Sunday, June 12, 2016

Harry's Brook and the Tale of Two Parking Lots

Though the parking lot at the Princeton Shopping Center will surely look and function much better after its renovation is complete, there was a missed opportunity in terms of reducing how much polluted runoff the parking lot generates. (Update, 8/20/16): Not completely lost. See more recent post.) This is something the aquatic life in Harry's Brook notices, but we don't. We perceive a rain as cleansing. But the brook, one tributary of which begins near the shopping center and flows down to Carnegie Lake, is on the receiving end of that film of pollutants that cars shed wherever they go.

Though reconfigured, the islands of turf and trees at the shopping center will have the same design they had in the past, convex and higher than the surrounding pavement. They will shed water rather than receive it. A more stream-friendly approach is to make the islands concave and lower than the pavement, so they can receive both the quantity and tainted quality of runoff from the pavement. The vegetation and soil can then absorb some of the runoff and filter out some of the pollutants before the stormwater enters the stream. The result is less flashy floods and cooler, cleaner water entering the brook.

One example of this concave shape can be found at Stone Hill Church, up on Bunn Drive. Another is near the shopping center at Westminster Choir College's parking lot. The photo below, taken during construction years back at Westminster, shows the wavy curb where runoff enters on the left, and the drains that take any excess runoff the swale can't handle. The reason Westminster used a more stream-friendly approach? Because their parking lot was an addition, they had to adhere to the latest regulations, which require more sensitivity to the watershed. The shopping center was renovating an existing parking lot, rather than adding additional impervious surface, so the more recent, creek-friendly regulations didn't apply.

The shopping center renovation would have been an opportunity to reduce harmful stormwater impacts on Harry's Brook. That didn't happen, most likely because developers tend to do only what the government requires, and nothing more.

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