stormwater infrastructure




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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stormwater infrastructure

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.


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.

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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.

stormwater infrastructure

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.

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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.

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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.,,

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, “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:

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


  1. Stormwater Management in the Everglades, Photo courtesy of WSP
  2. Photo courtesy of Build Together
  3. Photo courtesy of Build Together
  4. Photo by Anna Denecke
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