“Greening the Streetscape: Complete Streets & Stormwater Management” webinar recap

This month we closed out the first half of our monthly webinar series with “Greening the Streetscape: Complete Streets & Stormwater Management.” To learn more, view the recording of the webinar above, download the PDF of the presentation, or read the full recap below.

A discussion recap

Emiko Atherton, Director of the National Complete Streets Coalition, opened the conversation by highlighting the heavy economic burden of urban flooding nationwide. The challenge of managing stormwater, she explained, is exacerbated by increased rainfall and aging infrastructure, and city governments as well as residents who cannot afford to move bear the brunt of the expense. Fortunately, stormwater management through green streets infrastructure offers promising solutions that can be carried out in conjunction with Complete Streets. When cities or private developers are retrofitting or redesigning streets, there is a confluence of opportunities to implement both stormwater improvement projects as well as Complete Streets network enhancements. Together, both Green Streets and Complete Streets initiatives work to improve the economic, equity, and environmental impacts of the street network all while creating safer, more vibrant streets.

“A flooded street is not a Complete Street. When it rains, people biking, walking, and using mobility devices are the first ones to lose access to the street and the last to regain access.”

One organization that is leading the way in combining Green Streets with Complete Streets is the National Association of City Transportation Officials (NACTO), a peer network of innovative cities that work towards building people-oriented, multimodal street networks. Aaron Villere of NACTO introduced the organization’s series of street design guidance focused on various topics including bikeways, transit, and most recently, stormwater management. Aaron explained that streets are among cities’ most important assets for stormwater management – they make up about 40% of most cities’ impervious surface. The brand new Urban Street Stormwater Guide provides tools cities can use to transform their streets to be more resilient, comforting, and inviting. To emphasize the opportunity Green & Complete Streets present, Aaron gave the example of a bikeway in San Francisco that is protected from cars by stormwater infrastructure. This project not only manages 90% of stormwater runoff, it also makes 98% of cyclists surveyed feel safer while riding.

Aaron then turned it over to two of NACTO’s member cities to share their experiences implementing Green & Complete Streets on the ground. Philadelphia has been a national leader in these initiatives through their Green Cities, Clean Water program. Jessica Noon, Green Infrastructure Program Manager with the Philadelphia Water Department, explained how Philadelphia cut costs substantially by using green infrastructure, rather than subterranean infrastructure like tanks and tunnels, to manage their combined stormwater-sewage system. Between the public and private sector, over 440 green infrastructure projects have been implemented on Philadelphia’s streets, many of which also beautify the streetscape. Among other improvements, this has included the construction of over 1,000 tree trenches that provide shade and clean air in addition to playing a vital role in stormwater management.

Finally, Sarah E. Anderson, Water Quality Program Manager from the City of Denver explained how the city is launching their own Water Quality program by assembling an interdisciplinary team across the Departments of Public Works, Environmental Health, Parks and Recreation, and others. She explained how the city’s new Ultra-Urban Green Infrastructure Guidelines focus specifically on how to design green infrastructure to maximize safety and ease of maintenance. Sarah also gave examples of demonstration and corridor projects on Denver’s streets that work to maximize resilience while simultaneously improving walkability and bikeability.

Want to learn more?

To read more about the various design guides and programs discussed in the webinar, visit the following links:

  • NACTO’s new Urban Street Stormwater Guide can be viewed online or purchased from Island Press. Get 20% off with the discount code 2NACTO.
  • Other valuable resources from NACTO, including the Urban Bikeway Design Guide, the Urban Street Design Guide, the Transit Street Design Guide, and the Global Street Design Guide, all of which can be found on their website.
  • The City of Philadelphia’s Complete Streets Design Manual is another resource that provides a template for combined implementation of green infrastructure and Complete Streets.
  • Finally, Denver’s Ultra-Urban Green Infrastructure Guidelines includes strategies to introduce green infrastructure not only on city streets, but also in parks, open spaces, and floodplains.


As always, we received more questions than we had time to address during the webinar, but our presenters were able to provide answers for many of these questions in writing.

Are air quality-related components of transportation addressed in these design guidelines?
Aaron Villere: While the Urban Street Stormwater Guide is much more focused on water quality rather than air quality, these are often overlapping benefits of green infrastructure programs. The Guide addresses this most directly in the discussion of Performance Measures for green street projects and programs.

Adding trees and vegetation to the streetscape is an important tool for many cities seeking to expand urban tree canopy, which can reduce temperatures in the local climate, and reduce airborne particulates at the street and neighborhood level. One of the more important considerations in this regard is that micro-particulates disperse over fairly short distances, so providing vegetated buffer distance between the sidewalk or bikeway and the roadway can reduce the exposure of people biking and walking to motor vehicle pollution simply through spatial separation, while at the same time designers can select vegetation to capture and treat pollutants.

More broadly, it’s about building streets that are places people want to be. Safe and comfortable and green streets are streets that encourage people to walk, bike, and taking transit. There’s research that suggests people perceive shorter wait times for transit if there are green expressions in the streetscape. If the street is comfortable and inviting, cities are more likely to capture and convert trips to walking, biking, and transit, and when on-road transportation is responsible for a fifth to a quarter of all GHG emissions, reducing emissions coincides with mode shift away from motor vehicles to more efficient mobility.

Jessica Noon: I’d add that our Green Streets infrastructure typically includes trees/vegetation, so it has an air quality benefit that grey infrastructure does not. However, our program metrics are based on stormwater.

How are you tracking outcomes of success for Green Streets projects?
Sarah Anderson: Denver will track a number of Green Infrastructure Program metrics including pollutant loading reductions, reduced imperviousness, number of acres treated, number of acres of green/open space added, costs, number of trees planted/air quality benefits, neighborhood incomes, and plant species survivability.

Who maintains these Green Streets?
 As with any infrastructure project, planning for maintenance should be done as a part of the implementation process. While it depends a great deal by city and region what those maintenance strategies are, cities have been quite creative in allocating resources and finding partners to ensure that their assets are operating well, and they’re getting the most from investments.

Philadelphia, for instance, has a complete maintenance manual that enumerates deeper (more structural) tasks to be overseen by city-run crews, while vegetation and debris removal can be done by neighborhood partners and civic groups. Chicago has used GSI maintenance as an opportunity to partner on Greencorps Chicago, a public/private jobs training and employment program with both adult and youth participants, growing the green jobs economy while improving these facilities.

One last partnership structure is the public/institution structure. For instance, Louisville MSD partnered with the University of Louisville on their first projects to have the university study and report on maintenance practices. The agency (MSD) purchased new equipment to maintain special infrastructure, but the institution was able to fund monitoring and analysis, which cities often lack budget for. Finding ways to not just clean infrastructure but actually understand how that maintenance impacts performance is a critical capability to continuing to do better work.

What federal funding programs or local funding incentives/reduced fees are these cities using to implement Green Streets?
JN: Federal transportation funds from the Federal Highway Administration allow budgets to include up to 20% project costs for “drainage.” These funds, which cities and municipalities likely receive via their state transportation departments and/or their local MPO, can be used for green or grey stormwater management. Philadelphia uses them for green infrastructure as often as possible. Philadelphia also offers Stormwater Management Incentives Program (SMIP) grants to private property owners that retrofit their sites. The Water Department previously charged customers for stormwater as a percentage of the overall water bill, but in 2010 they changed that system to one that charges property owners based on the amount of impervious surface on site, so private property owners who retrofit are also eligible for reductions in stormwater fees by up to 80%.

Statistics on the ability for green infrastructure to capture stormwater vary widely. Some way it only captures 20-30% of stormwater runoff, yet today’s presenters say capture is 80-100% when fully implemented. Can you clarify how this is measured?
SA: In Denver, designs are based on the Water Quality Capture Volume (WQCV). The WQCV is directly related to the local rainfall pattern, watershed imperviousness, and drain time based on an analysis of rainfall and runoff characteristics for 36 years of record at the Denver Stapleton Rain Gage. The target for the WQCV is to absorb the runoff produced from 0.6 inches of precipitation, so the ‘80-100%’ refers to 80-100% of this WQCV target.

When the presenters refer to storm percentage capture, what rain event are they referring to and designing to?
AV: The percent stormwater capture is relative to a goal, typically set by a consent decree. While each place needs to set its own goals based on local climate and infrastructure conditions, a typical goal might be to manage a 10-year rain event, or the first inch of rainfall. The Guide does give guidance on these types of planning decisions, but they are ultimately local decisions. In many cities, that’s about reducing volume of runoff or peak flow rates (slowing the rate of stormwater discharge into traditional gray infrastructure), but can also include treating water for quality and pollutants.

JN: We design for the management of 1.5 inches of runoff from the drainage area. There majority of storms in the Philadelphia region result in 1.5 inches or less of precipitation. In cases where we have sufficient space, we will design for over 1.5 inches, up to a maximum of two inches. We do not see a significant benefit to managing over two inches.

Can you talk more about green gutters?
SA: The 21st & Broadway project will construct Denver’s first green gutter. It is being installed to separate the bicyclist form the pedestrian. Denver will track the success/failures of the gutter as it relates to water quality and safety for different modes.

Stay tuned for future webinars

Our Implementation & Equity 201: The Path Forward to Complete Streets webinar series is taking a brief hiatus in August, but we’ll be back with a jam-packed lineup starting in September. Stay tuned for more information! In the meantime, you can access all of our previous webinars on our blog.

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