Decoupling processes and scales of shoreline morphodynamics

Abstract

Behavior of coastal systems on time scales ranging from single storm events to years and decades is controlled by both small-scale sediment transport processes and large-scale geologic, oceanographic, and morphologic processes. Improved understanding of coastal behavior at multiple time scales is required for refining models that predict potential erosion hazards and for coastal management planning and decision-making. Here we investigate the primary controls on shoreline response along a geologically-variable barrier island on time scales resolving extreme storms and decadal variations over a period of nearly one century. An empirical orthogonal function analysis is applied to a time series of shoreline positions at Fire Island, NY to identify patterns of shoreline variance along the length of the island. We establish that there are separable patterns of shoreline behavior that represent response to oceanographic forcing as well as patterns that are not explained by this forcing. The dominant shoreline behavior occurs over large length scales in the form of alternating episodes of shoreline retreat and advance, presumably in response to storms cycles. Two secondary responses include long-term response that is correlated to known geologic variations of the island and the other reflects geomorphic patterns with medium length scale. Our study also includes the response to Hurricane Sandy and a period of post-storm recovery. It was expected that the impacts from Hurricane Sandy would disrupt long-term trends and spatial patterns. We found that the response to Sandy at Fire Island is not notable or distinguishable from several other large storms of the prior decade.Published by Elsevier B.V.

Characterizing storm response and recovery using the beach change envelope: Fire Island, New York

“…2b). Western Fire Island exhibits rapid westward spit progradation and relatively wide beaches backed by moderately sized dunes (4.5 m average) due to large sediment inputs via cross-shore and alongshore transport -as evidenced by consecutive recurved dune ridges and alongshore distance between Fire Island Inlet and extending four miles west of the Fire Island Lighthouse, which was originally constructed in 1826 to mark the eastern flank of the inlet (Leatherman, 1985, Leatherman andAllen, 1985;Hapke et al, 2010Hapke et al, , 2011Hapke et al, , 2016Lentz et al, 2013, Schwab et al, 2013. The central portion, approximately from Sailors Haven to Watch Hill, is thought to be the oldest part of the island and has many well established 10 + m-high dune ridges and has historically been the most stable of the three regions showing minimal landward migration of the past 1000 years (Leatherman, 1985;Psuty and Silveira, 2009).…”

“…By plotting percent deviation from profile specific average values on both axes to fully normalize the data (e.g. Hapke et al, 2016), the general position of individual data points around the 0% deviation on both axes provides loose categorical boundaries of four identified stages of recovery (Fig. 6, Table 4 Stages of post-storm beach and dune recovery with specific morphologic changes and processes associated with each described.…”

“…One category measures a single morphologic proxy (e.g. shoreline position (Morton et al, 1995;Thieler and Young, 1991;Farris and List, 2007;Houser et al, 2008;Hapke et al, 2010Hapke et al, , 2016Bramato et al, 2012;Phillips et al, 2017) or dune height (Houser et al, 2008(Houser et al, , 2015Stockdon et al, 2009;Wernette et al, 2016)); whereas the other simplifies spatial information along a cross-shore profile to an averaged value (e.g. beach volume and slope) (Morton et al, 1994;Stone et al, 2004;Stockdon et al, 2007;Houser and Hamilton, 2009;Mathew et al, 2010;Scott et al, 2016).…”

“…This information has been used to link observations with what is known about localized sediment supply and geology of a system (e.g. Aagaard et al, 2004;Houser et al, 2008;Lentz et al, 2013;Schwab et al, 2013;Warner et al, 2014;Hapke et al, 2016), providing better understanding of the signature these controls may exert on an area.…”

Statistical modeling of the long-range dependent structure of barrier island framework geology and surface geomorphology

“…Gutierrez et al (2015) used a Bayesian network to predict barrier island 123 geomorphic characteristics and argue that statistical models are useful for refining predictions of 124 locations where particular hazards may exist. These examples demonstrate the benefit of using 125 statistical models as quantitative tools for interpreting coastal processes at multiple spatial and 126 temporal scales (Hapke et al, 2016). 127 128…”