Quantifying thresholds of barrier geomorphic change in a cross-shore sediment-partitioning model

Abstract

Abstract. Barrier coasts, including barrier islands, beach-ridge plains, and associated landforms, can assume a broad spectrum of morphologies over multi-decadal scales that reflect conditions of sediment availability, accommodation, and relative sea-level rise. However, the quantitative thresholds of these controls on barrier-system behavior remain largely unexplored, even as modern sea-level rise and anthropogenic modification of sediment availability increasingly reshape the world's sandy coastlines. In this study, we conceptualize barrier coasts as sediment-partitioning frameworks, distributing sand delivered from the shoreface to the subaqueous and subaerial components of the coastal system. Using an idealized morphodynamic model, we explore thresholds of behavioral and morphologic change over decadal to centennial timescales, simulating barrier evolution within quasi-stratigraphic morphological cross sections. Our results indicate a wide diversity of barrier behaviors can be explained by the balance of fluxes delivered to the beach vs. the dune or backbarrier, including previously understudied forms of transgression that allow the subaerial system to continue accumulating sediment during landward migration. Most importantly, our results show that barrier state transitions between progradation, cross-shore amalgamation, aggradation, and transgression are controlled largely through balances within a narrow range of relative sea-level rise and sediment flux. This suggests that, in the face of rising sea levels, subtle changes in sediment fluxes could result in significant changes in barrier morphology. We also demonstrate that modeled barriers with reduced vertical sediment accommodation are highly sensitive to the magnitude and direction of shoreface fluxes. Therefore, natural barriers with limited sediment accommodation could allow for exploration of the future effects of sea-level rise and changing flux magnitudes over a period of years as opposed to the decades required for similar responses in sediment-rich barrier systems. Finally, because our model creates stratigraphy generated under different input parameters, we propose that it could be used in combination with stratigraphic data to hindcast the sensitivity of existing barriers and infer changes in prehistoric morphology, which we anticipate will provide a baseline to assess the reliability of forward modeling predictions.

Satellite-Derived Barrier Response and Recovery Following Natural and Anthropogenic Perturbations, Northern Chandeleur Islands, Louisiana

“…This work quantifies changes to the whole barrier system, including sandy (beach) and back-barrier (marsh and tidal flat) components, at annual to decadal scales, addressing knowledge gaps in decadal-scale barrier changes that result from incomplete historical records as well as the historical bias for focusing on shoreline and beach components without explicitly including the connectivity among barrier environments [1,101]. In doing so, we provide metrics that help better capture the timing and controls on the morphologic evolution of the northern Chandeleur Islands.…”

Predicted Sea‐Level Rise‐Driven Biogeomorphological Changes on Fire Island, New York: Implications for People and Plovers

“…For instance, model simulations have shown that barrier islands with closed sediment budgets will experience shoreface flattening and island narrowing as sea levels rise (Lorenzo‐Trueba & Ashton, 2014; Passeri et al., 2020). Declining sediment availability further accelerates this process and may drive equivalent state changes in neighboring barrier islands (Ciarletta et al., 2021). Historical barrier island state changes have been documented for Cedar, Hog, and Parramore islands off the coast of Virginia, which transitioned to low elevation, erosional states during periods of higher relative SLR punctuated by storms (Dueser et al., 1976; Raff et al., 2018; Shawler et al., 2019).…”

“…Barrier islands are highly dynamic landforms shaped by wind, waves, water levels, currents, and vegetation (Davis jr, 1994; Leatherman, 1983). As a result of these forces, barrier islands experience nearly constant alterations to the shoreline and subaerial footprint (Dolan et al., 1988; Morton & Sallenger, 2003; Philips, 2017), with evolution constrained by sediment availability and human modifications to the landscape (Armstrong & Lazarus, 2019; Ciarletta et al., 2021; Hapke et al., 2010; Lorenzo‐Trueba & Ashton, 2014). Highly complex relations among natural disturbance regimes, substrates, and biological communities present on a barrier island can lead to equilibrium conditions in geomorphology and ecological community composition that can remain stable over centennial or millennial time scales (Ahnert, 1994; Cooper et al., 2007; Holling, 1973; Stallins, 2006; Zinnert et al., 2017).…”

Implications for the resilience of modern coastal systems derived from mesoscale barrier dynamics at Fire Island, New York

“…Field and modeling studies have demonstrated that mesoscale barrier dynamics, defined as barrier-lagoon behavior at decadal/centennial timescales and meter to kilometer spatial scales (Cooper et al, 2018;Sherman, 1995), are primarily controlled by sediment accommodation and availability (Brenner et al, 2015;Ciarletta et al, 2021;Cooper et al, 2018;Psuty, 2008;Raff et al, 2018;Shawler et al, 2021a). These drivers are in turn a function of antecedent topography (e.g., pre-transgressive surface morphology; Shawler et al, 2021a); inlet dynamics (Nienhuis and Lorenzo-Trueba, 2019); climate and vegetation (Jackson et al, 2019;Mendes and Giannini, 2015); and relict or "inherited" morphology (Timmons et al, 2010).…”