Southeast End of the Drainage Divide between Chester Creek and West Branch Chester Creek at Chester Heights, PA

Authors

Figure 1 illustrates the drainage divide area at Chester Heights between Chester Creek and West Branch Chester Creek and also illustrates at locations 1 and 2 two well-defined gaps (or notches) linking northeast oriented tributary valleys with southwest oriented tributary valleys. Note how Chester Creek flows in a southeast direction from the north center edge of figure 1 to join West Branch Chester Creek and then in an east and south direction to the east edge of figure 1. East of figure 1 Chester Creek again flows in a southeast direction and eventually joins the southwest oriented Delaware River. Also note how West Branch Chester Creek flows in a southeast direction from the west center edge of figure 1 before turning abruptly to flow in a northeast direction to join Chester Creek.

ChesterHeights

Figure 1: Southeast end of the drainage divide between Chester Creek and West Branch Chester Creek at Chester Heights, PA. See text for detailed discussion. United States Geological Survey map digitally presented using National Geographic TOPO software.

The contour interval for figure 1 is ten feet and the floor of the gap (or notch in the drainage divide) at location 1 has an elevation of between 290 and 300 feet. Elevations on either side of the gap rise to more than 350 feet indicating the gap is at least 50 feet deep. The gap floor at location 2 has an elevation of between 260 and 270 and elevations east of the gap along the Chester Creek-West Branch Chester Creek divide rise to more than 340 feet and west of the gap elevations rise to more than 350 feet suggesting the gap at location 2 is at least 70 feet deep. Note how a rail line uses the gap at location 2 to cross the Chester Creek-West Branch Chester Creek drainage divide.

The gaps at locations 1 and 2 and the northeast oriented and southwest oriented tributary valleys they link along with the northeast oriented West Branch Chester Creek valley segment provide evidence of what were three closely spaced and roughly parallel southwest oriented flood flow channels that existed when the southeast oriented Chester Creek valley eroded headward into the region from what at that time was a newly eroded and much deeper southwest-oriented Delaware River valley. At that time massive and prolonged southwest oriented floods crossed southeast Pennsylvania and the Delaware River valley eroded headward along a major southwest oriented flood flow channel.

Southeast oriented tributary valleys such as the Chester Creek valley then eroded headward in sequence (from the southwest to the northeast) to capture southwest oriented flood flow moving north and west of the Delaware River. Floodwaters moving across the Chester Heights region were moving in anastomosing (or diverging and converging) complexes of shallow southwest oriented channels, evidence for which is preserved in the northeast and southwest orientation of the Chester Creek and West Branch Chester Creek tributary valleys and in the shallow gaps (such as those at locations 1 and 2) that link the northeast and southwest oriented tributary valleys as seen at locations 1 and 2.

Looking at figure 1 headward erosion of the deep Chester Creek valley beheaded a much shallower southwest oriented flood flow channel on the alignment of the present day northeast oriented West Branch Chester Creek segment. Water on the northeast end of the beheaded flood flow channel reversed direction to move to the deeper Chester Creek valley. Because the flood flow channels were shallow and diverged and converged the reversed flow captured southwest oriented flood flow moving north and west of the actively eroding Chester Creek valley head. This captured flood flow included water crossing the present day drainage divide at locations 2 and 1 and moved in a southeast direction along the present day southeast oriented West Branch Chester Creek segment to reach the reversed flood flow on the present day northeast oriented West Branch Chester Creek segment and helped erode the West Branch Chester Creek valley seen today.

As the southeast and northeast oriented West Branch Chester Creek valley eroded headward to capture the southwest oriented flood flow moving north and west of the actively eroding Chester Creek valley head the deep Chester Creek valley continued to erode headward across the southwest oriented flood flow channels and beheaded and reversed flood flow channels that West Branch Chester Creek valley headward erosion had previously captured. For example, Chester Creek valley headward erosion beheaded and reversed southwest oriented flow that had been moving across the present day gap at location 2. Apparently that reversed flow was able to capture some water moving along the still actively eroding southeast oriented West Branch Chester valley. The captured water helped erode what is today a significant northeast oriented Chester Creek tributary valley. The process was repeated as the deep southeast oriented Chester Creek valley beheaded and reversed flow moving across the gap at the present day location 1.

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