Low Impact Development: Opportunities for the PlanET Region
East Tennessee’s iconic water resources are a sustaining economic, social, and environmental asset. These resources are vulnerable to impacts from prevailing development patterns in the region, human activities, and existing stormwater infrastructure. With the Plan East Tennessee Region’s population poised to grow forty-three percent by 2040, reliance upon these water resources will increase while their health is further threatened by expanding development. Low Impact Development methods proposed in this publication offer existing and expanding communities an enhanced approach to watershed planning, community design, and site development that avoids, minimizes, and manages impacts to the region’s shared water resources. This publication is intended for a general audience ranging from homeowners to engineers. Everyone lives in a watershed and has a role to play in the stewardship of shared water resources.
Low Impact LOW IMPACT DEVELOPMENT OPPORTUNITIES FOR THE PlanET REGION Development Identifying Opportunities for the Knoxville MSA Program by the University of Tennessee, Knoxville, Landscape Architecture Prepared for the City of Knoxville and PlanET Consortium LOW IMPACT DEVELOPMENT OPPORTUNITIES FOR THE PlanET REGION Prepared for the City of Knoxville and PlanET Consor tium by the University of Tennessee, Knoxville, Landscape Architecture Program College of Architecture and Design College of Agricultural Sciences and Natural Resources Brad Collett, ASLA, RLA, 1 LEED AP Valerie Friedmann, Associate ASLA Wyn Miller Co-Authors Phil Zawarus Justin Allen Designers of Graphics and Illustrations Luke Murphree, Danielle Norman, Caroline Sneed, Xue Yue Graduate Research Assistants INVESTIGATION TEAM Lead Principal Investigator : Brad Collett, ASLA, RLA, 2 LEED AP Assistant Professor, University of Tennessee Department of Plant Sciences firstname.lastname@example.org Principal Investigators: Ken McCown, ASLA, Associate AIA Director, University of Nevada, Las Vegas, Downtown Design Center email@example.com Scott Wall Professor and Director, University of Tennessee School of Architecture firstname.lastname@example.org COPYRIGHT ÂŠ 2013 by Knoxville-Knox County Metropolitan Planning Commission All rights reserved. No part of this publication may be reprinted, reformatted, reproduced, or used in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the author and/or copyright holder. LEGAL DISCLAIMER This publication has been developed by the University of Tennessee, Knoxville, Landscape Architecture Program to provide conceptual planning, design, and stormwater management recommendations for stakeholders of the PlanET Region. Although ever y effort has been made to ensure the accuracy of the information and methods presented, the material is not insured as free of errors. The materials presented in this publication are not intended as construction details or stormwater engineering consultation. Qualified professionals should be engaged for projectspecific planning, design, and implementation consultation. PROJECT TEAM Sponsor Knoxville-Knox County Metropolitan Planning Commission (MPC) University of Tennessee, Knoxville, Landscape Architecture Program Brad Collett, Author Valerie Friedman, Author Wyn Miller, Author Phil Zawarus, Graphic and Illustration Designer Justin Allen, Graphic and Illustration Designer Xue Yue, Graduate Research Assistant Danielle Norman, Graduate Research Assistant Caroline Sneed, Graduate Research Assistant Luke Murphree, Graduate Research Assistant Justin Allen, Corrin Breeding, Jessica Bundy, David Dalton, Valerie Friedmann, Michael Payne, Brandon Smith, Erin Tharp, and Phil Zawarus, Fall 2011 Studio Participants Peer Reviewers Mike Carberry, Comprehensive Planning Manager, MPC Liz Albertson, Sectors and Environmental Resources, MPC Dr. Andrea Ludwig, UT Biosystems Engineering Department Chris Howley, The City of Knoxville Engineering Department, Stormwater Engineering Division Timothy Gangaware, Associate Director, Tennessee Water Resources Research Center LOW IMPACT DEVELOPMENT OPPORTUNITIES FOR THE PlanET REGION CONTENTS vi viii Preface 10 Introduction 40 PART II DEVELOPMENT IMPACTS ON WATERSHEDS Acknowledgements 51 12 PART I INTRODUCTION TO REGIONAL WATER RESOURCES Chapter 3 Development Impacts to Natural Hydrology:::;: Stormwater Quantity and Quality 52 Growth Pattern and Existing Development Form 15 Chapter 1 The value of the regionâ€™''' s 52 Stormwater Quantity, Rate, and Quality shared water resources 60 Compounded Stormwater Quantity and Quality Impacts 16 Shared Water Resources: Economic Value 18 Shared Water Resources: Social Value 67 Chapter 4 Stormwater threats to Shared Water Resources 20 Shared Water Resources: Environmental Value 68 Water Resource Monitoring: Threats and Impairments 23 Chapter 2 Watersheds, Water Resources, 68 Upstream, Downstream and the Hydrologic Cycle 70 Impaired Surface Water: Streams and Rivers 24 Watersheds 71 Impaired Surface Water: Reservoirs 28 Regional Water Resources 72 Groundwater Vulnerability 36 The Hydrologic Cycle 72 Impacts to Domestic Supply 39 Part I Conclusion 73 Impacts to Human Health 75 Chapter 5 Stormwater Management 76 Stormwater Management: Regulation and Practice 78 NPDES Phases I and II iv 80 Part II Conclusion 82 PART III OPPORTUNITIES FOR IMPROVEMENT 147 Chapter 8 LID BMP:s:: SELECTION, LOCATION, and challenges 148 Unique Conditions, Unique Solutions 91 CHAPTER 6 LOW IMPACT DEVELOPMENT: AN 148 Site and Contextual Conditions ENHANCED APPROACH 151 Post-development Hydrology 92 Low Impact Development: Avoid, Minimize, Manage 153 Project Goals and Client Mission 93 Lessons from Pre-development Hydrology 154 Challenges to LID Implementation 98 LID: Avoiding Impacts 158 Summary of the LID Approach 102 LID: Minimizing Impacts 106 LID: Managing Impacts 160 Chapter 9 Treatment Trains, Integrated Design, and green infrastructure planning 109 Chapter 7 LID Stormwater Best 162 Professional and PlanET Demonstration Projects Management Practices 110 Structural LID BMPs 180 Conclusion 138 Structural LID BMP Function and Benefit Summary 139 Specialized BMP Categories and Non-Structural BMPs 140 Construction Site BMPs 182 PART IV REFERENCE 142 Agricultural BMPs 144 Non-Structural BMPs 184 END NOTES 190 BIBLIOGRAPHY 192 abbreviations 193 GLOSSARY 202 RESOURCES 204 PHOTO CREDITS Preface Low Impact Development: Opportunities for the PlanET Region is the product of partnerships between the City of Knoxville, the Knoxville Knox County Metropolitan Planning Commission (MPC), The University of Tennessee, Knoxville (UT), College of Architecture and Design, and the UT Landscape Architecture Program. The PlanET Region’s population is projected to grow by 43 percent between 2010 and 2040. 3 With that growth will come increased demand upon regional water resources for consumptive uses, including public drinking supply. New development needed to support this growing population will generate additional stormwater runoff, exacerbating existing threats to the region’s water resources. The Plan East Tennessee (PlanET) regional planning initiative is supported by a grant from the U.S. Department of Housing and Urban Development. This grant was awarded to the City of Knoxville and its consortium partners to develop a regional plan for sustainable development and livable communities in the five-county PlanET Region: Anderson, Blount, Loudon, Knox, and Union Counties. The UT Landscape Architecture Program is working in partnership with PlanET to develop critical inquiry and demonstration projects that support PlanET goals. If the region continues to grow through the sprawling pattern prevalent in the region since the mid-twentieth centur y, accelerated degradation of the water resources that will be increasingly relied upon is certain. This conflict between regional growth and its inherent threats to the water resources needed to sustain communities has led to the enforcement of new rules under the federal Clean Water Act. These rules will require the implementation of stricter stormwater management regulations at the local level. WHY IS THIS PUBLICATION NECESSARY? As a partner of the PlanET regional planning initiative, the UT Landscape Architecture Program was engaged to explore regional growth and site design strategies that protect, restore, and enhance the health of shared water resources in compliance with Clean Water Act stormwater management regulations. The results and recommendations of that exploration are the basis of this publication. In East Tennessee, water is a resource that defines the landscape and the region’s identity. Precipitation, streams, rivers, reser voirs, wetlands, and groundwater, collectively as an interconnected system, sustain regional societies, economies, and the environment. The health of these water resources is threatened by the quantity and quality of stormwater runoff from existing urbanized and rural watersheds. vi FOR WHOM IS THIS PUBLICATION WRITTEN? This publication is written for ever yone living, working, or recreating within the PlanET Region, including residents, property owners, property managers, building operators, planning and design professionals, engineers, developers, community outreach coordinators, and regulator y officials. Each has a role to play in the stewardship of the region’s shared water resources. Regional watersheds are aggregated properties, neighborhoods, and communities. The opportunity, and ultimately the responsibility, to make a positive difference in the health of the region’s water resources comes down to the decisions and actions, both large and small, of individuals. While this publication’s focus is the five-county PlanET Region, the obser vations and recommendations offered herein are relevant and applicable to other parts of Tennessee and the Southeastern United States that face similar water resource stewardship and regulator y compliance challenges. ABOUT THIS PUBLICATION This publication is a visually-enriched resource that focuses on Anderson, Blount, Loudon, Knox, and Union counties in East Tennessee. It celebrates the region’s iconic landscape and water resources, discusses their existing condition and threats, and proposes Low Impact Development (LID) as an approach to watershed planning, community design, and site development that avoids, minimizes, and manages impacts to the region’s shared water resources. It is divided into three parts: Part 1 Regional Water Resources, Part 2 Development Impacts, and Part 3 Opportunities for Improvement. For ease of navigation, each page spread features a colored tab on the side of the page that corresponds to the current part. Intended for use as an educational resource, this publication is the latest chapter in an ongoing regional dialogue to identify enhanced water resource management opportunities and to inform policies. Its function as an educational resource is adaptable depending on the need of its audience. It may be used by extension programs and governments to educate constituents, by educators to inspire students, by design and engineering professionals to educate clients, and by regulator y officials to advocate to developers, peers, and policy-makers. This publication is not meant to be a technical reference or a construction manual. Rather, it is intended to promote an understanding of LID practices across watershed, community, and site scales, and to build an audience for a forthcoming Tennessee vii Stormwater Best Management Practices technical guide, presently being prepared by the Tennessee Water Resources Research Center (see Resources section in Part IV). Though the concepts presented herein are applicable across the PlanET Region and beyond, readers are encouraged to become familiar with stormwater management regulations effective in their jurisdiction, and to seek consultation from site design, engineering, and construction professionals to craft an appropriate implementation strategy for their watershed, community, or site. ACKNOWLEDGEMENTS The realization of this publication was possible through the support and commitment of a number of agencies, groups, and individuals. The City of Knoxville and the Knoxville Knox County MPC have generously provided funding for this publication as an extension of their PlanET partnership with the UT Landscape Architecture Program. Thanks are due to the Landscape Architecture graduate students from the fall 2011 studio whose work inspired this publication: Justin Allen, Corrin Breeding, Jessica Bundy, David Dalton, Valerie Friedmann, Michael Payne, Brandon Smith, Erin Tharp, and Phil Zawarus. viii A special thanks to: Mike Carberr y and Liz Albertson of the MPC for their vision and advocacy, Scott Wall and Ken McCown for their mentorship and leadership that led to the partnership with PlanET, Dr. Andrea Ludwig of the UT Biosystems Engineering Department, Timothy Gangaware of the Tennessee Water Resources Research Center, and Chris Howley from the City of Knoxville for their expertise and peer review, and Dr. Edmund Perfect of the UT Department of Earth and Planetar y Sciences and Dr. Keil Neff of the UT Civil Engineering Department for their technical input. Also, many thanks to the contributing photography partners for their time and talent, and to the participating landscape architects, architects, and engineers for their leadership and inspirational projects. Overlooking Knoxville and the Tennessee River Valley from Sharpâ€™s Ridge ix Overlooking Douglas Reservoir to the Great Smoky Mountains ÂŠ kmstewart photography ICONIC, INTERCONNECTED, AND VALUABLE TO THE REGION’S EAST TENNESSEE’S SHARED WATER RESOURCES ARE ECONOMY, SOCIETY, AND ENVIRONMENT Confluence of Third Creek and Fort Loudoun Lake (Tennessee River), Knoxville, TN TENNESSEE RIVER IS RANKED THE TH 14 MOST POLLUTED WATERWAY IN THE COUNTRY THE 4 A SPRAWLING GROWTH PATTERN, HUMAN ACTIVITIES ON LAND USES, AND STORMWATER MANAGEMENT INFRASTRUCTURE THREATEN THE HEALTH OF THE REGION’S SHARED WATER RESOURCES POPULATION OF THE PI ET REGION IS EXPECTED TO INCREASE BY 43% OVER THE NEXT THREE DECADES THE an 5 PROTECT THE FUTURE OF THE REGION’S SHARED WATER RESOURCES ACTION MUST BE TAKEN NOW TO Norris Elementary Wetland, Anderson County, TN THE REGION CAN BEGIN BY CONSIDERING AN ENHANCED APPROACH TO WATERSHED PLANNING, COMMUNITY DESIGN, AND SITE DEVELOPMENT... West Knoxville Shopping Centers and Residential Development AVOIDS, MINIMIZES, AND MANAGES IMPACTS TO WATER RESOURCES... ...THAT Middle Prong, a tributary to the Little River, which flows from the Great Smoky Mountains National Park through Blount County to the Tennessee River ...AND RECOGNIZES HC STORMWATER INFRASTRUCTURE AS AN OPPORTUNITY TO PROTECT THE REGIONâ€™S SHARED WATER RESOURCES HM Contam inated Stormw ater Runoff Manicured Landscape PA HM HC N P HM Stormwater Runoff Temperature Increase S HC Co nta min ate d Sto rmw ate r Run off HM S N Contaminant Index HM Heavy Metals HC Hydrocarbons S Sediment P Phosphorus Compounds N Nitrogen Compounds pa Pathogens Municipal Storm Sewer System: Discharged to Receiving Waters P HM PA S Municipal Storm Sewer System Enlargement O Evapotranspiration 2 O O O 2 O 2 O O 2 2 2 O O 2 O 2 2 2 HC HM Contaminated S t o r m w a t e r R u n of f O Sto Cap rmwa t u re t e r and Runo Filtr ff atio n Peak Flow Reduction Detention p Biological Treatment N Retention and Infiltration p N p 2 N p N INTRODUCTION The waters of East Tennessee: the phrase evokes visions of pristine mountain streams, rivers meandering through rolling ridges and valleys, and deep, cool reservoirs. It brings to mind fond memories of fly-fishing trips, summer afternoons on the lake, and childhood explorations in creeks, turning over rocks searching for crayfish and being mesmerized by water striders gliding delicately across the water ’s surface. Water resources are abundant here at the headwaters and upper tributaries of the Tennessee River, and they have helped define the region socially, economically, and environmentally. 10 commerce, and agriculture. 7 The power of these same rivers was harnessed in the 1930s by the Tennessee Valley Authority, which provided the low-cost electricity, infrastructure, and flood control that has since facilitated an increased pace of population growth and economic prosperity in the region. 8 The same water resources that enabled human habitation of the region’s landscapes continue to support the region’s communities and a robust recreation and tourism economy. However, the health of these water resources has become threatened and impaired. The PlanET Region’s history is inextricably connected to water. Native Americans of Southern Appalachia prized the rivers and streams for the ecological habitats and food resources they sustained, the trade they enabled, and the nutrient rich flood plains that allowed early societies to transition from hunting and gathering to settled agrarian communities.6 These waterways fueled early development and, eventually, trade with and among Europeans who established trading posts, forts, and settlements along their banks. In many developed areas, waterways, such as creeks and streams, that are heralded in undisturbed landscapes as treasured resources have become impaired and are no longer visible. They flow underground, piped and culverted beneath roads, buildings, and parking lots. A walk along a stream-side greenway leads one past posted signs warning of water that is not safe to touch. Trash, the rainbow sheen of oil, and other debris accumulate along the banks of rivers and reservoirs. Streams and rivers often run brown or red, laden with sediment, while stories of flash flooding and contaminated well-water persist in the news. River-bound settlements continued to grow during a period of westward expansion. Knoxville and surrounding communities evolved into Civil War-era distribution hubs and post-war centers of industr y, How did the region’s water resources arrive at this point? Many of the challenges faced by regional water resources originate from the disruption of natural hydrologic processes. These disruptions are caused by human actions, land uses, and development patterns within the region’s rural and urbanized watersheds. As a result, natural hydrologic processes that infiltrate, store, and clean runoff in undisturbed landscapes are disrupted in urban and rural communities, increasing the quantity of contaminated stormwater runoff that flows into the region’s shared water resources. The long-used stormwater infrastructure practices serving much of the region’s existing development also affect the health of regional water resources in a way that was neither understood nor intended at the time when they were designed, engineered, and installed. Fort Loudoun Lake, Knox County, TN As the PlanET Region continues to grow, and as it relies more heavily on water resources to sustain new growth, the region must recognize the value and function of its unique hydrology and shared water resources. Beyond that recognition, the opportunity must be seized to reevaluate existing stormwater management infrastructure, and to develop an enhanced, low impact development approach to watershed planning, community design, and site development practices. Such action is essential to ensuring that these waters remain healthy, plentiful, and continue to sustain the region’s economy, society, and environment. 11 part i Introduction to regional water resources 1 THE VALUE OF THE REGIONâ€™S SHARED WATER RESOURCES 2 WATERSHEDS, WATER RESOURCES, AND THE HYDROLOGIC CYCLE Shared Water Resources: Economic Value Watersheds Shared Water Resources: Social Value Regional Water Resources Shared Water Resources: Environmental Value The Hydrologic Cycle Part I Conclusion 12 13 14 CHAPTER 1 The value of the region''s shared water resources At a fundamental level, the PlanET Regionâ€™s shared water resources are of immeasurable value. Water is an essential resource needed to sustain life. In addition to fulfilling the basic need for safe drinking water, clean water resources also benefit the regionâ€™s economy, society, and natural environment. 15 Shared Water Resources: Economic Value Water resources and the natural environments that they sustain have shaped the economy of the PlanET Region. Tourism and recreation-based industries flourish regionally due in large part to readily-accessible water resources that also enhance the value of adjacent real estate. Additional economic benefits are offered by regional water resources that have been harnessed to generate a safe and renewable energy source. Clean water resources and the lifestyles they enable also support existing enterprises and continue to attract new job-creating businesses to the region while supporting an agricultural industr y that satisfies nutritional and commodity needs locally and beyond. TOURISM 16 East Tennessee is an international tourism destination, and the region’s iconic landscape is one of its main attractions. Rolling mountains, ridges, and foothills, abundant streams, rivers, and reser voirs, and the diversity of plant and animal life collectively attract visitors from within the region, across the countr y, and around the world. The region realizes significant financial benefits from these visitors. Within the five counties of the PlanET Region, tourism-related industries generate more than $1.3 billion each year and provide employment for an estimated 13,000 people. 9 The region’s hospitality industr y, including hoteliers, restaurants, marinas, retail shops, and transportation providers, as well as recreational outfitters, outdoor adventure companies, and ecotourism entrepreneurs, all depend on patronage from tourists seeking to actively and passively enjoy the region’s shared water resources. PROPERTY VALUE Views of and physical access to waterbodies also enhance property values in the region. All five counties within the PlanET Region boast properties with direct access to rivers, reser voirs, and streams. Studies have shown that the health of these water resources affects the value premium realized by adjacent properties. One study suggests that a one-meter change in water clarity—a measure of the depth of visibility below the water ’s surface—can influence property values in the range of tens of thousands to millions of dollars. 10 DAMS: FLOOD CONTROL AND HYDROELECTRIC POWER The PlanET Region is home to many dams, operated by the Tennessee Valley Authority (TVA) and Army Corps of Engineers (ACOE), that manage the flow and water level of the region’s rivers and the reser voirs impounded behind each dam. This management has significantly reduced instances of major flooding along main river channels and has enabled safe passage for recreational and commercial vessels. INDUSTRY AND AGRICULTURE The region is also home to four hydroelectric dams operated by the TVA: Melton Hill, Norris, Fort Loudoun, and Tellico Dams. The Norris and Fort Loudoun Dams have been pivotal to economic development in the region since the 1930s and continue to provide hydroelectric power to the region. Combined, these two dams produce enough energy to power over 13 million fluorescent bulbs, or more than 54,000 households. 11 Many of the regionâ€™s early cities and towns were located along water ways out of necessity. For these settlements, rivers provided the primar y means of transporting raw materials and finished goods to and from the region. Today, local businesses still rely on regional water resources to sustain their bottom lines, though not as significantly for transportation infrastructure. Ample clean water resources are essential to businesses such as bottling companies, paper mills, and other industries that rely heavily on water for Norris Dam Dams combined can power. . . ~OR~ 4million incandescent Fort Loudoun Dam ~OR~ 13 million fluorescent 54,000 households 17 production and manufacturing processes. Industries within the region utilize over eight million gallons of surface water each day. 12 The region’s agricultural industr y relies on an additional two million gallons of surface and groundwater withdrawals each day to irrigate crops and water livestock. 13 Reliable sources of clean water are essential to regional growers’ ability to maintain healthy crops and livestock for local, national, and international markets. rainfall to help replenish these resources against withdrawals for public supply. However, as the PlanET Region continues to grow, increasing demands upon these water resources and impacts of the developed landscape on water distribution within watersheds will threaten this already strained balance of supply and demand. WATER RECREATION Casual enthusiasts and intrepid adventure-seekers alike find an abundance of opportunities in the PlanET Region for recreation on SHARED WATER RESOURCES: SOCIAL VALUE The region’s mountain streams, winding rivers, scenic reser voirs, and groundwater resources benefit the health and welfare of East Tennesseans by providing a reliable drinking water supply and recreational networks that support active lifestyles and enhance quality of life. HUMAN CONSUMPTION 18 One of the most critical benefits water resources provide to society is supply for daily human use. Consumptive uses such as drinking, bathing, and other applications that bring water into physical contact with humans are fundamental to livable communities. Local sanitar y ser vices also depend on access to adequate quantities of healthy surface and groundwater resources to convey waste to treatment facilities. 14 East Tennessee receives plentiful Canoeing on the Holston River the water. From the rush of a whitewater canoeing excursion on the Little River to a casual paddle down the Holston, from casting a line in a cove to tubing the wake of a ski boat on the Melton Hill or Norris Reser voirs, and from rowing through the early morning mist on the Tennessee River to taking a swim in Watts Bar, regional water resources provide some manner of recreation to ever yone regardless of age, skill, or fitness level. Time spent on these water ways contributes to fitness of the mind, body, and spirit. BLUEWAYS, GREENWAYS, AND PARKS Many of the region’s parks, nature preser ves, and greenways are located around and along waterbodies, allowing for a dynamic outdoor recreation experience. Some communities are even taking advantage of the recreational benefits of streams and rivers by developing “blueways.” Similar in concept to greenways, blueways are water trails that are developed with launch points for canoeists, paddle boarders, and kayakers. Preserved natural corridors that surround reservoirs, rivers, and streams establish a robust, widespread infrastructure of green spaces. Such corridors include greenways, city, county, state, and national parks, and other protected landscapes. This “green infrastructure” also provides habitat for wildlife, improves air quality, and further enables active, healthy lifestyles for the region’s residents and visitors. Greenway at Neyland Drive, City of Knoxville There is growing support behind the planning and development of parks, greenways, and blueways and an acknowledgement that the region’s natural resource areas, one of its greatest assets, should be preser ved. Land trusts and governments alike have recognized that public open spaces enhance quality of life for current residents, and that a higher quality of life can attract new residents and businesses to the PlanET Region. Healthy water resources are a critical part of these preser ved areas. 19 SHARED WATER RESOURCES: ENVIRONMENTAL VALUE East Tennessee is renowned for its diverse plant and animal communities. These unique ecosystems are interconnected communities of terrestrial and aquatic plants, animals, and microorganisms that interact with the non-living environment. Ecosystems perform valuable ser vices through natural processes. BIODIVERSITY The PlanET Region is one home to some of the most diverse plant and animal communities in the countr y. This biodiversity is largely attributed to the regionâ€™s varied topography, abundance of rainfall, and expansive public lands, including a number of state and national parks and managed wildlife areas. 20 The elevation difference between the average pool elevation of Watts Bar Reservoir in Loudon County to the top of the highest mountain peak in Blount county is greater than 4,500 vertical feet. This change in elevation mimics the change in latitude one would experience traveling north from the PlanET Region into the Ohio River Valley, Great Lakes Region, and beyond. Higher elevations create a climate in which plants and animals more commonly found in northern regions are able to survive, while the lowlands support those communities more common to the Southeastern United States. 15 The dynamic topography and southern latitude of the region has protected certain wildlife communities from natural phenomena through the millennia, including glacial advances and oceanic flooding A thriving ecosystem is reliant upon plants, animals, and microorganisms as well as healthy water resources that forced many northern species to seek refuge at higher elevations in southern latitudes. The regionâ€™s various habitats and microclimates have allowed for hundreds of centuries of species diversification. all living organisms. Known as ecosystem ser vices, these are only a few examples of the many benefits that properly-functioning ecosystems provide. Vast expanses of contiguous public lands held in trust by private foundations or managed by public agencies such as the Department of Energy, National and State Park Ser vices, and the TVA also protect established diversity and provide refuge for wildlife species displaced by encroaching development. The Great Smoky Mountains National Park, home to over 17,000 documented species, has been designated an International Biosphere Reser ve by the United Nations, owing largely to its dynamic topography and over 800 square miles of federally protected landscape. Wetlands and other aquatic ecosystems are primar y providers of natural water purification. As water moves past plant and animal material, contaminants are sequestered and metabolized by microorganisms and plant materials while the purified water continues downstream or recharges groundwater resources. Tennessee is home to approximately 787,000 acres of wetlands, 16 an area representing less than three percent of the stateâ€™s total land cover. In contrast, 30 percent of Tennessee is classified as cropland or pasture, and over eight percent is classified as developed. 17 Considering that these and other land uses contribute to water contamination, the area currently held in wetlands is a meager reser vation for purifying the subsequently polluted water. Aquatic ecosystems, an integral part of this biodiversity, are foundational to the regional food chain and are home to threatened and endangered species that are found nowhere else on the planet. Just as people in cities and towns depend on clean water resources, healthy water resources are imperative to the vitality of these species and regional biodiversity. ECOSYSTEM SERVICES Healthy ecosystems perform processes, such as water and air purification, erosion control, and waste decomposition that ser ve Preser ving wetland ecosystems has significant financial benefits and is a priority of state environmental agencies. One study estimates a 20 percent decrease in wetland acreage due to development could cost Tennesseans between $55 million and $4 billion to restore an equivalent acreage of functioning wetland ecosystems. 18 21 22 CHAPTER 2 Watersheds, water resources, and the Hydrologic Cycle Water is an integral part of ever yday life in the PlanET Region, yet the dynamic processes through which it moves within and across our landscape are often taken for granted. Water resources, such as streams, rivers, and reser voirs, collect and flow within topographically defined regions known as watersheds. The hydrologic cycle is the continuous process that facilitates the movement of water through the atmosphere and across watersheds. This process recycles surface, subsurface, and atmospheric water in the region and provides important ecosystem ser vices such as water purification, water supply, and flood mitigation. 23 WATERSHEDS19 A watershed is a topographically-defined land area within which all surface water drains to a single outlet. Watersheds are divided by ridgelines that “shed” surface waters into different streams, rivers, reservoirs, or seas, as seen in the diagram below. Watersheds are composed of smaller, nested watersheds and subwatersheds that may range in size from hundreds of square miles to as small as a backyard. NESTED WATERSHEDS The nested character of watersheds, or drainage areas, at a continental scale is illustrated in the map series shown at right. Watershed Subwatershed Subwatershed Ridgeline Ridgeline Watershed Drainage Outlet 24 Subwatershed Drainage Outlets A map of North America depicts an extensive basin that drains the land between the continental divides of the Rocky Mountain and Appalachian Mountain ranges to the Mississippi River. This continental-scale watershed is known as the Mississippi River Basin, the fourth largest river basin in the world and the largest in the United States. The Mississippi River Basin is comprised of many smaller watersheds, including the area that drains to the Tennessee River. Located at the eastern headwaters of the Mississippi River Basin, the topographically-defined 40,000-square mile Tennessee River Watershed drains parts of Virginia, North Carolina, Georgia, Alabama, Mississippi, Kentucky, and Tennessee via tributar y streams and rivers. The area draining to the Tennessee River is composed of many still smaller, yet distinct drainage areas. Many of these watersheds extend beyond Tennessee’s political boundar y and reach into neighboring states. Regional watersheds overlap the PlanET Region and extend beyond the five counties’ boundaries into adjacent counties. Nested within regional watersheds are hundreds of still smaller subwatersheds, such as the Coal Creek Watershed in Anderson County and the First Creek Watershed in Knox County. MISSISSIPPI RIVER TENNESSEE RIVER REGIONAL BASIN WATERSHED WATERSHEDS MISSISSIPPI RIVER OHIO RIVER TENNESSEE RIVER TENNESSEE RIVER OHIO RIVER MISSISSIPPI RIVER TENNESSEE RIVER 25 watersheds and physiography PHYSIOGRAPHIC REGIONS 1 Central Appalachian Plateau 2 Ridge and Valley Province 3 Blue Ridge Province 26 1 2 Lower Clinch 3 Lower French Broad 4 Fort Loudoun Lake 5 Little Tennessee 6 Watts Bar 7 Lower Tennessee 8 South Fork 9 Upper Clinch 10 Powell Union 9 1 8 WATERSHEDS Watershed Boundary PlanET Region Holston 10 regional physiography 2 1 2 Anderson Knox 3 4 6 regional watersheds Blount Loudon 3 7 5 North Carolina REGIONAL WATERSHEDS The map at left shows the mosaic of watersheds that overlap the region’s borders. A majority of the land area within the five PlanET counties drains to the Tennessee River, though a small portion of northeast Anderson County drains to the Ohio River by way of the South Fork Watershed. East Tennessee is located in the Ridge and Valley Province—one of the five physiographic regions of the Southern Appalachian Mountains. Parallel ridges that run from southwest to northeast characterize the topography of the majority of the region. The ridges that dominate the landscape influence hydrology by shedding water into low-lying valleys. Valleys provide relatively level areas that are conducive to development. The region’s development patterns, like hydrologic drainage patterns, are influenced by the ridge and valley landscape. The region’s counties are defined by political boundaries while topography defines watersheds and directs the movement of water through them. These different systems of boundar y delineation often present challenges for upstream and downstream jurisdictions within the same watershed but under separate water resource management authorities. IN WHICH WATERSHED DO YOU LIVE? Fontana Reservoir, NC, lies within the Little Tennessee River Watershed 27 REGIONAL WATER RESOURCES The PlanET Region has abundant precipitation, surface water, and groundwater resources. Surface water, including runoff from accumulated precipitation, flows along the regionâ€™s topography into downstream watersheds by way of streams and tributaries to reser voirs and eventually to the Tennessee River. Groundwater resources, which are recharged by infiltrating precipitation and surface waters, lie beneath the regionâ€™s surface watersheds. In turn, groundwater recharges surface waters through springs and seeps in a continuous cycle of atmospheric, surface, and groundwater exchange. a winter day with constant misty rain and a summer afternoon thunderstorm may result in the same depth of rain, perhaps two inches, but they do so with different rainfall intensities. The summer storm event may occur over two hours at an intensity of one inch per hour, whereas the winter storm event may occur over 24 hours at an intensity closer to 0.1 inch per hour. Seasonal differences in rainfall intensity and landscape characteristics during each season are contributing factors to the potential, nature, and frequency of floods. In the PlanET Region, widespread flooding often occurs in spring due to increased runoff from a slightly greater rainfall depth, saturated soils, and PRECIPITATION 28 Regional rainfall depth averages about 4.3 inches per month. 21 Though slightly more precipitation falls in the summer months, the amount of rainfall received each month is fairly consistent throughout the year. However, rainfall intensity, which is measured in rainfall inches per hour, varies across the seasons. For example, 6 inches Monthly Precipitation Rate The PlanET Region receives an average of 47 inches of precipitation each year. In comparison, Seattle, WA, which is known for its persistently rainy weather, receives approximately 37 inches per year. Chicago, IL, with a much more populated region, receives only 36 inches per year, and Albuquerque, NM, receives just 9 inches a year.20 More Intense 3 inches Relative Storm Event Intensity Less Intense J F M A Precipitation M J J A Runoff S O N D Storm Event Intensity lack of deciduous leaf canopy that would other wise intercept and evaporate precipitation. However, summer high-intensity storm events paired with dr y, hardened (and therefore less-permeable) soil can also contribute to flash floods, especially in urban areas. 22 The PlanET Region’s annual precipitation is substantial when compared to other par ts of the United States. Together with groundwater seeps and springs, it is the origin of the region’s abundant streams, rivers, and reser voirs. East TN Tributary Stream STREAMS TO RIVERS Over the millennia, an abundance of rainfall and surfacing groundwater has car ved thousands of miles of perennial and ephemeral streams into the topography of the region. At the highest elevations, narrow drainageways, many of which only flow during or immediately after storm events, begin collecting and conveying water downhill. Streams increase in volume and flow rate as they move into lower elevations and combine with other streams, eventually draining into larger tributaries of the Tennessee River. These tributaries are the region’s major rivers: the Clinch, Holston, French Broad, Little, and Little Tennessee. Clinch River 29 RESERVOIRS Regional reser voirs are as iconic as the streams and rivers that supply and replenish them. The PlanET Region’s five counties boast five reser voirs including Melton Hill and Fort Loudon and portions of the Norris, Tellico, and Watts Bar Reser voirs. Regional reser voirs are such an integral feature of today’s East Tennessee landscape it is easy to forget that they were not always here. In the 1930s, the Tennessee Valley Authority (TVA) began 30 Melton Hill Reservoir, Oak Ridge, TN building dams in the region for flood control and production of hydroelectricity. Before TVA, East Tennessee did not have any large lakes and major flooding along regional rivers was frequent and costly. Today, reser voirs provide the region with reliable electricity, water for human consumption, wildlife habitat, and recreational amenities. They further ser ve as an iconic example of humankind’s capability to dramatically alter water resources and shape the regional landscape. surface water resources From Tazewell Kentucky Clinch River 1 Norris Reser voir 2 Melton Hill Reser voir 3 Fort Loudoun Reser voir 4 Tellico Reser voir 5 Watts Bar Reser voir 6 Cherokee Reser voir 7 Douglas Reser voir 8 Fontana Reser voir Dam Location Water Flow Direction 1 From Tri-Cities 6 TN River Watershed Holston River 7 French Broad River 2 5 PlanET Region From Asheville 3 Little River 4 Little Tennessee River To Chattanooga 8 North Carolina 31 GROUNDWATER AND AQUIFERS Equally important, but less visible than surface water, are the region’s groundwater resources. Water located beneath the earth’s surface is known as groundwater. Groundwater is stored in soil and rock pore spaces, in subsurface caverns, in voids between rock strata, and in aquifers. The depth at which soil pore spaces and other voids become saturated or submerged by groundwater is known as the water table. Groundwater is recharged by surface water that infiltrates into soil and subsurface geologic features. Some groundwater is held between soil particles, providing moisture needed by plants and soil-dwelling organisms. Soil moisture also plays a role in important atmospheric processes, including temperature regulation. In some areas, groundwater seeps into an aquifer, which is a subterranean layer of permeable rock, sand, or gravel. Groundwater may eventually return as surface water through springs, seeps, and wetlands when the water table intersects the earth’s surface. 32 Groundwater is also withdrawn from aquifers for human consumptive uses. The PlanET Region extracts over 10 million gallons of groundwater each day for human consumption, and Blount and Union Counties rely on groundwater for over half of their daily human consumptive water uses. 23 Just as topography defines the flow of surface water in watersheds, subsurface geology defines the flow of groundwater. Areas with an abundance of carbonate rock-based subsurface geology, such as within the PlanET Region, are characterized by a geologic formation known as karst topography. Karst topography is the result of surface and groundwater interacting with and dissolving carbonate rocks such as limestone and dolomite. As water dissolves the carbonate rocks, voids such as fissures, cracks, and caves are left in subterranean rock layers. When the water table intersects these voids, groundwater is stored in them. These waterfilled voids are known as carbonate rock aquifers and are depicted in the images on the facing page. Sinkholes may form when these voids fill with subsiding surface soils, sometimes causing significant property damage. 24 In karst regions, surface water and aquifers may freely exchange water through fissures, sink holes, caverns, and other connections through the easily eroded limestone bedrock, blurring the distinction of these waters as surface or groundwater resources. groundwater resources Pennsylvanian Aquifer (Sandstone) Valley and Ridge Carbonate-Rock Aquifer (Sandstone and Carbonate Rock) Piedmont and Blue Ridge Crystalline-Rock Aquifer PlanET Region Caverns and other karst features common to regionally prevalent, soluble carbonate (limestone) bedrock allow for uninhibited movement of contaminated runoff between ground and surface water. 33 WETLANDS Wetlands form where surface water, groundwater, and the landscape converge. Wetlands are located in areas where the water table is close to or at the land’s surface. They may be permanent or seasonal depending on rainfall patterns and movement of the water table. Wetland ecosystems are the product of the flow of water, nutrients, and energy from the sun and are characterized by their unique hydrology, soils, and vegetation. These valuable ecosystems are home to 31 percent of the nation’s plant species, and approximately half of the nation’s bird species depend on wetlands for habitat and nesting. 25 Wetlands provide many regulating and provisioning ecosystem ser vices, including water storage and filtration. Upland wetlands slow and absorb the flow of water in high elevations, while floodplain wetlands retain water from overflowing water ways. A one-acre wetland can store up to 1.5 million gallons of water 26 that may other wise contribute to flood events. 34 In addition to water storage capacities, high biological productivity within wetland ecosystems make them a primar y location for biological treatment processes that remove excess nutrients and other contaminants carried in water. Microorganisms living on the surface of submerged vegetation, in wetland water, and in soils recycle excess nutrients and make them available for plant use. Wetland vegetation slows the flow of water, creating conditions for sediment and other water-borne pollutants to settle out of the water. 27 Wetlands’ unique capacity to retain and filter water combined with their high biodiversity and biological productivity make them one of the region’s most valuable natural resources. Due to their significant value, wetland ecosystems in the PlanET Region (and across the state) are protected by the Tennessee Department of Environment and Conser vation (TDEC). Wetlands of significant size may be classified as waters of the United States and fall under the jurisdictional authority of the Army Corps of Engineers. Gum Swamp Seasonal Wetland, Cades Cove, TN 35 THE HYDROLOGIC CYCLE In order to protect and maintain the region’s water resources, it is important to understand the processes that facilitate the movement of water above, below, and across the regional landscape. REGIONAL HYDROLOGY The hydrologic cycle is the continuous movement of water on, above, and below the surface of the earth. This natural process recycles and purifies all water on the planet. The region’s surface water, groundwater, and atmospheric water are all part of this ongoing cycle of water conveyance. As water moves through the region, it takes many forms. Water vapor carried in clouds falls to the earth as precipitation. In vegetated areas, plant leaves intercept a significant amount of precipitation, preventing it from reaching the ground or reducing its velocity as it continues to fall. Precipitation intercepted by vegetation evaporates or falls to the ground below. Precipitation that lands on the earth’s surface either infiltrates into the ground or flows across the soil surface as runoff. Runoff collects to streams and rivers or another surface waterbody. 36 Water that infiltrates the ground is held in the space between soil particles and is used by plants and other soil-dwelling organisms. As water nourishes plants, some is lost through leaf surfaces as water vapor through a process called transpiration. The combination of water loss from plant transpiration and the evaporation of water from the earth’s surface is known collectively as evapotranspiration. Evapotranspiration is an important process that cools ambient air temperature in proximity to masses of plant materials and contributes significantly to the return of water vapor to the atmosphere. Evapotranspiration processes are especially active during summer months and partially account for the region’s infamously high humidity levels. Water that infiltrates the soil but is not absorbed by plants or evaporated into the atmosphere moves through the soil and subsurface geology as groundwater. Water that infiltrates deep into the earth’s surface percolates through bedrock into underground waterbodies and aquifers. As water percolates through soil and bedrock it is filtered by physical processes and biological treatment. As a result, some of the purest water in the world comes from healthy groundwater aquifers. Water that does not infiltrate into the ground moves across the earth’s surface as runoff. Directed by the earth’s topography, runoff collects and concentrates as surface waters in swales and valleys. Also fed by groundwater springs, regional surface waters begin as lower order tributar y creeks and streams that drain into the hydrologic cycle 1 Stream 1 Stream 2 Wetland 2 Wetland 3 Sink Hole 3 Sink Hole 4 Karst Opening (Cave) 4 Karst Opening (Cave) 5 Spring 5 Spring Regional Water Table Regional Water Table Precipitation Precipitation Condensation Condensation Canopy Canopy Evapotranspiration Evapotranspiration Interception Interception low tl oFw e e F Shet She 4 Retention Retention 1 1 F i l t ration + Strai ni n g F i l t ration + Strai ni n g Inďƒžltration Inďƒžltration Groundwater Groundwater Recharge Recharge Biological Biological Treatment Treatment 2 2 n F il t r a tnio F il t r a t io 4 5 5 Flow Attenuation + Sediment Removal Flow Attenuation + Sediment Removal l 3 iona 3 Rgei ognra lTal eb l e e R a rt eTa b We Wa t This drawing is meant to illustrate hydrologic processes and subsurface geologic features that commonly occur within the PlanET Region. Site professionals should inventory and analyze geology, hydrology, and climate systems and features on a site by site basis. 37 Limestone Limestone Shale Shale Sandstone Sandstone Limestone Limestone higher order rivers and reser voirs within nested watersheds until eventually emptying into the Gulf of Mexico. Water re-enters the atmosphere as water vapor once it evaporates from water bodies and other terrestrial surfaces or is transpired by plants. The effect of combined evaporation and transpiration returning moisture to the atmosphere can be obser ved regionally as fog, morning mists, and low-lying clouds. This stage within the hydrologic cycle inspired the name of the Great Smoky Mountains. When warm, moist air encounters cooler air temperatures, water vapor condenses and clouds form. Water vapor continues to condense into larger droplets of water in a cloud until they become too heavy to remain suspended in the atmosphere. Continuing the hydrologic cycle, these droplets fall once again as precipitation. PRECIPITATION TO RUNOFF 38 As water makes its cyclical journey from waterbodies to atmosphere to land and back again, many factors contribute to its quality and quantity. One of the most critical phases of the hydrologic cycle affecting water resource quality and quantity occurs when precipitation accumulates on the earth’s surface. Precipitation falls to the earth as rainwater, sleet, or snow. If upon contacting the ground it is not infiltrated into the soil or evaporated, it begins to move across ground surfaces and is considered runoff. As runoff moves across ground surfaces, it picks up debris, sediment, and other particles that it encounters along the way. Following periods of precipitation, a natural system’s capacity to absorb and retain water mitigates the accumulation of excessive runoff quantity and removes debris and particles that may be picked up by runoff. Many aspects of natural systems contribute to this resiliency. Large expanses of vegetation intercept rainwater, slowing its velocity and minimizing the amount that reaches the ground. In densely vegetated areas, up to 40 percent of rainwater is intercepted 28 and evaporated from vegetative surfaces such as plant leaves and stems. Precipitation that reaches the ground is readily infiltrated by deep, porous top soils generated by organic materials, soil organisms, and plant roots. Slopes and shorelines buttressed with dense vegetation withstand erosive flows during periods of high runoff volume and velocity, and filtration provided by the slow movement of water through soil and wetlands remove contaminants. Through these processes, natural systems mitigate the quantity and increase the quality of runoff. Occasionally, even in densely vegetated areas with porous soils, intense or prolonged storm events over whelm the natural systems’ holding capacity and result in excessive runoff. Given East Tennessee’s dramatic topography, runoff concentrated in drainageways, streams, and rivers can lead to soil erosion and flooding even in undeveloped watersheds, as seen in the photos below. The region’s topography combines with seasonal changes in vegetative cover and rainfall intensity to further impact runoff quantity. This is especially apparent during the winter months when the majority of the region’s deciduous tree canopy is absent. Without the deciduous leaf canopy, runoff rates and quantities across entire watersheds are significantly increased. This influx of runoff volume prompts the TVA to seasonally lower the standing level of its managed reser voirs, thereby increasing their holding capacity and mitigating downstream flooding. Mountain Stream Flooded Condition PART I CONCLUSION The health of the PlanET Region’s iconic streams, rivers, reser voirs, and groundwater resources are critical to the region’s economy, society, and natural environments. These waters are interconnected by the region’s topography, geologic characteristics, and the hydrologic cycle. Hydrologic processes within natural landscapes, ser vices performed by aquatic ecosystems, and the wildlife they sustain provide significant benefits. These benefits include mitigated runoff quantity and enhanced water quality. Water bodies and natural processes are vulnerable to alterations to the landscape, including those caused by the encroachment of a growing regional population into undeveloped watersheds, human activities on existing developed land uses, and the impacts of existing stormwater management infrastructure. By adopting an approach to watershed planning, community design, and site development that respects and harnesses natural hydrologic processes, these impacts may be avoided, minimized, and managed. 39 part iI Development impacts on watersheds 3 DEVELOPMENT IMPACTS TO NATURAL HYDROLOGY: STORMWATER QUANTITY AND QUALITY Growth Pattern and Existing Development Form Stormwater Quantity, Rate, and Quality 4 STORMWATER THREATS TO SHARED WATER RESOURCES 5 STORMWATER MANAGEMENT Water Resource Monitoring: Threats and Impairments Stormwater Management: Regulation and Practice Upstream, Downstream NPDES Phases I and II Impaired Streams and Rivers Part II Conclusion Impaired Reser voirs Compounded Stormwater Quality and Quantity Impacts Groundwater Vulnerability Impacts to Domestic Supply Impacts to Human Health 40 41 TREE CANOPY LOSS, SOIL COMPACTION, PROLIFIC IMPERVIOUS SURFACES, AND EXISTING STORMWATER MANAGEMENT INFRASTRUCTURE DISRUPT NATURAL HYDROLOGIC PROCESSES DISRUPTION OF NATURAL HYDROLOGIC PROCESSES CONTRIBUTES TO INCIDENTS OF FLASH FLOODING , PROPERTY DAMAGE, AND STREAM BANK EROSION 2011 Flash Flooding at N. Broadway and Fairmont, City of Knoxville NON-POINT SOURCE POLLUTANTS FROM HUMAN ACTIVITIES AND LAND USES IN DEVELOPED WATERSHEDS ARE CONVEYED TO RECEIVING WATERBODIES BY STORMWATER RUNOFf NON-POINT SOURCE POLLUTANTS INCLUDING SEDIMENT, PATHOGENS, NUTRIENTS, AND HYDROCARBONS ARE NOW THE LEADING CAUSE OF IMPAIRMENTS TO THE REGION’S SHARED WATER RESOURCES Third Creek at Tyson Park, City of Knoxville CELEBRATED RESOURCES TEAMING WITH BIODIVERSITY, THE REGION’S SHARED 46 Middle Prong, Little River ICONIC STREAMS, RIVERS, AND RESERVOIRS DRIVE TOURISM AND RECREATION ECONOMIES... ... YET ARE FORGOTTEN IN DEVELOPED AREAS AS POLLUTED, IMPAIRED DRAINAGEWAYS DUE TO CHANGES IN WATERSHED HYDROLOGY CAUSED BY EXISTING AND NEW DEVELOPMENT AND HUMAN ACTIVITIES 47 Third Creek near the confluence of the Tennessee River/Fort Loudoun Reservoir WATERSHED HYDROLOGY AND WATER RESOURCE HEALTH WILL BE FURTHER EXACERBATED BY THE PIanET REGION’S PROJECTED 43% POPULATION GROWTH OVER THE NEXT THREE DECADES 29 West Town Mall Shopping District and Residential Development REEVALUATE STORMWATER MANAGEMENT MUST BE SEIZED, OTHERWISE THE HEALTH OF THE THE OPPORTUNITY TO REGION’S WATER RESOURCES WILL CONTINUE TO DEGRADE 50 CHAPTER 3 Development' Impacts to Natural Hydrology: Stormwater quantity and quality The manner in which land has been developed within regional watersheds and the human activities that occur on various land uses affects the quantity and quality of stormwater runoff draining to shared water resources, impacting their ability to provide ecosystem ser vices, and inhibiting the performance of natural hydrologic processes. 51 GROWTH PATTERN AND EXISTING DEVELOPMENT FORM Population centers of var ying sizes and densities are located throughout the PlanET Region’s watersheds. Most of these cities and towns were founded in locations near water ways that ser ved as essential infrastructure for commerce, industr y, and transportation, and whose flood plains afforded fertile soils for agricultural production. As the region’s population has grown, what were once compact, walkable population centers have sprawled into previously undeveloped watersheds along vehicular transportation corridors. The region’s contemporar y growth pattern and the physical form of its existing developed areas can be characterized as landintensive, low density development built to facilitate the movement and parking of personal and commercial vehicles. These combined factors have earned the PlanET Region the distinction of being the eighth most sprawling metropolitan statistical area in the countr y. 30 STORMWATER QUANTITY, RATE, AND QUALITY 52 The pattern and form of conventional development interrupts natural hydrologic processes by replacing native vegetation and soils with impervious surfaces such as rooftops, parking lots, roadways, and compacted urban soils. In developed areas, precipitation that does not infiltrate into the surface on which it falls becomes stormwater runoff. Development impacts such as prolific impervious surfaces and the removal of native vegetation increase stormwater runoff quantity and flow rate, while human activities produce contaminants that may be picked up by stormwater runoff and carried to receiving waters. STORMWATER RUNOFF QUANTITY AND RATE As seen in the images below, the percentage of a site covered by roads, buildings, parking lots, and other impervious surfaces varies with a property’s location and land use. A study of impervious cover across the region, shown on the facing page, illustrates the extent of urbanized land across the region’s five counties and the relative percentage of those sites covered by impervious surfaces. regional impervious cover Percent Imper viousness Maynardville Major Interstates Plainview Norris Oliver Springs Clinton Oak Ridge Knoxville Farragut Lenoir City Loudon Alcoa Maryville Townsend Downtown areas and retail corridors with the highest rate of imper vious surfaces are shown with darker shades of gray, while suburban areas and residential neighborhoods with moderate rates of imper viousness are shown with lighter shades of gray. Imper vious surfaces in these areas are frequently contiguous, leaving little or no opportunity for stormwater runoff to be infiltrated or slowed before reaching storm sewer systems or receiving waterbodies. Additionally, the amount of imper vious cover in regional watersheds is becoming increasingly disproportionate to the resident population. Nationally, it is estimated that the rate of increase in imper vious cover has exceeded that of population growth by 500 percent over the last 40 years. 31 On developed sites, from agricultural landscapes to urban cities, tree canopies have been cleared to make way for pastures and parking lots. As a result, precipitation that would have been intercepted by tree canopies and evaporated off leaf surfaces now falls directly to the ground. Site development activities also modify existing site topography, removing topsoil and compacting the exposed clay that is left behind or imported to the site as fill. Instead of infiltrating into porous topsoil, being absorbed and evapotranspirated by vegetation, or recharging aquifers, precipitation now collects on and flows across imper vious surfaces and densely compacted clay soils with limited infiltration capacity. 53 Development activities and imper vious surfaces lead to an increase in the quantity and rate of stormwater runoff leaving a site as compared to pre-development conditions. As the percentage of a site that is covered with imper vious surfaces increases, so too does the percentage of total precipitation that leaves a site as stormwater runoff. The diagram below 32 illustrates this relationship for land uses commonly found throughout regional watersheds for a one-inch storm event. %by impervious landuse type 3% %from runoff 13% Site development practices common in the PlanET region inhibit natural hydrologic processes capable of reducing the volume and slowing the velocity of runoff. Such practices generate and discharge stormwater runoff from developed sites at a higher peak rate, measured in cubic feet per second, over a shorter period of time than would occur on the same site in its undisturbed condition. The difference between peak flow rate and the time peak flow is reached is especially notable when comparing urbanized and undeveloped sites, illustrated in the 28% 1â€? 23% Ranchette Low Density Housing 35% High Density Housing 87% 51% Campus: University 50% 43% Apartment Complex 40% Ofďƒžce Park 70% 64% 54 54% 12% storm event Agriculture 44% 69% Small Retail 88% 70% Large Retail 87% 69% Small Downtown 93% 74% Large Downtown 93% 57% Utility 74% Industry land use distribution in a watershed Agriculture High Density Small Low Density Ofďƒžce Park Apartment Housing Retail Housing Complex Surface Runoff Watershed Boundary Ranchette Campus Utility Large Downtown Small Downtown Industry Watershed Boundary Large Retail 55 hydrograph below. When aggregated over entire watersheds, the rapid discharge of increased stormwater runoff quantity from individual sites can overwhelm storm sewer systems and receiving waterbodies, sometimes contributing to costly flash flooding. 56 Rainfall Rainfall (depth) (depth) Runoff Runoff Flow Flow Rate Rate (volume/time) (volume/time) Attempts to manage flooding events, as well as perceived inconveniences and threats posed by waterbodies to development, have historically led to the channelization, straightening, or burying of streams in underground culverts. Such practices fundamentally modify the chemical, biological, and physical integrity of waterways and eliminate their ability to perform valuable ecosystem services. Impermeable streambeds, as seen in the image below at right, increase flow velocity (by design), prevent surface water from infiltrating, and do not support aquatic plant life with water treatment capabilities. STORMWATER RUNOFF QUALITY The quality of stormwater runoff is affected by the nature of the surfaces it contacts and the activities that occur upon them. Contaminants and debris that accumulate on roads, parking lots, driveways, residential lawns, construction sites, agricultural land, and other land uses between storm events are conveyed by stormwater runoff to historic stormwater management infrastructure. This infrastructure that serves much of the region (shown on the facing page) was not designed to treat contaminated runoff before discharging it into shared water resources. A summary of the most common contaminants found in regional waterways, their probable sources, and known impacts can be found in the contaminant matrix on the following pages. Urbanized Peak Flow Rate Urbanized Peak Flow Rate Urbanized Site Hydrograph Urbanized Site Hydrograph Rainfall Rainfall Undeveloped Peak Flow Rate Undeveloped Peak Flow Rate Undeveloped Site Hydrograph Undeveloped Site Hydrograph Time Time Fourth Creek Culvert, Knoxville, TN PA P N NN NPA N NN PA PA PP PP PP P PA PA PA PA N PA PA PA PA PA PA NN NN NN N P PP P P PA P P Sediment Sediment Sediment Sediment Sediment Runoff Runoff Runoff S SS Sediment Sediment Runoff Runoff S SS S S SS Runoff Runoff SS SS SS PA PP PP PP P PAPA PAPA PAPA N PP PP PP NN NN NN PA PA PA NN PA PA P PP NN PA PA NN P P P P Nutrient Nutrient Nutrient and Pathogen and andPathogen Pathogen Nutrient Nutrient and and Pathogen Pathogen PA PA Runoff Runoff Runoff Nutrient Nutrient and and Pathogen Pathogen P P P N NN PA PA Runoff Runoff PA PA PP Runoff Runoff N N PP NN HM PPS PP PP S S S S S S HMHM HMHM HMHM HC HC HC HC HC HC HC HM HC HC HC HC HC HM HM HC HC HM HM HM HM HM HM HM HM Hydrocarbon Hydrocarbon Hydrocarbon Runoff Runoff Runoff HM HM Hydrocarbon HydrocarbonRunoff Runoff Hydrocarbon HydrocarbonRunoff Runoff Compacted Compacted Compacted Compacted Compacted Subgrade Subgrade Subgrade Compacted Compacted Subgrade Subgrade Subgrade Subgrade NPN NN NN PP PP PP NN N N NN N SS SS P HM N N N HCN N N N HM Contaminant Contaminant Contaminant Contaminant Contaminant Concentration Concentration Concentration Contaminant Contaminant Concentration Concentration P PP Concentration Concentration N NN HCHC HCHC N HMHM HMHM HMHM PP PP HM HCHC S PA HMHM HC HC HC NN HC HC NN HC P HC PP NN NN S S S S S S HMHMPA PA HMHM SSHM HM HM SSSS HM HM HM HM PA PA NN S PA PA Typical Typical Typical Typical Typical StormStorm Drain Storm Drain Drain Typical Typical Storm StormDrain Drain Storm StormDrain Drain PNP PP NN NN NN HM Compacted Compacted Compacted Subgrade Subgrade Subgrade Compacted CompactedSubgrade Subgrade Compacted CompactedSubgrade Subgrade To Receiving ToToReceiving Receiving Waters Waters Waters PHC P P To To Receiving Receiving Waters HM HM NWaters NHC HC S ToToReceiving S Receiving S N Waters Waters HMHM HC HC P P PA HMHM SS SS PA PA PA PA PA PA NN NN HC HC PP Contaminant Contaminant Contaminant Index Index Index Contaminant ContaminantIndex Index SContaminant S SSediment HM Heavy HMHMMetals HC Hydrocarbons HCHCHydrocarbons Contaminant Index Index Heavy HeavyMetals Metals Hydrocarbons Sediment Sediment HMHMHeavy HC Hydrocarbons S SSediment HeavyMetals Metals HC Sediment S SSediment HMHMHeavy HCHCHydrocarbons Heavy Metals Metals Hydrocarbons Sediment P P PHydrocarbons N Nitrogen N NNitrogen pa Pathogens papaPathogens Nitrogen Phosphorus Phosphorus Phosphorus Pathogens P P N N 57 Compounds Compounds Compounds papaPathogens Nitrogen Nitrogen Compounds Compounds Compounds Phosphorus Phosphorus Pathogens P PPhosphorus N N papaPathogens Nitrogen Nitrogen Phosphorus Compounds Compounds Pathogens Compounds Compounds Compounds Compounds Compounds Compounds CONTAMINANT MATRIX MATRIX33 HEAVY METALS DESCRIPTION Metals that do not degrade over time and are thus an environmental concern Examples of heavy metals are cadmium, mercury, nickel, and lead ORIGINS Originates from roads and parking spaces as debris from vehicle batteries, brakes, and rust May also run off from industrial facilities and materials extraction areas TRANSPORT Heavy metals bind to sediment and are washed into waterbodies IMPACT Heavy metals bioaccumulate in human and other *This table animal bodies and summarizes the can lead to health hazards major contaminants including growth and affecting water developmental problems, quality in the PlanET reproductive and nervous Region watersheds. system damage 58 HIGH TEMPERATURE STORMWATER HYDROCARBONS NUTRIENTS: NITROGEN COMPOUDS Nitrogen in its different states, including ammonia, nitrate, and nitrite NUTRIENTS: PHOSPHORUS COMPOUNDS Phosphorus in its different states, including phosphates and phospheric acid Stormwater runoff heated to abnormally high temperatures while owing across hot impervious surfaces, such as asphalt parking lots and dark-colored roofs Compounds composed of hydrogen and carbon Primarily originates from stormwater runoff moving across impervious surfaces that have been heated by direct sunlight May also result from the removal of vegetation around a waterbody Primarily originates from gas stations, parking spaces, and roads, as well as from improper handing of fuels and solvents, such as gasoline, kerosene, diesel fuel, motor oil, paints and paint thinners Transfered via conduction and occasionally convection Moves from impervious surface, to stormwater, to water body Leaks from usage areas (fueling depots, airports, car ports, commercial garages, etc.) Carried over impervious surface by stormwater May dissolve, or attach to suspended sediment particles Particles dissolve and are carried in both surface and groundwater Phosphorus binds to and is carried on sediment particles Increased temperature affects water chemistry, including dissolved oxygen levels, which impacts aquatic habitat Toxic to human health and aquatic habitat Small amounts of hydrocarbons can build up to toxic concentrations as they do not easily degrade Eutrophication and associated impacts, including algal blooms, low dissolved oxygen, sh kills, and build-up of toxins produced by algal bloom Disruption to overall ecosystem Eutrophication and associated impacts, including algal blooms, low dissolved oxygen, sh kills, and build-up of toxins produced by algal bloom Disruption to overall ecosystem Primarily originates from fertilizer, including residential, agricultural, commercial, and municipal applications Primarily originates from fertilizer, including residential, agricultural, commercial, and municipal applications PATHOGENS PESTICIDES SALT SEDIMENT VOLATILE ORGANIC COMPOUNDS (VOCS) Microscopic organisms, such as certain viruses, bacteria, or fungi, capable of causing disease in another organism All chemical pesticides, including herbicides, insecticides, algæcides, fungicides, fumigants, and rodenticides Salt used to prevent icing on roads and other impervious surfaces Primarily originates from bio-solids, such as sewage, agricultural waste, and domestic pet waste Originates from residential, commercial, agricultural, and municipal pesticide applications Originates primarily from road salt application Stormwater sheet ow washes pathogens into waterbodies Pathogens may also be carried on sediment particles Leaking sanitary sewer infrastructure and septic systems Method of transport is determined by whether the pesticide is a liquid, solid, or gas Seasonal environmental conditions (temperature, wind, rain) affect pesticide transport Salts dissolve in melted snow or rain and are ushed into storm sewer systems and waterbodies Stormwater washes pathogens into waterbodies Pathogens may be carried on sediment Leaking sanitary sewer infrastructure and septic systems Livestock entering waterbodies Emitted as gases, VOCs move freely through the air, and may eventually settle into soil or water Increases water treatment costs Risk of human disease Risk for aquatic species Contaminated water unt for human contact and recreational purposes Exposure to pesticides can cause damage to the nervous system in humans and other animals Pesticides bioaccumulate in animals and move up through the food chain, having far-reaching effects Increased salt level alters water chemistry and affects aquatic habitat Chloride in road salts is toxic to sh Filtering out suspended sediment increases water treatment costs Sediment buildup may require dredging which increases maintenance costs Suspended sediment decreases light transmittance and may adversely affect aquatic habitat Heavy sediment load leads to increased potential to carry pathogens VOCs are difcult to conne and a major threat to groundwater in karst areas Health effects of many VOCs are known to be carcinogenic to people and other animals Particles of dust, soil, and debris that have been moved and deposited by water, wind, or gravity Synthetically-derived organic compounds that are likely to volatize, such as chlorocarbons, chlorouorocarbons, benzene, and methylene chloride Erosion is caused by human and natural processes Destabilized soils on construction, agricultural, and materials extraction sites Primarily originates from synthetic products such as solvents, paints, varnishes, and coatings 59 CONTAMINANT HOT SPOTS Areas where land use and activities generate stormwater runoff with higher contaminant concentrations than are typical in stormwater are referred to as hot spots. As shown in the exhibit on the facing page, hot spots are found on land uses widespread throughout regional watersheds. As a result, hot spots threaten the health of water resources from the headwaters in rural areas to stream and river corridors in dense urban contexts. Examples of hot spots common in the region include imper vious parking spaces and roads where particulates from tire wear, brake dust, and organic compounds accumulate; lawns and landscapes upon which chemical fertilizers, pesticides, and domestic animal wastes are common; and agricultural and construction sites, shown below at left, where destabilized soils may be exposed and eroded extended periods of time. Contaminants such as these from widespread, diffuse sources throughout a watershed are considered non-point source pollutants. Non-point source pollutants differ from point-source pollutants, which have isolated, single points of origin, such as an outfall pipe on an industrial site. COMPOUNDED STORMWATER QUANTITY AND QUALITY IMPACTS The exhibits on the following pages illustrate how accumulated contaminants and the disruption of natural hydrologic processes on multiple contiguous properties affect the PlanET Regionâ€™s shared water resources. Quality Impacts - The daily occurrence of seemingly harmless activities, such as improper application of domestic fertilizer, aggregated across the hundreds of thousands of individual residential properties in the PlanET Region, lead to watershedscale water quality threats (see p62). 60 Regional Construction Site Quantity Impacts - Likewise, imper vious surfaces on individual properties compound into large-scale stormwater runoff quantity impacts when aggregated across an entire watershed (see p64). contaminant hot spots Livestock Waste Area Materials Extraction and Processing Areas PA A N Gas Stations Surface Runoff N PA PA S P PA S N P S P S HC C HC H C HC HC P PA N N N N P HC C N PA S S N S H HC P HM H M P S HM HM S N HC HC PA HM P HC HC N S HM M P S P P P S N HM HM H M P HC N S HC C N HM HC S HC HC N P N Watershed Boundary HC HC PA S HM HM HC HC S N Parking Spaces S N Watershed e d Boundary n Construction Sites Residential Lawns N HC HC P HC S HM HM S HM HM H HC N S HM N HM M PA A HM M HC C P HC HC HC C HC HM H M HM M S Restaurant Grease Traps Heavy Industrial Facilities Contaminant Index HM Heavy Metals P Phosphorus Compounds HC Hydrocarbons S Sediment N Nitrogen Compounds pa Pathogens Materials Handling Areas 61 Roads Trash and Recycling Facilities Stormwater Quality Impacts Small actions Small individual acts of contamination add up to major problems for water quality. 1LB 20% S S S Hydrocarbons nutrients S P S S S N P PA N P Up to 20% of a residential application of nitrogen (N) and phosphorus (P) fertilizer can be lost through stormwater runoff, leaching, and atmospheric volitalization. 34 N, P, and PA are carried in stormwater runoff or irrigation overďƒ&#x;ow. PA N HC Gasoline and motor oil are two forms of hydrocarbons (HC) that are commonly used to power vehicles and lubricate their moving parts. HM HM HC HC HM HM HC S 62 S S S S S HM S PA N P S Contaminants accumulate on roads and driveways HM and are washed into storm drains, where they are HC PA carried away on sediment (S). S HM HC N N HC P N P P N HC PA HC PA P N HC P S N HC N P P S HC PA S HM PA S S S P S PA P HC S N P PA HC H C S HC C P P Exposure to contaminants can cause respiratory and neurological problems for people. PA A P HC S AQUATIC LIFE HEALTH CONCERNS N S N HC N N P PA P S HC P N P N HC S N Seemingly insigniďƒžcant activities on multiple P individual sites lead to N large-scale impacts on S Pshared water resources. HC H C Animals ingest contaminants when they eat or clean themselves. P S P N S S PA HC S N PA N P PA big impacts P S S HC HC P N P N S PA A HC HC S PA N S N N S HC HC S N P DAM MAINTENANCE Sediment accumulation behind dams requires costly dredging and raises reservoir water S levels. HC C PA A N S P 63 Stormwater Quantity Impacts Common CommonPatterns Patterns Contiguous Contiguousimpervious impervious surfaces surfacesresult resultinin concentrated concentratedstormwater stormwater runoff runoffvolumes volumesand and increase peak ďƒ&#x;ow increase peak ďƒ&#x;owrate. rate. 64 big impacts Compounded over the scale of an entire watershed, extensive developed areas with contiguous impervious surfaces increase the potential for ďƒ&#x;ash ďƒ&#x;ooding events. Flash flooding erosion Property damage 65 66 Chapter 4 Stormwater threats to Shared Water RESOURCES Stormwater runoff quantity and quality threatens the health of the PlanET Regionâ€™s shared water resources. Hundreds of miles of water ways and thousands of acres of waterbodies in the region are classified as impaired by the Tennessee Department of Environment and Conser vation, having significant economic, social, and environmental impacts. 67 WATER RESOURCE MONITORING: THREATS AND IMPAIRMENTS In compliance with Federal Clean Water Act regulations, the Tennessee Department of Environment and Conservation (TDEC) monitors waterbodies across the state and releases a report of their findings every two years. The surveyed condition of each waterbodyâ€™s physical, chemical, and biological health is evaluated against a list of uses for which each waterbody has been deemed capable of supporting in its unmodified, native condition. There are seven total uses described by TDEC for which a waterbody may be designated. These include 1) fish and aquatic life; 2) recreation; 3) irrigation; 4) livestock watering and wildlife; 5) drinking water supply; 6) navigation; and 7) industrial water supply. All waterbodies in Tennessee are designated for the first two uses: fish and aquatic life, and recreation. 68 If it is determined that the observed condition of a waterbody is likely to not support one or more of its designated uses, that waterbody is then classified as threatened. If it is determined that the observed condition of a waterbody no longer supports one or more of its designated uses, it is classified as impaired. TDECâ€™s biannual report on the health of state waterbodies includes a list of threatened and impaired waters called a 303(d) list. Out of all 50 states, Tennessee ranks 15th for the highest number of impaired waterbodies. 35 The waterbody assessment map to the right shows that more than 61,000 acres of assessed reservoirs and 1,000 linear miles of assessed streams in the region do not fully support their designated uses and are thus considered impaired. 36 Most waterbodies that fully support their designated uses are located within the regionâ€™s national and state parks, protected landscapes, and otherwise undisturbed land. Though it is the leading cause of waterbody impairment, non-point source pollution is not the only factor contributing to this classification. Modifications to riparian edges, including vegetation removal, channelization, and culverting practices increase sun exposure levels and the temperature of waterbodies and degrade the quality of aquatic habitats. The removal of riparian vegetation also destabilizes stream, river, and reservoir banks, leaving them more susceptible to erosion during storm events. These modifications often lead to an impaired designation. UPSTREAM, DOWNSTREAM Many streams, rivers, and reservoirs are already impaired as they flow into the PlanET Region. Impairments inherited by the region are caused by stormwater and other challenges identified in the previous chapter that also prevail on urban and rural land uses in upstream watersheds. Similarly, development patterns, impervious surfaces, and activities within the PlanET Region cause impairments and water resource regional waterbody assessment 37 Fully Supporting Not Supporting Not Assessed County Boundary PlanET Region 69 challenges that are inherited by downstream communities. The flow of water resources across political boundaries and their widespread impairment highlights the need for watershed-based water resource management and the necessity to address challenges at their source. IMPAIRED SURFACE WATER: STREAMS AND RIVERS Over 1,000 miles of impaired streams and rivers flow within the PlanET Region. 38 Pathogens such as E. coli, traced to waste from domestic animals and livestock, are the number one cause of impairment to the regionâ€™s streams and rivers, followed by sedimentation and siltation. 39 70 The recreational use of impaired streams may be prohibited if they are determined to be too polluted for human contact. Furthermore, the lack of plant and animal species diversity, and the resultant aesthetic effect may render these corridors less attractive to the regionâ€™s recreation enthusiasts and tourists. Projects aimed at restoring impaired streams and rivers, such as the Pistol Creek rehabilitation and reengineering project shown below, can be expensive. Partly aimed at addressing persistent issues posed by sediment accumulations, 40 the total estimated cost for the Pistol Creek project is greater than $3 million. 41 Pistol Creek at Greenbelt Park, Maryville, TN Impaired streams, rivers, and other waterbodies are symptoms of widespread challenges throughout the region’s watersheds, not the problem unto themselves. Costly restoration projects will continue to be necessar y, sometimes repeatedly for the same waterbody, if the sources of their impairments continue to go unaddressed. IMPAIRED SURFACE WATER: RESERVOIRS Across the state of Tennessee, over 180,000 acres of lakes, reser voirs, and ponds are impaired, 42 while in the PlanET Region, 89 percent of the assessed reser voirs’ surface area carr y that same designation. 43 Common causes of impairment to reser voirs in the region include polychlorinated biphenyls (PCBs), mercur y, chlordane, and low levels of dissolved oxygen, an important element to aquatic ecology. 44 The origin of these non-point source pollutants may be traced to contaminated precipitation and contaminated sediment carried in stormwater runoff. Sediment also has damaging effects on dams and navigable channels. Tributar y water ways and sheet flow from the surrounding landscape carr y sediment to reser voirs. Once there, the slowed movement of water allows suspended sediment to settle and accumulate on the reser voir floor. This creates deposits of sediment in reser voirs and behind dams that require periodic dredging and other costly maintenance activities. 45 Real and perceived impairments to water resources can have a financial impact on communities whose economies are built around water-based recreation and tourism. A recent example of such an impact is found at Grand Lake in St. Mar ys, Ohio. Grand Lake contributes to the local economy in much the same way as the PlanET Region’s shared water resources do. Boating and fishing activities attract tourists and residents alike who in turn support local businesses such as restaurants, marinas, and lodging. In June 2010, an overabundance of nutrients in Grand Lake from non-point sources triggered a severe algal bloom, rendering the lake unsafe for plant and animal life. Native wildlife, including fish and birds, as well as pets that drank from the lake became fatally ill. Human illnesses were also reported that may have also been related to the algal bloom. Fishing and boating completely ceased, reducing the lake’s estimated annual economic impact of $150 million. 46 A regatta that annually contributes more than $600,000 to the local economy was canceled and lakeside businesses closed. Local park revenues also decreased by $250,000 that year. In the PlanET Region, a similar scenario is not outside the realm of possibility given current impairments to waterbodies and projected population growth in existing urban areas and on presently undeveloped land. Closing marinas, coves, or even entire 71 reser voirs for part of a season or longer due to contamination could have far-reaching economic implications. GROUNDWATER VULNERABILITY East Tennessee’s karst topography accelerates the flow of surface stormwater to the aquifer, rendering groundwater especially vulnerable to contamination by non-point source pollutants carried in stormwater runoff. In regions of karst, groundwater moves freely through subsurface geologic features as underground rivers and lakes, making it difficult to predict where contaminated groundwater may be withdrawn or resurface. Considering that it takes only one quart of spilled motor oil to pollute 250,000 gallons of water, 47 the need to focus on protecting groundwater quality is well-founded. Common sources of groundwater contamination in the region include volatile organics released from improper handling, storage or leaking of solvents and petroleum products, as well as pathogens from failing septic systems, leaking sanitary sewer systems, and animal waste.48 72 Groundwater is the source for more than 72 percent of the region’s water withdrawn for crop irrigation, and 56 percent of water withdrawn for livestock watering.49 The quality of crops and the health of livestock are threatened by exposure to contaminated groundwater, as is the health of humans and other animals that may consume them.50 IMPACTS TO DOMESTIC SUPPLY The average American family of four uses approximately 400 gallons of water ever y day. 51 The total amount of water used for domestic purposes across the the PlanET Region is greater than 100 million gallons per day. 52 An avoidable part of this demand comes from Fixtures and appliances (such as toilets, shower heads, and wash machines) commonly found in structures built before today’s high-efficiency fixtures and appliances were available. Much of the region’s demand for domestic uses is met by water withdrawn from surface waters, such as rivers and reser voirs. In rural areas, groundwater is relied upon heavily for municipal supplies and private wells. Withdrawals from surface and groundwater resources for domestic uses will increase as the region’s population grows. In Tennessee, domestic water supplies from surface and groundwater resources are treated to meet quality standards suitable for drinking. It is a significant cost to municipalities and utility companies to build, operate, and maintain the facilities and infrastructure needed to treat and distribute water extracted from surface and groundwater supplies. As the instances and concentration of non-point source contaminants found in ground and surface water resources increase, and as demand grows, so too does municipalities’ and utility companies’ cost to treat water to drinkable quality standards. IMPACTS TO HUMAN HEALTH Many water resources in the region are classified as unsafe for human contact. Streams, rivers, and reser voirs that are contaminated by chemicals or pathogens may be not be safe for swimming, wading, or fishing. Human contact with these waterbodies can cause serious illnesses or even death. Many chemical contaminants can be traced back to now-prohibited pesticides and industrial fluids, such as the chlordane and PCBs, that will continue to threaten the regionâ€™s waters. Pathogen sources, including failing septic tanks, urban runoff, and animal waste, pose a serious threat to human health, especially in rural areas where groundwater is relied upon to supply water for domestic uses. An abundance of nutrients in streams can cause eutrophication: where blue-green algae reproduce in great numbers. Bacteria in these algae produce toxins that are harmful to human health, affecting the liver, nervous system, and skin. 53 A common source of nutrients carried by stormwater runoff to receiving waterways is chemical fertilizer from residential, commercial, and agricultural land uses. Fish living in impaired water ways can become contaminated through the process of bioaccumulation. Contaminants accumulate in fish that live in polluted waters or that ingest other organisms that have bioaccumulated contaminants, including heavy metals such as mercur y. These fish are dangerous when consumed by humans, especially children and pregnant women. 54 Local Impaired Stream Increased stormwater quantity and velocity also pose threats to human health. Incidents of flash flooding are connected to injuries and deaths in the region. Of flooding-related fatalities, 80 percent occur in vehicles when drivers attempt to cross flooded roadways, only to be swept downstream and drown. 55 Other drowning fatalities and injuries occur when individuals are carried away by surging, unexpected flash flood waters. 73 74 Chapter 5 Stormwater management Federal water management legislation and municipal stormwater regulations have been implemented over the last 50 years in response to the impacts of point source pollution. These regulations have recently been expanded to also address non-point source pollution and the unintended consequences of site and watershed drainage practices to shared water resources. These regulations are amended as the scale and nature of the impacts attributed to stormwater quantity and quality become better known and as stormwater best management practices evolve to provide enhanced watershed stewardship potential. 75 STORMWATER MANAGEMENT: REGULATION AND PRACTICE Introduced in the mid-twentieth century, stormwater management regulations and practices aimed at reducing runoff volume and nonpoint source contaminants have significantly increased protection of the chemical, physical, and biological health of surface and groundwater resources. State and local stormwater management laws originate from federal legislation. The Federal Water Pollution Control Act of 1948 was revised in 1972 to include the Clean Water Act (CWA) amendments. Initially focused on eliminating industrial point source discharges to waterways, the CWA was again amended in 1987 to regulate non-point source threats to water resource health, including stormwater runoff. 76 The U.S. Environmental Protection Agency (EPA) is the federal entity that enforces CWA legislation. The EPA administrates water management permits with state agencies through its National Pollutant Discharge Elimination System (NPDES). The Tennessee Department of Environment and Conser vation (TDEC) administrates water management permits for regulated communities in Tennessee, known as Municipal Separate Storm Sewer Systems, or MS4s. In the PlanET region, the cities of Farragut, Mar yville, Alcoa, Lenoir City, and Knoxville and all counties except for Union are discrete EPAregulated MS4s. Individual states have the authority to determine where the responsibility to regulate and enforce stormwater management practices resides. In Tennessee, that responsibility lies with city and county governments, and in some instances institutions such as the University of Tennessee. In other states, such as Florida, stormwater regulation and enforcement is administrated by watershed-based water management districts. Readers are encouraged to contact their municipal governments for more information on stormwater management regulations effective in their jurisdiction. In areas of the region developed before Clean Water Act legislation, historic stormwater infrastructure focuses on draining stormwater from developed sites and conveying it to receiving waters. As seen in the exhibit on the facing page and in the image below, site drainage systems and municipal storm sewers in these areas rapidly Storm Sewer Outfall to Third Creek, Knoxville TN historic site drainage practices concentrate and discharge Existing Tree Canopy Removal Limited Evapotranspiration No Landscape and Open Space Required Rapid Concentration Sheet Flow d ove em R l ill soi y F a l To p C ed act p m Co Li Inďƒž mite ltr d at ion Concentrated Discharge to Receiving Waters P N HC S pa HM 77 concentrate, pipe, and discharge polluted stormwater runoff directly into streams, creeks, rivers, and reservoirs. In a limited number of regional communities with combined storm and sanitary sewer systems (CSS), stormwater is conveyed to water treatment plants. 56 These areas will continue to pose threats to shared water resources regardless of current or future regulations affecting new construction Sites built after local municipalities began regulating stormwater management, 57 but before NPDES Phase I and Phase II Stormwater Rules (see next section) went into effect, are required to manage the rate of stormwater discharge to not exceed that of the site’s predevelopment condition. 78 The common stormwater management approach to meeting this requirement in urbanized areas is often referred to as an end-ofpipe solution, whereby runoff is concentrated on impervious surfaces to drain inlets and conveyed to a turf-lined detention basin using underground pipes. As shown in the image on the facing page, detention basins are engineered to temporarily hold and then discharge concentrated runoff into the municipal storm sewer system or a receiving surface waterway at a controlled rate. While detention basins effectively control the peak flow rate of runoff discharged into municipal storm systems and receiving waters, they are minimally effective at removing contaminants from stormwater runoff. 58 NPDES PHASES I AND II Recognizing the need to protect water resources from stormwater runoff quantity challenges as well as quality threats from non-point source pollutants, the EPA published National Pollutant Discharge Elimination System (NPDES) Phase I and Phase II Stormwater Rules in 1990 and 1999, respectively. According to TDEC, Phase I Stormwater Rules apply to Municipal Separate Storm Sewer Systems (MS4s) serving populations of 100,000 or greater and eleven classifications of industrial activities, including construction activities disturbing one or more acres of land. Knoxville is the only Phase I MS4 in the PlanET Region. Phase II Stormwater Rules require small MS4s to obtain NPDES stormwater discharge permits and to implement programs to manage the quality of stormwater runoff discharged to municipal stormwater systems. Phase II MS4s in the PlanET region include Knox, Anderson, Blount, and Loudon County MS4s, as well as Farragut, Maryville, Alcoa, Lenoir City, and the University of Tennessee MS4s. Union County does regulate stormwater management, but is not currently subject to EPA NPDES rules. NPDES Phase II stormwater permits will require that the “first inch of rainfall must be 100 percent managed with no stormwater runoff being discharged to surface waters.” 59 This means that the runoff from a one-inch storm event may not be discharged to receiving waters current stormwater management detention and controlled discharge Existing Tree Canopy Removal Limited Evapotranspiration Limited Landscape and Open Space Required Rapid Concentration pa N Sheet Flow Detention/ Retention d ove em R l Fill soi lay To p C ed act p m Co HC S P HM Mo Inďƒž der ltr ate at ion Controlled Discharge to Receiving Waters S pa HM HC P N 79 or municipal storm sewer systems that empty to the region’s shared water resources. The requirement responds to research that suggests the first flush of stormwater runoff carries a significantly higher concentration of contaminants that had accumulated on a site since the previous storm event. Sources of additional information about NPDES Phases I and II can be found in the Resources section of Part IV. A common approach to meeting NPDES Phase I and Phase II rules continues to be hard engineering-based; a retention basin at the end of a pipe. Retention basins are engineered to indefinitely retain concentrated site runoff from a prescribed design storm, in this case a one-inch storm event. Retained runoff may evaporate, infiltrate into the soil, or in some cases be reused on site to supply water demands for allowable uses such as irrigation. 80 Retention basins are commonly hidden at the back of a site, sometimes enclosed within a protective chain-link fence, and treated as a utility with little or no aesthetic value. They can be land-intensive, consuming significant amounts of property that may otherwise have been preserved in its pre-development condition or built upon to increase the development’s intensity. Additionally, the space requirements to construct an adequately sized retention basin may not be available on sloped sites, or be economically practical on sites with premium land values and high density development. PART II CONCLUSION While federal and municipal stormwater regulations have made significant contributions to the protection of the nation’s water resources, quantity and quality management challenges lie ahead. A significant percentage of the region’s streams, rivers, and reservoirs are already threatened or impaired. Stormwater management infrastructure that serves a large area of the existing development in the five counties will continue to discharge unmitigated volumes of contaminated stormwater runoff even as new development projects implement contemporary management practices. With an anticipated 43 percent population surge over the next three decades, 60 the region’s tendency to grow through low-intensity sprawling development on undeveloped sites will further threaten the region’s shared water resources: the same water resources that the region will rely upon for consumptive uses such as drinking supply. The PlanET Region must look critically upon its trajectory for the future and adopt a watershed-based resource management approach, site design and development standards, and stormwater management practices that enable it to grow in a manner that recognizes, protects, and enhances its valuable shared water resources. Additionally, the region must develop comprehensive growth planning and infrastructure retrofit strategies to address stormwater challenges at their source. Retention Basin, Knoxville, TN 81 part iII opportunities for improvement 6 LOW IMPACT DEVELOPMENT: AN ENHANCED APPROACH 7 LID STORMWATER BEST MANAGEMENT PRACTICES 8 LID BMPs: SELECTION, LOCATION, AND CHALLENGES Low Impact Development: Avoid, Minimize, Manage Structural LID BMPs Unique Conditions, Unique Solutions Lessons from Pre-development Hydrology LID: Avoiding Impacts LID: Minimizing Impacts Structural LID BMP Function and Benefit Summar y Specialized BMP categories and Non-structural BMPs Construction Site BMPs Agricultural BMPs Non-structural BMPs Site and Contextual Conditions Post-development Hydrology Project Goals and Client Mission Challenges to LID Implementation LID: Managing Impacts Summar y of the LID Approach 82 9 TREATMENT TRAINS, INTEGRATED DESIGN, AND GREEN INFRASTRUCTURE PLANNING New Norris House Hallsdale Powell Utility District Headquarters Living Market Place Oak Ridge Stormwater Plaza Fountain City Sponge Park Renaissance Park Jackson Square Vision Plan Beaver Creek Watershed Plan Greenplan Philadelphia CONCLUSION 83 AS THE CHALLENGES FACING THE REGION’S WATER RESOURCES ARE NESTED THROUGHOUT WATERSHEDS , SO TOO ARE THE OPPORTUNITIES FOR WATER RESOURCE STEWARDSHIP LOW IMPACT DEVELOPMENT PRACTICES CAN BE PLANNING, DESIGN, AND DEVELOPMENT ACROSS LAND USES AND AT A VARIETY OF SCALES INTEGRATED INTO RURAL URBAN RESIDENTIAL INSTITUTIONAL HISTORIC STORMWATER INFRASTRUCTURE EMPHASIZES COLLECTION, CONCENTRATION, AND DISCHARGE HC HM Contam inated Stormw ater Runoff Manicured Landscape PA HM HC N P HM Stormwater Runoff Temperature Increase S HC Co nta min ate d Sto rmw ate r Run off HM S N Contaminant Index HM Heavy Metals HC Hydrocarbons S Sediment P Phosphorus Compounds N Nitrogen Compounds pa Pathogens Municipal Storm Sewer System: Discharged to Receiving Waters P HM PA S Municipal Storm Sewer System Enlargement O Evapotranspiration 2 O O O 2 O 2 O O 2 2 2 O O 2 O 2 2 2 HC HM Contaminated S t o r m w a t e r R u n of f O Sto Cap rmwa t u re t e r and Runo Filtr ff atio n LID STORMWATER MANAGEMENT PRACTICES EMPHASIZES THE USE OF Peak Flow Reduction Detention p Biological Treatment N Retention and Infiltration N NATURAL HYDROLOGIC PROCESSES THAT CAN TREAT STORMWATER AND REDUCE RUNOFF QUANTITY p 2 p N p N STORMWATER MANAGEMENT FACILITIES HAVE POTENTIAL BEYOND UTILITARIAN FUNCTION Commercial Retention Basin, City of Knoxville LOW IMPACT DEVELOPMENT STORMWATER PRACTICES CAN BE DESIGNED AS AMENITIES THAT ENHANCE SITE AESTHETICS, PERFORM ECOSYSTEM SERVICES AND STEWARD SHARED WATER RESOURCES Constructed Wetland at Renaissance Park, City of Chattanooga 90 Chapter 6 Low Impact Development: an enhanced approach Threats to water resource health originating in rural and urbanized communities and new stormwater management regulations pose challenges to land owners, site design and engineering professionals, and regulators. Even with stricter stormwater management requirements on new construction projects, regional stormwater infrastructure that predates the Clean Water Act and NPDES regulations will continue to threaten the regionâ€™s water resources. As such, there is great need to adopt an enhanced Low Impact Development approach to planning, design, and development, to broaden the palette of municipally acceptable stormwater management practices for new projects, and to identify green infrastructure and strategic stormwater infrastructure retrofit opportunities in existing communities. 91 LOW IMPACT DEVELOPMENT: AVOID, MINIMIZE, MANAGE Low Impact Development (LID) is a multiscalar approach to watershed planning, community design, and site development that seeks to avoid, minimize, and manage impacts to water resources. LID seeks to reintroduce natural hydrologic processes into developed landscapes, communities, and sites, while protecting and reducing impacts to undeveloped land. Opportunities to avoid impacts to water resources begin with LID watershed-scale planning that directs development away from undeveloped land and from sites, or portions of a site, that are in immediate proximity to environmentally sensitive areas: riparian corridors, wetlands, and karst openings. Instead of the low-density, single use sprawl at the suburban fringe persistent in the region, an LID approach redirects a significant amount of the regionâ€™s growth to vacant properties or underutilized sites within strategicallyselected existing urban and suburban areas. 92 Impacts to water resources may also be avoided through behavior changes by individuals, businesses, and organizations that prevent stormwater runoff contamination and water use inefficiencies. Effective community education programs and the implementation of ser vices that enable the proper application and disposal of hazardous materials may prevent non-point source pollution from contaminating water resources in the first place, while waterefficient fixtures, planting and irrigation strategies, and water reuse practices may reduce demand for ground and surface water withdrawals. Widespread adoption of such behavior across the entire PlanET Region can prevent water resource impairment and the need for costly restoration and purification measures. They may also reduce the water consumption rates of a growing regional population. LID methods minimize impacts to native site hydrology during the project planning, design, and development stages by reducing the amount of site that is disturbed, providing adequate buffers between developed areas of a site and waterbodies, and decreasing the amount of imper vious surfaces from which nonpoint source contaminants may originate. Each is an effective practice to minimize the amount of stormwater runoff generated by a site, thus also minimizing the need for costly stormwater management infrastructure. The LID approach seeks to manage runoff volume and stormwater contamination close to its source. This is accomplished through a variety of stormwater best management practices distributed throughout a site or watershed that promote infiltration, retention, biological treatment, and evapotranspiration processes. LESSONS FROM PRE-DEVELOPMENT HYDROLOGY East Tennesseeâ€™s unique natural hydrologic patterns and ecosystems have evolved to mitigate excess runoff as well as remove natural water-borne debris and particles. This delicate balance of topography, soil, and vegetation promotes water infiltration, prevents erosion, and has purified surface and groundwater for millennia. Inspired by these natural hydrologic processes and ecosystems, LID addresses stormwater challenges through a network of decentralized Best Management Practices (BMPs) and green infrastructure. These practices preserve the performance of natural hydrologic processes, including biological treatment, on undisturbed landscapes and reintroduce them into developed communities and sites. DECENTRALIZED MANAGEMENT Decentralized management addresses stormwater quantity and quality challenges where they originate: throughout a watershed, community, or a site. Conventional, end-of-pipe methods concentrate stormwater runoff to centralized detention basins, municipal stormwater systems, or discharge directly to receiving waters. LID provides ecosystem benefits throughout the entire management system by reducing the amount of runoff that is generated, slowing the rate of runoff concentration, and by retaining, treating, and infiltrating stormwater runoff before it is ever discharged to receiving waters. To achieve decentralized management at the site scale, the LID approach utilizes site areas that are not typically included in conventional stormwater management systems. Rooftops, paved areas, and linear landscape buffers distributed around a site all have stormwater management potential and are commonly part of a LID stormwater treatment train; a series of BMPs that are strategically selected, sequenced, and located. At the community and watershed scales, the LID approach is also commonly implemented through green infrastructure planning, stormwater regulations, and incentives that promote the use of LID BMPs. GREEN INFRASTRUCTURE Green infrastructure refers to a system of interconnected landscapes distributed throughout a watershed that provide ecosystem ser vices, stormwater management opportunities, and other benefits, such as recreational amenities and protection for environmentally sensitive landscapes. Green infrastructure includes protected landscapes where disruptions to natural hydrologic processes are minimal or not permitted. Such landscapes are commonly open to the public as recreation areas. Regional examples include national and state parks, wildlife management areas, and undeveloped land held in trust under a conservation easement such as Knoxvilleâ€™s Urban Wilderness Corridors. 93 Green infrastructure also includes built or restored landscapes such as urban parks, cemeteries, and waterfronts, open space within master planned projects and infill development, greenway corridors, community gardens, and green schoolyards, plazas, and streetscapes. Here, natural hydrologic processes are reintroduced into urbanized areas through the integration of tree canopy, per vious surfaces, and other landscape features designed to absorb, infiltrate, retain, and treat stormwater. The Living Market Place (p165), Oak Ridge Stormwater Plaza (p167), Fountain City Sponge Park (p169), and open spaces within the Jackson Square Vision Plan (p173) and Halls Town Center (p98) are PlanET demonstration projects that include green infrastructure as part of the built environment. 94 Recent work completed in the Beaver Creek watershed is a regional example of green infrastructure planning with a water resource stewardship objective. The Beaver Creek Task Force, in collaboration with the University of Tennessee College of Architecture and Design and other partner agencies, has developed a green infrastructure master plan for the Beaver Creek Watershed that includes landscape protection, restoration initiatives, and built projects such as the Halls outdoor classroom, constructed wetlands, and the Halls Greenway. The greenway provides access for pedestrian to a number of civic amenities and community resources, such as the librar y, the Halls community park, senior center, and community building. Though LID is often associated with green infrastructure, the two are not synonymous. Green infrastructure is an important part of the LID approach across watershed, community, and site development scales, and LID principles may be incorporated in the design and development of green infrastructure amenities. For example, green infrastructure such as a greenway corridor may be part of a watershed-scale LID approach to minimize impacts to a nearby stream, while LID BMPs may be incorporated into the greenwayâ€™s site design to treat and infiltrate runoff from upstream development. Halls Greenway green infrastructure opportunities National Parks Lands Held in Trust Green Streets Green Schoolyards Public Parks Green Urban Plazas Green Inďƒžll Development Urban Cemeteries Community Garden Greenway Corridors 95 Biological treatment Many LID stormwater management practices are ecologically based, using plant materials and microorganisms to capture, degrade, and eliminate pollutants found in contaminated runoff, soil, and air. This biological treatment process, illustrated in the exhibit on the facing page, 61 is often referred to as phytoremediation. During the process of phytoremediation, stormwater runoff is typically conveyed over landscape surfaces (as opposed to in underground pipes) to distributed LID stormwater managment facilities. In these facilities, runoff is slowed and held for an extended period of time, allowing it to evaporate or infiltrate into the soil. In the soil, some contaminants are sequestered through absorption or storage around plant root zones (phytostabilization). Other contaminants are biochemically broken-down into a usable form through metabolic processes by microorganisms in the soil or on the surfaces of inundated plants and debris (phytodegradation). Still other contaminants are absorbed by plant roots (phytoextraction). 62 96 Contaminants move from plant roots into stems and leaves through plant vascular systems in a process called â€œuptake.â€? Here, contaminant compounds, such as those containing nitrogen and phosphorus, are either processed and released into atmosphere as gases (phytovolatization) or are absorbed as nutrients in plant biomass. 63 These ecologically-based stormwater management facilities provide additional ecosystem benefits, such as creating wildlife habitat, air quality improvement, and ambient air temperature reduction. LID BMP facilities can also contribute to the siteâ€™s aesthetic, essentially participating as part of a designed landscape. This contrasts with conventional stormwater infrastructure that relies heavily, if not exclusively, on buried drains, pipes, and culverts as a means to concentrate and discharge contaminated stormwater runoff, as illustrated below. conventional stormwater infrastructure (see p57) PA N P Sediment Runoff N P S N N HC HC HM HM S Hydrocarbon Runoff Compacted Subgrade N PA P Nutrient and Pathogen Runoff P PA HM P N N PA S S P PA P P Compacted Subgrade Contaminant Concentration P N HM N N HM HC S To Receiving Waters HC S HM S PA N HC P PA HM Typical Storm Drain P N Contaminant Index HM Heavy Metals HC Hydrocarbons S Sediment pa Pathogens P Phosphorus Compounds N Nitrogen Compounds biological stormwater treatment O Wildlife Habitat n 2 n 2 2 O Aesthetic Quality O O n N pa S P n 2 O 2 O 2 O 2 n N N S pa HC Root Storage Fungi O N S N Inďƒžltration N P P Groundwater Recharge HC HM S P P P N p N N P N p p Extended Biological Treatment HM P 2 2 N N p P Biochemical Breakdown n Plant Absorption p HC Bacteria p N 2 2 N HM 2 n 2 2 O HC 2 2 O S Nematodes n 2 2 O Uptake P n n O Stor Conta mw min ate ate F i l t r a r R u n od HM tion ff 2 2 2 2 n Evapotranspiration 2 S P N 97 LID: AVOIDING IMPACTS The LID approach to water resource stewardship first seeks to avoid impacts to undeveloped landscapes, waterbodies, and hydrologic processes across watershed, community, and site scales. At the watershed scale, landscapes preserved through impact avoidance, such as wildlife conservation areas, ridges and hillsides, and riparian corridors, may be strategically planned and connected as part of a comprehensive green infrastructure system. Planning and design strategies that fall under impact avoidance include: Avoid Disturbances to Undeveloped Landscapes: Preserving undeveloped landscapes protects delicate aquatic ecosystems and hydrologic processes from development and construction activities. Avoid Development on Ridgetops and Hillsides: The amount of excavation and grading required when developing in steeply sloped hillsides compromises the structural integrity of the soil and often requires the removal of native vegetation. This increases runoff, leaves the slope vulnerable to erosion, and may unearth karst features with direct connections to groundwater. 98 Avoid Development in Riparian Corridors: Development immediately adjacent to streams and rivers may disrupt sensitive riparian habitats necessary to stabilize banks and protect biodiverse ecosystems. Such development may also increase the likelihood that unmitigated site runoff be discharged directly into waterbodies. Avoid Development in Karst-Sensitive Areas: Development in areas where groundwater is especially vulnerable due to karst openings such as springs, seeps, fissures, and sinkholes should be avoided. Avoid Resource Inefficiency: Widespread use of high-efficiency domestic and commercial fixtures such as WaterSense labeled products, efficient irrigation strategies, and enabling reuse practices reduces demand on water resources and water treatment infrastructure. Avoid Suburban Fringe Development: Sprawling development at the fringes of existing urban and suburban communities consumes productive agricultural landscapes and woodland areas, threatens environmentally-sensitive, biodiverse landscapes, and creates impervious surfaces at a rate disproportionate to population growth. A principle method for avoiding impacts to these hydrologically sensitive areas is redirecting growth through infill development and redevelopment of vacant, underutilized, or abandoned sites within the existing urban core and suburban communities. Infill and redevelopment projects can yield the same amount of commercial, office, and civic uses and residential dwelling units on fewer acres LID: avoiding impacts Undeveloped Landscapes Fringe Development Stream Corridors Surface Runoff Watershed Boundary Wetlands Prevent Pollution Promote Water Use Efďƒžciency Promote Inďƒžll Development Ridgetops and Hillsides Watershed Boundary Karst-sensitive Areas 99 of land than low-density development at the suburban fringe. Studies also suggest that a low-density development at the suburban fringe can produce as much as ten times more stormwater runoff than a mixed-use infill project with the same development program.64 The PlanET demonstration project shown below and on the facing page proposes the redevelopment of a low-density greyfield site as a high-density mixed-use town center at Halls Crossroads. The proposal includes two- and three-story mixed-use buildings, parking structures, and extensive green infrastructure. The proposal avoids impacts to over 240 acres of undeveloped property that would have been disturbed if the site program had been developed at the suburban fringe using conventional development densities and intensities. 65 Hydrologic impacts are also reduced 100 by minimizing impervious rooftops, roads, and parking surfaces. Parks, rooftop gardens, and streetscapes incorporate LID practices that further minimize and manage stormwater impacts. By building vertically, the proposal yields a significant increase in the amount of building square footage within the site while increasing the amount of open space accessible to the public as recreation amenities and community gathering places (see p175). In addition to hydrologic benefits, infill and redevelopment projects also enhance walkability, transit viability, sense of place and community, and can increase property values while reducing reliance on personal automobiles to access basic services. By developing where road, emergency service, and utility infrastructure are already in place, municipal capital investment and maintenance costs to support growth can also be reduced compared to the economics of sprawl. 66 101 Halls Crossroads Town Center, PlanET Demonstration Project By: Luke Murphree University of Tennessee landscape Architecture Program LID: MINIMIZING IMPACTS Population growth and associated development often require some level of disruption to natural hydrologic processes, and may even require disturbance to previously undeveloped sites. In such cases, planners, engineers, and designers using an LID approach are tasked with minimizing the scale and scope of site impacts and their affect on shared water resources. The images at right and on the facing page contrast a conventional planning and design approach at the scale of a residential community against an LID approach on the same site. Both examples yield the same number of residential lots, but with marked differences between areas of site disturbance and resultant community aesthetics, amenities, and infrastructure costs. This is shown in the comparative site data on the facing page. 67 The LID concept, a conservation subdivision, demonstrates a number of impact minimization strategies: 102 Minimize Canopy Removal: The preservation of contiguous stands of existing trees maintains a dense canopy capable of intercepting and evaporating an appreciable percentage of precipitation during typical storm events. Such stands also absorb atmospheric carbon dioxide, reduce ambient air temperature, provide wildlife habitat corridors, and serve as a shared green infrastructure amenity for the benefit of all community residents. Minimize Top Soil Removal and Compaction: Top soils enriched with organic materials readily enable the infiltration of runoff through pore spaces between soil particles. Construction activities typically strip a site of its top soil, leaving behind heavy clay fill, or compacted soils with significantly reduced capacity for infiltration. Minimizing the amount of soil compaction and top soil removal reduces runoff and protects quality soils necessary for vigorous plant growth. Minimize Impervious Surfaces: Impervious surfaces may be minimized on a site by developing at a higher density and using innovative construction materials. In the LID example shown here, the compact development envelope requires fewer linear feet of roadways to DEVELOPMENT COMPARISON Standard Development : 142 Units conventional development LID: minimizing impacts Stormwater Infrastructure Area of Site Disturbance Imper vious Surfaces Existing Canopy Removal Soil Compaction Forest Preserved In n io at tr fil Comparative Site Data Conventional Development LID Development 142 Lots 0% Shared Open Space 29% Imper vious $400k Stormwater Infrastructure $2M Pavement Construction 142 Lots 50% Shared Open Space 15% Imper vious $164k Stormwater Infrastructure $663k Pavement Construction 103 access the individual lots than the conventional approach. The LID concept also uses permeable pavement that allows stormwater to pass through and recharge groundwater, as opposed to being diverted to costly subsurface infrastructure. Additional methods to reduce imper vious surfaces include building vertically and using vegetated roofs. In some cases, municipal ordinances may prevent the minimization of imper vious surfaces by requiring roads and driveways of a certain width or that a minimum number of parking spaces be provided in parking lots ser ving commercial and institutional properties. Such ordinances may result in oversized parking lots, drives, and roads, and may not permit shared parking between adjacent uses with peak parking demands at different times of day or days of a week. 104 Municipal zoning ordinances establish standards to which parking lots must be designed. These standards vary between municipalities and are driven by the projectâ€™s land use designation. Elements commonly found in parking lot design ordinances include a minimum number of parking spaces as a ratio to building area (minimum spaces per square-feet), parking space and driveway dimensions, and specifications for landscape islands and/or shade tree size and intervals. These elements affect the size of the overall parking lot, and thus significantly affect site hydrology. A survey of regional parking ordinances for commercial uses indicates that most municipalities require a minimum of four to five spaces per 1,000 square-feet of building space. Low impact parking codes are beginning to set minimum parking space requirements as low as three spaces per 1,000 square-feet, in addition to space maximums, shared parking allowances, and reduced stall and aisle dimensions to minimize the amount of impervious surfaces. The image on the facing page compares the minimum number of parking spaces as would be required by historic and some current parking codes in the PlanET Region against LID design standards. Under LID standards, spaces desired by the business that exceed the ordinancesâ€™ stipulated maximum must be built using pervious pavements. Shade trees with minimum caliper and spread requirements, plus minimum island dimensions, enhance the likelihood that a tree will survive and establish a healthy canopy, providing shade that reduces ambient air temperature, stormwater runoff quantity, and stormwater runoff temperatures following a storm event. By reducing impervious surfaces, minimizing topsoil removal and soil compaction, and preserving existing tree canopy, the amount of stormwater runoff and peak flow rate is also minimized. Reduced stormwater runoff requires less stormwater management infrastructure and may allow for significant infrastructure cost savings. 630 Parking Spaces historic 140,000 SF Retail Parking Lot Design Requirements - 4.5 spaces / 1,000 square feet minimum No Maximum Trees : Not Required Landscape Islands : Not Required Overow Parking 420 Parking Spaces lid Parking Lot Design Requirements - 3 Spaces / 1,000 square feet minimum Maximum Prescribed Overow Allowed as Permeable Pavement Trees : Required Landscape Islands : Required 140,000 SF Retail 105 LID: MANAGING IMPACTS Even with careful planning to avoid and minimize impacts to natural hydrology, most developed sites will generate some amount of stormwater runoff that needs to be managed. LID stormwater management can be implemented on new development projects and retrofitted into existing communities through a series of facilities known as LID BMPs. A BMP is a method that is recognized as an efficient, effective, and practical means of reducing stormwater runoff quantity and preventing or reducing the conveyance of pollutants into receiving waters. 68 Detention and retention basins, BMPs typically used in conventional stormwater management systems (see diagram at right), are effective at storing runoff and controlling discharge rates, but are limited in their ability to manage stormwater quality. 69 These basins are commonly utilitarian in appearance and consume significant amounts of land that may otherwise be developed or preserved. 106 In contrast, LID BMPs can be efficiently integrated into the design of a landscape as multi-functional amenities that provide valuable open spaces, perform ecosystem ser vices, and enhance site aesthetics in addition to performing stormwater management functions. LID uses a decentralized management approach, distributing BMPs throughout a site to manage stormwater at its origin. LID BMPs reduce runoff quantity, control peak flow rate, and improve stormwater quality by reintroducing natural hydrologic processes into developed landscapes. Porous soils, native plant materials (such as canopy trees, wildflowers, and aquatic plants), and microorganisms play a significant role in the performance of these processes, including the biological treatment of contaminated runoff. The diagram on the facing page illustrates these and other hydrologic processes fundamental to LID stormwater management approach at the site scale. Commonly used LID BMPs are described and illustrated in Chapter 7. conventional stormwater management (see p79) Existing Tree Canopy Removal Limited Evapotranspiration Rapid Concentration pa N Sheet Flow Detention/ Retention s To p HC S P Co HM Mo In ďƒž d e r ltr ate at io n o il mp Rem ed act ove Cla d il l y F Controlled Discharge to Receiving Waters S pa HM HC P N Limited Landscape and Open Space Required LID: managing impacts Existing Tree Canopy Maintained Evapotranspiration Rainwater Har vesting Storage + Reuse Peak Flow Reduction Disconnected Downspout Graywater Recycling Increased Per vious Surfaces Directed Sheet Flow S Filtration Biological Treatment Retention s To p N Inďƒž Note: This drawing is not meant to be a realistic representation of an actual LID BMP application on a developed site. Rather, it is intended to visualize processes and concepts fundamental to an LID stormwater management approach. ltr at oil ve ati Cla y ion 107 108 Chapter 7 LID STORMWATER best management practices The structural LID Stormwater BMP profiles included in this publication are listed at right and are presented according to their primary stormwater management outcome: runoff reduction, peak flow reduction, and water quality treatment. Though one outcome is identified as primary, a BMP may perform the others at a secondary or incidental level. Each profile illustrates the hydrologic functions, assembly, and potential appearance of a number of widely used LID BMP facilities. 70 Some diagrams may not show all components of a particular facility, such as forebays or overflow devices, while others may take liberties with the facility’s as-built condition to efficiently illustrate its function. The illustrations feature actual BMP installations located within the PlanET Region or elsewhere within Tennessee. While these illustrations reflect the basic assembly and materials used in the construction of each facility, they are not meant to be construction documents. Each facility’s construction detail was customized by site design and engineering professionals in the context of specific site conditions, effective regulations, and project objectives. Narratives that describe defining characteristics, including benefits, cost, maintenance, and construction considerations accompany each BMP facility illustration. Also described in this chapter are specialized BMPs that serve agricultural land uses and construction sites, as well as non-structural BMPs aimed at preventing water resource impacts through pollution prevention and water use efficiency. The reader should verify which LID BMP facilities are acceptable by code in his or her community. STRUCTURAL LID BMPS RUNOFF REDUCTION PEAK FLOW REDUCTION RAIN GARDEN RAINWATER HARVESTING PERMEABLE PAVING VEGETATED ROOF TREE BOX BIORETENTION CELL INFILTRATION STRUCTURE VEGETATED DETENTION BASIN WET POND SPECIALIZED BMPS NON-STRUCTURAL LID BMPS CONSTRUCTION SITE AGRICULTURAL BEHAVIORAL WATER QUALITY TREATMENT CONSTRUCTED WETLAND VEGETATED SWALE SAND FILTER FILTER STRIP 109 RAIN GARDEN + Native plants are recommended for rain gardens because of their adaptation to local environmental conditions and synergies with soil microorganisms that enable biological treatment processes. Rain gardens work well in a propertyâ€™s low spots, although rain gardens may not be an appropriate choice for areas that stay persistently wet (see Constructed Wetland p130). Locate rain gardens in full sun to encourage drying out between storms. Properly designed rain gardens drain within 24 hours following a storm event and do not support conditions for mosquito breeding. 110 Depending on existing site soil conditions, rain gardens may require soil amendment to increase infiltration rates. During installation or repair, avoid using heavy equipment in or around the area to protect underlying soil from compaction. Stormwater Management - - Runoff reduction - - Retention - - Infiltration Additional - - Wildlife habitat - - Aesthetic quality - - Improves air quality Rain gardens are planted depressions in the landscape designed to capture and infiltrate stormwater. Rain gardens reduce stormwater runoff through retention, infiltration and evapotranspiration. Suspended solids are removed through sedimentation and physical filtration by plant and soil media. Contaminants, such as nutrients and heavy metals, are mitigated by extended biological treatment. Benefits + + + - - Sedimentation - - Filtration - - Extended biological treatment - - Educational opportunity Cost & Maintenance Considerations - - Cost: Low to Medium - - Maintenance: Low once vegetation is established - - Check for maintenance following intense storm events and amend any erosion of berm - - Apply/amend mulch layer annually - - Maintain permeability of soil to prevent ponding - - Retained water should infiltrate after 24 hours - - Avoid use of fertilizers Construction & Site Considerations - - Avoid heavy equipment on and around Rain Garden - - Locate at least 10â€™ from building foundations - - Locate in full sun - - May amend soil for adequate permeability Contaminant Removal - - Suspended Solids - - Nutrients - - Heavy Metals East TN Rain Garden Sheet Flow Curb Cut Curb Cut Evapotranspiration Tur f Strip Filter Sedim n Rete entat ion Berm tion Inďƒžl Berm Mulc h r Laye trat ion ion tent e r Bio il Mix So ted pac l m o i Unc tive So a N 111 Sheet Flow + RESIDENTIAL RAINWATER HARVESTING - - Runoff reduction - - Aesthetic quality Rainwater har vesting involves collecting and storing rainwater from roofs for later use as a water Curbsupply. Cut Tur f StripHar vesting rainwater from downspouts can offset or fully supply Filter landscape irrigation needs. Considering that the region receives approximately 47 inches of precipitation each year, a 1,000 squarefoot roof area would produce nearly 30,000 gallons of rainwater. Rainwater har vesting tanks should be designed to overflow to a per vious landscape area, such as a rain garden. n Rete Berm Stormwater Management - - Retention Additional + Residential rainwater har vesting is a retention practice that aids in runoff reduction. This type of rainwater har vesting is relatively affordable and easy to install. Rain barrels and other collection Evapotranspiration tanks and cisterns are available in many sizes and shapes to fit homeowner â€™s needs. They can be designed as ornamental garden accents, dynamic water features that activate during and after storm events, or as understated utilitarian water storage tanks. 112 Benefits tion Rainwater harvesting systems should be sized appropriately to capture and store an adequate supply of rainwater. If not used frequently, rainwater storage devices may need to be drained to prevent yer stagnation and odors. The roofing from which rainwater is h Lamaterial Mulc harvested must be considered when establishing its end use. + - - Stores stormwater for alternative use Cost & Maintenance Considerations - - Cost: Low - - Stormwater as irrigation Curb supplyCut offsets utility costs - - Maintenance: Low - - Inspect after storm events for debris and proper inflow/outflow - - Install gutter screens to minimize debris - - Install a first flush diverter to minimize debris and potential contaminants - - Periodically drain unused water to prevent insect breeding - - Disconnect inlet and drain in freezing temperatures Construction & Site Considerations tion - - Use a dark opaque storage device and locate entacolored, im d e inS shade to decrease algae growth - - Locate near landscape areas requiring frequent irrigation -- Petroleum-based and treated wood products are known to leach toxins into rainwater that pose health risks if consumed. Rainwater i o n collected from these surfaces is trat I n ďƒž l for irrigating ornamental landscapes. Metal only suitable roofs (except coppernand those with lead components) io are generallyreregarded as ideal for rainwater harvesting. tent ix B i o a i lprofessional M Consult with regarding allowable uses and So potential treatment requirements for harvested rainwater d cte mpa oil o c Un tive S Na Berm East TN Rain Barrel GutteGruSttcerer eScreen GutteGruSttcenrer eScree n n Fir stshFlush Fir st Flu Fir Flu veFir shFlush rtster DivertDister Divert Dier verter Ovewrow Overo Ove Ove Devro icewrow Device Device Device Rain Rain BarrelBarrel Rain Rain BarrelBarrel 113 Alternative Irrigation Alternative Irrigation Alternative Alternative Irrigation Irrigation PERMEABLE PAVING Permeable (or pervious) paving allows water to flow vertically though hard, paved surfaces. Permeable paving aids in runoff reduction by allowing for retention and infiltration. It can be used as a substitute for impervious paving in areas such as parking lots, plazas, and walkways where hard surfaces are required. By utilizing areas that are already programmed for human or vehicular use for runoff reduction and stormwater management, permeable paving can reduce the amount of site area needed for additional structural management facilities, and add value to a property by preserving buildable space + + + Permeable options are available for asphalt, concrete, and unit pavers, which may add aesthetic appeal. Reinforced turf products are also available and are commonly used for overflow parking, fire lanes, and event spaces. All permeable pavement options reduce the amount of ponding and sheet flow, which is a benefit in pedestrian traffic areas. 114 This BMP requires a thorough maintenance plan of both the paved surface and the surrounding area. Twice annual vacuuming of the pervious paving is necessary to remove accumulated sediment, and vegetative buffers should be installed around the area to prevent sediment from washing onto the permeable surface. + Benefits Stormwater Management - - Runoff reduction - - Retention - - Infiltration - - Filtration Additional - - Aesthetic quality - - Improves air quality - - Provides additional per vious - - Educational surfaces opportunity Cost & Maintenance Considerations - - Cost: Medium to High - - Maintenance: High - - Vacuum twice annually to maintain permeability - - Pre-treat water flowing onto permeable paving with a filtration BMP Construction & Site Considerations - - Not suitable for sites with hazardous materials or high sediment runoff - - Variations on construction details are available for sites with soils with low infiltration rates - - Adaptable to a wide variety of site designs - - Research load-bearing capacity of per vious materials against anticipated vehicle types and traffic pattern - - Parking lots sloped greater than 5% require special consideration for subsurface grading and drainage Contaminant Removal - - Hydrocarbons - - Heavy Metals McFee Park Farragut, TN 1 1 Aggregate AggregateChips Chips 2 2 #54 #54Stone StoneWashed Washed Inltration Inltration 3 3 #2 #2Aggregate Aggregate Concrete Concrete Header HeaderCurb Curb Concrete ConcretePavers Pavers 11 22 Rock-lined Rock-linedSwale Swale 33 115 Underdrain Underdrain Compacted CompactedSoil Soil Subgrade Subgrade Filter FilterFabric Fabric VEGETATED ROOF + Vegetated roofs add additional thermal insulation and may lower heating and cooling costs for buildings. They also significantly reduce the heat reflected by building rooftops compared to conventional roofing materials, therefore reducing heat islands while introducing green space and biodiversity into urban environments. Additionally, they create rooftop pocket-parks, while native vegetation provides habitat for small wildlife such as pollinators. 116 Stormwater Management - - Runoff reduction - - Retention - - Evapotranspiration - - Filtration - - Extended biological treatment Additional - - Aesthetic quality - - Improves air quality - - Provides additional per vious - - Educational surfaces opportunity Vegetated roofs (green roofs) provide the benefits of a garden on top of buildings. Vegetated roofs reduce runoff through processes of retention and evapotranspiration most effectively from short, mild storm events. Studies have shown that in temperate climates, vegetated roofs are capable of reducing annual roof runoff by 50 percent. They can be classified as extensive and intensive types and consist of soil media, plant materials, and a range of insulation and waterproofing membranes. Extensive vegetated roofs typically use between four and six inches of soil media while intensive roofs consist of at least six inches of soil media. Intensive vegetated roofs sustain more diverse plant palettes, including shrubs and trees, and may be designed as rooftop gardens meant for human habitation. Benefits + + Cost & Maintenance Considerations - - Cost: Medium to High (extensive), High (intensive) - - Added insulation and evaporative cooling may reduce utility costs - - Maintenance: Low to Medium (extensive), High (intensive) Construction & Site Considerations - - Requires adequate roof structure; consult with a structural engineer for both new construction and potential retrofit applications - - Intensive green roofs can provide additional habitable amenity space 1 The Pinnacle Nashville, TN Growing Media 2 Filter 3 Drainage System 4 Root Barrier 5 Insulation 6 Waterprooďƒžng 7 Roof Structure Tree Planting (Intensive) Outdoor Recreation & Aesthetics ran Evapot spiratio n Filtratio tion n ete and R n Sedums & Succulents (Extensive) 1 2 3 4 117 5 6 7 TREE BOX + Tree boxes retain and promote the infiltration of stormwater while enabling the establishment of tree canopies in dense urban areas. A common impediment to sustaining healthy trees in urban environments is insufficient volume of quality planting soil. Urban soil is typically compacted clay with limited pore space, preventing water and oxygen from reaching tree roots. Tree boxes provide structural support for pavement above planting soils to facilitate tree growth and provide on-site stormwater management. The tree box structure prevents soil compaction, allowing air space in soils for infiltration and biological treatment, thus allowing the tree to absorb, uptake, and transpire stormwater. Tree boxes can vary in design, material, and cost based on available area and orientation of subsurface structures and utilities. This makes tree boxes an ideal BMP for dense urban areas where paved surfaces are necessary. Tree boxes may be implemented with other BMPs, such as permeable paving on plazas and parking lots. 118 Additional benefits to establishing urban tree canopies include air quality improvement, shade, building temperature regulation, increased property value, and aesthetic appeal. Trees also intercept, retain, and evaporate precipitation from their leaves and branches. + + + Benefits Stormwater Management - - Runoff reduction - - Retention - - Evapotranspiration - - Extended biological treatment Additional - - Aesthetic quality - - Improves air quality - - Provides additional per vious surfaces Cost & Maintenance Considerations - - Cost: Medium - - Maintenance: Medium - - Periodically test soil for high contamination levels and replace if necessar y - - Periodically aerate soil - - Remove litter and debris after storm events Construction & Site Considerations - - Tree boxes can be implemented in dense urban areas - - Research and choose trees appropriate to site cultural conditions - - Provide grate over root zone if implemented in high foot traffic areas - - Avoid low spots Contaminant Removal - - Suspended Solids - - Nutrients - - Heavy Metals Neyland Stadium Gate 21 Knoxville, TN Rainfall Rainfall Rainfall Rainfall Evapotranspiration Evapotranspiration Evapotranspiration Evapotranspiration Tree TreeCanopy Canopy Tree Canopy Interception Interception Interception Tree Canopy Interception 1 1 1 22 2 33 3 44 4 55 5 66 6 1 Aggregate Aggregate Aggregate Base Base Base Aggregate Base 2Gap AirAi r Gap Air Gap Air Gap BioBi3retenti oretenti Bioonretenti oSoi n Soi l ol n Soil Bioretention Soil 4 Backll Backll Backll Backll 5 Aggregate Aggregate Aggregate Base Base Base Aggregate Base 6 Compacted Compacted Compacted Subgrade Subgrade Subgrade Compacted Subgrade Concrete Concrete Concrete Curb Curb Curb Concrete Curb 3’ MIN 3’ MIN3’ MIN 3’ MIN Modular Modular Modular Tree TreeBox Box Tree Structure Structure Box Structure Modular Tree Box Structure Soil SoilStabilizing Stabilizing Soil Stabilizing Grid Grid Grid Soil Stabilizing Grid Filter FilterFabric Filter FabricFabric Filter Fabric Pervious Pervious Pervious Paving PavingMaterial Paving Material Material Pervious Paving Material Inltration Inltration Inltration Inltration 1 1 1 1 33 34 4 4 22 2 119 2 3 4 55 5 66 6 5 Drainage Drainage Drainage Pipe Pipe Pipe 6 Drainage Pipe BIORETENTION CELL + High velocity water entering the cell may dislodge plant material and cause erosion. Therefore, bioretention cells are most effective when located close to the source of stormwater runoff. Several cells may be located along a block to capture and slow runoff. Bioretention cells on sites with slopes greater than 20 percent should be terraced. 120 Additional benefits of bioretention cells include increased urban green space and wildlife habitat, improved air quality, ambient temperature reduction, and aesthetic appeal. Stormwater Management - - Runoff Reduction - - Retention - - Infiltration - - Evapotranspiration - - Extended biological treatment Additional - - Wildlife habitat - - Improves air quality - - Aesthetic quality - - Educational - - Provides additional per vious opportunity surfaces Bioretention cells capture and retain stormwater from imper vious road surfaces making them a component of an LID Steetscape. Used primarily to reduce runoff, bioretention cells are vegetated depressions contained within curbs or short retaining walls. Distributed bioretention cells collect and retain stormwater runoff, which is then infiltrated, biologically treated, and evapotranspired by trees and other vegetation within the cells. Runoff is directed to these features by curb cuts, drain pipes, and runnels that may be designed as part of a water feature amenity. Common implementations of bioretention cells include streetscapes and along urban plazas. Benefits + + + Cost & Maintenance Considerations - - Cost: Medium to High - - Maintenance: Medium to High - - Inspect monthly and after large storm events - - Inspect inlet/outlet for blockages such as plant debris/litter Construction & Site Considerations - - Locate at least 2 feet above groundwater table - - Site slope should be less than 20% Contaminant Removal - - Suspended Solids - - Nutrients - - Heavy Metals Deaderick Street Streetscape, Nashville, TN C ro w n Tree Canopy Interception Evapotransp Crowned Asphalt Paving Bioretention Soil Mix Underdrain iration Retention Inďƒžltration Soil Compacted e d ra Subg 121 COMMERCIAL RAINWATER HARVESTING Rainwater harvesting involves collecting and storing rainwater from roofs or other impervious surfaces for later use as a water supply. Commercial rainwater harvesting can have a significant impact on runoff reduction as it intercepts and retains stormwater from potentially expansive roof areas and in some cases ground surfaces. Commercial rainwater harvesting cisterns may be located above or below ground, and in some cases are located within a building. Some projects feature cisterns as iconic design elements to call attention to this practice. Potential uses for harvested rainwater include water supply for site irrigation systems, water features, and for non-potable uses, such as waste conveyance (when permissible by code). These uses yield potential cost savings to the owner by reducing municipal water consumption. Some master planned projects, including commercial and institutional campuses, may utilize district rainwater harvesting where rainwater harvested from multiple collection areas is stored in a common cistern for redistribution as needed. 122 Various levels of filtration and treatment may be a necessary part of the harvesting system to ensure the retained water is free of debris and is safe for its intended reuse. + + + Benefits Stormwater Management - - Runoff Reduction - - Retention Additional - - Stores stormwater for alternative reuse - - Aesthetic Quality - - Educational opportunity Cost & Maintenance Considerations - - Cost: Medium to High -- Irrigation with harvested rainwater can offset utility costs - - Maintenance: Medium - - Inspect after storm events for debris and proper inflow/outflow - - Install gutter screens to minimize debris - - Install a first flush diverter to minimize debris and potential contaminants - - Periodically drain/treat unused water to prevent insect breeding - - If located above freeze/thaw line, disconnect inlet and drain in freezing temperatures Construction & Site Considerations - - Size of storage facility based on rainfall patterns, rainfall intensity, roof size, and anticipated usage - - Possible odor if left stagnant and unused - - Storage vaults can be located above or below ground - - If above ground, use a dark colored, opaque storage device and locate in shade to decrease algae growth - - May be connected to an irrigation system -- Consult with a professional regarding allowable uses and potential treatment requirements for harvested rainwater Oak Ridge National Laboratory Roane County, TN Rooftop Rooftop Runoff Runoff Cistern Cistern 123 Irrigation System Irrigation Water Supply INFILTRATION STRUCTURE Infiltration structures refer to a number of practices designed to retain and infiltrate stormwater. Infiltration vaults are underground storage facilities for stormwater runoff retention and infiltration. Infiltration vaults may be supported by a vaulted structure or filled with aggregate for structural support. They are usually located underneath parking lots but may be used under lawns or athletic fields as well. Another infiltration structure, the infiltration trench, utilizes open, aggregate filled trenches lined with filter fabric. These structures are frequently used on sites with poorly-drained soils and usually require an underdrain. 124 Water may enter an infiltration structure through permeable paving, or through a pre-treatment system such as a filter strip to remove sediment. Infiltration structures only provide incidental stormwater treatment through infiltration, so a thorough site analysis is mandatory to protect against groundwater contamination. If correctly installed, infiltration structures can reduce the load on conventional stormwater conveyance systems while recharging local groundwater. Overflow devices should be installed to drain runoff volumes that exceed the structureâ€™s retention capacity. + Benefits Stormwater Management - - Runoff Reduction - - Retention - - Infiltration Additional - - Provides additional per vious - - Educational surfaces opportunity + + + Cost & Maintenance Considerations - - Cost: Low to High - - Maintenance: Medium to High - - Can be difficult to access and perform maintenance - - Sub-surface storage decreases land area needed for stormwater management; opportunity to add value to property by preser ving buildable space - - Maximum drainage area is approximately 2 acres - - Pre-treat contaminated runoff flowing onto infiltration structure with a filtration BMP Construction & Site Considerations - - Inspect for underlying karst topography - - Ideal for urban settings with limited space Contaminant Removal - - Hydrocarbons - - Heavy Metals Cedar Bluff Shopping Center Knoxville, TN Sheet Flow to Drain Inlet Sheet Flow in Gutter to Drain Inlet Stormwater Sedimentation Gravel Inďƒžltration Cast in Place Concrete Wall and Footing 125 VEGETATED DETENTION BASIN Vegetated detention basins, sometimes referred to as dr y ponds, are designed to temporarily hold and pre-treat the first flush of stormwater before regulating discharge to a receiving waterbody. Vegetated detention basins detain large volumes of stormwater, aiding in peak flow reduction and mitigation of potential downstream flooding. Detaining stormwater in vegetated basins also enables sediment removal as vegetation decreases stormwater velocity, allowing suspended solids to settle out. Vegetated detention basins provide the additional benefits of increased aesthetic appeal, wildlife habitat, and improved air quality. As the alternate name â€œdr y pondâ€? suggests, vegetated detention basins are designed to fully drain between storm events, preventing conditions for mosquito breeding. Depending on the elevation of the outlet device, basins may be designed to detain water for an extended period or retain it indefinitely, increasing other wise limited pollutant removal efficiency through infiltration and biological treatment. Extended treatment is beneficial as vegetated detention ponds capture the first flush of stormwater, which conveys the most concentrated amount of contaminants. 126 + Benefits Stormwater Management - - Peak flow reduction - - Detention Additional - - Wildlife habitat - - Aesthetic quality + + + - - Sedimentation - - Provides additional per vious surfaces - - Improves air quality Cost & Maintenance Considerations - - Cost: Low to Medium - - Maintenance: Medium to High - - Long lasting and durable - - Annual sediment removal - - Inspect inlet/outlet for blockages such as plant debris/litter after storm events Construction & Site Considerations - - Size: Approximately 1-3% of drainage area - - Inspect for underlying karst geology - - Locate at least 2 feet above groundwater table - - Needs differential inlet and outlet elevation - - Locate in full sun Contaminant Removal - - Suspended Solids Oak Ridge National Laboratory Roane County, TN Outlet OutletStructure Structure Extended ExtendedDetention Detention Filtration Filtration Berm Berm Sheet SheetFlow Flow Evapotranspiration Evapotranspiration Temporary TemporaryDetention Detention Sedimentation Sedimentation Inďƒžltration Inďƒžltration 127 WET POND + Benefits Stormwater Management - - Peak flow reduction - - Retention Additional - - Wildlife habitat A wet pond is a constructed basin designed to retain a permanent pool of stormwater with limited biological treatment. Wet ponds aid in peak flow reduction and promote sedimentation. Stormwater may enter the pond as sheet flow across a filter strip or via a pipe or swale. If stormwater enters through a pipe, it should pass through a forebay, allowing initial sedimentation and velocity reduction. Once water reaches permanent pool storage, additional sediment settling and biological uptake occur as stormwater is slowly released over 24-72 hours. Wet ponds can also detain stormwater runoff if there is available space between the permanent pool elevation and the outlet structure. 128 Wet ponds require continual drainage inputs to maintain the permanent pool level, making them appropriate BMP choices in areas with frequent storm events. Continuous input and outflow or evapotranspiration prevents stagnation and conditions required for insect breeding. To promote habitat, a pond aerator may be required to increase oxygen levels. Fertilizers should not be used near wet ponds as excess nutrients increase algae growth that may lead to eutrophication. Wet ponds can be designed as an amenity; providing aesthetic appeal and wildlife habitat. To ensure public safety, research local codes concerning standing waterbodies. + + + - - Sedimentation - - Aesthetic quality Cost & Maintenance Considerations - - Cost: Medium - - Maintenance: Medium to high - - Vegetation upkeep - - Pond aeration often required - - Inspect inlet/outlet for blockages such as plant debris/litter after storm events - - Requires base flow to prevent stagnation - - Avoid fertilizer use around wet pond - - Dredging necessar y once a percentage of pool is replaced with accumulated sediment Construction & Site Considerations - - Requires an impermeable liner/membrane or soil layer - - Inspect for underlying karst geology - - Permanent standing water may pose safety liability Contaminant Removal - - Suspended Solids Pigeon Forge Resort Hotel Pigeon Forge, TN Inlet Inlet Conveyance Conveyance Limit Limitof of Detention DetentionArea Area ion ennttion t e R ete R tlet Ouutlteutre O c re Structu Stru Evapotranspiration Evapotranspiration OOu tl e t O ri u tl e t O riﬁ ﬁc e E le v a LLimit of Perm c e E le vtiaoti on n imit of Permanent Po l anent Pooo l Sedimentati Sedimentaoti n on In ﬁ lt ra ti o n In ﬁ lt ra ti o n Compacte C pacted d Suobmgra Subgradede 129 CONSTRUCTED WETLAND + 130 Constructed wetlands should maintain a shallow permanent level of water at all times and therefore should be located close to the water table. This makes constructed wetlands an appropriate BMP choice for persistently wet areas. They can receive water from an extensive drainage area; a minimum of 10 acres drainage area up to 25 acres drainage area is preferable, however, smaller â€œpocket wetlandsâ€? or bog gardens may be used in low, wet areas of smaller sites. Pretreating stormwater before it enters the constructed wetland will decrease maintenance needed to remove sediment that may eventually clog the wetland. Stormwater Management - - Extended biological and chemical treatment - - Evapotranspiration - - Sedimentation Additional - - Wildlife habitat - - Aesthetic quality Constructed wetlands are shallow, vegetated depressions with permanent standing water that offer a spectrum of ecosystem services to manage and treat stormwater. Constructed wetlands offer the many benefits of natural wetlands and marshes to provide a comprehensive stormwater BMP. Constructed wetlands aid in peak flow reduction, and provide conditions for sediment drop-out. Their high biodiversity of plants, animals, and microorganisms enhance evapotranspiration, filtration, and biological and chemical stormwater treatment. The natural aesthetic quality and high potential for habitat make constructed wetlands an excellent choice for educational opportunities. Benefits + + + - - Straining - - Filtration - - Peak flow reduction - - Improves air quality - - Educational opportunity Cost & Maintenance Considerations - - Cost: High - - Maintenance: Medium - - Soil may need to be replaced ever y 5-10 years due to buildup of contaminants - - Periodic removal of debris and trash -- Maintenance of vegetation to prevent undesirable species Construction & Site Considerations - - Applicable to large drainage areas - - High educational opportunity; good for school yards - - Safety challenges posed by standing water need to be considered and addressed - - Locate in full sun Contaminant Removal - - Suspended Solids - - Nutrients - - Heavy Metals Dutch Valley Elementary School Constructed Wetland Anderson County, TN Aesthetic Quality Native Vegetation Wildlife Habitat Reduced Stormwater Runoff Velocity Educational Opportunity Extended Biological Treatment Evapotranspiration Evap Filtration Sedimentation Straining Water T able 131 VEGETATED SWALE + Vegetated swales are often located along roads or parking lots or in other linear applications such as landscape buffers near property lines. Vegetated swales may contain dense native plantings, turf grasses, or a combination of both. Their effectiveness is directly correlated to their size and vegetation density, with larger, more densely vegetated swales providing higher degrees of treatment. 132 Amended soil and gravel may be necessary to increase infiltration rates in areas with poorly draining or compacted soils. Additionally, an underdrain and overflow device may be required to prevent stormwater runoff from entering adjacent areas during larger storms. Stormwater Management - - Extended biological treatment - - Evapotranspiration Additional - - Wildlife habitat - - Aesthetic quality Vegetated swales, also known as bioswales, are gently sloped, planted channels for treating and conveying stormwater. Vegetated swales convey stormwater away from infrastructure such as sidewalks, roadways, parking lots, and building foundations. They differ from conventional channeling systems as they combine conveyance with stormwater treatment. In contrast to concrete-lined swales and pipes that are impervious, costly to install and maintain, and convey water quickly, vegetated swales slow stormwater velocity, allow for evapotranspiration, and remove debris while enhancing sediment drop-out and infiltration. Benefits + + + - - Sedimentation - - Straining - - Improves air quality Cost & Maintenance Considerations - - Cost: Low to Medium Maintenance: Medium - - Reduces need for conventional stormwater infrastructure - - Maintain vegetation and soil stability - - Inspect inlet/outlet for blockages such as plant debris/litter after storm events Construction & Site Considerations - - Locate at least 2 feet above groundwater table - - Ideal for sites with less than a 1-2% slope Contaminant Removal - - Suspended Solids - - Heavy Metals Richard H. Fulton Complex Parking Lot Nashville, TN Outlet Outlet Structure Structure Sheet SheetFlow Flow Extended Extended Biological BiologicalTreatment Treatment Sheet SheetFlow Flow Sedimentation Sedimentation Straining Straining Evapotranspiration Evapotranspiration Inltration Inltration Aggregate AggregateBase Base FilFtiletrerF F abarbicric Bioretention BioretentionSoil SoilMix Mix abarbicric FilFtiletrerF F 133 SAND FILTER Sand filters, below ground or at grade, are used to treat the first flush of stormwater runoff, especially from contaminant hot spots. Surface sand filters are primarily used to treat stormwater from contaminant hot spots, such as gas stations. Stormwater enters a forebay or filter strip where sediment drops out and runoff energy is dissipated. It is then distributed over a sand bed where nutrients, heavy metals, and hydrocarbons are captured in the sand on biofilm, a naturally occurring matrix of microorganisms that facilitate the biochemical breakdown of contaminants. An impervious liner may be utilized to prevent groundwater contamination. Underground sand filters (multi-chambered vaults often constructed of concrete) are suitable for dense urban conditions where detention and first flush treatment is desired. Underground sand filters utilize a pretreatment chamber that allows sediment to drop out. Stormwater then overflows into a sand-filled chamber where it is filtered before entering an outflow pipe. 134 Both types of sand filters are primarily designed for water quality enhancement; volume control is a secondary benefit. Regular maintenance to remove sediment and contaminated sand is necessary for both types of sand filters. + + + + Benefits Stormwater Management - - Extended biological treatment - - Sedimentation - - Filtration Cost & Maintenance Considerations - - Cost: Medium (Surface) to High (Underground) - - Maintenance: Medium to High - - Inspect at least once a month, or after large storm events - - Special disposal method may be required in cases of severe contamination Construction & Site Considerations - - Size: Approximately 2-3% of drainage area - - May require forebay in areas of high sediment runoff - - Vehicles should not drive on top of underground facilities - - Provide access to the devices for inspection/ maintenance Stormwater Management Characteristics - - Suspended Solids - - Nutrients - - Heavy Metals - - Hydrocarbons Knoxville Gas Station Surface Sand Filter Knoxville, TN HM HC HC HC HM HM Concentrated Contaminated Runoff from Hot Spot P Curb Cut HM HC HC Contam HM inated N P Runoff Filtration t en m t a Tre N lm Bio Underdrain (may be tted with an emergency shut-off valve to contain contaminant spills) Geotextile Fabric Optional Im pervious Liner for U se at Hot Spots 135 FILTER STRIP + Benefits Stormwater Management - - Sedimentation - - Filtration Additional - - Wildlife habitat Filter strips utilize gently sloping areas and vegetation to reduce stormwater velocity and allow suspended solids to drop out of stormwater runoff. Filter strips employ wide areas of dense, native vegetation to slow stormwater, allowing for sediment drop-out, filtration, and debris removal before runoff enters receiving waters. They are often designed to attenuate water from specific impervious surfaces, such as parking lots, roads, or roofs. They may also be used in riparian areas to protect streams from high-velocity or high-temperature runoff. Ideally, a filter strip should be equal in size to the impervious area it serves, making this BMP appropriate for large, open sites, such as along greenway corridors. However, smaller strips of lawn or plantings maybe used to slow runoff before it enters another BMP, such as a vegetated swale, or flows across permeable pavement. Filter strips utilizing native vegetation are mowed less often than traditional lawns, so converting a space from conventional turf to a native filter strip reduces maintenance. Filter stripsâ€™ low maintenance requirements make them one of the least expensive types of stormwater runoff mitigation. 136 + + + - - Straining - - Provides additional per vious surfaces Cost & Maintenance Considerations - - Cost: Low - - Maintenance: Low - - Mow only in late winter, frequent moving reduces effectiveness - - Stable groundcover must be maintained to ensure proper functioning of filter strip - - Occasional soil aeration may be required Construction & Site Considerations - - Size: 50-100% of drainage area - - Drainage area not to exceed 150 linear feet - - 50% maximum slope - - Not applicable to high-density sites due to high square-footage required Contaminant Removal - - Suspended Solids - - Nutrients (Incidental) - - Heavy Metals (Incidental) - - Litter Campbell Station Park and Greenway Farragut, TN Sheet Conventional Lawn Frequent Mowing Native Groundcover Filtration Straining Sedimentation Flow Infrequent Mowing Amended Topsoil 137 structural bmp function/benefit summary endnotes 71, 72 Stormwater Quantity Functions Retention Inltration Detention Evapotranspiration Sedimentation Stormwater Quality Functions Hydrologic Functions Primar y Function Secondar y Function Incidental Additional Benet Filtration Straining Extended Treatment (Chemical) Extended Treatment (Biological) Additional Benets Provides Wildlife Habitat 138 Aesthetic Quality Stores Runoff for Alternative Use Provides Additional Pervious Surfaces Improves Air Quality Provides Educational Opportunities Peak Flow Reduction Runoff Reduction Rain Garden Rainwater Harvesting Residential Permeable Paving Vegetated Roof Tree Box Bioretention Cell Rainwater Harvesting Commercial Inltration Structure Vegetated Detention Basin Wet Pond Improved Water Quality Biological Treatment Physical Filtration Constructed Vegetated Wetland Swale Sand Filter Filter Strip STRUCTURAL LID BMP FUNCTION AND BENEFIT SUMMARY The structural BMPs on the preceding pages are organized by their primary stormwater management outcome. This organization is reflected in the column groups of the summary matrix on the facing page. Quantity and quality hydrologic functions of each BMP are identified in the top row group as primary, secondary, or incidental, and additional benefits are indicated in the bottom row group. SUMMARY OF STRUCTURAL LID BMP FUNCTIONS BMPs in the left column group primarily focus on runoff reduction though retention and infiltration. BMPs in this group are also capable of treating stormwater quality through sedimentation and filtration while some facilitate biological treatment. The middle column group contains BMPs that focus on mitigating stormwater quantity though peak flow reduction. This group incidentally addresses stormwater quality concerns by enabling sedimentation and biological treatment. The primary focus of BMPs in the right column group is to improve water quality. This is accomplished through extended treatment and physical filtration. The biological treatment category provides the widest array of water quality functions while also mitigating stormwater quantity through runoff reduction and evapotranspiration. BMPs in the physical filtration category provide some water quantity and runoff reduction, but primarily facilitate contaminant and debris removal. Full definitions of water quantity and quality functions can be found in the glossary. As seen in the summary matrix, most BMPs are multifunctional but tend to primarily address either water quantity or quality concerns. Therefore, to address the dynamic stormwater quantity and quality challenges that present themselves within a single site, it is important to utilize multiple BMPs in series as part of a treatment train (see p159). ADDITIONAL BENEFITS OF LID BMPS While enhancing the hydrologic function of developed sites, structural LID BMPs also provide many additional social and environmental benefits. In urban areas, they enhance aesthetic quality and human comfort levels with temperature-regulating vegetation and shade-providing, air-purifying trees. Some BMPs provide or restore habitat for species that have been pushed out of developed areas. Many BMPs also reduce utility costs by storing water for reuse or providing ambient cooling and added insulation that may reduce heating and cooling demand. Finally, LID BMPs can ser ve as interpretive features that educate and inspire stewardship of the regionâ€™s shared water resources. SPECIALIZED BMP CATEGORIES AND NON-STRUCTURAL BMPS The following pages describe specialized structural BMPs that are commonly used on construction and agricultural sites, as well as non-structural behavior changes that serve to avoid, minimize, and manage stormwater impacts to shared water resources. 139 CONSTRUCTION SITE BMPS Sedimentation is one of the leading causes of water quality impairment in Tennessee. According to the stateâ€™s 2010 report on water quality, sediment impaired 21 percent of assessed stream miles in Tennessee. 73 Much of that sediment originated from construction sites. Erosion prevention and sediment control on construction sites is a priority, and there are state-wide programs working to improve this issue. BMPs used to reduce sediment pollution from construction sites are: 74 Soil Stabilization: Re-stabilize soils soon after a disturbance using mulch, seed and straw, or sod. Stockpile Protection: Cover or surround stockpiles of soil with silt fences installed during construction. Limit Disturbance Time: Minimize the amount of time that destabilized soil is exposed to erosive storm events. Erosion Control Blankets: Various mesh products may be installed on sites that are steeply sloped or that are near a waterbody to limit the soilâ€™s direct exposure to runoff until the area becomes re-vegetated. 140 Check Dams: Obstructions located within a swale or other water conveyance channels that prevent erosion by detaining runoff, enabling sediment fall out and incidental infiltration. Silt Fences: Fine-grained synthetic mesh fences allow stormwater runoff to pass through while filtering suspended sediment and debris. Installed parallel to the topography to intercept sheet flow, silt fences are fundamental to containing sediment within a site. Sediment Basins: Depressions that collect and fill with construction site runoff during a storm event, allowing sediment to settle while the water is gradually released through a specially designed outlet. Inlet Protection and Filtration: Devices such as silt drain covers and wattles filter sediment and other debris from stormwater before entering storm sewer inlets. Riparian Buffer : A riparian buffer is a preser ved or restored corridor of vegetation that keeps sediment and other contaminants out of waterbodies, as well as decreases runoff temperature and velocity. Contractors, developers, and site design professionals may take TN Erosion Prevention and Sediment Control Training, which explains how to implement these and other measures effectively. More information on training opportunities can be found in the Resources section of Part IV. Construction Site in the First Creek Watershed Knoxville, TN Riparian Buffer Riparian Buffer Silt Fence Silt Fence Stockpile Protection Stockpile Protection Check Dams Check Dams Storm Drain Cover Storm Drain Cover Slope Protection Slope Protection Wattle Wattle 141 AGRICULTURAL BMPS Another primary source of sedimentation that contributes to the impairment of the regionâ€™s water resources is agricultural activity: livestock, agronomic crop production, and forestry operations. The agricultural sector has developed and implemented methods that reduce the amount of sediment entering waterbodies. Continued attention to these challenges and the application of BMPs can further reduce water resource impacts. Agricultural operations also contribute significant amounts of nitrogen and phosphorus containing compounds and pathogenic contaminants to shared water resources. Examples of BMPs for agricultural land uses include: No-Till Crop Farming: No-till methods decrease the amount of soil disturbance caused by tilling. This practice keeps the soil surface stabilized throughout the dormant and early parts of the growing cycles when soil is otherwise especially vulnerable to erosion. Fertilizer Application Schedule: Careful timing of fertilizer application increases the likelihood that fertilizer is not washed into receiving waters. 142 Stream Crossing: Livestock activity near waterbodies affects bank stability and introduces pathogens from animal waste. Restricting animalsâ€™ access to designated areas with stabilized soils separate from the main flow channel can reduce this negative impact. Riparian Buffers: A riparian buffer is a preserved or restored corridor of vegetation that keeps sediment and other contaminants out of waterbodies, as well as to decrease runoff temperature and velocity. Heavy-Use Area Delineation: Heavy-use areas in livestock and forestry operations are parts of a site where machinery and/or livestock activity, such as feeding, is concentrated. Activities in these areas typically destabilize soil and produce sediment and pathogenladen runoff. It is useful to reinforce these areas with gravel or other materials to prevent erosion. Runoff from these areas may be treated with structural BMPs such as a constructed wetland. Alternative Watering Devices: A BMP for livestock farms, alternative watering devices are above-ground tanks or cisterns that provide water for animals. These devices eliminate the need for animals to enter a pond or stream to drink, reducing bank destabilization, erosion, and pathogen contamination. There are many existing programs and incentives to improve stormwater quality runoff from agricultural sites. Soil and Water Conservation District offices can provide the latest information on water quality measures for those in the agricultural industry. More information on training and regulations can be found in the Resources section of Part IV. Anderson County Farmstead Anderson County, TN Heavy HeavyUse UseArea Area Delineation Delineationand and Constructed ConstructedWetland Wetland Alternate AlternateWatering WateringDevice Device No-till No-tillCrop CropFarming Farming Stream StreamCrossing Crossing Fertilizer FertilizerApplication Application Schedule Schedule Riparian RiparianBuffer Buffer 143 NON-STRUCTURAL BMPS While many LID BMPs are physical structures, such as basins, vaults, and swales, there are also non-structural, or behavioral, LID BMPs. Behavioral LID BMPs include daily behaviors and activities that can be adopted and implemented by anyone. As discussed at the end of Chapter 3, small actions, such as residential fertilizer application, undertaken by individuals across the scale of a watershed can aggregate into widespread water resource threats. Likewise, if behaviors are adopted by many across the same scale, meaningful progress towards the stewardship and efficient use of shared water resources can be realized. Behavioral LID BMPs address water resource challenges proactively rather than reactively. As an example, it is easier and less costly for individuals to properly apply, store, and dispose of excess household chemicals, such as residential fertilizers, paints, and hydrocarbons, than it is to reverse the aggregate impact these contaminants have on the health of the regionâ€™s shared water resources. Other common examples of behavioral LID BMPs include: Proper Hazardous Waste Disposal: Contact local jurisdictions for information on household hazardous waste collection centers. 144 Pet Waste Disposal: Collect and properly discard domestic animal waste by proper methods such as composting. Proper Automobile Maintenance: Prevent leaking fluids through proper maintenance and properly dispose of used fluids. Wash vehicles over pervious surfaces such as lawn or gravel areas to prevent contaminated water from flowing into storm sewer systems. Integrated Pest Management: Utilize non-chemically based methods used to manage landscape pests and diseases, such as mechanical removal of pests or introducing non-invasive predator species. Native Plants: Native plants have adapted to thrive in the regionâ€™s climatic and soil conditions, lowering or eliminating their dependency on chemical fertilizers, pesticides, and supplemental irrigation. Downspout Disconnection: Downspouts can be disconnected from underground drainage pipes and allowed to drain onto pervious landscape areas such planting beds, lawns, and rain gardens, or into rain barrels. Downspouts that drain onto impervious surfaces, such as driveways, that subsequently convey stormwater to roads and ultimately storm sewers may also be redirected toward pervious landscape areas or rain gardens. Many water resource-oriented advocacy groups offer workshops and information about pollution prevention strategies. Information on local advocacy groups can be found in the Resources section of Part IV. 145 146 Chapter 8 LID BMPs:: SELECTION, LOCATION, and Challenges Ever y site, both developed and undeveloped and regardless of its size, has a unique hydrologic regime and context. Soil, climate, and geologic conditions, existing vegetation, imper vious surfaces, topography, and existing infrastructure both within and surrounding a project shape its hydrologic characteristics. The beginning of any watershed planning, community design, or site development project should include a thorough inventor y and analysis of these and other conditions within and surrounding a project area. Such diligence allows site design and engineering professionals to characterize the pre-development movement of surface and groundwater within a site and select LID BMPs best suited to manage post-development hydrology within the economic and regulator y challenges that face a given project. 147 UNIQUE CONDITIONS, UNIQUE SOLUTIONS SITE AND CONTEXTUAL CONDITIONS Working collaboratively, site engineers, landscape architects, and other site design professionals select and integrate BMPs as part of a holistic planning and design process. Selecting a BMP because it fits within the physical constraints of a site or because it is included on a list of municipally-acceptable practices does not ensure that the resultant management system will effectively address the quantity and quality of stormwater runoff generated within a given site. Site and contextual conditions that may affect the selection of appropriate BMPs, variations on their construction details, and construction material specifications include 1) site topography and slope, 2) existing soil characteristics, 3) subsurface hydrology, and 4) proximity to existing structures. The selection of appropriate LID BMPs is influenced by many factors, including 1) existing physical conditions of the site and its context, 2) post-development site hydrology, and 3) project goals and client mission. Economics, regulations, and maintenance considerations are common challenges to LID that also affect BMP selection. Factors affecting a site’s stormwater management approach are not limited to those identified in this publication. The ultimate selection, design, and integration of LID BMPs should be done in consultation with an engineer, landscape architect, or other qualified site design professional, regardless of the project’s size or complexity. 148 The following is a summar y of common factors that inform LID BMP selection for new construction and retrofit projects using an impact avoidance, minimization, and management approach. TOPOGRAPHY AND SLOPE In East Tennessee, topography affords multiple challenges to the implementation of LID stormwater BMPs. The topography of a site creates “microwatersheds,” or catchment areas within which runoff drains, often rapidly, to a common point or outlet. Additionally, the topography surrounding a site may direct runoff from adjacent landscapes and development onto or even through a project site. Most surface BMPs seek to slow stormwater runoff as it moves through a site, allowing suspended contaminants to settle while promoting infiltration. Steep slopes typical to East Tennessee accelerate stormwater runoff, decrease the time of runoff concentration, and increase erosion. These slopes commonly prohibit traditional expansive detention areas, placing higher importance on stormwater runoff volume reduction and decentralized retention practices. To overcome topographic challenges, rain gardens, bioswales, and other bioretention features may be terraced or subdivided using checkdams to create a sequence of multiple retention areas. The rain gardens shown below, in Norris, TN, demonstrates this terracing approach. Sites with slopes exceeding five percent seeking to use permeable pavement may require additional design consideration for grading of the soil subgrade and underdrain locations. Terracing the paved areas may also enable gentler slopes. Additionally, groundcover plantings on sloped sites should utilize plants known for their deep Terraced Rain Garden Norris, TN rooting capabilities, such as native meadow grasses and shrubs, to stabilize steep slopes and prevent erosion. Due to the regionâ€™s dramatic topography, it is not uncommon for runoff generated from sites up-slope to flow into and pass through a project site. This holds true for both rural and urbanized landscapes. Site design professionals should inventory the origins and the potential quantity and quality of stormwater entering a project area from off-site sources when considering opportunities for stormwater management. An appropriate site stormwater management plan will also prevent stormwater runoff generated on the project site from flowing downslope to adjacent properties. As examples, bioretention cells are commonly used along streetscapes to manage contaminated water volumes from off-site road infrastructure, while constructed wetlands have been integrated into municipal parks to manage the quantity and quality challenges posed by off-site runoff from the broader watershed. Such wetlands are an example of green infrastructure being used as part of a watershed management plan, and LID practices being integrated into green infrastructure features. This is demonstrated by the constructed wetland at Renaissance Park in Chattanooga, TN, shown on the following page, where topography directs runoff from a 470 acre offsite catchment area to the project site (see p171). 149 SOIL CHARACTERISTICS Soil characteristics should be inventoried as part of the BMP selection and design process. An understanding of soil texture - its composition of clay, silt, and sand particles - and soil structure - its tendencies to bind together - affect a soil’s capacity to infiltrate stormwater, enable biological treatment processes, and support healthy plant materials. Soil characteristics vary within the region, and often vary across a site. The volume of water that a soil is capable of absorbing over a period of time is known as its infiltration rate. Soils should have an infiltration rate of at least one-half inch per hour in order for LID BMPs to effectively infiltrate stormwater,75 Stormwater retained by BMP facilities should infiltrate within 24-48 hours after a storm event,76 thus avoiding prolonged ponding that may otherwise enable breeding of unwanted pests, such as mosquitos, or inhibit biological treatment processes. Soils near or below this infiltration rate threshold may be amended, and BMP construction details may include strategies to increase infiltration rates. On sites with low infiltration rates, project designers may wish to consider alternative runoff reduction and retention methods, such as pervious paving and rainwater harvesting. Maintaining high soil infiltration rates to provide for natural hydrologic processes further heightens the importance of conserving porous native top soils and establishing limits of construction to minimize soil compaction. SUBSURFACE HYDROLOGY An inventory and analysis of a site’s subsurface hydrology should examine groundwater levels, depth to bedrock, and proximity to karst features such as seeps, fissures, springs, and caverns. Each of these characteristics effects groundwater resources’ vulnerability to potential contamination from surface stormwater or infiltrated runoff. 150 Renaissance Park Constructed Wetland Chattanooga, TN A four feet (4’) minimum depth to bedrock and groundwater is recommended to enable adequate levels of treatment to infiltrating stormwater runoff and to avoid adverse affects to the soil’s stability. 77 On sites with proximity to karst openings and where groundwater is relied upon for consumptive uses, BMPs capable of pretreating stormwater prior to infiltration should be used. Such BMPs include constructed wetlands, rain gardens, extended bioretention basins, bioswales and other vegetated BMPs that enable the biological and chemical processes necessary to remove contaminants from infiltrating stormwater. An emphasis on BMPs capable of treating stormwater contamination is also placed on sites with groundwater wells, though infiltrating BMPs should not be located within one hundred and fifty feet (150’) of the well itself. 78 POST-DEVELOPMENT HYDROLOGY EXISTING STRUCTURES As discussed in Chapter 3, different types of land uses common throughout the PlanET Region have different functional requirements and varying percentages of impervious cover, resulting in different rates of stormwater runoff during a storm event (see p54). Varying Existing site structures, especially those with basements, require consideration when selecting and locating BMPs to avoid foundation disruption and water intrusion. When considering BMPs, it is recommended that infiltration BMPs be located no closer than five feet (5’) to a building foundation when on the downhill side, and no closer than fifty feet (50’) when on the uphill side. These recommended setbacks are increased to ten feet (10’) and one hundred feet (100’), respectively, when proximate to structures with a basement. 79 These setbacks may not be feasible in densely populated areas such as central business districts, emphasizing the need for alternative runoff reduction methods. Additional measures such as liners and protective coatings may also help prevent water intrusion and protect the structural integrity of a building’s foundation in urbanized locations. The quantity and quality of stormwater generated by postdevelopment site surfaces and human activities inform BMP selection. On new construction projects, the existing and proposed hydrology is studied, and LID BMPs that meet project goals and resolve anticipated stormwater challenges are evaluated, throughout the design process. For retrofit projects, the existing hydrologic characteristics and issues of a site are observed in action by the design team. Vegetated Roof at The Pinnacle, Nashville, TN 151 152 runoff rates and the type of impervious surfaces affect runoff quantity and the amount of site area that is available for LID BMP implementation, further informing BMP selection. the same site may collect runoff from landscaped areas that are regularly fertilized and irrigated, potentially making another BMP a more appropriate choice. Projects on low density suburban sites may have the land area necessary to build a single vegetated detention basin to satisfy stormwater management regulations. However, projects in higher density areas, such as downtowns or mixed-use redevelopment projects with high rates of impervious surfaces, may not have the site area available to commit to such land-intensive stormwater management methods. Instead, these projects first seek to minimize stormwater runoff using cisterns, vegetated roofs, tree canopy, and pervious pavements, and manage remaining runoff in smaller distributed basins or underground facilities. This stormwater runoff reduction and distributed management approach informed the implementation of a green roof and surrounding pervious pavement at the Pinnacle Tower in downtown Nashville, shown on the previous page, and the use of pervious pavement, tree canopy, and tree boxes at the Neyland Stadium Gate 21 renovation, shown at right. On regulated projects, site professionals calculate runoff volume, its rate of concentration, required retention volume, and allowable discharge rates stipulated by effective regulations. This information affects BMP selection and sizing. It may be possible that distributed LID BMPs alone are insufficient to completely manage stipulated runoff volumes, especially from infrequent high-volume storm events such as tropical depressions and stationary fronts. In such cases, a hybrid system that uses LID BMPs to manage first flush runoff and conventional practices to manage overflow may be necessary. Activities on a site affecting stormwater quality also drive the LID BMP selection processes. A site catchment area that contains hot spots, such as a parking lot, would suggest that a BMP suited for hydrocarbon contaminant removal be implemented. A separate catchment area on Neyland Stadium Gate 21 Plaza Knoxville, TN PROJECT GOALS AND CLIENT MISSION Project goals and the organizational mission of a property owner may also affect BMP selection. Some projects place a higher priority on LID BMPs that may not be the most cost-effective way to manage stormwater, but satisfy building and landscape performance goals or a property owner ’s desire to make a statement about their position on environmental stewardship through the design of their site and facilities. Vegetated roofs, for example, are also commonly used for their insulation, heat island reduction, habitat creation, and energy efficiency values in addition to runoff reduction potential. Vegetated Roof at HPUD Headquarters Knoxville, TN Clients may also wish to have their environmental stewardship and green building initiatives recognized by third parties such as the U.S. Green Building Council’s LEED rating system or the American Society of Landscape Architects’ Sustainable Sites Initiative. Both systems award points that contribute to prestigious certifications for the implementation of Low Impact Development planning, design, construction, and operation practices. Whether or not a project pursues third party certification, it may have a goal of becoming a showcase that demonstrates a wide range or focused selection of LID BMPs for educational purposes. Education and demonstration of leadership in environmental stewardship may be fundamental to a property owner ’s organizational mission. Such is the case at the Hallsdale Powell Utility District (HPUD) Headquarters, which features an array of BMPs as a demonstration for visiting customers and school groups (see p163). This project even includes a special viewing platform from which visitors can easily see the vegetated roof from the Headquarters’ lobby, shown at left. The University of Tennessee College of Architecture and Design’s New Norris House took the mission of demonstration and education one step further to also include evaluative research on the performance of rainwater harvesting and reuse systems intended to reduce inhome use of municipal water supply (see p161). 153 CHALLENGES TO LID IMPLEMENTATION Municipal stormwater management regulations, real and perceived implementation costs, and maintenance considerations factor into BMP selection across scales. Each is frequently-cited as a challenge to the LID approach becoming standard practice in watershed planning, community design, and site development in the PlanET Region. STORMWATER REGULATIONS A common impediment affecting the widespread implementation of LID BMPs is their acceptance by stormwater regulators and building officials in a projectâ€™s jurisdiction. Some jurisdictions have overcome this challenge by updating their stormwater management code to recognize LID BMPs as acceptable methods to reduce runoff volume or peak flow rate. Local municipalities should look to these communities and consider updating their own codes so as to avoid potentially discouraging LID water resource stewardship practices, prolonging permit application timelines, or prohibiting the implementation of common high-performance building practices. 154 For example, the incentive to harvest rainwater at commercial and residential scales is diminished if its reuse (for waste conveyance, laundry, or other uses compatible with non-potable water) is prohibited. This is becoming less of a challenge as pilot projects such as the New Norris House in Norris, TN, test rainwater harvesting and treatment technologies, and as additional case studies documenting LID BMP effectiveness, safety, and long-term performance become available. If LID BMPs, such as rainwater harvesting, vegetated roofs, and permeable pavement, were accepted as methods to reduce runoff or peak flow rate, their use could reduce the required size of additional stormwater management facilities on a site. In rural and suburban settings, such a reduction could allow the site area that would otherwise be needed for manage stormwater to be reprogrammed as open space or buildable area. Either may add value to that site. Similarly, projects in urban areas seeking to balance stormwater management requirements against higher land use intensities, dense lot coverage The New Norris House harvests and treats rainwater for waste conveyance, laundry, and irrigation rates, and economic return objectives would also benefit from a list of acceptable BMPs that include space-efficient LID practices. STORMWATER ECONOMICS Government officials, site design and engineering professionals, developers, and property owners considering the LID approach should understand how the economics of LID compare to conventional development and stormwater management approaches. The costs and benefits of the LID approach should be considered over its entire lifecycle, from planning through design, installation, operation and maintenance, and decommissioning. An extensive body of research that investigates the economics of implementing LID across watershed, community, and site scales relative to conventional hard engineering practices has been developed and continues to grow. With few exceptions, this research reveals that LID generally costs less than conventional stormwater management practices when life-cycle costs are taken into account. Links to a selection of these studies are included in the References section of Part IV. ECONOMICS AT THE WATERSHED SCALE In existing communities, stormwater management infrastructure undergoes routine maintenance and periodically need to be expanded to handle additional runoff from new development. To maintain infrastructure concurrency and meet NPDES requirements, communities may continue to spend capital resources on extending the reach and increasing the capacity of existing conventional infrastructure, or to invest in the LID approach. An increasing number of major municipalities, including Nashville and Chattanooga, TN, and Philadelphia, PA, 80 have made green infrastructure and other LID impact avoidance, minimization, and management practices a significant component of their growth management plan and NPDES compliance strategy. In Philadelphia, 81 both conventional and LID approaches were estimated to cost in the billions of dollars, but the green infrastructure approach also afforded public recreational amenities, potential increases to property values, and enhanced air quality: value-added benefits that buried pipes and tunnels could not offer. 82 This redirection of public improvement funds away from buried pipes and culverts towards multifunctional civic amenities and widespread implementation of LID BMPs was recently adopted at the scale of multiple watersheds by the City of Philadelphia as part of its “Green City, Clean Waters” initiative. This plan is also part of the city’s strategy to satisfy NPDES permit requirements (see p176). 155 LID methods that manage stormwater impacts at their source may also “buy back” capacity in existing storm sewer systems. The capacity of existing stormwater infrastructure remains constant while the developed area drained by this infrastructure continues to grow. By retrofitting existing developments and communities with LID and green infrastructure practices, and incorporating the same approach into new development projects, the volume of runoff draining to existing infrastructure can be reduced. Communities that utilize the LID approach may defer or eliminate the need to increase the capacity of existing stormwater infrastructure or to extend it in newly developed areas. Similarly, managing stormwater quality impacts at their source with LID BMPs or preventing them in the first place through behavior changes also offer economic efficiencies. When adopted across entire watersheds, such strategies may prevent widespread contamination, water resource impairment, and the need for costly cleanup and restoration initiatives. ECONOMICS AT THE COMMUNITY SCALE 156 Developers are also recognizing the cost efficiencies and value added benefits of using the LID approach for large-scale community and site development. Master planning projects that implement an LID approach have been shown to realize significant cost savings, ranging from thousands to millions of dollars, depending on the scale of the project. The LID neighborhood development proposal shown in Chapter 6 employs an impact minimization approach that allows for a compact development envelope, requiring less pavement and maintaining 50 percent of the site in its pre-development condition. When compared to a development plan that uses a conventional design approach and an end-of-pipe stormwater management system, the LID concept’s required pavement was $1.4 million less expensive and its stormwater management infrastructure saved the developer over $200,000 (see p101). Both concepts yielded the same number of residential units. Access to shared open space resulting from LID practices, as well as adjacency to green infrastructure networks, provide amenities and lifestyle benefits that can increase a property’s marketability and value. 83 ECONOMICS AT THE SITE SCALE At the site scale, BMPs should be selected that achieve a project’s stormwater management strategy in a cost-effective manner. Retention and detention basins are typically the most cost-effective BMP, meaning that they manage the most runoff volume relative to their installation cost. However, not all sites have the available land area needed for the implementation of basins. Projects in dense urban areas may need to rely on less land-intensive but more expensive runoff reduction and retention methods, such as permeable pavements, vegetated roofs, and rainwater harvesting cisterns. ECONOMIC INCENTIVES Governments and agencies seeking effective means to encourage the implementation of LID in local communities may consider offering economic incentives. Around the country and across Tennessee, communities, developers, and homeowners alike are taking advantage of incentive programs offered at the federal, state, and local levels to fund green infrastructure feasibility studies, enhance returns on investment, and reduce costs for LID projects. These programs include development incentives such as density and intensity bonuses, accelerated permitting, stormwater fee credits, 84 rebates, and grant program eligibility. 85 One such initiative is TDECâ€™s Green Development Grant Program through which local governments may apply for grants up to $30,000 to support the implementation of green infrastructure and low impact development practices in their community. 86 For residents of the PlanET Region, rain garden and rain water harvesting workshops are offered by water resource advocacy groups, extension services, and other non-profit organizations. These initiatives play an important role in the adoption of LID BMPs capable of preventing surface and groundwater pollution. PlanET communities may also look to rainwater harvesting rebate programs such as those in Austin, TX, and Chicago, IL, that incentivize homeowners to reduce the quantity of runoff leaving their properties. 87 Governments and agencies in Tennessee and the PlanET Region should be motivated to provide such incentive programs, as the widespread implementation of LID practices may reduce the need for costly infrastructure improvement projects and restoration initiatives, as well as offering a path towards NPDES compliance. MAINTENANCE An additional economic consideration that affects LID BMP selection and widespread green infrastructure implementation is the cost of maintenance. Proper maintenance is critical to an LID facilityâ€™s and green infrastructure practiceâ€™s enduring ability to perform hydrologic functions and to enhance site aesthetics. Tasks commonly required to maintain each LID BMP are identified in the profiles in Chapter 7. These maintenance activities have associated costs for labor, equipment, and materials comparable to those necessary to maintain similar landscape features and amenities. End-of-pipe systems and existing stormwater infrastructure also require routine maintenance, as well as periodic expansion. Maintenance programs for conventional stormwater management practices and infrastructure expansions cost developers and municipalities a significant amount of financial capital on an annual basis. 157 SUMMARY OF THE LID APPROACH Low Impact Development (LID) is an enhanced approach to planning, design, and development that avoids, minimizes, and manages impacts to the PlanET Regionâ€™s shared surface and groundwater resources. Inspired by natural hydrologic processes, LID addresses threats to water resources through an interconnected network of decentralized BMPs and green infrastructure practices. LID principles may be applied to new development, the retrofit of existing communities, sites, and infrastructure, as well as to common activities on individual properties. Exercising these principles and stewarding water resources is a responsibility shared by everyone who lives, works, and recreates within the PlanET Region. The LID approach avoids impacts to undeveloped landscapes and watershed hydrology through pollution prevention, the efficient use of water resources, and the preservation of undeveloped land and sensitive landscapes. Strategies such as infill development redirects growth to underutilized sites in existing communities and avoids disturbances to landscapes that protect valuable water resources. 158 New construction and retrofit projects that minimize impacts by limiting the amount of land area developed, reducing disturbance to vegetation and soil, and decreasing the amount of impervious surfaces can reduce the need for and size of stormwater management systems. LID manages stormwater quantity and quality at its source through decentralized, distributed BMPs and green infrastructure practices that reintroduce natural hydrologic functions and biological processes into developed landscapes. These methods are capable of reducing runoff, controlling peak flow rates, and improving stormwater quality before it is discharged to receiving waters or infiltrated into groundwater supplies. They are also capable of enhancing site aesthetics, improving air quality, creating wildlife habitat, and providing interpretive educational opportunities. Watersheds, communities, and project sites in the region have unique site and contextual conditions that affect the strategic selection, sequencing, and placement of management practices by planning, design, and engineering professionals. A projectâ€™s management strategy is further influenced by anticipated post-development hydrologic conditions, its stewardship goals, and client mission. Regulations that do not recognize the stormwater management capabilities or resource efficiency potential of LID methods pose challenges to its widespread implementation, as do the real and perceived costs of their implementation and maintenance. A growing body of research, innovative pilot projects, and municipal initiatives should be looked upon to overcome these challenges and enable the widespread implementation of LID in the PlanET Region. the LID approach ACROSS PLANNING, DESIGN, AND DEVELOPMENT SCALES, LOW IMPACT DEVELOPMENT SEEKS TO... WHEN IMPACTS ARE UNAVOIDABLE, MINIMIZE DISTURBANCE TO LANDSCAPES AND HYDROLOGY Prevent water pollution Use water resources efficiently Promote infill development Preserve undeveloped land and sensitive landscapes Connect green infrastructure Limit land area developed Reduce vegetation and soil disturbance Limit impervious surfaces Reduce need for and size of stormwater management systems LANDSCAPES AND WATERSHED HYDROLOGY MANAGE STORMWATER RUNOFF QUANTITY AND QUALITY Address impacts at their source Decentralized, distributed management Biological treatment Reduce runoff, control peak flow rate, and improve runoff quality Reintroduce natural hydrologic processes minimize cluster development natural hydrologic processes green infrastructure address at the source biological treatment increase density impervious surfaces infill build vertical AVOID IMPACTS TO UNDEVELOPED decentralized management resource efficiency 159 160 Chapter 9 Treatment Trains, Integrated design, and green infrastructure planning: LID BMP facilities are the fundamental building blocks of an integrated site stormwater management strategy. Designing and implementing these facilities in-series as a comprehensive, holistic system, or treatment train, further enhances their potential to positively affect site hydrology and the health of receiving waters. Watershed, community, and site stormwater management strategies should include LID BMPs that are appropriate to existing site and contextual conditions, post-development hydrology, project goals, and project limitations. A single BMP may not address the entirety of the dynamic stormwater challenges that a particular site may pose. As the function matrix in Chapter Seven highlighted, a number of different and properly sequenced BMPs may be needed to effectively address the range of stormwater challenges posed by an individual site or across an entire watershed. Following are a series of professional projects and PlanET demonstration projects from the studios of the University of Tennessee Landscape Architecture Program. Organized to ascend in scale, the projects demonstrate a holistic approach to the selection, design, and integration of LID stormwater BMPs into the built environment. These projects also demonstrate that stormwater management practices do not need to be concealed underground or hidden at the back of a site as unsightly infrastructure. Individually, each project avoids, minimizes, and manages impacts to shared water resources while simultaneously creating aesthetically pleasing, multifunctional landscapes that ser ve as open space amenities and provide interpretive educational opportunities. Collectively, they represent a low impact approach to planning, design, and development capable of restoring and stewarding the PlanET Regionâ€™s shared water resources. 161 rainwater harvesting a. cistern collecting water from the roof, treated and used in the house b. cistern collecting overflow water directed to the rain gardens c. rain gardens sustainable site d. invasive plants replaced by native grass meadow e. drought tolerant native plants f. permeable parking court b a c d f e d 162 Greywater designates lightly soiled household water, like the used water from the shower, clothes washer and bathroom sink (every appliance besides the kitchen sink and the toilet). The collected water is used for watering plants in the greywater garden, reducing strain on the municipal sanitary system. NEW NORRIS HOUSE Norris, TN Design/Build/Evaluate Project by the University of Tennessee College of Architecture and Design Principal Investigators Tricia Stuth, Robert French The New Norris House (NNH) is an award-winning, university-led design|build|evaluate project located in Norris, TN. A LEED for Homes Platinum project, NNH pursues complementary performance and design intentions where water systems provide greater independence from the central grid. Design goals include: collecting, treating and reusing rainwater; infiltrating greywater on site; and managing 100 percent of stormwater runoff on the project site. a c Rainwater from the roof is collected and treated for use in the house, for toilet flushing and the clothes washing machine, and for exterior faucets. State certified laboratory results show that rainwater stored and treated at NNH is safe for human contact under EPA human health criteria. During the first year of evaluation, treated rainwater supplied nearly 10,000 gallons of safe water to the home. NNH team members worked closely with city, county, and state water quality officials to develop temporary permits to allow rainwater use within the home during a two-year evaluative residency. Additional stormwater management methods include on-site infiltration of untreated cistern-overflow rainwater and native grass meadows and terraced rain gardens that capture and infiltrate sheet flow on the steep site. Combined, these practices manage 100 percent of stormwater generated from on-site impervious surfaces. b d/e/f 163 164 HALLSDALE POWELL UTILITY DISTRICT HEADQUARTERS Knoxville, TN Professional Project by McCarty Holsaple McCarty, Penland Design, and McGill Associates Engineering Through collaboration with a multidisciplinar y consulting team, the Hallsdale Powell Utility District extended their own initiatives of promoting water resource stewardship and water conser vation into the planning, design, and operation of its headquarter campus. A stormwater management treatment train is integrated into the design of the headquarters building and surrounding site, taking advantage of multiple impact minimization and management opportunities. Permeable pavement and a green roof, in addition to a rainwater har vesting cistern fed by runoff from non-vegetated roof surfaces, minimize the amount of stormwater runoff to be managed. The cistern supplies the site irrigation system and doubles as a water feature, spilling overflow water into a vegetated swale. Stormwater runoff from other site imper vious surfaces, and overflow from the cistern, is detained, treated, and infiltrated using a series of distributed vegetated swales, extended detention basins, bioretention areas, and constructed wetlands. This comprehensive implementation of structural best management practices also provides educational opportunities such as a dedicated second level viewing platform overlooking vegetated roof areas and an interpretive display for the visiting public, including utility customers, employees, and school groups. 165 166 LIVING MARKET PLACE Knoxville, TN PlanET Demonstration Project by Phillip Zawarus University of Tennessee Landscape Architecture Program To many residents and visitors, Market Square is the heart of downtown Knoxville: a dynamic forum within which a multitude of different events, activities, and gatherings occur at any given time of day, day of the week, or season of the year. Respecting the squareâ€™s function as a gathering place and recognition of its heritage as a place of regional commerce informed this urban stormwater retrofit. Unable to rely on land-intensive stormwater basins due to a need for multi-functionality of spaces and the premium value of downtown real estate, this proposal manages runoff from a one-inch storm event by first minimizing runoff with green roofs on existing buildings, permeable pavements on ground surfaces, in addition to district rainwater harvesting. Rainwater is harvested by iconic features (left) that intercept precipitation and convey water to underground cisterns. This stored water is used to irrigate crops growing on these featuresâ€™ surfaces as well as other landscape areas in the square. This produce may then be sold at seasonal farmers markets. Providing shade and cooling ambient air temperature, the harvesters may be moved as required by a particular gathering. Harvested rainwater also supplies a redesigned water feature at the foot of the TVA towers that resembles a mountain stream. The remaining runoff is then treated by rain gardens that use plants native to East Tennessee. 167 tnemeganaM retawniar/retawmrotS 168 OAK RIDGE STORMWATER PLAZA Oak Ridge, TN PlanET Demonstration Project by Luke Murphree University of Tennessee Landscape Architecture Program An element of a larger vision plan for the redevelopment of 200 acres surrounding Oak Ridgeâ€™s Jackson Square, this urban plaza creates a social gathering space while showcasing LID stormwater BMPs and stormwater treatment through natural hydrologic processes. This proposal challenges preconceptions of stormwater management features as unsightly utilities concealed underground or at the back of a site. Here, stormwater management is integrated into the design of an urban plaza as an elegant water feature: an interactive site amenity affording opportunities for interpretation and watershed stewardship education. Stormwater runoff collected within the broader projectâ€™s catchment areas is first treated with ultra violet light, and then directed through decorative architectural channels to terraced treatment bogs. Here, strategically selected plant materials, soils, and microorganisms enable biological treatment processes capable of reducing nonpoint pollution levels in the runoff, including nutrients, heavy metals, and organic compounds. The treated water then cascades to lower collecting pools and is carried to a central channel below the terrace level. The water flows beneath decorative stainless steel grates before eventually emptying to a stormwater wetland park for further treatment and retention. 169 Frog Bowl, Meadow Park, and Wetland Section 170 Meadow Play Area View Wetland Boardwalk V View FOUNTAIN CITY SPONGE PARK Knoxville, TN PlanET Demonstration Project by Valerie Friedmann University of Tennessee Landscape Architecture Program The Fountain City Sponge Park proposal reconfigures an existing park program within a matrix of urban wildlife habitat and stormwater management. The design reworks the boundar y of an existing public park and small downtown in order to remediate the headwaters of the currently channelized First Creek corridor. The proposal also provide stormwater runoff storage to meet first flush requirements. By removing First Creek from a culvert and expanding the creek into a wetland sponge, the proposed conditions will hold approximately three million gallons of water. This storage capacity could hold the first one inch of rain from an 110-acre drainage area surrounding the park, satisfying the first flush requirement for an area ten times the size of the park. This image reveals the various habitats and program for the northern section of the park. The creekâ€™s headwater spring feeds the frog habitat pool, the meadow provides walking, playing, and educational space, and the wetland buffer cleans runoff from the Broadway corridor before it is allowed to mix with clean spring water downstream. 171 172 RENAISSANCE PARK Chattanooga, TN Professional Project by Hargreaves Associates Image by Hargreaves Associates Located across the Tennessee River from downtown Chattanooga, TN, Renaissance Park was designed and developed as an urban open space that ser ves as part of the cityâ€™s waterfront park system, restores a contaminated site, and treats polluted stormwater runoff. Previously the site of an industrial manufacturing factor y, Renaissance Park is now a vibrant part of the Chattanooga Waterfront. A central amenity of the park is a constructed wetland. The wetland treats first flush stormwater from an intermittent stream fed by a 470-acre subwatershed. Gabion structures planted with native riparian species filter non-point source pollutants from stormwater runoff as it meanders through the wetland, allowing additional contaminants to settle and be treated through biological processes. The treated stormwater is then released to the Tennessee River. The park also boasts playful landforms for children constructed of remediated soil from the wetlandâ€™s excavation, extensive trails and outdoor gathering spaces, in addition to interpretive signage and multimedia experiences that educates visitors about the role the park plays in the stewardship of shared water resources. 88 The park has also been credited with stimulating significant investment by developers on nearby properties. 173 LEGEND 1 1 2 3 4 Amphitheater History Museum The Esplanade Jackson Square • Farmers Market • Lavender Festival 5 Intermodal Transit Hub • Transit Station • Public Plaza • Pedestrian Tunnel • Bicycle Rental/Storage Facility • Zip Car Rental Facility 6 7 8 9 10 4 BROADWAY AVE 9 2 TENNESSEE AVE Wetland Park • Stormwater Collection and Filtration • Reflection Pond • Passive Recreation • Garden Club Botanical Garden Business Park Neighborhood Linear Park Community Park Intermittent Stream Corridor 3 10 7 5 6 8 174 8 JACKSON SQUARE VISION PLAN Oak Ridge, TN PlanET Demonstration Project by Luke Murphree and Justin Bruno University of Tennessee Landscape Architecture Program Leveraging the historic assets of Oak Ridge’s original town site and the city’s heritage of energy technology research, this redevelopment plan contemplates a new vision for the core of the city as a mixeduse, form-based town center. The plan promotes a dense, walkable, transit-oriented development pattern, a socially invigorated live/work/ play atmosphere, and a distinct sense of place evocative of the city’s past, present, and future and of the surrounding regional landscape. OAK RIDGE TURNPIKE Watershed stewardship and green infrastructure are at the core of the proposal’s guiding principles, simultaneously avoiding, minimizing, and managing hydrologic impacts with LID methods. By redeveloping a greyfield site, the proposal avoids impacts to more than 280 acres of undeveloped property had the proposed site program been developed at the suburban fringe using conventional development densities and intensities.89 Despite a net increase of one million squarefeet of commercial space, 900 new residential units, and associated parking, the proposal actually increases the site’s pervious open space by 57 percent. Coupled with a comprehensive application of green roofs, urban tree canopy, pervious pavement, and district rainwater harvesting, all intended to minimize runoff, the proposal manages remaining stormwater with decentralized structural BMPs throughout the site, including a wetland park and green streets with bioswale medians and bioretention cells. 175 Proposed Future Settlement Pattern Plan Source: Beaver Creek Watershed Green Infrastructure Plan 90 176 BEAVER CREEK WATERSHED GREEN INFRASTRUCTURE PLAN Knox County, TN Professional Project (Watershed Plan) by UT College of Architecture and Design PlanET Demonstration Project by Luke Murphree, UT Landscape Architecture Images by UT College of Architecture and Design, Luke Murphree Prepared for the Beaver Creek Task Force (BCTF) in 2004 by faculty from the University of Tennessee College of Architecture and Design, the Beaver Creek Watershed Green Infrastructure Plan is an example of multiscalar LID planning at the scope of a watershed. Beaver Creek, an impaired stream, is a tributary to the Clinch River. This rapidly urbanizing watershed lies entirely within Knox County and is identified by regional planning agencies as home to two of the counties’ fastest growing communities: Karns and Gibbs. The green infrastructure plan includes recommendations that concentrate growth into development centers and connect those centers to natural areas with a network of natural open spaces—greenways, parks, and conservation areas—strategically located to avoid, minimize, and manage impacts to Beaver Creek and its tributaries. The plan has served as a guide for planning decisions, enhancement programs, and grass-roots initiatives to restore Beaver Creek. Since 1998, the Beaver Creek Watershed has benefited from numerous additional studies and enhancement projects, including constructed wetlands, greenways, outdoor classrooms, stream bank restorations, and a town center master plan for Halls Crossroads (see p98-99). 91 177 178 GREENPLAN PHILADELPHIA Philadelphia, PA Professional Project Lead Consultant: Wallace Roberts & Todd (WRT) Image by Green City, Clean Waters, Rendering and Concept by WRT Recognizing the importance of a vibrant, sustainable network of urban open spaces to Philadelphia’s future, city agencies collaborated with a team of consultants to develop GreenPlan Philadelphia. This comprehensive open space plan identifies a number of opportunities through which existing and proposed green infrastructure may perform multiple functions and provide a range of economic, social, and environmental benefits. A principal opportunity identified in the study was the role that green infrastructure may play in recovering capacity in an aging stormwater infrastructure, meeting NPDES requirements, and stewarding shared water resources through the widespread application of LID stormwater management practices on retrofit and new development projects. GreenPlan has served as a major resource for other initiatives, including the Philadelphia Water Department’s recently approved Green City Clean Waters plan.92 Instead of spending billions of dollars to upgrade buried stormwater infrastructure, this plan satisfies water management regulatory obligations by investing in green infrastructure solutions. The strategies laid out in this 25-year vision enable the city to reduce its reliance on the construction of underground infrastructure while enhancing property values, increasing air quality, creating jobs, and enhancing the region’s waterways. 93 179 180 Kayakers on the Tennessee River approaching Downtown Knoxville, TN CONCLUSION The shared water resources of East Tennessee define the region, stimulating a robust recreation and tourism economy, providing vital resources for human consumption and agricultural activities, and enabling valuable ecosystem services through rich biodiversity and natural hydrologic processes. These same water resources are threatened and impaired; chemically, biologically, and physically. Regional water resource impairments are symptoms of disruptions to watershed hydrology caused by a historically sprawling growth pattern, the nature of individual site surfaces and activities that occur thereon, and existing stormwater management infrastructure. Each contributes to the concentration and discharge of increased quantities of contaminated stormwater runoff to shared water resources. Underscored by requirements to meet new federal stormwater management regulations and a significant increase in regional population forecasted over the next 30 years, there is an immediate need to look critically upon the regionâ€™s strategy for future growth, as well as identify comprehensive, holistic opportunities to enhance existing stormwater management infrastructure. A multi-scalar Low Impact Development approach to avoid, minimize, and manage water resource impacts presents an enhanced planning, design, and development framework to address these growth challenges and manage stormwater quantity and quality issues. Decentralized LID BMPs that manage stormwater challenges at their origin, integrated site design, and comprehensive green infrastructure planning at the watershed scale can mitigate existing infrastructure challenges, meet federal and local stormwater management regulations, and enhance quality of life while, at the same time, restoring natural hydrologic processes within regional communities. Low Impact Development needs champions in the public and private sectors, both young and old, so that it may be understood, accepted, promoted, incentivized, and implemented throughout the region. Governments, developers, and everyday citizens alike must become advocates for this enhanced approach to stewarding the health of the regionâ€™s shared water resources, allowing those resources to remain iconic assets that continue to define and sustain the PlanET Region economically, socially, and environmentally. 181 Reference END NOTES BIBLIOGRAPHY ABBREVIATIONS GLOSSARY RESOURCES PHOTO CREDITS 182 183 end notes 1. Brad Collett holds a license to practice landscape architecture in the state of Florida at the time of this writing. 2. Ibid. 3. Plan East Tennessee, “Livability Report Card,” PlanET website, published 2012, accessed April 2013 at http://www.planeasttn.org/Learn/ LivabilityReportCard.aspx. 4. Rob Kerth and S. Vinyard, “Wasting Our Waterways 2012: Toxic Industrial Pollution and the Unfulfilled Promise of the Clean Water Act,” Frontier Group and Environment America Research and Policy Center, published March 22, 2012, revised May 2012, accessed April 2013 at http:// www.environmentamerica.org/reports/ame/wasting-our-waterways-2012. 5. Plan East Tennessee, “Livability Report Card.” (See Note 3). 6. Jefferson Chapman, “Prehistoric American Indians in Tennessee,” Frank H. McClung Museum and The University of Tennessee, Knoxville, published 2009, accessed November 2012 at http://mcclungmuseum.utk. edu/research/renotes/rn-27txt.htm. 7. City of Knoxville, “History of Knoxville,” City of Knoxville, accessed November 2012 at http://www.cityofknoxville.org/about/history.asp. 8. Tennessee Valley Authority (TVA), “From the New Deal to a New Century,” TVA, accessed November 2012 at http://www.tva.com/abouttva/ history.htm. 9. United States Travel Association Research Department, “ The Economic Impact of Travel on Tennessee Counties, 2011,” Tennessee Department of Tourist Development, published August 2012, accessed September 2012 at http://www.tnvacation.com/industr y/toolkitsresearch/. 10. Charles Kr ysel et al., “Lakeshore Property Values and Water Quality: Evidence from Property Sales in the Mississippi Headwaters Region,” Friends of the Cloquet Valley State Forest website, published May 14 2003, accessed September 2012 at http://www.friendscvsf.org/ bsu_study.pdf. 184 11. Tennessee Valley Authority, “Norris Reser voir ” and “Fort Loudoun Reser voir,” accessed December 2012 at http://www.tva.gov/sites/norris. htm and http://www.tva.gov/sites/fortloudoun.htm, respectively. 12. Joan F. Kenny, et al., “Estimated Use of Water in the United States in 2005,” U.S. Geological Sur vey Circular 1344, published 2009, accessed November 2012 at http://pubs.usgs.gov/circ/1344/. 13. Kenny et al., “Estimated Use of Water 2005.” (See Note 12). 14. At present, water used to convey raw sewage is treated at significant expense to reach potable (drinkable) standards. Regionally, projects wishing to reuse captured gray water or har vested rainwater face resistance, as current ordinances do not permit such practices. Many municipalities around the countr y are revising their codes to allow for such reuse, on a parcel by parcel as well as district basis, in order to reduce domestic consumption of potable water, reduce demands of growing population on existing water treatment facilities, and “buy back” capacity in existing water treatment and distribution infrastructure. Some municipalities across the southeast are going a step further and are installing “purple pipe” systems that deliver reclaimed, non-potable water to properties for sewage conveyance as well as irrigation. 15. The National Park Ser vice, “Great Smoky Mountains National Park: Nature and Science,” accessed April 2013 at http://www.nps.gov/ grsm/naturescience/index.htm. 16. Tennessee Wildlife Resources Agency (TWRA), “TN Climate Change Fact Sheet,” accessed 2012 at http://www.tn.gov/twra/climate.html. 17. The U.S. Geological Sur vey, “ The USGS Land Cover Institute (LCI): Tennessee Land Cover,” accessed June 2013 at http://landcover. usgs.gov/tennessee.php 18. TWRA, “ TN Climate Change Fact Sheet,” (See Note 16). 19. For the purposes of this publication and in the spirit of simplifying its language for the intended audience, the authors have departed from the official USGS Hydrologic Unit Code (HUC) nomenclature when referring to nested drainage areas of var ying scales. 20. These averages correspond to the period of 1971 to 2000. This and other rainfall data were retrieved from the U.S. National Oceanic and Atmospheric Administration website. Historic weather data can be found at the National Climatic Data Center, at http://www.ncdc.noaa.gov/. 21. Rainfall averages were retrieved from the Climatological Rankings webpage at the National Climatic Data Center, accessed October 2012 at http://www.ncdc.noaa.gov/temp-and-precip/ranks.php. Also see note 20. 22. National Climatic Data Center, “Climate of Tennessee,” Tennessee Climatological Ser vice webpage, accessed April 2013 at https://ag.tennessee.edu/climate/Pages/climatedataTN.aspx. 23. Kenny et al., “Estimated Use of Water 2005.” (See Note 12). 24. TDEC, “Protection of Potable Water Supplies in Tennessee Watersheds,” Division of Water Pollution Control and Division of Water Supply, published 2009, accessed October 2012 at http://www. tennessee.gov/environment/dws/pdf/potablewater_tnws2009.pdf. 25. USEPA, “Functions and Values of Wetlands,” Wetland Fact Sheets, Office of Water and Office of Wetlands, Oceans and Watersheds, published September 2001, accessed December 2012 at http://water.epa.gov/type/wetlands/outreach/facts_contents.cfm. 26. Ibid. 27. USEPA, “Wetlands Over view,” Wetland Fact Sheets, Office of Water, published December 2004, accessed December 2012 at http:// water.epa.gov/type/wetlands/outreach/facts_contents.cfm. 28. Vincent Cotrone, “ The Role of Trees and Forests in Healthy Watersheds: Managing Stormwater, Reducing Flooding, and Improving Water Quality,” Pennsylvania State University Extension, accessed March 2013 at http://www.dcnr.state.pa.us/cs/groups/public/documents/ document/dcnr_009116.pdf. 29. Plan East Tennessee, “Livability Report Card,” published 2012, accessed April 2012 at http://www.planeasttn.org/Learn/ LivabilityReportCard.aspx. 30. Reid Ewing, R. Pendall, and D. Chen, “Measuring Sprawl and its Impact,” Smart Growth America, published 2002, accessed November 2012 at http://www.smartgrowthamerica.org/documents/ measuringsprawl.pdf. 31. University of Arkansas Community Design Center, “Low Impact Development: A Design Manual for Urban Areas,” Arkansas Natural Resources Commission and U.S.EPA (Fayetteville: University of Arkansas Press, 2010). Sample available online at http://uacdc.uark.edu/books/ complete/26LID_Manual_Book_Sample.pdf. 32. Using an on-site inventor y and GoogleEarth assessment of land uses in the First Creek Watershed, sites estimated to be developed in form and surface quality representative of the same land uses elsewhere in the PlanET Region were selected by students. Surfaces, imper vious and per vious, were noted and quantified. Runoff quantity for these sites was generated using the Weighted Average Volume Technique (WAVT) and SCS cur ve numbers. The resultant runoff quantity was converted to a percentage of total precipitation expected to runoff the site during a one-inch storm event. Similar runoff percentages can be expected for sites with the indicated imper vious percentage and assumed soil characteristics, regardless of land use or size. WAVT is described in the following source: State of New Jersey Department of Environmental Protection, “New Jersey Stormwater Best Management Practices Manual,” published February 2004, accessed May 2013 at http://www.njstormwater.org/bmp_manual2.htm. 33. USEPA, “Drinking Water Contaminants,” Office of Water, updated June 5 2012, accessed October 2012 at http://water.epa.gov/drink/ contaminants/index.cfm; United States Geological Sur vey, “Pesticides in Groundwater,” USGS Water Science School website, accessed October 2012 at http:// ga.water.usgs.gov/edu/pesticidesgw.html; 185 Leonardo Trasande, P. J. Landrigan, and C. Schechter, “Public Health and Economic Consequences of Methyl Mercur y Toxicity to the Developing Brain,” Environ Health Perspect , 2005 May; 113(5): 590–596, available from National Center for Biotechnology Information at http:// www.ncbi.nlm.nih.gov/pmc/articles/PMC1257552/; Center for Watershed Protection, “Microbes and Urban Watersheds: Concentrations, Sources, & Pathways,” Watershed Protection Techniques , 3(1): 554-565; accessed September 2012 at http://www.cwp.org/documents.html; Center for Watershed Protection, “Hydrocarbon Hotspots in the Urban Landscape,” Watershed Protection Techniques , 1(1): 3-5; accessed September 2012 at http://www.cwp.org/documents.html; Joe Piotrowski, K. Wagner, and R. Gibson, “Nitrogen and Phosphorus Pollution and Harmful Algal Blooms in Lakes,” USEPA Watershed Academy Webcasts, produced Januar y 26 2011, accessed September 2012 at http://water.epa.gov/learn/training/wacademy/ upload/2011_1_26_slides.pdf ; Millennium Ecosystem Assessment, “Ecosystems and Human Wellbeing: Policy Responses,” Volume 3, Chapter 9: Nutrient Management, Primar y Authors: Howarth, R. and K. Ramakrrshna, eds. K. Chopra, R. Leemans, P. Kumar, and H. Simons (Washington, DC: Island Press, 2005, 295-311). Available online at http://www. millenniumassessment.org/. 34. USEPA , “National Summar y of State Information,” Office of Water, Water Quality Assessment and Total Maximum Daily Loads Information, accessed October 2012 at http://ofmpub.epa.gov/waters10/ attains_nation_cy.control. Regularly maintained to represent most up-todate state attainment data. 35. TDEC, “Year 2012 303(d) List Draft,” Division of Water Pollution Control, unpublished, accessed September 2012 at http://www.tn.gov/ environment/wpc/publications/pdf/2012_draft_303d_list.pdf. 36. Ibid. 37. Ibid. 186 38. Ibid. 39. USEPA, “National Summar y.” (See Note 34). 40. United States Army Corps of Engineers (U.S. ACOE), “Corps Awards $1.9 Million for Pistol Creek Lake Sediment Removal Project,” Nashville Tennessee District, District Digest , posted October 6 2011, accessed March 2013 at http://www.lrn.usace.army.mil/Media/ NewsStories/tabid/6957/Article/7813/corps-awards-19-million-contractfor-pistol-creek-lake-sediment-removal-project.aspx. 41. U.S. ACOE, “Pistol Creek Fact Sheet,” Nashville Tennessee District, Fact Sheet Articles , updated September, 2012, accessed May 2013 at http://www.lrn.usace.army.mil/Media/FactSheets/FactSheetArticleView/ tabid/6992/Article/6651/pistol-creek.aspx. 42. USEPA, “National Summar y.” (See Note 34). 43. TDEC, “Year 2012 303(d) List.” (See Note 35). 44. USEPA, “National Summar y.” (See Note 34). 45. TDEC, “2010 305(b) Report: The Status of Water Quality in Tennessee,” Division of Water Pollution and Control, accessed August 2012 at http://tn.gov/environment/wpc/publications/pdf/2010_305b.pdf. 46. Joe Piotrowski, K. Wagner, and R. Gibson, “Nitrogen and Phosphorus Pollution and Harmful Algal Blooms in Lakes,” USEPA Watershed Academy Webcasts, produced Januar y 26 2011, accessed September 2012 at http://water.epa.gov/learn/training/wacademy/ upload/2011_1_26_slides.pdf. 47. Massachusetts Department of Environmental Protection, “Nonpoint Source Pollution Education: Motor Oil,” Water, Wastewater and Wetlands educational webpage, accessed October 2012 at http://www. mass.gov/dep/water/resources/oilspill.htm. 48. Neil M. Dubrovsky and P.A. Hamilton, “Nutrients in the Nation’s Streams and Groundwater : National Findings and Implications, United States Geological Sur vey Fact Sheet 2010,” USGS National Water Quality Assessment Program website, accessed October 2012 at http://water. usgs.gov/nawqa/nutrients/pubs/circ1350/. 49. Kenny et al., “Estimated Use of Water 2005.” (See Note 12). 50. Centers for Disease Control and Prevention, “Other Uses and Types of Water : Water Contamination,” accessed June 2013 at http:// www.cdc.gov/healthywater/other/agricultural/contamination.html#five. 51. USEPA, “Indoor Water Use in the United States,” WaterSense webpage, accessed May 2013 at http://www.epa.gov/WaterSense/pubs/indoor.html. 52. Kenny et al., “Estimated Use of Water 2005.” (See Note 12). 53. Piotrowski et al., “Nitrogen and Phosphorus.” (See Note 46). 54. TDEC, “2010 305(b) Report.” (See Note 45). 55. “Flash Flooding,” WATE 6 News, accessed April 2013 at http:// www.wate.net/weather/understanding-weather/flash-flooding. 56. Whereas similar publications focus on the role of combined sewer systems and combined sewer overflows in great depth, the authors of this publication decided to not include a lengthy discussion of their impacts due the limited amount of areas served by such systems in the PlanET Region and ongoing initiatives to separate them. Readers in affected areas are encouraged to reference EPA resources for more information on this topic. 57. As an example, the City of Knoxville began requiring on-site stormwater detention and retention facilities in 1976. 58. Rebecca Winer, “National pollutant removal performance database for stormwater treatment practices, 2nd Ed.,” Office of Science and Technology, Center for Watershed Protection, Published 2000. Available online at http:// http://www.stormwatercenter.net/Librar y/STPPollutant-Removal-Database.pdf. 59. TDEC, “2010 Notice of Determination; NPDES Tennessee General Permit for Storm Water Discharges from Small MS4s Permit No. TNS000000,” Division of Water Resources: Stormwater Permitting webpage, accessed April 2013 at http://www.state.tn.us/environment/ wpc/stormh2o/finals/tns000000_ms4_phase_ii_nod_2010.pdf 60. Plan East Tennessee, “Livability Report Card.” (See Note 29). 61. University of Arkansas Community Design Center, “Low Impact Development: A Design Manual for Urban Areas.” (See Note 31). 62. Ibid. 63. Ibid 64. USEPA, “Using Smart Growth Techniques as Stormwater Best Management Practices,” EPA 231-B-05-002, accessed May 2013 at http:// www.epa.gov/smartgrowth/stormwater.htm. 65. The method for calculating equivalent land area for suburban fringe development extends a floor area ratio (FAR) of 0.25 and a gross residential density of 4 du/acre against the proposed development program. 66. Smart Growth America, “Building Better Budgets,” accessed June 2013 at http://www.smartgrowthamerica.org/building-better-budgets. 67. Shaver, E., 2009. Low Impact Design Versus Conventional Development: Literature Review of Developer-related Costs and Profit Margins. Prepared by Aqua Terra International Ltd. for Auckland Regional Council. Auckland Regional Council Technical Report 2009/045. 68. Ludwig, A., et al. “ Tennessee Storm-Smart Glossar y of Terms for Communities.” UT Extension, University of Tennessee, Department of Biosystems Engineering and Soil Science. Draft Published Januar y 2013. (Forthcoming). 69. Winer, “National pollutant removal performance database for stormwater treatment practices.” (See Note 58). 70. The BMP profiles shown in this document were compiled through consulting documents on specific BMP functions and construction methods, as well as other low-impact development manuals that summarize BMP characteristics. General references used for the profiles follow. North Carolina Department of Environment and Natural Resources, “Stormwater Best Management Practices Manual,” NCDENR Division of Water Quality, published July 2007; accessed October 2012 at http:// portal.ncdenr.org/web/wq/ws/su/bmp-manual; 187 Bruce A. Tschantz, T. R. Gangaware, & R. G. Morton, “ Tennessee Guide to the Selection and Design of Stormwater Best Management Practices,” Tennessee Department of Environment and Conser vation, Division of Water Pollution Control, published March 2003. Available online at http://isse.utk.edu/wrrc/publications/pdf/BMPPhaseII.pdf ; AMEC Earth & Environmental, “Knox County Tennessee Stormwater Management Manual, Volume 2: Technical Guidance,” Knox County Tennessee Department of Engineering and Public Works, published Januar y 2008, accessed October 2012 at http://www.knoxcounty.org/ stormwater/volume2.php; Arkansas, “Low Impact Development” (See note 31); Southeast Michigan Council of Governments, “Low Impact Development Manual for Michigan: A Design Guide for Implementers and Reviewers,” Michigan Department of Environmental Quality, published 2008, accessed October 2012 at http://librar y.semcog.org/ InmagicGenie/DocumentFolder/LIDManualWeb.pdf. 71. Data on the effectiveness of BMPs varies in its inclusion of BMPs and BMP functions, so several sources were consulted and synthesized to create this document’s summar y of BMP benefits. Denver Colorado Urban Drainage and Flood Control District, “Urban Storm Drainage Criteria Manual Volume 3: Best Management Practices,” published September 1992, updated November 2010, accessed September 2012 at http://www.udfcd.org/downloads/down_critmanual_volIII.htm; Southeast Michigan, “Low Impact Development” (See Note 68); Center for Neighborhood Technology, “ The Value of Green Infrastructure: A Guide to Recognizing its Economic, Environmental and Social Benefits,” published 2010, accessed October 2012 at http://www. cnt.org/repositor y/gi-values-guide.pdf ; AMEC, “Knox County” (See Note 70); 188 USEPA, “Results of the Nationwide Urban Runoff Program, Volume 1: Final Report,” Water Planning Division, published December 1983, accessed October 2012 at http://www4.ncsu.edu/~rcborden/CE383/ Stormwater_Refs/NURP_Results_Vol_1.pdf. 72. This document’s valuation system of primar y, secondar y, and incidental values is taken from the low impact development manual created by the Denver Colorado Urban Drainage and Flood Control District. Also see Note 69. 73. TDEC, “2010 305(b) Report.” (See Note 45). 74. John C. Price and R. Karesh, “ Tennessee Erosion and Sediment Control Handbook: A Guide for Protection of State Waters Through the Use of Best Management Practices During Land Disturbing Activities,” second edition, TDEC Division of Water Pollution Control, March 2002. 75. San Francisco Public Utilities Commission, “Stormwater Design Guidelines,” Fact Sheets, revised June 2012, accessed February 2013 at http:// www.sfwater.org/index.aspx?page=446.52. San Francisco Public Utilities Commission, “Stormwater Design Guidelines,” Fact Sheets, revised June 2012, accessed February 2013 at http://www.sfwater.org/index.aspx?page=446. 76. Mar yland Department of the Environment, “Mar yland Stormwater Design Manual, Volumes I and II (October 2000, Revised May 2009): Chapter 3: Performance Criteria for Urban BMP Design,” accessed June 2013 at http://www.mde.state.md.us/assets/document/ chapter3.pdf. 77. San Francisco Public Utilities Commission, “Stormwater Design Guidelines,” (See Note 75). 78. Ibid. 79. Ibid. 80. Wallace Roberts & Todd, “GreenPlan Philadelphia: Our Guide To Achieving Vibrant and Sustainable Urban Places,” 2010, accessed April 2013 at http://issuu.com/wrtdesign/docs/greenplan_philadelphia; Metro Water Ser vices, “Metropolitan Government of Nashvile and Davidson County Green Infrastructure Master Plan,” accessed April 2013 at https://www.nashville.gov/Portals/0/SiteContent/WaterSer vices/ Stormwater/docs/reports/GreenInfrastructureRpt101120.pdf ; The Chattanoogan.com, “Green Infrastructure Master Plan Under way for Chattanooga,” accessed May 2013 at http://www.chattanoogan. com/2013/5/22/251837/Green-Infrastructure-Master-Plan.aspx. 81. The economic incentive to implement LID practices in Philadelphia and other cities with extensive combined sewer systems is enhanced by the reduction of stormwater volume that would otherwise be treated at water treatment facilities, resulting in lower treatment costs. 82. Wallace Roberts & Todd, “GreenPlan” (See Note 80). 83. NC State Cooperative Extension, “Low Impact Development - An Economic Fact Sheet,” accessed May 2013 at http://www.ces. ncsu.edu/depts/agecon/WECO/nemo/documents/WECO_LID_econ_ factsheet.pdf. 84. In Chattanooga, TN, all properties are required to pay stormwater fees. The use of the revenues generated by the fees include maintaining the capacity of municipal stormwater infrastructure concurrently with expanding development, and other NPDES permit compliance initiatives. Fee reduction credits are available to properties whose stormwater management systems meet prescribed performance criteria which reduce the quantity and increase the quality of stormwater discharged to the municipal system. Nashville, TN, also has similar fee and fee credit programs. Communities in the PlanET Region do not charge stormwater fees at the time of this writing. 85. U.S. Environmental Protection Agency, “Encouraging Low Impact Development,” accessed June 2013 at http://water.epa.gov/polwaste/ green/upload/bbfs7encouraging.pdf ; U.S. Green Building Council, “Financing and Encouraging Green Building in Your Community,” accessed June 2013 at http://www.usgbc. org/sites/default/files/Docs6247.pdf ; Plant Connection, Inc. “Green Roof Legislation, Policies & Tax Incentives,” accessed June 2013 at http://www.myplantconnection.com/ green-roofs-legislation.php. 86. TDEC, “Green Development,” accessed June 2013 at http:// www.tn.gov/environment/greendev/. 87. Austin Water, “Rainwater Har vesting Rebates,” accessed June 2013 at http://www.austintexas.gov/department/rainwater-har vestingrebates; Chicago Sustainable Backyards Program, “Green Your Yard, Green Your Wallet,” accessed June 2013 at http://www.sustainablebackyards.org. 88. George Hargreaves, J. Czerniak, A. Berrizbeitia, L. Campbell Kelly, “Landscape Alchemy: The Work of Hargreaves Associates,” ORO Editions, 2009. 89. The method for calculating equivalent land area for suburban fringe development extends a floor area ratio (FAR) of 0.25 and a gross residential density of 4 du/acre against the proposed development program. 90. DeKay, M., Moir McClean, T., “Beaver Creek Watershed Green Infrastructure Master Plan,” The University of Tennessee College of Architecture and Design Green Vision Studio, 2006. 91. Knox County Government, “ The Beaver Creek Watershed,” Engineering and Public Works: Stromwater web page, accessed May 2013 at http://www.knoxcounty.org/stormwater/pdfs/beaver_creek_ over view.pdf. 92. Wallace Roberts & Todd, “GreenPlan Philadelphia,” 2011 ASLA Professional Awards, accessed April 2013 at http://www.asla. org/2011awards/610.html. 93. Philadelphia Water Department, “Green City Clean Waters: The City of Philadelphia’s Program for Combined Sewer Overflow Control, Program Summar y,” amended June 2011, accessed April 2013 at http:// www.phillywatersheds.org/. 189 Bibliography AMEC Earth & Environmental. “Knox County Tennessee Stormwater Management Manual, Volume 2: Technical Guidance.” Knox County Tennessee Department of Engineering and Public Works. Published Januar y 2008. Accessed October 2012. http://www.knoxcounty.org/ stormwater/volume2.php. Arnold, Craig A., C. Norton, and D. Wallen. “Kentucky Wet Growth Tools for Sustainable Development: A Handbook on Land Use and Water for Kentucky Communities.” University of Louisville Center for Land Use and Environmental Responsibility. Published 2009. Accessed October 2012. http://louisville.edu/landuse/healthy-watershedsland-use-initiative.html. Center for Neighborhood Technology. “ The Value of Green Infrastructure: A Guide to Recognizing its Economic, Environmental and Social Benefits.” Published 2010. Accessed October 2012. http:// www.cnt.org/repositor y/gi-values-guide.pdf. Denver Colorado Urban Drainage and Flood Control District. “Urban Storm Drainage Criteria Manual Volume 3: Best Management Practices.” Published September 1992. Updated November 2010. Accessed September 2012. http://www.udfcd.org/downloads/ down_critmanual_volIII.htm. Kenny, Joan F., et al. “Estimated Use of Water in the United States in 2005.” U.S. Geological Sur vey Circular 1344. Published 2009. Accessed November 2012. http://pubs.usgs.gov/circ/1344/. National Climatic Data Center. Climatological Rankings Webpage. Accessed October 2012. http://www.ncdc.noaa.gov/. 190 North Carolina Department of Environment and Natural Resources. “Stormwater Best Management Practices Manual.” NCDENR Division of Water Quality. Published July 2007. Accessed October 2012. http://portal.ncdenr.org/web/wq/ws/su/bmp-manual. Philadelphia Water Department. “Green City Clean Waters: The City of Philadelphia’s Program for Combined Sewer Overflow Control, Program Summar y.” Amended June 2011. Accessed April 2013. http:// www.phillywatersheds.org/. Piotrowski, Joe, K. Wagner, and R. Gibson. “Nitrogen and Phosphorus Pollution and Harmful Algal Blooms in Lakes.” USEPA Watershed Academy Webcasts. Produced Januar y 26 2011. Accessed September 2012. http://water.epa.gov/learn/training/wacademy/ upload/2011_1_26_slides.pdf. Plan East Tennessee. “Livability Report Card.” Published 2012. Accessed April 2012. http://www.planeasttn.org/Learn/LivabilityReportCard. aspx. Price, John C., and R. Karesh. “ Tennessee Erosion and Sediment Control Handbook: A Guide for Protection of State Waters Through the Use of Best Management Practices During Land Disturbing Activities.” Second edition. TDEC Division of Water Pollution Control. March 2002. San Francisco Public Utilities Commission. “Stormwater Design Guidelines.” Fact Sheets. Revised June 2012. Accessed Februar y 2013. http:// www.sfwater.org/index.aspx?page=446. Southeast Michigan Council of Governments. “Low Impact Development Manual for Michigan: A Design Guide for Implementers and Reviewers.” Michigan Department of Environmental Quality. Published 2008. http://librar y.semcog.org/InmagicGenie/ DocumentFolder/LIDManualWeb.pdf. USEPA. “National Summar y of State Information.” Office of Water. Water Quality Assessment and Total Maximum Daily Loads Information. Accessed October 2012. http://ofmpub.epa.gov/waters10/attains_ nation_cy.control. Tennessee Department of Environment and Conser vation (TDEC). “Year 2012 303(d) List Draft.” Division of Water Pollution Control. Unpublished. Accessed September 2012. http://www.tn.gov/ environment/wpc/publications/pdf/2012_draft_303d_list.pdf. USEPA. “Results of the Nationwide Urban Runoff Program, Volume 1: Final Report.” Water Planning Division. Published December 1983. Accessed October 2012. http://www4.ncsu.edu/~rcborden/CE383/ Stormwater_Refs/NURP_Results_Vol_1.pdf. TDEC. “2010 305(b) Report: The Status of Water Quality in Tennessee.” Division of Water Pollution and Control. Accessed August 2012. http://tn.gov/environment/wpc/publications/pdf/2010_305b.pdf. University of Arkansas Community Design Center. “Low Impact Development: A Design Manual for Urban Areas.” Arkansas Natural Resources Commission and U.S.EPA. Fayetteville: University of Arkansas Press, 2010. http://uacdc.uark.edu/books/complete/26LID_ Manual_Book_Sample.pdf. TDEC. “Protection of Potable Water Supplies in Tennessee Watersheds.” Division of Water Pollution Control and Division of Water Supply. Published 2009. Accessed October 2012. http://www.tennessee. gov/environment/dws/pdf/potablewater_tnws2009.pdf. Tennessee Wildlife Resources Agency. “ TN Climate Change Fact Sheet.” Accessed 2012. http://www.tn.gov/twra/climate.html. Tschantz, Bruce A., T. R. Gangaware, & R. G. Morton. “ Tennessee Guide to the Selection and Design of Stormwater Best Management Practices.” Tennessee Department of Environment and Conser vation, Division of Water Pollution Control. Published March 2003. http:// isse.utk.edu/wrrc/publications/pdf/BMPPhaseII.pdf. United States Environmental Protection Agency (USEPA). “Drinking Water Contaminants.” Office of Water. Updated June 5 2012. Accessed October 2012. http://water.epa.gov/drink/contaminants/index.cfm; 191 Abbreviations BMP CSO CSS CWA LID EPA MS4 NPDES PlanET TDEC TVA 192 Best Management Practice Combined Sewer Overflow Combined Sewer System Clean Water Act Low Impact Development Environmental Protection Agency Municipal Separate Storm Sewer Systems National Pollutant Discharge Elimination System Plan East Tennessee Tennessee Department of Environment and Conser vation Tennessee Valley Authority CONTAMINANT ABBREVIATIONS HC Hydrocarbon HM Heavy Metal N Nitrogen Compounds P Phosphorous Compounds PA Pathogens S Sediment VOC Volatile Organic Compounds Glossary 303(D) LIST A list held by the State as required by Section 303(d) of the Federal Clean Water Act of the waterbodies that do not support their designated uses. The Tennessee Department of Environment and Conservation publishes this list every two years: http://tn.gov/environment/wpc/publications/. AQUIFER An underground layer of permeable rock containing or conducting groundwater. Sub-surface rock types commonly containing aquifers include sandstone, conglomerate, fractured limestone and unconsolidated sand and gravel. ATMOSPHERIC VOLATILIZATION Loss of a substance to the atmosphere as a gas (in a gaseous state), such as nitrogen-based fertilizer applied to soil surface that may evaporate as gaseous ammonia. BASIN A physical facility that holds stormwater. BEST MANAGEMENT PRACTICES, STORMWATER (BMP) A method that is recognized as an efficient, effective, and practical means of reducing stormwater runoff quantity and preventing or reducing the movement of pollutants into receiving waters. A BMP may be a physical facility or a management practice achieved through action. BIOACCUMULATION The process by which contaminants accumulate within the tissues of a living organism. BIOCHEMICAL BREAKDOWN Metabolic processes that break down or degrade contaminant compounds into simpler molecules or elements. BIOLOGICAL DIVERSITY (BIODIVERSITY) The number and variety of living organisms in a defined geographic area in all forms and at all levels, including ecosystem diversity, species diversity, and genetic diversity. BIORETENTION A process enabled by various stormwater best management practice facilities where runoff is captured and pollutants are filtered through physical, chemical, and biological processes. Bioretention facilities are sized to retain a prescribed stormwater runoff volume, designed with specific vegetation and engineered media, and usually incorporate an underdrain to route treated water to a receiving drainage system. 193 Blueway Water trails that are developed with launch points for canoeists, paddle boarders, kayakers, and others seeking water recreation. CONCENTRATED FLOW Runoff that accumulates in defined conveyances, such as swales, gutters, channelized streams, or pipes, resulting in higher velocities. CHANNELIZATION 1) Hydrologic modification and straightening of a streamâ€™s shape that may cause destabilization of stream banks and stream bed; 2) the formation of steep channel walls that separate the stream from its primary floodplain. CONTAMINANT A substance in a concentration that adversely alters the physical, chemical, or biological properties of the natural environment. CLEAN WATER ACT (CWA) The primary federal law in the United States governing water pollution. This legislation provides the basic regulatory framework for the protection of water quality through control of discharge of pollutants into surface waters, including the management of stormwater runoff. Public Law 92500. COMBINED SEWER OVERFLOW (CSO) Discharge of the combination of stormwater and sanitary wastewater to receiving waters during storms when the capacity of the sewer system to transport, store, or treat the increased flow is exceeded. COMBINED SEWER SYSTEM (CSS) A sewer system that conveys and treats both stormwater runoff and municipal sewage simultaneously with shared infrastructure. 194 CONVEYANCE Constructed and/or natural features that function together as a system to collect, channel, or divert stormwater. CULVERT A constructed pipe or box structure that conveys surface water or runoff under another structure such as a roadway or embankment. DESIGN STORM The precipitation depth and intensity used to size stormwater management facilities and select materials for stormwater treatment. DETENTION The slowing, collecting, or temporary storage of stormwater to decrease peak flow rate into receiving waters. DEVELOPED LAND Any land that has been modified from its native, vegetated condition to support past or present human activities. DISCHARGE The release of contaminated water into receiving waters. DRAINAGE AREA (CATCHMENT AREA) The area of a site that contributes runoff; used to calculate dimensions for structural BMPs. ECOSYSTEM A clearly defined interconnected and dynamic system of interactions between all living organisms and the abiotic physical environment within a defined area. ECOSYSTEM SERVICE Resources and processes that are supplied by ecosystems and serve all living organisms. Ecological services provided by healthy watersheds are: atmospheric regulation, climate regulation, disturbance regulation, water supply, erosion control and sediment retention, soil formation, nutrient cycling, waste treatment, pollination, species control, refugia, food production, raw material production, genetic resources, recreation, and cultural enrichment. EPHEMERAL STREAM A stream that has flowing water only during, and for a short duration after, precipitation events in a typical year. Runoff from rainfall is the primary source of water for stream flow. EROSION The wearing away of rock and soil due to wind, water, ice, or other physical, chemical, or biological forces. The rate of erosion may be increased by land use activities. EUTROPHICATION Process by which a waterbody undergoes an increase in dissolved nutrients, often leading to algal blooms, low dissolved oxygen, and changes in community structure. This process occurs naturally over time, but can be accelerated by human activities that increase nutrient inputs into receiving watersâ€™ aquatic ecosystems. EVAPOTRANSPIRATION The sum of evaporation of water from land and water surfaces and the uptake and release of water by vegetation to the atmosphere through transpiration. 195 EXTENDED TREATMENT, BIOLOGICAL AND CHEMICAL A function of certain Best Management Practices (BMP) that retain water for an extended period of time, thus allowing for improved water quality through passive organic (biological) and/or inorganic (chemical) processes. FILTRATION Process through which contaminant levels in water are reduced by means of physical removal or chemical decomposition during the movement of water through a medium. Examples of filtering media include soils, root zones, vegetated areas, sand, and gravel. FIRST FLUSH Stormwater that initially runs off an area, more polluted than the stormwater that runs off later. Generally considered to be the runoff from the first inch of rainfall. FLOW RATE A measurement indicating a volume of water per unit of time, most often cubic feet per second. Sometimes used interchangeably with velocity. See: Concentrated Flow, Sheet Flow. FOREBAY A separate chamber through which stormwater is conveyed prior to entering a BMP; used to trap sediment, dissipate runoff energy, and reduce stormwater velocity to best support sedimentation and other treatment processes in the BMP. GREEN INFRASTRUCTURE Green infrastructure refers to a system of open or green spaces distributed throughout a watershed that provide ecosystem services and environmental benefits, including recreation opportunities, to enhance overall environmental quality and provide utility services. Green infrastructure includes preserved natural spaces and constructed landscapes such as urban parks and waterfronts. As a general principle, Green Infrastructure techniques use soils and vegetation to infiltrate, evapotranspirate, and/or recycle stormwater runoff. GROUNDWATER Water occurring beneath the earthâ€™s surface, typically in aquifers, that supplies wells and springs and is a key source of drinking water. HEAVY METALS Elements, such as zinc, mercury, lead, and copper. These elements can become dissolved in stormwater and are prone to accumulate in urban areas due to human activitiesâ€”mainly automobile use. 196 HOT SPOT A term used to describe areas where land use or activities generate highly contaminated runoff with concentrations of pollutants in excess of those typically found in naturally occurring stormwater runoff. HYDROCARBONS Organic chemical compounds made up of solely carbon and hydrogen. Predominantly used as combustible fuel and, in solid state, asphalt; a pollutant of concern in urban areas due to their contribution to ground level ozone and smog and persistence in soil and water. HYDROLOGIC CYCLE (WATER CYCLE) The continuous movement of water on, above, or below the earthâ€™s surface through processes including precipitation, canopy interception, condensation, evapotranspiration, infiltration/percolation, and storage. HYDROLOGY The study of the movement and distribution of surface water and groundwater in a system. IMPAIRED WATER BODY A water body, or segment thereof, that has been identified as failing to support one or more of its designated uses. See: 303(d) List, Threatened Water. IMPERVIOUS SURFACE A hard surface that either prevents or limits the movement of water into the soil as would naturally occur in a pre-development condition; a surface that causes water to runoff in greater quantities than that occurring under natural or pre-development conditions. INFILTRATION The movement of water into the ground through air spaces between soil particles. INTERCEPTION The process of precipitation being caught by trees, plants, or other objects that prevent it from reaching the ground and becoming runoff. Intercepted precipitation may eventually evaporate. KARST TOPOGRAPHY Geological formations shaped by the dissolution of soluble rock, usually carbonate rock like limestone or dolomite. LAND USE The way land is used or developed, such as the types of buildings, percentage of impervious surfaces, and activities permitted. Particular land uses are often associated with different types of water quality issues, such as hydrocarbons from refueling stations. 197 LOW IMPACT DEVELOPMENT (LID) An approach to site planning, design, and development that seeks to avoid, minimize, and manage impacts to water resources by stewarding and reintroducing natural hydrologic processes into developed watersheds. MUNICIPAL SEPARATE STORM SEWER SYSTEM (MS4) A stormwater drainage network (including road drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains) that is owned or operated by a local government or designated entity (such as a state, city, town, borough, county, parish, district, association, or other public body). NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES) A regulatory program in the Federal Clean Water Act that prohibits the discharge of pollutants into surface waters of the United States without a permit. NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES) PHASE I NPDES Phase I, issued in 1990, requires medium and large cities or certain counties with populations of 100,000 or more to obtain NPDES permit coverage for their stormwater discharges. NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES) PHASE II NPDES Phase II, issued in 1999, requires regulated small MS4s in urbanized areas, as well as small MS4s outside the urbanized areas that are designated by the permitting authority, to obtain NPDES permit coverage for their stormwater discharges. NON-POINT SOURCE (NPS) POLLUTION Pollution originating from diffuse sources without a single point of origin. NUTRIENTS Substances such as nitrogen and phosphorous that are required by plants and animals for growth. In some circumstances, excessive nutrient additions to surface waters may result in excessive algal or plant growth and, subsequently, the accumulation and decay of increased organic matter. See: Eutrophication. OPEN SPACE For the purposes of this publication, land set aside for public or private use within a development that is not built upon. Readers should check zoning ordinances for the effective definition in their jurisdiction. PATHOGEN A microscopic organism, such as certain viruses, bacteria, or fungi, capable of causing disease in another organism. 198 PEAK FLOW REDUCTION Peak flow refers to the rate of highest stormwater volume that flows during a storm event. Certain Best Management Practices (BMP) reduce peak flow and decrease the risk of floods, reduce pressure on stormwater infrastructure, and protect stream channels. Perennial Stream A stream that flows continuously throughout the year. Groundwater is the primary source of water for stream flow. PERMEABLE/PERVIOUS SURFACE Material or medium that allows the infiltration or passage of water or other liquids. PHYTOREMEDIATION The mitigation of contaminated soil, water, or air using plants to contain, degrade, or eliminate pollutants. See: Extended Treatment (Biological). POINT SOURCE POLLUTION Pollution that can be traced to a single point, or output, such as a pipe. RECEIVING WATERS Any river, stream, reservoir, or other waterbody into which stormwater or other material is discharged. RETENTION The process of collecting and holding stormwater runoff with no surface outflow. See: Bioretention. RIPARIAN AREA Terrestrial and aquatic ecosystems along a waterbody. Riparian areas characteristically have a high water table and are subject to periodic flooding. RIVER BASIN The watershed encompassing all the land drained by a major river. Water that falls within the river basin flows into the major river via lower order watersheds. See: Watershed. RUNOFF The rainfall that is shed by the landscape to a receiving waterbody when rainfall exceeds the infiltration capacity of the intercepting surfaces and soil. SEDIMENT Particles of dust, soil, and debris, commonly referred to as suspended solids, that have been moved and subsequently deposited by water, wind, or gravity. 199 SEDIMENTATION/SILTATION A mechanical process in which suspended solids settle to the bottom of a waterbody under the influence of gravity. SURFACE WATER Water collected on the landscape in any waterbody such as a stream, river, reservoir, lake, or ocean. SHEET FLOW Unconfined water that accumulates on the soil surface and moves down gradient as a thin layer of water. See: Concentrated Flow, Flow. SUSPENDED SOLIDS Organic and inorganic particles suspended in the water column and carried by the water. The presence of suspended solids in water is often associated with toxic contaminants that bind to particles. STORM EVENT A discrete period of precipitation with defining characteristics such as depth of precipitation, duration, and the resultant intensity usually measured in inches/hour. STORMWATER RUNOFF In developed areas, precipitation that does not soak into the surface on which it falls, but rather runs along the surface downslope to receiving waters. Generally, the volume of stormwater runoff is exacerbated by impervious surfaces such as rooftops, parking lots, roadways, and compacted soils on which it may pick up deposited contaminants. STRAINING Physical filtration that removes large particles and debris, such as sediment, organic debris, and litter. See: Filtration. 200 THREATENED WATER BODY A water body, or segment thereof, that has been identified as likely to not support its designated uses. See: 303(d) List, Impaired Water. TREATMENT TRAIN A series of structural BMPs sequenced to achieve stormwater quantity management and treatment of contaminated stormwater runoff. URBANIZATION Changing land use from rural characteristics to urban and sub-urban (citylike) characteristics; typically associated with an increase in impervious surfaces. WATER TABLE The depth at which soil is saturated by groundwater. WATERSHED Topographically defined land area within which surface water drains to a single point of reference. Watersheds are designated with Hydrologic Unit Codes (HUC). See: http://water.usgs.gov/GIS/huc.html GLOSSARY SOURCES WETLAND Areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas. Department of Environmental Resources, Programs and Planning Division. “Low-Impact Development Design Strategies: An Integrated Design Approach.” Prince George’s County, Mar yland. Published 1999. Accessed April 2013. http://www.lowimpactdevelopment.org/pubs/ LID_National_Manual.pdf. Definitions within this glossar y have been informed by, and have occasionally adopted wording from, the following sources: Ludwig, A., et al. “ Tennessee Storm-Smart Glossar y of Terms for Communities.” (See End Note 68). Perrin, C., et al. “Low Impact Development: A Guidebook for North Carolina (AG-716).” NC Cooperative Extension Ser vice, NC State University. Published 2009. Accessed April 2013. http://www.ncsu. edu/WECO/LID. United States Army Corps of Engineers. “2012 Nationwide Permit Information.” Accessed May 20 2013. http://www.usace.army.mil/ Portals/2/docs/civilworks/nwp/2012/NWP2012_corrections_21sep-2012.pdf. United States Environmental Protection Agency (USEPA). “Greening EPA Glossar y.” Office of Water. Accessed April 2013. http://www.epa. gov/oaintrnt/glossar y.htm. USEPA. “National Pollutant Discharge Elimination System (NPDES).” Office of Water. Accessed April 2013. http://cfpub.epa.gov/npdes/ stormwater/munic.cfm. University of Arkansas Community Design Center. “Low Impact Development: A Design Manual for Urban Areas.” (See End Note 31). 201 Resources LOCAL ORGANIZATIONS WITH WATER STEWARDSHIP INTERESTS B eaver Creek Task Force (See Water Quality Forum) Coal Creek Watershed Foundation http://www.coalcreekaml.com/ Farragut Stormwater Matters Program h ttp://townoffarragut.org/index.aspx?nid=171 Fort Loudoun Lake Association h ttp://fllake.org/ Friends of Williams Creek Legacy Parks Foundation http://www.legacyparks.org/ Little River Watershed Association http://www.littleriver watershed.org/ Lower Clinch Watershed Council http://www.lowerclinchwatershed.org/ Stock Creek Task Force (See Water Quality Forum) Tennessee Izaak Walton League http://www.tnike.com/ Water Quality Forum (Knox County area) http://waterqualityforum.org/ LOCAL WATER QUALITY PROGRAMS Adopt-A-Stream Program http://waterqualityforum.org/?page_id=76 Adopt-A-Watershed Program http://waterqualityforum.org/?page_id=30 Tennessee Yards & Neighborhoods https://ag.tennessee.edu/tnyards/Pages/default.aspx 202 REGIONAL AGENCIES AND ORGANIZATIONS Clinch-Powell Resource Conser vation and Development Council http://www.clinchpowell.net/ East Tennessee Development District http://www.etdd.org/front_page.htm Foothills Land Conser vancy http://www.foothillsland.org/ Knoxville-Knox County Metropolitan Planning Commission www.knoxmpc.org Plan East Tennessee (PlanET) http://www.planeasttn.org/ Smoky Mountain Resource Conser vation and Development Council http://www.smokymountainrcd.org/ STATE AGENCIES Tennessee Department of Agriculture, Water Resources http://www.tn.gov/agriculture/water/index.shtml Tennessee Department of Environment & Conser vation (TDEC), Water http://www.tn.gov/environment/water.shtml Tennessee Water Resources Research Center http://isse.utk.edu/wrrc/index.html Tennessee Wildlife Resources Agency http://www.tn.gov/twra/conser vation.html US Geological Sur vey (USGS) Tennessee Water Science Center h ttp://tn.water.usgs.gov/ University of Tennessee Extension h ttps://utextension.tennessee.edu/Pages/default.aspx STATE ORGANIZATIONS Tennessee American Water Resources Association http://tnawra.er.usgs.gov/ Tennessee Association of Utility Districts http://www.taud.org/ Tennessee Clean Water Network http://www.tcwn.org/ Tennessee Stormwater Association http://tnstormwater.org/ Tennessee Water and Wastewater Association http://www.twwa.us/ STATE AND FEDERAL WATER QUALITY REGULATIONS County Soil and Water Conser vation Districts Erosion Prevention and Sediment Control (EPSC) http://www.tnepsc.org/handbook.asp National Pollutant Discharge Elimination System (NPDES), EPA http://www.epa.gov/oecaerth/monitoring/programs/cwa/ npdes.html National Pollutant Discharge Elimination System (NPDES) Permits Program, Tennessee Department of Environment and Conser vation http://www.tn.gov/environment/permits/npdes.shtmlTN FEDERAL AGENCIES AND NATIONAL ORGANIZATIONS Natural Resources Conser vation Ser vice http://www.nrcs.usda.gov/wps/portal/nrcs/main/national/ water/ Oak Ridge National Laborator y (ORNL) Environmental Sciences Division http://www.esd.ornl.gov/index.shtml Tennessee Valley Authority (TVA), Water Quality http://www.tva.com/environment/water/index.htm United States Environmental Protection Agency (EPA), Region 4 Water Protection h ttp://www.epa.gov/region4/water/ United States Fish and Wildlife Ser vice www.fws.gov United States Geological Sur vey (USGS), Water Resources of the United States http://isse.utk.edu/wrrc/expertise/resources.html ECONOMIC STUDIES North Carolina Cooperative Extension http://www.ces.ncsu.edu/depts/agecon/WECO/nemo/ documents/WECO_LID_econ_factsheet.pdf ASLA Sustainable Landscapes Toolkit http://www.asla.org/ContentDetail.aspx?id=31837 GENERAL INFORMATION EPA “Surf Your Watershed” h ttp://cfpub.epa.gov/surf/locate/index.cfm Low Impact Development Center http://www.lowimpactdevelopment.org 203 photo credits Photos and images without attribution are by, and credited to, the University of Tennessee Landscape Architecture Program. Copyrights to all photos and images are held by the credited source. COVER Edward J. Dumas PREFACE AND INTRODUCTION ix Visit Knoxville (Knoxville CVB) 1 ©kmstewart Photography 5 ARCADIS 6 Aeroscenes Aerial Photography by Paul Varner 7 Paul Miller Photography PART I 17 204 18-19 27 29 (L) 29 (R) 30 33 35 39 Fort Loudoun Dam: flickr user tubesox_family Norris Dam: flickr user Br yce Giesler Visit Knoxville (Knoxville CVB) Aeroscenes Aerial Photography by Paul Varner Paul Miller Photography Legacy Parks Foundation Legacy Parks Foundation ©dreamstime.com Ibid Ralph Preston Photography PART II 42 (T) 43 44 (T) 46 48 52 (TL) 52 (Other) 63 (Base) 64 (Base) ©bingmaps.com Michael Patrick/Knoxville News Sentinel ©dreamstime.com Paul Miller Photography Aeroscenes Aerial Photography by Paul Varner ©dreamstime.com Aeroscenes Aerial Photography by Paul Varner Ibid Ibid PART III 85 (TL) 85 (TR, BL) 85 (BR) 89 94 95 (Base) 99 105 (Base) 111 (Base) 113 (Base) 115 (Base) 117 (Base) 119 (Base) 123 (Base) 127 (Base) 129 (Base) 131 (Base) 133 (Base) 137 (Base) 141 (Base) 141 (Insets) 143 (Base) 145 (Base) 150 151 152 154 162-163 172-173 176-177 178-179 180 Ralph Preston Photography Tennessee Department of Agriculture Oak Ridge National Laboratory, Natural Resources Hargreaves Associates Legacy Parks Foundation Ibid Various Government and Non Profit Websites Aeroscenes Aerial Photography by Paul Varner Tennessee Department of Agriculture Tennessee Yards and Neighborhoods Barge Waggoner Sumner and Cannon Hawkins Partners, Inc. Carol R. Johnson Associates Hedstrom Design, Inc. UT Environmental Design Lab Carol R. Johnson Associates ARCADIS Ashworth Environmental Design UT Environmental Design Lab Aeroscenes Aerial Photography by Paul Varner Dr. Bruce A. Tschantz, P.E. Aeroscenes Aerial Photography by Paul Varner Aeroscenes Aerial Photography by Paul Varner Hargreaves Associates Hawkins Partners, Inc. Carol R. Johnson Associates UT College of Architecture and Design, Ken McCown Ibid Hargreaves Associates UT College of Architecture and Design, Tracy Moir McClean, Mark DeKay Green City, Clean Waters + WRT Legacy Parks Foundation East Tennessee’s iconic water resources are a sustaining economic, social, and environmental asset. These resources are vulnerable to impacts from prevailing development patterns in the region, human activities, and existing stormwater infrastructure. Each increase the quantity of polluted stormwater runoff draining to the region’s streams, rivers, reser voirs, and groundwater resources, compromising their health and the health of the communities they sustain. With the Plan East Tennessee Region’s population poised to grow forty-three percent by 2040, reliance upon these water resources will increase while their health is further threatened by expanding development. Low Impact Development methods proposed in this publication offer existing and expanding communities an enhanced approach to watershed planning, community design, and site development that avoids, minimizes, and manages impacts to the region’s shared water resources. This publication is intended for a general audience ranging from homeowners to educators, government and stormwater officials, site designers and engineers, and developers. Ever yone lives in a watershed and has a role to play in the stewardship of shared water resources. While its focus is the five-county PlanET Region, the obser vations and concepts described in this publication are applicable to other parts of the state of Tennessee and the Southeastern United States that face similar water resource stewardship and NPDES compliance challenges. THE UNIVERSITY OF TENNESSEE, KNOXVILLE LANDSCAPE ARCHITECTURE www.archdesign.utk.edu 1715 Volunteer Blvd. Knoxville, TN 37996 program