Little Neshaminy Creek originates as a northeast oriented stream and then turns to flow in an east, southeast, and east direction to eventually join southeast and south oriented Neshaminy Creek, which then flows to a southwest oriented Delaware River segment. Wissahickon Creek originates as a southwest oriented stream just north of the northeast oriented Little Neshaminy Creek headwaters and then turns to flow in a south, east, southeast, and south direction to eventually join the southeast oriented Schuylkill River. Southwest oriented tributaries join the south and southeast oriented Wissahickon Creek segments while northeast oriented tributaries join the east and southeast oriented Little Neshaminy Creek segments. Shallow through valleys crossing the Little Neshaminy Creek-Wissahickon Creek drainage divide link headwaters of the northeast oriented Little Neshaminy Creek tributaries with southwest oriented Wissahickon Creek tributaries.
Figure 1: Little Neshaminy Creek-Wissahickon Creek drainage divide area west of the Willow Grove Naval Air Station. See text for detailed description. United States Geological Survey map digitally presented using National Geographic TOPO software.
Figure 1 illustrates the Little Neshaminy Creek-Wissahickon Creek drainage divide area west of the Willow Grove Naval Air Station. A southeast oriented Little Neshaminy Creek segment crosses the figure 1 northeast corner while a south oriented Wissahickon Creek segment can be seen in the southwest corner of figure 1. Trewellyn Creek and Willow Run are the two named southwest oriented Wissahickon Creek tributaries seen in figure 1. Park Creek is a northeast, south, and northeast oriented Little Neshaminy Creek tributary seen in figure 1. Location 1 marks the shallow through valley linking the southwest oriented Trewellyn Creek valley with the northeast oriented Park Creek headwaters valley and has an elevation approximately 40 feet lower than the drainage divide elevations on either side. Location 2 marks the shallow through valley linking the southwest oriented Willow Run valley with the valley of a northeast oriented tributary to the downstream northeast oriented Park Creek segment and has an elevation almost 100 feet lower than the drainage divide elevation on either side.
The shallow through valleys seen at locations 1 and 2 and along similar shallow through valleys linking other southwest and northeast oriented tributary valleys provide evidence that multiple channels of southwest oriented water once flowed across the Little Neshaminy Creek-Wissahickon Creek drainage divide. The presence of multiple flow routes suggests massive and prolonged southwest oriented floods rather than precipitation-generated runoff. Floodwaters came from the northeast and probably were derived from a melting continental ice sheet. Floodwaters initially flowed to and then along the Chester Valley to the present day Susquehanna River drainage basin before being captured in sequence by headward erosion of the West Brandywine Creek, East Brandywine Creek, Schuylkill River, and Wissahickon Creek valleys. Subsequently Little Neshaminy Creek valley headward erosion captured the southwest oriented flood flow to create the Little Neshaminy Creek-Wissahickon Creek drainage divide seen in figure 1. The northeast oriented tributary valleys were eroded by reversed flood flow moving to the much deeper Little Neshaminy Creek valley. The south oriented Park Creek valley segment may have eroded headward from the southwest oriented Willow Run valley to capture southwest oriented flood flow moving to what at that time was probably the actively eroding Trewellyn Creek valley and may have beheaded and reversed the northeast end of the southwest oriented flood flow channel responsible for supplying water that was eroding the Trewellyn Creek valley. Headward erosion of the deeper Little Neshaminy Creek valley beheaded and reversed southwest oriented flood flow to the southwest oriented Willow Run valley and in the process captured what is now the south oriented Park Creek segment. Southwest oriented flood flow to the Little Neshaminy Creek valley ended when headward erosion of the Neshaminy Creek valley to the east and north of figure 1 captured southwest oriented floodwaters to the figure 1 region.