Problems troubling the Darby-Cobbs Watershed and Solutions for Cleaner Water

There are many cited problems within the Darby-Cobbs watershed.  Some identified problems are described in the Cobbs Creek Integrated Watershed Management Plan, Darby Creek Watershed Conservation Plan, and the Darby-Cobbs Stormwater Management Plan (as part of PA Act 167):

• Sometimes during dry weather periods, bacteria contamination of the Cobb’s waters prevents achievement of water quality standards that would support swimming or other forms of primary contact recreation in the creek;
• There has been illegal litter and dumping, trash from stormwater discharges, and bank deterioration along the stream corridors;
• Urban runoff deteriorates aquatic and riparian habitat from flash flooding and polluted waters caused by combined sewer overflows after heavy rainfall;
• Impervious areas also reduce the baseflow of streams, which is imperative for aquatic life during drier summer months.

Many of these problems are, in part, from its historic development.  It is an urbanized watershed where development has often occurred at high densities.  Increased impervious (paved) surfaces causes flash flooding, especially in the lower watershed, that erode stream banks, scour away the natural pools and riffles critical to aquatic biota (Darby Creek Watershed Conservation Plan, 2005). 

Assessments, Plans, and Current Data Collection

Plans and assessments for the Darby-Cobbs watershed are a little dated—most are about a decade old.  The key documents that the PWD and its partners use to implement progress towards improving the watershed include the following:

• 2001 Trail Master Plan for Cobbs Creek Park
• 2004 Comprehensive Characterization Report
• 2004 Integrated Watershed Management Plan (IWMP)
• 2004 Stormwater Management Plan, Act 167
• 2005 Darby Creek Watershed Conservation Plan
• 2006 Cobbs Creek Wetlands Assessment

Leadership in the Darby-Cobbs Watershed

The Philadelphia Water Department (PWD) initiated the Darby-Cobbs Watershed Partnership (DCWP) and continues to financially support this important effort to unite watershed stakeholders in a variety of ways.   Philadelphia lies at downstream of their suburban neighbors in Delaware, Chester, Montgomery, and Bucks counties and watershed-wide solutions require coordination these municipalities.  The PWD notes, “without their cooperation and commitment to take similar protection measures, the efficacy of [the PWD’s] efforts would be limited” (PWD 2011).

Defining the Darby-Cobbs Watershed

Darby Creek originates in Easttown Township in Chester County and flows in a south/southeast direction through most of the watershed.  It changes direction in the southern portion of the watershed where it flows west/southwest direction until it discharges into the Delaware River between the Townships of Ridley and Tinicum. 

Darby Creek’s watershed is often referred to as the “Darby-Cobbs watershed” since its largest tributary, Cobbs Creek, is approximately one third of the Darby Creek watershed. The Darby-Cobbs watershed has a total area of 77.2 square miles [Source].

The major tributaries of Darby Creek:

• Cobbs Creek
• Little Darby Creek
• Julip Run
• Ithan Run
• Meadowbrook Run
• Wigwam Run
• Foxes Run 
• Muckinipattis Creek