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The depth of closure (DOC) is defined as the most landward depth seaward of which there is no significant change in bottom elevation. In this paper, the short-term DOC associated with a proximal energetic storm was determined based on time-series beach-offshore profiles and compared to the long-term (20-year) DOC at 5 study sites along Florida coast. At all the profile locations the time-series beach-offshore profiles showed an apparent convergence indicating the presence of a DOC at both the storm and long-term scales. There is no apparent and consistent relationship between the long-term DOC and storm DOC, suggesting that the long-term DOC is not directly controlled by a single energetic storm. The short-term storm DOC demonstrated a higher spatial variation alongshore, as compared to the long-term DOC. Alongshore extent of the study site is not a determining factor for longshore variation. Finetuning a crucial parameter like the DOC would have implications for many coastal engineering and management projects, such as the design of beach nourishment. 

Depth of closure (DOC) is defined as the most landward depth seaward of which there is no significant change in bed elevation and no significant net sediment exchange between the nearshore and the offshore over a certain period of time, such as 5 to 20 years. DOC is an essential parameter used in beach and shore protection, sediment management, and many other aspects of coastal studies. Taking advantage of advancements in wave hindcast and bathymetry measurement in the past 20 years (2000-2019), this study determined the DOC at 12 locations along the Florida coast, including three from the northwest Gulf coast, three from the west Gulf coast, and six from the east Atlantic coast. The 12 sites covered a wide range of coastal morphodynamic conditions, with considerable difference in tidal ranges, incident wave heights, as well as nearshore and offshore morphology. Hindcast wave data from WAVEWATCHIII, available since 2005, were analyzed and applied to calculate the closure depth using various empirical formulas. At all the 12 study sites, time-series profiles demonstrated an apparent convergence point indicating the presences of a DOC. The bed-level change at DOC, as quantified by the standard deviation of elevation variation, ranged from 0.05 m to 0.19 m. Along the studied northwest Florida Gulf coast the DOC ranged from 9.12 m to 9.76 m. The DOC along the studied west Florida Gulf coast ranged from 1.59 m to 4.06 m and is influenced by the shallow flat inner continental shelf. Along the studied east Florida Atlantic coast, the DOC ranged from 4.35 m to 8.20 m, with considerable alongshore variation. The Birkemeier formula yielded the closest predictions to the measured values. A linear relationship between the seaward slope of the outer bar and DOC was identified. Incorporating the seaward slope of the outer bar into the Birkemeier formula improved the accuracy of DOC prediction.