Gray vs. Green: Spongy Infrastructure

By Luke Carothers

More and more frequently in recent years, cities across the world have had to contend with increased flooding coming as a result of climate change.  Traditional flood mitigation techniques involving concrete infrastructure have been deployed to handle excess rainwater and runoff to varying degrees of effect, but many experts believe the solution to these challenges lies not in concrete infrastructure but in green infrastructure.  Rather than relying on concrete infrastructure solutions to manage water, cities can harness the natural processes of grass, trees, leaves, lakes, and ponds as green infrastructure.  These natural processes present a sustainable way of responding to climate change.  This concept of a city’s ability to absorb and manage rainwater through its green infrastructure is often described as its “sponginess”–a term that has been around for almost two decades.  

This concept of a “spongy” city is not only a sustainable solution in responding to climate change, it is also a powerful metaphor that resonates strongly with the public.  Vincent Lee, Civil and Water Lead at Arup, says that the concept of spongy cities has been around for the last twenty years, although the name varies from place to place.  Lee says that this shift from traditional ways of managing water like concrete channels and pipes to leveraging nature-based solutions has been global as cities are seeing the benefits of small-scale adoption.  Using a new machine learning land-use tool, Arup tested the ability of ten diverse global cities to naturally absorb rainwater–otherwise known as sponginess–in order to highlight the importance of cities moving beyond concrete infrastructure, encouraging them to look to nature for solutions to climate change-related challenges such as increased flooding.  According to the report website, Arup’s goal in creating the Global Sponge Cities Snapshot is to get people talking about green infrastructure.

According to Lee, there were ultimately two driving factors behind Arup’s development of the Global Sponge Cities Snapshot with the first being the movement for cities to harness the power of nature and leverage nature-based solutions and biodiversity for water management.  Lee believes there is a strong desire amongst cities to leverage these natural solutions.  The second factor behind the development of the Global Sponge Cities Snapshot is the evolution of data and technology.  With the availability of open source data, processes can become more consistent across different parts of the world.  Furthermore, technological advancements have increased the speed at which these sorts of analyses can be performed.  

Charles Ormsby, Climate and Sustainability services leader for Arup in Canada, says that this sort of analysis is a powerful tool for fields like civil engineering.  For Ormsby, this is a product of the great spirit of innovation within the group.  Still more, he believes that, even though he carries the perspective of a civil engineer, more and more disciplines and groups of professionals are thinking about these concepts perhaps through a different lens.  As these disciplines and groups are applying their own needs and goals onto the concepts, Ormsby believes these layers build on top of one another to show a “better picture of the intersection of different realities when it comes to urban systems.”

From such a layered analysis of urban systems emerge trends that define the impact of these systems on our most vulnerable populations.  For example, a snapshot that provides data as to the density of trees and vegetation identifies areas that are most at risk when it comes to things like heat island effect.  This, in turn, helps identify groups that are most at risk for mortality when it comes to extreme heat events.  Ormsby says that the Global Sponge Cities Snapshot gives a “good sense of the lay of the land” when it comes to green infrastructure and gets the ball rolling in terms of furthering the conversations within different groups.  Lee extends this, noting that the Global Sponge Cities Snapshot is a powerful tool for engaging with different stakeholders about leveraging water management while also thinking about aspects like land use, equity, and city planning.

As a tool for communicating concepts of green infrastructure with groups outside of the AEC profession, the concept of sponge cities brings a number of different people around a common table.  Recently, Arup brought together a group of academic, university professors, community organizations, non-profits, property developers, government officials, municipal officers, and students as well as design professionals, architects, landscape architects, and engineers, assembling at the United Nations Biodiversity Conference (COP-15) in Montreal.  With this assembled group, Arup unveiled the Snapshot data for the host city.  Working together with the data provided, this group began to discuss how a particular neighborhood could be improved by leveraging greenery and achieving biodiversity regeneration.  This generated conversations about ideas like connecting corridors that are historically habitat and rectifying historical inequity issues.  Arup’s Global Sponge Cities Snapshot is unique in that it presents concepts that occupy the same space of understanding between the AEC industry and the communities in which our projects exist.  As cities across the globe are responding to the effects of climate change, tools like this Snapshot will be instrumental in expanding the use of green infrastructure solutions.

Luke Carothers is the Editor of Civil + Structural Engineer Magazine. If you want us to cover your project or feature an article, he can be reached at lcarothers@zweiggroup.com.