Date of Award

1-1-2016

Document Type

Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

First Advisor

Paul T. Gayes

Second Advisor

Till J.J. Hanebuth

Third Advisor

Jenna C. Hill

Additional Advisors

Jennifer Miselis

Abstract

Increasing erosional pressures along coastal systems require a better understanding of the mechanisms of natural and human-induced alterations. This is especially important in sediment-starved coastal systems where the effects from geologic framework may exert a disproportionate influence on shoreline behavior. Existing studies into geologic framework and shoreline variability are comprehensive and well documented; yet analysis into the spatial relationships between shoreline variability, lower shoreface morphodynamics, and framework in South Carolina is limited. The Grand Strand region of South Carolina has an extensive set of geophysical data, such as CHIRP seismic, sidescan sonar, borehole logs, and inner shelf cores. In addition, there is a rich suite of RTK-DGPS surveys of a shoreline contour (MHW; 0.625 m) collected monthly since 2007 to consider shoreline variability over 52 km of coastline. Calculation of various statistical parameters using the USGS Digital Shoreline Analysis System v4.2 software, including end point rate (EPR), linear regression rate (LRR) and shoreline change envelope (SCE), provides quantitative assessment of shoreline behavior. Spectral analysis is utilized to define patterns in spatial variability. In effort to target the sediment-limited lower shoreface, a multibeam survey of the region was acquired and identified sections of low relief, low backscatter cuspate-like linear scour depression features in close proximity to the depth of closure. The 6-meter contour wad digitized onto backscatter imagery and intensity values were extracted and correlated to shoreline (MHW) change throughout the study area. Chi-square analysis and correlations between geologic and physical metrics (e.g. paleochannel presence, shoreface slope, backscatter intensity) were computed to identify spatial relationships. Analyses indicate a relationship between shoreline change and backscatter intensity where deep paleochannels were present. Furthermore, power spectral density of the rate-of-change statistics show dominant spatial frequencies consistent between shoreline change and backscatter variability. Findings suggest interplay between shoreface morphology and the spatial variability of the shoreline with framework geology. Further, an intriguing relationship between Cretaceous boundary outcrops along the lower shoreface and offshore cusps suggest a connection between the bathymetric features and framework. The offshore cusps further align with inner shelf linear scour depressions located further offshore and appear to reflect the transition from beach processes into shelf processes, propagating into the self-sustaining linear scour depressions further offshore.

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