Wet-Weather Flow in the Urban Watershed: Technology and Management [1 ed.] 1566769167, 9781566769167, 9781420012774

Citation preview

Wet-Weather Flow in the Urban Watershed Technology and Management Edited by

Richard Field and Daniel Sullivan

LEWIS PUBLISHERS A CRC Press Company Boca Raton London New York Washington, D.C.

Library of Congress Cataloging-in-Publication Data Wet-weather flow in the urban watershed : technology and management / edited by Richard Field and Daniel Sullivan. p. cm. Includes bibliographical references. ISBN 1-56676-916-7 (alk. paper) 1. Urban runoff--Management. I. Field, Richard, 1939- II. Sullivan, Daniel, 1948TD657 .W48 2002 628′.231—dc21

2002067138

This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the authors and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher. All rights reserved. Authorization to photocopy items for internal or personal use, or the personal or internal use of specific clients, may be granted by CRC Press LLC, provided that $1.50 per page photocopied is paid directly to Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923 USA The fee code for users of the Transactional Reporting Service is ISBN 1-56676-916-7/03/$0.00+$1.50. The fee is subject to change without notice. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from CRC Press LLC for such copying. Direct all inquiries to CRC Press LLC, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe.

Visit the CRC Press Web site at www.crcpress.com © 2003 by CRC Press LLC Lewis Publishers is an imprint of CRC Press LLC No claim to original U.S. Government works International Standard Book Number 1-56676-916-7 Library of Congress Card Number 2002067138 Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Printed on acid-free paper

Preface It is an honor for us to have this opportunity to present this book on management of urban wetweather flow (WWF) in the watershed. This book is based principally on seminars presented by international experts to those professionals interested in urban WWF management. These seminars took place at the U.S. Environmental Protection Agency (U.S. EPA) in Edison, New Jersey and were organized by the Urban Watershed Management Branch (UWMB), Water Supply and Water Resources Division, National Risk Management Research Laboratory, Office of Research and Development, U.S. EPA. Seminar attendees mainly comprised staff members of the UWMB but also included representatives of U.S. EPA Region 2, U.S. EPA Office of Water, New Jersey Department of Environmental Protection, New York City Environmental Protection Administration, academia, and the consulting engineering sector. Chapter 1 (Management of Wet Weather Flow in the Urban Watershed), Chapter 8 (Management of Urban Wet Weather Flow Solids), and Chapter 9 (Beneficial Use of Urban Stormwater) were coauthored by Richard Field and Daniel Sullivan (Chapter 1), Chi-Yuan Fan (Chapter 8), and ChiYuan Fan and Richard Field (Chapter 9) who are members of the UWMB. The significance of urban WWF upsets and storm-generated pollution was recognized by the predecessor organization of the U.S. EPA, The U.S. Department of Health, Education, and Welfare, Public Health Service in its report “Pollutional Effects of Stormwater and Overflows from Combined Sewer Systems — A Preliminary Appraisal,” No. 1246, published in November 1964. The most notable developments since have been The National Pollution Discharge Elimination System Permit Application Regulations for Stormwater Discharges, 55 Federal Register 47990, November 16, 1990, and The National Combined Sewer Overflow Control Policy, 59 Federal Register 18688, April 19, 1994. When the U.S. EPA predecessor began its research work in urban storm-generated pollution control and stormwater management in 1965, the field was in its infancy. It is gratifying to see this field growing and gaining the international recognition it deserves. Abatement or prevention of pollution from storm-generated flow is one of the most challenging areas in the environmental engineering field. The facts of life — from an engineering standpoint — are difficult to face in terms of design and cost. Operational problems can be just as foreboding. The full impacts of “marginal” pollution, particularly that caused by uncontrolled overflows, must be recognized now and planning initiated to improve sewerage system efficiencies and bring all wastewater flows under control. Municipal programs with this objective cannot begin too soon because corrective action is time-consuming. Efforts devoted to improved sewerage systems will pay significant dividends in complete control of metropolitan wastewater problems and pollution abatement. Research and development are making available important answers on the most efficient and least costly methods needed to restore and maintain water resources for maximum usefulness to humans. It is clear that abatement requirements for storm-flow pollution are forthcoming. Already, federal and local governments have promulgated WWF treatment and control rules and standards. Now developed and developing regions can take advantage of a crucial opportunity and assess what has transpired around the globe and determine their own best water management strategy. To exemplify this, we can consider the water pollution control efforts in the United States. Historically, this nation has always approached water pollution control in a serial and segmented manner with respect to time and pollutant sources, respectively. The result is that the nation is still fighting the problem after more than 70 years of effort and tens of billions of dollars of expenditures.

Initially, it abated sanitary sewage; first with primary treatment, and later, only after a long time, with secondary treatment. Somewhere between attempts to control sanitary sewage, industrial wastewater control became a requirement; however, pretreated industrial wastewaters are still released during an overflow event. Only recently was the nation forced to control combined sewer overflow (CSO), and now it is faced with requirements to abate separate stormwater pollution. The aforementioned historical approach to water pollution control has taken a very long time, and only after trial and error of each individualized and fragmented approach was it learned that receivingwater pollution problems remain. If, instead, an entire watershed or multidrainage area analysis had been conducted earlier, a determination could have been made of the overall pollution problem in the receiving water bodies; the pollution sources (or culprits) contributing to the problem; and an optimized, integrated, areawide program to correct the problem. After the macro- (or large-scale watershed) analysis is conducted, an optimized determination of what sources to be abated (or where to spend the monies) will be made. Then, with the resulting information, a micro- (or drainage area/pollutant source and control) analysis can be performed. Toxicants must also be part of the study. Past research has shown that storm-flow toxicants and resultant toxicity can significantly affect health and the environment. Regulations for toxicant control have been promulgated and will become more demanding. The control system designs should at least be made flexible to treat toxicants once toxicant control requirements are enforced. Prevention of toxic substance pollution must also be addressed. There is one other important factor that must be considered, i.e., the use and reclamation of stormwater for such beneficial purposes as aesthetic and recreational ponds, groundwater recharge, irrigation, fire protection, and industrial water supply. An optimal approach to integrated stormwater management is a total watershed or basinwide analysis including a macro- or large-basin-scale evaluation interfaced with a discretized micro- or small-catchment-scale evaluation involving the integration of (1) all catchments or drainage areas, tributaries, surrounding water bodies, and groundwater; (2) all pollutant source areas, land uses, and flows, i.e., combined sewer drainage areas, separate storm drainage areas including their dry weather discharges containing unauthorized or inappropriate cross-connections, existing water pollution control plant effluents, industrial wastewater discharges, discharges from other land uses, and air pollution fallout; and (3) added storm-flow sludge and residual solids handling and disposal. Flood and erosion control along with beneficial use and reclamation technology must also be integrated with pollution control, so that the retention and drainage facilities required for flood and erosion control can be simultaneously designed or retrofitted for pollution control and stormwater reclamation. In conclusion, knowledge of interconnecting basinwide waters and pollutant loads affecting the receiving water body and the subsurface and groundwater will result in knowing how to attain the optimum water resource and pollution abatement and a much more expedient and cost-effective water management program. This book covers a broad spectrum of urban WWF management and pollution abatement topics that will assist municipal engineers and consultants and be an important reference for academia. It includes WWF characteristics and a database, a Source Loading and Management Model (SLAMM), urban stormwater pollution abatement technologies and sediment management, lowimpact development, and stream protection and restoration. Richard Field Daniel Sullivan

Acknowledgments A book of this nature results from the experiences and expertise of many and, in particular, from the volunteer efforts of a dedicated few to whom we are grateful. To the U.S. EPA, Water Supply and Water Resources Division, National Risk Management Research Laboratory, Office of Research and Development, who provided for this extremely important Urban Wet Weather Flow Management Research Program without which this book would not have been written. To our colleagues, who over the last four decades have given us the opportunity to learn from them. To our co-authors, for their dedication and perseverance, who took the time from their active schedules to communicate and share their experiences. To Marie Casserly of the U.S. EPA Urban Watershed Management Branch (UWMB), who as Branch Secretary made outstanding contributions with her dedicated word processing. To Carl Carco and Jaime Marin of Computer Sciences Corporation, who provide computer technical support to the UWMB, for their dedicated efforts to convert book chapters to the publisher’s format. And, finally, and most important, to Richard Field’s wife, Joan, and his children, Robyn, Stacie, and Shawn, and to Daniel Sullivan’s dear friend, Lynette Hamara, and his son, Robert Michael, for their constant support by being there.

About the Editors Richard Field received a bachelor of civil engineering degree from the City College of New York (CCNY) in 1962 and a master of civil engineering degree (sanitary engineering option) from New York University (NYU) in 1963, graduating first in his class. He has since taken many postgraduate courses related to environmental engineering, construction technology, advanced mathematics, computer technology, etc. Mr. Field has worked in the environmental engineering field for 39 years. He is a registered professional engineer (P.E.) in the States of New York and New Jersey; a member of Chi-Epsilon National Civil Engineering Honor Fraternity; a member of the American Society of Civil Engineers (ASCE) and an executive committee member of its Urban Water Resources Research Council. He has been a member of the following committees: The Water Environment Federation (WEF) Water Environment Research Foundation Wet Weather Advisory Panel and Research Committee covering urban wet weather flows, the Environment Canada (the Canadian federal environmental agency) Steering Committee on CSO High-Rate Treatment, and the U.S. Environmental Protection Agency (U.S. EPA) Sanitary Sewer Overflow (SSO) Advisory Committee and Urban Wet Weather Flow Subcommittee. Since May 1970, he has been in charge of the U.S. EPA National Storm and CSO (combined sewer overflow) Technology Research and Development Program located at the National Risk Management Research Laboratory in Edison, New Jersey. Mr. Field has received numerous outstanding achievement awards and citations for on-the-job performance and technological contribution including two U.S. EPA bronze medals, the ASCE State-of-the-Art of Civil Engineering Award, two New York Water Pollution Control Association awards for excellence in technological advancement, three U.S. EPA Scientific and Technological Achievement awards including a first level award, and a first place U.S. EPA National Award in the CSO category. He has authored and coauthored, presented, and/or published a combination of more than 800 peer-reviewed articles/conference proceedings/papers/other papers/U.S.EPA reports/books and book chapters, some of which are internationally recognized publications in his field. He has been invited to lecture and present seminars throughout the world and has presented more than 300 times. Mr. Field is a U.S. EPA expert and an internationally recognized expert in urban wet weather discharge impacts and control technology including the areas of CSO, SSO, and infiltration/inflow (I/I), urban stormwater, diffuse or nonpoint sources, and watershed management. He is listed in Who’s Who in Engineering, Who’s Who in Technology Today, Who’s Who in Science and Engineering, Who’s Who in Finance and Industry, Who’s Who in the East, International Who’s Who of Professionals, and Who’s Who in the World.

Daniel Sullivan received a bachelor of science in civil engineering from the Polytechnic Institute of Brooklyn in 1968 and a master of science in environmental sciences and engineering from the University of North Carolina in 1970. He has worked in the environmental engineering field for 32 years, is a registered professional engineer in the states of New York and New Jersey; a professional planner in New Jersey; and a member of Chi Epsilon, the National Civil Engineering Honor Fraternity. Since 1995 he has been Chief of the Urban Watershed Management Branch, which conducts the U.S. EPA national wet weather flow and watershed management research program. He began his U.S. EPA career in 1972 and has authored and coauthored, presented, and/or published a combination of more that 100 peer-reviewed articles/conference proceedings/papers, U.S. EPA reports/book chapters in topics of hazardous waste control and wet weather flow. He has received two U.S. EPA bronze medals for work in the U.S. EPA wet weather flow research program and environmental technology verification program.

About the Contributors Richard M. Ashley is professor of environmental engineering and leads the Environmental Engineering Research Group at the University of Bradford, U.K. He is an accredited engineer, who has produced more than 150 publications. He is co-director of the Pennine Water Group (with the University of Sheffield) and an expert in sewer processes. He has researched all aspects of sewer solids over the past 20 years, and more recently has become involved in the development of wastewater systems that are more sustainable. He is currently working with Professor HvitvedJacobsen to produce a scientific and technical report on “Sewer Solids — State of the Art” for the International Water Association. Kelly A. Cave is the Director of the Watershed Management Division at the Wayne County Department of Environment, Detroit, Michigan. Ms. Cave manages the Rouge River National Wet Weather Demonstration Project (Rouge Project), a U.S. EPA-funded demonstration of a watershed approach to water pollution control in a major urban area. Ms. Cave has been involved with the Rouge Project since 1994, and has participated in design, implementation, and analysis of variety of watershed management and assessment techniques including combined sewer overflow control, stormwater management, water quality modeling and monitoring, public education and involvement, and habitat restoration. She has written various papers and given presentations about the Rouge Project. Prior to joining Wayne County, Ms. Cave worked on a variety of watershed and stormwater management projects nationwide during her 10-year employment by Camp Dresser & McKee. Ms. Cave received a B.S. and M.S. in civil engineering from Virginia Polytechnic Institute and State University in 1984 and 1986, respectively. Ms. Cave is a licensed professional engineer in Michigan and Virginia. Mow-Soung Cheng is the chief of the Technical Support Section in the Department of Environmental Resources, Prince George’s County, Maryland, and is responsible for promoting, enhancing, and advancing technologies for the county’s stormwater management programs. He is one of the major developers of the low-impact development concept being used in the county and being fostered by the U.S. EPA. He is a registered professional engineer in several states in the United States and is a graduate of Cheng-Kung University with a bachelor’s degree in hydraulic engineering, University of Pittsburgh with a master’s degree in civil engineering, and of the University of Iowa with a Ph.D. in water resources system engineering. He has published many technical papers in professional journals and conference proceedings and has made numerous technical presentations. Michael L. Clar, president of Ecosile, Inc., Ellicott City, Maryland, received his B.S. in civil engineering in 1971 from the University of Maryland and his M.S. in mining engineering in 1978 from the Pennsylvania State University. He is a registered professional engineer in Maryland and Pennsylvania, a member of the American Society of Civil Engineers (ASCE) serving as chairperson of ASCE Urban Water Resources Research Council, past president of Suburban Maryland Engineers Society, and President of the Maryland Society of Professional Engineers. Mr. Clar is a nationally recognized expert in stormwater management technology with over 30 years’ experience in the field. He is a key contributor to the development and implementation of low-impact development design, stream protection and restoration, and stormwater bioretention.

Shirley Clark received her Ph.D. in environmental health engineering and M.S.C.E. from the University of Alabama at Birmingham (UAB). She also holds a B.S. in chemical engineering from Washington University in St. Louis. She is a registered professional engineer in Alabama. She is currently an assistant professor in the Department of Civil and Environmental Engineering at UAB. Prior to returning to UAB as a faculty member, she completed a 1-year post-doctoral appointment as a research engineer at the U.S. EPA Urban Watershed Management Branch in Edison, New Jersey. Between getting her bachelor’s and master’s degrees, she was associated with two environmental consulting firms in the New England area. She is a member of the American Society of Civil Engineers, the American Water Works Association, the American Water Resources Association, and the Water Environment Federation. At UAB, she teaches classes in hydrology, water supply and drainage design, and water and wastewater treatment. She has also taught units on water quality in several School of Public Health classes at UAB. Her current research focus is on the treatment of urban stormwater runoff and on pollution prevention through construction material substitution. She has published more than 20 major journal articles, conference papers, and reports on stormwater runoff treatment. Larry S. Coffman is the associate director of the Programs and Planning Division within the Prince George’s County, Maryland Department of Environmental Resources. Currently, he is responsible for oversight of many of the county’s environmental programs, including water and sewer planning, comprehensive watershed planning activities, natural resources conservation/restoration, NPDES stormwater management program, capital improvement programs for flood control, environmental restoration, and urban retrofit programs. He receive a bachelor of science in biology and chemistry from Lehigh University and has over 28 years of experience in the planning, development, and administration of the Prince George’s County stormwater management and water quality protection program. Mr. Coffman pioneered the development of the bioretention technology or “rain gardens” and his work on the development of the county’s low-impact development design approach for ecologically based and environmentally sensitive site designs resulted in Prince George’s County winning the U.S. EPA 1998 First Place National Excellence Award for Municipal Stormwater Programs. Chi-Yuan (Evan) Fan has been working for the U.S. EPA for the last 30 years and has held several positions as an environmental engineer in the U.S. EPA Region II office and in the ORD National Risk Management Research Laboratory (NRMRL and predecessor organizations). His current primary research interests are the development and demonstration of methodologies for designing integrated wet weather flow collection, control, and treatment for urban watershed. From 1988 to 1995, he was a researcher with the Superfund Technology Demonstration Division, and involved in the development of a series of in situ soil vapor extraction–based systems for removing volatile organic chemicals in the unsaturated zone. Prior to this position, he was an environmental engineer in the U.S. EPA Region II Water Division, in the U.S. EPA ORD/MERL Storm and Combined Sewer Technology Program, and with a number of consulting engineering firms in New York City. He has received three U.S. EPA bronze medals and has published over 70 articles, book chapters, and reports on wet weather flow control and treatment, the assessment of organic-contaminated sites, and evaluation of technologies for cleaning up these sites. He received his master’s degree in civil engineering with a sanitary engineering major from New Mexico State University and his B.S. in civil engineering from Chung-Yuan College of Science and Engineering in Taiwan, Republic of China. He is a registered professional engineer and a diplomate in the American Academy of Environmental Engineers. James W. Gracie is founder and president of Brightwater, Inc., Ellicott City, Maryland. Mr. Gracie, during the past 30 years, has developed expertise in overall watershed management techniques for stream and wetland protection, stream restoration, and fisheries management. His experience

includes developing water quality monitoring efforts throughout the country and advancing the science of stream restoration in conjunction with Maryland State Highway projects and private development plans. Mr. Gracie has trained hundreds of individuals in short courses on “Applied Fluvial Geomorphology and Stream Restoration.” Mr. Gracie’s participation and leadership in state, local, regional, and national natural resource conservation efforts has provided him with extensive experience in water resources management. As twice chairman of the Board of Trout Unlimited, he provided leadership for an international conservation organization of 50,000 members and 350 local chapters in the United States interested in stream and fisheries management. Mr. Gracie organized and managed the Trout Unlimited chapter in Maryland and the Middle Atlantic council. He also assisted in the development of the Maryland citizens’ organization, Save Our Streams, and served as vice chairman of its Steering Committee. During this period, Mr. Gracie formed and managed the Maryland Cold Water Coalition, a coordinating body for groups concerned with the water quality of Maryland streams. He also served as director and executive committee member of the Maryland Wildlife Federation from 1979 through 1981. Jonathan Hird is a water resources engineer with FTN Associates, Ltd and received his M.S. degree in civil engineering from Louisiana State University in 2001 and B.S. from the University of East Anglia, England in 1993. While at Louisiana State University he worked diligently with his mentor, John Sansalone, on the subject of urban stormwater pollution control technology. T. Hvitved-Jacobsen is professor of environmental engineering, Aalborg University, Institute of Life Sciences, Department of Environmental Engineering, Denmark. He is an eminent engineer, with a substantial reputation in the field of wastewater system processes. He has undertaken research in drainage systems for several decades, and is currently chairman of the Sewer Systems and Processes Working Group of the Joint Urban Drainage Committee of the International Water Association (IWA)/International Association of Hydraulic Research (IAHR). He has produced more than 160 publications, many of which have been refereed. His latest publication is a book for CRC Press: Sewer Processes — Microbial and Chemical Process Engineering of Sewer Networks. Robert Pitt is currently a professor in the Department of Civil and Environmental Engineering at the University of Alabama, Tuscaloosa. He had previously served on the School of Engineering faculty at the University of Alabama at Birmingham, since 1987. Prior to that, he was a senior engineer for 16 years in industry and government, and continues to consult to many municipalities and engineering firms. He received his Ph.D. in civil and environmental engineering from the University of Wisconsin — Madison, his M.S.C.E. in environmental engineering/hydraulic engineering from San Jose State University, California and his B.S. in engineering science, from Humboldt State University, Arcata, California. He is a registered professional engineer (Wisconsin) and a diplomate of the American Academy of Environmental Engineers. During the past 30 years, Dr. Pitt has been the principal investigator for many water resources research projects conducted for the U.S. EPA, Environment Canada, Ontario Ministry of the Environment, and state and local governments concerning the effects, sources, and control of urban runoff. Bob has published more than 100 chapters, books, journal articles, and major research reports. He is a member of the ASCE, the WEF, the North American Lake Management Society, the AWRA, and the Society for Environmental Toxicology and Chemistry. John J. Sansalone is the Louisiana Land and Exploration Assistant Professor at Louisiana State University and has held faculty positions at the University of Cincinnati and the University of Calabria, Cosenza, Italy. He received his Ph.D. in environmental engineering from the University of Cincinnati in 1996 and is a professional engineer in Ohio. His research areas include physical and chemical treatment operations/processes for urban stormwater and snowmelt, and innovative treatment/reuse of wastewater, stormwater, residuals, environmental hydrology, high-rate anaerobic

digestion, geoenvironmental engineering, and development of multipurpose urban infrastructure. Dr. Sansalone has experience as an academic, a consulting engineer, and a design/build general contractor. He has written more than 25 peer-reviewed publications and given over 100 conference/symposium presentations. Dr. Sansalone is active on many national and international professional committees. James T. Smullen is the National Hydraulics and Hydrology Discipline Leader and a senior vice president with Camp Dresser & McKee, Edison, New Jersey. His 20 years of experience in surface water management and water resource program planning include combined sewer overflow (CSO), sanitary sewer overflow (SSO), and stormwater planning and permitting; evaluation of point and nonpoint pollution control strategies; stormwater best management practice (BMP) development and alternative screening; quantitative environmental analyses and assessments of aquatic and marine systems; modeling and assessments of watershed hydrology and water quality; field instrumentation, data collection, and reporting for urban and agricultural, rainfall/runoff/water quality monitoring. Dr. Smullen holds a bachelor of science in civil and environmental engineering, a bachelor of arts in economics, and a master of science in civil and environmental engineering, from Rutgers University, and a doctor of philosophy in marine studies from the University of Delaware. He is a diplomate of the American Academy of Environmental Engineers and is licensed as a professional engineer in Delaware, New Jersey, and Pennsylvania. John G. Voorhees III has more than 13 years experience on water resources–related projects. These include stormwater modeling, floodplain modeling, and groundwater flow and contamination. He is a codeveloper of the urban stormwater quality model WinSLAMM and WinDETPOND, a detention pond water quality model. He is currently employed at the Wisconsin Department of Transportation as a stormwater engineer, where he is updating the department’s stormwater and erosion control rule as well as preparing the statewide technical design guidelines and conducting training for stormwater and erosion control. He has a B.S and M.S. in civil and environmental engineering from the University of Wisconsin — Madison. John is a professional engineer in Wisconsin. He has taught seminars and short courses for the University of Wisconsin Extension, the Minnesota Department of Pollution Control, the Wisconsin Department of Transportation, and the New York Department of Transportation.

Table of Contents Chapter 1

Management of Wet Weather Flow in the Urban Watershed.....................................1

Richard Field and Daniel Sullivan Chapter 2

The Physical and Chemical Nature of Urban Stormwater Runoff Pollutants .........43

John Sansalone Chapter 3

National Stormwater Runoff Pollution Database .....................................................67

James T. Smullen and Kelly A. Cave Chapter 4

SLAMM: The Source Loading and Management Model ........................................79

Robert Pitt and John G. Voorhees III Chapter 5

Emerging Stormwater Controls for Critical Source Areas.....................................103

Robert Pitt and Shirley Clark Chapter 6

Treatment of Stormwater Runoff from Urban Pavement and Roadways..............141

John J. Sansalone and Jonathan Hird Chapter 7

Management of Sewer Sediments...........................................................................187

Richard M. Ashley and T. Hvitved-Jacobsen Chapter 8

Management of Wet Weather Flow Solids .............................................................225

Chi-Yuan Fan Chapter 9

Beneficial Use of Urban Stormwater......................................................................257

Chi-Yuan Fan and Richard Field Chapter 10 Low-Impact Development: An Ecologically Sensitive Alternative for Stormwater Management ........................................................................................271 Larry S. Coffman and Michael L. Clar Chapter 11 Low Impact Development: Hydrologic Analysis ...................................................295 Mow-Soung Cheng, Larry S. Coffman, and Michael L. Clar

Chapter 12 Geomorphic Considerations in Stream Protection .................................................315 Michael L. Clar Chapter 13 Geomorphic Considerations in Stream Restoration ...............................................343 James W. Gracie Index ..............................................................................................................................................369

1

Management of Wet Weather Flow in the Urban Watershed Richard Field and Daniel Sullivan

CONTENTS Introduction ........................................................................................................................................2 General Approach and Strategy .........................................................................................................2 Small Storm Hydrology..............................................................................................................2 Strategy .......................................................................................................................................3 Watershed Area Technologies and Practices .....................................................................................6 Regulations, Local Ordinances, and Public Education............................................................10 Source Control of Pollutants ....................................................................................................11 Source Treatment, Flow Attenuation, and Storm Runoff Infiltration .............................................14 Vegetative BMPs.......................................................................................................................14 Swales..............................................................................................................................14 Filter Strips......................................................................................................................14 Stormwater Wetlands.......................................................................................................14 Detention Facilities ...................................................................................................................15 Extended Detention Dry Ponds ......................................................................................15 Wet Ponds........................................................................................................................15 Infiltration Practices ..................................................................................................................16 Infiltration Trenches ........................................................................................................16 Infiltration Basins ............................................................................................................16 Porous Pavement .............................................................................................................16 Installed Drainage System ...............................................................................................................17 Illicit or Inappropriate Cross-Connections ...............................................................................18 Catchbasin Cleaning .................................................................................................................18 Critical Source Area Treatment Devices ..................................................................................19 Sand Filters......................................................................................................................19 Oil–Grit Separators .........................................................................................................20 Enhanced Treatment Device ...........................................................................................20 Infiltration..................................................................................................................................21 In-Line Storage .........................................................................................................................22 Off-Line Storage .......................................................................................................................23 Flow Balance Method .....................................................................................................23 Maintenance ..............................................................................................................................25 End-of-Pipe Treatment.....................................................................................................................25 Biological Treatment.................................................................................................................25 Use of Existing Treatment Facilities ........................................................................................25 Physical/Chemical Treatment ...................................................................................................25

1

2

Wet-Weather Flow in the Urban Watershed: Technology and Management

Screening .........................................................................................................................26 Filtration ..........................................................................................................................27 Dissolved Air Flotation ...................................................................................................30 High-Gradient Magnetic Separation ...............................................................................31 Powdered Activated Carbon-Alum Coagulation.............................................................32 Disinfection .....................................................................................................................32 Swirl Regulators/Concentrators ......................................................................................35 Storage and Treatment Optimization...............................................................................................35 Beneficial Reuse of Stormwater ......................................................................................................36 References ........................................................................................................................................37

INTRODUCTION This chapter covers the control and treatment of stormwater in relation to the removal or reduction of stormwater pollutant loads. Although the control of stormwater to prevent flooding is not the emphasis of this chapter; the pollution abatement technologies discussed will help attenuate stormwater flows. However, as they are generally designed for small storm events, they will not provide sufficient capacity for the large events. Although prevention of stormwater flooding is not discussed in this chapter, a drainage system design should consider both pollutant and flooding aspects of stormwater.

GENERAL APPROACH AND STRATEGY SMALL STORM HYDROLOGY The selection of suitable abatement technologies requires an understanding of the size and distribution of storm events. These contribute to total volume of storm runoff and, with knowledge of the pollutant concentrations, provide the total pollutant load. Generally the smaller storm events are the critical storms to consider because for many parts of the United States, 85% of all the rains are less than 0.6 in. (15 mm) in depth and can generate about 70% of the total annual storm runoff (Pitt, 1987). The characteristics of small and large storm events can be very different in terms of the storm runoff generated, pollutant load, and receiving water impacts. However, the frequent small storms will have a more persistent impact, and less frequent large storms will have a larger impact but allow time for recovery between events. For small storm events, any inaccuracy in the estimation of the initial abstractions and the soil infiltration rates can significantly change the calculated storm runoff pollutant load. The initial abstractions include the rainfall depth required to satisfy surface wetting, surface depression storage, interception by hanging vegetation, and evaporation. Together with soil infiltration rates, the initial abstractions need to be accurately estimated to calculate the storm runoff volume. Initial abstractions for relatively impervious urban surfaces have been found to account for the first 0.2 to 0.4 in. (5 to 10 mm) of a storm event (Pitt, 1987). Others (Pecher, 1969; Viessman et al., 1977) have reported initial abstractions of between 0.02 and 0.14 in. (0.5 and 3.5 mm) for pavement areas depending on whether the areas are flat or sloping steeply. Figure 1.1 illustrates the runoff capture volume rates in Cincinnati, Ohio. Note that 95% of the runoff will be captured for the first 0.5 watershed in. (12.7 mm) (as stated above, 85% of all storms are less than 0.6 in., or 15 mm). This indicates that small precipitation events need to be considered when designing stormwater quality treatment facilities. Increases in design detention volume above these values will not significantly affect the percent capture (Urbonas and Stahre, 1993). Traditional stormwater flood control is concerned with the peak storm runoff flow rates from relatively infrequent large storm events and their conveyance to prevent flooding. This is a different

3

Management of Wet Weather Flow in the Urban Watershed

Storage volume in millimeters* 5 10 15 20

100

25

Percent capture

90 80

Percent of runoff captured by various levels of storage

70

Runoff coefficient C = 0.5 Runoff = 15.8 in./yr (401 mm/yr) Storm events = 80/yr

60 50 0.0

0.2 0.4 0.6 0.8 1.0 Storage volume in inches* *Storage is the equivalent depth of water over entire tributary watershed.

FIGURE 1.1 Runoff capture volume rates in Cincinnati, Ohio. (From Urbonas, B. and Stahre, P., Stormwater: Best Management Practices and Detention, Prentice-Hall, Englewood Cliffs, NJ, 1993. With permission.)

set of criteria from that needed for storm runoff pollution control. Therefore, the data, storm runoff coefficients, models, etc. intended or developed to meet stormwater flood control requirements should be used with caution. This is illustrated by initial abstractions that can be a major portion of a small storm but will be a relatively insignificant portion of a large storm. In other words, just because a model for an area has been verified as providing accurate information for large storm events does not mean it will predict small events with the same level of confidence. A model developed and at present being updated for the calculation of urban stormwater runoff pollutant loads from small storms is Source Loading and Management Model: An Urban Nonpoint Source Water Quality Model (SLAMM) (Pitt, 1988). This model concentrates on the parameters discussed above to estimate better the urban storm runoff pollutant loads before and after application of best management practices (BMPs). However, this is mainly applicable to small areas and does not give a continuous time analysis. There are, however, a number of other models such as the U.S. EPA Storm Water Management Model (SWMM), which will allow a continuous time analysis for large drainage areas. Continuous time analysis will provide an optimum design for storage and treatment facilities based on long-term historical weather patterns. It should not be assumed from the above that the large, infrequent storm events do not cause polluted urban storm runoff or significant impacts on receiving waters but that their infrequency makes them a less significant factor than the smaller, frequent storms. Communities must design control systems that meet applicable regulations, and these systems may include large systems. There are several other factors that will affect the stormwater runoff pollutants and their concentrations, as discussed elsewhere, and these will also need to be taken into consideration when estimates are made of the urban storm runoff pollutant load.

STRATEGY The intermittent, widespread, and variable nature of urban stormwater runoff will require a flexible and creative approach to achieve the optimal control and treatment solution. This approach is likely to be a response to regulations and may not include BMPs and treatment processes. Traditional wastewater treatment methods, particularly secondary treatment processes that tend to operate under conditions closer to steady state, will not necessarily be suitable for the fluctuating loads of stormwater runoff. On the other hand, technologies used to control and treat combined sewer overflows (CSOs) are more likely to be applicable for the stormwater runoff and advantage should

4

Wet-Weather Flow in the Urban Watershed: Technology and Management

be taken of any experience or facilities of CSO origin that have application for separate stormwater runoff. Successful stormwater management to control urban storm runoff pollution will require an areawide approach combining prevention, reduction, and treatment practices/technologies. It is highly unlikely that one method will provide the best solution to control the widespread, diffuse nature of stormwater runoff and achieve the water quality required. Establishing an urban storm runoff pollution prevention and control plan requires a structured strategy, which will include the following steps: • • • • • • • • •

Define existing conditions. Set site-specific goals. Collect and analyze data. Refine site-specific goals. Assess and rank problems. Screen BMPs and treatment technologies. Select BMPs and treatment technologies. Implement plan. Monitor and reevaluate.

It is very likely that advantage can be taken of previous studies for either stormwater or CSO to get a head start. The above strategy is described in “Handbook: Urban Runoff Pollution Prevention and Control Planning” (U.S. Environmental Protection Agency, 1993a). Additional references that describe planning approaches for urban storm runoff pollution prevention and control are contained in Table 1.1. The above strategy will provide the control goals that are then used as the basis for selection of suitable technologies or approaches. The goals should initially be broad because the process of reviewing the technologies or approaches available will in itself generate information to focus and refine the goals to meet cost, level of control, public opinion, feasibility, and other restraints. A flexible approach, which through an iterative process of review and adjustment is focused to a specific action plan, is the only real way the complexity of urban stormwater can be managed. The specific action plan will also need to be subject to reassessment once feedback on its implementation is available. The above is only a very brief indication of the extensive work that will be required before the actual abatement technologies are implemented, and more detail is given in the above reference (U.S. Environmental Protection Agency, 1993a). The remainder of this chapter is concerned with an overview of the abatement technologies available. The chapter reviews the technologies by separating the drainage system into three physical areas: 1. Watershed area (i.e., storm runoff generation/collection area) 2. Installed and/or modified/natural drainage system (i.e., conveyance pipes, channels, storage, etc.) 3. End-of-pipe (i.e., point source) Technologies applicable to each of these areas are discussed and can be divided into structural and nonstructural. The nonstructural will cover approaches such as public education, regulations, and local ordinances which will have their main application to the upstream collection area. The structural approaches will be the main options for the drainage system and end-of-pipe areas and tend to be the more expensive items. The technologies and approaches for stormwater management referred to as BMPs generally cover the nonstructural or low-structural stormwater runoff controls. The point at which a stormwater management technology changes from a BMP to a unit treatment process (i.e., “highstructural” control) is often unclear; therefore, in this chapter BMPs refer to only the upstream watershed area prevention and/or control measures.

Developing and implementing the recommended plan

Analyze data and prepare forecasts

Quantifying pollution sources and effects Assessing alternatives

Formulate alternatives Compare alternatives and select recommended plan Prepare plan implementation program Implement plan

Establish objectives and standards Conduct inventory

Determining existing conditions

Urban Surface Water Management (Walesh, 1989)

Select alternative and record decision

Interpret, analyze, and evaluate data and forecasts Formulate and evaluate alternatives Evaluate and compare alternatives

Identify problems and opportunities and determine objectives Develop resource data

Developing the Watershed Plan (U.S. EPA, 1991a)

Select best alternatives and record decision

Identify problems Develop goals or objectives Formulate alternatives Evaluate alternatives

Inventory resources and forecast conditions

Developing Goals for Nonpoint Source Water Quality Projects (U.S. EPA, 1991b)

TABLE 1.1 Planning Approaches Suggested in Various Literature References

Identify NPS control measures Evaluate control measures Develop evaluation criteria Examine and screen measures Select measures Recommend control measures and implementation program

Define and describe problems

Initiate public participation Define existing conditions Review regulatory problems Define goals and objectives

Santa Clara Valley Nonpoint Source Study, Vol. II, NPS Control Program (SCVWD, 1990)

Implement near-term program Assess program effectiveness

Select near-term BMPs

Set priorities

Define goals Assess existing conditions

State of California Storm Water Best Management Practice Handbooks (Camp Dresser & McKee, 1993)

Determine attainable improvements

Assess existing data Compare conditions vs. objectives Determine extent of runoff problem Conduct selective field monitoring Refine problem estimates Assess alternatives

Urban Storm Water Management and Technology: Update and User’s Guide (U.S. EPA, 1977a)

Management of Wet Weather Flow in the Urban Watershed 5

6

Wet-Weather Flow in the Urban Watershed: Technology and Management

As stated previously, the optimal solution is likely to be an integrated approach using several practices and technologies. The management of the watershed using BMPs to prevent or control pollution at the source is likely to offer the most cost-effective solution and tend to be the basis of many stormwater management plans. However, although BMPs will be the preferred option, they will not always be feasible or by themselves sufficient to achieve the control objectives. For older and more heavily urbanized areas, BMPs are likely to have a limited application and some form of treatment prior to discharge may be required. There are a number of publications cited in Table 1.2 that cover the present state of the art on stormwater management using BMPs but do not generally review the end-of-pipe treatments that could be applied to stormwater as a final line of control. This chapter therefore includes treatment options available for stormwater pollution control that appear to be ignored in many stormwater management manuals. It should, however, be emphasized that it will be more cost effective to prevent potential urban storm runoff pollution problems and protect existing resources than to construct pollution controls once a problem exists. Unfortunately, for many areas the problems exist and retrospective prevention is not a feasible solution. The implementation of any stormwater management program will need to meet financial and probably schedule restraints; therefore, an early review and improved utilization of existing facilities can offer several advantages. These options are likely to be the quickest and least costly to be implemented, but they should also meet the objectives developed from the earlier stormwater management planning process. Examples might include the enforcement of existing regulations to control soil erosion during construction activities and adaptation of existing stormwater storage intended for flood control to also provide quality control for small storm events. New installations should consider design for both flood control and pollutant removals. The public does not generally perceive stormwater to be an environmental pollution problem. Furthermore, it does not appreciate the direct connection between some of its actions and the pollution consequences (e.g., disposal of engine oil and household toxic liquids down a storm drain or throwing litter on the street, which is transported by the storm runoff into the receiving water). Gaining public support to cooperate in the implementation and to pay for a stormwater management plan will be a major challenge. A strategy of concentrating efforts and resources on high-priority areas where results are likely to be achieved, or have been achieved, will help generate public support.

WATERSHED AREA TECHNOLOGIES AND PRACTICES There are many BMPs, but all BMPs are not suitable in every situation. It is important to understand which BMPs are suitable for the site conditions and can also achieve the required goals. This will assist in the realistic evaluation of the technical feasibility, implementation costs, and long-term maintenance requirements and costs. It is also important to appreciate that the reliability and performance of many BMPs have not been well established, with most BMPs still in the development stage. This is not to say that BMPs cannot be effective, in spite of not having a large bank of historical data on which to base design to enable confidence that the performance criteria will be met under site-specific conditions. The most-promising and best-understood BMPs are detention and extended detention basins and ponds. Less reliable in terms of predicting performance, but showing promise, are sand filter beds, wetlands, and infiltration basins (Roesner et al., 1989). A study of 11 types of water quality and quantity BMPs in use in Prince George’s County, Maryland (Metropolitan Washington Council of Governments, 1992a) was conducted to examine their performance and longevity. The report concluded that several of the BMPs had either failed or were not satisfying the designed performance. Generally, wet ponds, artificial marshes, sand filters, and infiltration trenches achieved moderate to high levels of removal for both particulate and soluble pollutants. Only wet ponds and artificial marshes demonstrated an ability to function

7

Management of Wet Weather Flow in the Urban Watershed

TABLE 1.2 Urban Runoff and CSO BMP References Document Title

Author

BMPs Included

Controlling Urban Runoff. A Practical Manual for Planning and Designing Urban BMPS, 1987

Schueler

Detention Infiltration Vegetative Filtration Quality inlets

Protecting Water Quality in Urban Areas, 1989

MPCA

Housekeeping Detention Infiltration Vegetative Quality inlets

Guide to NPS Control, 1987

U.S. EPA

Water Resource Protection Technology: A Handbook of Measures to Protect Water Resources in Land Development, 1981

Urban Land Institute

Housekeeping Detention Infiltration Housekeeping Detention Infiltration Vegetative Quality inlets

Urban Targeting and Urban BMP Selection, 1990

Woodward-Clyde

Combined Sewer Overflow Pollution Abatement, 1989

WPCF

Urban Stormwater Management and Technology: An Assessment, 1974

U.S. EPA

Decision Maker’s Storm Water Handbook: A Primer, 1992

Phillips–U.S. EPA Region V

Urban Storm Water Management and Technology: Update and User Guide, 1977

U.S. EPA

Control and Treatment of Combined Sewer Overflows, 1993

Moffa

Housekeeping Detention Infiltration Vegetative Housekeeping Collection system Storage Treatment Housekeeping Collection system Storage Treatment Housekeeping Detention Infiltration Vegetative Filtration Quality inlets Source control Collection system Storage Treatment Source Control Collections system Storage Treatment

Information Available General description Effectiveness Design Use limitations Maintenance Cost Examples General description Effectiveness Use limitations Maintenance Cost Examples General description Effectiveness Cost General description Effectiveness Design Use limitations Maintenance Cost General description Effectiveness Design Use limitations General description Design Effectiveness Maintenance Cost General description Design Maintenance Use limitations General description Effectiveness Design Use limitations

General description Design Maintenance Use limitations General description Design Maintenance Use limitation

8

Wet-Weather Flow in the Urban Watershed: Technology and Management

TABLE 1.2 (continued) Urban Runoff and CSO BMP References Document Title

Author

BMPs Included

Coastal Nonpoint Source Control Program: Management Measures Guidance, 1993

U.S. EPA

Housekeeping Infiltration Vegetative Filtration Quality inlets

The Florida Development Manual: A Guide to Sound Land and Water Management, 1992

Livingston et al.

Housekeeping Infiltration Vegetative Quality inlets

Storm Water Management Manual for the Puget Sound Basin, 1991

WA DOE

Housekeeping Infiltration Vegetative Quality inlets

Stormwater Management, 1992

Wanielista and Yousef

Water quality Infiltration Detention

Stormwater: Best Management Practices and Detention for Water Quality, Drainage, and CSO Management, 1993

Urbonas and Stahre

Integrated Stormwater Management

Field, O’Shea, and Chin

Storage Source control Detention Treatment Water quality Detention Management Vegetative Infiltration Flood control Reclamation Collection systems

Information Available General description Effectiveness Design Use limitations Maintenance Cost Examples General description Effectiveness Design Use limitations Maintenance Cost Examples General description Effectiveness Design Use limitations Maintenance Cost Examples General description Effectiveness Examples Cost General description Effectiveness Design Use limitations General description Effectiveness Design Use limitations

for a relatively long time without routine maintenance. BMPs with poor performance ratings were infiltration basins, porous pavement, grass filters, swales, smaller “pocket” wetlands, extended detention dry ponds, and oil–grit separators. Infiltration BMPs had high failure rates, which could often be attributed to poor initial site selection and/or lack of proper maintenance. The above report contains many more details and recommendations on the use of BMPs. It is important to note that the reported poor performance of some of the BMPs is likely to be a function of one or more of the following: the design, installation, maintenance, or suitability of the area. Greater attention to these details is likely to reduce significantly the failure rate of BMPs. Other important design considerations include safety for maintenance access and operations, hazards to

Management of Wet Weather Flow in the Urban Watershed

9

the general public through safety (e.g., drowning) or nuisance (e.g., mosquito breeding area), acceptance by the public (e.g., enhanced area aesthetics), and to assume conservative performances in the design until the historical data can justify a higher reliable performance. For any BMP involving soil infiltration of the storm runoff, it is important to consider the possible effects this could have on the groundwater. These could range from a relatively minor local raising of the water table resulting in reduced infiltration rates to more serious pollution of the groundwater, particularly if the groundwater is also used as a water source. Stormwater runoff is likely to have very low levels of pollution when compared with chemical and gasoline leaks/discharges and the soil will have some natural capacity to hold pollutants. However, the long-term buildup of pollutants in the soil or groundwater from storm runoff infiltration is not well known. Therefore, infiltration of urban storm runoff, especially from industrial and commercial areas that are likely to have higher levels of pollution, should be treated with caution. Infiltration of storm runoff can offer significant advantages of controlling storm runoff at the source, reduced risk of downstream flooding, and recharge of groundwater and groundwater supply to streams (i.e., low-flow augmentation or maintaining stream flow during dry weather periods). All of these and possibly other advantages can be offered at a relatively low cost by infiltration, and therefore the advantages will need to be judged against any pollution risks from urban runoff. The majority of treatment processes that can be readily applied to urban storm runoff are only effective for removal of the settleable solids. Removal of dissolved or colloidal pollutants will be minimal and therefore pollution prevention or control at the source offers an effective way to control the dissolved pollutants. Fortunately, however, many pollutants in the form of heavy metals and organic chemicals show significant association with the suspended solids (SS) (Pitt and Field, 1990; Pitt et al., 1991; 1993; 1994). Consequently, removal of the solids will also remove the associated pollutants. The previously mentioned goals for a stormwater management plan can be achieved in the watershed area via three basic avenues: 1. Regulations, Local Ordinances, and Public Education. This avenue should be the primary objective because it is likely to be the most cost-effective. Mainly nonstructural practices will be involved and application to new developments should be particularly effective. 2. Source Control of Pollutants. This will be closely related to the above. Both nonstructural and structural practices can be used to prevent pollutants from coming into contact with the stormwater and hence storm runoff. Management and structural practices will include flow diversion practices that keep uncontaminated stormwater from contacting contaminated surfaces or keep contaminated stormwater from contacting uncontaminated stormwater by a variety of structural means; exposure minimization practices that minimize the possibility of stormwater contacting pollutants by structural (diking, curbs, etc.) and management (coverings, loading and unloading practices) practices; mitigative practices that include plans to recover released or spilled pollutants in the advent of a release; preventative practices that include a variety of monitoring techniques intended to prevent releases; controlling sediment and erosion by vegetative and structural means; and infiltration practices that provide for infiltration of stormwater into the groundwater (structural and vegetative means) thereby reducing the total runoff. 3. Source Treatment, Flow Attenuation, and Storm Runoff Infiltration. These are mainly structural practices to provide upstream pollutant removal at the source, controlled stormwater release to the downstream conveyance system, and ground infiltration or reuse of the stormwater. Upstream pollutant removal enables treatment of stormwater runoff at high pollution source locations or “hot spots” before the pollutants enter the stormwater conveyance system. Areas of this type include but are not limited to vehicular parking areas, vehicular service stations, bus depots, industrial loading areas, etc.

10

Wet-Weather Flow in the Urban Watershed: Technology and Management

The following provides brief details of BMPs. Many of these BMPs can be combined and/or modified to best suit the conditions of the watershed under consideration. More information on BMPs can be found in the references listed in Table 1.2.

REGULATIONS, LOCAL ORDINANCES,

AND

PUBLIC EDUCATION

The regulatory approach can address a wide variety of stormwater management aspects, some of which are listed below. For any regulations to work there will need to be an existing framework within which to place the regulations (e.g., local ordinances, zoning, planning regulations, etc.) together with dedicated resources to enforce them. Without the institutional systems to set regulations in place and enforce them, regulations will not be effective. Regulations can be an important pollution prevention BMP with particular application to new developments to ensure that the pollution is prevented or controlled at the source and any implementation and maintenance costs are included in the development costs. New York State has compiled a manual on BMPs for new developments (New York State, 1992). Some typical regulations include the following: • Land use regulations • Zoning ordinances • Subdivision regulations • Site plan review procedures • Natural resource protection • Comprehensive storm runoff control regulations • Land acquisition Further details on a regulatory approach are contained in “Handbook: Urban Runoff Pollution Prevention and Control Planning” (U.S. Environmental Protection Agency, 1993a) and Urban Stormwater Management and Technology: Update and Users’ Guide (U.S. Environmental Protection Agency, 1977). Public education can have a significant role to play because an aroused and concerned public has the power to alter behavior at all levels. However, if the stormwater management plans are not adequately communicated and public opinion responded to, this power of the public can work against the implementation of a stormwater plan if it is viewed as an unnecessary extra cost and restriction on freedom. Gaining the public support as with all education does not stop but is a continuous process and applies to all sectors of the public. These sectors are listed below and discussed in the following paragraphs: • • • •

Residential Commercial Industrial Governmental

The residential sector is composed of all persons living in a drainage area and therefore education should focus on large groups. Long-range education goals can be tackled through school programs and shorter-range goals may be achieved through community groups. Advantage should be taken of working with groups looking for community improvement projects and opportunities arising from news media coverage and the associated publicity. The commercial sector is a fairly large and often diffuse group with which to communicate. The owners/managers and their staff will need to be included in any communication together with new businesses that are opening; existing businesses that are moving, expanding, and closing; and

Management of Wet Weather Flow in the Urban Watershed

11

personnel that is changing. Methods of communication may include news announcements in the local press, mailed news items, individual contact by a public official, and follow-up repeated contacts to answer questions and cope with employee turnover. Public education can benefit from failures, such as violations of regulations that result in a fine and are reported in the local press. This not only informs the public about regulations, but also provides an incentive for the regulations to be followed because regulations are shown to be enforceable. The industrial sector is a smaller group and can be educated by direct contact with public officials, education of the consultants from whom industry seeks advice, and by education of trade associations. Indirect education opportunities are provided by speaking to meetings of professional organizations and by writing in professional newsletters and journals. Industrial decision makers are a relatively small group, which when informed or made aware of their obligations are likely to respond. Public officials should also communicate with other public officials and governmental institutions to ensure that they are aware of a stormwater management program and its implications. Examples include road, sanitation, and parks departments and workers at public institutions such as hospitals and prisons. A multilevel, multitarget public education program can help to avoid problems in implementing a stormwater management program. Further information on communicating a stormwater management program to the public can be found in “Designing an Effective Communication Program: A Blueprint for Success” (U.S. Environmental Protection Agency, 1992a), and “Urban Runoff Management Information/Education Products” (U.S. Environmental Protection Agency, 1993b). The latter reference is a catalog of available material and publications.

SOURCE CONTROL

OF

POLLUTANTS

Source controls are usually nonstructural practices, many of which can be termed “good housekeeping” practices. They are pollution prevention options that can be very effective. Some source controls are as follows: • • • • • • • • •

Cross-connection identification and removal Controlled construction activities Street sweeping Solid waste management Animal waste removal Toxic and hazardous waste management Reduced use of fertilizer, pesticide, and herbicide Reduced roadway sanding and salting Material and chemical substitution

Research on illicit or inappropriate cross-connections into separate stormwater drainage systems has shown that these can add a significant pollutant loading (Pitt and McLean, 1986; Schmidt and Spencer, 1986; Montoya, 1987; Washtenaw Co., 1988). This is also recognized in the National Pollution Discharge Elimination Permits System (NPDES) for stormwater discharges that require investigation of dry weather flows (DWFs) at stormwater outfalls. This will involve inspecting outfalls for DWFs, identifying illicit discharges from analysis of DWF samples, tracing the discharge source, and corrective action. DWF can originate from many sources; the most important sources may include sanitary wastewater (from sewer lines or septic tank systems), industrial and commercial pollutant entries, and vehicle service activities. It should be recognized that not every DWF will be a pollutant source and they may be caused by infiltrating potable water supply and clean groundwater. A full illicit connections investigation is likely to be time-consuming and costly. A methodology for identifying illicit discharges in the DWF and tracing the source using distinct

12

Wet-Weather Flow in the Urban Watershed: Technology and Management

Street surface Solids load (lb/curb-mi)

700 600 Total solids

500 400 300 200 100 50

100 150 200 250 Number of passed per year

300

FIGURE 1.2 Street sweeping: annual amount removed as a function of the number of passes per year at San Jose test site. (From U.S. EPA, EPA-600-79-161, 1979.)

characteristics of potential sources is described in “Investigation of Inappropriate Pollutant Entries into Storm Drainage Systems: A User’s Guide” (U.S. Environmental Protection Agency, 1993c) and “Investigation of Dry-Weather Pollutant Entries into Storm Drainage Systems” (Field et al., 1994). The User’s Guide concentrates on procedures that are relatively simple and that do not require sophisticated equipment or training. At a minimum the most severely contaminated outfalls must identified to assist in prioritizing areas to be investigated first, and at best the pollutant source should be identified. A stormwater management plan that ignores investigation of DWF is very likely to find that goals set to improve receiving water quality will not be achieved because of pollutants discharged in DWF. Soil erosion from construction sites together with wash off from stockpiled material and readymix concrete trucks can be a major source of pollutants (SS) for the relatively short construction duration. Requirements for phased removal of vegetative cover and early reestablishment of ground cover combined with detention of stormwater for sedimentation and filtering will help reduce the pollution from construction site stormwater runoff. It is important also to consider the period following construction when vegetative ground cover still needs to be fully established and occupants of new buildings may undertake landscaping. Further information can be found in “Reducing the Impacts of Stormwater Runoff from New Development” (New York State, 1992) and “Storm Water Pollution Prevention for Construction Activities” (U.S. Environmental Protection Agency, 1992b). Street sweeping studies (U.S. Environmental Protection Agency, 1979d; 1985) concluded that typical reduction in storm runoff pollutant loadings can be between 5 and 10% for street sweeping carried out every 2 days (sweeping more frequently than 2 days per week does not significantly reduce the solids loading any further, as illustrated in Figure 1.2); street cleaners did not significantly remove the smallest particulates (200 µm); the reduction in storm runoff pollutant load is much less than the pollutant load removed by sweeping (as street surfaces only contribute ≤0.5 the total pollutant load), which can lead to a false sense of effectiveness; pavement type and condition have a pronounced effect on performance (as illustrated in Figure 1.3); and street sweeping results are highly variable such that the results from one city cannot be applied to another city. The above comments together with the fact that street storm runoff is only a part of the outfall discharge would imply that street cleaning is not particularly effective on its own but should be part of an overall program. Street cleaning is likely to be more effective for removal of heavy metals from vehicle emissions, which tend to associate with the particulates. Sweeping of parking areas, storage, and loading/transfer areas should be included in a cleaning program. Concentrated cleaning during

13

Total solids removed (lb/curb-ml/yr)

Management of Wet Weather Flow in the Urban Watershed

50,000

Oil and screens surfaced streets or asphalt streets in poor condition

40,000 30,000

Asphalt streets in good condition

20,000 10,000 0

0

10

100

1,000

Number of passes per year

FIGURE 1.3 Street cleaner productivity in Bellevue, Washington. (From U.S. EPA, EPA-600-2-85/038, 1985.)

certain seasons is likely to be effective, e.g., during early spring in the snowbelt, when leaves accumulate in the fall, and prior to rainy seasons. Although the effectiveness of the above has not been shown, street cleaning does offer aesthetic improvements in the removal of large items from the streets and receiving water. Fugitive emissions from street sweeping will lead to increased air pollution and may need to be considered if an intensive street sweeping program is part of a stormwater management plan. Solid waste management involves the collection and proper disposal of solid waste to maintain clean streets, residences, and businesses. It can also be extended to the collection of items such as leaves during the fall. A study of stormwater runoff into Minneapolis lakes found that phosphorus levels were reduced by 30 to 40% when street gutters were kept free of leaves and lawn clippings (Minnesota Pollution Control Agency, 1989). Wastes from domesticated and wild animals represent a source of bacteria and other pollutants such as nitrogen that can be washed into the receiving waters. A study in San Francisco, California (Colt et al., 1977) estimated that the dogs, cats, and pigeons produced 54,500, 9000, and 2200 lb (247, 4, and 1 metric tons), respectively, of nitrogen a year for an area of 30,480 acres (12,343 ha). On an annual basis, bulk precipitation, dog wastes, and fertilizer accounted for 49, 23, and 22%, respectively, of the total nitrogen runoff. Controls through regulation and public education, if successful, could therefore have a major impact based on these figures. Toxic and hazardous waste management should review methods to prevent the dumping of household and automotive toxic and hazardous wastes into municipal stormwater inlets, catchbasins, and other storm drainage system entry points. Public education, special collection days for toxic materials, and posting of labels on stormwater inlets to warn of the pollution problems of dumping wastes are possible management options. Fertilizers, pesticides, and herbicides washed off the ground during storms can contribute to water pollution. Agriculture, recreation parks, and gardens can be sources of these pollutants. Controlling the use of these chemicals on municipal lands and educating gardeners and farmers to use the minimum amounts required and appropriate application methods can help reduce nutrient and toxic pollutants washed off by storm runoff. Sand and salt are applied as deicing agents to roads in many areas of the United States that experience freezing conditions and are then washed off by the meltwater and stormwater runoff. Effects of highway deicing appear most significant in causing contamination and damage of groundwater, public water supplies, roadside wells, farm supply ponds, and roadside soils, vegetation, and trees (U.S. Environmental Protection Agency, 1971). Deicers also contribute to deterioration of highway structures and pavements, and to accelerated corrosion of vehicles. Studies (U.S. Environmental Protection Agency, 1971) indicate that major problems in the control of deicing chemicals were the excessive application, misdirected spreading, poor storage practices, inaccurate weather forecasting, and the logistics of setting up the deicing operation. To address these problems

14

Wet-Weather Flow in the Urban Watershed: Technology and Management

two manuals of practice on the application and storage of deicing chemicals (U.S. Environmental Protection Agency, 1974a, c) were produced to give recommendations and improvements. They provide comprehensive details on storage management, layout, handling, application for various storm and temperature conditions, and use and calibration of equipment to minimize the amount of chemicals used. Studies were conducted on alternative deicing methods (U.S. Environmental Protection Agency, 1972a; 1976a; 1978) but these were more costly than the use of rock salt and therefore would be unlikely to have general economic application.

SOURCE TREATMENT, FLOW ATTENUATION, AND STORM RUNOFF INFILTRATION VEGETATIVE BMPS These developing practices have been the subject of many publications in the last 20 years, a few of which are listed in Table 1.2. Readers are directed to these or similar publications for more detailed information. Knowledge of the performance of these systems is limited, but the cited publications do contain lessons learned from their implementation and in some cases failure. Existing urbanized areas are unlikely to have the land space available for installation of many of these practices and in these situations their application will be restricted. Swales These are generally grassed stormwater conveyance channels that remove pollutants by filtration through the grass and infiltration through the soil. A slow velocity of flow, 25%)

20

Impacted (11 to 25%) Sensitive (0 to 10%)

0 good

far

low

Source: Schueler and Clayton, 1995

FIGURE 12.13 Impervious cover vs. stream quality.

exhibit physical habitat changes (erosion and channel widening) and decreasing water quality where impervious cover is in the range of 10 to 25%. Streams in watersheds where the impervious cover exceeds 25% are typically degraded, have a low level of stream quality, and do not support a rich aquatic community.

TEMPERATURE Water temperature is an important measure of water quality. As described by Malina (1996), “the temperature of water affects some of the important physical properties and characteristics of water, such as, specific conductivity and conductance, salinity, and the solubility of dissolved gases (e.g., oxygen and carbon dioxide).” Specifically, water holds less oxygen as it becomes warmer, resulting in less oxygen available for respiration by aquatic organisms. Furthermore, elevated temperatures increase the metabolism, respiration, and oxygen demand of fish and other aquatic life, approximately doubling the respiration for a 10°C(18°F) temperature rise; hence the demand for oxygen is increased under conditions where supply is lowered (California, SWRCB, 1963). Certain species of fish, such as salmon and trout, are particularly sensitive and require relatively low water temperatures. Brown and rainbow trout die when water temperatures exceed 82°F. Brook trout die when water temperature exceeds 72°F. Even lower water temperatures are required for spawning and egg hatching (U.S. EPA, 1976). If the temperature of a stream reach is raised by 5 to 10°C (9 to 18°F), it is probable that such cold-water game fish will avoid this reach and that they will be replaced by “rougher,” more tolerant fish (California, SWRCB, 1963). Thus, even without direct mortality, the character of the fish life will change. Sudden changes in temperature directly stress the aquatic ecosystem. Some states have adopted varying criteria to protect fisheries from such stresses. Typically, states limit in-stream temperature rises above natural ambient temperatures to 2.8°C (5°F). Allowable temperature rises in streams that support cold-water fisheries may be lower; some states adopt values as low as 1°C (1.8°F) and 0.6°C (1°F) (U.S. EPA, 1988). The temperature of urban waters is often affected directly by urban runoff. Urban runoff can be heated as it flows over rooftops, parking lots, and roadways. When it reaches urban waterways it can cause a temporary fluctuation in the in-stream water temperature. Other factors that tend to increase summer water temperature in urban waters include the removal of vegetation from stream banks, reduced groundwater base flow, and discharge from stormwater facilities with elevated water temperature. Frequent fluctuations in steam temperatures stress the aquatic ecosystem, and make it difficult for temperature-sensitive species to survive. Severe thermal impacts associated with summer thunderstorms have been reported in the MidAtlantic states. Runoff from impervious surfaces such as roads and parking lots can reach temperatures of 85 to 90°F. This runoff is generally delivered to the nearest receiving stream through a series of storm drain inlets and pipes with little or no dilution with cooler water.

Geomorphic Considerations in Stream Protection

335

TRADITIONAL CONTROL APPROACHES Technical efforts to control and manage these hydrologic impacts of urbanization have evolved through a number of phases or levels of control over the last 30 years in response to increasing understanding of the complexity of the issues that are involved. A brief review of past and current efforts to manage these impacts is provided using the concepts of “levels of control.”

LEVEL 1: PEAK DISCHARGE CONTROL The early efforts (1970s) at managing urban runoff, described as Level 1 focused on reducing the risk of downstream flooding. Often a secondary objective, Level 1a, was to reduce channel erosion. The major tool used in this effort was the use of a stormwater management pond, wet or dry, that temporarily stores and releases runoff from large storms to reduce peak stormwater discharges downstream of the pond. This approach referred to by some as the “end-of-pipe” or “pond” approach is very popular and remains the mainstay of most stormwater management programs throughout the country. Many areas of the United States are still currently using a Level 1 type of control as the only management tool for urban runoff.

LEVEL 2: FLOODPLAIN ZONING A second level of control, Level 2, implemented by some states and local governments at about the same time consists of restricting development along stream floodplains that are susceptible to frequent flooding. Typically, the 100-year floodplain limit is used for this purpose. Many local governments have also purchased floodplains for public use as stream valley parks. Because this is a nonstructural technique, it is often overlooked as a level of stormwater management.

LEVEL 3: WATER QUALITY CONTROL Although it was generally taken for granted that Levels 1 and 2 were reasonably effective in curtailing flooding problems, practitioners began to realize that these levels of control could not mitigate the adverse impacts of urbanization on stream habitat or increased pollutant export. This awareness gave rise to the development of Level 3 during the 1980s. In Level 3 a series of best management practices (BMPs) was developed for urbanizing areas that could remove urban pollutants and, it was hoped, provide some protection for downstream aquatic life. Most of these BMPs consisted of modifications to the old standby end-of-pipe pond, which involved the use of multiple outlet structures to provide extra detention or retention. The use of infiltration practices, both trenches and ponds, was added, as well as the use of wetland ponds and marshes. All these new BMPs were focused on enhancing pollutant removal and providing additional stormwater management. Efforts at improving and adding additional BMPs have continued throughout the 1990s.

PEAK DISCHARGE STRATEGIES

AND

CONTROL

OF

PHYSICAL IMPACTS

Some of the objectives and assumptions inherent in the peak discharge control strategy were described earlier in this chapter. Table 12.8 provides a brief qualitative assessment of the effectiveness of peak discharge strategies with respect to the physical impact category (Clar et al., 2001). Control of Increased Flooding The ability of land use changes, and in particular land development activities, to increase runoff quantity and cause downstream flooding and erosion has been recognized for several decades. This recognition has led many states, counties, municipalities, and other agencies to require on-site detention of increased project area runoff with peak site outflows set equal to the predeveloped conditions. This requirement has become popular, as it can be applied during development design

336

Wet-Weather Flow in the Urban Watershed: Technology and Management

TABLE 12.8 Qualitative Assessment of Peak Discharge Control Strategies with Respect to Physical Impact Category Physical Impact Category

Control Strategy

Increased flooding

Peak discharge control of 10- and 100-year storms

Channel instability and erosion

Peak discharge control of 2-year storm

Reduction in groundwater recharge and related issues Increased sediment transport

Not addressed by peak discharge control

Thermal impacts

Not addressed by peak discharge control

Peak discharge of 2-year storm

Assessment Peak discharge strategy provides limited downstream control; in some cases, it aggravates downstream flooding condition; requires coordinated permitting at watershed scale Both geomorphic science and limited fieldmonitoring indicate that this strategy does not work N/A Both geomorphic science and limited fieldmonitoring indicate that this strategy does not work N/A

and review process on a case-by-case basis without large-scale watershed analysis. This popularity has led to the frequent use of on-site detention and retention basins, which have become standard features on many land development projects. However, the limitations of peak discharge control strategies documented by Leopold and Maddock in 1954 have been largely ignored. Recent research conducted by the Somerset County, New Jersey and others (Skupien, 2000) indicates that this approach may not be adequate to prevent downstream peak flow increases and subsequent erosion and flooding problems. Studies conducted by the New Jersey Department of Environmental Protection (NJDEP) and the Natural Resources Conservation Service (NRCS) demonstrate that the sue of this standard peak outflow rate may in fact cause greater downstream peak flow increases than if no on-site detention had been used at all (Skupien, 2000). Additional research by Somerset County suggest that, if an effective on-site detention policy is to be pursued, peak allowable site outflow rates must be determined on a watershed basis and, in many instances, must be set at a rate 25 to 50% less than the predeveloped peak rates. Channel Instability, Bank Erosion, and Sediment Transport A related issue associated with the peak discharge control strategy is the well-documented problem of increases in the frequency and duration of stormwater discharges. As demonstrated by McCuen et al. (1987), the practice of detaining the extra volume of stormwater runoff and discharging it at preconstruction peak discharge rates until the extra volume is fully dissipated has the result of creating more in-stream erosion than if no stormwater control were present. This occurs when the selected design storm focuses predominant on downstream flood control and not on in-stream erosion (channel protection) and the protection of aquatic habitat and biology. Reduction in Groundwater Recharge and Related Issues Peak discharge control strategies are often referred to as end-of-pipe control strategies, because they typically make use of small BMP ponds placed at the low topographic point on development sites. This approach does not usually address groundwater recharge and related issues, such as

337

Geomorphic Considerations in Stream Protection

TABLE 12.9 Qualitative Assessment of Peak Discharge Control Strategies with Respect to Habitat and Biological Impact Categories Habitat and Biologic Impact Category

Control Strategy

Assessment

Impairment or loss of habitat

Peak discharge of design storms (100-, 10-, 2-year)

Reduction or elimination of biologic species

Peak discharge of design storms (100-, 10-, 2-year)

BMP systems designed to control peak discharge are not protective of biologic habitats (Jones, 1997; Maxted, 1997; Stribling, 2001) BMP systems designed to control peak discharge are not protective of biologic habitats (Jones et al., 1997; Maxted and Shaver, 1997; Stribling, 2001)

lowering of groundwater levels and reduction or loss of base flows in small streams. One minor exception to this condition consists of recent initiatives in the State of Florida, where stormwater management ponds are used as sources of gray water for lawn watering. This initiative is in part a response to the alarming lowering of water tables in many areas of Florida. Thermal Impacts A negative consequence of the peak discharge control strategy and the associated use of pond BMPs is the associated increase in thermal warming of runoff waters. The problem is particularly acute in regions of the country that support cold-water habitat, particularly trout and salmon fisheries.

PEAK DISCHARGE STRATEGIES

AND

CONTROL

OF

HABITAT

AND

BIOLOGIC IMPACTS

With respect to the habitat and biologic impact categories, the major areas of impairment include impairment or loss of habitat, reduction or elimination of biologic species, and incursion of invasive species. Table 12.9 provides a brief qualitative assessment of the effectiveness of peak discharge strategies with respect to the habitat and biologic impact category (Clar et al., 2001).

SUMMARY

OF

PEAK DISCHARGE STRATEGIES

Peak discharge strategies represent a Level 1 approach to control or mitigation of impacts from urban runoff. As described in Chapter 10, this level of control is provided by the NPDES stormwater regulatory approach. It provides two performance criteria that are closely related: (1) flood control and (2) peak discharge control. The technology assessment for the major impact categories as presented in this Level 1 approach are based solely on peak discharge control and are not adequate to address the range of impacts associated with urban runoff issues. The following is a summary of findings: • Although this approach provides some limited degree of flood control from moderate and large storms, it can in some instances actually transfer or aggravate flooding conditions downstream of the control points. • This approach not only fails to provide protection for stream channel stability, but also may actually aggravate stream channel impacts. • The approach does not address groundwater recharge issues. • The approach does not address, but can actually aggravate, thermal impacts on receiving waters.

338

Wet-Weather Flow in the Urban Watershed: Technology and Management

• This approach does not address or guarantee water quality management and pollutant removal, although both can be achieved if the BMPs are properly designed. • This approach does not provide control for the degradation and loss of riparian habitat. • This approach does not provide control for the degradation and loss of biological communities.

FUTURE DIRECTIONS AND INNOVATION IN CONTROL TECHNOLOGY As knowledge and awareness of issues and problems associated with hydrologic impacts of urbanization continue to increase, many practitioners and local governments have come to realize that existing levels of stormwater management are falling short of the intended overall goal of maintaining receiving streams and rivers in urban areas “fishable and swimmable.” Consequently, they have begun to adopt a broader perspective of performance criteria for stormwater management programs, which addresses the full range of hydrologic impacts of urbanization including physical, chemical, and biologic issues. In adopting this parametric approach to performance definition, they have begun to identify gaps, or missing pieces, in the management strategies. These missing pieces include the following: • Criteria to maintain the natural groundwater recharge capacity, and the related base flow contributions during dry weather condition • Criteria to provide control of thermal impacts from urban areas • Criteria to provide effective geomorphically based channel degradation protection • Provision of stormwater credits for innovative site planning techniques Two significant developments in stormwater management technology include the development of the Maryland 2000 SWM Design Manual (MDE, 2000), and also the development of the lowimpact development (LID) technology by Prince George’s County, Maryland. The MDE 2000 manual provides a multiparameter control approach referred to as a Level 4 approach (Clar et al., 2001). This multiparameter approach includes five design criteria or parameters referred to as the “Unified Sizing Criteria,” as follows: 1. 2. 3. 4. 5.

Groundwater recharge criteria, Rev Water quality criteria, WQv Channel protection criteria, Cpv Overbank flooding criteria, Q10 Extreme flood volume criteria, Qf

Criterion 1, groundwater recharge, is a relatively new criterion for stormwater management and was developed to address the concern for the impacts on groundwater recharge, lowering of wells, lowering or loss of base flow to small streams, saltwater intrusion in coastal areas, and settlement of structures. Only a few jurisdictions including the States of Maryland and Massachusetts have adopted these criteria. Criterion 2, the water quality criterion, is not new, but Maryland increased the control requirement from the first 1/2 in. to the first inch to capture and treat 90% of the annual runoff volume. Criterion 3, the channel protection criterion, is also not new, but Maryland replaced the use of the 2-year predevelopment storm as a surrogate for channel protection, with the use of the 1-year storm with extended detention, which effectively reduces the allowable release rate to a 2-in. storm event, or approximately 25 to 50% of the predevelopment peak discharge rate. Criteria 4 and 5 are the traditional flood control requirements for the 10- and 100-year storms.

Geomorphic Considerations in Stream Protection

339

The LID approach to stormwater management is the subject of a separate chapter and is addressed in detail in a number of publications (PGC, 1997a, b; U.S. EPA 2000a, b). It represents a Level 5 approach to stormwater management. This level has been described as an attempt to provide an ecologically sensitive approach to stormwater management (Clar et al., 2001). This level uses an integrated approach including biologic, chemical, and physical criteria to define BMP performance. A combination of water quality, biohabitat, and geomorphic criteria is used to evaluate whether a receiving stream is at the targeted goal of “fishable and swimmable,” or the extent of departure from this goal. A number of additional parameters are added to the Level 2 performance criteria: (1) stream buffer retention and thermal impact considerations; (2) volume control considerations, such as considerations presented in the LID concept approach, are added to the peak discharge and groundwater recharge criteria to achieve maintenance of hydrologic function at a site-specific level; and (3) geomorphic criteria as described by Dunne and Leopold (1978), Lane (1955), Leopold and co-workers (1964; 1994), Rosgen (1996), and others are incorporated to supplement or replace extended detention approaches to achieving channel stability. In summary, it can be observed that stormwater management technology has experienced a considerable degree of maturity and improvement over the past 30 years, which has reflected the increased understanding of the complicated cause-and-effect relationships between land disturbance activities and the corresponding responses of the natural systems, particularly the riparian zones and receiving waters. However, the massive land development activities that have occurred over the last 40 years have left a legacy of impaired receiving waters whose primary source of impairment is due to channel degradation resulting from hydrologic modifications. The application of the fluvial geomorphology concepts presented earlier, together with the Rosgen classification system, as tools to assess and restore these impaired streams are described in Chapter 13.

REFERENCES California State Water Resources Control Board (SWRCB). 1963. Water Quality Criteria. 2nd ed. Publication No. 3-A, pp. 284–285. Clar, M., Collins, J., Loftin, H. et al., 2001. Stormwater BMP technology assessment protocols — preliminary findings, paper presented at the Conference on Linking Stormwater BMP Designs and Performance to Receiving Water Impacts Mitigation, Snowmass, CO, United Engineering Foundation, New York. Collins, J., Clar, M., Loftin, H. et al., 2001. Compilation of regulatory requirements for stormwater runoff, paper presented at the Conference on Linking Stormwater BMP Designs and Performance to Receiving Water Impacts Mitigation, Snowmass, CO, United Engineering Foundation, New York. Delaware Department of Natural Resources and Environmental Control (DNREC). 1997. Conservation Design of Storm Water Management. A joint effort between DNREC and the Brandywine Conservancy, Dover, DE. Dunne, T. and Leopold, L.B., 1978. Water in Environmental Planning, W.H. Freeman, San Francisco, 818 pp. Ferguson, B.K., 1990. Urban stormwater infiltration: Purposes, implementation, results, J. Soil and Water Conservation, 45(6). Gordon, N., McMahon, T., Finlayson, B., 1982. Stream Hydrology: An Introduction for Ecologists, John Wiley & Sons, New York. Jones, R.C., Via-Norton, A., and Morgan, D.R., 1997. Bioassessment of BMP effectiveness in mitigating stormwater impacts on aquatic biota, in Effects of Watershed Development and Management on Aquatic Ecosystems, L.A. Roesner, Ed., American Society of Civil Engineers, New York. Lane, E.W., 1955. The importance of fluvial morphology in hydraulic engineering, Am. Soc. Civil Eng. Proc., 81, paper 745, 1–17. Langbein, W.B., 1960. Plotting positions in frequency analysis, U.S. Geological Survey Water Supply Paper 1543-A, A48–A51. Leopold, L.B., 1968. Hydrology for Urban Land Planning — A Guidebook on the Hydrologic Effects of Urban Land Use, U.S. Geological Survey, Water Supply Paper, 1591-C. Leopold, L.B., 1994. A View of the River, Harvard University Press, Cambridge, MA, 298 pp.

340

Wet-Weather Flow in the Urban Watershed: Technology and Management

Leopold, L.B. and Maddock, T., 1953. The hydraulic geometry of stream channels and some physiographic implications, U.S. Geological Survey Prof. Paper 252, U.S. Government Printing Office, Washington, D.C., 57 pp. Leopold, L.B. and Maddock, T., Jr., 1954. The Flood Control Controversy, Ronald Press Corp., New York. Leopold, L.B., Wolman, M.G., and Miller, J.P., 1964. Fluvial Processes in Geomorphology, Freeman & Sons, San Francisco, 522 pp. Linsley, R.K., Kohler, M., Paulhus, J., 1958. Hydrology for Engineers, McGraw-Hill, New York. MacRae, C., 1996. Experience from morphological research on Canadian streams: is control of the two-year frequency runoff event the best basis for stream channel protection? in Effects of Watershed Development and Management on Aquatic Ecosystems, L. Roesner, Ed., American Society of Civil Engineers, Snowbird, UT, 144–162. Malina, J.F., 1996. Water quality, in Water Resources Handbook, Mays, L.W., Ed., McGraw Hill, New York, chap. 8. Masterson, J.P. and Bannerman, R.T., 1994. Impacts of stormwater on urban streams in Milwaukee County, Wisconsin, National Symposium on Water Quality, Nov. 1994. Maxted, J. and Shaver, E., 1997. The use of retention basins to mitigate stormwater impacts on aquatic life, in Effects of Watershed Development and Management on Aquatic Ecosystems, L. A. Roesner, Ed., American Society of Civil Engineers, New York. McCuen, R.H., Moglen, G., Kistler, E., and Simpson, P., 1987. Policy Guidelines for Controlling Stream Channel Erosion with Detention Basins, prepared by the Department of Civil Engineering, University of Maryland, College Park, for the Water Management Administration, Maryland Department of the Environment, Baltimore. MDE (Maryland Department of the Environment), 2000. 2000 Maryland Stormwater Design Manual, Vol. I and II, prepared by the Center for Watershed Protection and the Maryland Department of the Environment, Water Management Administration, Baltimore. Mosley, M.P., 1981. Semi-determinate hydraulic geometry of river channels, South Island, New Zealand, Eart Suf. Prof. Landforms, 6, 127–137. MWCOG,1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban BMPs, Metropolitan Washington Council of Governments, Department of Environmental Programs, Washington, D.C. NRCS, 1986. Urban Hydrology for Small Watersheds, Technical Release 55, U.S. Department of Agriculture, Natural Resources Conservation Service, Conservation Engineering Division, Washington, D.C. NRCS, 1998. Stream Corridor Restoration: Principles, Processes and Practices, prepared by the Federal Interagency Stream Restoration Workgroup, published by the Natural Resources Conservation Service, U.S. Department of Agriculture, Washington, D.C. PGC (Prince George’s County, Maryland), 1993. Design Manual for Use of Bioretention in Stormwater Management, prepared by Engineering Technologies, Associates, Inc., Ellicott City, MD. PGC (Prince George’s County, Maryland), Department of Environmental Resources, 1997a. Low-Impact Development Design Manual, prepared by Tetra Tech, Inc., Fairfax, VA. PGC (Prince George’s County, Maryland), Department of Environmental Resources, 1997b. Low-Impact Development Guidance Manual, prepared by Tetra Tech, Inc., Fairfax, VA. Rosgen, D. L., 1996. Applied River Morphology, Wildland Hydrology, Pagosa Springs, CO. Schueler, T., 1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban BMPs, Metropolitan Washington Council of Governments, Washington, D.C. Skupien, J.J., 2000. Establishing effective development site outflow rates, paper presented at the Delaware Sediment and Stormwater Issues for a New Millennium, Conference 2000, University of Delaware, Newark, DE. Snodgrass, W.J., Kilgour, B.W., Leon, L., Eyles, N., Parish, J., and Barton, D.R., 1998. Applying ecological criteria for stream biota and an impact flow model for evaluation sustainable urban water resources in southern Ontario, in Sustaining Urban Water Resources in the 21st Century. Proceedings for an Engineering Foundation Conference, A.C. Rowney, P. Stahre, and L.A. Roesner, Eds., Malmo, Sweden, September 7–12, 1997. Stribling, J.B., 2001. Relating instream biological condition to BMP activities in watersheds, paper presented at the Conference on Linking Stormwater BMP Designs and Performance to Receiving Water Impacts Mitigation, Snowmass, CO, United Engineering Foundation, New York.

Geomorphic Considerations in Stream Protection

341

Swietlik, W.F., 1997. Stormwater management in the United States — key challenges and possible solutions, in Proceedings of Conference on Sustaining Urban Water Resources in the 21st Century, September, Malmo, Sweden, United Engineering Foundation/American Society of Civil Engineers, Reston, VA. Swietlik, W.F., 2001. Urban aquatic life uses — a regulatory perspective, paper presented at the Conference on Linking Stormwater BMP Designs and Performance to Receiving Water Impacts Mitigation, Snowmass, CO, United Engineering Foundation, New York. Tetra Tech, Inc., 2000. Effluent Limitations Guidelines, Draft Report, prepared for Office of Science and Technology, U.S. Environmental Protection Agency, Washington, D.C. U.S. EPA, 1976. Water Quality Criteria for Water. Washington, D.C., pp. 218–231. U.S. EPA, 1983. Results of Nationwide Urban Runoff Program (NURP), Final Report, Water Planning Division, Washington, D.C. U.S. EPA, 1988. Water Quality Standards Criteria Summaries: A Compilation of State/Federal Criteria: Temperature. EPA 440/5-88/023. U.S. EPA, 1999. Preliminary Data Summary of Best Management Practices, Office of Water, U.S. Environmental Protection Agency, Washington, D.C. EPA-821-2-99-012. U.S. EPA, 2000a. Low Impact Development Design Strategies: An Integrated Design Approach, prepared by Tetra Tech, Inc., Fairfax, VA for Department of Environmental Resources, Prince George’s County, MD, funding provided by the U.S. Environmental Protection Agency, Washington, D.C. U.S. EPA, 2000b. Low Impact development (LID) Hydrology, prepared by Tetra Tech, Inc., Fairfax, VA for Department of Environmental Resources, Prince George’s County, MD, funding provided by the U.S. Environmental Protection Agency, Washington, D.C. Yoder, C.O., 1995. Incorporating ecological concepts and biological criteria in the assessment and management of urban nonpoint source pollution, National Conference on Urban Runoff Management: Enhancing Urban Watershed Management at the Local, County and State Levels, U.S. Environmental Protection Agency, Washington, D.C., EPA/625/R-95/003, 183–197. Williams, G.P., 1978. Bankfull discharge of rivers, Water Resour. Res., 14(6), 1141–1153. Wolman, M.G. and Miller, J.P., 1960. Magnitude and frequency of forces in geomorphic processes, J. Geol., 68, 54–74.

13

Geomorphic Considerations in Stream Restoration James W. Gracie

CONTENTS Introduction ....................................................................................................................................344 Elements of Fluvial Geomorphology and Geomorphic Features .................................................344 Field Procedures.............................................................................................................................345 Bankfull Stage and Slope .......................................................................................................345 Bankfull Width and Depth......................................................................................................345 Sinuosity..................................................................................................................................346 Particle Size Distribution ........................................................................................................346 Sediment.........................................................................................................................................346 Channel Processes...................................................................................................................347 Stream Classification......................................................................................................................347 Applications of the Rosgen Classification System .......................................................................348 Stability/Instability..................................................................................................................350 Patterns of Adjustment and Disequilibrium ...........................................................................352 Factors That Lead to Instability .............................................................................................357 Erosion Rates ..........................................................................................................................358 Aggradation/Degradation or Vertical Instability ....................................................................358 State Assessment and Departure.............................................................................................358 Stream Restoration Techniques......................................................................................................359 Channel Geometry ..................................................................................................................359 Structures ................................................................................................................................360 Bank Stabilization Structures........................................................................................360 Root Wads............................................................................................................360 Vanes ....................................................................................................................360 Live Fascines .......................................................................................................360 Biologs .................................................................................................................361 Other Bioengineering Techniques .......................................................................361 Grade Control Structures ..............................................................................................361 Vortex Rock Weirs ...............................................................................................362 Step Pools ............................................................................................................362 Case Studies ...................................................................................................................................362 Quail Creek .............................................................................................................................362 Tributary 9 to Sawmill Creek.................................................................................................364 References ......................................................................................................................................368

0-56676-916-7/03/$0.00+$1.50 © 2003 by CRC Press LLC

343

344

Wet-Weather Flow in the Urban Watershed: Technology and Management

INTRODUCTION The Rosgen stream classification system has provided many engineers and environmental scientists with a much needed key to the understanding and application of the complex processes of fluvial geomorphology. The Rosgen stream classification system is a practical and universally applicable scheme for classifying stream channels, which involves the main parameters that operate in the processes of river mechanics and maintenance. The classification depends on knowledge of processes and is therefore useful not only to describe channels but also to evaluate how a stream will react to change through time.

ELEMENTS OF GEOMORPHOLOGY AND GEOMORPHIC FEATURES Bankfull stage is the elevation of the water surface during a bankfull discharge. Bankfull discharge is the flow that just overtops the floodplain. The floodplain is defined as the flat depositional surface adjacent to the stream and formed by the stream during the current hydrologic regime. In practical terms the bankfull stage is identified as a change in slope, the top of the point bar, or a change in vegetation. Most geomorphologists agree that the bankfull discharge is the discharge that forms and maintains the channel. It is the discharge that moves the most water and sediment over time. Streams that are stable are sized to move the sediment and water associated with the bankfull discharge. The bankfull discharge occurs on average about 2 out of every 3 years. Its return period is, therefore, about 1.5 years. Dimensions of the channel at bankfull discharge are critical properties of a stream channel. When attempting to identify bankfull stage in the field one looks for flat depositional surfaces adjacent to the stream. In meandering streams a good indicator is the tops of point bars that form on the inside of meander bends. There is usually a break in slope at the highest point on the bar, where the bar flattens out. This is the elevation of the bankfull stage. In many streams the floodplain is not fully developed and flat depositional surfaces are intermittent, not continuous, but the bankfull discharge is closely correlated with the drainage area. This fact is highly useful. However, even in those streams that do not have well-developed floodplains these surfaces exist and are at a consistent elevation. Field procedures for identifying the bankfull stage are discussed later. Identification of the bankfull stage is the first step in collecting the data that enable measurement of the critical parameters of a stream channel. The basic measurements that are taken are bankfull width, bankfull depth, sinuosity, entrenchment, slope, and particle size distribution of the materials in bed and bank. The bankfull width is the width at bankfull stage of the channel measured in a straight reach. Bankfull depth is the average depth of the bankfull stage in the same reach where width is measured. Sinuosity is simply the ratio of the channel length divided by the down-valley distance. In other words, it is a ratio expressing how much the stream meanders. Entrenchment (Figure 13.1) is the ratio of the width of the flood-prone area divided by the bankfull width. The flood-prone width is measured at a distance above the channel invert equal to twice the maximum bankfull depth. Slope is the change in elevation of bankfull stage divided by the channel length. It is usually measured by the slope of the water surface at base flow. It is measured over a distance equal to 20 to 28 times the bankfull width. Starting and ending points must be a similar geomorphic point in the channel so that the reach being measured has the same number of pools and riffles, for example, from top of riffle to top of riffle. Otherwise, the energy slope will be either overstated or understated. Particle size distribution is measured using the Wolman pebble count method. A cumulative distribution is plotted and the median size is calculated.

Geomorphic Considerations in Stream Restoration

345

FIGURE 13.1 Entrenchment. (From Rosgen, D.L., A classification of natural rivers, Catena, 22, 169–199, 1994. Elsevier Science. With permission.)

These parameters are a basic key for geomorphic classification, for discharge estimates, and characterization of pattern, energy, management implications, and many key elements of restoration design.

FIELD PROCEDURES BANKFULL STAGE

AND

SLOPE

The best way to identify and survey the bankfull stage is by use of what Emmett calls the “long profile method.” The investigator walks along the channel for a distance of at least two wavelengths and marks the apparent bankfull stage with pin flags or flagging tape. These points are surveyed in a long profile in which the invert of the channel, the water surface, and the bankfull indicators are all recorded. The profile is then plotted with all three features (bankfull, water surface, and invert) shown along the channel length. There will be some scatter in the data, but the best straight line fit to the bankfull indicators should represent the energy slope. A good check is that the high points along the bed should be parallel to the bankfull slope. A line through the tops of the riffles should also be parallel to the bankfull slope line. Divide the change in elevation between two convenient points by the distance along the channel between the points and the result is the slope in units of feet per foot. Slope is often represented as a percentage. To obtain the percent slope, divide the slope in ft/ft by 100.

BANKFULL WIDTH

AND

DEPTH

The procedure is as follows. Select a location for a cross section measurement in a straight reach free of obstructions such as large boulders, logs, midchannel bars, etc. Stretch a tape measure with zero on the left side of the channel while looking downstream. Stretch the tape from a point on the left and right banks that is at least twice the distance of the maximum depth above the channel invert. Install monuments with either cement and carriage bolts or reinforcing rods. Record the location and elevation of points at every break in slope along the tape measure. Make a note of the left and right bank bankfull stage indicators as well as the water surface on both sides of the channel. Draw a sketch map showing the location of the cross section monuments.

346

Wet-Weather Flow in the Urban Watershed: Technology and Management

SINUOSITY Sinuosity is most easily measured in the office from aerial photographs. Obtain recent aerial photographs that are taken in winter or that are color infrared photographs so the stream channel is visible. Select a typical reach from the aerials that includes the area to be measured. Mark off limits of the reach that is of interest and measure the distance between the upstream and downstream ends. Then measure the channel length between the same two points. Use a wheel scale so that the actual length along the channel can be measured. Divide the distance along the channel by the down-valley, straight line distance. The result is the sinuosity. Topographic maps should not be used for this purpose. They nearly always understate the channel length significantly, unless one is measuring a very large river. Sometimes it is not possible to obtain suitable aerial photographs for measuring sinuosity. If this is the case, sinuosity will have to be measured in the field. Select a reach that is at least 20 to 28 channel widths long and lay a tape along the centerline of the channel using chaining pins to approximate the channel meanders. Measure the channel length and measure the distance between the starting and ending points in a straight line. Divide the channel length by the down-valley distance to obtain the sinuosity.

PARTICLE SIZE DISTRIBUTION The pebble count procedure involves a stratified random sampling method of measuring the particle size distribution of the materials in the bed and bank of the active channel. The procedure involves an examination of the reach being characterized to estimate the percent of pool, riffle, and run in the reach. Once this is determined, select transects from pool, riffles, and runs in the same proportion that they exist in the reach. In other words if the reach is 25% pool, 25% riffle, and 50% run, the transects should be in the ratio of one pool, one riffle, and two runs. It will be necessary to measure at least 100 particles and also to measure the right proportions of complete transects of pool, riffle, and run. Once the transects have been selected, one walks along each one, taking a particle at every step by reaching under the big toe, without looking, and measuring the first particle touched. This is done until the minimum requirement of at least 100 particle and full transects in the correct proportions has been met. The particle dimension measured is the length of the intermediate axis. The reason for this is the intermediate axis will determine the size sieve that the particle will pass through. After measuring the required number of particles, group them into phi intervals (increasing powers of two; i.e., 20 = 1, 21 = 2, 22 = 4, etc.) and plot the cumulative distribution with the particle intermediate axis on the horizontal scale and the percent less than on the vertical scale. The resulting graph is a cumulative particle size distribution. Locate 50% on the vertical scale and draw a horizontal to intersect the curve. From that intersection draw a vertical line to the horizontal axis. Where it intersects the horizontal axis is the median size or D50.

SEDIMENT Streams move sediment and water. A stream may be thought of as the manifestation of a process converting the potential energy of elevation into the kinetic energy of movement. Streams shape their channels and form floodplains. The movement of sediment is not constant. It varies in both space and time. Sediment moving in streams is classified in two forms: suspended sediment and bed load sediment. Suspended sediment is fine enough to be suspended in the water and transported as “washload.” Bed load sediment is coarser and moves in a process called saltation. Saltating particles are momentarily lifted or entrained and move along the bed, bouncing and starting and stopping. Bed load does not move at normal flows but only when there is enough energy in the flowing water to move it. It has been estimated that bed load begins to move in most streams when flow exceeds about one third of bankfull depth.

Geomorphic Considerations in Stream Restoration

347

In general, sediment comes from two sources: overland and in channel. Usually, overland sources of sediment mainly comprise fine sediment because shallow flow cannot entrain and transport coarse sediment. Some mass failure such as landslides, hill slope failures, etc. can introduce coarse sediment.

CHANNEL PROCESSES Erosion of outside meander bends is a natural process in all meandering stream channels. In stable channels it occurs at low rates and and is matched by deposition rates on point bars. In this way the stream builds its floodplain behind the advancing point bars. When a channel is maintaining its pattern and dimensions but neither degrading nor aggrading it is said to be in equilibrium. Note that a stream in equilibrium may be changing its position with lateral migration, but as long as it meets the conditions of maintaining its pattern and dimension and neither degrading nor aggrading it is still in equilibrium. One of the conditions of this equilibrium is that sediment supply is in equilibrium with sediment transport. The farmer losing pasture and the engineer whose bridge is threatened may not like this definition of equilibrium, but geomorphologically it is correct. The river is following its natural equilibrium tendencies. As long as the climate and land use do not change, streams will stay in equilibrium. If something happens to change the flow regime or the sediment supply or the pattern or dimensions of the channel, streams respond in a process of adjustment and can enter a condition of disequilibrium. Disequilibrium results when a change in the flow regime, sediment supply, or energy distribution in the channel occurs. A change in climate can induce disequilibrium; a change in land use that alters the hydrologic regime can induce disequilibrium. A change in sediment supply, either an increase or decrease in sediment supply, can also induce this condition of disequilibrium. Degradation of channels is well documented downstream of dams because of the dramatic decrease in sediment supply, which is trapped in the pool of the dam. An increase in sediment supply from human activities such as construction mining is not uncommon. The distribution of energy in stream channels can change when channels are straightened, resized, or otherwise altered. A common process of destabilization is when changes in land use activities alter the hydrologic regime. Removal of vegetation and installation of impervious area and storm drain systems alter the hydrologic cycle by decreasing the amount of infiltration, increasing the amount of runoff, and reducing or eliminating evapotranspiration. Depression storage is also decreased. The peak flows from the same rainfall events increase, often severalfold. Since channels are in equilibrium with the peak annual flows from their watersheds, enlargement must follow these hydrologic changes. Enlargement occurs as erosion either by accelerated lateral erosion or by incision, or both. If erosion rates increase, enough sediment supply increases beyond the competence of the stream to transport it and disequilibrium occurs. Excess sediment from channel erosion exceeds transport capacity. This excess sediment forms depositional features, which affects channel capacity, thereby inducing more erosion in an effort to regain channel capacity. This sediment increases sediment supply even more, which leads to more erosion, which yields still more excess sediment, and on and on. Thus, a self-feeding, or positive feedback, mechanism is under way. Many streams in urbanizing areas are in this condition. Equilibrium may not reestablish itself for decades or longer. While these processes dominate, many stream are devoid of normal aquatic life. Either the fine sediment fills the interstitial gravel habitat or the frequent shifting of substrate grinds delicate creatures to death. One of the important goals of restoration is to reestablish the equilibrium between sediment supply and sediment transport and to reduce the rate of channel adjustment so that aquatic habitat can recover.

STREAM CLASSIFICATION Efforts to classify streams are not new. One of the early classification systems by Davis (1899) grouped streams into three stages of adjustment: youthful, mature, and old. The youthful streams

348

Wet-Weather Flow in the Urban Watershed: Technology and Management

were steep-gradient, low-sinuosity streams and had large channel materials. Mature streams were sinuous, lower gradient, and carried intermediate-sized sediment. Old streams were very sinuous, flowed in low-gradient valleys, and had still smaller sediment. Straight, meandering, and braided streams were identified by Leopold and Wolman (1957). Lane (1957) developed slope–discharge relationships for braided, intermediate, and meandering streams. Another classification system was developed by Schumm (1963) based upon descriptive and interpretive characteristics such as channel stability and mode of sediment transport. Descriptive classification systems were developed by Culbertson et al. (1967), Thornbury (1969), and Khan (1971). Most of these early classification systems relied on qualitative interpretation of geomorphic features, thus leading to inconsistency in classification and limited predictive abilities. There have been many attempts to classify streams most of which have limited usefulness. A current, widely useful classification system is the Rosgen classification system. Specific objectives of the system are as follows: 1. To predict the behavior of a river from measurable morphologic features 2. To develop specific hydraulic and sediment relationships for a given stream type and its state 3. To provide a mechanism to extrapolate site-specific data to stream reaches with similar characteristics 4. To provide a consistent frame of reference for communicating stream morphology and condition among a variety of disciplines and interested parties The Rosgen classification system is hierarchical. Combinations of morphologic variables useful for different scales of analysis from coarse to fine resolution are used in a hierarchy of river morphology. The coarse level analysis can be performed using aerial photographs and topographic maps. This level, Level 1, can distinguish the major stream types, A, B, C, D, E, F, and G. The next level, Level 2, is the reach specific classification; then there is a Level 3, which includes a state assessment and prediction, and, finally, Level 4, which is validation or monitoring. The discussion here concentrates on Level 2, the reach classification in this work. Table 13.1 is a key to classification of natural rivers (Rosgen, 1996). The parameters used have been discussed above along with the procedures for measuring them. The first step is to decide whether the stream is a single thread channel or a multiple thread channel. If it is a single thread, then entrenchment is the next determination and there are three categories: entrenched, moderately entrenched, and slightly entrenched. Examples of different entrenchment ratios are shown in Figure 12.6. Next, look at width/depth ratio. Bankfull width and depth are used in this simple calculation. Then sinuosity and, finally, slope. These parameters will enable one to determine the major stream type. Add the D50 from the cumulative particle size distribution and a number from 1 to 6 can be assigned based upon the median size from boulder to silt-clay. Figures 13.2 through 13.15 are examples of different stream types.

APPLICATIONS OF THE ROSGEN CLASSIFICATION SYSTEM The Rosgen classification system in its full version is a hierarchical system. It allows classification at different levels of specificity. At its most generic level, Level 1, it allows the classification of streams and rivers into the major stream types. This classification can be performed with available data such as topographic maps and aerial photographs. In its most familiar form, Level 2, it is a reach-specific classification, which can be performed only after the collection of data specific to the reach being classified. At an even finer level of detail, Level 3, it is a tool for state assessment and prediction of future adjustment direction and rates. Finally, at Level 4, the system suggests methods for monitoring and validating prediction from Level 3.

A4a+

A5a+

A6a+

Gravel

Sand

Silt/Clay

A6

A5

A4

A3

A2

A1

G6

G5

G4

G3

G2

G1

G6c

G5c

G4c

G3c

G2c

G1c

12)

B6a

B5a

B4a

B3a

B2a

B1a

0.04– 0.099

B6

B5

B4

B3

B2

B1

0.02– 0.039

Slope Range

B

B6c

B5c

B4c

B3c

B2c

B1c

1.2)

Moderate (W/O (>12)

Mod. Entrenched (1.4–2.2)

E6b

E5b

E4b

E3b

0.02– 0.039

E6

E5

E4

E3

1.5)

C6b

C5b

C4b

C3b

C2b

C1b

0.02– 0.039

C6

C5

C4

C3

C2

C1

0.001– 0.02

Slope Range

C

C6c-

C5c-

C4c-

C3c-

C2c-

C1c-

1.4)

Mod.-High W/O (>12)

Slightly Entrenched (>2.2) Very Low W/O (0.10

Moderate Sinuosity (>1.2)

Low Sinuosity (