Geomorphic Response to the Removal of the Ward’s Mill Dam on the Watauga River, North Carolina

Abstract

Though economic situations of individual dams vary, current dam removal studies largely indicate that ecological benefits of river re-connectivity may outweigh the costs of maintaining aging infrastructure. However, there is a lack of comprehensive studies in certain regions of the United States, including Southern Appalachia. We used the removal of the 6 m high Ward’s Mill Dam on the Watauga River in North Carolina to conduct a before-after/control-impact study to monitor geomorphic impacts to such removals in this understudied region with the objective of identifying changes in channel form, analyzing bed sediment characteristics, and quantifying rates of volumetric evacuation and deposition. To capture geomorphic change repeated pre- and post-removal cross- sectional surveys, longitudinal profiles, and in-situ particle size sampling was conducted in upstream and downstream reaches. Field collections the day after removal show significant deposition of gravel sized particles immediately downstream of the dam (≤200 m). Channel bed texture remains significantly finer across the 2 km downstream study reach 506 days following removal. Erosion rates of the impoundment during the deconstruction period were on average ~860 m3/day and decreased to 75.5 m3/day by day 74. Below average mean daily flows during this period were able to exhume ~62.9 percent of impounded sediment.