16-11 Spatial Variations in Sediment Grain size in two Reservoirs in the Chattahoochee-Flint Watershed, Alabama, Georgia and Florida

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

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Abstract:

Dams impose significant impacts on the geology of river systems by forming reservoirs. Communities benefit from dams for flood mitigation, hydroelectric power generation, water storage, and recreation. However dams also unnaturally alter the river system and cause sediment to build up. As sediment-laden flows enter a reservoir, reduced velocities drive deposition and the development of both fluvial and lacustrine facies. Sedimentation processes reflect the unique hydrologic and geomorphic characteristics of each watershed and reservoir bathymetry, and resulting grain‑size patterns can vary widely. Examining examples in different geologic and geomorphic settings is important for understanding the sustainability of managed river systems. This study examines lake-bottom grain size spatial variation in two reservoirs, Lake Walter F. George and Lake Seminole, using 11 and 53 grab samples from each, respectively. A grain size analysis with consideration of bathymetry and tributaries is in progress to determine how differing local conditions play a role in reservoir sedimentation. Collected measurements for each sample include grain size minimum, maximum, and percentiles (d₁₀, d₅₀, and d₉₀). From samples analyzed thus far in both reservoirs, median grain size (d₅₀) classes range from clay to very coarse sand. We analyze median grain size for any spatial patterns in each reservoir, hypothesizing a fining with distance from each river mouth and tributaries. We expect to gain a better understanding of how grain size spatial variation relates to reservoir geomorphology and sedimentation. Our study will inform sustainable sediment management strategies for communities using these two reservoirs, and contribute to understanding the impact dams have on fluvial systems.

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