LEGACY SEDIMENT AND INCISION: THE VERY MESSY ANTHROPOGENIC STREAMS OF THE NORTH CAROLINA PIEDMONT

Streams in the Piedmont of North Carolina are generally incised up to 3 meters into their broader valleys. We initiated this study with the goal of better understanding the drivers of incision in the area. We examined 20 archival dam locations as breached mill dams are a known cause of incision in the mid-Atlantic Piedmont. We additionally studied stream banks at sites not known to have dams. At each site we record the sedimentology and any soil development in the stream banks. What we found was an aggradational-degradational sequence in the late 1700s and early 1800s resulting from deforestation in the region. After this initial event, incision continued via stream straightening, headward erosion, and, more recently, an increase in discharge caused by suburbanization. While these drivers of erosion were occurring, legacy sedimentation continued on the floodplain. This later legacy sediment is alluvial in nature and can be differentiated from the earlier, fluvial deposits which are sandier. Overall, our results suggest that human impacts on streams have been nearly constant since the arrival of Euroamerican settlers to the region.