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

Anuar Ali, Anuar Bin Md. Ali

• Publisher: CRC Press
• Year: 2018
• eBook ISBN: 9780429889486
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

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.

Contents

Summary

Samenvatting

Table of Contents

Chapter 1 Introduction

1.1 Background

1.2 Problem statement

1.3 Flood mapping

1.4 Uncertainty in flood hazard mapping

1.5 Research questions

1.6 Aim and research objective

1.7 Dissertation Structure

Chapter 2 Literature Review

2.1 What is floods

2.2 Types of flood

2.3 Flood prone areas

2.4 Hazard and flood hazard

2.4.1 Definition

2.5 Flood modelling

2.5.1 Mathematical model application

2.5.2 GIS environment

2.5.3 Input data for flood modelling

2.6 Uncertainty in flood modelling and mapping

2.6.1 Definition of uncertainty

2.6.2 Types of uncertainty

2.6.3 Sources of uncertainty

2.7 Flood mapping

2.7.1 Types and content of flood map

2.7.2 Use of flood maps

2.7.3 Flood hazard map in Malaysia

Chapter 3 Study area and data availability

3.1 Study area

3.1.1 Administrative

3.1.2 River systems

3.1.3 Climate

3.1.4 Land use

3.1.5 Floodissues

3.2 Data Availability

3.2.1 Hydrological data

3.2.2 Topography data

Chapter 4 1-D hydraulic modelling: the role of cross‐sections spacing

4.1 Introduction

4.2 Methodology

4.2.1 Hydraulic Modelling

4.2.2 Cross‐section spacing

4.3 Results and Discussion

4.3.1 Model performance

4.3.2 Comparing flood water profiles and inundation maps

4.3.3 Representation of bridge structures in the model

4.4 Concluding remarks

Chapter 5 2-D hydraulic modelling: the role of digital elevation models

5.1 Introduction

5.2 Differentiation of DEMs re‐sampling technique

5.3 Results

5.3.1 Model Calibration and validation

5.3.2 Flood simulation

5.4 Conclusions

Chapter 6 1-D hydraulic modelling: the role of digital elevation models

6.1 Introduction

6.2 Available data

6.2.1 Hydraulic Modelling

6.2.2 Digital Elevation Model

6.3 Methodology

6.3.1 Evaluating the DEMs quality

6.3.2 Model calibration and validation

6.3.3 Quantifying the effect of the topographic data source on the water surface elevation and inundation area (sensitivity analysis)

6.3.4 Uncertainty Estimation‐ GLUE analysis

6.4 Results and discussion

6.4.1 Quality of DEMs compared with the reference points

6.4.2 Model calibration and validation

6.4.3 Quantifying the effect of the topographic data source on the water surface elevation and inundation area

6.5 Conclusions

Chapter 7 Uncertainty in simulating design flood profiles and inundation maps on the Johor River, Malaysia

7.1 Introduction

7.2 Methodology

7.2.1 Model calibration and validation

7.2.2 Estimation of design flood profile

7.2.3 Simulation of flood inundation maps

7.3 Results and discussion

7.3.1 Calibration and validation

7.3.2 Estimation of design flood profile

7.3.3 Simulation of flood inundation map

7.4 Conclusions

Chapter 8 Conclusions and Recommendations

8.1 Conclusion

8.1.1 Summary of contributions

8.1.2 Recommendations

References

Acknowledgment

About the Author

Index of Notation and Abbreviations

Summary

Flood is a natural disaster that occurs almost regularly in Malaysia particularly during the monsoon seasons. Hence, it is of no surprise that flood is considered one of the most significant natural hazards in the country in terms of number of affected population, fatalities and economic damage. One of the efforts to minimize flood losses is providing useful information through floodplain inundation maps, i.e. spatial distribution of flood hazard. Traditionally, many modellers have used deterministic approaches in flood inundation modelling. Deterministic approaches are based on a single simulation with the “best fit model” and do not explicitly consider uncertainties in model parameters, terrain data, and model structure. When model results are then used to generate a flood hazard map, neglecting uncertainties may lead to precise, but inaccurate maps and lead to wrong or misleading information to decision makers. Thus, the scientific literature has recently proposed a number of probabilistic methods to recognize, assess and account for uncertainties affecting flood inundation modelling. In this context, this research work aims to contribute to this research work by further exploring the impact of various sources of uncertainty on the results of hydraulic models. The case study of this research is the Sungai Johor river basin in Malaysia. Both 1-D and 2-D hydraulic models were utilized.

In using 1-D hydraulic models, the geometric description of rivers and floodplains is performed by using a number of cross-sections, which play an important role in the accuracy of model results. In this work, criteria for cross-section spacing were tested and verified via numerical experiments.

Similarly, digital elevation models (DEMs) used as geometrical input significantly affect the results of flood inundation modelling exercises. DEM is essential input that provides topographical data in flood inundation modelling. However, it can be derived from several sources either through remote sensing techniques (space-borne or air-borne imagery) or from more traditional ground survey methods. These DEMs are characterized by different precision and accuracy. This study quantified the effect of using different DEM data source and resolution in a 1-D hydraulic modelling of floods.

This study also explored the differences arising from the use of deterministic and uncertainty approaches in deriving design flood profiles and flood inundation maps. To this end, the generalized likelihood uncertainty estimation (GLUE) technique was used and the uncertainty in model predictions was derived through Monte Carlo analysis. In particular, this work focused on impact of uncertain inflow data and roughness coefficients in the accuracy of flood inundation models.

As part of this research, 2-D hydraulic modelling software (LISFLOOD-FP) was also used to assess the effect of spatial data re-sampling (e.g. from high to low resolution) on model outcomes. This study evaluated two re-sampling techniques with combination of three different aggregation functions, i.e. minimum, maximum and mean values.

This research work has not only provided useful results, but has also suggested further research and improvement of flood risk and mapping practices. The knowledge generated by, as well as the findings of this thesis, will be transferre...

Table of contents

• Cover
• Halftitle Page
• Title Page
• Copyright
• Table of Contents