RATES OF RESERVOIR DEPOSITION IN LAKE SEMINOLE, GEORGIA USING CESIUM-137 CHRONOLOGY

Lake Seminole, formed by the Jim Woodruff Dam at the confluence of the Chattahoochee and Flint Rivers, provides a valuable case study for understanding the impact of dam construction on sedimentation processes. Regnier (2024, Boston College thesis) analyzed sediment cores to assess sedimentation rates and textural differences, which were interpreted to be pre-dam and post-dam deposits. Cesium-137, a radionuclide produced during mid-20th century thermonuclear bomb testing, serves as a distinctive marker for post-dam sedimentation. Its presence in sediment cores indicates deposition after the dam’s construction in 1954, while its absence signals pre-dam conditions. This project applies this method to sediment cores from two key locations—LS4, the Chattahoochee and Flint Rivers confluence, and LS8, the Chattahoochee paleo-floodplain. These sites will allow us to test Regnier’s (2024) interpretations of these cores. Within LS4, a likely pre-dam sediment contact is identified at 21 cm, indicating an average sedimentation rate of 0.30 cm/yr from 1954 to 2023. Above this depth, we expect to find ¹³⁷Cs marking post-dam sedimentation, while below 21 cm ¹³⁷Cs should be absent representing the pre-dam floodplain. Similarly, at LS8, pre-dam sediment is interpreted at 144 cm indicating a sedimentation rate of 2.10 cm/yr from 1954 to 2023. ¹³⁷Cs is expected to be present above this depth of 144 cm and absent below. This research will contribute to a refined understanding of sedimentation dynamics and spatial patterns of sediment accumulation in Lake Seminole, enhancing estimates of sedimentation rates and providing insights into the long-term impacts of dam construction. The findings will inform reservoir management strategies and process-based descriptions of reservoir sedimentation.