Tacony Creek Cheltenham Elbow of Capture

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Tacony Creek (known also as Tookany Creek further upstream and as Frankford Creek further downstream) flows in roughly a southeast direction from Elkins Park to between Cheltenham and Ashmead Village and then turns abruptly to flow in a southwest direction between Ashmead Village and Lawndale. This abrupt change of direction is here named the Cheltenham Elbow of Capture and can be linked with a Pennypack Creek elbow of capture to the northeast and possibly with Schuylkill River elbows of capture to the southwest. Figure 1 below shows the Cheltenham Elbow of Capture at location 1 and the related Pennypack Creek elbow of capture at location 2.

PennypackTacony

Figure 1: Tacony Creek Cheltenham Elbow of Capture is found at location 1 and the Pennypack Creek elbow of capture is found at location 2. United States Geological Survey map digitally presented using National Geographic TOPO software.  

Both Tacony Creek and Pennypack Creek have eroded 80-100 foot deep valleys into the underlying bedrock (they both have deeper valleys further upstream). Bedrock in this region is erosion resistant metamorphic and igneous material, although urbanization obscures most bedrock details. Both streams are tributaries to the southwest oriented Delaware River segment, which is located south of the map area, and regional elevations decrease in a south direction as the Delaware River is approached. South and west of figure 1 Tacony Creek turns to flow in a south and south-southeast direction (where it is known as Frankford Creek) before reaching the Delaware River.

While evidence seen in figure 1 is limited there are hints of a former aligned drainage pattern in the southwest oriented Tacony Creek segment downstream from location 1, a southwest oriented Tacony Creek tributary flowing along the Montgomery County-Philadelphia County line, and a southwest oriented tributary to Jenkintown Creek (the “Creek” which joins Tacony Creek just north of Ashmead Village). In addition the southwest and northeast oriented Pennypack Creek segments and the northeast oriented tributary joining Pennypack Creek at location 2, support the aligned drainage hypothesis.

If correctly interpreted the aligned drainage evidence is probably a relic of what were once diverging and converging southwest oriented flood flow channels that crossed the region. The southwest oriented Delaware River valley to the south of the map area would be further evidence and probably eroded headward along one of the southwest oriented flood flow channels. The Tacony Creek valley eroded headward from the newly eroded Delaware River valley to capture southwest oriented flood flow moving in flow channels located north and west of the actively eroding Delaware River valley.

The southwest oriented Tacony Creek valley segment downstream from the Cheltenham Elbow of Capture was eroded headward along a captured southwest oriented flow channel. Before being captured by Tacony Creek valley headward erosion water in that channel probably continued in a southwest direction to a southwest oriented Schuylkill River valley segment downstream from the Roosevelt Avenue Bridge. Urban development has obscured much of the evidence along the former flow route although at least segments of the flow channel route may have been used by railroad builders to cross the Schuylkill River-Tacony Creek drainage divide in the Wayne Junction area.

Much more obvious is how the southwest oriented Tacony Creek segment downstream from the Cheltenham Elbow of Capture at location 1 is aligned with the southwest and northeast oriented Pennypack Creek elbow of capture at location 2 and also with the northeast oriented tributary joining Pennypack Creek at location 2. The Pennypack Creek elbow of capture at location 2 was probably where two southwest oriented flood flow channels converged to form a single flood flow channel that continued in a southwest direction to location 1 and then along the present day southwest oriented Tacony Creek alignment. Headward erosion of the deep Pennypack Creek valley beheaded and reversed flow on the northeast end of the southern converging channel. The reversed flow then captured southwest oriented flow still moving in the northern converging channel to create the abrupt southwest to northeast Pennypack Creek elbow of capture at location 2.

Creation of the Pennypack Creek elbow of capture also beheaded the southwest oriented flow route to location 1. Flood flow on the northeast end of the beheaded flow channel reversed its flow direction to flow to the much deeper and newly eroded Pennypack Creek valley and to create the northeast oriented tributary joining Pennypack Creek at location 2. The CSX rail freight line between locations 1 and 2 may use the former southwest oriented flow channel route to cross the Pennypack Creek-Tacony Creek drainage divide, although urbanization has obscured most of the evidence.

The actively eroding Tacony Creek valley head could no longer received large volumes of southwest oriented flood flow after the Pennypack Creek capture of the converging southwest oriented flow channels at location 2, which ended its headward erosion in a northeast direction. However the newly eroded Tacony Creek valley was deep enough that it captured flood flow from north of the actively eroding Pennypack Creek valley head. In other words there still was plenty of flood water moving north of location 1 and as that flood flow moved to the newly eroded and deep Tacony Creek valley it enabled the Tacony Creek valley to erode headward in a north and northwest direction across still active southwest oriented flood flow channels before Pennypack Creek valley headward erosion also captured that southwest oriented flood flow.

 

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