H A E S T A D M E T H O D S WASTEWATER COLLECTION SYSTEM MODELING AND DESIGN F i r s t E d i t i o n Authors Haestad Methods Thomas M. Walski Thomas E. Barnard Eric Harold LaVere B. Merritt Noah Walker Brian E. Whitman Managing Editor Thomas E. Barnard Project Editors Kristen Dietrich, Adam Strafaci, Colleen Totz Contributing Authors Christine Hill, Gordon McKay, Stan Plante, Barbara A. Schmitz Peer Review Board Jonathan 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 PRESS Waterbury, CT USA
Table of Contents Preface Continuing Education Units About the Software xi xv xvii Chapter 1 Introduction to Wastewater Collection System Modeling 1 1.1 Wastewater Collection System Overview 1 Terminology... 2 Sources of Wastewater... 2 Types of Conveyance... 3 1.2 Modeling 5 Applications of Collection System Models... 5 Types of Collection System Modeling... 7 1.3 Historical Perspective on Collection System Analysis 7 Collection Systems... 7 Hydraulics History... 11 Historical Summary... 16 1.4 The Modeling Process 16 Chapter 2 Steady Gravity Flow Hydraulics 23 2.1 Fluid Properties 24 Density and Specific Weight... 24 Viscosity... 24 Fluid Compressibility... 27 Vapor Pressure... 27 2.2 Fluid Statics and Dynamics 28 Static Pressure... 28 Absolute Pressure and Gauge Pressure... 29 Velocity and Flow... 30 Reynolds Number... 31 Velocity Profiles... 31
ii Table of Contents 2.3 Fundamental Laws 32 Conservation of Mass... 32 Conservation of Energy... 33 Conservation of Momentum... 36 2.4 Hydraulic Design Variables 38 Flow Rate or Discharge... 38 Channel/Pipe Slope... 38 Depth of Flow... 38 Velocity... 39 2.5 Energy and Head Losses 40 Energy Equation... 41 2.6 Hydraulic Elements 44 Open-Top Cross Sections... 44 Closed-Top Cross Sections... 46 Noncircular Cross Sections... 49 2.7 Manning s n Variation 49 Calculating n with the Darcy-Weisbach Equation... 50 Variation of n with Depth... 52 Recommended Values of Manning s n... 53 2.8 Minor Losses in Junction Structures 54 Energy-Loss Method... 55 Composite Energy-Loss Method... 60 2.9 Tractive Force Self-Cleansing 63 Tractive Tension... 63 Sediment Carrying Capacity Experimental Analysis... 65 Camp Formula... 69 Yao s Method... 69 Abwassertechnische Vereinigung (ATV) Method... 71 Additional Considerations... 71 2.10 Specific Energy and Critical Flow 72 Specific Energy... 72 Froude Number... 74 Subcritical and Supercritical Flow... 74 Hydraulic Jumps... 75 Flow Profiles... 76 Backwater Curves... 77 2.11 Hydraulics of Flow-Control Structures 78 Orifices... 79 Weirs... 79 Gates... 84 Chapter 3 Unsteady Gravity Flow Hydraulics 91 3.1 Basics of Unsteady Flow Analysis 93 3.2 Types of Routing 94
iii 3.3 Hydrodynamic Equations 95 Saint-Venant Equations... 95 Approximation to Hydrodynamic Equations... 96 Diffusion Analogy... 97 Kinematic Wave... 97 Muskingum Routing... 98 Muskingum-Cunge Routing... 98 Convex Routing... 100 Weighted Translational Routing... 100 Level Pool Routing... 100 Summary of Methods... 101 3.4 Complications to Routing Methods 101 Manholes and Junction Tables... 103 Surcharging... 103 Overflows and Diversions... 104 Parallel Pipes and Loops... 105 Flow Reversal... 106 Dry Pipes... 107 Drop Structures... 107 Chapter 4 Force Main and Pumping Hydraulics 113 4.1 Friction Losses 113 Darcy-Weisbach Equation... 116 Colebrook-White Equation and the Moody Diagram... 117 Hazen-Williams Equation... 118 Swamee-Jain Equation... 120 Manning Equation... 120 Pipe Roughness Changes... 121 Comparison of Friction Loss Methods... 121 4.2 Minor Losses 122 Minor Loss Valve Coefficients... 123 4.3 Energy Addition Pumps 125 Pump Head-Discharge Relationship... 125 System Head Curves... 126 Other Pump Characteristic Curves... 128 Fixed-Speed and Variable-Speed Pumps... 129 Affinity Laws for Variable-Speed Pumps... 129 Power and Efficiency... 130 Chapter 5 Model Construction 137 5.1 Developing the Modeling Plan 137 5.2 The Modeling Process 138 Purpose and Objectives of a Model... 138 Develop Alternatives... 141 Scales of Models... 141 Software Selection and Training... 143
iv Table of Contents Define Data Requirements... 143 Identify Data Sources... 144 Collect Data... 146 Validate the Data... 147 Build the Model... 148 Identify Data Gaps... 148 Sensitivity Analysis... 148 Calibrate the Model... 148 Validate the Model... 148 Run Simulations... 149 Develop Solutions... 150 Bookkeeping... 151 5.3 Constructing the Sewer Model 152 Level of Detail... 153 Subbasin Delineation... 154 Pipes... 154 Manholes... 160 Pumps... 164 Wet Wells... 168 Chapter 6 Dry Weather Wastewater Flows 173 6.1 Definition of Flow Rates 175 New Systems... 175 Existing Systems... 176 6.2 Unit Load Factors 176 Residential... 176 Commercial Sources... 177 Industrial Wastewater Flows... 179 Fixture Unit Method... 181 Land-Use Methods... 183 Measured-Flow Methods... 185 Assigning Loads to a Model... 187 6.3 Peaking Factors 187 Peaking Factor Charts and Equations... 188 Minimum Flows... 190 Selection of Flow Generation Rate and Peaking Factor... 191 6.4 Time-Varying Flows 193 Diurnal Curves... 193 Developing Systemwide Diurnal Curves... 195 Defining Usage Patterns Within a Model... 196 Chapter 7 Wet Weather Wastewater Flows 203 7.1 Wet Weather Flow Definitions 204 What Is Wet Weather Flow?... 204 Components of Flow in Wastewater Collection Systems... 204 Modeling Wet Weather Flows... 206
v 7.2 Wastewater Collection System Hydrology 208 Combined Sewer System Hydrology... 208 Modeling Combined Sewer Systems... 210 Separate Sanitary Sewer System Hydrology... 212 Modeling Separate Sanitary Sewer Systems... 213 Continuous versus Event Hydrology... 216 7.3 Rainfall 217 Rainfall Data... 217 Selecting Model Simulation Events... 218 Calibration Events... 219 Design Storms... 219 Continuous Records... 228 7.4 Modeling Runoff 229 Rainfall Abstractions... 230 Horton Equation... 233 Green-Ampt Equation... 233 Rational Method... 234 NRCS (SCS) Method... 236 7.5 Determining Hydrographs from Runoff Volumes 239 Determining Peak Flow and Time to Peak... 240 Snider Triangular Hydrograph... 240 Unit Hydrograph Approach... 242 NRCS (SCS) Dimensionless Unit Hydrograph... 243 Nonlinear Reservoir... 246 7.6 Empirical Methods for Generating Hydrographs 248 Percentage of Rainfall Volume (R-Factor)... 249 Unit Hydrographs from Flow Measurements... 249 Simplifications to Unit Hydrograph... 250 Inflow Coefficient Method... 250 Rainfall/Flow Regression... 252 RTK Hydrograph Method... 254 Unit Loads for Design Studies... 261 7.7 Snowmelt 262 Runoff Potential... 262 Snowmelt Models... 263 Chapter 8 Data Collection and Flow Measurement 271 8.1 Flow Measurement Considerations 271 Components of Flow... 272 Review of Existing Information... 273 Selection of Metering Locations... 273 Safety Considerations... 274 8.2 Flow Measurement 275 Hydraulic Control Sections in Open Channels... 275 In-Pipe Methods... 280 Manual Methods... 281
vi Table of Contents 8.3 Instrumentation 283 Depth... 284 Velocity Meters... 287 8.4 Precipitation Measurement 292 Precipitation Data Acquisition... 293 Measurement of Rainfall... 293 Gauge Operation Considerations... 294 Radar Imagery... 295 Chapter 9 Model Calibration 301 9.1 Basic Calibration Concepts 302 Overview of Calibration... 302 Calibration Parameters... 303 Building-Block Approach... 305 Steady-State and Extended-Period Simulations... 305 9.2 Dry Weather Flows 305 9.3 Wet Weather Flows 309 Constant Unit Rate Method... 310 Percentage of Rainfall Volume (R-Value)... 312 Percentage of Stream Flow... 313 RTK Hydrograph... 315 Predictive Equation Based on Rainfall-Flow Regression... 316 9.4 Special Considerations in Calibration 320 Volume Differences... 321 Shape Considerations... 322 Timing Shifts... 323 9.5 Understanding Overflows 324 Estimating Combined Sewer Overflow... 325 Estimating SSOs... 326 Detecting Overflows with Scattergraphs... 326 Chapter 10 Design of New Gravity Wastewater Collection Systems 333 10.1 Materials 334 Pipes... 334 Manholes... 335 Other Appurtenances... 336 10.2 Initial Planning 337 Decision to Provide Sewer Service to an Area... 337 Types of Conveyance... 338 Separate versus Combined Systems... 338 10.3 Preliminary Design Considerations 339 Data Requirements... 340 Alternatives... 341
vii 10.4 Initial System Layout 341 Gravity Sewer Layout... 342 Manhole Location and Spacing... 342 Location of Pumping Facilities... 343 Sewer Easements... 343 Example of a Sewer Network Layout... 344 10.5 Flows in Sanitary Sewers 346 Low Flows in Early Years... 346 Allowances for Infiltration and Inflow... 346 Phased/Staged Construction... 348 10.6 Horizontal and Vertical Alignment 348 Pipe Slopes... 348 Curved Sewer Alignment... 349 Minimum Depth of Cover... 349 Maximum Depth... 352 10.7 Hydraulic Design 352 Pipe Sizing... 354 Manholes... 355 Computer Modeling for System Design... 356 Steady Flow versus Extended-Period Simulation (EPS) Analysis... 356 Design Maximum Flow Rates with Pumping... 358 10.8 Special Installations 358 Sewers in Steep Terrain... 358 Sewers Along Streams... 359 Elevated Crossings... 359 Inverted Siphons (Depressed Sewers)... 360 10.9 Wastewater Collection System Optimization 361 Chapter 11 Wastewater Collection System Evaluation and Rehabilitation 371 11.1 Planning for System Characterization 372 Performance Requirements... 373 Current Performance... 374 Approach to System Characterization... 375 11.2 System Characterization 376 Review Existing Records... 376 Update System Inventory... 378 Collection System Condition Investigation... 379 Inspection of the Condition of Controls and Ancillary Structures... 382 11.3 Hydraulic Investigations 384 Field Data Collection... 385 Data Analysis... 386 Application of Hydraulic Modeling... 390 Assess Hydraulic Performance... 394
viii Table of Contents 11.4 Evaluating Rehabilitation Strategies 395 Preventive Maintenance Program... 399 Source Controls... 399 Sewer Separation... 400 Pipe Rehabilitation/Replacement... 401 Inflow/Infiltration Control... 402 Interbasin Transfers... 405 Real-Time Controls... 405 Storage Facilities... 406 Wet Weather Treatment Facilities... 407 Chapter 12 Force Mains and Pump Stations 419 12.1 Need for Pump Stations 420 12.2 Pump Station Overview and Design Considerations 423 Components... 423 Design Decisions... 425 Pump Capacity... 425 Pump Station Configuration... 426 Pump Types and Selection... 427 Wet Well Sizing... 432 Net Positive Suction Head... 433 Appurtenances... 435 12.3 Force Main Sizing with a Single Pump Station 435 Determining Pipe Sizes... 436 Developing System Head Curves... 437 Selecting Economical Pipe Size... 438 12.4 Modeling Pumped Systems 441 Modeling Pumps... 442 Downstream Flow Attenuation... 442 Identifying Potential Problems... 443 Modeling a Pipeline with Multiple High Points... 444 12.5 Efficiency Considerations 448 Constant-Speed Pumping... 448 Variable-Speed Pumping... 451 Automated Energy Calculations... 455 12.6 Force Mains with Multiple Pump Stations 455 12.7 Hydraulic Transients 457 Chapter 13 Low-Pressure Sewers 467 13.1 Description of Pressure Sewers 468 Storage Tanks... 470 Service Lines... 470 Pressure Mains... 471 Air-Release/Vacuum-Breaker Valves... 471 Discharge Points... 471
ix 13.2 Estimating Flows 472 Empirical Approaches... 473 Poisson Distribution to Estimate Loads... 475 13.3 Pressure Sewer Design Considerations 478 13.4 Modeling Pressure Sewers 479 Modeling to Size Pressure Mains... 480 Representing All Service Connections as Nodes... 481 Detailed Models... 482 Chapter 14 Utilizing GIS 489 14.1 GIS Fundamentals 490 Data Management... 491 Geographic Data Representations... 494 14.2 Developing an Enterprise GIS 495 Keys to Successful Implementation... 495 Needs Assessment... 496 Design... 497 Pilot Study... 504 Production... 504 Rollout... 505 14.3 Model Construction 505 Model Sustainability and Maintenance... 506 Communication Between the GIS and Modeling Staff... 507 Network Components... 508 Wastewater Loads... 510 Building the Model... 515 Pitfalls in Constructing Models from GIS... 517 Loading Model Results to GIS... 520 14.4 GIS Analysis and Visualization 520 Basic GIS Uses and Examples... 520 Advanced GIS Uses and Examples... 522 Chapter 15 Regulatory Issues 529 15.1 United States Laws and Regulations 529 Clean Water Act... 530 U.S. Federal Regulations... 531 Water Quality Standards and Total Maximum Daily Loads (TMDLs)... 537 Section 404 Dredge and Fill Permits... 538 15.2 Canadian Laws and Regulations 538 Sanitary Sewer Systems... 539 Combined Sewer Systems... 539 15.3 European Union Laws and Regulations 546 Urban Wastewater Treatment Directive (UWWTD)... 546
x Table of Contents Water Policy Framework Directive (WPFD)... 549 Integrated Pollution Prevention Control Directive (IPPC)... 549 Product Directives... 549 Control of CSOs in EU Member States... 549 Design 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