic models and different modeling approaches, and develops recommendations for practitioners. Explicit account for uncertainties and studying their impact in flood inundation mapping allow for more informed and effective decision making.