USING A BEACH CHANGE ENVELOPE (BCE) TO ASSESS POST-STORM RECOVERY AND LONG TERM RESILIENCY

Given the high frequency of storms along US coastal margins, the ability to measure storm impacts and post storm beach recovery is critical in assessing and understanding the physical components that influence beach resiliency. To quantify alongshore variations in beach resiliency at Fire Island, NY we use the beach change envelope (BCE). Introduced by Hapke et al. (2015), the BCE was initially developed to measure beach response and subsequent recovery caused by Hurricane Sandy. Here, we further assess the ability of the BCE to capture post-storm response and recovery of Hurricane Sandy; extend it to other storms (Nor’Ida 2009; Irene 2011); and explore links between BCE behavior (i.e. changes in BCE width and elevation) and the processes and stages of beach recovery. The BCE defines the portion of the upper beach that typically experiences erosion during storm events for a given stretch of coast. Located landward of the highly dynamic swash zone and seaward of the more slowly evolving and less frequently impacted primary dunes, the BCE captures changes to the berm, upper beach, and foredune region. Changes to the BCE occur on relatively short time scales (weeks to months), but still play a critical role in characterizing the state of the beach at a given time. During Nor’Ida the BCE experienced substantial erosion with average width declining by 24m, as the lower BCE boundary was eroded landward (Zl) and the upper boundary (Zu) remained stationary. The BCE shows a different signal following Hurricane Irene. During this storm, sand moved onshore, accumulating along frontal dune system, causing seaward migration of Zu and an increase in average elevation (0.1 m). Although BCE width remained constant in response to Sandy as Zu and Zl both migrated ~7m landward, BCE elevation declined by 0.44m on average, showing landward translation of the subaerial system. Additionally, the temporally dense post-Sandy (Nov2012 – May 2015) dataset captures patterns of BCE configuration associated with various states, or stages, of beach recovery. By defining BCE characteristics specific to each recovery stage and assessing states through time, we are able to evaluate alongshore variations in storm response, recovery, and overall resiliency.