Bioswale Helps Millvale with Flooding Problem

  • The bioswale on Hawthorne Road is built to look like a natural stream bed. It blends into the existing hillside. Photo: Kara Holsopple

  • This weir helps slow down the water within the bioswale. Monitors in the weir will help determine how effective the bioswale is. Photo: Kara Holsopple

  • Jeff Bergman, director of TreeVitalize Pittsburgh, says gren infrastructure like bioswales is possible on Pittsburgh's hilly terrain. He's standing in front of the smaller bioswale on the Mt. Alvernia campus. Photo: Kara Holsopple

  • Sister Donna Zwigart says having a bioswale on their property fits with their commitment to the environment and their relationship with the town of Millvale, behind her. Photo: Kara Holsopple

June 13, 2014
First published November 22, 2013

This story is part of “Think Outside the Pipes”, a local reporting initiative funded by the Park Foundation and sponsored by Penn State Public Media and its "Water Blues Green Solutions" documentary.

Pennsylvania's climate change forecast is wet. More frequent and increasingly intense storms than in the past are expected.  One community which has already faced devastating floods is finding that a particular kind of green infrastructure called a bioswale could be part of the solution.

The story starts with the Sisters of St. Francis, whose convent sits on top of a steep hill called Mount Alvernia.  It looks down onto the town of Millvale, just outside of Pittsburgh. The sisters are Franciscans, which means they have a special commitment to nature, like their namesake St. Francis, the patron saint of the environment.

"He called things like Mother Earth and Brother Sun and Sister Moon.  And Sister Water," says Sister Donna Zwigart, one of the residents at Mount Alvernia.

Looking down from the top of the hill, you can see that the well- manicured landscape and trees mean a lot to the Sisters.  Zwigart says that during Hurricane Ivan in 2004, the hillside was washed out.

The flooding cost the sisters thousands of dollars, and the town of Millvale was a federal disaster area. It flooded again in 2007.  That’s why when the Western Pennsylvania Conservancy offered to build a $100,000 bioswale on the Sisters' property, it didn’t take much convincing.

Bioswales are a type of green infrastructure being used in an increasing number of cities to prevent pollution and flooding.

The one built on Hawthorne Road, along the Sisters' property, is 400 feet long—the largest of its kind in the U.S.  Art Gazdik was the engineer on the project(see his drawing below).

It's designed to look like a natural creek bed.  As stormwater washes down the road, some runs into the bioswale, along with any debris and pollution.  Plants help soak up the water as it pools in staggered depressions surrounded by boulders. Without the bioswale, stormwater would wash down the slope in about five minutes.  The bioswale slows that down substantially. That’s water that’s not ending up in a flood-prone tributary of the Allegheny River.

This is just one of the green infrastructure projects advocates are pointing to as a way to prevent flooding and pollution.  In Millvale, there’s also an urban farm that can retain some water. The local library has rain barrels, and more than 800 trees have been planted.  These are all attempts at a new way of doing things in a hilly region.

"One of the arguments against doing green infrastructure is that, 'Well, you can’t do it on our slopes in Pittsburgh.'  And this is an example of one that is working," says Jeff Bergman, director of the conservancy’s TreeVitalize Pittsburgh program.  He oversees this bioswale and a smaller one in parking lot on the property.

So far, built-in monitors show that water which has gone into the bioswale hasn’t come out the bottom side, even during recent thunderstorms.  Bergman says green infrastructure like the bioswale isn’t going to fix the billion-dollar plus rain water and sewer overflow problems in Millvale or Allegheny County, but it could be part of the solution.

A solution would be welcome to residents who live near the bottom of the nuns’ property. Al Walsh, a retired postal worker, is fed up with the flooding here.  He bought his house just a few months before Hurricane Ivan.

"When I bought the house, I was told it never flooded for 50 years," he says.

After Ivan, his yard was a muddy lake, and his house was flooded from the basement up to the first floor.  The insurance adjuster said it would cost almost $200,000 to restore. That’s more than the 140-year-old house was worth. 

"You know, it’d be worth more to torch it, in a roundabout way," says Walsh.

His house has flooded a few times since. Walsh says while he appreciates the newly planted trees and the efforts to build structures to prevent flooding, he doesn’t have a lot of confidence it will help.  He’s moving to a nearby suburb.