Changes in particle size distribution and suspended sediment concentrations following the removal of a dam in Southern Appalachia

Keywords: dam removal, suspended sediment, particle size, geomorphology, southern appalachia
Session Type: Virtual Poster Abstract
Day: Monday
Session Start / End Time: 2/28/2022 11:20 AM (Eastern Time (US & Canada)) - 2/28/2022 12:40 PM (Eastern Time (US & Canada))
Room: Virtual 33

Abstract

Dam removals are a growing trend in the United States with an average of 90 per year in the past decade. Current removal studies largely indicate that ecological benefits of river re-connectivity outweigh the economic benefits and the costs of maintaining aging infrastructure. However, there is a lack of comprehensive studies in certain regions of the United States, including Southern Appalachia. The deconstruction of the Ward’s Mill Dam (5m) on the Watauga River, North Carolina took place in May 2021. Sample collection for total suspended sediment (TSS), and in-situ measurement of bed sediment particle sizes began 18 months prior to the removal, and is currently ongoing to determine post-removal effects. TSS concentrations were monitored pre removal, during the breach, and post removal at 500 meters upstream and 2000 meters downstream of the dam. Upstream and downstream TSS concentrations were not significantly different prior to dam removal. However, downstream concentrations were significantly higher during deconstruction of the dam (p < .001). Particle size distributions were determined using a modified Wolman pebble count at two upstream sites and four downstream sites before removal and after the deconstruction process was complete. Immediately following the removal, median particle sizes (D50) directly below the dam and 600m downstream experienced significant fining (p < .0001) and became more heterogeneous. Within 6 weeks, these sites experienced significant coarsening (p < .01) of material but still remain finer than pre-removal conditions.