Stormwater Management and Water Quality

When precipitation occurs, the resulting stormwater from natural and developed areas can carry natural and anthropogenic debris, sediment, and chemicals into receiving waters. Impervious surfaces such as roofs, parking lots, roadways and compacted soils can increase the proportion of precipitation that becomes runoff and these increased flows can convey debris, sediment, and chemicals at a greater rate than over natural land covers. Construction and maintenance activities on natural and developed land covers can substantially increase the debris, sediment, and chemicals flowing with runoff to receiving waters if robust countermeasures are not used.

The FHWA provides the following reports and guidance for controlling stormwater runoff along highways and minimizing the effects of transportation projects on water quality:

Best Management Practices

Long-Term Performance and Life-Cycle Costs of Stormwater Best Management Practices 2016, National Cooperative Highway Research Program (NCHRP) Report 792 - This report focuses on the long-term performance and life-cycle costs for highway-related stormwater best management practices (BMPs). Management of stormwater runoff from the highway network is a major concern for municipalities, state departments of transportation (DOTs), and other transportation agencies. BMPs are designed to minimize the effects of stormwater runoff on receiving waters and ecosystems through changes in water quality and hydrology. Decisionmakers need information about the performance and cost of various BMPs.
Guidelines for Evaluating and Selecting Modifications to Existing Roadway Drainage Infrastructure to Improve Water Quality in Ultra-Urban Areas 2012, National Cooperative Highway Research Program (NCHRP) Report 728 - This report provides guidelines to evaluate and select hydraulic modifications to existing drainage infrastructure that will help mitigate potential impacts of highway runoff on receiving waters. The guidelines are directed specifically at roadway facilities in dense urban areas that can be particularly difficult and costly to retrofit because of space limitations, high pollutant loadings, hydrologic flashiness, hydraulic constraints, legacy contamination, utility conflicts, and other issues.
Stormwater Infiltration in the Highway Environment: Guidance Manual 2020, National Cooperative Highway Research Program (NCHRP) Report 922 - This report provides information, guidance, and tools for planners, designers, regulators, and policymakers to determine when it is appropriate to use infiltration approaches to manage stormwater in the highway environment. The limitations, risks, and benefits of infiltration best management practices (BMPs) are examined in the context of the built and natural environments (e.g., surface water, groundwater, soils, and infrastructure). The Guidance Manual supports decision-making about the siting, selection, and design of stormwater infiltration BMPs, including effective system design in cases when projects include infiltration.
Evaluation of Best Management Practices for Highway Runoff Control, 2006 - This report focuses on improving the scientific and technical knowledge base for the selection of best management practices (BMPs) through a better understanding of BMP performance and application. This report documents an extensive program of research on the characterization of BMPs and stormwater, and the influence of factors such as land use practice, hydraulic characteristics, regional factors, and performance evaluation. The report includes a CD containing a spreadsheet model and three additional volumes: User’s Guide for BMP/LID Selection, Appendices to the User’s Guide, and Low Impact Development Design Manual for Highway Runoff Control.
Statistical methods for simulating structural stormwater runoff best management practices (BMPs), 2020 - This report documents statistics for simulating structural stormwater runoff best management practices (BMPs) with the Stochastic Empirical Loading and Dilution Model (SELDM). The U.S. Geological Survey developed SELDM and the statistics documented in this report in cooperation with the Federal Highway Administration to indicate the risk for stormwater flows, concentrations, and loads to exceed user-selected water-quality goals and the potential effectiveness of mitigation measures to reduce such risks. Analyses for this study were done with data extracted from a modified copy of the December 2019 version of the International Stormwater Best Management Practices Database. Statistics for volume reduction, hydrograph extension, and water-quality treatment were developed with selected data.
International Stormwater BMP Database, 2019 - The International Stormwater Best Management Practices Database (BMPDB) is a repository of BMP field studies and related web tools, performance summaries, and monitoring guidance. Initiated over 25 years ago, the original focus was urban stormwater BMPs (stormwater control measures). Through the support of long-term partners, the project has expanded to develop additional resources related to both urban and agricultural runoff, treatment and management.
Determining the State of the Practice in Data Collection and Performance Measurement of Stormwater Best Management Practices, 2014 - The objective of this research project is to assess the state of practice of data collection and performance measurement in stormwater management programs at state Departments of Transportation (DOTs). Specifically, this study evaluates if it is feasible to develop performance measures for stormwater that state DOTs can use in performance-based planning and programming. The study focused on both construction-phase as well as post-construction application of BMPs to protect water quality.

Research and Reports

Development of the North Carolina stormwater-treatment decision-support system, 2023 - Transportation agencies need information about the potential effects of climate change on the volume, quality, and treatment of stormwater to mitigate potential effects of runoff on receiving waters. To address these concerns, the U.S. Geological Survey and the Federal Highway Administration used the Coupled Model Intercomparison Project tool and the Stochastic Empirical Loading and Dilution Model to perform space-for-time stormwater quality analyses. This study does not question the potentially large climate-related changes in hydrologic and hydraulic variables expected to occur in the foreseeable future. It does indicate that uncertainties in the current data and potential effects of land use change on stormwater quality and treatment variables are larger than the projected effects of climate change.
Assessing potential effects of climate Change on highway-runoff flows and loads in southern New England by using planning-level space-for-time analyses, 2023 - The Federal Highway Administration and State departments of transportation nationwide need an efficient method to assess potential adverse effects of highway stormwater runoff on receiving waters to optimize stormwater-treatment decisions. To this end, the U.S. Geological Survey, in cooperation with the Federal Highway Administration and the North Carolina Department of Transportation (NCDOT), developed a decision-support software tool. This decision-support tool is designed to identify potential adverse effects of highway runoff by using a criterion based on a measurable change in water quality from a surrogate pollutant.
Approaches for assessing flows, concentrations, and loads of highway and urban runoff and receiving-stream stormwater in southern New England, 2024 - This report by the U.S. Geological Survey, in cooperation with the Federal Highway Administration and the Connecticut, Massachusetts, and Rhode Island Departments of Transportation, documents approaches for assessing flows, concentrations, and loads of highway- and urban-runoff and receiving-stream stormwater in southern New England This report documents simulation methods, methods for interpreting stochastic model results, sensitivity analyses to identify the most critical variables of concern, and examples demonstrating how simulation results can be used to inform scientific decision-making processes.
Approaches for assessing long-term annual yields of highway and urban runoff in selected areas of California, 2021 - The California Department of Transportation, commonly known as CalTrans, and other municipal separate storm sewer system permittees in California as well as other State departments of transportation nationwide need information about potential loads and yields (loads per unit area) of constituents of concern in stormwater runoff and discharges from stormwater best management practices (BMPs). In this study, a series of regional and local yields were simulated to provide statewide planning-level estimates and more refined TMDL-specific yield values. SELDM was used to analyze 368 State roadway and urban runoff yields for 53 runoff quality constituents.
Assessing the impact of chloride deicer application in the Siskiyou Pass, southern Oregon, 2022 - Chloride deicers have been applied by the Oregon Department of Transportation (ODOT) to Interstate Route 5 (I–5) from the Oregon-California border north to mile marker 10 for several years in the high-elevation area known as the Siskiyou Pass. This study found that (1) the inclusion of local streamflow data is important for obtaining accurate downstream EMCs, (2) the inclusion of precipitation data is important for highway and concurrent runoff load calculations, and (3) water-quality constituent EMC data from highway runoff and upstream stormflows are the most important data to collect for highway runoff and upstream water-quality constituent concentration statistics.
Comparison of SELDM simulated total-phosphorus concentrations with ecological impervious-area criteria EE.1943-7870.0001763), 2020 - Ecological studies indicate that impervious cover (IC) greater than approximately 5%–20% may have adverse effects on receiving-stream ecology. It is difficult to separate the effects of runoff quality from other effects of urbanization on receiving streams. This study presents the results of a numerical experiment to assess the effects of increasing IC on water quality. Simulation results mirror the results of ecological studies; event mean concentrations (EMCs) of total phosphorus (TP) increase proportionally to the logarithms of imperviousness for a given risk percentile. Simulation results indicated that commonly used stormwater treatment methods may be insufficient for mitigating the effects of imperviousness. Therefore, disconnection, rather than treatment, may be needed to protect water quality, and efforts to preserve undeveloped stream basins may be more effective than efforts to remediate conditions in highly developed basins. Results also indicate that commonly used water-quality criteria may be too restrictive for stormwater because TP EMCs frequently exceed these criteria, even in minimally developed basins.
Simulating runoff quality with the Highway-Runoff Database and the Stochastic Empirical Loading and Dilution Model, 2019 - Stormwater practitioners need quantitative information about the quality and volume of highway runoff to assess and mitigate potential adverse effects of runoff on the Nation’s receiving waters. The U.S. Geological Survey developed the Highway Runoff Database (HRDB) in cooperation with the FHWA to provide practice-ready information to meet these information needs on the local or national scale. This paper describes the datasets that are available in version 1.1 of the HRDB and demonstrates how data and statistics from the HRDB can be used with the Stochastic Empirical Loading and Dilution Model (SELDM) to simulate highway runoff. The HRDB includes 249 sites, 6,849 runoff events, and 106,869 event mean concentrations (EMCs) collected during the 1975–2017 period. It includes data from 16 States in the conterminous United States and from Hawaii. The EMCs in the HRDB include measurements for 415 different water-quality constituents. These water-quality measurements include 32,944 trace-metal; 27,496 organic; 15,684 nutrient; 13,016 physical property; 10,307 major inorganic; 6,773 sediment; and 649 other constituent values. There are large variations in the data. For example, EMCs for total suspended solids and total phosphorus range from 0.4 to 5,440 mg/L and 0.004 to 22 mg/L, respectively; geometric means range from 1.58 to 1,379 mg/L and 0.017 to 2.82 mg/L for these constituents, respectively. The example simulations indicate that risks for adverse effects of runoff can vary by orders of magnitude; the HRDB and SELDM facilitate selection of representative statistics from available datasets.
Assessing potential effects of highway and urban runoff on receiving streams in total maximum daily load watersheds in Oregon, 2019 - Ecological studies indicate that impervious cover (IC) greater than approximately 5%–20% may have adverse effects on receiving-stream ecology. It is difficult to separate the effects of runoff quality from other effects of urbanization on receiving streams. This study presents the results of a numerical experiment to assess the effects of increasing IC on water quality. Simulation results mirror the results of ecological studies; event mean concentrations (EMCs) of total phosphorus (TP) increase proportionally to the logarithms of imperviousness for a given risk percentile. Simulation results indicated that commonly used stormwater treatment methods may be insufficient for mitigating the effects of imperviousness. Therefore, disconnection, rather than treatment, may be needed to protect water quality, and efforts to preserve undeveloped stream basins may be more effective than efforts to remediate conditions in highly developed basins. Results also indicate that commonly used water-quality criteria may be too restrictive for stormwater because TP EMCs frequently exceed these criteria, even in minimally developed basins.
Characterization of stormwater runoff from bridge decks in eastern Massachusetts, 2014–16, 2018 - The quality of stormwater runoff from bridge decks (hereafter referred to as “bridge-deck runoff”) was characterized in a field study from August 2014 through August 2016 in which concentrations of suspended sediment (SS) and total nutrients were monitored. The runoff-quality risk analysis indicated that bridge-deck runoff would exceed discharge standards commonly used for large, advanced wastewater treatment plants, but that commonly used stormwater best-management practices may reduce the percentage of exceedances by one-half. Results of simulations indicated that long-term average yields of TN, TP, and SS may be about 21.4, 6.44, and 40,600 pounds per acre per year, respectively. These yields are about 1.3, 3.4, and 16 times simulated ultra-urban highway yields in Massachusetts; however, simulations indicated that use of a best-management practice structure to treat bridge-deck runoff may reduce discharge yields to about 10, 2.8, and 4,300, pounds per acre per year, respectively.
Assessing roadway contributions to stormwater flows, concentrations and loads by using the StreamStats application, 2018 - The Oregon Department of Transportation (ODOT) and other state departments of transportation need quantitative information about the percentages of different land-cover categories above any given stream crossing in the state to assess and address roadway contributions to water-quality impairments and resulting Total Maximum Daily Loads. The U.S. Geological Survey, in cooperation with ODOT and the FHWA, added roadway and land-cover information to the online StreamStats application to facilitate analysis of stormwater runoff contributions from different land covers. Analysis of 25 delineated basins with drainage areas of about 100 square miles indicates the diversity of land covers in the Willamette Valley, Oregon. On average, agricultural, developed, and undeveloped land covers comprise 15, 2.3, and 82 percent of these basin areas. On average, these basins contained about 10 miles of State highways and 222 miles of non-state roads. This analysis indicated that highway yields were larger than yields from other land covers because highway-runoff concentrations were higher than other land covers and the highway is fully impervious. However, the total highway area was a small fraction of the other land covers. Consequently, while highway-runoff mitigation measures can be effective for managing water quality locally, they may have limited effect on achieving basin-wide stormwater reduction goals.
Estimating Total Maximum Daily Loads with the Stochastic Empirical Loading and Dilution Model, 2017 - The Massachusetts Department of Transportation (DOT) and the Rhode Island DOT are assessing and addressing roadway contributions to total maximum daily loads (TMDLs). Example analyses for total nitrogen, total phosphorus, suspended sediment, and total zinc in highway runoff were done by the U.S. Geological Survey in cooperation with FHWA to simulate long-term annual loads for TMDL analyses with the stochastic empirical loading and dilution model known as SELDM. Example simulations indicate that both concentration reduction and flow reduction by structural best management practices are
Compilation of streamflow statistics calculated from daily mean streamflow data collected during water years 1901–2015 for selected U.S. Geological Survey streamgages, 2017 - Streamflow statistics are needed by decision makers for many planning, management, and design activities. The U.S. Geological Survey (USGS) StreamStats Web application provides convenient access to streamflow statistics for many streamgages by accessing the underlying StreamStatsDB database. In 2016, non-interpretive streamflow statistics were compiled for streamgages located throughout the Nation and stored in StreamStatsDB for use with StreamStats and other applications.
Quantifying the Components of Impervious Surfaces, 2007 - The objectives of this study are to (1) determine the makeup of total area and the relative contribution of individual components; and (2) assess the accuracy of various techniques in use for determining total impervious area. Six urban and suburban watersheds were selected for study that represent a wide geographic distribution across the country. High-resolution orthoimagery (1 meter or better) was obtained for each watershed. Six classes of impervious cover were manually digitized as polygon features in a geographic information systems (GIS) environment. Relevant GIS data were obtained from County or City GIS departments. The six classes of cover were roads, buildings, parking lots, driveways, sidewalks, and other (such as sport courts). Quality control was provided by independent validation and mapping spot checks. The total area for each impervious surface class was totaled for the six watersheds and the percentage of each class was calculated against the total area of impervious cover. The largest area class of impervious cover was buildings at 29.1 percent, followed by roads (28.3 percent), and parking lots (24.8 percent); with the remaining three totaling 14 percent - driveways, sidewalks, and other, where other were any other features that were not contained within the first five.
Stormwater Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring, 1997 - The purpose of this report is to provide a planning-level review of the applicability and use of new and more traditional BMPs in ultra-urban areas. This report focuses on the unique characteristics specific to ultra-urban settings and provides specific guidance for selecting and siting stormwater management technologies. The information is structured in an informative, user-friendly format, with case studies highlighting examples of BMP monitoring throughout the country and tables illustrating the characteristics of each BMP to facilitate comparison and identification of specific technologies appropriate to a given site. BMP information is provided in fact sheets, which address applicability, effectiveness, siting and design, maintenance, and cost considerations. The report is organized into separate chapters that address ultra-urban considerations, BMP design information tailored to the ultra-urban environment, monitoring program design, and BMP selection.

Stormwater Models

Stochastic Empirical Loading and Dilution Model for analysis of flows, concentrations, and loads of highway runoff constituents, 2014 - The Stochastic Empirical Loading and Dilution Model (SELDM) was developed by the U.S. Geological Survey in cooperation with the Federal Highway Administration (FHWA) to supersede use of the 1990 FHWA runoff-quality model. SELDM is designed to be a tool that can be used to transform disparate and complex scientific data into meaningful information about the risk for adverse effects of runoff on receiving waters, the potential need for mitigation measures, and the potential effectiveness of such measures for reducing these risks. SELDM is easy to use because much of the information and data needed to run SELDM are embedded in the model and are obtained by defining the location of the site of interest and five simple basin properties. Information and data from thousands of sites across the country were compiled to facilitate use of SELDM. Use of SELDM for doing the types of sensitivity analyses needed to properly assess water-quality risks are provided in a case study. For example, use of deterministic values to model upstream stormflows instead of representative variations in pre-storm flow and runoff may substantially overestimate the proportion of highway runoff in downstream flows. Also, risks for total phosphorus excursions are substantially affected by the selected criteria and the modeling methods used. For example, if a single deterministic concentration rather than a stochastic population of values is used to model upstream concentrations, then the percentage of water-quality excursions in the downstream receiving waters may depend entirely on the selected upstream concentration.
Stochastic Empirical Loading Dilution Model (SELDM), 2013 - The USGS, in cooperation with the FHWA, developed the Stochastic Empirical Loading and Dilution Model (SELDM) to replace the FHWA runoff-quality model developed in the 1980’s and published in 1990. That model was limited to a few water-quality constituents, was based on the assumption that upstream concentrations are equal to zero, was based on water-quality standards from the 1980’s, was not compatible with newer operating systems, and there was no mechanism for continuing model support. SELDM is designed as a tool that can be used to transform disparate and complex scientific data into meaningful information about the risk for adverse effects of runoff on receiving waters, the potential need for mitigation measures, and the potential effectiveness of such management measures for reducing these risks. SELDM is designed to help develop planning-level estimates of event mean concentrations, flows and loads from a highway site and an upstream or lake basin. The model has been tested by the FHWA, many State DOTs, the EPA, and several other regulatory agencies. This resulted in a robust model that will be acceptable to DOTs, regulators, and resource-management agencies.
Stochastic Empirical Loading and Dilution Model (SELDM) software archive, 2022 - The Stochastic Empirical Loading and Dilution Model (SELDM) was developed by the U.S. Geological Survey (USGS), in cooperation with the Federal Highway Administration (FHWA) Office of Project Delivery and Environmental Review to transform complex scientific data into meaningful information about the risk of adverse effects of runoff on receiving waters, the potential need for mitigation measures, and the potential effectiveness of such management measures for reducing these risks. The SELDM was developed as a database application with a simple graphical user interface (GUI) by using Microsoft Access® to facilitate highway and urban runoff analyses by scientists, engineers, and decisionmakers without specialized modeling skills.

Additional Resources

The International Stormwater Best Management Practices (BMP) Database project website features a database of over 600 BMP studies, performance analysis results, tools for use in BMP performance studies, monitoring guidance and other study-related publications.
Stormwater Discharges from Transportation Sources - Similar to traditional stormwater management authorities (cities and counties), transportation authorities are also responsible for managing the stormwater runoff that discharges to our nation’s waters via regulated municipal separate storm sewer systems (MS4s) along streets, roads, and highways.
TRB Publications about Environment - The Transportation Review Board maintains an updated list of publications related to transportation and the environment.
Evaluation of Best Management Practices for Highway Runoff Control, 2006 - This report focuses on improving the scientific and technical knowledge base for the selection of best management practices (BMPs) through a better understanding of BMP performance and application. This report documents an extensive program of research on the characterization of BMPs and stormwater, and the influence of factors such as land use practice, hydraulic characteristics, regional factors, and performance evaluation. The report includes a CD containing a spreadsheet model and three additional volumes: User’s Guide for BMP/LID Selection, Appendices to the User’s Guide, and Low Impact Development Design Manual for Highway Runoff Control.

Subject/Title	Resource URL	Agency
Erosion and Sediment Control on Highway Construction Projects (23 CFR 650B)	Regulation	FHWA
Erosion and Sediment Control on Highway Construction Projects (NS 23 CFR 650B)	Guidance	FHWA
Guidance on 23 U.S.C. §328 Environmental Restoration and Pollution Abatement	Memorandum	FHWA