2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 56-8
Presentation Time: 3:30 PM


RIEDEN, Hannah, Environmental Studies, Davidson College, 209 Ridge Rd., Davidson, NC 28035 and JOHNSON, Bradley G., Environmental Studies, Davidson College, Davidson, NC 28035, harieden@davidson.edu

The majority of Piedmont region streams in North Carolina have incised vertically into their floodplains and the magnitude of incision in first to third order streams is significant enough to have created a terrace out of the historic floodplain. Previous research in the Piedmonts of Pennsylvania and Maryland pointed to historic mill dams and their subsequent breaches as the source for similar stream incision. We evaluated the hypothesis that mill dams were the cause of incision in the North Carolina Piedmont.

Since the establishment of dams results in impounded sediment upstream of the dam and not downstream, we compared stream reaches above and below eight dam locations in order to determine the impact of dams on incision. The dams were located using historical records and maps in Mecklenburg, Cabarrus, Rowan, and Iredell counties, and then plotted in ArcGIS. We then went into the field with the aim of finding remnants of the dams. Where ruins were found (4 sites), the stream reach was examined at least 100 meters in both directions from the dam location. When physical evidence of a dam could not be located (4 sites), the entire reach of the stream was examined. At each site we measured incision, described the soils and sediment, looked at stream morphology, and examined any dam remnants.

There was variability in the amount of incision from site to site. However, within the individual streams, the banks immediately upstream and downstream of the dams were roughly uniform. In fact, the magnitude of the incision tended to extend more than 100 meters in either direction from the dam. Similarly, soil development and sediment was comparable above and below individual dam sites. Additionally, by looking closely at the dams’ construction we determined whether they extended across the floodplain or if they were built within the incised channels. The dam sites that still had visible ruins were built into preexisting incised channels suggesting that they were installed after the majority of incision occurred. Based on our survey of these sites, we interpret it to be unlikely that mill dams were the prevailing cause of the widespread incision in North Carolina’s Piedmont streams. Future research will look into the effects that stream straightening, poor farming practices, deforestation, and urbanization have had on the local morphology.