AUTOMATIC DETECTION OF KNICKPOINTS AND COMPARISON OF STREAM DIRECTIONS RELATIVE TO FOLIATION ALONG STREAMS OF THE WESTERN NORTH CAROLINA BLUE RIDGE

Stream geometry can be used to interpret landscape histories and to understand the connections between the geomorphology of a region and the underlying bedrock geology. Knickpoints are sections of river profiles where the slope is greater downstream than upstream, and can form as a result of tectonics, climate, lithologic boundaries, or internal rock fabrics. Knickpoints are geometric features that can arise from multiple mechanisms and understanding of local rock fabrics is necessary before using these features as proxies for landscape evolution. We present new methods for automatic knickpoint selection and comparison to stream direction at the knickpoint. ArcMap Hydrology tools and open-source R script were used to extract knickpoints from stream profiles and to create an interactive 3-D mapping interface. Viewing streams in three dimensions is highly advantageous to longitudinal profiles, which can be wrongfully interpreted as cross-sections.

By looking at 77 streams in the Cheoah River basin of Graham County, NC, 89 knickpoints were identified. Knickpoints facing to the northwest are more common than would be expected if the knickpoints were uniformly distributed along all parts of the streams. This suggests that some knickpoints may exist because of the interaction of the stream with a regionally SE-dipping foliation, but does not exclude the possibility that these knickpoints are migrating and were formed during a Miocene-aged base level change (Gallen et al., 2013) and are better preserved in streams that drain against foliation than other directions.

The Cheoah River drains northward into the E-W-striking Swannanoa lineament, a topographic trench separating Graham County from the Great Smoky Mountains National Park of Swain County to the north. The Smoky Mountain streams that drain southward into the lineament contain virtually no knickpoints, excluding those found at lithologic contacts. This juxtaposition of stream geometry across the lineament supports the idea that Southern Appalachians are a disequilibrium landscape formed by blocky uplift, differential erosion, or a combination of the two.