SINKHOLE FORMATION AND THEIR AFFECT ON STREAM MIGRATION: EXAMPLES FROM NORTHAMPTON AND ADAMS COUNTIES, PENNSYLVANIA

The Bushkill Creek and Schoeneck Creeks (Northampton County) and the South Branch of the Conewago Creek (Adams County) lie within two different karst regions in Pennsylvania. Along their reaches, these streams are transitional fluvial systems with characteristics attributable to both a straight channel stream and a meandering stream. Both streams are characterized by stretches of deep pools, riffles and periodic mid-stream bars. An inordinate number of sinkholes have formed since the fall of 2000 through the present along the Bushkill Creek that directly influenced the alignment of its main channel. The coalescing of sinkholes along the bank and subsequent pirating of waters from the mainstream channel initiated the creation of a small meander channel. Over time, this meander served as a nick point and a focus for stream bank erosion. Sinkholes continued to form ahead of the prograding stream and threatened to pirate the entire creek. The creation of the meander loop associated with the formation of sinkholes resulted in much speculation as to whether this mechanism has occurred elsewhere. Similar features have been observed along the nearby Schoeneck Creek and along the South Branch of the Conewago Creek in Adams County. What has been observed along the Bushkill may serve as a time-lapse model of stream evolution in a karstic terrain.