Barrier Islands Research Papers - Academia.edu (original) (raw)

Publication is required by Alaska Statute 41, "to determine the potential of Alaskan land for production of metals, minerals, fuels, and geothermal resources; the location and supplies of groundwater and construction materials; the potential geologic hazards to buildings, roads, bridges, and other installations and structures; and shall conduct such other surveys and investigations as will advance knowledge of the geology of Alaska.

CULVER, S.J.; AMES, D.V.; REIDE CORBETT, D.; MALLINSON, D.J.; RIGGS, S.R.; SMITH, C.G., and VANCE, D.J., 2006. Foraminiferal and sedimentary record of late Holocene barrier island evolution, Pea Island, North Carolina: the role of storm overwash, inlet processes, and anthropogenic modification. Journal of Coastal Research, 22(4), 836-846. West Palm Beach (Florida), ISSN 0749-0208.

- by Reide Corbett
- •
- Engineering, Earth Sciences, Ground Penetrating Radar, Coastal

Four drowned shelf-edge delta complexes, two drowned shelf deltas, three drowned barrier islands, large areas of "hardground", and fields of bedforms on the mid and outer continental shelf and uppermost slope north of the head of De Soto Canyon, NE Gulf of Mexico were mapped with high-resolution multibeam echosounder. Deltas formed not during the last eustatic low stand, but during one or more interstadials when eustatic sea levels were only 60 to 80 m below present sea level. The barrier islands and deltas must have been cemented prior to rapid falls of eustatic sea level that occurred during global glaciations. Cementation is necessary to have preserved the barrier islands from erosion and subsequent destruction by the rapid sea-level rise during the last deglaciation. The preservation of the relict bathymetry is so good that features that superficially resemble trough blowouts are found in association with one of the relict barrier islands. Asymmetric bedforms on the midshelf in water depths of 50 to 60 m indicate transport directions to the SW but asymmetric bedforms in water depths of the upper slope between 100 and 120 m on the S and SE flanks of the drowned shelf-edge deltas indicate a different current direction, a separate flow that is a continuation of a SW-flowing current that was previously found on the upper slope off NW Florida.

- by Larry Mayer
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- Geology, Geomorphology, Sea Level, Depth
- by Alan Brech
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- Barrier Islands, Santa Lucia, Florida Indians, Spanish Period

Algarve barrier islands: A noncoastal-plain system in Portugal. Journal of Coastal Research, 5(2): 239-261 (1989).
The small barrier island system of the Algarve (South Portugal) exhibits several unique characteristics that differ from more widely studied systems. The islands exist on a noncoastal-plain coast as a result of a platform on the inner shelf which acted as a cape during the sea level rise. Initial spits became islands as the platform was transgressed, and the islands are transgressive in appearance, although west-to-east lateral processes (inlet migration, spit growth) dominate. The islands exist under moderate to high wave energy and mesotidal conditions. Flood-tidal deltas are dominant and inlet migration is rapid. Aeolian and overwash processes are important to vertical growth of the islands. The largest islands have widened as a result of flood-tidal delta Incorporation. After incorporation, aeolian processes modify the delta surface into a dune field before stabilization by vegetation.
Backbarrier dissection by spring tide (4 m.) flooding works in opposition to the constructional effects of delta Incorporation, over-wash and dune formation. An extensive network of erosional channels has developed on backbarriers as a result of erosion by the ebbing flood. Channel location is controlled by antecedent morphology such as incorporated delta channels, interdune areas, and troughs between incorporated recurved spits. Once established, the channels incise, erode laterally and extend into the island, sometimes joining with overwash passes, and forming important conduits of sediment transport to the lagoon/marsh. The lagoonward sediment transport is partially offset by floating sand and shells carried toward the island interior on the incoming flood tide. Spring tide flooding also results in vegetation kills and groundwater contamination.

- by João Dias and +1
- •
- Portugal, Barrier Islands

Anomalous morphological features within large estuaries may be: (1) recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes, and (2) possible predictors of cycles of future coastal change. At the entrance to Willapa Bay, Washington, chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of Cape Shoalwater. Northward channel migration since the late 1800s conforms to the long-term net sediment transport direction. What requires explanation is periodic southward relocation of the trunk channel by as much as 5 km, and attendant construction of moderately large sand spits on the north side of the bay such as Kindred Island, Tokeland Peninsula, and Cape Shoalwater.

- by Edward Clifton
- •
- Earth Sciences, Marine Geology, Sea Level, Barrier Islands

The dynamic growth, migration, and evolution of barrier islands such as St. George and Dog Islands are factors to be considered for archaeological survey and inventory of historic shipwrecks in near-coastal settings. Research examining the formation, evolution, and historic shoreline changes occurring on barrier islands such as those in Franklin County, Florida (Dog Island, St. George Island, Little St. George Island and St. Vincent Island) can supplement shipwreck surveys. The geological history of St. George and Dog Islands lays the foundation for a new model of implementing shipwreck surveys around barrier islands in near-coastal environments. HMS Fox, a 150-ton British military schooner, reportedly sank off the eastern end of St. George Island in 1799 after wrecking on a shoal during a storm. Fox gains its historical significance due to its relation to William Augustus Bowles, a British Loyalist. Bowles’ attempts to create a separate and sovereign Indian Nation of Muskogee were thwarted after HMS Fox wrecked.
The Dog and St. George Islands Shipwreck Survey, an ongoing archaeological research project, reconstructed the geomorphology of St. George Island to define a high probability survey area for HMS Fox. As a result, remote sensing surveys recorded a multitude of magnetic and sonar anomalies in 2000 and 2001 which may represent historic cultural remains such as shipwrecks. The model of reconstructing barrier island geomorphology to define shipwreck survey areas, likely to contain shipwrecks and other historic cultural resources, succeeded by identifying several significant anomalies in 2000 and 2001. Even though all magnetic and sonar anomalies have not yet been investigated, the functionality of this model and its application to shipwreck survey is certain.

- by Melanie Damour
- •
- Maritime Archaeology, Remote Sensing, Maritime History, Coastal Geomorphology
- by Chris Houser
- •
- Geology, Geomorphology, Coastal Management, Migration

Classification of barrier island morphology stems from the seminal work of M. O. Hayes and others, which linked island shape to tidal range and wave height and defined coastal energy regimes (i.e., wave-dominated, mixed energy , tide-dominated). If true, this general relationship represents a process-based framework to link modern and ancient systems, and is key for determining paleomorphodynamic relationships. Here we present a new semi-global database of barrier islands and spits (n = 702). Shape parameters (aspect, circularity, and round-ness) are used to quantify island boundary shape, and assess potential correlation with coastal energy regime using global wave and tide models. In adopting the original energy classification as originally put forth (i.e., wave dominated, wave-influenced mixed, tide-influenced mixed, tide dominated), results show that wave-dominated islands have statistically different mean shape values from those in the mixed energy fields, but the two mixed energy designations are not distinct from each other. Furthermore, each energy regime field contains a wide range of island shapes, with no clear trends present. Linear regression modeling shows that tidal range and wave height account for b 10% of the documented variance in island shape, a strong indication that other controls must be considered. Therefore, while energy regime distinctions can be used descriptively , their utility in predicting and constraining island shape is limited: barrier island shape is not indicative of coastal energy regime, and vice versa. Our analysis also demonstrates empirical scaling relationships among modern barrier islands for the first time, with implications for subsurface prediction.

- by Julia Mulhern
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- Coastal Processes, Coastal Geomorphology, Barrier Islands, Coastal Geology

This paper presents an overview of the Dutch Wadden Sea from a sedimentological point of view. After the pioneering work of scientists new impulses to this kind of research are being given by the need for detailed recent analogues of fossil hydrocarbon-containing rock successions and by the great concern about the future of our coastline in relation to accelerated sea-level rise. After many studies of a descriptive nature in the past, there is now a growing tendency so a more dynamical view to the Wadden Sea system. There is a strong interdependence between various tidal sub-environments within individual inlet systems. Together these sub-environments form so-called Sand Sharing Systems, whose behaviour is largely defined by the tidal prism and the wave climate. Such a dynamical approach may greatly facilitate the research and understanding o fossil barrier-related sediments. Apart from the physical processes the abundant biota plays also an important role in the sedimentological development of the Wadden Sea. The large amount of data on the development of the Wadden Sea in pre-historical and historical times, moreover, allows to test hypotheses about the evolution of the system on the scale of centuries to millennia.

- by Poppe L de Boer
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- Wadden Sea, Barrier Islands, Tidal, Delta

An archaeological survey of Back Bay was conducted along coastal Virginia immediately south of Virginia Beach for the Virginia Department of Historic Resources. The fieldwork was conducted between October and December of 2015. The survey documented eleven actively eroding shorelines with archaeological deposits. The archaeology, geology and soil profiles for each site were evaluated. During the late prehistoric period through the early 19th century, Back Bay was a high salinity barrier island lagoon with a high-tidal amplitude. When the "new" and "old" Currituck Inlets closed in the early 19th century, the salinity of Back Bay plummeted and the tidal amplitude was greatly reduced. Not only did the ecology of Back Bay change, the reduction of tidal amplitude greatly increased the rates of shoreline erosion and associated archaeological site loss. The results of this research will help future researchers prioritize and assess the loss of archaeological sites within a coastal lagoon system that has very low tidal amplitude.

A process-based facies model for asymmetric wave-influenced deltas predicts significant river-borne muds with potentially lower quality reservoir facies in prodelta and downdrift areas, and better quality sand in updrift areas. Many ancient barrier-lagoon systems and 'offshore bars' may be better reinterpreted as components of large-scale asymmetric wave-influenced deltaic systems. The proposed model is based on a re-evaluation of several modern examples. An asymmetry index A is defined as the ratio between the net longshore transport rate at the mouth (in m 3 year )1 ) and river discharge (in 10 6 m 3 month )1 ). Symmetry is favoured in deltas with an index below 200 (e.g. Tiber, lobes of the Godavari delta, Rosetta lobe of the Nile, Ebro), whereas deltas with a higher index are asymmetric (e.g. Danube -Sf. Gheorghe lobe, Brazos, Damietta lobe of the Nile). Periodic deflection of the river mouth for significant distances in the downdrift direction occurs in extreme cases of littoral drift dominance (e.g. Mahanadi), resulting in a series of randomly distributed, quasi-parallel series of sand spits and channel fills. Asymmetric deltas show variable proportions of river-, wave-and tide-dominated facies both among and within their lobes. Bayhead deltas, lagoons and barrier islands form naturally in prograding asymmetric deltas and are not necessarily associated with transgressive systems. This complexity underlines the necessity of interpreting ancient depositional systems in a larger palaeogeographic context.

- by Liviu Giosan
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- Geology, Sedimentology, Barrier Islands, Barrier Island

1 2 3 4 ACKNOWLEDGEMENTS During this project, numerous people have helped and provided me with information, knowledge, and data. First and foremost, I would like to thank Mr. David Hazzard of the Virginia Department of Historic Resources, Threatened Sites Program for supporting and ultimately funding this project. Dave tried several times to get out to the site, but fate interceded and did not permit it. One day, he waited for me on one side of the harbor, while I waited for him on the other. Our paths only crossed for a brief moment, when I departed from the harbor on the boat and he saw me as I swatted at some greenhead flies buzzing around my head. Dave interpreted my hand motions as a wave. As he saw it, I proceeded on towards Mockhorn Island without turning the boat around. I would also like to extend my sincere thanks to Mr. Norman K. Brady for donating the use of his boat to conduct this project. The donated boat and trailer reduced the cost of the project immensely. I would like to thank both Norm and Mr. David R. Thompson for helping me during this project. Like myself, these two individuals had the honor and the privilege to see a "virgin" site first-hand. The various people who helped me with the fieldwork and research are also thanked. Dr. John Wah performed the soils analysis. Dr. Dan Wagner contributed his knowledge about the soils of Mockhorn Island, as well. Mr.

Coastal vulnerability in barrier island systems is extremely high. The barrier island shoreline is exposed to many threats, such as storm erosion, reductions in sediment longshore drift and sea level rise. Many of these threats to coastal areas, such as Ria Formosa, are likely to increase in the near future. The main objectives of the present study are to identify the areas in the system that are at most risk by assessing the evolution of the Ria Formosa barrier island system since the 1940s, and determine which interventions would be necessary to protect these areas.

- by Filipe Ceia
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- Management, Earth Sciences, Sea Level, Institution

Barrier islands and spits are geological young, highly dynamic and represent a complex coastal system that includes a number of different but closely related sedimentary depositional environments. In this study ground-penetrating radar data of different antenna frequencies and sedimentological data were combined to reveal the sedimentary structure and architecture of the southern barrier island spit of Sylt and to set up a barrier island stratigraphy. Based on these data, two sedimentological models have been generated for Southern Sylt which describes the inter-action between extreme
events, coastal processes and sedimentary development and contains the major episodes of barrier island evolution. The first model is concerned with the spit add-on zone where the barrier spit is attached to the central island moraine core and shows a landward migration through barrier rollover affected by an interplay of barrier retreat and washover flooding associated with accumulation of sediment in a backbarrier environment as a result of several storm surges. The spit add-on zone reveals a transgressive coarsening upward sequence starting with sandy mud flat deposits at the bottom which turn into coarser sandy tidal flat deposits toward the top. Sandy tidal flat deposits are overlain by washover sheet and washover fan deposits. The second model demonstrates a barrier spit accretion through southerly directed progradation. Eroded sediment was transported along the west coast of Sylt by longshore drift and was added to the southern spit-end. Progradation and barrier spit accretion were interrupted by severe storm surges. Storm surge generated erosion unconformities in a foreshore to shoreface environment redraw old spit-end positions that represent stages of barrier spit progradation.

- by Tanja Dr. Tillmann
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- Geography, Geology, Geomorphology, Sedimentology
- by David Mallinson
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- Barrier Islands, Technical Report

The availability of nearly 100 years of bathymetric measurements allows the analysis of the morphodynamic evolution of the Dutch Wadden Sea under rising sea-level and increasing human constraint. The historically observed roll-over mechanisms of landward barrier and coastline retreat cannot be sustained naturally due to numerous erosion control measures that have fixed the tidal basin and barrier dimensions. Nevertheless, the large continuous sedimentation in the tidal basins (nearly 600 million m3), the retained inlets and the similar channel-shoal characteristics of the basins during the observation period indicate that the Wadden Sea is resilient to anthropogenic influence, and can import sediment volumes even larger than those needed to compensate the present rate of sea-level rise. The largest sedimentation occurs in the Western Wadden Sea, where the influence of human intervention is dominant. The large infilling rates in closed-off channels, and along the basin shoreline, rather than a gradual increase in tidal flat heights, render it likely that this sedimentation is primarily a response to the closure of the Zuiderzee and not an adaptation sea-level rise. Most of the sediments were supplied by the ebb-tidal deltas. It is, however, unlikely that the sediment volume needed to reach a new equilibrium morphology in the Western Wadden Sea can be delivered by the remaining ebb-tidal deltas alone.

- by Ad van der Spek
- •
- Coastal Geomorphology, Barrier Islands, Coastal Evolution, Tidal inlets

This study systematically classifies washover dynamics with reference to coastal changes along the Ria Formosa barrier islands (Southern Portugal). Identification of washovers using a sequence of 11 sets of aerial photographs dated between 1947 and 2001 allowed a classification to be developed based on: (1) overwash evolution (increasing, decreasing, or constant overwash processes); (2) the mechanisms promoting washover formation (exceptional to infrequent oceanographic conditions, washout processes, structural erosion, inlet dynamics, and human interventions); and (3) the mechanisms promoting washover cessation (berm development, structural erosion, dune development, inlet dynamics, and human interventions). A total of 369 different washovers were observed along the Ria Formosa barriers during the study period, with 209 washovers being formed in various types of dune morphology and 303 being obliterated. The number of washovers was relatively stable from 1947 to 1972, and increased dramatically between 1972 and 1976 probably as a result of the development of immature inlet margins and downdrift starvation. From 1976 to 2001, washover occurrences declined and their spatial dimensions decreased, leading to a decrease in overwash activity over this time. Overall, the dominant formation mechanisms of washovers in the Ria Formosa were inlet dynamics (accounting for 57% of washovers formed) and structural erosion (20%), with human intervention mechanisms accounting for 12%. The cessation of washovers was dominated by dune development (33% of the washovers obliterated) followed by inlet dynamics (24%) and structural erosion (19%), while human intervention mechanisms accounted for 13%. The classification should be of use for the coastal management of barrier systems including the definition of overwash-prone areas and the determination of the relative importance of the mechanisms contributing to washover formation and cessation.

- by Ana Vila-Concejo and +1
- •
- Management, Geology, Geomorphology, Coastal Management

Islands are bodies of land surrounded by water; albeit well connected via the waves of ocean, movements of people and flows of technology. Smallness is both aesthetically pleasing and intensely practical. There are increasing challenges for small islands in our connected planet with the added risk for some of mounting global warming. This conference welcomes the presentation of research and reflection to address the nature of islands from the past to the future, to achieve a better understanding of the uniqueness, connections, cultures, ethics, technologies, innovation and sustainability for the many possible futures of islands and archipelagos. Sub-themes proposed are as follows:

- by Ana Matias and +1
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- Management, Geology, Geomorphology, Coastal Management

Geological sciences thomas harriot College of arts and sciences, institute for Coastal science and Policy east Carolina university froNt Cover PhotoGraPh. The shoreline in this South Nags Head photograph has flanked the sand-bagged houses... more

- by Reide Corbett
- •
- Coastal Erosion, Barrier Islands, Erosion, Coastal Zone

A series of regular bathymetric surveys of Texel Inlet and its ebb-tidal delta spanning a period of over 400 years forms a unique long-term morphodynamic dataset of this largest inlet of the Wadden Sea. The substantial changes in ebb-tidal delta evolution provide a clear example of the response of the inlet system to the cumulative effects of human intervention.
Analysis of the evolution of the ebb-tidal delta morphology shows different stages, each characterized by specific orientations of the main channels and shoals. Prior to construction of extensive coastal defense works on the southern shore of the inlet in 1750 A.D., the ebb-tidal delta showed a downdrift asymmetry. Periodic shoal breaching and downdrift channel relocation were the dominant mechanisms for sediment by-passing (major shoal bypassing). After construction of the coastal defence works, a stable ebb-tidal delta with a westward stretching main ebb-channel developed over a period of ca. 60 years. Damming of the Zuiderzee, the major part of the back-barrier basin in 1932 A.D., distorted this stable state and over a period of about 40 years the main channel switched to a southward course, remaining stable ever since. During the pre- and post-damming stable states the sediment bypassing took place as minor shoal by-passing; the main channel remained in position and smaller parts of the swash platform (periodically) migrated landward over the ebb-tidal delta.
The well-monitored large-scale changes on the ebb-tidal delta which were initiated by the construction of the coastal defence works and closure of the Zuiderzee show that incorporation of inlet modifications and back-barrier processes is vital for a correct description of the ebb-tidal delta dynamics and processes of Texel Inlet. A conceptual model is introduced to describe the process–response relation between intervention and ebb-tidal delta change.

- by Ad van der Spek
- •
- Coastal Geomorphology, Ebb-Tidal Deltas, Barrier Islands, Coastal Evolution

Santa Rosa Island is an 85 km-long, wave-dominated low-lying barrier island situated along the northwestern Florida coast, facing the Gulf of Mexico. The entire island was severely impacted by Ivan, a strong category 3 hurricane that made landfall about 45 km to the west in September of 2004. Ten months later in July of 2005, Dennis, another category 3 hurricane, made landfall about 30 km east of the western tip of the island. Santa Rosa Island is characterized by well-developed but relatively low dunefields, described in this paper as incipient and established dunes, based on the presence of grassy and woody types of vegetation, respectively. The dunes were severely eroded by the two hurricanes. This paper investigates the factors controlling the regional-scale destruction and survival of the dunefields.

- by Vanda Claudino Sales
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- Geology, Geomorphology, Coastal Dunes, Barrier Islands
- by Amy Moorman
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- Property Rights, Barrier Islands, Barrier Island

Sediment mineralogy, quartz-grain surface-textures, grain-size analysis, bore-hole logging and ground penetrating radar are combined to develop a three dimensional stratigraphic model of a back-barrier sand island in southeast Queensland, Australia. The island consists of an unconsolidated sedimentary pile above an erosional bounding surface at the top of the underlying bedrock. The stratigraphy is complex, recording the shift in depositional environments from fluvio-deltaic to strandplain, via estuarine stages of evolution. The back-barrier island deposits are correlated with the stratigraphy of the adjacent coastal plain to the west and the barrier island to the east. Extrapolation of optically stimulated luminescence dates obtained from the barrier island combined with direct dating of the back-barrier island sediments is used to constrain the depositional age and chronology of the back-barrier island stratigraphy. The modern depositional environment evolved from a chenier plain into a barrier island system by the flooding of an interdune swale and development of a shore-parallel back-barrier tidal lagoon. The lithological heterogeneity of the back-barrier island succession was controlled by the presence of a bedrock incised palaeovalley and changes in relative sea-level. Sedimentary facies associations constrain the spatial distribution of hydraulic properties controlled by lithological heterogeneity. Post-depositional alteration horizons are integrated with the facies model to account for the effects of weathering and diagenesis on hydraulic behaviour. The derived hydrostratigraphy describes a vertically stacked, dual aquifer, island groundwater system consisting of a semi-confined palaeovalley aquifer overlain by an unconfined strand-plain aquifer. Hydrostratigraphic analysis based on sedimentary facies associations, integrated with post-depositional alteration characteristics reveals great complexity of groundwater systems within small island settings. The facies modelling approach employed in this study more accurately estimates the distribution of lithological heterogeneity and the associated variations in hydraulic properties in the sedimentary pile.

- by Jonathan Hodgkinson
- •
- Geology, Geomorphology, Hydrogeology, Stratigraphy

The asymmetric Sf. Gheorghe lobe is the only active lobe in the Danube delta associated with a river-mouth bar (and related barrier islands and spits) that has continuously displayed cyclic development during the last 1500 years. During the early cycles, the Sf. Gheorghe distributary experienced a significant increase in sediment load (by an order of magnitude) as a result of the successive avulsions occurred 1.5-1.2 ka, which redistributed more water and sediment captured from the neighboring branches of Împuţita (southern distributary of the Sulina arm) and Dunavăţ. Morphological and sedimentological analyses together with a newly obtained chronology throw light on the multiple ridgeset (10) structure of Sf. Gheorghe lobe, each of them (excepting the first one) following a common evolutionary pattern reflected by the cyclic succession of the recurring stages: i) subaqueous mouth bar building, ii) barrier island emergence, and iii) transformation into a barrier spit with several secondary spits. The spits become encased into the muddy deltaic plain as narrow sandy ridges building out on the downdrift side of the lobe as a barrier-marsh plain, whereas the updrift side constantly accreted fed by longshore currents, forming a classic beach ridge plain. The size of each ridgeset increased exponentially with every new cycle due to the constant lengthening of the coastline as the downdrift side of the lobe advanced seaward through a series of progressively larger similar quadrilaterals, yielding a corresponding geometric progression of the delta front size. Even though each newly formed ridgeset (cycle) had a longer lifespan (the latest cycles lasting 4-5 times longer than the first ones: 200-440 years versus 50-80 years), the evolutionary model remained unchanged as long as the balance between wave-and river-borne sediments, defined by the sedimentary index (Si), remained constantly low (Si ≤ 0.1), whereas the mean advance rates of the river mouth remained constant at c.10 m/year. Abrupt changes occurred within the last cycle (since the beginning of the 20th century) as a consequence of human-induced depletion of sediment supplied by the Danube flow, and is mainly expressed by the complete cessation of the updrift coastal progradation and the prevalence of erosion in front of the river mouth. These changes, which engendered a threefold increase of the Si (0.37 at present), are reflected by the recent (1930s-present) river mouth dynamics, characterized by cessation of its long-term seaward expansion in favor of downdrift migration. This is indicative of the transition of the Sf. Gheorghe mouth from an asymmetric to a deflected wave-influenced delta morphology whose current developments mark a significant change in the multicentennial cyclic evolutionary pattern. The asymmetric to deflected transition reflects the net increase in the influence of wave-driven sediment circulation on river mouth morphology, corresponding to a critical Si threshold of ca. 0.2 (≤0.2: asymmetric; N0.2: deflected).

- by Luminita Preoteasa and +1
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- Archaeology, Barrier Islands

The Ria Formosa barrier island system is the most remarkable physiographic unit of the Algarve, south Portugal. This system composed of sand spits, beaches and dunes constitutes a Natural Park that has undergone artificial nourishment under the pro- ject “Rehabilitation of the lagoon system of Ria Formosa”. The main objective of this study is to evaluate the effects of a beach and dune rehabilitation program in particle size and morphology in two contrasting sites of the system (Ancão Peninsula and Tavira Island). A monitoring program was performed from June 1999 until September 2000, in order to determine the mor- phological and grain size changes along these beaches, before and after nourishment. The results of particle size analysis show the predominance of coarse sand at Ancão Peninsula and medium sands in Tavira Island. Nourished beaches presented coarser sands and bimodality, due to the heterogeneity of the dredged sediment used for nourishment. The nourished profiles, with increased sand stock, quickly developed natural profile morphology and proved to be able to decrease the effects of acting storms, namely avoiding dune erosion and overwashes. The soft interventions conducted at Ria Formosa proved to be useful on protecting the natural system, being a positive indication for future interventions at sensitive areas prone to marine erosion.

- by João Dias and +1
- •
- Barrier Islands

Various tide-related sediment transport mechanisms near a barrier island coast are addressed on the basis of analytical theory and numerical simulations carried out with a three-dimensional (3-D) numerical model. The theory proposed gives an explanation of the observed ''twin peaks'' in the concentration of suspended sediment; however, it does not adequately describe the whole variety of sediment responses. The major idea in this paper assumes that it is not only the change of the level of turbulence and advection individually but also the correlation between the two which controls the concentration of sediment. Because the horizontal gradients of sediment concentration are created not only by sources at the coast (e.g., fluxes from rivers) but also by the transport and turbulence, the system is highly nonlinear. Several simulations have been carried out aimed at revealing the nonlinear mechanisms in the sediment transport and individual contribution of turbulence and velocity field. An experiment in which the sediment model is driven only by turbulent kinetic energy fails to simulate most of the characteristic temporal and spatial sediment patterns. With another experiment it is demonstrated that the velocity gradient in the vertical gives an important mechanism shaping the patterns of temporal and spatial variability (and tidal asymmetries). Without shear diffusion, the sediment dynamics are largely governed by the ''displacement mechanism''; that is, the system is more linear. One practical conclusion from the numerical simulations is that using simplified (2-D) dynamics in sediment transport modeling along with externally prescribed turbulence characteristics could lead to large artifacts.

- by Emil Stanev
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- Geology, Case Studies, Multidisciplinary, Concentration

- by David Mallinson
- •
- Coastal Erosion, Barrier Islands, Erosion, Coastal Zone

This paper focuses on a small back-barrier sand-island on the southeast coast of Queensland. The freshwater lens in the study area exhibits anomalously high short-range salinity gradients at shallow depths, which cannot be explained using a standard seawater intrusion model. The island groundwater system consists of two aquifers: a semiconfined aquifer hosting saline to hypersaline groundwater and an overlying unconfined freshwater aquifer. The deeper aquifer is semiconfined within an incised paleovalley, and groundwater flow is restricted to an east – west direction. Tidal response observations show that the tidal signal propagates far more rapidly and is of much higher magnitude in the semiconfined aquifer than the unconfined aquifer. The tidal wave-pulse amplitude is also subject to greater attenuation in the unconfined aquifer. A conceptual hydrogeological model illustrates how upwelling of hypersaline groundwater, induced by density-dependent flow and tidal pumping, has contaminated the shallow groundwater resource. Salinisation at shallow depths is restricted to an area proximal to the paleovalley aquifer. The spatial distribution of lithological heterogeneity is an initial limiting control on the movement of the upwelling saline plume. The extent of shallow groundwater contamination is also limited by the presence of a baroclinic field, resulting from lateral variations in fluid density. Hydrochemical signatures have been used to support the model hypothesis and link the salinisation of fresh groundwater with the semiconfined aquifer as opposed to the surrounding estuarine surface water. The geometry and thickness of the freshwater lens are further controlled by the presence of the largely impermeable bedrock paleosurface between 9 and 12 m depth. The combination of hypersaline groundwater and hydraulically restrictive lithology at shallow depths has produced excessive thinning of the freshwater lens, demonstrating that the application of a model such as the Dupuit – Ghyben – Herzberg relationship would grossly overestimate the available groundwater resource.

- by Jonathan Hodgkinson
- •
- Earth Sciences, Geomorphology, Groundwater Contamination, Quaternary Geology

Barrier island longevity is threatened by the observed and modeled accelerating rates of sea-level rise. It has been suggested that subsurface geologic structure is also an important factor controlling barrier island morphology and long-term island evolution, yet the precise role of antecedent geology on the response and recovery of barrier islands to hurricanes and sea-level rise remains unclear. Thus, this study aims to provide more detailed insight into the role of the antecedent geology on barrier island evolution at two sites along the Texas, USA coast: Follets Island and a portion of North Padre Island. Alongshore and across-island ground-penetrating radar (GPR) and electromagnetic inductance (EMI) surveys are used in this study to infer subsurface geologic structure. The accuracy of the interpreted geophysical survey data was assessed using selective vibracoring. Information about island morphology is derived from airborne and terrestrial LiDAR-derived digital elevation models (DEMs). Preliminary results suggest that dune height is generally lower and washover frequency higher in areas where the antecedent geologic surface is deeper. Another important factor influencing dune breaching and washover locations is offshore bathymetry. The barrier island is generally narrower in areas where an offshore swale is present. The antecedent geologic structure is an important factor influencing barrier island morphology. Integrating EMI, GPR, and seismic subsurface geologic structure information and surficial morphology information helps improve our understanding of factors affecting barrier island evolution and the role that antecedent geology plays in island morphology.

- by Phil Wernette
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- Geology, Geophysics, Coastal Geomorphology, Barrier Islands

This paper focuses on a small back-barrier sand-island on the southeast coast of Queensland. The freshwater lens in the study area exhibits anomalously high short-range salinity gradients at shallow depths, which cannot be explained using a standard seawater intrusion model. The island groundwater system consists of two aquifers: a semiconfined aquifer hosting saline to hypersaline groundwater and an overlying unconfined freshwater aquifer. The deeper aquifer is semiconfined within an incised paleovalley, and groundwater flow is restricted to an east – west direction. Tidal response observations show that the tidal signal propagates far more rapidly and is of much higher magnitude in the semiconfined aquifer than the unconfined aquifer. The tidal wave-pulse amplitude is also subject to greater attenuation in the unconfined aquifer. A conceptual hydrogeological model illustrates how upwelling of hypersaline groundwater, induced by density-dependent flow and tidal pumping, has contaminated the shallow groundwater resource. Salinisation at shallow depths is restricted to an area proximal to the paleovalley aquifer. The spatial distribution of lithological heterogeneity is an initial limiting control on the movement of the upwelling saline plume. The extent of shallow groundwater contamination is also limited by the presence of a baroclinic field, resulting from lateral variations in fluid density. Hydrochemical signatures have been used to support the model hypothesis and link the salinisation of fresh groundwater with the semiconfined aquifer as opposed to the surrounding estuarine surface water. The geometry and thickness of the freshwater lens are further controlled by the presence of the largely impermeable bedrock paleosurface between 9 and 12 m depth. The combination of hypersaline groundwater and hydraulically restrictive lithology at shallow depths has produced excessive thinning of the freshwater lens, demonstrating that the application of a model such as the Dupuit –Ghyben– Herzberg relationship would grossly overestimate the available groundwater resource.

- by Stephen McLoughlin
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- Geomorphology, Quaternary Geology, Groundwater modeling, Groundwater Hydrology

International Geological Correlation Programme, International Geoscience Programme, IGCP 495, Outer Banks (N.C.), Barrier Islands, North Carolina Coastal System, Subaerial headlands, Submarine headlands, North Carolina Coastal Plain,... more

- by David Mallinson
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- Geology, Barrier Islands, Technical Report
- by Donald R Young
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- Carbon, Ecology, Global change, Actinobacteria

Barrier islands of the Pacific coast of Colombia repeatedly experience severe washover even when breaking waves in the eastern Pacific are low and onshore winds are calm. On the barrier island of El Choncho, recent non-storm washover events have breached a new inlet, caused rapid beach retreat, destroyed a shoreline protection structure, and flooded a small village of indigenous people so frequently that it had to be relocated. Barrier washover may be augmented by lowered land elevations associated with earthquake-induced subsidence or long-term beach retreat, but temporally it is most closely associated with a 20 to 30 em regional increase in sea level caused by El Nino. The contradiction of a tranquil tropical island scene simultaneously disturbed by hostile turbulent washover may be unique at present, but it exemplifies how coastal plains throughout the world would be affected if sea level were to rise rapidly as a result of global warming.

- by Gloria I. López
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- Engineering, Earth Sciences, Geology, Coastal Processes

The aim of the present paper is to analyse the recent morphological evolution of the sandy barriers of Ria Formosa, a multi-inlet system located in South Portugal, to assess evolution regimes and related controlling factors and to identify resilience mechanisms in response to natural and artificial drivers of change. The data collected comprise aerial photographs and wave buoy and hindcast time-series, covering the period from the 1950s to 2014. The results show that the barriers have either been growing, or remaining stable. The growth patterns were either promoted by natural mechanisms, or triggered by stabilization works and supported by natural factors (e.g. longshore transport, shoal attachment). The presence of a broad marsh platform in the backbarrier was found to promote barrier stability, while the sustainance of transgressive barriers is advocated by frequent overwash, combined with low depths in the backbarrier lagoon and localised replenishment of sand. These long-term evolution regimes and their relation to artificial and natural factors show that the barriers of Ria Formosa have been resilient during the time-frame of the study, either absorbing disturbances (Armona and Tavira), or adapting to change while maintaining their functions (rest of the barriers).

- by Katerina Kombiadou and +2
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- Resilience, Morphological evolution, Barrier Islands

Hurricane flooding is a leading natural threat to coastal communities. Recent evidence of sea level rise coupled with potential future global warming indicate that sea level rise will accelerate and hurricanes may intensify over the coming decades. In regions fronted by barrier islands, the protective capacity of these islands may diminish as they are degraded by rising sea level. Here we present a hydrodynamic and geospatial analysis of the relative role of barrier island degradation on potential future hurricane flooding. For the City of Corpus Christi, Texas, USA, hurricane flooding is projected to rise between 20% and 70% by the 2030s, resulting in an increase in property damages and impacted population. These findings indicate that adaptive management strategies should be developed and adopted for mitigating loss of natural barrier islands when these islands act as protective features for populated bayside communities. Finally, this study illustrates a method for applying models to forecast future storm protection benefits of barrier island restoration projects.

- by James Kaihatu and +1
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- Management, Earth Sciences, Climate Change, Sea Level

Sediment mineralogy, quartz-grain surface-textures, grain-size analysis, bore-hole logging and ground penetrating radar are combined to develop a three dimensional stratigraphic model of a back-barrier sand island in southeast Queensland, Australia. The island consists of an unconsolidated sedimentary pile above an erosional bounding surface at the top of the underlying bedrock. The stratigraphy is complex, recording the shift in depositional environments from fluvio-deltaic to strandplain, via estuarine stages of evolution. The back-barrier island deposits are correlated with the stratigraphy of the adjacent coastal plain to the west and the barrier island to the east. Extrapolation of optically stimulated luminescence dates obtained from the barrier island combined with direct dating of the back-barrier island sediments is used to constrain the depositional age and chronology of the back-barrier island stratigraphy. The modern depositional environment evolved from a chenier plain into a barrier island system by the flooding of an interdune swale and development of a shore-parallel back-barrier tidal lagoon. The lithological heterogeneity of the back-barrier island succession was controlled by the presence of a bedrock incised palaeovalley and changes in relative sealevel.
Sedimentary facies associations constrain the spatial distribution of hydraulic properties controlled by lithological heterogeneity. Postdepositional alteration horizons are integrated with the facies model to account for the effects of weathering and diagenesis on hydraulic behaviour. The derived hydrostratigraphy describes a vertically stacked, dual aquifer, island groundwater system consisting of a semi-confined palaeovalley aquifer overlain by an unconfined strand-plain aquifer.
Hydrostratigraphic analysis based on sedimentary facies associations, integrated with post-depositional alteration characteristics reveals great complexity of groundwater systems within small island settings. The facies modelling approach employed in this study more accurately estimates the distribution of lithological heterogeneity and the associated variations in hydraulic properties in the sedimentary pile.

- by Stephen McLoughlin
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- Geomorphology, Hydrogeology, Stratigraphy, Geoarchaeology

A regional scale modeling system is being developed for the Mississippi Sound and adjoining Mobile Bay, Biloxi Bay, Bay St. Louis, and Lake Borgne. The modeling system, consisting of a three-dimensional circulation model, a cohesive and non-cohesive sediment transport model and a wave model, will provide a reliable means to forecast littoral circulation, sediment suspension and transport, and surface waves. The modeling framework adopts a high-resolution orthogonal curvilinear grid that adequately resolves the bathymetric and coastline features of the Sound, especially the region of the barrier islands. The southern model boundary follows the 200m isobath, a natural dynamical barrier between the Sound and the rest of the Gulf of Mexico. The model performance has been evaluated to date by conducting tidal simulations using boundary conditions derived from a global tidal model and then compared with tides at the IHO stations across the Mississippi Sound. Freshwater plume dynamics emanating from various estuarine systems dynamically connected to the Sound have also been evaluated using the current model. Future model improvements will involve novel open boundary condition schemes and waveinduced physical processes. A comprehensive model calibration/validation effort will then follow.

- by Quamrul AHSAN
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- Atmospheric Modeling, System Dynamics, Geophysical Fluid Dynamics, Tides

David J. Mallinson, Stanley R. Riggs, Stephen J. Culver, Dorothea Ames East Carolina University Dept. Of Geological Sciences Greenville, NC, USA 27858 mallinsond@ecu.edu riggss@ecu.edu culvers@ecu.edu ... Benjamin P. Horton, Andrew C.... more

- by Stephen Culver
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- Barrier Islands, Technical Report

The Chesapeake Watershed Archaeological Research Foundation conducted a shoreline survey of the Atlantic seashore of Virginia in 2001 (see Lowery 2003a) and limited archaeological testing at site 44NH440 in 2003. These projects involved the Mockhorn Island area along the coast of Northampton County, Virginia. The present work was initiated because in 2003 we recognized that 44NH440, a low inundated former upland ridge, does not seem to have any Late Woodland archaeological components. The working hypothesis being that sea level rise over the last 1,000 years required the Late Woodland-era occupants of the area to focus their settlements on or near the forested hummocks located near the central and western sides of Mockhorn Island. As such, 44NH440 was abandoned because tidal processes linked to slightly higher regional sea levels were more regularly inundating the landform, which encompasses the site. To test this hypothesis shell refuse surface exposures located near or adjacent to the forested hummocks were selected for testing. It was assumed that some of these shell refuse areas might indeed represent the Late Woodland use of Mockhorn Island and its surrounding coastal environment. The investigation to test the working hypothesis was conducted from February 1, 2004 through June 31, 2004 in accordance with an agreement with the Virginia Department of Historic Resources. Our investigations concluded that sea level rise did impact human settlement locations on Mockhorn Island and that the Late Woodland occupants did relocate their settlements near the forested hummocks. The results of our work have ramifications relative to the reconstruction of regional sea level rise histories, as well as, human subsistence and settlement patterns.

Mineral and aqueous geochemical data are combined with a conceptual groundwater flow model, to establish the origin and fate of iron, aluminium and manganese in the groundwater system of a small backbarrier island. The flow model domain consists of an unconfined island fresh groundwater lens overlying a semi-confined hypersaline aquifer. The two aquifers are separated by a discontinuous, clay-rich aquitard and both contain diffusion governed variable density flow fields. High concentrations of dissolved iron and manganese are associated with brackish to hypersaline groundwater, although there is no systematic relationship with salinity. Calculation of S 2− /SO 4 2− and Fe 2+ /Fe 3+ redox couples and the results of thermodynamic modelling show that redox disequilibrium in the groundwater is widespread. Groundwater samples containing aqueous sulphide and ferric iron complexes are supersaturated with respect to pyrite, goethite and haematite but the prevailing state of redox disequilibrium controls mineral dissolution and precipitation. Aqueous iron in the deeper regions of both aquifers is derived from the dissolution of iron oxide-hydroxides in lateritic palaeosols controlled by seasonal fluctuations in groundwater redox state. Aqueous manganese is potentially derived from the dissolution of ilmenite and amorphous oxidehydroxides. The oxidation of iron sulphides contributes to the aqueous iron concentration and sulphuric acid production in the shallow groundwater. The solubility of aluminium is also limited by this process, governed by acidity regulation. A significant proportion of aqueous iron is transmitted from the semi-confined to the overlying unconfined aquifer through discontinuities in the aquitard layer. Movement of metals in solution outside the island groundwater system is restricted by the presence of diffusion boundaries within variable density transition zones.

- by Jonathan Hodgkinson
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- Geology, Geochemistry, Geomorphology, Hydrogeology

- by Ana Matias
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- Management, Geology, Geomorphology, Coastal Management

Studies of dune vegetation patterns have emphasized two structuring agents: local environmental gradients that shape the prominent zonation of coastal plant species, and disturbance patches initiated by overwash during coastal storms. For dune systems of two barrier islands in the Georgia Bight, we investigate how the interplay of these two conceptual frames generate patterns in (1) longitudinal (along-shore) and transverse (across-shore) compositional variability and (2) the arrangement of species along transverse gradients. We describe how this interplay constitutes a complex biogeomorphic system in which disturbance and recovery along gradients reinforce one another in positive feedback. Topographic and cover data were sampled within strip transects aligned perpendicular to the shoreline at study sites along a frequently storm-overwashed microtidal (South Core Banks, North Carolina) and an infrequently overwashed mesotidal (Sapelo Island, Georgia) barrier island. Multiresponse permutation procedures revealed that Sapelo has significantly greater transect-level longitudinal and transverse compositional variability. Nonmetric multidimensional scaling indicated that a single dominant transverse species gradient characterizes South Core, versus two spatially intersecting vegetation gradients for Sapelo. On South Core, reduced relief promoted by plant species of horizontally extensive growth forms reinforces the spread of overwash events across the landscape, thus overlaying disturbance and recovery gradients. Species-mediated dune topographic roughness on Sapelo buffers the dune vegetation from potential stand-wide disturbances, thereby juxtaposing disturbance and recovery gradients to a greater extent. We discuss the benefit of incorporating a complex adaptive-systems framework into the reductionist methodologies invoked in field-based biogeographical studies.

- by Travis Winkler
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- Human Geography, Complex Adaptive Systems, Complex System, Barrier Islands
- by Tae Goun Kim
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- Applied Economics, Contingent valuation, Barrier Islands, Barrier Island

- by Edwin Elias
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- Earth Sciences, Marine Geology, Coastal Geomorphology, Ebb-Tidal Deltas