Aligned and barbed tributaries are commonly found along south and southeast oriented Delaware River valley segments marking the Pennsylvania and New Jersey border. One such region is the New Hope, PA and Lambertville, NJ region where the Delaware River flows in a southeast and south direction as seen in figure 1. Most tributaries from the New Jersey side (east) flow in southwest directions to enter the south oriented Delaware River. Streams on the Pennsylvania side (west) however flow in northeast directions to enter the south oriented Delaware River valley as barbed tributaries. Why are streams on the Pennsylvania side aligned in northeast directions so as to join the south oriented Delaware River as barbed tributaries while many, but not all streams on the New Jersey side tare aligned in a southwest direction?
Figure 1; Delaware River valley near New Hope, PA and Lambertville, NJ. Aquetong Creek, Dark Hollow Run, and Rabbit Run are among the northeast oriented streams flowing to the Delaware River as barbed tributaries. United States Geological Survey map digitally presented using National Geographic TOPO software.
Delaware River tributaries provide clues to drainage routes that can be used to reconstruct drainage routes that existed prior to Delaware River valley headward erosion across the figure 1 map region. The southwest oriented New Jersey tributaries and northeast oriented Pennsylvania tributaries suggest the deep Delaware River valley eroded headward across a southwest oriented anastomosing channel complex. Anastomosing channel complexes form during large floods as diverging and converging flood flow channels move immense water volumes across a region. If correctly interpreted southwest oriented floodwaters moving across the figure 1 map region flowed on a surface at an elevation at least as high as the Delaware River-Neshaminy Creek drainage divide to the west (more than 300 feet while the Delaware River elevation in figure 1 is less than 75 feet, although sea level may have been lower than it is today).
South of the figure 1 map region the Delaware River valley in the Washington Crossing area has similar aligned drainage and barbed tributaries as illustrated and described in a separate essay on this website. Further south the Delaware River turns to flow in a southwest direction to reach Philadelphia. The southwest oriented Delaware River valley segment was probably eroded headward along what at that time was a major southwest oriented flood flow channel. The deep Delaware River valley head turned from eroding headward along one specific southwest oriented flood flow channel to eroding headward across southwest oriented flood flow channels into the Washington Crossing and New Hope areas and then further north. By doing so the actively eroding Delaware River valley head captured the southwest oriented flood flow channels and those captured flood flow channels began to erode southwest oriented valleys into the newly eroded southeast oriented Delaware River valley wall until the southwest oriented flood flow ended.
Headward erosion of the deep Delaware River valley also beheaded Pennsylvania side southwest oriented flood flow channels in sequence from south to north. Water on northeast ends of beheaded flood flow channels reversed direction to flow in northeast directions to the newly eroded and much deeper south-oriented Delaware River valley. Because flood flow channels diverged and converged and flood flow channels were beheaded one at a time from south to north, reversed flow in a newly beheaded flood flow channel captured flood flow from yet to be beheaded flood flow channels north of the actively eroding Delaware River valley head. Such captures provided the water volumes necessary to erode the northeast oriented Delaware River tributary valleys seen in figure 1. In time Delaware River valley headward erosion captured all flood flow channels supplying floodwaters to the Pennsylvania side and the Pennsylvania side tributaries now flow in those reversed (northeast oriented) flood flow eroded valleys.
Leave a Reply