Could vacant lots double as green infrastructure projects?

The idea of using green infrastructure, from rain gardens and rain buckets to porous streets and simple sidewalk grass and plantings, is among the few environmental solutions that exists virtually unopposed. Big, old cities in the U.S. tend to have outdated sewer systems that overflow when it rains a lot, thanks to the built environment’s inability to slow all that water down. As one would imagine, “combined sewer overflow” is something cities would like to avoid. Adding in all those little green bits around a city allows soil and vegetation to slow up the water and use it before it can get into the sewer systems. In Philadelphia, for example, a $3 billion program aims to reduce sewer overflows by 85 percent.

Building up enough of such green projects, though, takes a lot of time and money. What if we could leverage another major problem in many economically struggling cities toward closing that green infrastructure gap? Researchers from the Environmental Protection Agency along with Penn State and Ohio State Universities and engineering firms examined how vacant lots in Cleveland currently manage storm water, and laid out some fairly simple adjustments to how lots are demolished and razed that could take urban blight and turn it into a net benefit for the city. Their study was published in the journal Landscape and Urban Planning.

They took a look at 52 vacant lots in Cleveland and divided them based on differing demolition practices before and after 1996. They found, generally, significant “disturbance” in the soils and vegetation of vacant lots; demolition crews often just bury debris from the structure being demolished, though the houses knocked down after 1996 did seem to have debris buried a bit deeper than in earlier-demolished lots. The older demo sites also had more sand and less silt, which play a role in how well the soil can retain water.

They also measured hydrologic properties of the soils and then used computer modeling to estimate how these lots deal with rainfall runoff. As it is, your average Cleveland vacant lot is a net producer of runoff, meaning it isn’t helping keep water out of sewer systems. In fact, that average lot, covered with naturally growing vegetation, can generate 3,800 liters per year of “uncontrolled runoff.”

But they found that simple fixes to how properties are handled when demolition is in the cards could change that dramatically. Actually removing the debris instead of burying it is a good first step, as is making sure the lot is level rather than sloped and ensuring the whole area can feasibly be covered in vegetation. Do all that, and you’ve got a vacant lot that contributes zero runoff. That means it’s now a net-positive to the water system in the city.

If lots could be engineered to actually hold excess water instead of discharging it into the system, that’s a big deal: In Cleveland alone, there are 28,000 vacant lots. Other cities have similar issues (see: Detroit), and there is an undeniable appeal in turning what most consider an eyesore, a problem to be solved, into a solution for an apparently unrelated problem. - Dave Levitan | April 15 2014

Source: Shuster WD, Dadio S, Drohan P, et al (2014). Residential demolition and its impact on vacant lot hydrology: Implications for the management of stormwater and sewer system overflows, Landscape and Urban Planning, 125 (2014) 48-56. DOI: 10.1016/j.landurbplan.2014.02.003

Image: Flickr/habeebee

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