West Branch Chester Creek-Brandywine Creek divide east and south of Chadds Ford, PA and north of Delaware border

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Multiple wind gaps (or water-eroded notches) carved in the West Branch Chester Creek-Brandywine Creek divide east and south of Chadds Ford, PA and north of the Delaware border provide evidence that multiple channels of flood flow moved in a southwest direction to the south oriented Brandywine Creek valley prior to headward erosion of the east, southeast, and northeast oriented West Branch Chester Creek valley, which drains to the southeast oriented Chester Creek valley. Harvey Run is a west oriented tributary with northeast oriented barbed tributaries joins Brandywine Creek at Chadds Ford. South of Harvey Run other tributaries north of the Delaware border flow in southwest directions.

WchesterBrandywineChadds

Figure 1: West Branch Chester Creek-Brandywine Creek divide east and south of Chadds Ford, PA and north of the Delaware border (contour interval is ten feet). See text for detailed discussion. United States Geological Survey map digitally presented using National Geographic TOPO software.

Brandywine Creek flows in a south direction near the west margin of figure 1 and West Branch Chester Creek flows in an east direction across the northeast corner of figure 1. The labeled Pennsylvania-Delaware state boundary is located near the south edge of figure 1. US Highway 1 is shown with a red line extending from West Branch Chester Creek near the northeast corner to figure 1 to the west oriented Harvey Run valley south of the Brandywine Battlefield State Park and then to Chadds Ford where it crosses Brandywine Creek before reaching the west edge of figure 1. Note north oriented Webb Creek, which originates in the south center section of figure I (east of Johnsons Corner), and which joins the West Branch Chester Creek near where Highway 1 crosses it (in northeast corner of figure 1). An old railroad grade is shown extending south and then west in the Webb Creek valley before crossing the West Branch Chester Creek-Brandywine Creek divide just north of Brandywine Summit (location 6) and continuing in a west direction on the Harvey Run valley south side to Chadds Ford.

The old railroad grade crosses the divide at a shallow wind gap carved into the divide (near location 6) with a floor elevation of approximately 360 feet, at least 60 feet lower than hillcrests on either side of the notch. Similar wind gaps or notches can be found at locations 1, 2, 3, 4, and 5 and at several other unmarked locations. The wind gaps at locations 2, 5, and 6 are carved in the West Branch Chester Creek-Brandywine Creek divide while the wind gaps at locations 3 and 4 link a northeast oriented Harvey Run tributary valley with southwest oriented Brandywine Creek tributary valleys and at location 1 links a northeast and northwest oriented Harvey Run tributary headwaters valley with a southwest oriented Brandywine Creek tributary valley. Southwest oriented water flowing to the deep south oriented Brandywine Creek valley eroded all of the labeled (and the unlabeled) wind gaps and initially flowed across a surface at least as high as the highest identifiable wind gap floor elevation (about 380 feet), which means the deep West Branch Chester Creek and Webb Creek valleys did not exist at that time. The multiple wind gaps provide evidence of multiple diverging and converging channels such as might be found in a southwest oriented anastomosing channel complex.

West oriented Harvey Run with several northeast oriented tributary valleys provides intriguing evidence supporting the anastomosing channel complex hypothesis. The Harvey Run headwaters flow in a south-southwest direction into the larger west oriented Harvey Run valley, which extends from location 6 to Chadds Ford. A northeast and northwest oriented tributary originates near location 1 and flows to the west oriented Harvey Run valley. The northeast oriented headwaters of that tributary are located in a through valley extending from a southwest oriented Brandywine Creek tributary valley to locations 1 and 5 and then to an east oriented Webb Creek tributary valley. Locations 3 and 4 link a northeast oriented Harvey Run barbed tributary valley with two different southwest oriented Brandywine Creek tributary valleys. Location 2 links the Webb Creek valley with a southwest oriented Brandywine Creek tributary valley. While not identical floor elevations of all of these wind gaps or notches are similar suggesting they were all eroded by the same event at approximately the same time.

The northeast oriented barbed tributary valleys draining to the west oriented Harvey Run valley and the north and northeast oriented Webb Creek valley suggest there were significant reversals of flow first when the deep west oriented Harvey Run valley eroded headward across the southwest oriented flow moving to locations 3 and 4, second a deep northwest oriented Harvey Run tributary valley eroded headward beheaded the southwest oriented flow moving in the channel marked by locations 5 and 1, and third headward erosion of the still deeper east oriented West Branch Chester Creek valley subsequently beheaded and reversed flow in the south and southwest oriented Webb Creek valley. There must have been significant water moving across divides between the various channels as each of these beheaded flow event permitted the beheaded channels to obtain enough flood flow to erode significant and deep northeast and north oriented valleys

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