Tacony Creek East Oriented Headwaters Segment

· Tacony Creek, valley orientation
Authors

Tacony Creek originates as Tookany Creek just south of the Westminster Theological Seminary in Laverock and flows in an east direction on a route just north of the Arcadia University campus into and then through Glenside to reach its Jenkintown elbow of capture near the SEPTA West Trenton and Landsdale Regional Rail line junction located just north of the Jenkintown-Wyncote station. Baederwood Creek flows in a south and southwest direction to join Tacony Creek near its Jenkintown elbow of capture, with its southwest oriented segment being located at the southwest end of large and 150-foot deep through valley linking the Tacony Creek Jenkintown elbow of capture with the Pennypack Creek valley at Bethayres. To the north of this east-oriented Tacony Creek headwaters segment a northeast trending ridge, referred to here as the Edge Hill Ridge, forms the Wissahickon Creek-Tacony Creek drainage divide. Ridge crest elevations are generally greater than 350 feet and at points exceed 400 feet, although four wind gaps with elevations of 350 or less cross the ridge. Tacony Creek is flowing at an elevation of approximately 300 feet where its headwaters cross route 309 and of less than 200 feet at its Jenkintown elbow of capture.

Prior to south oriented Tacony Creek valley headward erosion to the present day Jenkintown elbow of capture location all elevations throughout what is now the upper Tacony Creek drainage basin and throughout the Sandy Run drainage basin (the west oriented Wissahickon Creek tributary drainage basin just north of the Edge Hill Ridge) were at least as high as the 400 foot plus high elevations found along the present day Edge Hill Ridge. Tacony Creek valley headward erosion occurred when massive and prolonged southwest oriented floods were moving across this former high-level surface. Floodwaters came from the northeast and crossed the Pennypack Creek drainage basin and flowed across the present day Tacony Creek drainage basin to reach what at that time was an actively eroding Wissahickon Creek valley head. Southwest oriented flow moving north of the Wissahickon Creek valley head (in the present day Sandy Run drainage basin) continued in a southwest direction to reach actively eroding south oriented Schuylkill River tributary valleys located west of the present day south oriented Wissahickon Creek drainage basin. Water flowing across what is now the east oriented Tacony Creek headwaters segment flowed to the actively eroding southwest oriented Wissahickon Creek tributary valleys that today drain into the Wissahickon Creek Gorge, such as the Cresheim Creek, Rex Avenue, and Thomas Mills valleys, which like the Wissahickon Creek valley head were eroding headward into erosion resistant bedrock.

When the deep Wissahickon Creek valley head successfully eroded headward across the erosion resistant bedrock surrounding the present day Wissahickon Gorge and into the more easily eroded bedrock found north of the Wissahickon Gorge in the present day present day Whitemarsh Valley region erosion of the that created the present day Edge Hill ridge began began. Southwest oriented flood flow moving to the Morris Arboretum area began to erode deeper valleys headward in a northeast direction along the south side of what is today the Edge Hill erosion resistant ridge. Today a west oriented Wissahickon Creek tributary draining to the Wissahickon Gorge north entrance originates just west of the east-oriented Tacony Creek headwaters at Laverock and a 50-foot deep wind gap links the two opposing valleys. The west-oriented valley eroded headward as it captured southwest oriented flow that had been moving to the southwest oriented Wissahickon Gorge tributary valleys (that had the disadvantage of being eroded across more erosion resistant bedrock). This west oriented valley probably eroded headward into the region where Glenside is now located although the valley floor east of Laverock would have been at an elevation greater than 350 feet (the elevation of the Laverock Wind Gap). Headward erosion of the much deeper south oriented Tacony Creek valley beheaded this newly eroded west oriented valley and in doing so reversed flow on channel the east end to create the start of an east oriented valley on the Tacony Creek headwaters alignment. .

The south oriented Tacony Creek valley was significantly deeper than the west oriented flow channel to the Wissahickon Gorge north entrance that it beheaded and reversed to create an east oriented valley. Had the flow reversal only entailed water already in the beheaded channel the Tacony Creek east oriented headwaters valley would be very shallow and short. However, at that time the present day Whitemarsh Valley area to the north of the present day Edge Hill Ridge had not yet been eroded and southwest oriented flow was spilling over the future ridge location to reach both the actively eroding west oriented Wissahickon Creek tributary valley and the newly reversed east oriented Tacony Creek headwaters segment. At least for a time gradients on the newly created east oriented Tacony Creek headwaters valley were steeper than gradients to the actively eroding Wissahickon Creek valley and the Tacony Creek headwaters valley was able to capture much of the spill over flow. The story of these captures is told by four wind gaps that today are notched into the Wissahickon Creek-Tacony Creek drainage divide. These wind gaps are the Laverock Wind Gap, the Seminary Wind Gap, the Edge Hill Wind Gap, and the Ardsley Wind Gap and each is illustrated and discussed separately.

Figure 1: Tacony Creek east oriented headwaters.

Figure 1: Tacony Creek east oriented headwaters. Tacony Creek originates at the marked Tacony Creek head location and flows in an east direction through Glenside to reach the marked elbow of capture location where Tacony Creek turns to flow in a south-southeast direction to eventually reach the Delaware River. Location 1 is the Laverock wind gap, which was used by west oriented flow moving to what at that time was the actively eroding Wissahickon Gorge prior to being beheaded and reversed by headward erosion of the deeper south oriented Tacony Creek valley. Locations 2, 3, and 4 are wind gaps notched into the Edge Hill Ridge, which today serves as the Wissahickon Creek-Tacony Creek drainage divide. Southwest oriented flow moving on a high-level surface (now removed) north of the Edge Hill Ridge was captured by headward erosion of Tacony Creek valley and helped erode the Tacony Creek headwaters area in Glenside, but was subsequently beheaded when Wissahickon Creek headward erosion through the Wissahickon Gorge area captured all southwest oriented flow north of the present day Edge Hill Ridge, which emerged as southwest oriented flow eroded the more easily eroded bedrock found north of the present day northeast oriented ridge.United States Geological Survey map digitally presented using National Geographic TOPO software.

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