Planning May 2018
Ever Green
Resurfacing Our Cities
By Timothy Beatley
Redesigning the surfaces of our cities is a highly beneficial and cost-effective solution to address a variety of urban environmental challenges, including climate change, urban heat, and stormwater management. At least that is the conclusion of a new study of "smart surfaces," authored by Capital-E and funded by the JPB Foundation. The calculated benefits (in terms of such things as energy, stormwater, and health) of these redesigns are quite impressive — in the billions, even.
Our cities have plenty of surfaces, and they offer unusual opportunities with relatively high benefit-cost ratios. The study above looked at cool roofs (with the highest best-to-cost ratios), green roofs, permeable paving, and more in three specific cities. These are already mainstream tools, though more needs to be done to use them.
In our efforts to make cities greener and wilder, we have the chance to rethink and redesign other spaces. Every facade or vertical flat surface — above and below water — can be doing more.
The sky above
Living walls represent one such promising surface. Ana Deletic, an engineering professor and now vice chancellor for research at the University of New South Wales in Sydney, has been doing some of the leading work on this idea. I recently spoke with her about her innovative work on living walls.
Specifically, she and her lab have developed and tested a living wall system in which its clinging plants and flowers are fed either by stormwater or graywater (or a combination of both). What Deletic calls a "living wall" has a very specific meaning: It is a system of plants with their roots in a box or trench, growing and climbing up a wall.
These are options that make a lot of sense in a place like Australia. Australia "can't afford" the usual water consumption necessary to support the more standard green wall, she says. A single square meter of green roof can require up to 20 liters of water during the summer.
To her, the graywater option is especially attractive. To water and sustain a living wall, a city like Perth might have to invest in desalination capacity. But, as she says, the living wall plants are essentially fertilized by the nutrients in the stormwater, and the wall ends up treating and cleansing the water. And gravity is on its side: After a shower on an upper third floor, moving the graywater requires no pumping. The walls also provide shade, of course, and might even grow food.
A pilot living wall has been installed on the side of a building at Monash University, where until recently Deletic taught, and where she has done much of her work. She has been monitoring this dual system, utilizing both graywater and stormwater. Her verdict? "It works," she says.
Deletic's current challenge is to convert the more conventional form of green wall (with green plants growing from the wall itself) into one sustained by graywater and/or stormwater. She and her lab have been testing different plants and planting media. The plants must be resilient, and designs need to avoid media that actually add pollutants.
"You need plants that will be able to suck up pollution but not die," she says. And the design of these systems will need to be region-specific. "You can't just cut and paste these systems ... you have to tailor them to local conditions."
This is all very promising. Reimagining our graywater as a resource (and perhaps, later, our blackwater as well), and naturally treating and reusing it to support the nature around us, could help cool our urban neighborhoods.
The sea below
Yet another promising set of surfaces that need rethinking and redesigning are the many seawalls and structural elements common in coastal and port cities around the world. There is a trend here, as more and more seawalls are being viewed as an opportunity to support and encourage marine biodiversity. Seattle's new seawall, part of its larger plan to reconnect residents with Elliot Bay and Puget Sound, has been redesigned to incorporate features that will harbor marine life and create a salmon migration corridor. There are textured surfaces and habitat shelves jutting out from the wall. And on the promenade above are glass panels that allow light to penetrate to the seawall surfaces below (important for the growth of algae, and the salmon it runs out avoid the shadows).
Another interesting example can be found in Sydney harbor, where 60 "flower pots" have been attached to the sides of vertical seawalls in an effort to enhance marine habitat —and it seems to be working. An underwater camera has shown just how much marine nature is attracted to them.
One of the most interesting examples can be seen in Singapore, where the National Parks Board has been testing different tidal pool blocks to see how effective they are in supporting marine life. Lena Chan and Nhung Nguyen, two NParks staff involved in the design and monitoring, showed them to me on a recent visit. A row of horizontal square blocks are meant to mimic natural tidepools. One version tests a design of "pits and grooves," and another includes a series of parallel "shelves." They fill with water during high tide and then, like natural tidal pools, remain flooded. What I saw that day was a remarkable degree of marine life: Several different species of seaweed and algae, sponges, small fish, even crabs had taken up residence.
The secret is the complexity and diversity of the spaces. And they are dynamic environments, Chan tells me. "Every time you come here, you see something new."
It will be some time before the research is completed, but the results so far are promising —and can easily be seen. "It is a fantastic open lab," Chan says, noting that students from a nearby technical college do the biological monitoring. No longer can we view the surfaces of the city, either above the skyline or below the water, as wasted spaces; rather, these are productive opportunities to fit ecological services into cities where space will be increasingly limited.
Timothy Beatley is the Teresa Heinz Professor of Sustainable Communities at the University of Virginia, where he directs the Biophilic Cities project.