Stormwater Management for Smart Growth Stormwater Management for Smart Growth Allen P. Davis and Richard H. McCuen Department of Civil and Environmental Engineering University of Maryland College Park, Maryland Springer Library of Congress Cataloging-in-Publication Data A C.I,P. Catalogue record for this book is available from the Library of Congress. ISBN-10: 0-387-26048-X ISBN-10: 0-387-27593-2 (e-book) ISBN-13: 9780387260488 ISBN-13: 9780387275932 Printed on acid-free paper. © 2005 Springer Science+Business Media, Inc. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, Inc., 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed in the United States of America. 9 8 7 6 5 4 3 21 SPIN 11424451 sprmgeronline.com PREFACE Land development to support population increases and shifts requires changes to the hydrologic cycle. Increased impervious area results in greater volumes of runoff, higher flow velocities, and increased pollutant fluxes to local waterways. As we learn more about the negative impacts of these outcomes, it becomes more important to develop and manage land in a smart manner that reduces these impacts. This text provides the reader with background information on hydrology and water quality issues that are necessary to understand many of the environmental problems associated with land development and growth. The variability of runoff" flows and pollutant concentrations, however, makes the performance of simple technologies erratic and predicting and modeling their performance difficult. Chapters on statistics and modeling are included to provide the proper background and tools. The latter chapters of the text cover many of the different technologies that can be employed to address runoff flows and improve water quality. These chapters take a design approach with specific examples provided for many of the management practices. A number of methods are currently available for addressing the problems associated with stormwater runoff quality from urban areas; more continue to be developed as research is advanced and interest in this subject continues to surge. Traditionally, techniques for the improvement of runoff quality were borrowed applications from water and wastewater treatment, such as large sedimentation ponds Recently, increased interest has been placed on using natural systems to improve water quality. This includes grassy filters, forested buffers, wetlands, and bioretention areas. These natural areas can slow flow, store water, filter sediments, and promote physical, chemical, and biological processes that can attenuate pollutants. Finally, novel approaches are being developed to improve stormwater quality by minimizing surface flow volumes and rates, and overall pollutant production in the first place. These ideas are receiving considerable interest throughout the U.S. and Europe where severe and haphazard development has lead to negative environmental impacts on local water bodies. On-site roof gardens, rain gardens and bioretention, permeable pavements, and specialty landscaping can minimize runoff, hold pollutants, and promote evapotranspiration and infiltration. Integrating these techniques into new land development and retrofitting existing developed areas provides new challenges to professionals who are concerned with urban water quality. This book is intended both as a textbook for classroom use and as a guide for professionals who are responsible for mitigating the detrimental effects of land development. This includes engineers, hydrologists, land use planners, natural resources managers, and environmental scientists. Those responsible for the development of stormwater policies may also find value in the approaches to design discussed herein. On the cover: Bioretention is a stormwater management technology that can be implemented in variety of land development situations, (clockwise from top left): 1) In a parking lot median. 2) Accepting runoff from a roadway. 3) A schematic of bioretention. 4) Bioretention in a condominium development. Bioretention is discussed in Section 9,4. ACKNOWLEDGMENTS Allen p. Davis would like to express his appreciation to the various agencies that have supported his work on stormwater and stormwater management technologies. These include The Prince George's County Government, The Maryland State Highway Administration, The Cooperative Institute for Coastal and Estuarine Environmental Technology (CICEET), The Maryland Water Resources Research Center, and The District of Columbia Department of Health. A heartfelt thanks is also offered to his wife Dolores for her support during the preparation of this text. CONTENTS INTRODUCTION 1 1.1 URBAN SPRAWL: THE PROBLEM 1 1.1.1 A Historical Perspective 1 1.1.2 Characteristics of Urban Sprawl 3 1.1.3 Pollution of Waterways 4 1.1.4 The Effects of Urban Sprawl 5 1.1.5 Difficulties Faced in Improving Stormwater Quality 6 1.2 SMART GROWTH: THE SOLUTION 8 1.2.1 Urban Sprawl or Smart Growth 8 1.2.2 Alternative Perspective on Smart Growth 8 1.3 PROBLEMS 9 1.4 REFERENCES 10 WATER QUALITY PARAMETERS 11 2.1 INTRODUCTION 11 2.2 MASS, CONCENTRATION, AND LOADING 14 2.2.1 Mass Balances 14 2.2.2 Concentration-Flow Relationships 16 2.3 FACTORS NECESSARY FOR LIFE 18 2.3.1 Dissolved Oxygen 19 2.3.2 pH 19 2.3.3 Temperature 20 2.4 WATER POLLUTANTS 21 2.4.1 Suspended Solids 21 2.4.2 Oxygen Demanding Substances 23 2.4.3 Nitrogen Compounds 24 2.4.3.1 Nitrogen Chemistry 24 2.4.3.2 Nitrogen in the Environment 25 2.4.4 Phosphorus 27 2.4.5 Microbial Pathogens 27 X STORWATER MANAGEMENT FOR SMART GROWTH 2.4.6 Heavy Metals 28 2.4.7 Oils and Grease 29 2.4.8 Toxic Organic Compounds 29 2.4.8.1 Pesticides 29 2.4.8.2 Polycyclic Aromatic Hydrocarbons 30 2.4.8.3 Solvents 30 2.4.9 Trash 30 2.5 WATER QUALITY INDICES 31 2.6 TOTAL MAXIMUM DAILY LOADS-TMDLS 32 2.7 PROBLEMS 34 2.8 REFERENCES 36 3 STATISTICAL METHODS FOR DATA ANALYSIS 37 3.1 INTRODUCTION 38 3.2 POPULATION AND SAMPLE MOMENTS 38 3.2.1 Mean 38 3.2.2 Variance 40 3.2.3 Standard Deviation 40 3.2.4 Coefficient of Variation 41 3.3 PROBABILITY DISTRIBUTIONS 42 3.3.1 Probability 42 3.3.2 Types of Random Variables 42 3.3.3 Uniform Distribution 43 3.3.4 Normal Distribution 44 3.3.4.1 Standard Normal Distribution 45 3.3.4.2 Log-Normal Distribution 47 3.3.5 t Distribution 48 3.4 A PROCEDURE FOR TESTING HYPOTHESES 48 3.4.1 Step 1: Formulation of Hypotheses 49 3.4.2 Step 2: The Test Statistic and its Sampling Distribution 50 3.4.3 Step 3: The Level of Significance 50 3.4.4 Step 4: Data Analysis 51 3.4.5 Step 5: The Region of Rejection 51 3.4.6 Step 6: Select the Appropriate Hypothesis 51 3.4.7 Summary of Common Hypothesis Tests 53 3.5 OUTLIER DETECTION 56 3.6 PROBLEMS 59 4 STORMWATER HYDROLOGY 63 4.1 INTRODUCTION 64 4.2 THE HYDROLOGIC CYCLE 64 4.2.1 Water Quantity Perspective 64 4.2.2 Water Quality Perspective 66 4.3 PRECIPITATION 67 4.3.1 Depth-Duration-Frequency 67 4.3.2 RainfallMaps 68 4.3.3 Intensity-Duration-Frequency 68 CONTENTS xi 4.3.4 Development of a Design Storm 69 4.4 WATERSHED CHARACTERISTICS 76 4.4.1 Watershed: Definition and Delineation 77 4.4.2 Drainage Area 78 4.4.3 Watershed Length 78 4.4.4 Watershed Slope 78 4.4.5 Land Cover and Use 79 4.4.6 Surface Roughness 80 4.4.7 Channel Cross Sections 80 4.4.8 Channel Roughness 81 4.4.9 Runoff Curve Numbers 82 4.4.9.1 Soil Group Classification 83 4.4.9.2 Hydrologic Condition 84 4.4.9.3 Curve Number Tables 84 4.4.9.4 Estimation of CN Values for Urban Land Uses 84 4.4.9.5 Effect of Unconnected Impervious Area on Curve Numbers 88 4.4.10 Time of Concentration 88 4.4.10.1 Velocity Method 89 4.4.10.2 Sheet-Flow Travel Time 90 4.5 RATIONAL FORMULA 95 4.6 TR-55 GRAPHICAL PEAK-DISCHARGE METHOD 97 4.7 PROBLEMS 98 4.7 REFERENCES 104 5 INTRODUCTION TO MODELING 105 5.1 INTRODUCTION 106 5.2 UNIVARIATE FREQUENCY ANALYSIS 106 5.2.1 Population versus Sample 107 5.2.2 Regionalization 107 5.2.3 Probability Paper 107 5.2.4 Mathematical Model 108 5.2.5 Procedure 109 5.2.6 Sample Moments 109 5.2.7 Plotting Position Formulas 110 5.2.8 Return Period 110 5.2.9 The Normal Distribution 110 5.2.10 The Log-Normal Distribution Ill 5.3 BIVARIATEMODELING Ill 5.3.1 Correlation Analysis 112 5.3.1.1 Graphical Analysis 112 5.3.1.2 Bivariate Correlation 113 5.3.2 Regression Analysis 113 5.3.2.1 Principle of Least Squares 113 5.3.2.2 Zero-Intercept Model 114 5.3.2.3 Reliability of the Regression Equation 115 5.4 MULTIPLE REGRESSION ANALYSIS 117 5.4.1 Correlation Matrix 118 xii STORWATER MANAGEMENT FOR SMART GROWTH 5.4.2 Calibration of the Multiple Linear Model 119 5.4.3 Evaluating a Multiple Regression Model 119 5.5 NONLINEAR MODELS 121 5.5.1 The Power Model 121 5.5.2 Transformation and Calibration 122 5.6 PROBLEMS 125 5.7 REFERENCES 129 6 STORMWATER QUALITY 131 6.1 INTRODUCTION 132 6.2 POLLUTANT LEVEL DETERMINATIONS 132 6.2.1 Grab Sample Measurements 133 6.2.2 Composite Sample Measurements 134 6.3 STORMWATER RUNOFF QUALITY DATA 136 6.3.1 pH 137 6.3.2 Suspended Solids and Oil and Grease 137 6.3.3 Organic Carbon/Oxygen Demand 137 6.3.4 Nutrients 137 6.3.5 Metals 141 6.3.6 Toxic Organics 141 6.3.7 Pathogens 141 6.4 POLLUTANT MASS LOADS 142 6.5 THE FIRST FLUSH 143 6.5.1 Defining the First Flush 144 6.5.2 First Flush Measurements 148 6.5.3 The Antecedent Dry Weather Period 149 6.6 PARTICULATES IN STORMATER RUNOFF 151 6.6.1 Physical Characteristics 151 6.6.2 Chemical Characteristics 152 6.7 POLLUTANT SOURCES 153 6.7.1 Contributions from Different Land Uses 153 6.7.2 Specific Pollutant Sources 155 6.8 EMPIRICAL HIGHWAY RUNOFF MODELS 159 6.9 STOKES LAW 159 6.10 UNIVERSAL SOIL LOSS EQUATION 163 6.11 PROBLEMS 168 6.12 REFERENCES 172 7 IMPROVEMENT OF STORMWATER QUALITY 175 7.1 INTRODUCTION 175 7.2 BEST MANAGEMENT PRACTICES 176 7.3 PROBLEMS 182 7.4 REFERENCES 184