Harnessing Nature to Strengthen Communities

August 5, 2024 / Blogs

co-authored by Ryan Wilson, MPC Director

MPC’s Terra Firma pilot report quantifies the ways green stormwater infrastructure pays off

Addressing a multi-pronged land use challenge

In Chicago, urban flooding is an inequitable reality, disproportionately affecting predominantly Black and Latinx neighborhoods on the city’s South and West sides. These are areas that face long-term disinvestment and a surplus of vacant land, negatively impacting community well-being, as highlighted by a survey conducted with our partners at the Emerald South Economic Development Collaborative. With climate change expected to alter rainfall patterns, the risk of urban flooding in cities will increase. Given that there is finite public funding to address the inequities created by urban flooding, Chicago must prioritize stormwater infrastructure that generates the greatest public good.

The green stormwater infrastructure (GSI) opportunity

The Chicago region’s municipalities and utilities have an opportunity to tackle both urban flooding and vacant land issues simultaneously with green stormwater infrastructure (GSI). GSI uses soil and vegetation to manage stormwater runoff, through techniques like rain gardens, green roofs, and “tree pits” that collect and filter rain. By incorporating these nature-based solutions into our stormwater control and sewer planning toolboxes, we can make improvements for flood control while addressing resident concerns about vacant land.

However, to integrate GSI into stormwater management—including both capital planning and the regulations and incentives that guide other public and private development—we need better information about GSI’s cumulative costs and benefits. Together with Emerald South and other project partners, One Water Econ and Environmental Consulting and Technology (ECT), MPC has developed a report that is a significant step toward demonstrating that GSI can be a powerful tool to address local flood risk to basements and streets. The key: prioritizing GSI in the highest-impact locations based on local sewer conditions and the availability of vacant land.

Selecting a site with Terra Firma for a case study evaluating the benefits of GSI

Terra Firma is “a landcare initiative to clean, green, beautify, and activate over 400 acres of vacant land on Chicago’s South Side,” according to Demetri Alexakos, a Director at Emerald South, which leads the initiative. Emerald South has created a vacant land toolkit based on their experience transforming vacant land into green space with residents, which Demetri said “instill[s] local residents with a sense of ownership in the neighborhood and feelings of empowerment.”

For this case study, the site for the hypothetical GSI design was selected from a set of City-owned vacant lots with suitable drainage conditions within the Terra Firma focus area. Among those lots, we looked for the sites with the highest potential for downstream flooding and significant expected community benefits (as measured by proximity to locations like parks, schools, and faith-based organizations). The final location for the hypothetical GSI project, at 6840 S. Stony Island Avenue, is in a census tract with a 21% land vacancy rate and a resident population that is 97% Black, with a median household income of $32,000. This site is also within the area of the South Shore Corridor Study.

The hypothetical GSI design, which also includes redesigning the lots for public access and recreation options, would manage the stormwater runoff for the entire block. In the report, we calculated the proposed design’s construction and maintenance costs, its effects on stormwater runoff, and the dollar value of the benefits it would deliver to the community that often go unaccounted for in planning.

Looking back: Findings and lessons learned from our report

The first key finding that emerged from the report was that strategically-placed and maintained GSI can bring stormwater management benefits comparable to—and even exceeding—those from gray infrastructure investments. The proposed GSI design would reduce peak flow by 93% for a 5-year storm event, compared to 23% reduction under current minimum stormwater requirements.

The second key finding was that the benefits of GSI—estimated in dollar terms—can significantly exceed costs. In this case study, the estimated total benefits of the proposed design exceeded the costs (including both construction and maintenance) by more than $4 million over a 50-year project lifespan.

Some of the largest estimated benefits came from increased property values, reduction of urban heat islands, and increased opportunities for recreation. Other benefits included avoided costs from more traditional gray infrastructure, air quality improvement, energy savings, and job creation. As Tom Price, Principal Engineer at ECT and collaborator on the report, put it, GSI “has many benefits beyond flood reduction and water quality improvement and those benefits are quantifiable.” This includes operation and maintenance, which “provide opportunities for job creation as well as neighborhood cohesiveness.”

Though calculating the potential impact of GSI may look different in different places—in different sewer sheds, for example, the effects on stormwater management may vary—this case study is a step towards smarter GSI planning.

Looking ahead: launching Right Infrastructure, Right Place

This summer, MPC is launching an initiative called Right Infrastructure, Right Place. Building on the Terra Firma case study, the initiative aims to ensure decision-makers can make informed choices about incorporating green infrastructure alongside gray infrastructure in stormwater management. With a team of both technical partners—Confluency, One Water Econ, and Discovery Partners Institute—and our community partners Emerald South and Blacks in Green, we have received a two-year grant from the Walder Foundation’s Resilient by Nature initiative to pursue this work. Stay tuned for more details!