Incision in North Carolina Piedmont Streams:
A Mill Dam Case Study
Throughout the Piedmont of North Carolina low-energy streams have incised, or eroded vertically, into their banks. We explored the hypothesis that historic mill dams impounded sediment upstream, increasing potential for incision when dams were breached and the base level lowered and the flow velocity increased. Sites were found in the counties of Mecklenburg, Iredell, Rowan, and Cabarrus using historic maps and ArcGIS. We measured bank heights 100m upstream and downstream of the estimated dam location and observed remains when visible. We examined the bank wall for fluvial sediments or mill pond sediments, to determine if they’d been deposited by flowing water or during the time the stream was dammed. 18 sites were visited, and 13 of those stream reaches were incised. Only one incised site had mill sediments, and the other 12 had fluvial sediments (that continued downstream of dam). Local research, opposed to findings in the mid-Atlantic, suggested that North Carolina dams post-dated the stream incision, as stream reaches were consistent in both sediment and magnitude of incision upstream and downstream of dams. Additionally, remains were found that did not extend onto the banks, suggesting they were built into preexisting incised channels. These factors indicate that mill dams were not the cause of incision in the North Carolina Piedmont, and other hypotheses, including the effects of poor agrarian practices and stream straightening, need to be examined.