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.
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
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 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.
