PROPOSED EXAMINATION OF EROSION RATES IN WALNUT CREEK, ERIE COUNTY, PENNSYLVANIA

Streams in northern Erie County, Pennsylvania flow generally northward and westward into Lake Erie. In their northern reaches they have incised through drift from the Wisconsin Glaciation and into flat-lying Upper Devonian bedrock. This incision occurred due to base level falling from the levels of proglacial lakes Whittlesey and Warren. These streams have carved canyons >30 m deep and are flanked by several sets of strath terraces. Locally, the surfaces of the presumably oldest terraces are offset along meter-scale folds and thrust faults, possibly indicating postglacial deformation. Rectangular drainage patterns have formed due to interaction with the Ashtabula and Girard moraines, but also suggest influence from local tectonic features. Modern erosion rates may be affected by anthropogenic influences such as climate change and land use changes.

Walnut Creek is a bedrock stream that flows south and west of the city of Erie. Casual visits to the creek have found evidence of ongoing bedrock erosion. Historical maps and aerial photographs suggest that an avulsion formed an oxbow (42° 3'5.7"N, 80°13'13.7" W) between 1899 and 1939. At least one gravel bar has become increasingly vegetated in the past ~10 years and rests on bedrock that is above the normal stream level, suggesting it may be an incipient terrace. However, erosion rates have not been quantified.

We propose investigating both historic and prehistoric erosion rates. OSL dating of strath terraces will be the primary method of establishing prehistoric incision rates. Strath terrace ages could also constrain the ages of deformation if the offset terraces indeed indicate postglacial deformation. OSL or carbon-14 dating of sediment may also be used to establish the ages of oxbows along the creek. To quantify modern erosion rates, we are working to obtain schematics for the bridge of Old Sterretania Road (42° 3'7.8"N, 80°10'1.3"W) over the creek, to determine if measurable erosion has occurred on that reach of the stream since the bridge was built. We also plan to establish annual checks of select portions of the stream, including upstream migration of knickpoints, to quantify erosion rates moving forward.