Ashton Andrew D.

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Ashton
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Andrew D.
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0000-0002-0241-3090

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  • Article
    Large-scale coastal and fluvial models constrain the late Holocene evolution of the Ebro Delta
    (Copernicus Publications on behalf of the European Geosciences Union, 2017-09-25) Nienhuis, Jaap H. ; Ashton, Andrew D. ; Kettner, Albert J. ; Giosan, Liviu
    The distinctive plan-view shape of the Ebro Delta coast reveals a rich morphologic history. The degree to which the form and depositional history of the Ebro and other deltas represent autogenic (internal) dynamics or allogenic (external) forcing remains a prominent challenge for paleo-environmental reconstructions. Here we use simple coastal and fluvial morphodynamic models to quantify paleo-environmental changes affecting the Ebro Delta over the late Holocene. Our findings show that these models are able to broadly reproduce the Ebro Delta morphology, with simple fluvial and wave climate histories. Based on numerical model experiments and the preserved and modern shape of the Ebro Delta plain, we estimate that a phase of rapid shoreline progradation began approximately 2100 years BP, requiring approximately a doubling in coarse-grained fluvial sediment supply to the delta. River profile simulations suggest that an instantaneous and sustained increase in coarse-grained sediment supply to the delta requires a combined increase in both flood discharge and sediment supply from the drainage basin. The persistence of rapid delta progradation throughout the last 2100 years suggests an anthropogenic control on sediment supply and flood intensity. Using proxy records of the North Atlantic Oscillation, we do not find evidence that changes in wave climate aided this delta expansion. Our findings highlight how scenario-based investigations of deltaic systems using simple models can assist first-order quantitative paleo-environmental reconstructions, elucidating the effects of past human influence and climate change, and allowing a better understanding of the future of deltaic landforms.
  • Article
    Wave reworking of abandoned deltas
    (John Wiley & Sons, 2013-11-19) Nienhuis, Jaap H. ; Ashton, Andrew D. ; Roos, Pieter C. ; Hulscher, Suzanne J. M. H. ; Giosan, Liviu
    River deltas and individual delta lobes frequently face reduction of sediment supply, either from the geologic process of river avulsion or, more recently, due to human activities such as river damming. Using a process-based shoreline evolution model, we investigate wave reworking of delta shorelines after fluvial input elimination. Model results suggest that littoral sediment transport can result in four characteristic modes of delta abandonment, ranging from diffusional smoothing of the delta (or delta lobe) to the development of recurved spits. A straightforward analysis of delta shape and wave characteristics provides a framework for predicting the mode of delta abandonment. The observed morphologies of historically abandoned delta lobes, including those of the Nile, Ebro, and Rhone rivers, fit within this framework. Our results provide quantitative insight into the potential evolution of active delta environments in light of future extreme reduction of fluvial sediment input.
  • Article
    Large-scale responses of complex-shaped coastlines to local shoreline stabilization and climate change
    (American Geophysical Union, 2010-09-16) Slott, Jordan M. ; Murray, A. Brad ; Ashton, Andrew D.
    When modeling the large-scale (> km) evolution of coastline morphology, the influence of natural forces is not the only consideration; ongoing direct human manipulations can substantially drive geomorphic change. In this paper, we couple a human component to a numerical model of large-scale coastline evolution, incorporating beach “nourishment” (periodically placing sand on the beach, also called “beach replenishment” or “beach fill”). Beach nourishment is the most prevalent means humans employ to alter the natural shoreline system in our case study, the Carolina coastline. Beach nourishment can cause shorelines adjacent to those that are nourished to shift both seaward and landward. When we further consider how changes to storm behaviors could change wave climates, the magnitude of morphological change induced by beach nourishment can rival that expected from sea level rise and affect the coast as far as tens of kilometers away from the nourishment site. In some instances, nonlocal processes governing large-scale cuspate-cape coastline evolution may transmit the human morphological “signal” over surprisingly large (hundreds of kilometer) distances.
  • Article
    High-angle wave instability and emergent shoreline shapes : 2. Wave climate analysis and comparisons to nature
    (American Geophysical Union, 2006-12-15) Ashton, Andrew D. ; Murray, A. Brad
    Recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore, giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms, including capes, flying spits, and alongshore sand waves. This instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle, a maximum that occurs between 35° and 50° for several common alongshore sediment transport formulae. Here we introduce metrics that sum over records of wave data to quantify the long-term stability of wave climates and to investigate how wave climates change along a coast. For Long Point, a flying spit on the north shore of Lake Erie, Canada, wave climate metrics suggest that unstable waves have shaped the spit and, furthermore, that smaller-scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable. A shoreline aligned along the trend of the Carolina Capes, United States, would be dominated by high-angle waves; numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast. Local wave climates along these simulated capes and the Carolina Capes show similar trends: Shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability.
  • Article
  • Preprint
    Increased typhoon activity in the Pacific deep tropics driven by Little Ice Age circulation changes
    (Nature Research, 2020-11-16) Bramante, James F. ; Ford, Murray R. ; Kench, Paul S. ; Ashton, Andrew D. ; Toomey, Michael R. ; Sullivan, Richard M. ; Karnauskas, Kristopher B. ; Ummenhofer, Caroline C. ; Donnelly, Jeffrey P.
    The instrumental record reveals that tropical cyclone activity is sensitive to oceanic and atmospheric variability on inter-annual and decadal scales. However, our understanding of the influence of climate on tropical cyclone behaviour is restricted by the short historical record and the sparseness of prehistorical reconstructions, particularly in the western North Pacific, where coastal communities suffer loss of life and livelihood from typhoons annually. Here, to explore past regional typhoon dynamics, we reconstruct three millennia of deep tropical North Pacific cyclogenesis. Combined with existing records, our reconstruction demonstrates that low-baseline typhoon activity prior to 1350 ce was followed by an interval of frequent storms during the Little Ice Age. This pattern, concurrent with hydroclimate proxy variability, suggests a centennial-scale link between Pacific hydroclimate and tropical cyclone climatology. An ensemble of global climate models demonstrates a migration of the Pacific Walker circulation and variability in two Pacific climate modes during the Little Ice Age, which probably contributed to enhanced tropical cyclone activity in the tropical western North Pacific. In the next century, projected changes to the Pacific Walker circulation and expansion of the tropics will invert these Little Ice Age hydroclimate trends, potentially reducing typhoon activity in the deep tropical Pacific.
  • Article
    High-angle wave instability and emergent shoreline shapes : 1. Modeling of sand waves, flying spits, and capes
    (American Geophysical Union, 2006-12-15) Ashton, Andrew D. ; Murray, A. Brad
    Contrary to traditional findings, the deepwater angle of wave approach strongly affects plan view coastal evolution, giving rise to an antidiffusional “high wave angle” instability for sufficiently oblique deepwater waves (with angles between wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport, ∼45°). A one-contour-line numerical model shows that a predominance of high-angle waves can cause a shoreline to self-organize into regular, quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers. The numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash, which is assumed to maintain a minimum barrier width. Systematic analysis shows that the wave climate determines the form of coastal response. For nearly symmetric wave climates (small net alongshore sediment transport), cuspate coasts develop that exhibit increasing relative cross-shore amplitude and pointier tips as the proportion of high-angle waves is increased. For asymmetrical wave climates, shoreline features migrate in the downdrift direction, either as subtle alongshore sand waves or as offshore-extending “flying spits,” depending on the proportion of high-angle waves. Numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude, a rate that is insensitive to the proportion of high-angle waves. The proportion of high-angle waves determines the offshore versus alongshore aspect ratio of self-organized shoreline undulations.
  • Article
    Risk averse choices of managed beach widths under environmental uncertainty
    (Wiley, 2021-07-26) Jin, Di ; Hoagland, Porter ; Ashton, Andrew D.
    Applying a theoretical geo-economic approach, we examined key factors affecting decisions about the choice of beach width when eroded coastal beaches are being nourished (i.e., when fill is placed to widen a beach). Within this geo-economic framework, optimal beach width is positively related to its values for hazard protection and recreation and negatively related to nourishment costs and the discount rate. Using a dynamic modeling framework, we investigated the time paths of beach width and nourishment that maximized net present value under an accelerating sea level. We then analyzed how environmental uncertainty about expected future beach width, arising from natural shoreline dynamics, intermittent large storms, or sea-level rise, leads to economic choices favoring narrower beaches. Risk aversion can affect a coastal property owner's choice of beach width in contradictory ways: the expected benefits of hazard protection must be balanced against the expected costs of repeated nourishment actions.
  • Article
    Sea-level rise will drive divergent sediment transport patterns on fore reefs and reef flats, potentially causing erosion on Atoll Islands
    (American Geophysical Union, 2020-09-25) Bramante, James F. ; Ashton, Andrew D. ; Storlazzi, Curt D. ; Cheriton, Olivia M. ; Donnelly, Jeffrey P.
    Atoll reef islands primarily consist of unconsolidated sediment, and their ocean‐facing shorelines are maintained by sediment produced and transported across their reefs. Changes in incident waves can alter cross‐shore sediment exchange and, thus, affect the sediment budget and morphology of atoll reef islands. Here we investigate the influence of sea level rise and projected wave climate change on wave characteristics and cross‐shore sediment transport across an atoll reef at Kwajalein Island, Republic of the Marshall Islands. Using a phase‐resolving model, we quantify the influence on sediment transport of quantities not well captured by wave‐averaged models, namely, wave asymmetry and skewness and flow acceleration. Model results suggest that for current reef geometry, sea level, and wave climate, potential bedload transport is directed onshore, decreases from the fore reef to the beach, and is sensitive to the influence of flow acceleration. We find that a projected 12% decrease in annual wave energy by 2100 CE has negligible influence on reef flat hydrodynamics. However, 0.5–2.0 m of sea level rise increases wave heights, skewness, and shear stress on the reef flat and decreases wave skewness and shear stress on the fore reef. These hydrodynamic changes decrease potential sediment inputs onshore from the fore reef where coral production is greatest but increase potential cross‐reef sediment transport from the outer reef flat to the beach. Assuming sediment production on the fore reef remains constant or decreases due to increasing ocean temperatures and acidification, these processes have the potential to decrease net sediment delivery to atoll islands, causing erosion.
  • Article
    Wave-angle control of delta evolution
    (American Geophysical Union, 2011-07-07) Ashton, Andrew D. ; Giosan, Liviu
    Wave-influenced deltas, with large-scale arcuate shapes and demarcated beach ridge complexes, often display an asymmetrical form about their river channel. Here, we use a numerical model to demonstrate that the angles from which waves approach a delta can have a first-order influence upon its plan-view morphologic evolution and sedimentary architecture. The directional spread of incoming waves plays a dominant role over fluvial sediment discharge in controlling the width of an active delta lobe, which in turn affects the characteristic rates of delta progradation. Oblique wave approach (and a consequent net alongshore sediment transport) can lead to the development of morphologic asymmetry about the river in a delta's plan-view form. This plan-form asymmetry can include the development of discrete breaks in shoreline orientation and the appearance of self-organized features arising from shoreline instability along the downdrift delta flank, such as spits and migrating shoreline sand waves—features observed on natural deltas. Somewhat surprisingly, waves approaching preferentially from one direction tend to increase sediment deposition updrift of the river. This ‘morphodynamic groin effect’ occurs when the delta's plan-form aspect ratio is sufficiently large such that the orientation of the shoreline on the downdrift flank is rotated past the angle of maximum alongshore sediment transport, resulting in preferential redirection of fluvial sediment updrift of the river mouth.
  • Article
    The effects of storms and a transient sandy veneer on the interannual planform evolution of a low-relief coastal cliff and shore platform at Sargent Beach, Texas, USA
    (European Geosciences Union, 2021-09-08) Palermo, Rose V. ; Piliouras, Anastasia ; Swanson, Travis E. ; Ashton, Andrew D. ; Mohrig, David
    Coastal cliff erosion is alongshore-variable and episodic, with retreat rates that depend upon sediment as either tools of abrasion or protective cover. However, the feedbacks between coastal cliff planform morphology, retreat rate, and sediment cover are poorly quantified. This study investigates Sargent Beach, Texas, USA, at the annual to interannual scale to explore (1) the relationship between temporal and spatial variability in cliff retreat rate, roughness, and sinuosity and (2) the response of retreat rate and roughness to changes in sand and shell hash cover of the underlying mud substrate as well as the impact of major storms using field measurements of sediment cover, erosion, and aerial images to measure shore platform morphology and retreat. A storm event in 2009 increased the planform roughness and sinuosity of the coastal cliff at Sargent Beach. Following the storm, aerial-image-derived shorelines with annual resolution show a decrease in average alongshore erosion rates from 12 to 4 m yr−1, coincident with a decrease in shoreline roughness and sinuosity (smoothing). Like the previous storm, a storm event in 2017 increased the planform roughness and sinuosity of the cliff. Over shorter timescales, monthly retreat of the sea cliff occurred only when the platform was sparsely covered with sediment cover on the shore platform, indicating that the tools and cover effects can significantly affect short-term erosion rates. The timescale to return to a smooth shoreline following a storm or roughening event, given a steady-state erosion rate, is approximately 24 years, with the long-term rate suggesting a maximum of ∼107 years until Sargent Beach breaches, compromising the Gulf Intracoastal Waterway (GIWW) under current conditions and assuming no future storms or intervention. The observed retreat rate varies, both spatially and temporally, with cliff face morphology, demonstrating the importance of multi-scale measurements and analysis for interpretation of coastal processes and patterns of cliff retreat.
  • Article
    Coastline responses to changing storm patterns
    (American Geophysical Union, 2006-09-20) Slott, Jordan M. ; Murray, A. Brad ; Ashton, Andrew D. ; Crowley, Thomas J.
    Researchers and coastal managers are pondering how accelerated sea-level rise and possibly intensified storms will affect shorelines. These issues are most often investigated in a cross-shore profile framework, fostering the implicit assumption that coastline responses will be approximately uniform in the alongshore direction. However, experiments with a recently developed numerical model of coastline change on a large spatial domain suggest that the shoreline responses to climate change could be highly variable. As storm and wave climates change, large-scale coastline shapes are likely to shift—causing areas of greatly accelerated coastal erosion to alternate with areas of considerable shoreline accretion. On complex-shaped coastlines, including cuspate-cape and spit coastlines, the alongshore variation in shoreline retreat rates could be an order of magnitude higher than the baseline retreat rate expected from sea-level rise alone.
  • Article
  • Article
    Labeling poststorm coastal imagery for machine learning: measurement of interrater agreement
    (American Geophysical Union, 2021-09-03) Goldstein, Evan B. ; Buscombe, Daniel ; Lazarus, Eli ; Mohanty, Somya D. ; Rafique, Shah Nafis ; Anarde, Katherine A. ; Ashton, Andrew D. ; Beuzen, Tomas ; Castagno, Katherine ; Cohn, Nicholas ; Conlin, Matthew P. ; Ellenson, Ashley ; Gillen, Megan N. ; Hovenga, Paige A. ; Over, Jin-Si ; Palermo, Rose V. ; Ratliff, Katherine M. ; Reeves, Ian R. B. ; Sanborn, Lily H. ; Straub, Jessamin A. ; Taylor, Luke A. ; Wallace, Elizabeth J. ; Warrick, Jonathan ; Wernette, Phillipe ; Williams, Hannah E.
    Classifying images using supervised machine learning (ML) relies on labeled training data—classes or text descriptions, for example, associated with each image. Data-driven models are only as good as the data used for training, and this points to the importance of high-quality labeled data for developing a ML model that has predictive skill. Labeling data is typically a time-consuming, manual process. Here, we investigate the process of labeling data, with a specific focus on coastal aerial imagery captured in the wake of hurricanes that affected the Atlantic and Gulf Coasts of the United States. The imagery data set is a rich observational record of storm impacts and coastal change, but the imagery requires labeling to render that information accessible. We created an online interface that served labelers a stream of images and a fixed set of questions. A total of 1,600 images were labeled by at least two or as many as seven coastal scientists. We used the resulting data set to investigate interrater agreement: the extent to which labelers labeled each image similarly. Interrater agreement scores, assessed with percent agreement and Krippendorff's alpha, are higher when the questions posed to labelers are relatively simple, when the labelers are provided with a user manual, and when images are smaller. Experiments in interrater agreement point toward the benefit of multiple labelers for understanding the uncertainty in labeling data for machine learning research.
  • Article
    Complex coastlines responding to climate change : do shoreline shapes reflect present forcing or “remember” the distant past?
    (Copernicus Publications on behalf of the European Geosciences Union, 2016-12-02) Thomas, Christopher W. ; Murray, A. Brad ; Ashton, Andrew D. ; Hurst, Martin D. ; Barkwith, Andrew K. A. P. ; Ellis, Michael A.
    A range of planform morphologies emerge along sandy coastlines as a function of offshore wave climate. It has been implicitly assumed that the morphological response time is rapid compared to the timescales of wave climate change, meaning that coastal morphologies simply reflect the extant wave climate. This assumption has been explored by focussing on the response of two distinctive morphological coastlines – flying spits and cuspate capes – to changing wave climates, using a coastline evolution model. Results indicate that antecedent conditions are important in determining the evolution of morphologies, and that sandy coastlines can demonstrate hysteresis behaviour. In particular, antecedent morphology is particularly important in the evolution of flying spits, with characteristic timescales of morphological adjustment on the order of centuries for large spits. Characteristic timescales vary with the square of aspect ratios of capes and spits; for spits, these timescales are an order of magnitude longer than for capes (centuries vs. decades). When wave climates change more slowly than the relevant characteristic timescales, coastlines are able to adjust in a quasi-equilibrium manner. Our results have important implications for the management of sandy coastlines where decisions may be implicitly and incorrectly based on the assumption that present-day coastlines are in equilibrium with current conditions.
  • Preprint
    Instability and finite-amplitude self-organization of large-scale coastline shapes
    ( 2012-12-21) Murray, A. Brad ; Ashton, Andrew D.
    Recent research addresses the formation of patterns on sandy coastlines on alongshore scales that are large compared with the cross-shore extent of active sediment transport. A simple morphodynamic instability arises from the feedback between wave-driven alongshore sediment flux and coastline shape. Coastline segments with different orientations experience different alongshore sediment fluxes, so that curvatures in coastline shape drive gradients in sediment flux, which can augment the shoreline curvatures. In a simple numerical model, this instability, and subsequent finite-amplitude interactions between pattern elements, lead to a wide range of different rhythmic shapes and behaviours—ranging from symmetric cuspate capes and bays to alongshore migrating ‘flying spits’—depending on the characteristics of the input wave forcing. The scale of the pattern coarsens in some cases because of the merger of migrating coastline features, and in other cases because of non-local screening interactions between coastline protrusions, which affect the waves reaching other parts of the coastline. Features growing on opposite sides of an enclosed water body mutually affect the waves reaching each other in ways that lead to the segmentation of elongated water bodies. Initial tests of model predictions and comparison with observations suggest that modes of pattern formation in the model are relevant in nature.
  • Article
    Seismic evidence of glacial-age river incision into the Tahaa barrier reef, French Polynesia
    (Elsevier, 2016-04-13) Toomey, Michael R. ; Woodruff, Jonathan D. ; Donnelly, Jeffrey P. ; Ashton, Andrew D. ; Perron, J. Taylor
    Rivers have long been recognized for their ability to shape reef-bound volcanic islands. On the time-scale of glacial–interglacial sea-level cycles, fluvial incision of exposed barrier reef lagoons may compete with constructional coral growth to shape the coastal geomorphology of ocean islands. However, overprinting of Pleistocene landscapes by Holocene erosion or sedimentation has largely obscured the role lowstand river incision may have played in developing the deep lagoons typical of modern barrier reefs. Here we use high-resolution seismic imagery and core stratigraphy to examine how erosion and/or deposition by upland drainage networks has shaped coastal morphology on Tahaa, a barrier reef-bound island located along the Society Islands hotspot chain in French Polynesia. At Tahaa, we find that many channels, incised into the lagoon floor during Pleistocene sea-level lowstands, are located near the mouths of upstream terrestrial drainages. Steeper antecedent topography appears to have enhanced lowstand fluvial erosion along Tahaa's southwestern coast and maintained a deep pass. During highstands, upland drainages appear to contribute little sediment to refilling accommodation space in the lagoon. Rather, the flushing of fine carbonate sediment out of incised fluvial channels by storms and currents appears to have limited lagoonal infilling and further reinforced development of deep barrier reef lagoons during periods of highstand submersion.
  • Article
    Interaction of sea-level pulses with periodically retreating barrier islands
    (Frontiers Media, 2019-10-31) Ciarletta, Daniel J. ; Lorenzo-Trueba, Jorge ; Ashton, Andrew D.
    Submerged barrier deposits preserved on continental shelf seabeds provide a record of paleocoastal environmental change from the last glacial maximum through the Holocene. The formation of these offshore deposits is often attributed to intermittent periods of rapidly rising sea levels, especially glacial meltwater pulses, which are expected to lead to partial or complete drowning – overstepping – of migrating barrier islands. However, recent cross-shore modeling and field evidence suggests that even for constant sea-level rise and shelf slope, the internal dynamics of migrating barriers could plausibly drive periodic retreat accompanied by autogenic partial overstepping and deposition of barrier sediment. We hypothesize that the interaction of periodic retreat with changes in external (allogenic) forcing from sea-level rise may create novel retreat responses and corresponding relict barrier deposits. Specifically, we posit that autogenic deposits can be amplified by an increased rate of relative sea-level rise, while in other cases internal dynamics can disrupt or mask the production of allogenic deposits. Here, we model barriers through a range of autogenic–allogenic interactions, exploring how barriers with different inherent autogenic periods respond to discrete, centennial-scale sea-level-rise pulses of variable magnitude and timing within the autogenic transgressive barrier cycle. Our results demonstrate a diversity of depositional signals, where production of relict sands is amplified or suppressed depending on both the barrier’s internal dynamic state and the pulse magnitude. We also show that millennial-scale autogenic periodicity renders barriers vulnerable to complete drowning for relatively low pulse rates of rise (<15 mm/year).
  • Article
    Mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition
    (John Wiley & Sons, 2013-12-24) Ortiz, Alejandra C. ; Ashton, Andrew D. ; Nepf, Heidi M.
    The transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems, and the fate of these particles is closely linked to vegetation. We describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition. Patches of rigid, emergent, and flexible, submerged vegetation were considered, with two different stem densities. For the rigid emergent vegetation, flow adjustment was primarily two-dimensional, with flow deflected in the horizontal plane. Horizontal shear layers produced a von Kármán vortex street. Flow through the patch shifted the vortex street downstream, resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished. Net deposition was enhanced within this region. In contrast, for the flexible, submerged vegetation, flow adjustment was three-dimensional, with shear layers formed in the vertical and horizontal planes. Because of strong vertical circulation, turbulent kinetic energy was elevated directly downstream of the patch. Consistent with this, deposition was not enhanced at any point in the wake. This comparison suggests that morphological feedbacks differ between submerged and emergent vegetation. Further, enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced, relative to the open channel. Reduced deposition (indicating enhanced resuspension) occurred in regions of high turbulence kinetic energy, regardless of local mean velocity. These observations highlight the importance of turbulence in controlling deposition.
  • Article
    Anthropogenic controls on overwash deposition : evidence and consequences
    (John Wiley & Sons, 2015-12-29) Rogers, Laura J. ; Moore, Laura J. ; Goldstein, Evan B. ; Hein, Christopher J. ; Lorenzo-Trueba, Jorge ; Ashton, Andrew D.
    Accelerated sea level rise and the potential for an increase in frequency of the most intense hurricanes due to climate change threaten the vitality and habitability of barrier islands by lowering their relative elevation and altering frequency of overwash. High-density development may further increase island vulnerability by restricting delivery of overwash to the subaerial island. We analyzed pre-Hurricane Sandy and post-Hurricane Sandy (2012) lidar surveys of the New Jersey coast to assess human influence on barrier overwash, comparing natural environments to two developed environments (commercial and residential) using shore-perpendicular topographic profiles. The volumes of overwash delivered to residential and commercial environments are reduced by 40% and 90%, respectively, of that delivered to natural environments. We use this analysis and an exploratory barrier island evolution model to assess long-term impacts of anthropogenic structures. Simulations suggest that natural barrier islands may persist under a range of likely future sea level rise scenarios (7–13 mm/yr), whereas developed barrier islands will have a long-term tendency toward drowning.