The Delaware River flows in a southeast direction to the Washington Crossing area and then gradually turns to flow in a south-southeast direction. As seen in figure 1 closely spaced and aligned southwest oriented tributaries enter the Delaware River from the New Jersey side (east). Also as seen in figure 1 many streams from the Pennsylvania side (west) flow in northeast directions to enter a south oriented valley as barbed tributaries. Some but not all of the closely spaced tributaries on the Pennsylvania side are oriented in northeast directions, although others are oriented in east-northeast directions. Why would multiple streams on the Pennsylvania side flow in northeast directions to join the south oriented Delaware River as barbed tributaries, especially when the closely spaced New Jersey tributaries are all aligned in a southwest direction?

Figure 1; Delaware River valley in Washington Crossing area. Note aligned southwest oriented tributaries on the New Jersey side (east) and northeast oriented and barbed tributaries on the Pennsylvania side (west). United States Geological Survey map digitally presented using National Geographic TOPO software. 

The Delaware River tributaries provide clues to drainage routes that existed prior to Delaware River valley headward erosion across the figure 1 map region. The closely spaced and aligned 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 50 feet today, although sea level may have been much lower at that time than it is today).

South of the figure 1 map region 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. South and east of figure 1 the deep Delaware River valley head turned from eroding headward along one specific southwest oriented flood flow channel to eroding headward across the southwest oriented flood flow channels. By doing so the actively eroding Delaware River valley 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. For reasons not determinable from the figure 1 map evidence the southwest oriented flood flow then ended and today southwest oriented Delaware River tributaries flow in those valleys.

Headward erosion of the deep Delaware River valley also beheaded the Pennsylvania side southwest oriented flood flow channels in sequence from south to north. Water on the northeast ends of the beheaded flood flow channels reversed direction to flow in a northeast direction to the newly eroded and much deeper southeast-oriented Delaware River valley. Because the flood flow channels diverged and converged and the 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 east-northeast and 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 flood flow eroded valleys.