Watson Creek is a relatively minor stream located east of Doylestown and flows in a south and northeast direction to join southeast oriented Mill Creek, which then joins southeast and south oriented Neshaminy Creek. In its short distance Watson Creek passes through two water gaps and abruptly changes direction at an elbow of capture. The Watson Creek route is shown in figure 1 where Watson Creek originates near location 1, passes through its first water gap at location 2, passes through its second water gap at location 3, and abruptly changes its flow direction at location 4, and finally joins Mill Creek as a barbed tributary at location 5. Also of interest in figure 1 is the Mill Creek water gap at location 6, the elbow of capture (Lahaska Creek) at location 7, and headwaters of a southwest and south oriented Neshaminy Creek tributary at location 8.
Figure 1: Watson Creek drainage basin east of Doylestown, PA. See text for discussion. United States Geological Survey map digitally presented using National Geographic TOPO software.
The south oriented Watson Creek drainage route cuts across southwest-to-northeast streamlined ridges seen in figure 1 before turning to flow in a northeast direction on a valley floor between two of the streamlined ridges. However, instead of continuing to flow between the ridges Watson Creek joins south and southeast oriented Mill Creek to cut across another streamlined ridge at location 6. The streamlined ridges are composed of erosion resistant bedrock while the valleys are underlain by more easily eroded material. The problem the Watson Creek route raises is how was a stream with such a small drainage basin able to cut water gaps across the streamlined ridges?
Obviously Watson Creek as it exists today did not erode the valleys between the streamlined ridges and probably did not erode the water gaps at locations 2 and 3. To visualize how the Watson Creek drainage route evolved first imagine the region prior to the erosion of the valleys between the streamlined ridges. In other words, imagine a high-level surface, at least as high as the top of Buckingham Mountain (northeast of location 6), extending across southeast Pennsylvania. Also imagine massive and prolonged southwest oriented floods being channeled between southwest-to-northeast oriented erosion resistant bedrock units not just in the figure 1 map region, but also throughout southeastern Pennsylvania.
Not seen in figure 1 is the Delaware River, which east of figure 1 flows in a south direction before turning to flow in a southwest direction south of figure 1. The deep Delaware River valley eroded headward into this high-level surface along what was probably a major southwest oriented flood flow channel to create its present day southwest oriented valley and then turned to erode headward across the southwest oriented flood flow channels to create its present day south oriented valley. As the southwest oriented Delaware River valley eroded headward south oriented tributary valleys eroded headward from the newly eroded Delaware River valley to capture southwest oriented flood flow moving north and west of the Delaware River valley.
Also not seen in figure 1 is east, southeast, and south oriented Neshaminy Creek, which flows south and west of figure 1 and eventually reaches the southwest oriented Delaware River. The Neshaminy Creek valley eroded headward from the actively eroding Delaware River valley to capture southwest oriented flood flow moving north and west of the newly eroded Delaware River valley and to divert that captured floodwater to the much deeper Delaware River valley. Prior to headward erosion of the Neshaminy Creek valley floodwaters moving across the high-level surface that existed in the figure 1 map area were flowing to south oriented Schuylkill River tributary valleys (e.g. Wissahickon Creek). At that time floodwaters may have begun to cut shallow channels between the present day streamlined ridges seen in figure 1 although the real change occurred as the deep Neshaminy Creek valley and its tributary valleys eroded headward into the region.
Imagine now the deep Neshaminy Creek valley being eroded headward across the southwest oriented flood flow in the region just south and west of figure 1. The southwest oriented flood flow then began to erode deep valleys headward between and in some cases across the erosion resistant ridges. But as those deep southwest oriented channels were being eroded headward in a northeast direction the deep Mill Creek valley eroded headward from the newly eroded southeast oriented Neshaminy Creek valley and began to capture the southwest oriented flood flow in the figure 1 map area and diverted the water more directly to the deep Neshaminy Creek valley.
In other words headward erosion of the deep Mill Creek valley beheaded southwest oriented flood flow routes to the actively eroding Neshaminy Creek valley (which was by that time capturing floodwaters moving north and west of the actively eroding Mill Creek valley head). At location 5 the deep Mill Creek valley captured a southwest oriented flood flow channel on the southwest oriented Lahaska Creek alignment. Floodwaters on the northeast end of the beheaded flood flow channel reversed flow direction to create the northeast oriented Watson Creek segment (between locations 4 and), which then captured floodwaters moving north and west of the Mill Creek valley head and the captured floodwaters enabled the deep Watson Creek valley to erode headward first along the beheaded flood flow route and then in a north direction across southwest oriented flood flow channels being carved between the erosion resistant ridges.
Headward erosion of the deep Mill Creek valley (east of Buckingham in figure 1) eventually captured the southwest oriented flood flow moving to the actively eroding Watson Creek drainage basin. Headward erosion of the deep south oriented Delaware River valley east of figure 1 ended all southwest oriented flood flow across the figure 1 map region and the Watson Creek drainage basin and Mill Creek drainage basin have not been significant altered since that time.