WASTEWATER COLLECTION SYSTEM MODELING AND DESIGN

Transcription

1 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

2 Table of Contents Preface Continuing Education Units About the Software xi xv xvii Chapter 1 Introduction to Wastewater Collection System Modeling Wastewater Collection System Overview 1 Terminology... 2 Sources of Wastewater... 2 Types of Conveyance Modeling 5 Applications of Collection System Models... 5 Types of Collection System Modeling Historical Perspective on Collection System Analysis 7 Collection Systems... 7 Hydraulics History Historical Summary The Modeling Process 16 Chapter 2 Steady Gravity Flow Hydraulics Fluid Properties 24 Density and Specific Weight Viscosity Fluid Compressibility Vapor Pressure Fluid Statics and Dynamics 28 Static Pressure Absolute Pressure and Gauge Pressure Velocity and Flow Reynolds Number Velocity Profiles... 31

3 ii Table of Contents 2.3 Fundamental Laws 32 Conservation of Mass Conservation of Energy Conservation of Momentum Hydraulic Design Variables 38 Flow Rate or Discharge Channel/Pipe Slope Depth of Flow Velocity Energy and Head Losses 40 Energy Equation Hydraulic Elements 44 Open-Top Cross Sections Closed-Top Cross Sections Noncircular Cross Sections Manning s n Variation 49 Calculating n with the Darcy-Weisbach Equation Variation of n with Depth Recommended Values of Manning s n Minor Losses in Junction Structures 54 Energy-Loss Method Composite Energy-Loss Method Tractive Force Self-Cleansing 63 Tractive Tension Sediment Carrying Capacity Experimental Analysis Camp Formula Yao s Method Abwassertechnische Vereinigung (ATV) Method Additional Considerations Specific Energy and Critical Flow 72 Specific Energy Froude Number Subcritical and Supercritical Flow Hydraulic Jumps Flow Profiles Backwater Curves Hydraulics of Flow-Control Structures 78 Orifices Weirs Gates Chapter 3 Unsteady Gravity Flow Hydraulics Basics of Unsteady Flow Analysis Types of Routing 94

4 iii 3.3 Hydrodynamic Equations 95 Saint-Venant Equations Approximation to Hydrodynamic Equations Diffusion Analogy Kinematic Wave Muskingum Routing Muskingum-Cunge Routing Convex Routing Weighted Translational Routing Level Pool Routing Summary of Methods Complications to Routing Methods 101 Manholes and Junction Tables Surcharging Overflows and Diversions Parallel Pipes and Loops Flow Reversal Dry Pipes Drop Structures Chapter 4 Force Main and Pumping Hydraulics Friction Losses 113 Darcy-Weisbach Equation Colebrook-White Equation and the Moody Diagram Hazen-Williams Equation Swamee-Jain Equation Manning Equation Pipe Roughness Changes Comparison of Friction Loss Methods Minor Losses 122 Minor Loss Valve Coefficients Energy Addition Pumps 125 Pump Head-Discharge Relationship System Head Curves Other Pump Characteristic Curves Fixed-Speed and Variable-Speed Pumps Affinity Laws for Variable-Speed Pumps Power and Efficiency Chapter 5 Model Construction Developing the Modeling Plan The Modeling Process 138 Purpose and Objectives of a Model Develop Alternatives Scales of Models Software Selection and Training

5 iv Table of Contents Define Data Requirements Identify Data Sources Collect Data Validate the Data Build the Model Identify Data Gaps Sensitivity Analysis Calibrate the Model Validate the Model Run Simulations Develop Solutions Bookkeeping Constructing the Sewer Model 152 Level of Detail Subbasin Delineation Pipes Manholes Pumps Wet Wells Chapter 6 Dry Weather Wastewater Flows Definition of Flow Rates 175 New Systems Existing Systems Unit Load Factors 176 Residential Commercial Sources Industrial Wastewater Flows Fixture Unit Method Land-Use Methods Measured-Flow Methods Assigning Loads to a Model Peaking Factors 187 Peaking Factor Charts and Equations Minimum Flows Selection of Flow Generation Rate and Peaking Factor Time-Varying Flows 193 Diurnal Curves Developing Systemwide Diurnal Curves Defining Usage Patterns Within a Model Chapter 7 Wet Weather Wastewater Flows Wet Weather Flow Definitions 204 What Is Wet Weather Flow? Components of Flow in Wastewater Collection Systems Modeling Wet Weather Flows

6 v 7.2 Wastewater Collection System Hydrology 208 Combined Sewer System Hydrology Modeling Combined Sewer Systems Separate Sanitary Sewer System Hydrology Modeling Separate Sanitary Sewer Systems Continuous versus Event Hydrology Rainfall 217 Rainfall Data Selecting Model Simulation Events Calibration Events Design Storms Continuous Records Modeling Runoff 229 Rainfall Abstractions Horton Equation Green-Ampt Equation Rational Method NRCS (SCS) Method Determining Hydrographs from Runoff Volumes 239 Determining Peak Flow and Time to Peak Snider Triangular Hydrograph Unit Hydrograph Approach NRCS (SCS) Dimensionless Unit Hydrograph Nonlinear Reservoir Empirical Methods for Generating Hydrographs 248 Percentage of Rainfall Volume (R-Factor) Unit Hydrographs from Flow Measurements Simplifications to Unit Hydrograph Inflow Coefficient Method Rainfall/Flow Regression RTK Hydrograph Method Unit Loads for Design Studies Snowmelt 262 Runoff Potential Snowmelt Models Chapter 8 Data Collection and Flow Measurement Flow Measurement Considerations 271 Components of Flow Review of Existing Information Selection of Metering Locations Safety Considerations Flow Measurement 275 Hydraulic Control Sections in Open Channels In-Pipe Methods Manual Methods

7 vi Table of Contents 8.3 Instrumentation 283 Depth Velocity Meters Precipitation Measurement 292 Precipitation Data Acquisition Measurement of Rainfall Gauge Operation Considerations Radar Imagery Chapter 9 Model Calibration Basic Calibration Concepts 302 Overview of Calibration Calibration Parameters Building-Block Approach Steady-State and Extended-Period Simulations Dry Weather Flows Wet Weather Flows 309 Constant Unit Rate Method Percentage of Rainfall Volume (R-Value) Percentage of Stream Flow RTK Hydrograph Predictive Equation Based on Rainfall-Flow Regression Special Considerations in Calibration 320 Volume Differences Shape Considerations Timing Shifts Understanding Overflows 324 Estimating Combined Sewer Overflow Estimating SSOs Detecting Overflows with Scattergraphs Chapter 10 Design of New Gravity Wastewater Collection Systems Materials 334 Pipes Manholes Other Appurtenances Initial Planning 337 Decision to Provide Sewer Service to an Area Types of Conveyance Separate versus Combined Systems Preliminary Design Considerations 339 Data Requirements Alternatives

8 vii 10.4 Initial System Layout 341 Gravity Sewer Layout Manhole Location and Spacing Location of Pumping Facilities Sewer Easements Example of a Sewer Network Layout Flows in Sanitary Sewers 346 Low Flows in Early Years Allowances for Infiltration and Inflow Phased/Staged Construction Horizontal and Vertical Alignment 348 Pipe Slopes Curved Sewer Alignment Minimum Depth of Cover Maximum Depth Hydraulic Design 352 Pipe Sizing Manholes Computer Modeling for System Design Steady Flow versus Extended-Period Simulation (EPS) Analysis Design Maximum Flow Rates with Pumping Special Installations 358 Sewers in Steep Terrain Sewers Along Streams Elevated Crossings Inverted Siphons (Depressed Sewers) Wastewater Collection System Optimization 361 Chapter 11 Wastewater Collection System Evaluation and Rehabilitation Planning for System Characterization 372 Performance Requirements Current Performance Approach to System Characterization System Characterization 376 Review Existing Records Update System Inventory Collection System Condition Investigation Inspection of the Condition of Controls and Ancillary Structures Hydraulic Investigations 384 Field Data Collection Data Analysis Application of Hydraulic Modeling Assess Hydraulic Performance

9 viii Table of Contents 11.4 Evaluating Rehabilitation Strategies 395 Preventive Maintenance Program Source Controls Sewer Separation Pipe Rehabilitation/Replacement Inflow/Infiltration Control Interbasin Transfers Real-Time Controls Storage Facilities Wet Weather Treatment Facilities Chapter 12 Force Mains and Pump Stations Need for Pump Stations Pump Station Overview and Design Considerations 423 Components Design Decisions Pump Capacity Pump Station Configuration Pump Types and Selection Wet Well Sizing Net Positive Suction Head Appurtenances Force Main Sizing with a Single Pump Station 435 Determining Pipe Sizes Developing System Head Curves Selecting Economical Pipe Size Modeling Pumped Systems 441 Modeling Pumps Downstream Flow Attenuation Identifying Potential Problems Modeling a Pipeline with Multiple High Points Efficiency Considerations 448 Constant-Speed Pumping Variable-Speed Pumping Automated Energy Calculations Force Mains with Multiple Pump Stations Hydraulic Transients 457 Chapter 13 Low-Pressure Sewers Description of Pressure Sewers 468 Storage Tanks Service Lines Pressure Mains Air-Release/Vacuum-Breaker Valves Discharge Points

10 ix 13.2 Estimating Flows 472 Empirical Approaches Poisson Distribution to Estimate Loads Pressure Sewer Design Considerations Modeling Pressure Sewers 479 Modeling to Size Pressure Mains Representing All Service Connections as Nodes Detailed Models Chapter 14 Utilizing GIS GIS Fundamentals 490 Data Management Geographic Data Representations Developing an Enterprise GIS 495 Keys to Successful Implementation Needs Assessment Design Pilot Study Production Rollout Model Construction 505 Model Sustainability and Maintenance Communication Between the GIS and Modeling Staff Network Components Wastewater Loads Building the Model Pitfalls in Constructing Models from GIS Loading Model Results to GIS GIS Analysis and Visualization 520 Basic GIS Uses and Examples Advanced GIS Uses and Examples Chapter 15 Regulatory Issues United States Laws and Regulations 529 Clean Water Act U.S. Federal Regulations Water Quality Standards and Total Maximum Daily Loads (TMDLs) Section 404 Dredge and Fill Permits Canadian Laws and Regulations 538 Sanitary Sewer Systems Combined Sewer Systems European Union Laws and Regulations 546 Urban Wastewater Treatment Directive (UWWTD)

11 x Table of Contents Water Policy Framework Directive (WPFD) Integrated Pollution Prevention Control Directive (IPPC) Product Directives Control of CSOs in EU Member States Design Criteria for CSOs 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