GEOMORPHIC ASSESSMENT OF BACHMAN RUN IN THE LITTLE CONESTOGA WATERSHED, LANCASTER PA

Over the last few decades there have been intensive efforts to improve the water quality of the Chesapeake Bay. EPA point source pollution regulations are effectively controlling some of the pollutants that enter the Bay, however, non-point sources continue to be a problem. The Susquehanna watershed and particularly the Conestoga River is the main source of pollutants to the Bay. This study, part of a KECK Geology Consortium funded project, focused on the geomorphology of Bachman Run, a tributary of the Little Conestoga Creek, which is in turn a major tributary of the Conestoga River. The Bachman Run watershed covers an area of 6.2 square miles. Land use of the watershed is 10% urban, 85% agricultural, and 4% forest land but the area is rapidly being suburbanized.

The watershed was deforested and converted to agricultural lands in the 1700’s, resulting in soil erosion and deposition of sediment in the floodplains and stream channels. Improved farming practices have reduced soil erosion. Ongoing suburbanization is further reducing the sediment flow into the floodplain and channel deposits but is increasing runoff. This study identified a significant sediment wedge at the confluence of two branches of Bachman Run. The sediment is being remobilized, contributing to sediment pollution downstream. Where channel bottom sediments occur, the stream is incising and meanders are rapidly migrating down gradient. In areas where bedrock is exposed in the channel, channel widening and stream bank erosion is occurring. Many local landowners are responding to these changes with hard engineering solutions such as rip rapping the stream banks. These practices are in turn exacerbating the already highly impacted streams and will accelerate the negative effects these tributaries have on the Chesapeake Bay. A recently formed grassroots watershed alliance is working to improve the Little Conestoga watershed by educating the public and sponsoring stream restoration projects.

Streams are complex dynamic systems. A clear understanding of stream dynamics on the stream reach and watershed scales is crucial if stream restoration efforts are to be successful. Ultimately improving the condition of the Chesapeake Bay will depend on the success of these local efforts.