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US EPA Green Roofs for Stormwater Runoff Control

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US EPA Green Roofs for Stormwater Runoff Control EPA/600/R-09/026 | February 2009 | www.epa.gov/ord Green Roofs for Stormwater Runoff Control Office of Research and Development National Risk Management Research Laboratory - Water Supply and Water Resources Division EPA/600/R-09/026 February, 2009 Green Roofs for Stormwater Runoff Control By Robert D. Berghage David Beattie Albert. R. Jarrett Christine Thuring Farzaneh Razaei The Pennsylvania State University University Park, PA 16802 Thomas P. O’Connor Urban Watershed Management Branch Water Supply and Water Resources Division National Risk Management Research Laboratory Edison, NJ 08837 Cooperative Agreement No. 83124401 NATIONAL RISK MANAGEMENT RESEARCH LABORATORY OFFICE OF RESEARCH AND DEVELOPMENT U.S. ENVIRONMENTAL PROTECTION AGENCY CINCINNATI, OH 45268 Notice The U.S. Environmental Protection Agency (EPA) through its Office of Research and Development performed and managed the research described here. It has been subjected to the Agency‘s peer and administrative review and has been approved for publication as an EPA document. Any opinions expressed in this report are those of the author and do not, necessarily, reflect the official positions and policies of the EPA. Any mention of products or trade names does not constitute recommendation for use by the EPA. ii Abstract This project evaluated green roofs as a stormwater management tool. Specifically, runoff quantity and quality from green and flat asphalt roofs were compared. Evapotranspiration from planted green roofs and evaporation from unplanted media roofs were also compared. The influence of media type, media depth and drought during plant establishment on plant growth and long-term management of media pH were investigated. The goal of the project was to provide high-quality replicated data which could be used to develop and refine reliable anticipated runoff volumes and loadings from green roofs, respectively, as well as evaluate factors which impact plant growth and establishment. Results indicate that the green roofs are capable of removing 50% of the annual rainfall volume from a roof through retention and evapotranspiration. Rainfall not retained by green roofs is detained, effectively increasing the time to peak, and slowing peak flows for a watershed. There are seasonal considerations as more runoff is generated during winter and for many summer storms there was no runoff. Green roof runoff does contain concentrations of some nutrients and other parameters, but values are in line with other planted systems. Due to the volume reduction, actual nutrient loadings from green roofs are less than asphalt roofing runoff or otherwise manageable at the downspout. iii Foreword The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the Nation’s land, air, and water resources. Under a mandate of national environmental laws, the Agency strives to formulate and implement actions leading to a compatible balance between human activities and the ability of natural systems to support and nurture life. To meet this mandate, EPA’s research program is providing data and technical support for solving environmental problems today and building a science knowledge base necessary to manage our ecological resources wisely, understand how pollutants affect our health, and prevent or reduce environmental risks in the future. The National Risk Management Research Laboratory (NRMRL) is the Agency’s center for investigation of technological and management approaches for preventing and reducing risks from pollution that threaten human health and the environment. The focus of the Laboratory’s research program is on methods and their cost- effectiveness for prevention and control of pollution to air, land, water, and subsurface resources; protection of water quality in public water systems; remediation of contaminated sites, sediments and ground water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies that reduce the cost of compliance and to anticipate emerging problems. NRMRL’s research provides solutions to environmental problems by: developing and promoting technologies that protect and improve the environment; advancing scientific and engineering information to support regulatory and policy decisions; and providing the technical support and information transfer to ensure implementation of environmental regulations and strategies at the national, state, and community levels. This publication has been produced as part of the Laboratory’s strategic long-term research plan. It is published and made available by EPA’s Office of Research and Development to assist the user community and to link researchers with their clients. Sally C. Gutierrez, Director National Risk Management Research Laboratory iv Contents Notice…………………………..………………………………….…………………………………………………ii Abstract………….……………...……………...……………….……………………………………………………iii Foreword………….……..……………………….…………..………………………………………………………iv Contents………………………………………………………………………………………………………….......v List of Figures….…..…………………………………………….…………………………………………………..vii List of Tables…..…………………………………………….…………….…………………………………...…….ix Acronyms and Abbreviations…………………………………………………………..…………………………….x Acknowledgements………………………………………………………………..…………………………………xi Executive Summary……………………………………………………………..…….………………………..………1 Chapter 1 Introduction.................................................................................................................................................. 1-1 Field Data .............................................................................................................................................................. 1-3 Greenhouse and Laboratory Experiments ............................................................................................................. 1-4 Chapter 2 Conclusions and Recommendations ............................................................................................................ 2-1 Conclusions............................................................................................................................................................... 2-1 Monitoring Stormwater Runoff from Green Roofs............................................................................................... 2-1 Monitoring Runoff Water Quality from Green Roofs........................................................................................... 2-1 Evaluating Evaporation and Evapotranspiration Rates of Green Roofs................................................................ 2-2 Factors Affecting Green Roof Establishment and Maintenance ........................................................................... 2-2 Implications........................................................................................................................................................... 2-2 Recommendations..................................................................................................................................................... 2-3 Chapter 3 Green Roof Effects on Runoff Quantity ...................................................................................................... 3-1 Introduction............................................................................................................................................................... 3-1 Methods..................................................................................................................................................................... 3-1 Precipitation Summary.............................................................................................................................................. 3-2 Analysis..................................................................................................................................................................... 3-5 Roof Runoff Volumes ........................................................................................................................................... 3-5 Peak Hydrograph Analysis.................................................................................................................................. 3-12 Summary................................................................................................................................................................. 3-14 Chapter 4 Green Roof Effects on Runoff Quality ........................................................................................................ 4-1 Introduction............................................................................................................................................................... 4-1 Runoff Summary....................................................................................................................................................... 4-1 Methods and Analyses .............................................................................................................................................. 4-3 Color and Turbidity............................................................................................................................................... 4-3 pH.......................................................................................................................................................................... 4-5 Electrical Conductivity.........................................................................................................................................
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