Hurricane Sandy at Fire Island, New York presented unique challenges in the quantification of storm impacts using traditional metrics of coastal change, wherein measured changes (shoreline, dune crest, and volume change) did not fully reflect the substantial changes in sediment redistribution following the storm. We used a time series of beach profile data at Fire Island, New York to define a new contour-based morphologic change metric, the Beach Change Envelope (BCE). The BCE quantifies changes to the upper portion of the beach likely to sustain measurable impacts from storm waves and capture a variety of storm and post-storm beach states. We evaluated the ability of the BCE to characterize cycles of beach change by relating it to a conceptual beach recovery regime, and demonstrated that BCE width and BCE height from the profile time series correlate well with established stages of recovery. We also investigated additional applications of this metric to capture impacts from storms and human modification by applying it to several post-storm historical datasets in which impacts varied considerably; Nor'Ida (2009), Hurricane Irene (2011), Hurricane Sandy (2012), and a 2009 community replenishment. In each case, the BCE captured distinctive upper beach morphologic change characteristic of these different beach building and erosional events. Analysis of the beach state at multiple profile locations showed spatial trends in recovery consistent with recent morphologic island evolution, which other studies have linked with sediment availability and the geologic framework. Ultimately we demonstrate a new way of more effectively characterizing beach response and recovery cycles to evaluate change along sandy coasts.Published by Elsevier B.V.

This paper presents an analysis of the transport conditions of a storm deposit (i.e. tempestite) produced by a non-local cyclone. Observations and analysis of 'sand to boulder' transport and washover deposition in March 2018 at Gaulding Cay Quarry, Eleuthera, The Bahamas, confirm that swell waves can cause coastal change and affect the depositional record >1000 km from the storm centre. Drone video, news reporting, deposit stratigraphy, grain-size measurements and wave data were all used to define three phases of washover fan construction: an aggradational phase associated with baselevel rise as the quarry filled with water; a progradational phase associated with quasi-constant base-level; and fan incision tied to base level fall as discharge through an outlet channel exceeded input discharge by overtopping waves. Washover fan location was controlled by antecedent topography and represented only a fraction of the swell-impacted coastline. Sand and boulders were transported simultaneously, forming a complex poorly sorted deposit. Drone video, bedrock erosion and sediment-transport estimates all indicated that overwash exceeded sediment availability. As a result, the measured washover fan was estimated to be an order of magnitude smaller than its potential volume if conditions had been transport-limited. This study highlights the importance of pre-event topography and independent measures of event duration on accurately reconstructing storm properties from the sedimentary record, as well as the challenges in reconstructing storm location, and therefore storm intensity and frequency, from sedimentary deposits alone.

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