Conclusion

Analysis of sidescan-sonar imagery, swath bathymetry, and surface sediment texture reveals four general sea floor environments within Long Bay: inlet shoal complexes, shore-detached shoals, hardgrounds, and mixed zones. Generally, inlet shoal complexes lie offshore of modern inlet systems, with the exception of a shore-detached shoal lying offshore of Myrtle Beach. The shoal complexes comprise the greatest accumulations of modern sediment within the inner shelf and represent the most significant bathymetric highs. They consist of moderately sorted fine sand and are defined by low-backscatter within the sidescan-sonar imagery. Hardground areas lie offshore of Surfside Beach and Pawley's Island and are characterized by exposures of Cretaceous and Tertiary strata and Pleistocene channel-fill deposits reflected as high-backscatter within the sidescan-sonar imagery. Little to no bathymetric variability is displayed within these areas, and surficial sediments generally contain poorly sorted coarse sand. Mixed zones show small-scale spatial variations in bathymetry, surface texture, and backscatter. These areas are characterized by a thin layer of modern sediment, generally less than 1.5 m, and exposures of Cretaceous strata and Pleistocene channel-fill deposits corresponding to low and high backscatter, respectively. The variability in sediment cover is thought to reflect an increased temporal and spatial sediment flux driven by proximity to sediment source and changes in nearshore hydrodynamics due to seasonal and climactic forcing.

Variations in surface texture and acoustic backscatter appear to be related to sea floor morphology within Long Bay. Low-relief, ridgelike features characteristic of the study area display a high-backscatter, poorly sorted, coarse-grained NE face and trough, with a low-backscatter, moderately to well sorted, medium to fine sand crest and SW face. Textural and geomorphic variations suggest a long-term net southerly flow within the study area. The general acoustic and textural character of the inner shelf within Long Bay suggests long-term erosion, reworking and continued modification of inner-shelf deposits by modern nearshore processes.