Saturday, February 20, 2016

Tear-up Abandoned Parking Lots

Less Costly Shortcut to Urban Stormwater Control 

Commercial property owners like to lay down as much concrete as they can, beyond what might be deemed necessary for parking and sidewalks, because in the long run it saves them the cost of labor, equipment and materials to cut grass and control weeds.  Some like asphalt even more because it’s cheaper than concrete, at least in the short run.

The drawback is that stormwater runs right off of concrete and asphalt (and roofs), straight into city sewers. In cities that have two sewer systems, one for household, commercial and industrial wastewater and a separate system for stormwater runoff, the consequences of storm runoff are less severe. It’s easier, thus less costly, to treat and moderate rainwater runoff.

Many older, larger cities like Detroit, however, have combined sewer systems where wastewater and stormwater flow together, often overwhelming wastewater treatment plants.

To meet the demands of clean water laws, some cities with combined sewers (like Chicago or Atlanta, for example) have been required to build huge tunnels to temporarily hold combined sewer discharges during and after storms, thereby preventing combined sewer overflows (CSOs) from inundating treatment plants or being released untreated into natural water bodies.

Several years ago, there were plans to build such a tunnel in Detroit, but the city’s insolvency prevented implementation. Instead, a number of smaller facilities called retention treatment basins (RTBs) were chosen to control overflows. Whether or not RTBs, some still under construction, will be sufficient to manage overflows and prevent the pollution of lakes and streams remains to be seen.

In the meantime, various types of green infrastructure or low impact development (LID) offer some relief from the polluted runoff problem. These would include rain barrels, ground-level and roof-top rain gardens, permeable pavers, detached downspouts and bioswales. Note the success of one such LID project, a retrofit in the Towar neighborhood near East Lansing, Michigan;

But I digress. The point is that an overabundance of concrete and asphalt, mostly in underused or abandoned parking lots, contribute significantly to urban stormwater runoff and combined sewer overflows.

In metropolitan areas like Detroit, where populations have declined, sprawling parking lots at commercial, industrial, municipal, sports venue and similar sites could be reduced in size, sometimes drastically.

Consider the acres of unused pavement at abandoned sites like Northland Mall or the Pontiac Silverdome. Funds to remove hard surfaces would be available if we got our priorities straight.

Simply returning such areas or large parts thereof to their natural surface, augmented with vegetation of some kind, would be a lot cheaper than installing more concrete and steel RTBs or sophisticated green infrastructure improvements farther downstream.

Satellite view of Northland Mall’s empty parking lots:,-83.2060912,1375m/data=!3m1!1e3

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