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Dams disrupt sediment and hydrologic connectivity, fragmenting river ecosystems and altering geomorphic and ecological processes. In response, dam removals have increased to restore longitudinal stream connectivity and ecosystem function. However, we still lack a comprehensive understanding of the geomorphic responses to dam removal, particularly for low-head dams in high-gradient environments. This study examines the geomorphic and ecological effects following the removal of the Lake George diversion structure, a small diversion dam on the South Fork of the South Platte River, CO, in 2023. During removal, reservoir sediment was removed and the channel was re-shaped. Using a Before-After-Control-Impact design, we are monitoring three control cross-sections far enough upstream of the former dam to be unaffected by the removal, three cross-sections in the former impoundment immediately upstream of the dam, and three cross-sections immediately downstream of the structure location, collecting pre- and post-removal data.Ìý

At each cross-section, we are conducting RTK-GPS surveys to assess morphologic change caused by, and in the years following, dam removal. We are also collecting bed and subsurface sediment samples for grain size analysis to evaluate textural changes in response to the removal and restoration work. We are collecting benthic macroinvertebrates to provide insight into the early ecological responses to the removal. Preliminary results indicate that although the dam removal and restoration work dramatically reshaped the channel (width and depth changes of several meters), only minor natural geomorphic change has occurred in the year since removal (maximum width and depth changes of a few decimeters). Ongoing and future work will include developing models to predict geomorphic responses to dam removals and channel restoration in steep mountain streams. This research enhances our understanding of how rivers adjust to human-driven disturbances, both in the short term and over longer timescales, following dam removal and restoration.