Graduation Year

2018

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Geology

Major Professor

Ping Wang, Ph.D.

Co-Major Professor

Ruiliang Pu, Ph.D.

Committee Member

Philip Van Beynen, Ph.D.

Committee Member

Jun Cheng, Ph.D.

Keywords

Beach erosion, Beach profile changes, Hurricane, Sediment transport

Abstract

The beach profiles pre-and post-the Hurricane Hermine (2016) and Irma (2017) along the Sand Key barrier island were collected to quantify longshore variations in storm induced beach changes as well as to compare the beach changes caused by hydrodynamic conditions of the two different hurricanes.

Cross-shore beach profile are examined in 4 sections including dune field, dry beach, sand bar and whole beach to calculate beach change. The volume change for each section and shoreline contour change before and post the hurricane was computed. Hydrodynamic conditions were obtained from adjacent NOAA’s tide and wave gauges.

Both hurricanes generated high offshore waves, with Hurricane Hermine generated waves mostly from southwest, and Irma generated waves dominantly from northeast. Hurricane Hermine generated a storm surge of up to 1 m. While hurricane Irma generated negative surge of -1.1 m.

Several beach profile parameters such as the foreshore slope, as well as volume changes of dune field, dry beach and sand bar induced by the two hurricanes were computed. Under both storms, the foreshore slope became steeper after the storm north of the headland, while the foreshore slope became gentler south of the headland. Storm surge plays an important role in inducing beach erosion. Hurricane Hermine with 1 m surge caused significant dune erosion in terms of dune volume loss and dune line retreat. On the other hand, hurricane Irma with negative surge only caused minor dune erosion. Sand bar moved seaward during both hurricanes, with Irma induced a much greater offshore movement than that of Hermine. In addition, the sand bar height decreased significantly during Irma. In contrast, during Hermine the sand bar height remained largely similar before and after the storm.

Large alongshore variations in beach erosion was observed during both hurricanes as influenced by background erosion rate and direction of incident waves as they approaching the curved shoreline. For both storms, the erosional hot spot at North Sand Key with the highest background erosion rate suffered the most sand loss over the entire profile. More sand was eroded from the dry beach along the broad headland than along the beaches both north and south of it. Corresponding to the higher volume of dry beach erosion, shoreline retreat was also the largest around the headland. During Hurricane Hermine, the headland sheltering of the southerly approaching waves resulted in more erosion to the south than to the north. The opposite happened during Hurricane Irma with northerly approaching wave. More erosion occurred to the north of the headland than that to the south. Systematic measurement of beach profile beach and after hurricanes can improve our understanding on beach morphodynamics on storm induced beach changes.

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