Wednesday, August 24, 2011

Historic Channels of Negley Run, Site of Pittsburgh's Recent Flash Flood

After writing earlier this week about Negley Run's flash flood on Washington Street in Pittsburgh, I became curious about the historic watershed.  Since I hadn't heard anything about it before, I figured it would be a small one, so I started mapping the historic channels, based on topography and this map from the Darlington Digital Collection.  Turns out it is a huge watershed - comparable to the Junction Hollow watershed in many ways.  In fact, it once included a lake called Silver Lake that appears to have been similar to Panther Hollow Lake.  Unlike Junction Hollow, however, this watershed does not have any intact streams present except very small ones in Highland Park and perhaps in other very steep areas.

Negley Run and Junction Hollow watersheds

Negley Run is the northern of these two watersheds, and Junction Hollow the southern.  Note that the colors mean different things for each map (oops).  For Negley Run, the dark blue lines are creeks that appeared on historic maps while the light blue lines are areas that probably had flow based on topography.  The yellow/orange channels around Penn Hills appear to have drained into Negley Run but the water that falls in that area is now routed into the Nine Mile Run 'sewershed'.  So, in a way, Negley Run is even 'beheaded' like Panther Hollow run is, although there is no aboveground stream to offer evidence of this.

Anyway, here's the Google Map:

View Negley Run Historic Channels in a larger map

Notice just how much area of dense urbanization drains down towards Washington Avenue.  Imagine two inches of rain in an hour, over that whole area, being forced into old sewage pipes that were possibly build before all that development was in place.  All of that sewage water was pouring towards the river, but the system got overwhelmed, or clogged, with horrible tragic results.

Negley Run doesn't have a visible creek, and to my knowledge doesn't have a watershed advocacy organization.  It's still important to the people of Pittsburgh though, if for no other reason than the fact that in its current state it is dangerous.  For that reason, the watershed health of Negley Run is every bit as important as that of Junction Hollow and Nine Mile runs.

On a side note, Junction Hollow was impacted by this flood as well.  Check out these pictures, taken by Martha Riecks, of Panther Hollow Lake after the deluge.

panther hollow flooding

panther hollow flooding

I wonder if the water got high enough in the lake to overtop into the historic Four Mile Run channel beyond...

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