Wadeable Stream Habitat Monitoring at Ocmulgee Mounds National Historical Park: 2023 Change Report

McDonald, Jacob

doi:10.36967/2318541

This report presents findings from long-term stream habitat monitoring conducted under the Southeast Coast Network (SECN) protocol, which evaluates the status and trends of stream and near-channel conditions to inform resource management. The study focuses on a permanently established reach (OCMU001) along Walnut Creek within Ocmulgee Mounds National Historical Park, with surveys conducted in 2017, 2019, and 2023. Baseline data collected in 2017 characterized the reach as having “poor-to-fair” in-stream habitat, despite abundant large woody debris, due to limited habitat diversity and sediment composition. The channel was smaller than expected for its watershed, likely influenced by floodwater diversion into adjacent wetlands. By 2019, substantial degradation occurred, including reduced habitat diversity, shallower thalweg depth, and increased fine sediment deposition, resulting in a downgraded habitat classification of “poor.” These changes were interpreted as potentially reflecting natural variability associated with complex fluvial responses. This 2023 resurvey indicated continued geomorphic adjustment, with persistent dominance of run habitats, further thalweg shallowing, and significant reach-wide bed aggradation. Although bed material coarsened relative to earlier surveys, it remained predominantly sandy. Increased sediment supply is evident from both in-channel and floodplain aggradation, as well as erosion and deposition patterns across transects. Notably, portions of the floodplain were eroded while other areas accumulated sediment, suggesting the influence of one or more high-magnitude hydrologic events. Despite these changes, slight improvements in large woody debris abundance, bed material composition, and geomorphic unit heterogeneity led to an upgraded habitat classification of “poor-to-fair” in 2023. However, the extent of sediment deposition suggests recent geomorphic changes may persist, with ongoing aggradation potentially altering channel capacity and morphology over time. No immediate management concerns were identified, but continued monitoring is recommended to determine whether observed changes represent a sustained trend. Additional analyses, including evaluation of storm events between survey periods, are needed to better understand the drivers of geomorphic change and to inform future management decisions within the park.

Wadeable Stream Habitat Monitoring at Ocmulgee Mounds National Historical Park: 2023 Change Report

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