Where Should the Green Go?

What makes some infrastructure green and other infrastructure grey? For planners, engineers, and researchers focused on cities and sustainability, green infrastructure a buzzword that is often championed, but equally difficult to define.

In the context of water management, Grey Infrastructure is the rigid pipe network, concrete, and treatment facilities that have allowed cities to grow ever larger while capturing and conveying water from storms and the waste stream away from concentrated populations. In mechanistic terms, these networks are efficient and effective. Yet the realities of today’s urban places – rapid population growth, crumbling infrastructure, and budget constraints – have put serious strain on grey infrastructure. Further complicating the matter, more extreme weather events fueled by a changing climate are putting many metropolitan areas in growing peril. Hurricane Sandy’s damage to New York City’s housing and infrastructure, estimated at $42 billion, is perhaps the most attention-grabbing example. And other low-lying cities, like Miami, face serious flood control challenges. Sea level rise often cause storm surges to push up through the drains and onto Miami streets. Herein lies the role of green infrastructure.

The US EPA defines green infrastructure as “a cost-effective, resilient approach to managing wet weather impacts that provides many community benefits.” To unpack this definition, green infrastructure is commonly understood to be the use of plants, soils, and other natural processes to manage stormwater runoff on-site. If grey infrastructure manages water like a machine, green infrastructure manages water like an ecosystem. Facilities such as of rain gardens, bioswales, constructed wetlands, and conserved natural spaces show a remarkable ability to store excess runoff created during wet weather events and capture harmful pollutants such as heavy metals. Additionally, there can be serious cost savings in installing green infrastructure over the grey variety.

So, the value proposition is rather compelling. Investment in the greener types of infrastructure has taken off in the last decade. New York City has an ambitious green infrastructure plan in place that aims to manage both storm overflows and flood events (i.e. Hurricane Sandy type storms) and has spent more that $187 million on green infrastructure to date. In 2013, Chicago announced one of the nation’s large volunteer green infrastructure programs, with $50 million committed over five years to complete green infrastructure projects tied other capital investments in strategic locations throughout the city. Milwaukee has similarly ambitious strategies in action. The Fresh Coast 740 Plan looks to manage the first half-inch of rainfall across the entire city, equating to 740 million gallons of stormwater managed through green infrastructure. These investments are important first steps in improving water quality, reducing the burden on overtaxed grey infrastructure, and creating more resilient cities.

Yet there is still a notable opportunity for the services of green infrastructure to extend beyond stormwater management to address other urban challenges such as urban heat island effect, air pollution, habitat loss, and lack of access to green space. Simply increasing the number of street trees, for example, can reduce ambient air temperatures by up to five degrees. And according to Tori Kjer, PLA, the Program Director for the Trust for Public Land’s Los Angeles Program, “[d]eveloping green features in cities has important public safety benefits for vulnerable and underserved populations.” In Los Angeles, only one in three children are in walking distance of a park. Quantifying these benefits can be a little more challenging. But they directly and visibly address quality of life for residents.

Locating green infrastructure then becomes a considerable challenge once climate variability and the other socio-environmental criteria discussed above are properly considered. Scholars, city managers, and major non-profit organizations are moving toward a more informed approach to planning and siting green infrastructure to best capture its multiple benefits.

The Urban Sustainability Research Group in the University of Michigan has been working on the Green Infrastructure Spatial Planning (GISP) model. A framework that utilizes a multi-criteria spatial analysis to assess the tradeoffs of various green infrastructure benefits and identify priority areas. Geographic Information Systems (GIS) layers serve to describe six green infrastructure planning priorities: stormwater management, social vulnerability, access to green space, air quality, the urban heat island effect, and landscape connectivity. Individual criterion layers are compared and spatial trade-offs analyzed through a composite score. While this type of spatial analysis operates at a relatively course scale, the data used is commonly available for cities across the country and the world. Thus allowing for a fist level of spatial prioritization with minimal investment of time and resources.

The Trust for Public Land’s Climate Smart Cities initiatives are also using spatial data in a similar fashion to help prioritize green infrastructure investment in Los Angeles, New York, Seattle, and Chattanooga, Tennessee. TLP’s GIS data is organized around four green infrastructure objectives: connection, cool, absorb, and protect – and composite mapping can provide more granular prioritization than the University of Michigan’s GISP model. Milwaukee’s MMSD is also organizing data at a similar spatial resolution for green infrastructure planning down to the street level. However, these types of efforts require detailed, site-specific mapping. Data that is often unavailable to municipalities and funding organizations.

Infrastructure, in any form, is expensive. These types of citywide, data-driven approaches can improve strategic decision making while helping each capital investment to capture multiple benefits.

The tangle of concrete and pipes of cities is not going away. Grey infrastructure serves a critical role in making our urban places possible. The density and connectivity provided by cities is arguably a far more viable future for the world’s populations than sprawling development. But we are increasingly dealing with extreme and unpredictable environments, and the flexibility of green infrastructure has a proven place in this messy system. Using data and drawing upon the growing knowledge of how to urban ecosystems function, we can continue to find ways to make infrastructure work better.


Image courtesy of Flickr. Originally published by S&S on May 23, 2016.


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