East and West Branch Brandywine Creek headwaters between Welsh Mountain and the Baron Hills

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The East and West Branches of Brandywine Creek both originate in the area east of Honey Brook and between Welsh Mountain and the Baron Hills. From their common headwaters area the two streams diverge to take completely different south oriented routes to cross the east-northeast oriented Chester Valley and to carve separate narrow and deep valleys in the highlands south of the Chester Valley before finally converging to form Brandywine Creek, which then flows to the Delaware River at Wilmington, Delaware. Why would two streams originate in the same location, diverge to flow along completely different routes, and then eventually converge to form a single stream?

Also originating in the region between Welsh Mountain and the Baron Hills are west and southwest oriented Pequea Creek, which flows to the Susquehanna River, and east oriented South Branch French Creek, which joins French Creek and flows to the Schuylkill River. The Honey Brook basin between Welsh Mountain and the Baron Hills, while surrounded by hills, is a triple drainage divide where water flows on four different routes to three major rivers. This entry looks at the drainage divide between the East and West Branches of Brandywine Creek and separate entries address the drainage divide between West Branch Brandywine Creek and Pequea Creek and the drainage divide between the East Branch Brandywine Creek and the South Branch French Creek.

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Figure 1: Drainage divide area between the East Branch Brandywine Creek and the West Branch Brandywine Creek in the Honey Brook basin between Welsh Mountain (near northwest corner) and the Baron Hills (along south center edge). United States Geologic Survey map digitally presented using National Geographic TOPO software. 

Figure 1 illustrates the East and West Branch Brandywine Creek headwaters area in the Honey Brook basin between Welsh Mountain and the Baron Hills. Welsh Mountain can be seen crossing the figure 1 northwest corner and the Baron Hills can be seen along the figure 1 south center edge. The West Branch Brandywine Creek flows from north of the town of Honey Brook in a southeast direction to Icedale (near the figure 1 south edge). After flowing around the Baron Hills east end the West Branch Brandywine Creek (south of figure 1) turns to flow in a southwest direction before turning in a south direction to cross the Chester Valley and to enter the South Valley Hills. In the highlands south of the Chester Valley the West Branch Brandywine Creek flows in a southeast direction with some jogs to the northeast before joining the East Branch to form Brandywine Creek.

The East Branch Brandywine Creek headwaters are found near Isabella (near figure 1 north edge-east of center) and flow in east, south, and east directions to the figure east edge (north of center). East of figure 1 the East Branch Brandywine Creek flows in a southeast direction before eventually turning to flow in a south direction across the east-northeast oriented Chester Valley and then enters a south-southeast oriented valley carved in the highlands south of the Chester Valley before finally joining the West Branch Brandywine Creek to form south and southeast oriented Brandywine Creek.

Of special interest in figure 1 is the East Branch headwaters area in the small lake located between Isabella and Church Hill. West of Church Hill is a larger reservoir, which drains in a southeast and then in a northeast direction to join the east oriented East Branch. Note how the railroad line from Fontaine (near figure 1 north center edge) to Birdell (near figure 1 south center edge) crosses the drainage divide between the East Branch and the West Branch near the town of Suplee at an elevation of 660 feet. A road west of Suplee also crosses the drainage divide at an elevation of less than 660 feet. These and other somewhat higher shallow valleys cross the drainage divide and provide evidence water once flowed from the East Branch drainage basin to the West Branch drainage basin. If so, why did water flow between the two divergent drainage routes and how was the drainage divide between the East and West Branches of Brandywine Creek created?

To understand how this situation could develop go back to the time when the entire figure 1 map region was at least as high or higher than the present day Welsh Mountain crest (more than 1000 feet, although the region probably had a different elevation related to sea level at that time). At that time there was no deep Honey Brook basin between Welsh Mountain and the Baron Hills. Instead massive and prolonged southwest oriented floods from north and east of the present day Schuylkill River valley moved across the region to what at that time was the actively eroding and deep west and southwest oriented Pequea Creek valley (west of figure 1). The Pequea Creek valley eroded headward from what was at that time a newly eroded south-oriented Susquehanna River valley and had the advantage of eroding headward across relatively easy to erode carbonate bedrock.

Why massive and prolonged southwest oriented floods? Local drainage routes would not be capable of removing the volume of erosion resistant material that once occupied the region between Welsh Mountain and the Baron Hills. Not only was that material removed, the entire Pequea Creek drainage basin west of figure 1 was eroded. Further, similar erosion was occurring north and west of Welsh Mountain and south and east of the Baron Hills. In other words volumes of southwest oriented flow had to be great enough to deeply erode the entire region surrounding what are today high ridges of the region’s most erosion resistant bedrock. Such water movements suggest floodwaters moved in a southwest oriented anastomosing channel complex that was being captured by headward erosion of the deep south-oriented Susquehanna River valley to the west.

Looking at figure 1 there is evidence multiple southwest-oriented flood flow channels crossed the present day drainage divide between East Branch Brandywine Creek and West Branch Brandywine Creek. These multiple channels suggest diverging and converging southwest oriented flow channels once crossed the present day Honey Brook basin and were captured first by headward erosion of the deeper West Branch Brandywine Creek valley and subsequently by headward erosion of the East Branch Brandywine Creek valley. But even more significant, the fact both the East and West Branches Brandywine Creek originate in the same region and then diverge before converging suggests they were eroded as diverging and converging flood flow channels in what was a south and southeast oriented anastomosing channel complex that eroded headward from what was probably a newly eroded Delaware River valley to capture floodwaters from a southwest oriented anastomosing channel complex that was eroding headward from what was probably a newly eroded Susquehanna River valley. The flood water source cannot be determined from southeast Pennsylvania evidence, although gigantic melt water floods from a large North American ice sheet might be the source.

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