29-38 Beach Grainsize Dynamics of Folly Beach, SC (USA) Post-Nourishment and One Year Later (2024-2025)

Session: Undergraduate Research, Part II (Posters)

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Abstract:

With continuing and accelerating exploitation and development of coastal regions, combined with natural shoreline retreat due to rising sea levels and erosional coastal processes, beach nourishment cycles have become a commonly accepted solution to rebuilding depleted beach sand supplies. Folly Beach, SC, a mixed-energy barrier system with deep inlets and large ebb-tidal deltas, has undergone seven nourishment episodes since 1993, with the latest from February 2024 into Fall of 2024 (PSDS at WCU). This latest nourishment episode covered an ~9-km section of the shoreline with a volume of ~917,000-m³ of sand from the Folly River (landward of Folly Beach) pumped on the beaches. The purpose of this study has been to quantify grainsize distributions along beach transects covering the seaward-facing portion of the island. The transects were sampled just after the 2024 renourishment was completed and were resampled again in the Fall of 2025. Sediment samples were collected at 31 cross-beach transects at intervals of approximately 300-500-m from south to north along the barrier island’s shoreline. Six samples were collected across the beach profile at each transect from the waterline at low tide to the base of the dunes based on landform position. The Fall 2025 sediment samples were collected at every other transect. Samples were dried, split, and analyzed with a CILAS laser particle size analyzer, and grain metrics were calculated using python scripts producing output similar to Gradistat processing. Data were then spatially graphed to visualize and identify trends and patterns within and between sample periods. Results show a statistically significant coarsening trend from the south to the north in both sampling years (mean d50 in μm for 2024: South 202.3+/-17.5 and North 231.9+/-19.2; for 2025: South 201.8+/-18.3 and North 223.5+/-17.7). Although research pulling together wind patterns and wave orientations continue, the 2024 patterns are possibly related to variability in the nourishment source area during dredging, while the 2025 patterns exhibit more organization in various sections of the island after a year. Ongoing research with offshore mapping projects indicates that onshore patterns after physical readjustment of nourishment sediments may be related to organized bedforms and patterns identified by other student research offshore.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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