Computational Hydrology in Flood Control Design and Planning

Preface

Computational Hydrology in Flood Control Design and Planning is a book prepared for use by practitioners. The main emphasis is towards application of the most frequently used computational algorithms in rainfall-runoff modeling techniques. The Book's presentation carries the reader from an extensive literature review of the reported progress in surface runoff modeling, to the development of a computer program which accommodates an entire spectrum of modeling techniques, including various design storm approaches, loss rate submodels, basin and channel routing methods, and subarea runoff generation.

Chapter 1 presents a review of the literature concerning the development, calibration, and application, of surface runoff models. It is an important chapter in that the reader becomes acquainted with som of the reported successes and failures in the use of various types of hydrologic models.
Chapter 2 includes discussions on precipitation, statistical analyses of precipitation, and the more comonly used algorithms in the application of rainfall data to- the development of runoff data. Computer codes are developed which provide a variety of design rainfall conditions and approaches.
Chapter 3 focuses upon loss rates and other rainfall extractions which must be considered in correlating rainfall data to runoff data. Because of the variety of loss functions utilized in the several surface runoff modeling approaches, many of the more popular loss rate techniques are included in this chapter. The several loss rate functions are then summrized into computer program form.

Chapter 4 concentrates on the development, calibration, and application of the most coomnly used rainfall-runoff predictor technique-the rational method. Computer programs are developed which provide a rational method modeling capability. As an application, a City Master Plan of Drainage is considered which was developed using the Chapter 4 computer software and a personal computer.

The well-known unit hydrograph technique is developed in detail in Chapter 5. Culminating in a design storm/unit hydrograph computer program, a detailed exanple problem carries the reader through the develcptmnt of a runoff hydrograph based on the unit hydrograph method. Channel and basin routing mc>dels are considered in Chapter 6. Several channel routing techniques are presented, and corresponding computer codes are developed. Flow-through and f low-by detention basin modeling techniques are also examined. The routing methods of this chapter, combined with the design storm, loss rate, and unit hydrograph techniques of Chapters 2, 3, and 5, provide a complete link-node conputer modeling capability for a personal computer environment.

Chapter 7 focuses upon the important unit hydrograph, loss rate, and routing model calibration process. Use of calibration in hydrologic models enables for a better correlation between rainfall and runoff data.

The final chapter presents the total link-node model computer program. The Chapter 8 computer codes utilize the previous computer codes of Chapters 2, 3, 5, and 6 to formulate a comprehensive link-node computer program for use on personal coqmters.

Should the reader wish to key-in the several computer programs, an estimated time investment of about 200 hours is suggested for program entry, debugging, and testing. Another option is to purchase an available personal coqmter disc with the Chapters 2, 3, 5, 6, and 8 computer codes already compiled and ready-to-use. Further -information regarding the available computer disc is included after the book index. The Chapter 4 computer codes are available in form-field fillout mode by the firm Advanced Engineering Software, 17782 Sky Park Boulevard, Irvine, California, 92714. Not only will this book be of key interest to practitioners involved with the use of surface runoff models in flood control facility design and planning, but also to water resources engineers and students as a reference to the state-of-the-art in design storm hydrology methods.

    Table of Contents

    CHAPTER 1 HYDROLOGY MODELS IN
    MUNICIPAL ENGINEERING 1

    1.1. Objectives 1
    1.2. Stormflow Determination Methods 2
    1.3. Method for Development of Synthetic Flood Frequency Estimates 4
    1.4. Watershed Modeling Uncertainty 12
    1.5. Watershed Runoff 19
    1.6. Selection of a Flood Flow Modeling Approach 20
    1.6.1. Choice of Modeling Category 20
    1.6.2. Runoff Hydrograph Generation Techniques.. 36
    1.6.3. The Choice of Design Storm 38
    1.6.4. The Design Storm/Unit Hydrograph Approach 39
    1.7. Hypothetical Floods. Balanced Floods. and Design Storm Methods 40

    CHAPTER 2 PRECIPITATION 46

    2.1. Introduction 46
    2.2. Classification of Precipitation 46
    2.3. Mechanisms for Cooling 47
    2.4. Measurement and Synthesis of Precipitation Data. 47
    2.5. Comparison of Point Rainfall Information 48
    2.6. Precipitation Depth-Duration-Frequency 48
    2.7. Event Depth-Duration 54
    2.8. Point Precipitation Data and The Design Storm.. 55
    2.9. Intensity-Duration-Frequency Curves 55
    2.10. Depth-Duration-Frequency Relationships 57
    2.11. Area-Averaged Point Rainfall 57
    2.12. Depth-Area Relationships 59
    2.13. Synthetic Critical Storm Patterns 59
    2.14. Modified Composite Storm Pattern 66
    2.15. Program 2.1: Subroutine RAIN 71
    2.15.1. The 24-Hour Nested Design Storm Patterns 73
    2.15.2. Depth-Area Adjustment 73
    2.15.3. SCS Storm Patterns 73
    2.15.4. Constant Rational Method 81
    2.15.5. Linear Interpolation Method 81
    2.15.6. Program Data Entry Sequences 81
    2.15.6.1. 24-Hour Nested Design Storm Pattern 83
    2.15.6.2. SCS Storm Pattern 83
    2.15.6.3. Constant Rainfall Intensity for a Given Duration 83
    2.15.6.4. Linear Interpolation Method 84
    2.15.6.5. User Pre-Set Storm Pattern 84
    2.15.6.6. Design Storm Pattern with Continuous Depth-Area Adjustment.. 84
    2.16. Program 2.1 85

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    CHAPTER 3 ESTIMATION OF EFFECTIVE RAINFALL 99

    3.1. Introduction 99
    3.2. Physical Processes: An Overview 99
    3.3. Phi-Index Method 103
    3.4. Constant Proportion Loss Rate 104
    3.5. Coupled Phi-Index and Constant Proportion Loss Rate Function 105
    3.6. Horton Loss Rate 107
    3.7. Exponential Loss Rate Function 107
    3.8. Initial Abstraction 107
    3.9. SCS Loss Separation 109
    3.10. SCS Hydrologic Soil Groups 111
    3.11. Soil Cover 113
    3.12. Watershed Development Conditions 119
    3.13. Impervious Areas 119
    3.14. Program 3.1: Subroutine SLOSS 121
    3.14.1. Initial Abstraction Models 121
    3.14.1.1. SCS Model 121
    3.14.1.2. Total Depth of Abstraction 121
    3.14.1.3. Percentage of Precipitation to a Maximum Total Depth of Abstraction 121
    3.14.2. Loss Models 123
    3.14.2.1. SCS Model 123
    3.14.2.2. Phi-Index 123
    3.14.2.3. Percentage of Rainfall 123
    3.14.2.4. Percentage of Rainfall Limited
    by a Phi-Index 123

    ix
    3.14.2.5. Horton Equation 123
    3.14.2.6. Exponential of Rainfall Intensity. 126
    3.14.3. Applications of Loss Function Models..... 126
    3.14.4. Data Entry Sequences 133
    3.14.4.1. SCS Model 133
    3.14.4.2. Total Depth of Initial Abstraction 133
    3.14.4.3. Percent of Precipitation to a Maximum Total Depth of Initial Abstraction 133
    3.14.4.4. Phi-Index 134
    3.14.4.5. Percentage of Rainfall 134
    3.14.4.6. Percentage of Rainfall Limited
    by a Phi-Index 134
    3.14.4.7. Horton Equation 134
    3.14.4.8i Exponential Loss Function 134
    3.15. Program 3.1 135

    CHAPTER 4 PEAK DISCHARGE ESTIMATIO14 142

    4.1. Introduction 142
    4.2. Time of Concentration Estimation 142
    4.3. Rational Method 148
    4.4. Runoff Coefficient 149
    4.5. Limitations of the Rational Method 156
    4.6. Modeling with the Rational Method 157
    4.7. The Link-Node Method 157
    4.8. The Nodal Point Method 158

    x
    4.9. The Subarea Summation Method 159
    4.10. Confluence of Streams (Junction Analysis) 159
    4.11. Presentation of Product 160
    4.12. A Regional Master Plan of Drainage (MPD) 162
    4.13. Application: A City Master Plan of Drainage 163
    4.13.1. MPD Data Collection 163
    4.13.2. Existing Conditions and Ultimate Development Conditions 165
    4.13.3. Development of Major Facility Watershed Boundaries 165
    4.13.4. Development of MPD Link-Node Schematics. 165
    4.13.5. Development of the Link-Node Models 169
    4.13.6. Calibration of the Rational Method 169
    4.13.7. Preparation of MPD System Information 170
    4.14. A Rational Method Planning/Design Computer Program 170
    4.15. Computer-Aided Design Interaction 174
    4.16. Example 4.2. Rational Method Program Application 177
    4.17. Program 4.1 187
    4.18. Program 4.2 192
    4.19. Program 4.3 195
    4.20. Program 4.4 195
    4.21. Program 4.5 197
    4.22. Program 4.6 201
    4.23. Program 4.7 205
    4.24. Program 4.8 213

    xi
    4.25. Program 4..9 220
    4.26. Program 4.10 223
    4.27. Program 4.11 225

    CHAPTER 5 SYNTHETIC UNIT HYDROGRAPH METHODS 227

    5.1. Introduction 227
    5.2. Unit Hydrograph Terminology 228
    5.3. Conceptual Evaluation of Unit Hydrographs 230
    5.4. Convolution 232
    5.5. Unit Hydrograph Analysis 233
    5.6. Forming Synthetic Unit Hydrographs 235
    5.7. The SCS Unit Hydrograph 243
    5.8. Variation on the SCS Unit Hydrograph 244
    5.9. The Espey-Altman Unit Hydrograph 247
    5.10. Design Storm Effective Rainfall 248
    5.11. Synthetic Runoff Hydrograph Development 248
    5.12. The Rational Method as a Unit Hydrograph Method. 250
    5.13. Presentation of Product 252
    5.14. A Design Storm Runoff Hydrograph Computer Program 252
    5.15. Program 5.1: Subroutine SGRAPH 273
    5.16. Data Entry Sequences 276
    5.16.1. Watercourse IAG Time Model 276
    5.16.2. S-Graph Development 277
    5.16.3. Review of Computational Results 277
    5.16.4. Accepting/Rejecting Computational
    Results and Output 277

    xii
    5.17. Program 5.1 278
    5.18. Program 5.2 284

    CHAPTER 6 RUNOFF HYDROGRAPH ROUTING TECHNIQUES 288

    6.1. Introduction 288
    6.2. Benefits and Concerns of Detention Storage 288
    6.3. Detention Basin Routing Procedure (Modified Puls Method) 290
    6.4. Flow-by Channel Model (Runoff Hydrograph Separation) 295
    6.5. The Modified Convex Channel Routing Method 295
    6.6. The Modified Att-Kin Method 301
    6.7. Muskingum Channel Routing 303
    6.8. A Pipeflow Routing Model 305
    6.9. Hydrograph Translation 306
    6.10. Kinematic Wave Routirig-Approximation 306
    6.11. Subroutine FLOWBY 306
    6.11.1. Application: Flow-by Basin 309
    6.11.2. Data Entry Sequence 311
    2 6.12. Subroutine FLOWTR 312
    3 6.12.1. Application: Flow-through Basin 312
    6 6.12.2. Data Entry Sequence 313
    6 6.13. Subroutine RCHAN 315
    77 6.13.1. Convex Routing Model 316
    77 6.13.2. Pipeflow Routing Model 316
    6.13.3. Hydrograph Translation Model 316
    77 6.13.5. Muskingum Routing Model 31
    6.13.6. Application: Channel Routing Modeling Techniques 317
    6.13.7. Data Entry Sequence: Translation 319
    6.13.8. Data Entry Sequence: Convex Routing 321
    6.13.9. Data Entry Sequence: Pipe Routing 322
    6.13.10. Data Entry Sequence: Kinematic Wave 322
    6.13.11. Data Entry Sequence: Muskingum Routing 323
    6.14. Program 6.1 325
    6.15. Program 6.2 341

    CHAPTER 7 CONSIDERATIONS IN CALIBRATING ELEMENTS OF DESIGN STORM MODELS 370

    7.1. Introduction 370
    7.2. Goals and Objectives of Model Calibration 371
    7.3. Criteria f6r-Model Assessment 373
    7.4. Calibrating Unit Hydrographs and Loss Functions. 379
    7.5. Least Squares Calibration of Unit Hydrographs 384
    7.6. Fitting Synthetic Unit Hydrographs 387
    7.7. Calibration of S-Hydrographs 388
    7.8. Calibration to Flood Frequency Discharges 391
    7.9. Calibration of Time of Concentration Models 393
    7.10. Calibration of Channel Routing Parameters 397
    7.11. Calibration df the Convex Method 397
    7.12. Calibration of the Modified Att-Kin Method...-... 400
    7.13. Calibration of the Muskingum Method 400

    CHAPTER 8 COMPLEX WATERSHED MODELING 402

    8.1. Link-Node Model 402
    8.2. A Watershed Computer Program 403
    8.3. Link-Node Model Functions 404
    8.4. Data Bank Development 407
    8.4.1. Depth-Area Adjustment Curve Sets 407
    8.4.2. User Specified 24-Hour Storm Pattern 407
    8.4.3. User Specified Storm Pattern with Continuous Depth-Area Adjustment 407
    8.4.4. S-Graphs 408
    8.4.5. Interactive Procedure 408
    8.4.5.1. Depth-Area Curve Sets 411
    8.4.5.2. User Specified 24-Hour Storm Patterns 413
    8.4.5.3. User specified 24-Hour Storm Pattern with Continuous Depth-Area Adjustment 414
    8.4.5.4. S-Graphs 416
    8.4.5.5. Data Bank Summary 417
    8.4.5.6. Program 8.1 419
    8.5. Link-Node Model Development 435
    8.5.1. Interactive Procedure 435
    8.5.2. Utility Commands 438
    8.5.2.1. ADD Command 438
    8.5.2.2. SPLIT Command 439
    8.5.2.3. CLEAR Command 439
    8.5.2.4. VIEW and PRINT Commands 440

    xv
    8.5.2.5. EXECUTION and EXIT RUNOFF
    Program 440
    8.6.2.6. Program 8.2 441
    8.6.2.7. Program 8.3 448
    8.6. INPUT/OUTPUT Units 454
    8.7. Application of Link-Node Model 454

    Bibliography 496
    Author Index 504
    Subject Index 507

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