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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
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.
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Green Stormwater Infrastructure Fundamentals and Design
Allen P. Davis, William F. Hunt, and Robert G. Traver
This edition first published 2022
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Contents
Cover
Title page
Copyright
Dedication
Preface
About the Authors
Acknowledgements
About the Companion Website
1 Introduction to Urban Stormwater and Green Stormwater Infrastructure
1.1 Population and Urban Infrastructure
1.2 Impacts of Urbanization
1.3 The US Regulatory Environment
1.4 Urban Stormwater Management
1.4.1 Flood Control
1.4.2 Peak Flow Control
1.4.3 Watershed Approach to Peak Flow
1.4.4 Water-Quality Control
1.5 Climate Change and Stationarity
1.6 Green Stormwater Infrastructure
1.7 Stormwater Control Measures
1.8 Stormwater Infrastructure and Equity
References
Problems
2 Precipitation: The Stormwater Driver
2.1 Introduction
2.2 The Urban Hydrologic Cycle
2.3 Precipitation
2.4 Precipitation Depths
2.5 Rainfall Patterns
2.6 Inter-event Interval
2.7 Extreme Event Precipitation
2.8 Introducing the Rainfall-Runoff Relationship
2.9 Precipitation and Water Quality
2.10 Climate Change
References
Problems
3 Water Quality
3.1 Introduction
3.2 Designated Water Uses
3.3 Water-Quality Parameters and Measures
3.4 Temperature
3.5 pH
3.6 Dissolved Oxygen
3.7 Turbidity and Particulate Matter
3.8 Biodegradable Organic Matter or “Oxygen Demand“
3.9 Nitrogen
3.9.1 Nitrate
3.9.2 Nitrite
3.9.3 Ammonium
3.9.4 Organic Nitrogen
3.9.5 Nitrogen Measurements
3.10 Phosphorus
3.11 Heavy Metals
3.12 Hydrocarbons and Other Organic Pollutants
3.12.1 Hydrocarbons
3.12.2 Pesticides and Other Organic Chemicals
3.13 Pathogens
3.14 Dissolved Solids and Conductivity
3.15 Trash
References
Problems
4 Ecosystem Services
4.1 What Are Ecosystem Services?
4.2 Ecosystem Services and Stormwater Management
4.3 Stormwater Wetlands and Ecosystem Services
4.4 Regulation Services
4.4.1 Water Treatment
4.4.2 Hydrologic Regulation
4.4.3 Climate Regulation
4.4.4 Air Quality Regulation
4.5 Habitat Services
4.6 Production Services
4.7 Information Services
4.8 Designing SCMs for Ecosystem Services
References
Problems
5 Stormwater Quality
5.1 Introduction
5.2 Event Mean Concentrations
5.3 Urban Runoff Pollutant Concentrations
5.3.1 Particulate Matter and Particle Size Distributions
5.3.2 Nitrogen and Nitrogen Speciation
5.3.3 Phosphorus and Phosphorus Speciation
5.3.4 Heavy Metals Concentrations and Speciation
5.3.5 PAH and PCBs
5.4 Urban Stormwater Pollutant Sources
5.5 Pollutant Buildup and Wash Off
5.5.1 Pollutographs
5.5.2 First Flush
5.6 Annual Pollutant Loads
5.7 Sampling and Measurements
5.8 A Note about Stormwater Quality
References
Problems
6 Watershed Hydrology
6.1 Introduction
6.2 Precipitation
6.2.1 Design Storms
6.2.2 Continuous Simulation
6.3 Watershed Hydrology
6.3.1 Drainage Area Delineation
6.3.2 Interception and Depression Storage
6.3.3 The Simple Method
6.3.4 NRCS Curve Number Method
6.3.5 NRCS “Time of Concentration”
6.3.6 NRCS Unit Hydrograph
6.3.7 Creating the Storm Hydrograph
6.4 Peak Flow Methods
6.4.1 The Rational Method
6.4.2 The NRCS Unit Hydrograph Method
6.5 Watershed and SCM Hydraulics
6.5.1 Open Channel Flow
6.5.2 Orifices
6.5.3 Weirs
References
Problems
7 SCM Hydrologic Unit Processes
7.1 Introduction
7.2 SCM Soil Physics and Infiltration
7.2.1 Soil Texture
7.2.2 Soil–Water Interactions
7.2.3 Soil Hydraulic Properties
7.2.4 Green and Ampt Model
7.2.5 Karst Areas
7.3 Evapotranspiration
7.4 Soil Moisture Accounting
7.5 Storage Indication Routing
7.6 Computer-Based Stormwater Models
References
Problems
8 Unit Processes for Stormwater Quality Mitigation
8.1 Introduction
8.2 Reactions, Reactors, and Reactor Engineering
8.3 Removal of Particulate Matter
8.3.1 Sedimentation
8.3.2 Filtration
8.4 Removal of Dissolved Pollutants: Adsorption
8.4.1 Adsorption Equilibrium Models
8.4.2 Batch Adsorption
8.4.3 Adsorption Column Dynamics
8.4.4 Adsorption of Hydrophobic Organic Compounds
8.4.5 Adsorption of Heavy Metals
8.4.6 Adsorption of Phosphorus
8.4.7 Adsorption of Ammonium
8.5 Leaching Processes
8.6 Microbiological Processes
8.6.1 Microbial/Pathogen Survival
8.6.2 Organic Matter Degradation
8.6.3 Nitrification
8.6.4 Denitrification
8.7 Phytobiological Processes
8.8 Heat Transfer
References
Problems
9 Stormwater Performance Measures and Metrics
9.1 Introduction
9.2 Reference Conditions and Defining Thresholds
9.3 Volume Control
9.3.1 Runoff Depth
9.3.2 Curve Number Reduction
9.4 Peak Flow, Flow, and Geomorphology
9.5 Pollutant Percent Removal
9.6 Chesapeake Bay Retrofit Curves
9.7 Target Effluent Concentrations
9.8 Annual Mass Load
9.9 Probability and Exceedance
9.10 Pollutant Durations
References
Problems
10 Preventing Runoff and Stormwater Pollution
10.1 Introduction
10.2 Site Design and Low Impact Development
10.3 Compacted Urban Surfaces
10.3.1 Avoiding Compaction and Promoting Infiltration
10.3.2 Soil Restoration
10.3.3 De-paving
10.3.4 Removing Abandoned Housing
10.4 Street Trees
10.5 Disconnecting Impervious Surfaces
10.5.1 Defining Disconnected Impervious Surface
10.5.2 Calculating the Benefit of Disconnecting Imperviousness
10.5.3 Design
10.5.4 Water-Quality Benefits
10.5.5 Performance Results
10.6 Pollution Prevention
10.6.1 Street Sweeping
10.6.2 Product Prohibition
10.7 Education
References
Problems
11 Green Infrastructure Stormwater Control
11.1 Introduction
11.2 Fundamentals of Stormwater Control Measures
11.3 Designing to Climate and the Watershed
11.4 Types of Stormwater Control Measures
11.5 Nonvegetated Stormwater Control Measures
11.5.1 Infiltration Basins and Rock Beds
11.5.2 Permeable Pavements
11.5.3 Cisterns and Rain Barrels
11.5.4 Sand Filters
11.6 Vegetated Stormwater Control Measures
11.6.1 Vegetation Challenges
11.6.2 Green Roofs
11.6.3 Bioretention
11.6.4 Vegetated Swales and Filter Strips
11.6.5 Stormwater Wetlands
11.7 Selecting the SCM Site
11.8 Stormwater Treatment Media
11.8.1 Rock, Gravel, and Coarse Sand
11.8.2 Silts and Clays
11.8.3 Organic Media
11.9 Volumetric Storage
11.10 Drains and Underdrains
11.11 “Irreducible Concentrations”
References
Problems
12 Inlets, Bypasses, Pretreatment, and Proprietary Devices
12.1 Introduction
12.2 Inlets
12.3 Stormwater Bypass
12.4 Catch Basin and Inlet Filters
12.5 Pretreatment
12.6 Forebays
12.6.1 Forebay Design
12.6.2 Forebay Maintenance
12.7 Proprietary Devices
12.8 Accumulated Trash and Sediment
References
Problems
13 Green Roofs
13.1 Introduction
13.2 Climate and Green Roofs
13.3 Types of Roofs
13.3.1 Green Roofs
13.3.2 Blue Roofs
13.4 Extensive Green Roof Components
13.5 Hydrologic Design Strategies
13.5.1 Rainfall Capture
13.5.2 Evapotranspiration
13.6 Water Quality Design
13.6.1 Phosphorus
13.6.2 Nitrogen
13.6.3 Metals
13.7 Inspection and Maintenance
13.8 Other Green Roof Benefits
References
Problems
14 Rainwater Harvesting
14.1 Introduction
14.2 Potential as a Water Resource
14.3 Harvested Roof Water Quality
14.4 Rain Barrels
14.5 Rainwater Harvesting Regulations
14.5.1 Non-stormwater Regulations
14.5.2 Stormwater Regulations
14.6 Designing Rainwater Harvesting Systems
14.6.1 General Characteristics and Purpose
14.6.2 Rainwater Storage Sizing Techniques
14.6.3 Design
14.7 Designing for Enhanced Stormwater Performance
14.7.1 Passive Release Mechanism
14.7.2 Active Release Mechanism
14.7.3 Alternative Approaches for Irrigation-based Systems
14.7.4 Designing an Infiltration or Filtration Area
14.8 Treatment for High-quality Use
14.9 Inspection and Maintenance
References
Problems
15 Permeable Pavement
15.1 Introduction
15.2 Types of Permeable Pavements
15.3 Permeable Pavement Installation
15.4 Designing for Infiltration and Percolation
15.4.1 Surface Infiltration
15.4.2 Run-on Ratio
15.4.3 Depth/Volume of Storage Layer
15.4.4 Underdrain Need
15.4.5 Underdrain Configuration
15.4.6 In Situ Soils
15.5 Permeable Pavement Hydrologic Design Strategies
15.6 Permeable Pavement Hydrology
15.6.1 Hydrographs
15.6.2 Curve Numbers and Storage
15.6.3 Evaporation
15.7 Water Quality Design
15.7.1 Particulate Matter
15.7.2 Metals
15.7.3 Nutrients
15.7.4 Hydrocarbons
15.7.5 pH
15.7.6 Thermal Pollution (Temperature)
15.7.7 Pollutant Loads
15.7.8 Long-term Pollutant Fate
15.8 Maintenance
15.9 Design Summary
15.10 Permeable Pavement Cost Factors
15.11 Permeable Friction Course
References
Problems
16 Infiltration Trenches and Infiltration Basins
16.1 Introduction
16.2 Types of Basins
16.3 Mechanisms of Treatment
16.4 Infiltration
16.5 Surface Infiltration Basins
16.6 Infiltration Trench and Subsurface Infiltration Basin Design
16.7 Infiltration Trench and Basin Performance
16.8 Inspection and Maintenance
References
Problems
17 Sand Filters
17.1 Introduction
17.2 Basic Sand Filter Operation
17.3 Sand Filter Options and Configurations
17.4 Sand Filter Design
17.5 Water Quality Performance
17.5.1 Particulate Matter Removal
17.5.2 Dissolved Pollutant Removal
17.6 Sand Filter Headloss
17.7 Solids Accumulation and Clogging
17.8 Sorptive and Reactive Media
17.9 Geotextile Filters
17.10 Inspection and Maintenance
References
Problems
18 Bioretention
18.1 Introduction
18.2 Bioretention Classifications
18.3 Bioretention Components
18.4 Siting and Configuration
18.5 Bioretention Flow Entrances, Inlets, and Forebays
18.6 Storage Bowl
18.7 Bioretention Design: Static Storage and Hydrologic Performance
18.8 Dynamic Storage
18.9 The Media
18.9.1 Rain Gardens
18.9.2 Standard Media
18.9.3 Surface Mulch Layer
18.10 Evapotranspiration
18.11 The Media and Particulate Matter Removal
18.12 The Media and Heavy Metals Removal
18.13 The Media and Organic Pollutants Removal
18.14 The Media and Phosphorus Removal
18.14.1 Phosphorus Removal in Bioretention
18.14.2 Quantifying Phosphorus Removal
18.14.3 Media Enhancements for Phosphorus Removal
18.15 The Media and Nitrogen Removal
18.15.1 Nitrogen Processing in Standard Bioretention Systems
18.15.2 Enhanced Nitrogen Removal
18.15.3 Biological Nitrogen Transformations
18.16 The Media and Bacteria Removal
18.17 Vegetation
18.18 The Underdrain and Subsurface Storage
18.19 Internal Water Storage and Nitrogen Removal
18.20 Bioretention Pollutant Load Reductions
18.21 Bioretention Exfiltration and Groundwater
18.22 Inspection and Maintenance
References
Problems
19 Swales, Filter Strips, and Level Spreaders
19.1 Introduction
19.2 Characteristics
19.2.1 Swales
19.2.2 Filter Strips and Level Spreaders
19.3 Swale Design
19.3.1 Configurations
19.3.2 Hydraulic Design
19.4 Filter Strip Design
19.4.1 Configurations
19.4.2 Flow Conveyance
19.5 Filter Strips Conveying to Swales
19.6 Water Quality Considerations
19.6.1 Designing for Pollutant Capture: Length of Swale
19.6.2 Designing for Particulate Matter Removal
19.6.3 Designing for Particulate Matter Removal with Particle-size Distribution Available
19.6.4 Designing for Metals Removal
19.6.5 Filtration through Swales and Filter Strips
19.6.6 Check Dams
19.7 Swale Performance
19.7.1 Hydrologic Considerations
19.7.2 Water Quality Considerations
19.8 Construction, Inspection, and Maintenance
19.9 Summary
References
Problems
20 Stormwater Wetlands
20.1 Introduction
20.2 Sizing Stormwater Wetlands
20.3 Stormwater Wetland Features and Design
20.3.1 Zone I–Deep Pools
20.3.2 Zone II–Deep to Shallow Water Transition Zone (Transition Zone)
20.3.3 Zone III–Shallow Water Zone
20.3.4 Zone IV–Temporary Inundation Zone
20.3.5 Zone V–Upper Bank
20.4 Wetland Vegetation
20.5 Wetland Soils and Vegetation Growth Media
20.6 Wetland Outlet Configuration
20.7 Wetland Construction
20.8 Wetland Variations
20.8.1 Wetland Design for Cold Water Species (Salmonids)
20.8.2 Off-line Stormwater Wetlands
20.8.3 Wetlands with High Flow Bypass
20.9 Water Quality Improvements in Stormwater Wetlands
20.10 Other Stormwater Wetland Designs
20.10.1 Submerged Gravel Wetlands
20.10.2 Ponds Transitioning to Wetlands
20.10.3 Floating Wetlands
20.11 Inspection and Maintenance
References
Problems
21 Putting It All Together
21.1 Introduction
21.2 SCM Hydrologic Performance Summary
21.3 SCM Water Quality Performance Summary
21.3.1 Green Roofs and Water Harvesting
21.3.2 Permeable Pavements
21.3.3 Infiltration Basins
21.3.4 Sand Filters
21.3.5 Bioretention
21.3.6 Vegetated Swales
21.3.7 Stormwater Wetlands
21.4 Treatment Trains
21.5 SCM Treatment Train Examples
21.5.1 Treatment Trains within Individual SCMs
21.5.2 Incorporating Treatment Trains in Traditional SCMs
21.5.3 SCMs in Series
21.6 Quantifying Performance in SCM Treatment Trains
21.7 Real Time Controls
21.8 Designing for Climate Change
21.9 Greener Infrastructure: What Does the Future Hold?
References
Problems
Appendix A
Index
End User License Agreement
List of Figures
Chapter 1
Figure 1.1 Spatial Patterns and Rates...
Figure 1.2 Water Balances for Different...
Figure 1.3 Stream Impacts from Uncontrolled...
Figure 1.4 Continuous Flow Measured...
Figure 1.5 Nuisance Flooding New Bern...
Figure 1.6 Severely Eroded Neighborhood...
Figure 1.7 Significant Flooding of the Perkiomen...
Figure 1.8 Incised Streams in Maryland...
Figure 1.9 Data Indicating the Reduction...
Figure 1.10 Stormwater Regulatory Drivers...
Figure 1.11 Shift of Balance of Impairment...
Figure 1.12 A Combined Sewer System...
Figure 1.13 Combined Sewer Overflow...
Figure 1.14 Hardened Urban Stream, Crow...
Figure 1.15 Stormwater Management Retention...
Figure 1.16 Land Development Using the Various...
Figure 1.17 Water Balances for Different...
Chapter 2
Figure 2.1 The Natural Hydrologic Cycle...
Figure 2.2 The Urban Hydrologic Cycle...
Figure 2.3 Rainfall Distribution with 24-h Interval...
Figure 2.4 Average Monthly Precipitation...
Figure 2.5 2014 Daily Precipitation Variation...
Figure 2.6 Single Day Rainfall Pattern...
Figure 2.7 Intensity–Duration–Frequency...
Figure 2.8 Contributing Drainage Area...
Figure 2.9 Rainfall, Runoff, and Ponding...
Chapter 3
Figure 3.1 Low Summer Dissolved Oxygen...
Figure 3.2 Example Particle Size Distribution...
Figure 3.3 The Nitrogen Cycle in the Environment.
Figure 3.4 The Phosphorus Cycle in the Environment.
Chapter 4
Figure 4.1 Relationship between Ecosystem...
Figure 4.2 Ecosystem Services Offered by Green...
Figure 4.3 Stormwater Wetlands Can Support...
Figure 4.4 Incorporating Walking Trails,...
Chapter 5
Figure 5.1 Diagram Showing the Hydrograph...
Figure 5.2 Particle Size Distribution...
Figure 5.3 Fractionation of Stormwater...
Figure 5.4 Heavy Metal Concentrations...
Figure 5.5 Grass Clippings and Leaves...
Figure 5.6 Architectural Copper as a Possible...
Figure 5.7 Measured TSS Water-Quality...
Figure 5.8 Concentrations of Total (Inflow TN)...
Figure 5.9 Runoff Samples Washed...
Figure 5.10 Relationships between Runoff...
Figure 5.11 Relative TKN Mass Flushed...
Chapter 6
Figure 6.1 A) Plot of Types I, IA, II...
Figure 6.2 NOAA Atlas 14 Volume 2 Region...
Figure 6.3 Comparison of a 24-h Recorded...
Figure 6.4 Cumulative Plot of an Outlier...
Figure 6.5 Villanova BioInfiltration Drainage...
Figure 6.6 Example of NRCS Dimensionless...
Figure 6.7 Example Summation Storm Hydrograph...
Figure 6.8 Open Channel Geometries Showing...
Figure 6.9 Diagram Showing Parameters...
Figure 6.10 Diagram of V-notch Weir.
Figure 6.11 Dual-Weir System Used to Control...
Chapter 7
Figure 7.1 Water Balance Pathways in a Rain...
Figure 7.2 Water Balance in a Rain Garden...
Figure 7.3 Soil Textural Triangle Showing...
Figure 7.4 A Volumetric Soil Moisture...
Figure 7.5 Diagrams of Water Storage...
Figure 7.6 Typical Soil Water Characteristic...
Figure 7.7 Plot of Average Event Recession...
Figure 7.8 Soil Water Characteristics Hydraulic...
Figure 7.9 Diagram of Wetting Front Proceeding...
Figure 7.10 Soil Moisture Accounting Diagrams,...
Chapter 8
Figure 8.1 Ideal Treatment Reactors:...
Figure 8.2 Sedimentation of Particles...
Figure 8.3 Sedimentation of Particles...
Figure 8.4 Removal of Particulate Matter...
Figure 8.5 Transport Mechanisms for Particles...
Figure 8.6 Adsorption Equilibrium between...
Figure 8.7 Mass Balance for Batch System...
Figure 8.8 Adsorption Zone of Pollutant....
Chapter 9
Figure 9.1 Cumulative Rainfall Depth...
Figure 9.2 Streamflow in Mercer Creek...
Figure 9.3 Water Quantity Measures...
Figure 9.4 Continuous Flow Measured...
Figure 9.5 Continuous Flow Measured...
Figure 9.6 Stream Flow Duration Curves...
Figure 9.7 Probability Distribution of TSS ...
Figure 9.8 Probability Distribution of TSS...
Figure 9.9 TSS Pollutant Duration Curves...
Chapter 10
Figure 10.1 Land Clear-Cut for Construction...
Figure 10.2 Schematic of Residential Lot...
Figure 10.3 Stormwater Control Treatment...
Figure 10.4 Disconnected Downspouts and Disconnected...
Figure 10.5 Schematic Plan View of a Disconnected...
Figure 10.6 Converter Joint for Directing....
Figure 10.7 Disconnected Downspout Connected...
Figure 10.8 Advanced Street Sweeper Truck...
Figure 10.9 Sign to Encourage Pet...
Chapter 11
Figure 11.1 Water Balance Approach...
Figure 11.2 Water Treatment Unit Processes...
Figure 11.3 SCM Treatment Train at Villanova...
Figure 11.4 Bioretention Cell in Summer...
Figure 11.5 Bioretention Cell in Winter...
Figure 11.6 Bioinfiltration Cell at Villanova...
Figure 11.7 Static Volumetric Storage...
Figure 11.8 SCM with Underdrain and Internal...
Figure 11.9 Concentrations of Three Particle...
Figure 11.10 Input and Outpoint Phosphate...
Chapter 12
Figure 12.1 (a–f) Various Types...
Figure 12.2 Various Types of Bypass...
Figure 12.3 Forebays for (a) Wet Ponds...
Figure 12.4 Street Inlet Structure...
Figure 12.5 Plan View Schematic...
Figure 12.6 A Typical Cross-section...
Figure 12.7 Heavy Duty Plastic Structures...
Figure 12.8 Proprietary Stormwater Treatment...
Chapter 13
Figure 13.1 PECO Green Roof in Philadelphia...
Figure 13.2 Paseo Verde Apartment Green...
Figure 13.3 Row Home Green Roof...
Figure 13.4 North Carolina State University...
Figure 13.5 Uncommon Green Roof Applications:...
Figure 13.6 Blue Roof Media...
Figure 13.7 Blue Roof Overflow Device...
Figure 13.8 Cross-section of Typical...
Figure 13.9 Sedums on the Green...
Figure 13.10 Green Roof Photographs:...
Figure 13.11 A Newly Planted Green...
Figure 13.12 A Tray Green Roof System...
Figure 13.13 Cumulative Water Balance...
Chapter 14
Figure 14.1 Rainwater Harvesting Systems...
Figure 14.2 Residential Rain Barrel...
Figure 14.3 Typical Rainwater Harvesting...
Figure 14.4 Finding Rainwater Volumes...
Figure 14.5 Daily Volumetric Balances...
Figure 14.6 Rainwater Harvesting System...
Figure 14.7 Soil/Media Area Needed...
Figure 14.8 Soil/Media Area Needed...
Chapter 15
Figure 15.1 Permeable Pavement Cross-Section...
Figure 15.2 Types of Permeable Pavement...
Figure 15.3 Transition between Traditional...
Figure 15.4 Permeable Asphalt Maintenance...
Figure 15.5 Permeable Brick Pavers...
Figure 15.6 Two Installations of CGP...
Figure 15.7 Installing Permeable Concrete...
Figure 15.8 Installing Permeable Asphalt...
Figure 15.9 An Upturned Underdrain Elbow...
Figure 15.10 Seasonal Infiltration Rate...
Figure 15.11 Flows from Asphalt...
Figure 15.12 Runoff Response as a Function...
Figure 15.13 The Simple Infiltration Test...
Chapter 16
Figure 16.1 Infiltration Basins and Trenches...
Figure 16.2 Subsurface Infiltration...
Figure 16.3 Stormwater Infiltration Tree Trench...
Figure 16.4 Subsurface Infiltration System...
Figure 16.5 Surface Infiltration Basins...
Figure 16.6 Infiltration Trench in Pennsylvania...
Figure 16.7 Observing a Properly Functioning...
Chapter 17
Figure 17.1 Austin Sand Filter:...
Figure 17.2 Schematic Drawing of Delaware...
Figure 17.3 Schematic Drawing of DC Sand...
Figure 17.4 Surface Sand Filter:...
Figure 17.5 Impact of Accumulated...
Chapter 18
Figure 18.1 Bioretention SCM in Dare County...
Figure 18.2 Home Rain Garden in Burnsville, MN...
Figure 18.3 Diagram of Bioretention Facility...
Figure 18.4 Urban Stormwater Planter Box...
Figure 18.5 Bioretention Cell Outlined...
Figure 18.6 Urban Rain Gardens–Sidewalk...
Figure 18.7 Suburban Rain Gardens...
Figure 18.8 Bioretention Retrofit Sites...
Figure 18.9 Various Ineffective Bioretention...
Figure 18.10 Raised Grate for Control...
Figure 18.11 Outlet Weir for Control...
Figure 18.12 Inflow/Outflow Volumetric...
Figure 18.13 Media Being Mixed During...
Figure 18.14 Monthly Summations of Daily...
Figure 18.15 Removal Efficiency of Particles...
Figure 18.16 Concentrations of Zn Entering...
Figure 18.17 Diagram Showing the Sources...
Figure 18.18 Diagram Showing the...
Figure 18.19 Adsorbed P at 0.12 mg/L Dissolved...
Figure 18.20 Measured Oxalate Ratio...
Figure 18.21 Simplified Pathway of Nitrogen...
Figure 18.22 Summary Data of N Concentrations...
Figure 18.23 Layering of Bioretention Media...
Figure 18.24 Redox Layering of Bioretention...
Figure 18.25 Photograph of Joe Pye Weed...
Figure 18.26 Maryland Bioretention Facility...
Figure 18.27 Maryland Bioretention Facility..
Figure 18.28 Diagram of a Bioretention System...
Figure 18.29 Water Balance for Bioretention...
Figure 18.30 Conceptual Designs of Water...
Figure 18.31 Distribution of Measured...
Chapter 19
Figure 19.1 Swales Are Used World-wide,...
Figure 19.2 Grass Filter Strip along...
Figure 19.3 Grass Filter Strip Feed...
Figure 19.4 Plan View of Level Spreader...
Figure 19.5 Cross-section of Level Spreader...
Figure 19.6 Summary of Particulate Matter...
Figure 19.7 Grass Swale along Highway...
Figure 19.8 Volumetric Performance of Grass...
Figure 19.9 Flow Duration Performance...
Chapter 20
Figure 20.1 Four Stormwater Wetlands...
Figure 20.2 Plan View of Stormwater...
Figure 20.3 Interior Wetland Zones:...
Figure 20.4 Small Deep Pool with Water...
Figure 20.5 A Stormwater Wetland...
Figure 20.6 Select Herbaceous Species...
Figure 20.7 Top Soil Being Replaced...
Figure 20.8 Downturned Pipe on an Orifice...
Figure 20.9 An Outlet Employing the...
Figure 20.10 Small Flashboard Riser Boards...
Figure 20.11 Adjustable Outlet Structures...
Figure 20.12 Off-line Stormwater Wetland...
Figure 20.13 Water Quality Improvement...
Chapter 21
Figure 21.1 Layering of Bioretention...
Figure 21.2 Pond Retrofits That Create...
Figure 21.3 Diagram of Bioretention/Rock...
Figure 21.4 SCM Treatment Train Consisting...
Figure 21.5 A Permeable Pavement-cistern...
Figure 21.6 Grass Swale–bioswale–infiltration...
Figure 21.7 A Typical Stormwater Treatment...
Figure 21.8 Series Approach to Evaluating...
Figure 21.9 A Real-time Control (Gray Box)...
Figure 21.10 Projected Changes in Seasonal...
Figure 21.11 Intensity-duration-frequency...
List of Tables
Chapter 1
Table 1.1 Volumetric Retention Standards...
Chapter 2
Table 2.1 Comparison of Annual Precipitation...
Chapter 3
Table 3.1 Saturated Dissolved Oxygen...
Chapter 4
Table 4.1 Ecosystem Services Provided...
Chapter 5
Table 5.1 Summary of Urban Runoff...
Table 5.2 Summary of Urban Runoff...
Table 5.3 Total Metal Concentrations...
Table 5.4 Annual Sediment and Nutrient...
Table 5.5 Annual Pollutant Loads...
Chapter 6
Table 6.1 Differences between Design...
Table 6.2 NOAA 14 Rainfall Intensities...
Table 6.3 Mean Ratios for Fourl...
Table 6.4 Rainfall Interception for...
Table 6.5 Depression Storage for...
Table 6.6 NRCS Runoff Curve Numbers...
Table 6.7 Manning’s Roughness ...
Table 6.8 Ratios Used to Create...
Table 6.9 Values of Rational Method...
Table 6.10 Values of Manning’s...
Chapter 7
Table 7.1 Wilting Point (WP), Field...
Table 7.2 Saturated Hydraulic Conductivities...
Table 7.3 Extraterrestrial Radiation (Ra) Expressed...
Table 7.4 Mean Daily Percentage (p) of Annual...
Chapter 8
Table 8.1 Mass Balance Reactor Equations...
Table 8.2 Transport Mechanisms for...
Chapter 9
Table 9.1 Example of percent removal as...
Table 9.2 Fresh water concentration thresholds...
Chapter 10
Table 10.1 Minimum Criteria for Impervious...
Table 10.2 Example Sizing and Credit for...
Table 10.3 Example Siting and Feasibility...
Table 10.4 Example Efficiencies of Pollutant
Chapter 11
Table 11.1 Common Stormwater Control...
Chapter 13
Table 13.1 Moisture Storage Potential...
Chapter 14
Table 14.1 Water balances for..
Chapter 15
Table 15.1 Water Quality Performance...
Table 15.2 Permeable Pavement Design...
Chapter 18
Table 18.1 Pollutant Loads, in kg/(ha year)...
Chapter 19
Table 19.1 Suitably Stiff and Tall...
Table 19.2 “Apparent” Manning’s...
Table 19.3 Actual and Theoretical...
Table 19.4 Total Metal Concentrations...
Table 19.5 Range of Concentrations...
Table 19.6 Influent and Effluent...
Chapter 20
Table 20.1 Stormwater Wetland Vegetation...
Table 20.2 Tier 2 Stormwater Wetland...
Table 20.3 Mass Balance Reactor...
Table 20.4 Values of Manning’s...
Chapter 21
Table 21.1 Summary of Hydrologic...
Table 21.2 Runoff Water Quality...
Guide
Cover
Title page
Copyright
Dedication
Table of Contents
Preface
About the Authors
Acknowledgements
About the Companion Website
Begin Reading
Appendix A
Index
End User License Agreement
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Preface
The intention of the authors is to present the fundamentals of green urban stormwater infrastructure from an engineering design and performance analysis perspective. This book is intended to be used as a textbook in senior-undergraduate and first-year graduate courses in water resources/environmental engineering. It is also envisioned to be a reference for practicing engineers and other water/environment professionals. The book focuses on novel stormwater control measures (SCMs) and related technologies for the reductions of detrimental impacts from urban stormwater. Stormwater challenges have risen in importance as clean water focus has shifted from point to non-point source pollution as a source of water impairments. Stormwater also becomes part of the “one water” focus on long-term sustainable urban water. Many novel SCMs are nature-based and are considered as part of a “green infrastructure” approach that includes bioretention, vegetated swales, vegetated filter strips, green roofs, pervious pavements, water harvesting, and wetlands.
It is expected that users of this book would have had a course in engineering hydraulics/hydrology and some exposure to environmental engineering treatment processes and water quality. It is also complementary to graduate surface water hydrology and traditional water and wastewater treatment engineering. While written with an engineering focus, nonengineers such as landscape architects, planners, and environmental scientists should find the text useful. Specific attempts have been made to integrate both English (US customary) and metric units throughout the book.
The initial chapters provide background information on urban hydrology, water quality, and stormwater generation and characteristics. The preponderance of the book focuses on stormwater control and improvement via a suite of different green infrastructure technologies and techniques. Within this context, background information on engineering unit processes for affecting the water balance and improving water quality are presented. The evolving challenge of setting and meeting stormwater control metrics is discussed. The latter chapters provide specific details on categories of SCMs; topics such as selection, design, performance, and maintenance are presented in detail. SCM selection, treatment trains, and climate change are included as a final chapter. This text provides a baseline as this topic is a rapidly changing field.
About the Authors
Allen P. Davis, Ph.D., P.E., 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 Architecture at the University of Maryland, College Park, MD. He is the Editor of the ASCE Journal of Sustainable Water in the Built Environment.
William F. Hunt III, Ph.D., P.E., D. WRE, 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, Ph.D., P.E., 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 Stormwater Partnership.
Collectively, the authors have 90 years of research, education, and outreach experience encompassing the topics covered in this book. They have built, maintained, and monitored hundreds of SCM research practices and have authored over 300 refereed journal articles, including several together. They have presented research results all over the world, hosted international conferences, while also helping address state and local water challenges. The authors love each other, the field in which they work, and the people with whom they partner.
Acknowledgments
The authors are grateful for the contributions of many, many colleagues in the various research projects that have led to many subjects of this text. These include students, post-doctoral researchers, and faculty colleagues. We also thank the various agencies that supported, and continue to support and promote, green stormwater infrastructure research.v
About the Companion Website
About the Companion WebsiteThis book is accompanied by a companion website which includes a number of resources created by author for instructors that you will find helpful.www.wiley.com/go/davis/greenstormwater
The Instructor website includes answers to the end-of-chapter problems
Please note that the resources in instructor website are password protected and can only be accessed by instructors who register with the site.
1 Introduction to Urban Stormwater and Green Stormwater Infrastructure
1.1 Population and Urban Infrastructure
Human population continues to increase in most areas of the world, including developed countries such as the United States. Two of the basic needs of humans are shelter and community. As we have progressed over the millennia, the ideas of shelter and community have evolved, first from simple villages to larger cities. More recently, these populations are shifting, generally from rural and inland areas to the coasts, while residents of inner cities are migrating to less dense suburban development. Frequently, the result is the consumption of pristine and agricultural land at rates disproportionately greater than population growth. As part of the development process, natural vegetation is replaced by lawn or pavement, soils are disrupted and compacted, pipes replace natural water courses, and the native topography is smoothed. Even in areas of urban redevelopment, frequently the impervious footprint increases as the living infrastructure becomes larger (Boorstein 2005; Hekl and Dymond 2016; MacGillis 2006).
Our past and current land development practices rely heavily on the use of impervious area infrastructure (materials that cover the ground and do not let water infiltrate down into the ground as it would in an undeveloped area) and piped systems. Large-area rooftops for homes and garages, highways, sidewalks, wide driveways, and generous patios are all desired attributes of increasingly affluent (sub)urban areas. Commercial and institutional properties provide for similar large impervious infrastructure and ample (if not excessive) parking. This urban network has replaced lands that were once undeveloped, such as forest, meadow, or open plains.
Rain that falls on developed areas is transported via impervious conveyance systems rapidly away from the original surface contact point, typically being discharged into the nearest waterway. This impervious area, coupled with a drainage system that accelerates the movement of runoff, vastly alters the water balance in the urban system. A variety of problems, including flooding, stream damage, loss of aquatic habitat, and significant downstream water body degradation, are the result. The amount of urbanization and related impervious area created has, and continues to, expand in many areas as demonstrated in Figure 1.1 for the greater Las Vegas area.
Figure 1.1 Spatial Patterns and Rates of Change Resulting from Urbanization of the Las Vegas Areas. (Credit: US Geological Survey).
1.2 Impacts of Urbanization
Our cities, towns, and villages, and the transportation networks that connect them, all rely on impervious infrastructure. Rooftops, roadways, sidewalks, driveways, parking lots, basketball and tennis courts, and patios all direct rainfall rapidly to their periphery, eliminating the natural runoff reduction and filtration of the vegetated systems that have been replaced.
Figure 1.2 shows the water balance around areas with different levels of urban development. In the undeveloped lands (humid regions), about half of the annual incoming water via rainfall infiltrates, supplying both shallow and deep groundwater. Another large fraction of this volume is evaporated from the soil and vegetation and transpired through the leaves of the vegetation, the combined processes known as evapotranspiration (ET). This leaves only a small fraction of the incoming rainfall to become surface runoff.
Figure 1.2 Water Balances for Different Land Use Conditions: (A) Natural Water Balance Showing Primary Water Pathways of Evapotranspiration and Infiltration and (B) Urban Water Balance Includes Runoff from Impervious Surfaces.
As the amount of development increases within an area, so does the amount of impervious area. The vegetated land area available for the infiltration and ET of runoff becomes increasingly small. In highly urbanized areas, the water balance changes drastically, as shown in Figure 1.2B. Infiltration and ET are now greatly reduced. The bulk of the incoming rainfall now is converted to surface runoff, which must be responsibly managed so as to not to create public safety and health concerns, and to protect our waterways and water bodies from environmental problems.
Environmental impacts of land development are well known and additional details on these impacts continue to be forthcoming (Booth 2005). The increased volume and flows of stormwater runoff from urbanized areas, coupled with impaired water quality and increased temperature, amplify the magnitude and increase the probability of flooding, decrease stream baseflow, degrade downstream river channels, adversely affect the quality of receiving waters, and impact stream ecology (e.g., Walsh et al. 2005; Wang et al. 2003). High sustained flow rates (not just peaks) are associated with accelerated stream bank erosion and gully formation (Figure 1.3). Elimination of stream baseflow in headwater areas by eliminating rainfall infiltration can greatly impact downstream ecology and ecological processes (Sweeney et al. 2004). Loss of biological nutrient cycling processes in small streams will adversely impact water quality in downstream areas (Peterson et al. 2001).
Figure 1.3 Stream Impacts from Uncontrolled Stormwater. (Photo by Authors).
While certainly flooding occurs with or without urbanization, the changes to the land increase the frequency and magnitude of such events, magnifying the impact to the local waterways. Figure 1.4 shows the great increase in amplitude in flow rate from a highly impervious watershed as contrasted to that of a lower impervious watershed (note the log scale). In Figure 1.4A, the flow of a forested stream is given (in units of mm/day, which represents the stream flow divided by the stream catchment area). The flow averages about 1 mm/day, with limited excursions to about 10 mm/day during high flow events and as low as 0.01 mm/day during a very dry period.
Figure 1.4 Continuous Flow Measured from Streams in Maryland (Normalized by Drainage Area): (A) Forested Stream and (B) Urban Stream. (Shields et al. 2008).
Contrast these data to Figure 1.4B, which shows the same data for a highly developed catchment area. The flows are much more erratic and vary significantly throughout the study. Both high and low flows are frequent as the stream responds rapidly to rainfall that falls on the catchment areas.
In the watershed, impervious surface without adequate drainage leads to pooled water during large rain events. This pooled water is dangerous to vehicle travel and pedestrians and can cause flooding of buildings in the urban area. Figure 1.5 shows nuisance flooding in a residential area of New Bern N.C. Note the depth of water as the vehicles pass each other.
Figure 1.5 Nuisance Flooding New Bern NC. (Photo by Authors).
Figures 1.6 and 1.7 show other effects of excess water related to high impervious area. Figure 1.6 clearly shows the accelerated erosion of a drainage swale threatening the stability of the adjacent house. Figure 1.7 shows a flood on the larger Perkiomen Creek in Pennsylvania.
Figure 1.6 Severely Eroded Neighborhood Swale. (Photo by Authors).
Figure 1.7 Significant Flooding of the Perkiomen Creek, PA. Note Heavy Sediment Load Carried by the River. (Photo by Authors).
While not visible on the photo, cars on the bridge could not move because the bridge approaches were under water. In addition to obvious flood hazards, standing water can lead to other health concerns.
Increased imperviousness from urbanization leads to high flows that also change the river channels through erosion and deposition. Figure 1.8 shows incisions and bank erosion from high flows in streams in Maryland. Over time, soil is washed from tree root structures, the trees become unstable and will fall into the stream.
Figure 1.8 Incised Streams in Maryland, Resulting from Erosive Flows: (A) Small Stream and (B) Large Stream. (Photos by Authors).
The relationship between impervious cover and stream biotic health has been documented by many researchers. Figure 1.9 shows declines of macroinvertebrate indicator taxa in streams in Maryland as a function of the impervious cover in the watershed (King et al. 2011). The dramatic increase in the decline of the taxa demonstrates changes in the physical and chemical conditions of the stream ecosystems. As the fraction of impervious area increases, various alterations to the stream characteristics result, making it a less-favorable habitat for many diverse aquatic species, and indicating poor stream health. This change occurs dramatically, from only about 0.5% to 2% impervious cover.
Figure 1.9 Data Indicating the Reduction of Various Organism Populations with Increasing Watershed Urbanization (Impervious Coverage) (King et al. 2011). MT, PD, and CP Represent Mountain, Piedmont, and Coastal Plain Geology, Respectively. HS Represents High Slope Small Watersheds; LL Represents Low Slope Large Watersheds.
1.3 The US Regulatory Environment
The governing legislation driving urban stormwater management in the United States is the Clean Water Act (CWA). The CWA was promulgated in the early 1970s to address water pollution in waters of the United States, with a goal to “restore and maintain the chemical, physical, and biological integrity of the nation’s waters.” Initially enforcement of the CWA focused on discharges of wastewater (sometimes untreated) from municipal wastewater treatment plants and from various industries. This enforcement led to the development of the National Pollutant Discharge Elimination System (NPDES) program. NPDES programs are managed by the states and establish a permitting process for any entity that discharges to the nation’s waters. NPDES permits for industry and wastewater treatment plants commonly specify limits for several water-quality parameters. The limits will depend on the industry and the water body into which the discharge occurs.
In 1987, the Water Quality Act, a modification to the CWA, required stormwater discharges to operate under the NPDES system. This includes municipal, construction, and industrial stormwater; agricultural runoff was removed so that it is not regulated under the CWA.
Regulation of municipal separate storm sewer systems (MS4s) was implemented in two phases. In the first, implemented in 1990, large jurisdictions (cities and counties), defined as those with population of 100,000 or more, were issued NPDES permits for their stormwater. Phase I covers about 750 municipalities in the United States (www.epa.gov). Figure 1.10 displays a timeline of stormwater regulatory actions and milestones.
Figure 1.10 Stormwater Regulatory Drivers and Milestones in the United States (with Permission, Water Environment Federation, WEF 2015).
Early CWA regulatory actions primarily focused on point source impacts and have been successful at reducing their impact significantly. Point sources are direct (treated) wastewater discharges from municipal wastewater treatment plants and from industries. As a result of this regulatory structure, the majority of the US water body impairment sources shifted from point to non-point sources (Figure 1.11). Non-point sources are primarily stormwater from urban, highway, industrial, construction, and agricultural land uses.
Figure 1.11 Shift of Balance of Impairment Sources from Point to Non-Point after Initial Enforcement of the Clean Water Act (with Permission, Water Environment Federation, WEF 2015).
Recognizing the need to address non-point sources, NPDES Phase II was implemented in 1999 targeting smaller urbanizing areas. Phase II covers approximately 6700 jurisdictions (www.epa.gov) and requires programs to reduce pollutant discharge to the “maximum extent practicable” (MEP), protect water quality, and meet the water-quality requirements of the CWA.
In all but five cases, the authority for NPDES permitting and enforcement for Phases I and II has been delegated to each respective state. MS4 NPDES permits are generally issued in 5-year cycles. Stormwater NPDES permits have focused on implementing “Best Management Practices” and public education for stormwater control, targeting runoff from diffuse surfaces. These best management practices (BMPs) can be structural stormwater control measures (SCMs) or nonstructural practices, such as street sweeping, both of which are discussed in later chapters. Recently, especially in areas in which surface water quality has remained poor, NPDES permits are becoming increasingly stringent for both Phases I and II communities.
Twenty-seven industrial sectors are included under the industrial stormwater program. The US EPA has created a multi-sector general permit (MSGP) that specifies benchmark monitoring for most of these sectors. The benchmark monitoring is used as a measure of the effectiveness of stormwater management at the site. Construction permits cover construction activities and focus on land disturbances. The general permits have identical provisions for all facilities under the same sector. For large facilities with unique challenges, an individual NPDES permit can be issued. Frequently, an individual permit would cover all water discharges at a facility: stormwater and process wastewater.
Late in 2000, the CWA was amended to address combined sewer overflows (CSOs). Many older cities combined street drainage and sewage collection and conveyance in the same piping system; originally these networks discharged directly to local water bodies (Figure 1.12). Over time these pipe networks were redirected to wastewater treatment plants. However, with these combined systems, larger stormwater events (0.5 in. (1.2 cm) and up) can overload the pipe and treatment systems, causing discharge of untreated stormwater and sewage, an event known as a CSO. The new legislation requires cities with combined sewers to develop long-term control plans to reduce the impacts of CSOs, to bring them into compliance with the CWA. Figure 1.13 shows CSO locations in the New York City area.
Figure 1.12 A Combined Sewer System. During Dry Weather (and Small Storms), All Wastewater and Stormwater Flows are Handled by the Publicly Owned Treatment Works (POTW). During Large Storms, the Relief Structure Allows Some of the Combined Stormwater and Wastewater to Be Discharged Untreated to an Adjacent Water Body.
Figure 1.13 Combined Sewer Overflow Locations in the New York City Metro Area. (Credit: U.S. EPA 2011a).
Another section of the CWA that impacts stormwater is the Total Maximum Daily Load (TMDL). Water bodies of the United States are designated for specific uses, usually by the respective states. These uses can include drinking, swimming, fishing, and so on. Under Section 303(d) of the CWA, water bodies that cannot meet their designated use, because of poor water quality, are labeled as impaired. The impairment is attributed to a specific water-quality parameter, such as bacteria, nutrients, or sediment.
When a water body is classified as impaired, the CWA requires the establishment of a TMDL. A TMDL is set for a water body based on estimates of the pollutant load (mass) that the water body can adequately manage yet still meet its designated uses. In an impaired water body, the overall pollutant load to a water body exceeds the TMDL. In this case, specific reductions to the various water discharge sectors will be required, a so-called pollution diet plan to eliminate the water body state of impairment and return the water quality to the designated use condition. These sectors include municipal and industrial wastewater discharges, agricultural runoff, and urban runoff. Increasingly, TMDL concerns are being written into MS4 NPDES permits. The result can be very stringent requirements for the management and control of urban stormwater.
In addition, many states have developed their own regulations to address stormwater impacts. Most of these state requirements started as flood control criteria and focused on peak runoff flow rates from the site during extreme events. Pennsylvania, for example, passed its stormwater management act in 1978 in response to Hurricane Agnes. While the language of the act addressed increase of runoff from developing areas, the act was interpreted as requiring that the peak flow leaving the project site be maintained at preconstruction levels for extreme events. Later this requirement evolved into reducing peak flow after construction to less than preconstruction in an effort to consider the downstream watershed (Traver and Chadderton 1983).
As the focus of stormwater management has shifted over the past decade to addressing smaller storms, many states and municipalities added volume control to their stormwater regulations. While it is argued that volume or peak rates are not addressed under the CWA, it is not possible to address environmental quality without it (NRC 2009). Table 1.1 compares stormwater volumetric requirements for a few states for comparison.
Table 1.1 Volumetric Retention Standards for Discharges from New Development (Compiled from U.S. EPA 2011b).
State or locality (date enacted)
Size threshold
Standard
Vermont (2003, draft 2010)
1 acre
Capture 90% of the annual storm events
New Hampshire (2009)
1 acre/100,000 ft
2
outside MS4
Infiltrate, evapotranspire or capture first 1.0 in. from 24-h storm
Wisconsin (2010)
1 acre
Infiltrate runoff to achieve 60–90% of predevelopment volume based on impervious cover level
West Virginia (2009)
1 acre
Keep and manage on site 1 in. rainfall from 24-h storm preceded by 48 h of no rain
Montana (2009)
1 acre
Infiltrate, evapotranspire, or capture for reuse runoff from first 0.5 in. of rain
Portland, OR (1990)
500 ft
2
of impervious cover
Infiltrate 10-year, 24-h storm
Anchorage, AK (2009)
10,000 ft
2
Keep and manage the runoff generated from the first 0.52 in. of rainfall from a 24-h event preceded by 48 h of no measurable precipitation
1.4 Urban Stormwater Management
As stated earlier, without the ability to infiltrate, rain that falls on impervious surfaces will collect and travel quickly over these surfaces, moving polluted waters to our stream systems and causing erosion and sediment deposition. In a highly developed area, without a place to go, this water will pool, creating a flooding hazard, and increase flooding in area streams.
1.4.1 Flood Control
The first generation of stormwater management was developed to reduce flooding hazards. Storm drains and storm sewer networks were installed to collect runoff from impervious areas. These drains were directed into the nearest stream or river so that rainfall that fell on the impervious area could be conveyed away as quickly as possible. In many older cities, the sanitary sewer system (for conveyance of wastewater to treatment plants) was already in place. In some situations, the urban flooding challenge was addressed by piping the stormwater into the sanitary sewer networks, creating combined sewers. These engineering projects addressed the urban flooding problem but created others.
During heavy rainfall events, these drainage systems put a tremendous water burden on the repository of the flow, either the stream outfall or the sanitary conveyance and treatment network. This increased flow comes quickly, with high volumes and velocities. The streamflows are increased dramatically, resulting in erosion of the streambed, scour, and stream flooding. Loss of aquatic habitat occurs, including beneficial stream processes, such as nitrogen processing. These problems associated with stormwater discharges have been termed urban stream syndrome (Barco et al. 2008; Walsh et al. 2005). In many cases, due to the perceived need for space and to prevent erosion, entire streams were replaced with concrete channels and ditches (Figure 1.14).
Figure 1.14 Hardened Urban Stream, Crow Branch in Laurel, MD. (Photo by Authors).
During heavy rains in combined sewer areas, very large volumes of water are dumped to the sanitary sewer system. This runoff volume can be too much for the sewer network and wastewater treatment plant to handle. As a result, relief areas are constructed into the sewer system so that if the flows become too large, they will overflow into the nearby streams and rivers. The result of this relief is that during large rainfall events, runoff, mixed with raw sewage, is directly discharged, untreated into the environment. This condition, obviously, creates major public health and environmental problems and is a violation of the CWA. CSOs can occur many times per year in some cities.
1.4.2 Peak Flow Control
Recognizing that direct connections to the nearby streams were causing environmental damage to the streams and surroundings, efforts were subsequently made to incorporate some degree of runoff storage to reduce extreme event peak flows into the newer stormwater systems that were being installed. Generally, this consisted of some type of dry or wet pond that was placed between the new impervious infrastructure and the receiving stream. This pond would fill during the rain event and was managed with weirs so that it would restrict the outflow to preconstruction levels. Figure 1.15 shows an early 1980s Pennsylvania wet pond, designed to hold peak flows at preconstruction levels for the 24 hour 2–100-year design storms (Chapter 6). The ponds were designed to be deep to prevent growth of vegetation.
Figure 1.15 Stormwater Management Retention Pond Circa 1980s. (Photo by Authors).
The ponds addressed the peak flow problem directly at the point of design, but still the challenge of high erosive flows remained, which was commonly exacerbated by the combination effect of multiple individually designed storage facilities within a watershed (Emerson et al. 2005; Traver and Chadderton 1983). While arguably effective at the property line for extreme events, the increased volume and extended increased velocities exacerbated the erosive discharge for the stream. McCuen and Moglen (1988) stated, “Both theory and experience indicate that, while detention basins designed to control peak discharge are effective in controlling the peak rates, the basins are ineffective in controlling the degradation of erodible channels downstream of the basin.”
1.4.3 Watershed Approach to Peak Flow
Recognizing that timing of release from detention basins could actually increase flood peaks (Emerson et al. 2005; McCuen and Moglen 1988), many regions in the 1980s started to require downstream analysis for extreme events to ensure that the cumulative increased peak flow effects from detention basins did not increase river flows downstream of the developed properties. Termed Release Rates, this analysis was codified based on watershed modeling of extreme design storms, often requiring that outflows from individual extreme events be reduced below preconstruction levels to avoid unintentional downstream peak flow increases due to the extended outflow of runoff. For example, it is common to require that the 2-, 10-, and 100-year storm to be reduced to a fraction of the preconstruction peak level, often as much as 50%, resulting in much larger regulatory structures.
A few areas, early on moved away from individual storm analysis, instead using a continuous simulation approach to look at the annual impact. As the mechanisms for stream erosion and sedimentation are related to both flow rate and duration of these flows, Western Washington requires a continuous simulation analysis that demonstrates that the postconstruction flow durations are held for selected extreme events ranging from 50% of the 2-year storm to that of the 50-year storm (Ecology 2005).
1.4.4 Water-Quality Control
In the 1990s, it was recognized that more and more, urban runoff was a significant contributor to quality problems in receiving waters. Regulations promulgated in the 1970s and 1980s placed severe restrictions on discharges from point sources, that is, industrial and municipal wastewater treatment plants. As the water quality from industrial discharges improved, and more urban infrastructure was installed, pollutant loads from non-point sources, such as urban runoff, were becoming a significant contributor of the overall pollutant burden of many water bodies (Amandes and Bedient 1980).
In response, water-quality requirements were added to stormwater regulations. In many jurisdictions, this led to the definition of a water quality volume
