Year
2025
Season
Summer
Paper Type
Master's Thesis
College
College of Computing, Engineering & Construction
Degree Name
Master of Civil Engineering: Coastal and Port Engineering (MSCE)
Department
Engineering
NACO controlled Corporate Body
University of North Florida. School of Engineering
Committee Chairperson
William Dally, Ph.D., P.E.
Second Advisor
Raphael Crowley, Ph.D., P.E.
Third Advisor
Ryan Shamet, Ph.D., P.E.
Department Chair
Alan Harris, Ph.D. Director
College Dean
William F. Klostermeyer, Ph.D., Dean
Abstract
The morphological behavior of the beaches north of Sebastian Inlet, Florida is investigated by applying Empirical Orthogonal Function (EOF) analyses to a series of beach surveys conducted semi-annually (winter and summer) over a period of fifteen years (2005-2019), with the primary objectives being to 1) determine the extent to which the inlet’s influence to the north typically fluctuates on a short-term basis (e.g. annually), and 2) identify any long-term trends of accretion or erosion that might exist. Each survey is comprised of thirty-one cross-shore profiles that are referenced to permanently installed range monuments (“R-monuments”) that are spaced nominally 305 m (1,000 ft) apart along the top of the aeolian dune system. The domain examined extends roughly 9,150 m (30,000 ft) from R-189 at the northern end to R-219 immediately adjacent to the inlet’s north jetty. Unlike previous studies (e.g. Dally, 2023) that constructed Digital Terrain Models (DTM) for a much smaller domain between R-213 and R-219 and shorter time period (1993-2003) in the hopes of using planform EOF analysis to identify 2D-H morphologic behavior, the study herein confines the EOF analysis to the actual profile survey data collected at each individual monument from R-189 to R-219, as well as spans the entire timeframe for which survey data are available (2005-2019). The spatial eigenfunctions and temporal coefficients generated from nominally thirty surveys at each monument are compared by overlaying the mean profiles and each corresponding eigenfunction. Through consistent signaling in the first eigenfunction, it was found that the annual effects of the inlet typically extend approximately two kilometers to the north, with noticeable impacts reaching as far as R-212. EOF analysis revealed consistent morphodynamic trends, including seasonal signals, longshore bar movement, and terrace features. To further investigate spatial patterns, an EOF analysis was performed on the collection of mean profiles from each monument, allowing detection of alongshore transitions in beach shape. This less common, spatial form of EOF exposes a clear morphological shift near R-211, supporting the estimated spatial reach of the jetty’s influence. Additionally, contour maps of mean and seasonal profiles reveal steepened nearshore profiles and altered sandbar patterns south of R-209, confirming the presence of more uniform and natural beach morphology north of this transition. These results provide insight into how shoreline and nearshore morphology vary over time and space, particularly in response to inlet stabilization and longshore sediment transport processes.
Suggested Citation
O'Gorman, Aidan, "Long-term assessment of the morphological behavior of the beaches north of Sebastian Inlet, Florida" (2025). UNF Graduate Theses and Dissertations. 1354.
https://digitalcommons.unf.edu/etd/1354