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Analysis of Bioswale Efficiency in Treating Surface Runoff Analysis of Bioswale Efficiency for Treating Surface Runoff A Group Project submitted in partial satisfaction of the requirements of the degree Master of Environmental Science and Management Donald Bren School of Environmental Science and Management University of California, Santa Barbara By William W. Groves Phillip E. Hammer Karinne L. Knutsen Sheila M. Ryan Robert A. Schlipf Advisors: Jeff Dozier, Ph.D. Thomas Dunne, Ph.D. Analysis of Bioswale Efficiency for Treating Surface Runoff As authors of this group project, we are proud to archive it in the Davidson Library so that the results of our research are available for all to read. Our signatures on the document signify our joint responsibility in fulfilling the archiving standards set by Graduate Division, Davidson Library, and the Bren School of Environmental Science and Management. William W. Groves Phillip E. Hammer Karinne L. Knutsen Sheila M. Ryan Robert A. Schlipf This Group Project is approved by: Jeff Dozier, Ph.D. Thomas Dunne, Ph.D. Analysis of Bioswale Efficiency for Treating Surface Runoff Page ii Acknowledgements The Bioswale Group would like to thank the following organizations for their contributions in funding our research: • Wynmark Company • University of California Toxic Substances Research & Teaching Program, Coastal Component We also thank the following individuals for their valuable assistance: Mark Linehan, Wynmark Co. Kim Schizas, Wynmark Co. J.T. Yean, Fuscoe Engineering Cal Woolsey, Fuscoe Engineering Tom Dunne, Bren School Professor Jeff Dozier, Dean of the Bren School John Melack, Bren School Professor Trish Holden, Bren School Professor Linda Fernandez, Visiting Professor Darcy Aston, Santa Barbara County Water Agency Analysis of Bioswale Efficiency for Treating Surface Runoff Page iii Description of the Group Project The group project is a major component of the degree requirements for Master’s students in the Donald Bren School of Environmental Science and Management at the University of California, Santa Barbara. The project allows a group of students to tackle an issue involving both scientific investigation and management considerations. This process is meant to serve as a realistic introduction to working as an environmental professional. It provides the opportunity to work and communicate successfully in a team and to complete a professional project. The group structure allows for broader research and analysis of environmental problems than an individual could achieve. The process prepares individuals to successfully apply both technical and managerial skills to solving the myriad of complex issues that face the environmental community. The time frame for project completion is one year. Analysis of Bioswale Efficiency for Treating Surface Runoff Page iv Abstract Analysis of Bioswale Efficiency for Treatment of Surface Runoff William W. Groves Phillip E. Hammer Karinne L. Knutsen Sheila M. Ryan Robert A. Schlipf A bioswale is a low-gradient, open channel possessing a cover of vegetation through which all surface runoff is directed. Our analysis focused on the use of a bioswale to improve water quality exiting the site of a new project development in Goleta, CA. Field samples and modeling predictions were used to evaluate the overall performance of the bioswale and its contribution to decreasing pollutant loading to the sensitive estuary, Devereux Slough. The U.S. EPA Storm Water Management Model (SWMM) aided our understanding of future bioswale functioning when vegetation is fully established, and this model was used to analyze potential design modifications. We determined that the bioswale is a cost-efficient method for addressing the project developer’s main concerns: flood containment capacity, wetland mitigation, and reduction of pollutant loading off site. Analysis of Bioswale Efficiency for Treating Surface Runoff Page v Executive Summary The Camino Real project is a commercial development located in Goleta, California that includes a shopping center, entertainment facilities, associated parking lots, and playing fields. Stormwater runoff from the project site eventually reaches Devereux Slough, a nearby estuary. A bioswale was installed to minimize the potential impacts of stormwater runoff to Devereux Slough. This bioswale is expected to reduce the peak rate and total volume of stormwater runoff and to reduce total suspended solids and pollutants in stormwater runoff exiting the site. The bioswale is a low-gradient, open channel possessing a dense cover of vegetation through which all surface runoff is directed. The bioswale decreases the speed of flows, acts as a stormwater detention facility, and allows suspended solids to settle out. Aboveground plant parts filter particulates and their associated pollutants as runoff passes slowly and evenly through the channel. The pollutants are then incorporated into the soil where they may be immobilized and/or decomposed by plants and microbes. The bioswale is considered a creative means of controlling runoff, and has the potential to improve water quality, mitigate wetland loss, provide flood containment, and improve the aesthetics of the project site. As such, the bioswale has hydrologic, chemical, and biological functions. Economic considerations are also an important aspect for assessment of the bioswale and are addressed in the report. The three main questions the Bioswale Group Project sought to answer were: 1) To what extent does the bioswale improve water quality? 2) What is the total impact of the bioswale in the Devereux Creek Watershed? 3) Given other available options, is the bioswale a cost-effective water treatment method? Analysis of Bioswale Efficiency for Treating Surface Runoff Page vi To answer these questions, the bioswale group modeled the hydrology and water quality of the bioswale, sampled and analyzed stormwater at the site, and evaluated economic aspects of the use of a bioswale. The bioswale group project used the Storm Water Management Model (SWMM) to simulate the hydrologic and water quality processes of stormwater runoff for the Camino Real Project site. Modeling output included total flow volumes, total pollutant loads, hydrographs, and pollutographs for a wide range of storm events. These output values allowed for the assessment of potential changes in stormwater runoff quantity and quality resulting from the presence of the bioswale. We determined that the bioswale is cost-effective, taking into account its threefold purpose: flood containment capacity, wetland mitigation, and reduction of pollutant loading off site. Conclusions and recommendations were based on interpretations of field data and site observations, as well as on information from relevant documented studies. Analysis of Bioswale Efficiency for Treating Surface Runoff Page vii Table of Contents TABLE OF CONTENTS VIII 1.0 INTRODUCTION ................................................................................................... 1 1.1 PURPOSE AND NEED OF INVESTIGATION .................................................................4 2.0 BACKGROUND ..................................................................................................... 7 2.1 GENERAL DESCRIPTION OF CAMINO REAL PROJECT SITE AND ASSOCIATED AREAS ........................................................................................7 2.2 BIOSWALE DESCRIPTION .......................................................................................11 2.3 DEVEREUX SLOUGH ..............................................................................................16 2.4 STUDY DESCRIPTION .............................................................................................18 3.0 HYDROLOGIC AND HYDRAULIC PROCESSES .............................................. 21 3.1 CLIMATE ................................................................................................................21 3.2 HYDROLOGY OF THE SITE......................................................................................21 3.2.1 MEASUREMENTS AND CALCULATIONS OF OBSERVED FLOW .........................22 3.2.2 METHODOLOGY FOR CALCULATIONS OF PREDICTED FLOWS WITHOUT THE ORIFICE PLATE..........................................................................33 3.2.3 RESERVOIR ROUTING ......................................................................................38 3.2.4 DETENTION TIMES ...........................................................................................40 3.3 HYDRAULIC DESIGN ..............................................................................................42 3.4 SEDIMENT TRANSPORT..........................................................................................44 4.0 MODELING ......................................................................................................... 47 4.1 PURPOSE OF MODELING HYDROLOGIC AND CHEMICAL QUALITY PROCESSES ....47 4.2 SCREENING MODELS .............................................................................................48 4.3 DESCRIPTION OF SWMM ......................................................................................50 4.4 DESIGNATING SUBCATCHMENTS...........................................................................52 4.5 PARAMETERIZATION..............................................................................................55 4.6 CALIBRATION ........................................................................................................63 4.6.1 CALIBRATION OF STORMWATER RUNOFF QUANTITY.....................................63
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