In June I visited Schenley Park during a rainstorm. However, most of Four Mile Run and other watersheds in Pittsburgh is not parkland, so I thought it would be interesting to watch what rain does in an urban area as well. A line of thunderstorms presented a chance of doing this today. I chose the corner of Bartlett Street and Murdock Street in Squirrel Hill, because this is part of the historic Panther Hollow Run and because there are several different types of pavement in this area.
Sure enough, the weather started getting stormy fast.
The sky was impressively dark and tempestuous. Lightning began lighting up the sky to the south - a quick check of the radar showed that the heaviest of the rain was passing just to the south. Nevertheless, the lightning was quite impressive, and I saw a few bolts light up the sky (but was not able to get good pictures, since it was daytime). Still, some rain did come through Squirrel Hill...
As you can see in this rain-splotched picture, the foreground area has large, coarse bricks or cobblestones. The opposing hill has smoother, tightly-packed bricks, and the cross-street is paved with conventional asphalt.
The rain never was particularly heavy here, though areas south of town appear to have been hammered by severe storms.
After about 15 minutes of light to moderate rain, runoff began from the concrete and asphalt areas.
Some runoff appeared to also occur from the tightly-spaced bricks. Throughout the entire storm, no runoff was noted from the coarser bricks/cobbles, though some puddles did form.
Interestingly, 15 minutes in, there was still no water making it through the denser tree canopies
26 minutes after the rain started, there were quite a few puddles in concrete areas.
Rain continued on and off for about an hour and a half without ever becoming intense. 'Rain' was falling under the trees for at least 15 minutes after the storm had passed. In some cases this was heavy enough to continue runoff from pavement when it had stopped elsewhere. All in all, about a tenth of an inch of rain fell at a nearby weather station. I suspect slightly less fell on Squirrel Hill, and perhaps a bit more in East Liberty and Highland Park.
It appears that for a small storm like this, just the presence of trees and cobble streets was enough to stop runoff. A tenth of an inch can sometimes cause sewage overflows into the river if it comes all at once. For this light storm, it is unlikely that any overflow occurred, though I don't know for sure. Storms like this are quite common in Pittsburgh and other areas of the East during the summer, and my observations confirm that even small efforts to reduce runoff can definitely stop some storms from causing sewage overflows.
As the storm passed, I learned that I had left my lights on and my car battery was dead! Although this was unpleasant, my later departure meant that I was able to see a beautiful sunset from two different locations.
Schenley Park golf course
East Liberty near Penn Street and the bus bypass.