SPATIAL VARIATION OF GRAIN SIZE OF RESERVOIR DEPOSITS IN LAKE SEMINOLE, WITH SPECIFIC REFERENCE TO 2024 FLOOD EVENTS

Lake Seminole, a reservoir formed at the confluence of the Chattahoochee and Flint Rivers and marks the beginning of the Apalachicola River, is part of the greater Apalachicola-Chattachoochee-Flint River watershed. We study the spatial variations in grain size of recent sedimentation in the reservoir. Twenty-five sediment samples along the Flint and Chattahoochee arms of the reservoir were collected from the lakebed using a Ponar grab sampler during fieldwork in November 2024. Grain size of the samples are analyzed using a Microtrac CAMSIZER X2 particle size analyzer. These data are used to determine the spatial transition from sand- to silt-dominated deposits within the paleo-channels of the Flint and Chattahoochee Rivers, which are now located within the two arms of the reservoir. These newly collected samples will be compared with twenty-eight similar grab samples collected in April 2022, April 2023, and May 2024, which have median grain sizes ranging from ~12.5 to 1245 µm in the Flint arm and ~15 to 327 µm in the Chattahoochee arm. We assess whether the spatial distribution and grain size of reservoir sediments record the high flow associated with the passage of Hurricane Helene through the watershed in late September 2024. We hypothesize that the high-flow event, combined with ongoing progradation of the delta in the Chattahoochee arm, resulted in a downstream migration of the transition from sand to mud in the reservoir.