Discovering Chestnut Hill: Trickling Streets Becoming Eroded Gullies

By Emily Schricker, Conservation and Easements Manager, Chestnut Hill Conservancy
Posted 1/14/22

And the damage is not limited to forested areas on city-owned land.

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Discovering Chestnut Hill: Trickling Streets Becoming Eroded Gullies


The unique features that make Northwest Philadelphia the picturesque treasure it is are also the characteristics that put it at risk. Peaks and valleys, hills and vistas create the landscape that has drawn generations of residents and visitors. Colorful palettes of trees are set on hillsides so spectators can enjoy each hue that reaches up to the sky and down to the Wissahickon Creek below. But this gorge that we hike, photograph, and escape to can also allow unmanaged stormwater to runoff and barrel towards the Wissahickon Creek at an alarming rate. 

Where there were once trickling streams in the Wissahickon Valley Park, there are now eroded gullies. And the damage is not limited to forested areas on city-owned land. Private property owners have channels worn through their lawns created by rushing stormwater, while property abutting the Wissahickon Creek is eroding and disappearing by the square foot, intensified by every large storm event we experience. 

The effects and the damage surround us, but a way to reduce the destruction is also hiding in plain sight. 

Vegetated and landscaped areas can generally handle the first 1.5 inches of rain that falls during a storm. Grass, landscaping, and wooded areas can absorb a portion of rainwater (the latter much better than the prior) and reduce the channels of water that run down the sides of the road, come across lawns, and tear through the Wissahickon Valley Park. But what about the storms that bring more than 1.5 inches? What about the Hurricane Idas, Irenes, and Sandys? How can the amount of existing greenspace keep up with rain coming down at that accelerated pace? It can’t.

But there are ways to improve the situation. We can work to increase the permeability of our existing paved (impervious) surfaces and ensure that valuable existing greenspace remains intact. Currently, the Chestnut Hill Conservancy (working jointly with the Friends of the Wissahickon) permanently protects more than 100 acres of open space in the Chestnut Hill area. Just half of that conserved land equals more than two million gallons of mitigated stormwater runoff (10,000 square feet of pervious coverage can absorb approximately 9,340 gallons of rainwater per storm). That’s more than two  million gallons of water soaking into the ground where it falls instead of running down the street, eroding small streams, and polluting the Wissahickon Creek. 

Open spaces protected by conservation easements - like those held by the Chestnut Hill Conservancy - secure these benefits in perpetuity. The land will continue absorbing rainwater for generations and add to the resiliency of the landscape, which is important not only for the short term, but also for the aftereffects of excessive stormwater runoff. Water that rapidly runs over surfaces like roads and treated lawns picks up chemicals and sediment. After the rainwater drains into the Wissahickon Creek it makes its way to the Schuylkill River, which in turn supports the water supply for Philadelphia. Clean drinking water is something everyone can be concerned about, no matter how many acres your home is situated on. 

When discussing the impact of stormwater runoff, Ruffian Tittmann, Executive Director of the Friends of the Wissahickon puts it into perspective. “What are the ways we can protect the greenspaces we still have? Residential and private institutionally-held parcels can have a large impact on the community. It’s not about today, it’s really about tomorrow and beyond, and how can we prepare for the next storm?”

Even if a conservation easement isn’t right for a property, there are other ways to support the health of the Wissahickon Watershed and greening in your community. Reduce chemicals on your lawn, plant a tree, attend a community meeting, and stay in touch with the Chestnut Hill Conservancy and the Friends of the Wissahickon to continue learning more about how you can help. Encouraging responsible development (both buildings and reduced impervious ground surfaces like parking lots) can ensure that those who stand to gain from this beautiful area also work to ensure that it remains a treasure for future generations.