Green Stormwater Infrastructure Fundamentals and Design

Discover novel stormwater control measures to make for a greener tomorrow!

The protection of our aquatic resources is growing in importance as the effects of climate change and continued urbanization are felt throughout the world. While most rain that falls onto vegetated spaces infiltrates the soil, rain that falls onto impervious surfaces will not, increasing downstream flooding and erosion and causing impaired water quality. Impervious surfaces such as road infrastructure, rooftops, and parking areas all increase runoff and mobilize many pollutants that have deposited on these surfaces that are then carried into our waterways. Proper management of this stormwater through green infrastructure is essential to address these challenges and reduce the environmental and ecological impacts brought about by this runoff.

This book brings into focus resilient stormwater control measures (SCMs) for the reduction of stormwater flows and associated pollutants that can detrimentally impact our local environmental and ecological systems. These interventions are green infrastructure based, utilizing natural hydrologic and environmental features using soil and vegetation to manage stormwater. These technologies include water harvesting, bioretention and bioinfiltration, vegetated swales and filter strips, permeable pavements, sand filters, green roofs, and stormwater wetlands, among others. The basic science and engineering of these technologies is discussed, including performance information and best maintenance practices.

Green Stormwater Infrastructure readers will also find:

• Research-informed resilient SCM design fundamentals
• Diagrams developed by the authors to enhance understanding
• Case studies to illustrate the points elucidated in the book
• End-of-chapter problems with a separate solutions manual

Green Stormwater Infrastructure is an ideal resource for environmental, civil, and biological engineers and environmental scientists in the consulting field. Landscape architects, managers and engineers of watershed districts, and members of federal, state, and local governmental agencies—especially those in the departments of environmental protection and transportation—will find many uses for this guidebook. It will also be of interest to professors, upper-level undergraduates and graduate students in environmental, civil, and biological engineering programs.

Allen P. Davis, PhD, PE, D. WRE, F. EWRI, F. ASCE, is the Charles A. Irish Sr. Chair in Civil Engineering and Professor in the Department of Civil and Environmental Engineering, and Affiliate Professor in Plant Science and Landscape Architure at the University of Maryland, College Park, MD.

William F. Hunt III, PhD, PE, D. WRE, M. ASCE, is a William Neal Reynolds Distinguished University Professor and Extension Specialist in the Department of Biological and Agricultural Engineering at the North Carolina State University, Raleigh, NC. He is the leader of the Stormwater Engineering Group at NC State.

Robert G. Traver, PhD, PE, D. WRE, F. EWRI, F. ASCE, is a Professor in the Department of Civil and Environmental Engineering at Villanova University, Villanova, PA, and former Edward A. Daylor Chair in Civil Engineering. He is the Director of the Villanova Center for Resilient Water Systems, and the Villanova Urban Stormwater Partnership.

Preface xix

About the Authors xxi

Acknowledgements xxiii

About the Companion Website xxv

1 Introduction to Urban Stormwater and Green Stormwater Infrastructure 1

1.1 Population and Urban Infrastructure 1

1.2 Impacts of Urbanization 2

1.3 The US Regulatory Environment 7

1.4 Urban Stormwater Management 12

1.4.1 Flood Control 12

1.4.2 Peak Flow Control 13

1.4.3 Watershed Approach to Peak Flow 14

1.4.4 Water-Quality Control 14

1.5 Climate Change and Stationarity 15

1.6 Green Stormwater Infrastructure 15

1.7 Stormwater Control Measures 17

1.8 Stormwater Infrastructure and Equity 17

References 18

Problems 19

2 Precipitation: The Stormwater Driver 21

2.1 Introduction 21

2.2 The Urban Hydrologic Cycle 21

2.3 Precipitation 23

2.4 Precipitation Depths 24

2.5 Rainfall Patterns 26

2.6 Inter-event Interval 27

2.7 Extreme Event Precipitation 27

2.8 Introducing the Rainfall–Runoff Relationship 29

2.9 Precipitation and Water Quality 30

2.10 Climate Change 31

References 31

Problems 31

3 Water Quality 33

3.1 Introduction 33

3.2 Designated Water Uses 33

3.3 Water-Quality Parameters and Measures 34

3.4 Temperature 34

3.5 pH 35

3.6 Dissolved Oxygen 35

3.7 Turbidity and Particulate Matter 37

3.8 Biodegradable Organic Matter or “Oxygen Demand” 40

3.9 Nitrogen 41

3.9.1 Nitrate 41

3.9.2 Nitrite 42

3.9.3 Ammonium 42

3.9.4 Organic Nitrogen 43

3.9.5 Nitrogen Measurements 43

3.10 Phosphorus 44

3.11 Heavy Metals 46

3.12 Hydrocarbons and Other Organic Pollutants 46

3.12.1 Hydrocarbons 46

3.12.2 Pesticides and Other Organic Chemicals 47

3.13 Pathogens 48

3.14 Dissolved Solids and Conductivity 49

3.15 Trash 50

References 50

Problems 50

4 Ecosystem Services 53

4.1 What Are Ecosystem Services? 53

4.2 Ecosystem Services and Stormwater Management 56

4.3 Stormwater Wetlands and Ecosystem Services 56

4.4 Regulation Services 56

4.4.1 Water Treatment 56

4.4.2 Hydrologic Regulation 56

4.4.3 Climate Regulation 57

4.4.4 Air Quality Regulation 57

4.5 Habitat Services 58

4.6 Production Services 59

4.7 Information Services 60

4.8 Designing SCMs for Ecosystem Services 61

References 61

Problems 63

5 Stormwater Quality 65

5.1 Introduction 65

5.2 Event Mean Concentrations 66

5.3 Urban Runoff Pollutant Concentrations 68

5.3.1 Particulate Matter and Particle Size Distributions 70

5.3.2 Nitrogen and Nitrogen Speciation 71

5.3.3 Phosphorus and Phosphorus Speciation 72

5.3.4 Heavy Metals Concentrations and Speciation 73

5.3.5 PAH and PCBs 74

5.4 Urban Stormwater Pollutant Sources 74

5.5 Pollutant Buildup and Wash Off 76

5.5.1 Pollutographs 76

5.5.2 First Flush 76

5.6 Annual Pollutant Loads 83

5.7 Sampling and Measurements 84

5.8 A Note about Stormwater Quality 84

References 84

Problems 87

6 Watershed Hydrology 89

6.1 Introduction 89

6.2 Precipitation 90

6.2.1 Design Storms 91

6.2.2 Continuous Simulation 97

6.3 Watershed Hydrology 98

6.3.1 Drainage Area Delineation 98

6.3.2 Interception and Depression Storage 99

6.3.3 The Simple Method 100

6.3.4 NRCS Curve Number Method 101

6.3.5 NRCS “Time of Concentration” 106

6.3.6 NRCS Unit Hydrograph 108

6.3.7 Creating the Storm Hydrograph 112

6.4 Peak Flow Methods 113

6.4.1 The Rational Method 113

6.4.2 The NRCS Unit Hydrograph Method 115

6.5 Watershed and SCM Hydraulics 115

6.5.1 Open Channel Flow 115

6.5.2 Orifices 117

6.5.3 Weirs 118

References 120

Problems 121

7 SCM Hydrologic Unit Processes 127

7.1 Introduction 127

7.2 SCM Soil Physics and Infiltration 128

7.2.1 Soil Texture 129

7.2.2 Soil–Water Interactions 130

7.2.3 Soil Hydraulic Properties 134

7.2.4 Green and Ampt Model 137

7.2.5 Karst Areas 140

7.3 Evapotranspiration 141

7.4 Soil Moisture Accounting 147

7.5 Storage Indication Routing 148

7.6 Computer-Based Stormwater Models 148

References 149

Problems 150

8 Unit Processes for Stormwater Quality Mitigation 153

8.1 Introduction 153

8.2 Reactions, Reactors, and Reactor Engineering 154

8.3 Removal of Particulate Matter 158

8.3.1 Sedimentation 158

8.3.2 Filtration 161

8.4 Removal of Dissolved Pollutants: Adsorption 163

8.4.1 Adsorption Equilibrium Models 164

8.4.2 Batch Adsorption 165

8.4.3 Adsorption Column Dynamics 168

8.4.4 Adsorption of Hydrophobic Organic Compounds 169

8.4.5 Adsorption of Heavy Metals 170

8.4.6 Adsorption of Phosphorus 170

8.4.7 Adsorption of Ammonium 171

8.5 Leaching Processes 171

8.6 Microbiological Processes 171

8.6.1 Microbial/Pathogen Survival 172

8.6.2 Organic Matter Degradation 172

8.6.3 Nitrification 173

8.6.4 Denitrification 174

8.7 Phytobiological Processes 175

8.8 Heat Transfer 176

References 177

Problems 178

9 Stormwater Performance Measures and Metrics 183

9.1 Introduction 183

9.2 Reference Conditions and Defining Thresholds 184

9.3 Volume Control 184

9.3.1 Runoff Depth 184

9.3.2 Curve Number Reduction 185

9.4 Peak Flow, Flow, and Geomorphology 186

9.5 Pollutant Percent Removal 189

9.6 Chesapeake Bay Retrofit Curves 190

9.7 Target Effluent Concentrations 190

9.8 Annual Mass Load 192

9.9 Probability and Exceedance 193

9.10 Pollutant Durations 195

References 198

Problems 199

10 Preventing Runoff and Stormwater Pollution 201

10.1 Introduction 201

10.2 Site Design and Low Impact Development 201

10.3 Compacted Urban Surfaces 203

10.3.1 Avoiding Compaction and Promoting Infiltration 204

10.3.2 Soil Restoration 204

10.3.3 De-paving 205

10.3.4 Removing Abandoned Housing 205

10.4 Street Trees 206

10.5 Disconnecting Impervious Surfaces 207

10.5.1 Defining Disconnected Impervious Surface 208

10.5.2 Calculating the Benefit of Disconnecting Imperviousness 208

10.5.3 Design 210

10.5.4 Water-Quality Benefits 212

10.5.5 Performance Results 212

10.6 Pollution Prevention 213

10.6.1 Street Sweeping 213

10.6.2 Product Prohibition 216

10.7 Education 217

References 217

Problems 218

11 Green Infrastructure Stormwater Control 221

11.1 Introduction 221

11.2 Fundamentals of Stormwater Control Measures 221

11.3 Designing to Climate and the Watershed 222

11.4 Types of Stormwater Control Measures 223

11.5 Nonvegetated Stormwater Control Measures 224

11.5.1 Infiltration Basins and Rock Beds 224

11.5.2 Permeable Pavements 224

11.5.3 Cisterns and Rain Barrels 225

11.5.4 Sand Filters 225

11.6 Vegetated Stormwater Control Measures 225

11.6.1 Vegetation Challenges 227

11.6.2 Green Roofs 229

11.6.3 Bioretention 230

11.6.4 Vegetated Swales and Filter Strips 230

11.6.5 Stormwater Wetlands 230

11.7 Selecting the SCM Site 230

11.8 Stormwater Treatment Media 231

11.8.1 Rock, Gravel, and Coarse Sand 232

11.8.2 Silts and Clays 232

11.8.3 Organic Media 232

11.9 Volumetric Storage 233

11.10 Drains and Underdrains 234

11.11 “Irreducible Concentrations” 235

References 237

Problems 238

12 Inlets, Bypasses, Pretreatment, and Proprietary Devices 239

12.1 Introduction 239

12.2 Inlets 239

12.3 Stormwater Bypass 240

12.4 Catch Basin and Inlet Filters 241

12.5 Pretreatment 242

12.6 Forebays 242

12.6.1 Forebay Design 243

12.6.2 Forebay Maintenance 245

12.7 Proprietary Devices 246

12.8 Accumulated Trash and Sediment 248

References 249

Problems 249

13 Green Roofs 251

13.1 Introduction 251

13.2 Climate and Green Roofs 251

13.3 Types of Roofs 252

13.3.1 Green Roofs 252

13.3.2 Blue Roofs 253

13.4 Extensive Green Roof Components 256

13.5 Hydrologic Design Strategies 259

13.5.1 Rainfall Capture 259

13.5.2 Evapotranspiration 262

13.6 Water Quality Design 264

13.6.1 Phosphorus 265

13.6.2 Nitrogen 266

13.6.3 Metals 266

13.7 Inspection and Maintenance 266

13.8 Other Green Roof Benefits 266

References 267

Problems 268

14 Rainwater Harvesting 271

14.1 Introduction 271

14.2 Potential as a Water Resource 272

14.3 Harvested Roof Water Quality 273

14.4 Rain Barrels 274

14.5 Rainwater Harvesting Regulations 275

14.5.1 Non-stormwater Regulations 276

14.5.2 Stormwater Regulations 276

14.6 Designing Rainwater Harvesting Systems 277

14.6.1 General Characteristics and Purpose 277

13.6.2 Rainwater Storage Sizing Techniques 278

14.6.3 Design 279

14.7 Designing for Enhanced Stormwater Performance 282

14.7.1 Passive Release Mechanism 282

14.7.2 Active Release Mechanism 284

14.7.3 Alternative Approaches for Irrigation-based Systems 285

14.7.4 Designing an Infiltration or Filtration Area 286

14.8 Treatment for High-quality Use 288

14.9 Inspection and Maintenance 289

References 289

Problems 290

15 Permeable Pavement 293

15.1 Introduction 293

15.2 Types of Permeable Pavements 295

15.3 Permeable Pavement Installation 298

15.4 Designing for Infiltration and Percolation 298

15.4.1 Surface Infiltration 299

15.4.2 Run-on Ratio 299

15.4.3 Depth/Volume of Storage Layer 301

15.4.4 Underdrain Need 301

15.4.5 Underdrain Configuration 301

15.4.6 In Situ Soils 302

15.5 Permeable Pavement Hydrologic Design Strategies 302

15.6 Permeable Pavement Hydrology 305

15.6.1 Hydrographs 305

15.6.2 Curve Numbers and Storage 306

15.6.3 Evaporation 307

15.7 Water Quality Design 307

15.7.1 Particulate Matter 308

15.7.2 Metals 308

15.7.3 Nutrients 308

15.7.4 Hydrocarbons 309

15.7.5 pH 309

15.7.6 Thermal Pollution (Temperature) 310

15.7.7 Pollutant Loads 310

15.7.8 Long-term Pollutant Fate 311

15.8 Maintenance 312

15.9 Design Summary 312

15.10 Permeable Pavement Cost Factors 312

15.11 Permeable Friction Course 314

References 315

Problems 317

16 Infiltration Trenches and Infiltration Basins 319

16.1 Introduction 319

16.2 Types of Basins 319

16.3 Mechanisms of Treatment 321

16.4 Infiltration 323

16.5 Surface Infiltration Basins 323

16.6 Infiltration Trench and Subsurface Infiltration Basin Design 326

16.7 Infiltration Trench and Basin Performance 327

16.8 Inspection and Maintenance 328

References 329

Problems 329

17 Sand Filters 331

17.1 Introduction 331

17.2 Basic Sand Filter Operation 331

17.3 Sand Filter Options and Configurations 331

17.4 Sand Filter Design 333

17.5 Water Quality Performance 335

17.5.1 Particulate Matter Removal 335

17.5.2 Dissolved Pollutant Removal 336

17.6 Sand Filter Headloss 336

17.7 Solids Accumulation and Clogging 337

17.8 Sorptive and Reactive Media 339

17.9 Geotextile Filters 339

17.10 Inspection and Maintenance 340

References 340

Problems 341

18 Bioretention 343

18.1 Introduction 343

18.2 Bioretention Classifications 344

18.3 Bioretention Components 345

18.4 Siting and Configuration 346

18.5 Bioretention Flow Entrances, Inlets, and Forebays 348

18.6 Storage Bowl 350

18.7 Bioretention Design: Static Storage and Hydrologic Performance 351

18.8 Dynamic Storage 353

18.9 The Media 354

18.9.1 Rain Gardens 354

18.9.2 Standard Media 354

18.9.3 Surface Mulch Layer 354

18.10 Evapotranspiration 355

18.11 The Media and Particulate Matter Removal 356

18.12 The Media and Heavy Metals Removal 358

18.13 The Media and Organic Pollutants Removal 359

18.14 The Media and Phosphorus Removal 360

18.14.1 Phosphorus Removal in Bioretention 361

18.14.2 Quantifying Phosphorus Removal 362

18.14.3 Media Enhancements for Phosphorus Removal 363

18.15 The Media and Nitrogen Removal 366

18.15.1 Nitrogen Processing in Standard Bioretention Systems 366

18.15.2 Enhanced Nitrogen Removal 368

18.15.3 Biological Nitrogen Transformations 368

18.16 The Media and Bacteria Removal 370

18.17 Vegetation 370

18.18 The Underdrain and Subsurface Storage 373

18.19 Internal Water Storage and Nitrogen Removal 376

18.20 Bioretention Pollutant Load Reductions 377

18.21 Bioretention Exfiltration and Groundwater 380

18.22 Inspection and Maintenance 380

References 381

Problems 386

19 Swales, Filter Strips, and Level Spreaders 393

19.1 Introduction 393

19.2 Characteristics 393

19.2.1 Swales 393

19.2.2 Filter Strips and Level Spreaders 393

19.3 Swale Design 394

19.3.1 Configurations 396

19.3.2 Hydraulic Design 396

19.4 Filter Strip Design 399

19.4.1 Configurations 399

19.4.2 Flow Conveyance 399

19.5 Filter Strips Conveying to Swales 400

19.6 Water Quality Considerations 402

19.6.1 Designing for Pollutant Capture: Length of Swale 402

19.6.2 Designing for Particulate Matter Removal 402

19.6.3 Designing for Particulate Matter Removal with Particle-size Distribution Available 405

19.6.4 Designing for Metals Removal 406

19.6.5 Filtration through Swales and Filter Strips 408

19.6.6 Check Dams 409

19.7 Swale Performance 410

19.7.1 Hydrologic Considerations 410

19.7.2 Water Quality Considerations 412

19.8 Construction, Inspection, and Maintenance 414

19.9 Summary 414

References 415

Problems 416

20 Stormwater Wetlands 421

20.1 Introduction 421

20.2 Sizing Stormwater Wetlands 422

20.3 Stormwater Wetland Features and Design 423

20.3.1 Zone I—Deep Pools 424

20.3.2 Zone II—Deep to Shallow Water Transition Zone (Transition Zone) 426

20.3.3 Zone III—Shallow Water Zone 426

20.3.4 Zone IV—Temporary Inundation Zone 427

20.3.5 Zone V—Upper Bank 428

20.4 Wetland Vegetation 428

20.5 Wetland Soils and Vegetation Growth Media 430

20.6 Wetland Outlet Configuration 431

20.7 Wetland Construction 437

20.8 Wetland Variations 437

20.8.1 Wetland Design for Cold Water Species (Salmonids) 437

20.8.2 Off-line Stormwater Wetlands 437

20.8.3 Wetlands with High Flow Bypass 438

20.9 Water Quality Improvements in Stormwater Wetlands 439

20.10 Other Stormwater Wetland Designs 442

20.10.1 Submerged Gravel Wetlands 442

20.10.2 Ponds Transitioning to Wetlands 443

20.10.3 Floating Wetlands 444

20.11 Inspection and Maintenance 447

References 447

Problems 449

21 Putting It All Together 451

21.1 Introduction 451

21.2 SCM Hydrologic Performance Summary 451

21.3 SCM Water Quality Performance Summary 453

21.3.1 Green Roofs and Water Harvesting 453

21.3.2 Permeable Pavements 453

21.3.3 Infiltration Basins 454

21.3.4 Sand Filters 454

21.3.5 Bioretention 454

21.3.6 Vegetated Swales 455

21.3.7 Stormwater Wetlands 455

21.4 Treatment Trains 455

21.5 SCM Treatment Train Examples 456

21.5.1 Treatment Trains within Individual SCMs 456

21.5.2 Incorporating Treatment Trains in Traditional SCMs 457

21.5.3 SCMs in Series 457

21.6 Quantifying Performance in SCM Treatment Trains 462

21.7 Real Time Controls 463

21.8 Designing for Climate Change 464

21.9 Greener Infrastructure: What Does the Future Hold? 466

References 467

Problems 469

Appendix A 471

Index 473

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