Sources: Valley Creek Trustee Council, National Park Service, Pennsylvania Fish and Boat Commission
The Valley Creek Watershed encompasses 23.4 square miles primarily (90%) within Tredyffrin and East Whiteland Townships, Chester County, Pennsylvania. Approximately 10% of the watershed is within small parts of Charlestown and Willistown Townships and the Borough of Malvern (Chester County) and Upper Merion Township (Montgomery County). The last two miles of Valley Creek pass through Valley Forge National Historical Park to the confluence with the Schuylkill River (See maps on right).
Valley Creek has been designated an “Exceptional Value” Watershed, which affords it the Pennsylvania Department of Environmental Protection’s highest level of protection. Valley Creek also has been designated a “Class A Wild Trout Fishery” by the Pennsylvania Fish and Boat Commission. These designations demonstrate the significance of this resource at the local, state and national level and to the residents of the watershed.
The Valley Creek Watershed is bounded on the north and south by hills of resistant crystalline rock. The floor of the watershed is a carbonate (or karst) valley that presents challenges for some of the restoration techniques that are evaluated in this plan. Sixty-eight percent of the basin is underlain by Cambrian and Ordovician limestone and dolomite (Sloto 1990). The stream channel has changed considerably over the decades due to both natural processes (erosion and deposition) and human influences.
Valley Creek flows from southwest to northeast, joining its main tributary, Little Valley Creek, 3.1 miles above the confluence with the Schuylkill River. The subbasins of Little Valley Creek and its tributaries represent about one-third of the acreage of the watershed (See map on right). Overall, approximately 30, mostly unnamed, tributaries flow into Valley and Little Valley Creeks from the surrounding watershed. About one-half of these tributaries flow perennially; the remainder flow intermittently.
A U.S. Geological Survey stream gauge is located on Valley Creek just upstream of Valley Forge National Historical Park. Installed in 1981, the stream gauge reflects a 20.8 square-mile drainage area within the watershed. The available quantitative flow data for the Valley Creek Watershed comes from this gauge and provides trends over time in both baseflow and extreme high water events.
Baseflow is the amount of stream flow coming from groundwater. Groundwater comprises a large percentage of the flow to Valley Creek. Between 1983 to 1987, groundwater was found to comprise 76% of the flow of Valley Creek. Groundwater flows through a network of interconnected secondary openings since primary porosity is virtually nonexistent (Cowardin et al. 1979). Some of these openings have been enlarged by the collapse of dissolution openings that causes subsequent subsidence. Fifty percent of water-bearing zones are present within 100 feet of the land surface, and 81% are within 200 feet (Sloto 1990). Significant groundwater recharge supports a cold water aquatic community for brown trout within Valley Creek. The significant contribution of groundwater to the flow within Valley Creek maintains the water temperature at approximately 55 degrees F.
Average baseflow in Valley Creek between 1983 to 1987, was 26.15 cubic feet per second (cfs). The official lowest 7-day flow during the past 10-year period was an average of 10.7 cfs, or less than half of the 1983-87 average baseflow. The lowest average flow for one-day was 7.4 cfs. There were also 10 days in 1999 when mean daily flow flows were below 9.6 cfs (pers. comm. Kirk White, USGS 2003). The highest instantaneous flow in the past 20 years was 6,280 cfs in September 1999 during Hurricane Floyd.
Groundwater flows to the northeast toward the Schuylkill River within the Valley Creek Watershed (Sloto 1990). The Valley Creek basin receives an estimated 0.75 million gallons per day (mgd) from the adjacent West Valley Creek basin and 0.85 mgd from the southeastern side of the basin. The Valley Creek basin loses 1.76 mgd on the east side of the basin, for a net hydrologic loss in basin groundwater of 0.16 mgd.
The basin also is subject to a modest amount of water withdrawals. A regional water company has public drinking water wells and there are withdrawals for quarrying and residential wells. During the highest groundwater flow periods, up to 1 mgd can infiltrate public sewer lines (VFSA 2001). Groundwater withdrawals are estimated to be 10% of the water available for stream recharge (Sloto 1990). The Chester County Water Resources Authority determined that groundwater withdrawals or exports at these modest levels do not pose a significant threat to the Valley Creek Watershed (CCWRA 2002).
There are numerous water quality and water quantity challenges to maintaining the health of the Valley Creek Watershed. Many of the threats to Valley Creek are related to changes in land use and urbanization of the watershed. As in many other watersheds near major urban centers, land use over the last 50 years is characterized by change from a primarily agricultural landscape to more industrial uses such as corporate and industrial centers, strip malls, residential developments and associated infrastructure (e.g. highways). Between 1987 and 1995, the amount of impervious surface area within the Valley Creek Watershed increased from 9% to 18%, with some estimates as high as 24% impervious (CCWRA 2002)(See map on right). Chester County officials predict that the amount of impervious surface area will increase to 26% by the year 2020. An increase in impervious surface area has resulted in an increase in the frequency and intensity of flood events and associated impacts such as streambank destabilization, erosion, and sedimentation. Stormwater also may have significant impacts on water temperature. Within Valley Forge National Historical Park during one storm event in 2005, water temperature over a 12 hour period increased from 64 degrees F to 70 degrees F – a critical difference for temperature sensitive coldwater species such as trout.
In addition to the non-point source pollution from stormwater, point-source discharges also threaten stream resources. For example, in the mid-1980’s the stream was contaminated with polychlorinated biphenyls (PCB’s) originating from the 28-acre Paoli Rail Yard site (See map on right). PCB’s were documented in three tributaries near the Paoli Rail Yard, as well as Little Valley Creek and Valley Creek. In addition to the Paoli Rail Yard there are several other contaminated sites that present potential water quality challenges for Valley Creek.
Examples of up-coming or on-going activities within the watershed that may positively or negatively affect future water quality and quantity include:
- An Act 167 stormwater management study by the Water Resources Authority of Chester County
- Development of a total maximum daily load program by Pennsylvania Department of Environmental Protection
- Widening of Route 202 from four lanes to six lanes – Pennsylvania Department of Transportation intending to mitigate the runoff
- Insertion of a slip ramp and the 6-mile widening of Pa Turnpike from Rte. 29 to Rte 422
- The redevelopment of the former Worthington Steel site at the upstream end of Little Valley Creek
- Continuing work to remedy several hazardous waste sites in the watershed
- Implementation of the Valley Creek Coalition agreement with Pennsylvania Department of Environmental Protection for improved stormwater management on new or redeveloped lands
- Purchases of land for parks, open space or preservation by townships and land conservancies
- Stream stabilization projects in Valley Forge National Historical Park, undertaken by the National Park Service and Pennsylvania Department of Transportation
Chapter 3 of the Valley Creek Restoration Plan describes the Valley Creek Watershed in more detail (http://www.valleyforgetu.org/wp-content/uploads/Valley-Creek-Restoration-Plan.pdf)
Other descriptive material for Valley Creek is contained in the Fluvial Geomorphology study prepared for Valley Creek Watershed by the Water Resources Authority of Chester County (http://dsf.chesco.org/water/cwp/view.asp).