H A E S T A D M E T H O D S

WASTEWATER COLLECTIONSYSTEM MODELING AND DESIGN

F i r s t E d i t i o n

AuthorsHaestad Methods

Thomas M. WalskiThomas E. Barnard

Eric HaroldLaVere B. Merritt

Noah WalkerBrian E. Whitman

Managing EditorThomas E. Barnard

Project EditorsKristen Dietrich, Adam Strafaci, Colleen Totz

Contributing AuthorsChristine Hill, Gordon McKay, Stan Plante, Barbara A. Schmitz

Peer Review BoardJonathan Gray (Burns and McDonnell), Ken Kerri (Ret.),

Neil Moody (Moods Consulting Pty, Ltd.), Gary Moore (St. Louis Sewer District),John Reinhardt (Massachusetts Department of Environmental Protection),

Reggie Rowe (CH2M Hill), Burt Van Duin (Westhoff Engineering Resources)

HAESTAD PRESSWaterbury, CT USA

Preface xi

Continuing Education Units xv

About the Software xvii

Chapter 1 Introduction to Wastewater Collection System Modeling 11.1 Wastewater Collection System Overview 1

Terminology.............................................................................................. 2Sources of Wastewater ............................................................................ 2Types of Conveyance............................................................................... 3

1.2 Modeling 5Applications of Collection System Models .......................................... 5Types of Collection System Modeling .................................................. 7

1.3 Historical Perspective on Collection System Analysis 7Collection Systems................................................................................... 7Hydraulics History................................................................................ 11Historical Summary .............................................................................. 16

1.4 The Modeling Process 16

Chapter 2 Steady Gravity Flow Hydraulics 232.1 Fluid Properties 24

Density and Specific Weight ................................................................ 24Viscosity .................................................................................................. 24Fluid Compressibility............................................................................ 27Vapor Pressure ....................................................................................... 27

2.2 Fluid Statics and Dynamics 28Static Pressure ........................................................................................ 28Absolute Pressure and Gauge Pressure ............................................. 29Velocity and Flow .................................................................................. 30Reynolds Number.................................................................................. 31Velocity Profiles ..................................................................................... 31

Table of Contents

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2.3 Fundamental Laws 32Conservation of Mass ............................................................................ 32Conservation of Energy ........................................................................ 33Conservation of Momentum ................................................................ 36

2.4 Hydraulic Design Variables 38Flow Rate or Discharge ......................................................................... 38Channel/Pipe Slope................................................................................ 38Depth of Flow......................................................................................... 38Velocity .................................................................................................... 39

2.5 Energy and Head Losses 40Energy Equation..................................................................................... 41

2.6 Hydraulic Elements 44Open-Top Cross Sections ...................................................................... 44Closed-Top Cross Sections.................................................................... 46Noncircular Cross Sections................................................................... 49

2.7 Manning’s n Variation 49Calculating n with the Darcy-Weisbach Equation ............................ 50Variation of n with Depth ..................................................................... 52Recommended Values of Manning’s n................................................ 53

2.8 Minor Losses in Junction Structures 54Energy-Loss Method ............................................................................. 55Composite Energy-Loss Method ......................................................... 60

2.9 Tractive Force Self-Cleansing 63Tractive Tension ..................................................................................... 63Sediment Carrying Capacity – Experimental Analysis.................... 65Camp Formula........................................................................................ 69Yao’s Method........................................................................................... 69Abwassertechnische Vereinigung (ATV) Method............................. 71Additional Considerations ................................................................... 71

2.10 Specific Energy and Critical Flow 72Specific Energy ....................................................................................... 72Froude Number...................................................................................... 74Subcritical and Supercritical Flow....................................................... 74Hydraulic Jumps.................................................................................... 75Flow Profiles ........................................................................................... 76Backwater Curves .................................................................................. 77

2.11 Hydraulics of Flow-Control Structures 78Orifices..................................................................................................... 79Weirs ........................................................................................................ 79Gates ........................................................................................................ 84

Chapter 3 Unsteady Gravity Flow Hydraulics 913.1 Basics of Unsteady Flow Analysis 93

3.2 Types of Routing 94

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3.3 Hydrodynamic Equations 95Saint-Venant Equations......................................................................... 95Approximation to Hydrodynamic Equations ................................... 96Diffusion Analogy ................................................................................. 97Kinematic Wave ..................................................................................... 97Muskingum Routing ............................................................................. 98Muskingum-Cunge Routing ................................................................ 98Convex Routing ................................................................................... 100Weighted Translational Routing........................................................ 100Level Pool Routing .............................................................................. 100Summary of Methods.......................................................................... 101

3.4 Complications to Routing Methods 101Manholes and Junction Tables ........................................................... 103Surcharging .......................................................................................... 103Overflows and Diversions.................................................................. 104Parallel Pipes and Loops..................................................................... 105Flow Reversal ....................................................................................... 106Dry Pipes............................................................................................... 107Drop Structures.................................................................................... 107

Chapter 4 Force Main and Pumping Hydraulics 1134.1 Friction Losses 113

Darcy-Weisbach Equation .................................................................. 116Colebrook-White Equation and the Moody Diagram.................... 117Hazen-Williams Equation .................................................................. 118Swamee-Jain Equation ........................................................................ 120Manning Equation............................................................................... 120Pipe Roughness Changes ................................................................... 121Comparison of Friction Loss Methods ............................................. 121

4.2 Minor Losses 122Minor Loss Valve Coefficients ........................................................... 123

4.3 Energy Addition – Pumps 125Pump Head-Discharge Relationship ................................................ 125System Head Curves ........................................................................... 126Other Pump Characteristic Curves ................................................... 128Fixed-Speed and Variable-Speed Pumps ......................................... 129Affinity Laws for Variable-Speed Pumps ........................................ 129Power and Efficiency........................................................................... 130

Chapter 5 Model Construction 1375.1 Developing the Modeling Plan 137

5.2 The Modeling Process 138Purpose and Objectives of a Model................................................... 138Develop Alternatives........................................................................... 141Scales of Models................................................................................... 141Software Selection and Training........................................................ 143

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Define Data Requirements.................................................................. 143Identify Data Sources .......................................................................... 144Collect Data........................................................................................... 146Validate the Data.................................................................................. 147Build the Model.................................................................................... 148Identify Data Gaps............................................................................... 148Sensitivity Analysis ............................................................................. 148Calibrate the Model ............................................................................. 148Validate the Model............................................................................... 148Run Simulations................................................................................... 149Develop Solutions ................................................................................ 150Bookkeeping ......................................................................................... 151

5.3 Constructing the Sewer Model 152Level of Detail....................................................................................... 153Subbasin Delineation........................................................................... 154Pipes....................................................................................................... 154Manholes ............................................................................................... 160Pumps.................................................................................................... 164Wet Wells............................................................................................... 168

Chapter 6 Dry Weather Wastewater Flows 1736.1 Definition of Flow Rates 175

New Systems ........................................................................................ 175Existing Systems................................................................................... 176

6.2 Unit Load Factors 176Residential............................................................................................. 176Commercial Sources ............................................................................ 177Industrial Wastewater Flows.............................................................. 179Fixture Unit Method............................................................................ 181Land-Use Methods .............................................................................. 183Measured-Flow Methods.................................................................... 185Assigning Loads to a Model............................................................... 187

6.3 Peaking Factors 187Peaking Factor Charts and Equations............................................... 188Minimum Flows................................................................................... 190Selection of Flow Generation Rate and Peaking Factor ................. 191

6.4 Time-Varying Flows 193Diurnal Curves ..................................................................................... 193Developing Systemwide Diurnal Curves......................................... 195Defining Usage Patterns Within a Model......................................... 196

Chapter 7 Wet Weather Wastewater Flows 2037.1 Wet Weather Flow Definitions 204

What Is Wet Weather Flow? ............................................................... 204Components of Flow in Wastewater Collection Systems............... 204Modeling Wet Weather Flows............................................................ 206

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7.2 Wastewater Collection System Hydrology 208Combined Sewer System Hydrology ............................................... 208Modeling Combined Sewer Systems ................................................ 210Separate Sanitary Sewer System Hydrology ................................... 212Modeling Separate Sanitary Sewer Systems.................................... 213Continuous versus Event Hydrology ............................................... 216

7.3 Rainfall 217Rainfall Data ......................................................................................... 217Selecting Model Simulation Events................................................... 218Calibration Events ............................................................................... 219Design Storms ...................................................................................... 219Continuous Records ............................................................................ 228

7.4 Modeling Runoff 229Rainfall Abstractions ........................................................................... 230Horton Equation .................................................................................. 233Green-Ampt Equation......................................................................... 233Rational Method .................................................................................. 234NRCS (SCS) Method............................................................................ 236

7.5 Determining Hydrographs from Runoff Volumes 239Determining Peak Flow and Time to Peak....................................... 240Snider Triangular Hydrograph.......................................................... 240Unit Hydrograph Approach .............................................................. 242NRCS (SCS) Dimensionless Unit Hydrograph ............................... 243Nonlinear Reservoir ............................................................................ 246

7.6 Empirical Methods for Generating Hydrographs 248Percentage of Rainfall Volume (R-Factor) ........................................ 249Unit Hydrographs from Flow Measurements................................. 249Simplifications to Unit Hydrograph ................................................. 250Inflow Coefficient Method ................................................................. 250Rainfall/Flow Regression.................................................................... 252RTK Hydrograph Method.................................................................. 254Unit Loads for Design Studies ........................................................... 261

7.7 Snowmelt 262Runoff Potential ................................................................................... 262Snowmelt Models ................................................................................ 263

Chapter 8 Data Collection and Flow Measurement 2718.1 Flow Measurement Considerations 271

Components of Flow ........................................................................... 272Review of Existing Information......................................................... 273Selection of Metering Locations......................................................... 273Safety Considerations ......................................................................... 274

8.2 Flow Measurement 275Hydraulic Control Sections in Open Channels ............................... 275In-Pipe Methods................................................................................... 280Manual Methods.................................................................................. 281

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8.3 Instrumentation 283Depth ..................................................................................................... 284Velocity Meters..................................................................................... 287

8.4 Precipitation Measurement 292Precipitation Data Acquisition........................................................... 293Measurement of Rainfall..................................................................... 293Gauge Operation Considerations...................................................... 294Radar Imagery...................................................................................... 295

Chapter 9 Model Calibration 3019.1 Basic Calibration Concepts 302

Overview of Calibration ..................................................................... 302Calibration Parameters........................................................................ 303Building-Block Approach ................................................................... 305Steady-State and Extended-Period Simulations.............................. 305

9.2 Dry Weather Flows 305

9.3 Wet Weather Flows 309Constant Unit Rate Method................................................................ 310Percentage of Rainfall Volume (R-Value) ......................................... 312Percentage of Stream Flow ................................................................. 313RTK Hydrograph ................................................................................. 315Predictive Equation Based on Rainfall-Flow Regression ............... 316

9.4 Special Considerations in Calibration 320Volume Differences.............................................................................. 321Shape Considerations.......................................................................... 322Timing Shifts......................................................................................... 323

9.5 Understanding Overflows 324Estimating Combined Sewer Overflow............................................ 325Estimating SSOs ................................................................................... 326Detecting Overflows with Scattergraphs ......................................... 326

Chapter 10 Design of New Gravity Wastewater Collection Systems 33310.1 Materials 334

Pipes....................................................................................................... 334Manholes ............................................................................................... 335Other Appurtenances .......................................................................... 336

10.2 Initial Planning 337Decision to Provide Sewer Service to an Area................................. 337Types of Conveyance........................................................................... 338Separate versus Combined Systems.................................................. 338

10.3 Preliminary Design Considerations 339Data Requirements .............................................................................. 340Alternatives........................................................................................... 341

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10.4 Initial System Layout 341Gravity Sewer Layout ......................................................................... 342Manhole Location and Spacing ......................................................... 342Location of Pumping Facilities .......................................................... 343Sewer Easements.................................................................................. 343Example of a Sewer Network Layout ............................................... 344

10.5 Flows in Sanitary Sewers 346Low Flows in Early Years ................................................................... 346Allowances for Infiltration and Inflow............................................. 346Phased/Staged Construction .............................................................. 348

10.6 Horizontal and Vertical Alignment 348Pipe Slopes............................................................................................ 348Curved Sewer Alignment ................................................................... 349Minimum Depth of Cover .................................................................. 349Maximum Depth.................................................................................. 352

10.7 Hydraulic Design 352Pipe Sizing ............................................................................................ 354Manholes............................................................................................... 355Computer Modeling for System Design........................................... 356Steady Flow versus Extended-Period Simulation

(EPS) Analysis ................................................................................ 356Design Maximum Flow Rates with Pumping ................................. 358

10.8 Special Installations 358Sewers in Steep Terrain....................................................................... 358Sewers Along Streams......................................................................... 359Elevated Crossings .............................................................................. 359Inverted Siphons (Depressed Sewers) .............................................. 360

10.9 Wastewater Collection System Optimization 361

Chapter 11 Wastewater Collection System Evaluationand Rehabilitation 37111.1 Planning for System Characterization 372

Performance Requirements ................................................................ 373Current Performance........................................................................... 374Approach to System Characterization.............................................. 375

11.2 System Characterization 376Review Existing Records .................................................................... 376Update System Inventory................................................................... 378Collection System Condition Investigation ..................................... 379Inspection of the Condition of Controls and

Ancillary Structures....................................................................... 382

11.3 Hydraulic Investigations 384Field Data Collection........................................................................... 385Data Analysis ....................................................................................... 386Application of Hydraulic Modeling ................................................. 390Assess Hydraulic Performance.......................................................... 394

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11.4 Evaluating Rehabilitation Strategies 395Preventive Maintenance Program ..................................................... 399Source Controls .................................................................................... 399Sewer Separation.................................................................................. 400Pipe Rehabilitation/Replacement ...................................................... 401Inflow/Infiltration Control.................................................................. 402Interbasin Transfers ............................................................................. 405Real-Time Controls .............................................................................. 405Storage Facilities .................................................................................. 406Wet Weather Treatment Facilities ...................................................... 407

Chapter 12 Force Mains and Pump Stations 41912.1 Need for Pump Stations 420

12.2 Pump Station Overview and Design Considerations 423Components.......................................................................................... 423Design Decisions .................................................................................. 425Pump Capacity ..................................................................................... 425Pump Station Configuration .............................................................. 426Pump Types and Selection.................................................................. 427Wet Well Sizing .................................................................................... 432Net Positive Suction Head.................................................................. 433Appurtenances ..................................................................................... 435

12.3 Force Main Sizing with a Single Pump Station 435Determining Pipe Sizes ....................................................................... 436Developing System Head Curves...................................................... 437Selecting Economical Pipe Size.......................................................... 438

12.4 Modeling Pumped Systems 441Modeling Pumps.................................................................................. 442Downstream Flow Attenuation ......................................................... 442Identifying Potential Problems .......................................................... 443Modeling a Pipeline with Multiple High Points ............................. 444

12.5 Efficiency Considerations 448Constant-Speed Pumping................................................................... 448Variable-Speed Pumping .................................................................... 451Automated Energy Calculations ....................................................... 455

12.6 Force Mains with Multiple Pump Stations 455

12.7 Hydraulic Transients 457

Chapter 13 Low-Pressure Sewers 46713.1 Description of Pressure Sewers 468

Storage Tanks........................................................................................ 470Service Lines ......................................................................................... 470Pressure Mains ..................................................................................... 471Air-Release/Vacuum-Breaker Valves ................................................ 471Discharge Points................................................................................... 471

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13.2 Estimating Flows 472Empirical Approaches......................................................................... 473Poisson Distribution to Estimate Loads ........................................... 475

13.3 Pressure Sewer Design Considerations 478

13.4 Modeling Pressure Sewers 479Modeling to Size Pressure Mains ...................................................... 480Representing All Service Connections as Nodes ............................ 481Detailed Models ................................................................................... 482

Chapter 14 Utilizing GIS 48914.1 GIS Fundamentals 490

Data Management ............................................................................... 491Geographic Data Representations..................................................... 494

14.2 Developing an Enterprise GIS 495Keys to Successful Implementation .................................................. 495Needs Assessment ............................................................................... 496Design.................................................................................................... 497Pilot Study ............................................................................................ 504Production ............................................................................................ 504Rollout ................................................................................................... 505

14.3 Model Construction 505Model Sustainability and Maintenance............................................ 506Communication Between the GIS and Modeling Staff .................. 507Network Components......................................................................... 508Wastewater Loads................................................................................ 510Building the Model.............................................................................. 515Pitfalls in Constructing Models from GIS ........................................ 517Loading Model Results to GIS ........................................................... 520

14.4 GIS Analysis and Visualization 520Basic GIS Uses and Examples ............................................................ 520Advanced GIS Uses and Examples ................................................... 522

Chapter 15 Regulatory Issues 52915.1 United States Laws and Regulations 529

Clean Water Act ................................................................................... 530U.S. Federal Regulations..................................................................... 531Water Quality Standards and Total Maximum

Daily Loads (TMDLs) .................................................................... 537Section 404 Dredge and Fill Permits ................................................. 538

15.2 Canadian Laws and Regulations 538Sanitary Sewer Systems ...................................................................... 539Combined Sewer Systems .................................................................. 539

15.3 European Union Laws and Regulations 546Urban Wastewater Treatment Directive (UWWTD) ...................... 546

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Water Policy Framework Directive (WPFD) ................................... 549Integrated Pollution Prevention Control Directive (IPPC) ............ 549Product Directives ............................................................................... 549Control of CSOs in EU Member States ............................................. 549Design Criteria for CSOs..................................................................... 550

15.4 Use of Models for Regulatory Compliance 551

Appendix A Symbols 557

Appendix B Conversion Factors 563

Appendix C Physical Properties 567

Bibliography 573

Index 589