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More Than a Rain Garden: Green Infrastructure Addresses Environmental Problems Across Scales

by Kate Cholakis and Seth Charde

What is Green Infrastructure?

Green infrastructure is trending, achieving buzzword status within the fields of civil engineering, landscape architecture, city planning, and climate resiliency. Professionals in these fields might use this term to describe a rain garden, green roof, or plant-based sewage treatment plant. The term might also be used to describe a forested city park, restored urban stream corridor, or expanded coastal marsh. These strategies share the connecting thread of water management.

The broad category of “water” might include rainfall (intercepted by trees and green roofs), stormwater runoff (slowed and treated in rain gardens), wastewater (treated through the use of plants in ecological sewage facilities), or floodwater (accommodated by restored stream corridors, floodplain forests, or marshes). The conservation organization American Rivers defines green infrastructure as “an approach to water management that protects, restores, or mimics the natural water cycle.”1 Within the natural water cycle, plants and soil clean water and return it to the sky, groundwater reservoirs, or waterbodies. Specific green infrastructure interventions, such as rain gardens, mimic this process through the use of plant material, engineered soils, and other biotic materials.


Green infrastructure can take the form of a rain garden filled with flowering perennials and grasses (left, Pulaski Park in Northampton, photo Kate Cholakis), or a large-scale stormwater treatment wetland (right, Alewife Stormwater Wetland, photo Ryan Corrigan of Parterre Ecological).

The Environmental Protection Agency defines green infrastructure within the context of one type of water, posing this approach as an alternative to “single-purpose gray stormwater infrastructure—conventional piped drainage and water treatment systems.”2 Many towns and cities use conventional piped drainage systems to collect stormwater runoff and convey it away from developed areas. This functions as a flood prevention strategy, but can result in degradation of waterbodies by spiking flow, temperature, and sediment loads, and conveying toxics and heavy metals that are washed off roadways and other impervious surfaces. In contrast, a rain garden, commonly defined as a depression in the earth filled with plants, slows stormwater runoff (rainfall that hits a surface and moves across it), cools the water on a hot day, filters the flow through soils and plant roots, and gives the water a chance to evaporate, infiltrate into the ground, and absorb into plant roots. A forested city park also mimics the water cycle by intercepting rainfall, encouraging infiltration, and absorbing water. Unlike gray infrastructure, green infrastructure tends to serve multiple functions in addition to water management, such as providing habitat and cleaning the air.

Runoff infiltration is limited in highly impervious, urban areas. Green infrastructure seeks to mimic the water balance typical of vegetated, less developed areas, where infiltration tends to be higher.

Green infrastructure does not only refer to stormwater management; the term is also used to describe plant-based approaches to managing floodwaters. For example, coastal marshes absorb storm surges and dissipate wave energy, whereas floodwalls, an example of gray infrastructure, push surges and wave energy back into the ocean or to nearby coasts. Engineers, landscape designers, planners, urban foresters, and ecologists may use the term green infrastructure to refer to a range of specific physical interventions, and/or to a more general, alternative approach to managing water that mimics or restores ecological functions.

As with any change to the status quo, embracing green infrastructure as an approach and installing specific interventions comes with many challenges. It demands educating clients, communities, contractors, and designers; experimenting with new techniques and learning from failures; and making changes to policy and regulations.

A Pilot Project Combining Science and Art in Washington, D.C.

Recent initiatives by DC Water (the District of Columbia Water and Sewer Authority) and the District of Columbia face these challenges head on. Washington, D.C. has two types of sewer systems, a municipal separate storm sewer system (MS4) where one pipe is dedicated to stormwater and the other to sanitary flow (greywater and sewage), and a combined sewer system (CSS) in which a single pipe conveys both sanitary and stormwater flow. The MS4 area comprises about two thirds of the city while the CSS area comprises about a third. Neither system mimics the natural water cycle.

The MS4 system quickly conveys rainwater that falls on surfaces, such as city streets, into storm drains, releasing it untreated and in large volumes, into waterbodies. There is little time or opportunity for evaporation or infiltration. As it moves across surfaces, runoff picks up pollutants, such as gasoline, trash, fertilizers, pesticides, dog waste, and more. The good news is that new stormwater regulations enacted in 2013 now require new and redevelopment projects over a specific size threshold to capture and retain stormwater onsite using green infrastructure and rainwater harvesting practices. While it will take many years to undo the damage caused by the old MS4 system, incremental improvements implemented under the new regulations are already showing results.

In the case of the CSS, dry weather sanitary sewer flows and smaller combined flows (storm and sanitary) are directed to the city’s sewage treatment plants for filtration. The bad news is that these combined sewer systems (CSS) quickly become overwhelmed during large rain events, and divert the excess stormwater, combined with untreated sewage, into Rock Creek, and the Anacostia and Potomac Rivers. The habitat and human health implications of these overflows are severe, and it is not a surprise that this type of system is heavily regulated through the Clean Water Act. The cost of renovating or replacing these combined sewer systems is substantial (DC Water’s Clean Rivers Project is estimated to cost $2.7 billion over 25 years) and prevents many cities from achieving compliance with the law. Many cities are, as a result, sued by and required to pay fees to the federal government as long as they continue to pollute water bodies. Some municipalities sign consent decrees with the government to settle this legal dispute: the decrees lay out a process for moving toward meeting the requirements set by the government.

The DC Clean Rivers Project combines gray and green infrastructure strategies: eighteen miles of massive new underground tunnels (gray) will hold combined stormwater and sewage until it can be treated at Blue Plains Advanced Wastewater Treatment Plant, and green infrastructure facilities such as bioretention, permeable pavements, and rooftop collection (green) will slow, treat, infiltrate, and reuse stormwater. Graphic courtesy of DC Water.

In 2016, DC Water and the District of Columbia modified the consent decree they signed in 2005 with the Environmental Protection Agency and the United States Department of Justice to include green infrastructure as part of their plan to reduce combined sewer overflow (CSO) volumes. Although modifying legal documents might not be particularly thrilling to some, this shift in approach meant that DC Water and the District are legally bound to implement sustainable stormwater management strategies.

Conway School alum, Seth Charde, played a key role in the development and execution of this modification. He works as the Green Infrastructure Manager on DC Water’s Clean Rivers Project. The modifications resulted in a combination of both gray and green infrastructure strategies: eighteen miles of massive new underground tunnels (gray) will hold hundreds of millions of gallons of combined stormwater and sewage until it can be treated at Blue Plains Advanced Wastewater Treatment Plant, and green infrastructure facilities such as bioretention, permeable pavements, and rooftop collection (green) will slow, treat, infiltrate, and reuse stormwater from approximately 500 impervious acres before it enters the city’s system.

To achieve the green part of this proposal, DC Water needed to educate and experiment. In 2013, DC Water launched the Green Infrastructure Challenge, asking landscape designers and engineers to develop green infrastructure proposals for city streets. A proposal for the 100 block of Kennedy Street NW won a construction contract, and installation was completed in 2018. This pilot project will be monitored for success, with the idea that strategies will be replicated throughout the watershed.

Before implementation of green infrastructure, Kennedy Street contained a high amount of impervious surface. Photo: Seth Charde of DC Water.

Implementing green infrastructure on this portion of Kennedy Street included porous pavements, bioretention bump-outs, and more. In this photo, a seating wall engraved with features of the watershed marks the edge of a bioretention area covered with a steel grate and an open bioretention bump-out. Changes in pavement material mark the edge of on-street parking spaces, replacing the curb.

Kate Cholakis, current Conway School faculty member and alum of the program, worked on this project while employed at Nitsch Engineering in Boston. The design team for the project crossed disciplines, including landscape architect Kevin Robert Perry of Urban Rain Design, environmental artist Stacy Levy, and Nitsch Engineering, known for green infrastructure design and stormwater master planning. When the team entered the construction document phase, it grew to include consultants with roots in the DC area (Warner Larson Landscape Architects, EBA Engineering, McKissack & McKissack, and community outreach firm Tina Boyd & Associates). The design process included multiple opportunities for community involvement. The team learned from residents and business owners, and residents learned about novel green infrastructure strategies. DC Water additionally has implemented a local jobs program that trains residents to construct, inspect, and maintain green infrastructure projects. This pilot project demonstrates the potential of green infrastructure as a multi-functional approach to stormwater management.

Testing Solutions Across Scales

At the Conway School, where Kate now teaches, students integrate green infrastructure into site design and planning projects for real clients. Over the course of the Conway School’s one-year graduate program in ecological landscape design and planning, students work on projects at three different scales (residential/commercial or public site design, regional planning, and large-scale site design/master planning). The school shares these projects online for free (click on the links in the following sentences to browse the projects). In 2014, students Michele Carlson, Willia Caughey, and Nelle Ward developed a guidebook presenting and applying green infrastructure templates across the city of Holyoke. These templates included the use of bioswales, bump-outs, tree trenches, stormwater planters, tree boxes, permeable pavers, and green roofs. In 2016, students volunteered to plant a rain garden proposed for a site in Springfield, MA, by Molly Burhans ‘15 as part of her student project. In 2017, two student teams produced plans for green infrastructure on specific city streets in the cities of Holyoke and Chicopee, MA. In 2018, students Greta Moore and Lisa Krause developed green infrastructure strategies for streets and public sites in Mystic, CT. All students examine drainage patterns for their studio project sites, and consider the use of green infrastructure techniques to capture, slow, and clean water.

Every year at the Conway School, Kate and fellow faculty member Anne Capra present to the students about stormwater management history and regulations. They worry that the acronyms, technical details, and regulatory hurdles associated with this topic will induce yawns among audience members. However, every year multiple students discover a passion for stormwater management, and, after graduating, find themselves working on green infrastructure projects. There are many ways for professionals from different disciplines, such as engineering, planning, community organizing, environmental consulting, and more, to engage in sustainable stormwater work. Realizing the social, economic, and environmental benefits of green infrastructure will require collaboration across all of these disciplines.

Footnotes

1 “What is Green Infrastructure?” American Rivers, www.americanrivers.org/threats-solutions/clean-water/green-infrastructure/what-is-green-infrastructure/. Accessed 8 November 2019.

2 “What is Green Infrastructure?” EPA, www.epa.gov/green-infrastructure/what-green-infrastructure. Accessed 8 November 2019.

About the Authors

Seth Charde Seth Charde, PLA, LEED AP, is the Green Infrastructure Manager at DC Water. Seth has been implementing DC Water’s green infrastructure program for combined sewer overflow control under the DC Clean Rivers Project since 2013. Prior to joining DC Water, Seth was the Environmental Planner for the University of Maryland where his work included master planning and site planning for watershed restoration and stormwater management projects. Seth holds an MA from the Conway School, and an MBA from the University of Maryland.

Kate Cholakis teaches landscape design and planning at the Conway School, a one-year graduate program in ecological design located in Northampton, MA. Kate is particularly interested in cultural landscape history, green infrastructure design and planning, and ecological planting design.

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