Graduation Year

2021

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Geology

Major Professor

Ping Wang , Ph.D.

Committee Member

Jun Cheng, Ph.D.

Committee Member

John Bishop, Ph.D.

Keywords

Beach Erosion, Coastal Sustainability, Nearshore Sediment Transport, Storm Erosion Index

Abstract

Tropical Storm Eta impacted the coast of west-central Florida from November 11 to 12, 2020, and generated high waves over elevated water levels for over 20 hours. A total of 148 beach and nearshore profiles, spaced about 300 m apart, were surveyed one to two weeks before and one to eight days after the storm to examine the beach changes along four barrier islands, including Sand Key, Treasure Island, Long Key and Mullet Key. Storm waves superimposed on elevated water levels reached the toe of dunes, causing modest dune erosion as well as overwash in some areas. Most of the sand eroded by the storm from the dune area, the dry beach, and the nearshore, can be accounted for by sand accumulation on the nearshore sand bar, particularly the seaward slope of the sand bar. Based on the Sallenger (2000) storm impact scale, the impact of Tropical Storm Eta was mostly of Swash Regime, with Collision Regime and Overwash Regime occurring in some areas. The numerical model CMS-WAVE was used to simulate nearshore wave field with the purpose of identifying longshore variations in nearshore wave height and angle during the storm. Sand volume loss throughout the study area demonstrates an overall southward decreasing trend, mainly due to a southward decrease in wave height. The Storm Erosion Index (SEI), developed by Miller and Livermont (2008) is applied in this study to explore its applicability in predicting erosion potential from the storm impact. Through sensitivity analysis, breaking wave height was found to be the major contributor to storm induced beach erosion and SEI values, followed by temporal variation of water level, and spatial variation of berm elevation. The longshore variations in erosion rates were captured reasonably well by the SEI using the modeled nearshore wave conditions. Accurately capturing nearshore wave-height variation using a numerical model plays a major role in reproducing the measured longshore variation in beach erosion. Although wider beaches tended to experience more volume loss from the TS Eta due to the availability of sediment, they were effective in protecting the back beach and dune area from erosion. On the other hand, smaller profile-volume loss from narrow beach did not necessarily relate to less dune/structure damage. The opposite is often true. Accurate evaluation of storm’s severity in terms of erosion potential would benefit beach management especially under the circumstance of increasing storm activities due to climate change.

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