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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. 

Three cycles of beach nourishment at two barrier islands: Sand Key and Treasure Island, were studied over 17 years. Seventy-four and 17 beach profiles spaced ∼300 m apart were surveyed bimonthly to quarterly on Sand Key and Treasure Island, respectively. Six beach sections were distinguished based on beach dynamics, including 2 erosional hotspots, 1 gap in the nourishment and 3 typical erosive beaches. At most locations, the shoreline (defined at +1 m contour) returned to a similar location at the end of each cycle, indicating the nourishment successfully maintained the target beach width. The Treasure Island erosion hotspot experienced increased beach loss over time, suggesting that the current nourishment design may not be adequate. The gap in the nourishment did not experience significant sand gain on the dry beach. A mechanism to impound sand on the dry beach is necessary. The current nourishment successfully compensated the sand deficit. The mechanism causing sand deficit was not eliminated at all the sites, suggesting that the current nourishment design serves as a long-term maintenance strategy.