Quantifying Green Infrastructure: How Cities Can Reduce Runoff and Avoid Capital Costs
When a heavy storm falls on a city with a combined sewer system, the public sees the result quickly. Streets can flood, wastewater can enter local waterways, and public works teams must explain why the system could not absorb the surge. The problem is not limited to rare disasters. Many older systems were built for rainfall patterns and development conditions that no longer match the demands placed on them.
For years, the usual response was to add more gray infrastructure. Larger pipes, deep storage tunnels, and expanded treatment capacity can play an important role. They also require substantial capital, long construction timelines, and continuing costs for pumping and treatment. Cities need to compare those costs with approaches that reduce the volume of water entering the system in the first place.
Green infrastructure offers that option. Practices such as porous pavement, tree trenches, rain gardens, green roofs, and water-capture features manage rainfall where it lands. When these tools are incorporated into routine public works projects, they can help reduce pressure on pipes and treatment facilities while improving streets, parks, and other public spaces.
LANCASTER SHOWS WHY THE FINANCIAL CASE MATTERS
The City of Lancaster, Pennsylvania, provides a useful municipal example. Lancaster operates a combined sewer system that carries sewage and rainfall in the same pipes. In its 2011 Green Infrastructure Plan, the city reported that roughly one billion gallons of untreated combined wastewater and stormwater overflowed into the Conestoga River each year during wet weather. The city estimated that storing and treating that volume through conventional gray infrastructure could cost more than $250 million.[1]
Lancaster did not present green infrastructure as a decorative add-on. Its plan treated runoff reduction as a core part of infrastructure planning. City staff identified places where existing public assets could be used to manage more water. Streets, parking areas, roofs, parks, schools, and city-owned properties became part of the stormwater strategy.
The plan’s first 20 demonstration projects were estimated to remove 21 million gallons of urban runoff from the combined sewer system each year.[1] One example was the Sixth Ward Memorial Park porous basketball court. The project was expected to reduce runoff from nearby paved areas by about 700,000 gallons annually. Lancaster reported that the court could deliver that runoff reduction at about half the cost of separate gray controls designed to provide a comparable benefit.[1]
These figures matter because local governments rarely begin with unlimited capital. City managers must decide how to extend the useful life of existing assets, meet regulatory requirements, and maintain basic services at the same time. A stormwater program that works through scheduled street repair, park renovation, and facility upgrades can make the best use of projects that must happen anyway.
THE NUMBERS SHOULD GUIDE THE CONVERSATION
A U.S. Environmental Protection Agency and Center for Neighborhood Technology analysis examined the long-term value of Lancaster’s approach. The analysis estimated that, after approximately 25 years of implementation, the plan could reduce average annual runoff in the study area by 1.053 billion gallons. Within the combined sewer area, the analysis estimated $120 million in avoided gray-infrastructure capital costs and $661,000 in annual wastewater pumping and treatment savings.[2]
Those are planning estimates, not a guarantee of future results. Their value lies in the method. Lancaster measured anticipated runoff reduction, capital needs, operating costs, and the broader benefits associated with more trees and green space. That gives elected officials and department leaders a basis for comparing alternatives with more than a construction bid.
A strong local analysis should ask several clear questions. Which drainage areas create the greatest pressure on the system? Which city-owned projects are already scheduled? How much runoff can each proposed practice manage? What is the cost difference between a green feature and a conventional alternative? What maintenance work will be required after installation?
The answers will differ from one community to another. Cities with dense downtown blocks may focus on curb extensions, tree trenches, and permeable sidewalks. A park renovation may create room for bioretention areas or underground storage. A public facility can capture roof runoff for irrigation or direct it to landscaped areas. The point is to fit the approach to the condition of local assets and the path that rainfall already takes through the community.
PUT STORMWATER WORK INTO EVERYDAY ASSET DECISIONS
A city does not need to wait for a single, large stormwater project to begin. The most practical starting point is often the capital plan already on the books. When a roadway is scheduled for resurfacing, staff can assess whether a curb extension, tree trench, or porous parking area would help manage runoff. When a school, recreation center, or library undergoes site work, the project team can consider where roof drainage should go. Each decision can be small on its own. Across several budget cycles, the work can reshape how a city handles rainfall.
This approach also makes coordination more useful. Public works, planning, parks, finance, and utilities do not need identical priorities, but they should be working from the same understanding of drainage risks and project timing. A shared project map and asset inventory can reveal where planned work overlaps with frequent flooding, combined sewer overflows, or costly maintenance calls.
Private property also matters. Lancaster’s plan found that much of the city’s impervious surface was outside direct city ownership.[1] Updated development standards, voluntary grant programs, and clear guidance for property owners can help extend runoff management beyond public land. The city’s role is to set practical expectations and make the requirements easy to understand.
START WITH A FIRST PHASE THAT CAN BE MEASURED
Local leaders can begin with a small set of sites that have clear drainage problems and a scheduled capital project. The first phase should document baseline conditions, construction cost, expected runoff reduction, and the maintenance responsibility for each feature. That record gives staff a better basis for the next round of decisions.
The lesson from Lancaster is straightforward. Green infrastructure works best when it is treated as public infrastructure, tied to local capital planning and maintained with the same discipline as any other city asset. It is not a substitute for every pipe, pump, or treatment upgrade. It is a practical part of a larger stormwater program that can reduce system demand and help cities manage capital more carefully.
Making Cities Smarter begins with choices that match local conditions, public budgets, and measurable needs. Pathway Community Foundation works with municipalities to explore stormwater solutions, municipal sensors, asset-management practices, and testbeds that support better public-service decisions. Contact our team to discuss how a focused first phase could fit your city’s existing plans.
SOURCES
[1] City of Lancaster, Pennsylvania. Green Infrastructure Plan, April 2011. https://www.cityoflancasterpa.gov/wp-content/uploads/2014/01/cityoflancaster_giplan_fullreport_april2011_final_0.pdf
[2] U.S. Environmental Protection Agency and Center for Neighborhood Technology. The Economic Benefits of Green Infrastructure: A Case Study of Lancaster, PA. https://www.epa.gov/sites/default/files/2015-10/documents/cnt-lancaster-report-508_1.pdf
[3] U.S. Environmental Protection Agency. Performance of Green Infrastructure. https://19january2021snapshot.epa.gov/green-infrastructure/performance-green-infrastructure_.html
