Retrofitting with Green Infrastructure

California Avenue Rain Garden, University of Calinfornia, Davis / Kevin Robert Perry

Why retrofit cities and suburbs with green infrastructure? Re-inserting the landscape back into the built environment helps us strike a better balance with nature, boost neighborhood health, and solve stormwater management problems. In a session at the Congress for New Urbanism (CNU) in Savannah, Georgia, a landscape architect, an urban designer, and a civil engineer offered fresh takes on why green infrastructure is so valuable.

According to landscape architect Kevin Robert Perry, ASLA, founder of Urban Rain Design, the issue is the sheer amount of impervious surfaces, the oceans of asphalt in our cities and suburbs, which can account for half of the built environment. “We need to get more water into the ground.” He said communities should take a “decentralized, natural approach” to getting more stormwater off pavement and into the ground, where it can recharge underlying aquifers.

In increasing levels of optimization, communities can maximize landscape along streets; increase their tree canopies; create park-like streets, sidewalks, and driveways; scale up networks of green, complete, streets; or build an “entire green envelope, covering buildings and streets” across the entire city or suburb.

But Perry noted the need to keep actual green infrastructure solutions simple and low-cost. His well-known Siskiyou Green Street in Portland, Oregon, cost just $20,000.

ASLA 2007 Professional General Design Honor Award. Siskiyou Green Street, Portland, Oregon / Kevin Robert Perry

Ellen Dunham-Jones, professor of urban design at Georgia Tech and author of Designing Suburban Futures, and her students collaborated with the Atlanta city government, as it begins to realize its vision of a new city design, which is rooted in Atlantans’ love of the legacy of Martin Luther King, Jr, who was born and raised there, and the city’s luxuriant tree canopy, which covers some 45 percent of the city. The design paints a picture of equitable growth in an urban forest.

Dunham-Jones and her students began to examine how a city expecting to triple in population could still maintain its tree canopy, with all its health and stormwater management benefits.

Beyond concentrating development in centers and corridors, so as to protect old growth trees, another way to do this is to retrofit trees into neighborhoods through novel regulations.

Using the Cascade Road neighborhood, a majority African American community in southwest Atlanta, as a study site, she sent out seven pairs of students to identify some options. Her team recommended re-planting or relocating trees off private property into nearby public conservation easements, and “fee-simple” donations of wetlands and flood zones that have mature trees to the city government.

“The idea is to move more trees into the public realm. We can protect them better if they are on public property; and we can also protect the rights of private property owners.”

She said Atlanta hopes to enshrine many of these ideas in a new, more stringent “nature ordinance,” designed to replace the current tree ordinance, which has relatively lax rules on tree removal.

And Paul Crabtree, a civil engineer who runs the Crabtree Group, concluded that those who are forging innovative green infrastructure solutions in communities should be considered “shock troops, highly-skilled soldiers on the front line, taking heavy casualties, even when successful.” After much persuasion and many grants, he managed to create an innovative “tree zipper” in the middle of a street in Ojai, California.

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