Stormwater

Overview

Stormwater systems range from large concrete storm sewers, roadside ditches, and flood control reservoirs, to rain gardens and natural riverine systems. While stormwater utilities are on the rise, with more than 40 states having at least one, the impervious surfaces in cities and suburbs are also expanding, exacerbating urban flooding, which results in $9 billion in damages annually. Stormwater also affects water quality as polluted runoff from pavement enters water bodies. Nearly 600,000 miles of rivers and streams and more than 13 million acres of lakes, reservoirs, and ponds are considered impaired. Federal funding, though up in recent years, averages about $250 million annually, which leaves a growing annual funding gap of $8 billion just to comply with current regulations. With few dedicated funding sources, complicated governance and ownership structures, expansive networks of aging assets, increasingly stringent water quality regulations, and concerning climate change projections, the expected performance of stormwater systems is declining. Many of the country’s legacy stormwater systems, are struggling with the high cost of retrofits needed to address urban flooding and climate change. Upgrading large networks of aging systems underneath densely populated areas carries significant costs and engineering challenges.

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Highlights

There are about

3.5 million miles of

storm sewers in the U.S.

There are around

270 million

storm drains in the country.

Approximately 2.5 million

stormwater treatment assets

can be found throughout America.

Introduction

Stormwater runoff is defined as rain or snowmelt that travels over impervious surfaces such as roadways, buildings, or parking lots, and landscaped or agricultural areas and is then collected and conveyed into streams, rivers, lakes, bays, or oceans. As impervious surfaces in increasingly developed cities and suburbs expand, so do the impacts of increased runoff from larger rainfall events which can lead to urban flooding.

Nationally, stormwater infrastructure can take many forms, including piped systems, detention basins, ditches, canals, channels, and roadway conveyance systems. In recent years, green stormwater infrastructure has been introduced in new developments and coupled with traditional “gray infrastructure” to maximize the benefits from natural hydrologic cycles using vegetation, soils, site grading, and natural filtration processes. Green infrastructure provides benefits by reducing runoff, minimizing erosion, and contributing to water quality improvements; examples include rain gardens, constructed wetlands, vegetative roadway bioswales, and permeable pavements.

The United States Environmental Protection Agency (EPA) classifies stormwater systems as those that are publicly owned, discharge into waters of the U.S., and are not part of a sewage treatment plant such as Municipal Separate Storm Sewer Systems (MS4s). MS4s are regulated by the EPA under the National Pollution and Discharge Elimination System (NPDES) program.Apart from EPA regulations, states, counties, and local governments may also require stormwater management practices through local ordinances, building codes, and development plans.

Condition & Capacity

The condition of stormwater infrastructure is indicated, in part, by the system’s age. Without better stormwater asset records, the average age of the system cannot be directly determined, so the lifespan of the primary construction material is used as a proxy. Stormwater conveyance systems may be constructed of corrugated metal, reinforced concrete, or plastic, and their lifespan is projected to be 50 to 100 years. Storage and treatment systems such as detention and retention ponds have an average lifespan between 20 to 30 years. Based on this, systems constructed in the 1970s or prior have exceeded or are nearing the end of their useful lives and are likely undersized given current stormwater management practices.

Capacity

The stormwater sector is relatively data-poor with no comprehensive national database of assets. Estimates suggest there are 3.5 million miles of storm sewers, 270 million storm drains, and 2.5 million stormwater treatment assets across the U.S. Under the NPDES MS4 program, municipalities are required to map their stormwater systems and, as of 2018, nearly 40% of stormwater utilities have taken this step.

Stormwater infrastructure capacity is principally derived from the design standards used for construction. Terms like “10-year” and “100-year storms” (meaning those with a 10% and 1% annual probability of occurrence, respectively) are currently used to describe a system’s capacity. However, such design standards have only been used in recent decades, and the standards differ within and between states.

While design standards govern a stormwater system’s theoretical capacity, routine operation and maintenance (O&M), age, and the changing frequency and intensity of storm events are the main drivers affecting a stormwater system’s actual capacity. Given the recent increase in rainfall trends and urbanization, the actual capacity of a stormwater system is often less than the design standard. Many of the country’s legacy stormwater systems, such as those in Chicago and Philadelphia, for example, are now struggling with the high cost of retrofits that are needed to accommodate these changes. Upgrading large networks of aging systems that are now underneath densely populated areas carries significant costs and engineering challenges.

Condition

Another key indicator of stormwater infrastructure condition is the system’s ability to reduce negative impacts to local waterbodies. Under the NPDES program, stormwater systems are required to meet the overarching goal of reducing the discharge of pollutants from runoff. While water quality is a priority across the nation, from 2010 to 2018, the length of impaired rivers and streams increased from about 424,000 miles to more than 588,000 miles.

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Operations & Maintenance

Stormwater infrastructure may be owned and managed by various public or private entities such as state or local governments, individual or corporate property owners, or homeowners’ associations. All stormwater systems require some level of routine maintenance, but the ongoing management of stormwater systems can be complex and expensive. Storm sewers require jetting and cleaning, and stormwater detention basins, bio-retention facilities, permeable pavement, and bioswales all require unique maintenance tasks with specialized knowledge. This can be a challenge for all levels of government, private property owners such as shopping centers, or homeowners’ associations.

The MS4 NPDES permitting process has been an effective regulatory lever influencing O&M practices and frequency due to the expectation of routine inspections. Under the NPDES program, all MS4s are required to have maintenance plans. However, private entities, cooperatives, and individual homeowners responsible for O&M are often not routinely monitored and left to manage critical and sometimes expensive components of the stormwater system on their own. Deferred maintenance increases the likelihood of urban flooding and increases threats to water quality protection.

Funding & Future Need

Funding for stormwater infrastructure across the country is limited and comes from multiple sources — local revenue, state and/or federal grants and financing, and non-traditional funding streams. Because the financial responsibility for managing stormwater systems can sometimes be unclear and draw from entities’ general funds, hundreds of public entities in at least 40 states have taken the initiative to create stormwater utilities to collect fees based on property size, impervious area, and other site-specific characteristics. Out of communities with municipal MS4s, the percentage with stormwater utilities or fees has grown from approximately 19% in 2013 to upward of 26% in 2018. For a single-family home, the average monthly stormwater fee in 2018 was $5.34.

Funding

For large capital improvements, state entities or municipalities may use general obligation bonds. They may also seek federal resources like those from the EPA’s Clean Water State Revolving Fund (CWSRF) which has provided nearly $2.2 billion for more than 1,100 stormwater projects since its inception. More recently, the CWSRF’s program funding for stormwater projects has trended upward from more than $58 million in 2012 to more than $387 million in 2019 with the portion of funding for green infrastructure also increasing. Though trends are improving, only 3% of all CWSRF funds have gone toward stormwater and similar types of projects. Additionally, the EPA’s Water Infrastructure and Finance Innovation Act (WIFIA) is another federal funding mechanism. In 2019, at least three stormwater infrastructure projects applied for $673 million in WIFIA loans out of the program’s $7.7 billion in overall support.

Source: Clean Water SRF Program Information National Summary (2019)

While there are limited and highly competitive grant programs at the local, state, and federal levels that cover a very small portion of the overall need, non-traditional mechanisms for funding stormwater infrastructure have also emerged and include public-private partnerships; leveraged synergies among solid waste, transportation, and/or wastewater sectors; and market-based solutions that monetize permit requirements like nutrient and/or stormwater volume trading.

Future Need

As water quality measures for MS4 permitting become more stringent, local governments and stormwater utilities are having to update or expand their systems, stretching their limited economic resources. In 2020, the Water Environment Federation’s National MS4 Needs Assessment estimated that the sector’s annual funding gap is $8 billion among MS4 permittees compared to the $19.2 billion funding need reported in 2012 by the EPA’s Clean Watershed Needs Survey. Separately, an economic analysis by ASCE shows a water-related infrastructure investment gap of $434 billion over 10 years for drinking water, wastewater, and stormwater combined.

The trajectory of urban flooding impacts will likely continue the upward trend as our older stormwater assets cannot accommodate the changing rainfall patterns and intensity.[ii] Many utilities are behind in accounting for the condition of their assets, planning, and funding for short- and long-term maintenance, and strategizing necessary capital improvements. A clear picture of the existing assets and their condition is needed to provide flood projection models with data to identify areas of significant risk where limited, available resources may be targeted for improvements.

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^{Source: Clean Water SRF Program Information National Summary (2019)}

Public Safety

Flooding is one of the nation’s greatest natural hazards, carrying catastrophic public safety and economic tolls. Annually, from 2004 to 2014, urban flooding alone cost communities an average of $9 billion in direct damages and 71 deaths.

Public Safety

When stormwater systems become overwhelmed, there are acute and long-term public safety implications that create ripple effects on other infrastructure systems. Effects throughout the community may include sinkholes, flash floods, collapsed roadways, extensive property damage, inflow into sanitary systems which inundates wastewater treatment plants and pollutes waterways, and loss of life. Over the last two decades, to buttress the impact of these losses, the National Flood Insurance Program has more than doubled its enacted policies while the number of private insurance companies entering the market between 2016 to 2019 has also more than doubled.

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Resilience & Innovation

Real-Time Control Systems

Impacts from climate change will have variable effects on the form and frequency of extreme events across the nation. To withstand these effects, stormwater infrastructure should be implemented with a context-sensitive approach, namely a localized understanding of flood risk in combination with an awareness of land-use practices and regulatory expectations. This approach should inform the types, designs, locations, and long-term sustainability of stormwater systems. Resilience for stormwater infrastructure should increasingly reflect a mix of optimized green, gray, and natural infrastructure, land planning and urban growth, updated asset management, and, in water-scarce areas, the productive reuse of stormwater.

Current innovations include the use of real-time control systems that leverage complex modeling, cloud computing, data storage, and predictive analysis. Large datasets can be used to optimize the capacity of stormwater conveyance, storage and treatment systems, investments in O&M activities, and other costs. The affordability of sensors has also improved, expanding the potential for system implementation of real time data and control.

Finally, some areas employ a regional approach to stormwater management through volume and nutrient trading within watersheds. This can economically incentivize stormwater innovation.

Raising the Grade

Solutions that Work

Fully fund and disseminate information from the EPA’s Clean Watersheds Needs Survey on a routine basis (every four years) and elicit more stormwater-related detail, including information about maintenance, repair, pollution prevention, and urban flooding.

Develop a stormwater-specific funding and financing program based upon the best practices from the existing Clean Water State Revolving Fund.

Develop state-based peer-to-peer partnerships to build local government capacity to create and manage stormwater utilities that sustainably fund, operate, maintain, assess, and, when necessary, expand stormwater infrastructure.

Develop a comprehensive publicly facing education campaign on the true costs, savings, risks, and avoided hazards associated with stormwater infrastructure investments, and disseminate these details through broadly accessible platforms.

Establish a grant program for 21st century technical career training for “green collar jobs” in the stormwater sector that recruit the next generation’s talent and mainstream tools for data-driven decision-making, such as asset management software, life-cycle cost analysis, and affordable rate structuring.

Expand the inclusion of current and forecasted climate variability in codes and standards for the design, operation, maintenance, and expansion of stormwater infrastructure and routinely provide funding to NOAA to update the climate data.

Ensure stormwater infrastructure is fully eligible and aggressively pursued via federal funding and financing mechanisms that are supporting the nation’s drinking water and wastewater systems.

Communities should create stormwater utilities that institute rates that reflect the true cost of treating and handling stormwater runoff.

Stormwater infrastructure and design regulations are critical for protecting communities from costly urban flooding and protecting water quality in our waterways. Stormwater systems should be a combination of gray, green, and natural infrastructure and should be mainstreamed in planning and development processes nationwide.

Point source and nonpoint source pollution should be addressed through a watershed approach that encourages regional coordination to improve impacts from stormwater-induced flooding.

View Report Sources

The National Academies of Sciences, Engineering, and Medicine. “Framing the Challenge of Urban Flooding in the United States,” 2019.

U.S. Environmental Protection Agency, “National Summary of State Information.”

U.S. Environmental Protection Agency, “Stormwater Management Practices at EPA Facilities.”

National Academies of Sciences, Engineering, and Medicine, “Framing the Challenge of Urban Flooding in the United States,” 2019.

Geosyntec Consultants and Wright Water Engineers, Inc., “Urban Stormwater BMP Performance Monitoring,” October 2009.

The Water Environment & Reuse Foundation, “Stream Restoration BMP Database: Version 1.0 Summary Report,” 2017.

U.S. Environmental Protection Agency, “Stormwater Discharges from Municipal Sources

McPhillips LE and Matsler AM, Frontiers in Build Environment, “Temporal Evolution of Green Stormwater Infrastructure Strategies in Three U.S. Cities,” May 15, 2018.

https://onlinelibrary.wiley.com/doi/full/10.1002/hyp.13144,

https://www.fs.usda.gov/treesearch/pubs/46916,

https://pubs.usgs.gov/wri/wri014278/

https://ir.library.illinoisstate.edu/etd/399/

PALS – Partnership for Action Learning in Sustainability, “Community Engagement for Vulnerable Communities: Flooding Impacts and Adaptation in East Riverdale-Beacon Heights,” Fall 2019.

City of Duvall, Washington, “Surface and Stormwater Plan: SEPA Draft,” January 29, 2018.

Black & Veatch Management Consulting, LLC, “2018 Stormwater Utility Survey,” 2018.

Moglen GE and Vidal GER, Journal of Hydrologic Engineering, “Climate Change and Storm Water Infrastructure in the Mid-Atlantic Region: Design Mismatch Coming?” November 2014.

A Handbook of Constructed Wetlands: A Guide to Creating Wetlands for Agricultural Wastewater, Domestic Wastewater, Coal Mine Drainage, and Stormwater in the Mid-Atlantic Region,” Volume 1: General Considerations.

Water Research Foundation, “Recommended Operation and Maintenance Activity and Cost Reporting Parameters for Stormwater Best Management Practices Database,” 2018.

Pitt R, Maestre A, and Clary J, “The National Stormwater Quality Database (NSQD), Version 4.02,” February 17, 2018.

The National Association of Clean Water Agencies, “MS4 Stormwater Permitting Guide,” 2018.

U.S. Environmental Protection Agency, “National Summary of State Information.”

National Academies of Sciences, Engineering, and Medicine, “Framing the Challenge of Urban Flooding in the United States,” 2019.

Water Research Foundation, “Recommended Operation and Maintenance Activity and Cost Reporting Parameters for Stormwater Best Management Practices Database,” 2018.

Western Kentucky University, “Stormwater Utility Survey,” 2018.

Kane JW and Shivaram R, The Brookings Institute, “As Flood Risks Intensify, Stormwater Utilities Offer a More Resilient Solution,” September 21, 2017.

Western Kentucky University, “Stormwater Utility Survey,” 2018.

U.S. Environmental Protection Agency, “Clean Water SRF Program Information National Summary,” December 6, 2019.

U.S. Environmental Protection Agency, “EPA Water Finance Support to Nutrient Credit Markets.”

U.S. Environmental Protection Agency, “Water Infrastructure Finance and Innovation Act (WIFIA).”

Congressional Research Service Report, “Federally Supported Projects and Programs for Wastewater, Drinking Water, and Water Supply Infrastructure,” July 30, 2020.

Financial Advisory Board, “Evaluating Stormwater Infrastructure Funding and Financing,” March 30, 2020.

Water Environment Federation, WEF’s Stormwater Institute, “National Municipal Separate Storm Sewer System (MS4) Needs Assessment Survey Results,” 2020.

U.S. Global Change Research Program, “Climate Science Special Report.”

The National Academies of Sciences, Engineering, and Medicine. “Framing the Challenge of Urban Flooding in the United States,” 2019.

Insurance Information Institute, “Facts + Statistics: Flood Insurance.”

Optirtc, Inc., Website: https://optirtc.com/

S, Duchesne S, and Pelletier G. “Predictive Real-Time Control Optimization of a Stormwater Management System.” 2019.

PHOTO ATTRIBUTIONS

Stormwater Management in the Everglades, Photo courtesy of WSP
Photo courtesy of Build Together
Photo courtesy of Build Together
Photo by Anna Denecke

Stormwater

Overview

There are about

There are around

Approximately 2.5 million

Introduction

Condition & Capacity

Capacity

Condition

Operations & Maintenance

Funding & Future Need

Funding

Future Need

Public Safety

Public Safety

Resilience & Innovation

Raising the Grade

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Innovating Infrastructure Solutions by State

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