Stormwater Runoff

The need for the FOW to assume a stronger role with regard to stormwater runoff became apparent when two intense rainstorms pounded the Park in the late summer and early fall of 2004.

In the densely-developed neighborhoods around the Park, the stormwater ran off the roofs, sidewalks, driveways and streets into what are normally scarcely noticeable streams. These streams overflowed their banks and raged into the Wissahickon doing millions of dollars in damage to the Park and wrecking bridges that had weathered decades of storms in the past.

The stormwater issue has two aspects that must be tamed — quantity and quality. Excessive quantity of runoff can have devastating effects throughout the watershed, causing flooding and carving erosion channels wherever storm sewer pipes empty into the ground. Generally, the severity of the problem is related to intensity of development. The older, more densely developed locations that have higher percentages of their area covered by streets, rooftops and parking spaces, produce more runoff.

More subtle are the water quality aspects of runoff. Sediment is carried by the rushing water as it erodes stream banks and the landscape. Over time, these soil particles settle to the bottom of the Wissahickon where they may bury aquatic organisms such as insect larvae that inhabit rocks in the streambed. These tiny creatures are an important food source for fish living in the creek, so sedimentation has broad effects on the aquatic ecosystem.

As fallen-rain washes across the watershed, it picks up remnants of urban lifestyles. Lawn chemicals, motor oil, antifreeze and pet droppings are all swept up by the flowing water and carried to storm sewers. For many citizens, once water has gone down the storm sewer inlet, it is out of sight and out of mind. In some sections of Philadelphia, there are combined sewers that transport both stormwater and sewage to treatment plants, but outside the city, this is never the case. Mostly, storm sewers are tributaries of the Wissahickon, so whatever is in the storm runoff ends up in the creek.

The Philadelphia Water Department (PWD) has launched a study designed to better understand the flow of water into all the streams in the Wissahickon watershed so it can come up with a model for improving their ecology. The study will also help the PWD understand how storm water pollution affects water quality and, as a consequence, fish and other aquatic life.

Upon completion of the study, PWD will develop a long-range Watershed Management Plan, which will serve as a comprehensive management tool that facilitates restoration and revitalization efforts throughout the watershed.

The FOW is cooperating with the study and is pursuing initiatives aimed at resolving the problems caused by excessive stormwater runoff. For more information see Watershed Protection Initiative and Easements.