i AN URBAN DENSITY-BASED RUNOFF SIMULATION FRAMEWORK TO ENVISAGE FLOOD RESILIENCE OF CITIES. P.N.P. Wijayawardana 218030 R Degree of Master Science by Research Department of Town & Country Planning University of Moratuwa Sri Lanka JULY 2023 ii AN URBAN DENSITY-BASED RUNOFF SIMULATION FRAMEWORK TO ENVISAGE FLOOD RESILIENCE OF CITIES. P.N.P. Wijayawardana 218030 R Degree of Master Science by Research Department of Town & Country Planning University of Moratuwa Sri Lanka JULY 2023 i Declaration “I declare that this is my own work and this thesis does not incorporate without acknowledgement any material previously submitted for a Degree or Diploma in any other University or institute of higher learning and to the best of my knowledge and belief it does not contain any material previously published or written by another person except where the acknowledgement is made in the text. Also, I hereby grant to University of Moratuwa the non-exclusive right to reproduce and distribute my thesis/dissertation, in whole or in part in print, electronic or other medium. I retain the right to use this content in whole or part in future works (such as articles or books). Name of the Candidate: P.N.P. Wijayawardana Registration Number: 218030 R Signature:……………………… Date: ………………………. The supervisor/s should certify the thesis/dissertation with the following declaration. The above candidate has carried out research for the Masters/MPhil/PhD thesis/ Dissertation under my supervision. Name of the supervisor: Signature of the supervisor:………………… Date : …………………… Dr.(Ms) Chethika Abenayake Signature of the supervisor:………………… Date : …………………… (Dr. Amila Jayasinghe) 02.07.2023 Supervisor1 : Dr.(Ms) Chethika Abenayake Supervisor2 : Dr. Amila Jayasinghe 03.07.2023 03.07.2023 ii Abstract Urban form densities play a decisive role in complex urban form scenarios. Therefore, learning to ‘live with the floods’; has become a challenging issue to practice in most urban planning approaches. Several simulation studies have been conducted to examine the influence of urbanization scenarios on urban flood risk management. Yet, there is a gap remaining to optimize every component of flood hydrodynamics across a distinct urban form density. As a result, the economic loss to the urban system is hard to minimize. But planning an intervention with a proper quantification approach for a long-term flood management strategy is useful for making cities resilience to floods. The primary aim of this research is to create a spatial simulation framework that can evaluate how urban density(UD) affects surface runoff (SR) in urban watersheds in various urban form scenarios. First, examine the potential quantification indicators of urban form density. Second, develop a framework to quantify urban form density at the urban watershed scale, which applies to spatial structure. The third step involves creating an SR simulation model that utilizes the 13 selected UD indicators to verify and validate the previously developed framework with real- world data, with the main three categories (3Ds') as per the developed framework. The model evaluates itself with AI-based Decision Tree Analysis incorporated with correlation and experts’ opinions. The model results indicate that the UD indicators including impervious coverage (accuracy level 98.7%), OSR (accuracy level 94.8%), and road density ( accuracy level 93.5%) are the key indicators combined with the population density, accessibility, and built_up coverage to regulate SR in urban catchments. The ground verification of model results indicates an R2 value greater than 0.88. The ultimate goal of this study is to create a method of quantitatively evaluating the effects of physical UD as an independent variable, allowing for a more location specific manner. This study contributes a novel framework incorporating 3Ds (density, diversity, design) to quantify UD, which will aid subsequent processes of decision-making in the realm of urban flood mitigation and planning techniques. Keywords: Urban flood, Urban density (UD), Surface runoff (SR), planning & decision-making, resilience iii Table of Contents Declaration .......................................................................................................................... i Abstract .............................................................................................................................. ii Table of Contents .............................................................................................................. iii List of Figures .................................................................................................................... v List of Table ...................................................................................................................... vi Acknowledgment ............................................................................................................. vii List of Abbreviations ....................................................................................................... viii 1. CHAPTER 1: INTRODUCTION .............................................................................. 1 1.1 Introduction ......................................................................................................... 1 1.2 Research Need ..................................................................................................... 3 1.3 Research Problem ................................................................................................ 2 1.4 Research Aim and Objectives .............................................................................. 4 1.5 Significance of the Study ..................................................................................... 5 1.6 Scope of the Study and Limitations ..................................................................... 5 2 CHAPTER 2: LITERATURE REVIEW ................................................................... 7 2.1 Introduction ......................................................................................................... 7 2.2 Urban Density(UD) impact on Urban Flood ....................................................... 7 2.2.1 Urban flood .................................................................................................. 8 2.3 Summary of the Systematic Review .................................................................. 10 2.3.1 Search strategy ........................................................................................... 10 2.3.2 Eligibility Criteria ...................................................................................... 11 2.3.3 Study selection and data extraction ............................................................ 11 2.3.4 Findings for Systematic Review ................................................................ 12 2.4 Existing Possibilities and Practical Examples of Managing Urban Floods. ...... 15 2.5 Flood Resilience City ........................................................................................ 19 3 CHAPTER 3: METHODOLOGY AND PROPOSED CONCEPTUAL FRAMEWORK ................................................................................................................ 22 3.1 Introduction ....................................................................................................... 22 3.2 Identifying the most influencing Indicators ....................................................... 22 3.3 Identifying the Theories and Concepts .............................................................. 24 iv 3.4 Concepts ............................................................................................................ 27 3.5 Conceptual Framework ...................................................................................... 29 3.6 Model the surface runoff and identify the relative importance. ........................ 30 3.7 Identification of simulation tool ........................................................................ 33 3.7.1 Selection of case study area/s ..................................................................... 34 3.8 Data collection and modeling ............................................................................ 38 3.9 Model Validation ............................................................................................... 39 3.10 Overall methodology ..................................................................................... 39 4 CHAPTER 4: ANALYSIS AND RESULTS ........................................................... 41 4.1 Introduction ....................................................................................................... 41 4.2 Correlation Analysis .......................................................................................... 42 4.3 Decision Tree Analysis (DTA) .......................................................................... 43 4.3.1 Model Accuracy ......................................................................................... 46 4.4 Real ground verification with actual flood data ................................................ 47 4.5 Overall Results Discussion ................................................................................ 49 5 CHAPTER 5: CONCLUSION AND RECOMMENDATIONS ............................. 50 5.1 Introduction ....................................................................................................... 50 5.2 Applicability of the proposed framework to make flood resilience cities. ........ 50 5.2.1 Identifying the most critical factors/ indicators with a stakeholder perspective. ............................................................................................................... 50 5.2.2 Clarify the model results with a stakeholder perspective. .......................... 51 5.2.3 The possibility of applying the developed framework in planning practices as stakeholder perspective ........................................................................................ 52 5.2.4 Suitable suggestions to improve the efficiency of developed framework in a stakeholder perspective. ........................................................................................... 53 5.2.5 Limitations/ opportunities in applying the proposed framework in planning practices in Sri Lanka in a stakeholder perspective. ................................................ 54 5.3 Key contributions of the study ........................................................................... 56 5.4 Recommendations ............................................................................................. 57 5.5 Conclusion ......................................................................................................... 58 Publications ...................................................................................................................... 60 References ........................................................................................................................ 61 6 Appendices ............................................................................................................... 68 v 6.1 Appendix A: Identified Density-Based Indicators through systematic review . 68 6.2 Appendix B: Semi-structured interview guide for the focus group discussion . 69 6.3 Appendix C: Leaf lets - aims and the existing results of the research ............... 72 6.4 Appendix D: Existing flood and future flood reduction under three models .... 74 6.5 Appendix E ........................................................................................................ 75 6.5.1 Limitations of existing model and local level applicability in Sri Lankan Context 77 6.5.2 Need of combined Urban density and Flood Modelling to make Decision Making Tool ............................................................................................................. 78 List of Figures Figure 1:Difference between natural and urban hydrographs ............................................ 9 Figure 2: Water balance characteristics in a natural (a) and urban watershed(b) .............. 9 Figure 3: How urban form density increase runoff and make flood-related urban problems. .......................................................................................................................................... 10 Figure 4: Systematic literature review framework using PRISMA protocol ................... 12 Figure 5: New urban water management strategies and techniques based on "Sustainable Development .................................................................................................................... 15 Figure 6: Increasing built form density of the water balance through Urban Water Mass Balance ............................................................................................................................. 17 Figure 7: Example case, implementing Sustainable Strategies for Urban Stormwater Management in Germany ................................................................................................. 18 Figure 8: Example , Improvement urban flood Mitigation in long term - Vietnam ....... 18 Figure 9: Flood-resilient city with a diverse urban setting ............................................... 21 Figure 10: Dimensions of flood resilience city ................................................................ 21 Figure 11: Process of urban maturation - different stages................................................ 25 Figure 12: New town development, incorporating urban density, city functions, special structures, and surface runoff ........................................................................................... 26 Figure 13: Conceptual Framework of this study .............................................................. 30 Figure 14: The layout of procedural systems compared to that of real-world systems ... 35 Figure 15: density classification in Spacemate ................................................................ 37 vi Figure 16: SR in catchments generated with SWMM ...................................................... 38 Figure 17: Overall Methodology ...................................................................................... 40 Figure 18: Correlation values (a) | Correlation heat map (b) ........................................... 43 Figure 19: Optional Model 1 generated through DTA ..................................................... 45 Figure 20: Optional Model 2 generated through DTA ..................................................... 45 Figure 21: Optional Model 3 generated through DTA ..................................................... 46 Figure 22: Difference between real ground flood and simulated flood ........................... 48 Figure 23: Differences between model results and real-world data on surface runoff – sub catchment level ................................................................................................................. 48 Figure 24: Validation of accuracy level – left indicates the flood depth in meters and right indicates the inundation duration in hours ....................................................................... 49 Figure 25: Focus area by the study ................................................................................... 79 List of Table Table 1: Criteria included or excluded from the systematic review................................. 11 Table 2: Variable explanation for 3D s ............................................................................ 28 Table 3: Overview of urban flood simulation approaches applied in different urban scales, input data and model limitations. ..................................................................................... 30 Table 4: Selection of simulation model for SR ................................................................ 32 Table 5: Parameter – AI based Procedural City Generator .............................................. 34 Table 6: Unique features of the selected case study areas based on UD.......................... 36 Table 7: Measurement of variables .................................................................................. 38 Table 8: Analysis types carryout ...................................................................................... 41 Table 9: Accuracy of the each model of DTA ................................................................. 47 Table 10: Limitations/ opportunities in applying the proposed framework ..................... 54 vii Acknowledgment First, I would like to express my sincere gratitude to my research supervisors, Dr.(Ms) Chethika Abenayake and Dr. Amila Jayasinghe from the University of Moratuwa, Faculty of Architecture, Department of Town and Country Planning, for their invaluable guidance, support, and encouragement throughout my research journey. I would also like to extend my heartfelt appreciation to Dr. Nuwan Dias from the University of Huddersfield in the UK, my external supervisor, for providing me with his expert opinion, valuable suggestions and comments on my work. Special thanks are also due to the Urban Development Authority (UDA) in Sri Lanka, for providing me with valuable data and resources during the course of my research. I am also grateful to Prof. J.N. Munasinghe, Head of the Department of Town and Country Planning and Dr. R.M.S.R. Rathnayake, Postgraduate Coordinator in the department, for their support and advice throughout my study. I would like to thank my colleagues at the Laboratory of ‘Urban Simulation Lab’ who have been a constant source of inspiration, encouragement, and support. Their academic, logistic, and emotional support has been invaluable to me throughout my research journey. Finally, I would like to thank my family and friends for their unwavering support, love, and encouragement throughout my academic pursuit. viii List of Abbreviations 2D RRI Two-Dimensional Rainfall-Runoff-Inundation 3Di Three-dimensional flood model 3Ds Density, Diversity, Design AI Artificial Intelligence ARW Access Road Width BD Building Density BEATS Biophysical Environments and Technologies Simulator BH Building Height CD Colombo District DD Derange Density DE Design Elements DEM Digital Elevation Model DS Digital Simulation DTA Decision Tree Analysis EPA Environmental Protection Agency FAR Floor Area Ratio FSI Floor Space Index GI Green Infrastructure GIS Geographic Information System GSI Ground Space Index HEC-RAS Horologic Engineering Center’s River Analysis System IC Impervious Coverage KD Kalutara District L Local LID Low Impact Development ML Machine Learning NBS Nature based solution OSR Opens space ratio PCSWMM Personal Computer Storm Water Management Model PD population density PRISMA Preferred Reporting Items for Systematic Reviews and Meta-Analyses R Regional RD Road density RS Remote Sensing based SD Spatial Density SR Surface Runoff SUDS sustainable urban drainage system SWMM Storm Water Management Model UD Urban Density UNDP United Nations Development Programme UNDRR United Nations Office for Disaster Risk Reduction USD United States Dollar USMS Urban water management system/techniques WSUD water sensitive urban design