A man sits on a bench reading a book in an urban green space of newly plants trees and shrubs.
Sacred Places A man sits and enjoys a new memorial greenspace at Mt. Olivet cemetery following the June 8, 2019 dedication ceremony. © Matt Kane / TNC

Stories in Maryland/DC

Building Green Cities

Using the power of nature to make cities in the capital region more resilient and livable places.

Over the past two years, the mid-Atlantic region has experienced record rain and heat. In the capital region, we're working with community partners and landowners to implement natural solutions to address the challenges of deadly heat waves, flooding and stormwater runoff, the fastest growing source of pollution to our rivers and to the Chesapeake Bay.

Storm water rushes down a city street into a storm drain. Cars in the background try to navigate the flooded street.
Stormwater Runoff Stormwater pollution is caused when rainwater falls on impervious surfaces where it mixes with pollutants before flowing into our cities' sewer systems and rivers. © Tyrone Turner

Growing Problem, Natural Solutions

Stormwater pollution is caused when rainwater falls on impervious surfaces—including sidewalks, parking lots and roads—where it mixes with oil, sediment, trash and other pollutants. It then flows into our cities’ sewer systems and rivers. 

Replacing, buffering or retrofitting impervious surfaces with water retaining green infrastructure like “rain gardens” allows polluted stormwater to be captured and cleaned. Water is absorbed and filtered by the plants, topsoil, sand and gravel layered within a rain garden.

A woman holding a red umbrella waits to cross the street. Street lights and headlights are reflected on the wet pavement.
Reducing Stormwater A storm blankets Washington, DC with heavy rain along K Street just after rush hour. The heavy line of storms dropped more than an inch of rain in an hour. © Greg Kahn

Investing for Impact

With a focus on using green infrastructure to retain and filter stormwater runoff, TNC—through a wholly owned subsidiary called District Stormwater—has become the largest voluntary supplier of Stormwater Retention Credits (SRC) in the district's stormwater credit trading market, 80 percent of which were sold to developers.

In 2015, when TNC first decided to launch an urban stormwater program in DC, the long-term goal was to help establish the city's stormwater credit-trading market concept. Since then, we have worked hard to raise impact capital, hire dedicated staff, work patiently with landowners and help the city create policies and incentives. 

A parking area floods during a rain storm in Chicago. Ankle deep water surrounds two cars parked next to a brick building.
Reducing Stormwater Many neighborhoods in Chicago suffer from chronic flooding. © Noel Rozny/TNC

Today, our efforts have paid off, and we are thrilled that 2020 was a breakthrough year for the stormwater market. Cities around the world are looking at DC as a model and many are now taking steps toward implementing similar market-based approaches to tackling their stormwater problems.

TNC’s Illinois chapter has partnered with the Chicago Metropolitan Planning Council to launch a new initiative called StormStore. Developed in part through consultation with the Maryland/DC chapter, StormStore is a county-wide stormwater market that incentivizes developers to disperse stormwater management requirements throughout the watershed with nature-based green infrastructure both on and offsite.

A group of people pose for a photo.
Smart Solutions Representatives from TNC, Opti, and Maryland partner agencies attend a smart pond announcement event, Fruitland, MD. © Matt Kane/TNC

Old Problem, New Solution

One of the oldest methods for capturing runoff, the stormwater pond, is getting a digital makeover. No longer simply collecting rainfall washing off pavement and lawns, "smart" ponds anticipate precipitation before it begins and adjusts to reduce downstream pollution and flooding.

In a program that could serve as a national model of environmental stewardship, TNC is partnering with the Maryland Department of Transportation (MDOT), the Maryland Department of the Environment (MDE) and technology firm Opti to implement advanced stormwater control technology at existing sites to help curb local flooding and reduce stormwater runoff to the bay.

Smart pond technology uses sensors and software to monitor real-time conditions such as water level and storage volume. The system uses internet-based forecasts to remotely operate valves that control timing and volume of water discharge. Longer retention time increases water quality by capturing more sediment and nutrients. When rain is forecast, the system can automatically open valves to drain the pond prior to precipitation. This helps maximize storage efficiency and can reduce downstream flooding. 

Working together to harness technologies that deliver low-cost solutions to water pollution, our hope is that this innovative approach can be replicated across the bay watershed and beyond.

Native plants and flowers thrive in a newly planted rain garden at Mount Olivet Cemetery.
Green Infrastructure Rain gardens installed at Washington, DC's historic Mt. Olivet Cemetery to capture stormwater. © Matt Kane / TNC

Investing in Partnership

In 2019, we made substantial progress with our D.C. stormwater program. We completed the construction of the second phase of stormwater retention infrastructure at Mount Olivet Cemetery—a project that now captures more than 3-5 million gallons of stormwater runoff each year.

Mount Olivet Cemetery was founded in 1858 in what was then a rural part of Washington, D.C., to carry out the Catholic Church’s ministry. Now that the cemetery is almost full, the church is exploring new ways to use the cemetery grounds to answer Pope Francis’ Encyclical on the Environment, Laudato Si', to respect and care for the earth.

This shared interest in the natural world has led to an innovative collaboration with the Archdiocese of Washington to use non-burial lands to address the growing environmental problem of urban stormwater pollution.

Designs for the green infrastructure project were aimed to maintain the sanctity of the grounds while also enhancing them. All work conducted in the surveying, planning and implementation of the modifications was done in close collaboration with the cemetery to ensure that the burial sites would not be disturbed, and construction would not disrupt scheduled burials or impede the ability of people coming to visit loved ones buried at the cemetery.

The project at Mount Olivet Cemetery also generates more than 160,000 stormwater retention credits annually, which are sold on D.C.’s stormwater credit-trading market, generating returns on investment that go right back into the ground in the form of new projects.

Cemeteries and Stormwater A first-of-its-kind green infrastructure project aims to capture stormwater runoff at DC's historic Mt. Olivet Cemetery.
The sun sets over the Baltimore skyline. Tall building dominate the background with low rowhouses lining the foreground.
Charm City The sun sets over the Baltimore city skyline and Inner Harbor. © Patrick Gillespie/Flickr CC BY 2.0

Charm City: Baltimore Expansion

Thanks to a recent grant from the Baltimore-based France-Merrick Foundation, we are launching an urban conservation program in Baltimore, with the goal of weaving our mission into the fabric of this vibrant community.

Baltimore is one of the most densely populated coastal cities in America. Residents’ lives are heavily impacted by heat waves and flooding, both of which are exacerbated by climate change. TNC’s conservation focus in Baltimore will be centered around making the city more resilient and adapted to the climate impacts that are already being felt with each heat wave, each high tide and each storm.

As we embark on this journey, it’s important that we understand the injustices that exist today and the history of systemic racism, segregation and discriminatory housing and urban planning practices that led to them. 

The lasting impacts of these legacy racist policies—including redlining—have created neighborhoods that lack access to green spaces and trees. This is especially dangerous in light of COVID-19, which has kept more people in their homes, sometimes without air conditioning.

Communities and organizations in Baltimore are facing these challenges head on, demonstrating that the city’s past doesn’t have to dictate its future. With innovative city programming, community organizing and public–private partnerships, Baltimore is in the midst of the type of transformative change needed in cities across the country.

As we launch this program and deploy on-the-ground projects in Baltimore, we are committed to applying an equity and justice lens to everything we do. As an organization that works both globally and locally, we bring solutions and lessons that have been tested in other cities. We also bring pre-existing relationships with government agencies and state officials that can accelerate the pace and scale of conservation in Baltimore. We envision a future where Charm City is America’s most resilient city.


Kahlil Kettering
Urban Conservation Program Director
Email: kahlil.kettering@tnc.org

  • Natural Solutions to Environmental Challenges in Urban Communities.

    Build Green Cities

    Natural solutions to environmental challenges in urban communities.