Barrier Island Research Articles

OBSERVATIONS AND MODELING OF EROSION AND RECOVERY OF A COUPLED BEACH-DUNE SYSTEM

The geomorphic and ecological vulnerability of barrier islands is influenced by the way they respond to oceanographic and anthropogenic forcing over a broad range of temporal scales. Integrated models capable of simulating these processes are increasingly necessary to understand barrier island trajectories under future conditions and to aid in management decisions by evaluating the impact of potential restoration activities. While there are numerical models capable of simulating some of the dominant barrier processes, the role of beach berm evolution is rarely included despite the important function of berms in sustaining beaches, enabling dune growth via Aeolian transport, and mitigating backshore and dune erosion during storm events. This is primarily due to a lack of available data that resolves details of beach profile evolution at necessary temporal scales (e.g., seasonal, post-storm recovery, etc.) to test and develop models and the inherent difficulty of including these intra-annual processes into decadal scale models of barrier island evolution. Here we describe a unique and growing dataset of environmental forcing and barrier island topographic change. We also use the dataset to develop and test a model for barrier island evolution and quantify the role of storms, moderate wave conditions, and wind-driven transport in dictating coastal change on various timescales.

Hydrogeologic controls on barrier island geomorphology: Insights from electromagnetic surveys

Barrier islands provide a first line of defense for coastal communities against storms, hurricanes, and sea-level rise. The geomorphology of barrier islands exerts a major control on storm impact and island recovery. In turn, barrier island geomorphology is affected by subsurface hydrogeologic conditions. In this study, we investigated the relationship between subsurface hydrogeologic conditions and geomorphology of Padre Island, with a focus on the influence of human development. We measured apparent electrical conductivities using frequency-domain electromagnetic (FDEM) surveys and spatially correlated them with the island's morphology. The latter was generated from a 1 m resolution digital elevation model. Four distinct zones were identified from the observed variations in apparent conductivity and elevation, revealing their inverse correlation. The beach area (Zone I) exhibits the highest apparent conductivity (289.7 ± 66.3 mS/m) and the lowest elevations (1.4 ± 0.2 m). These trends are largely due to the proximity of the beach to saline groundwater and maritime floods. Conversely, the foredune area (Zone II) presents the lowest apparent conductivity (19.0 ± 3.4 mS/m) and the highest elevation (4.5 ± 0.4 m) due to a greater distance from saline waters, deeper groundwater levels, and relatively dry soil conditions. Human development has significantly impacted Zones III (east central zone) and IV (west central zone), contributing to an increase in apparent conductivity (Zone III: 40.3 ± 21.8 mS/m; Zone IV: 159.5 ± 83.0 mS/m) and a reduction in elevation (Zone III: 2.1 ± 0.5 m; Zone IV: 1.3 ± 0.4 m). Anthropogenic activities have modified hydrologic patterns, introduced conductive materials, and altered vegetation cover and soil composition. This research elucidates the interplay between subsurface electrical conductivity, surface morphology, and the impact of human development on barrier island geomorphology, providing crucial insights for coastal management and conservation efforts.

EFFECTS OF WAVE SKEWNESS AND ASYMMETRY ON THE EVOLUTION OF FIRE ISLAND, NEW YORK

Bedload transport of sediment by waves and currents is one of the key physical processes that affect the evolution of coasts, nearshore areas, and the engineering practices there. Wave skewness and asymmetry, both of which increase as waves shoal, result in a net bedload sediment flux over a wave cycle. The impacts of this mechanism on large-scale coastal and shoreline change are investigated in this study, using field observations and Coupled Ocean Atmosphere Wave Sediment Transport (COAWST), a hydrodynamic process-based numerical modeling system (Warner et al., 2010). The study site is Fire Island, New York, located at the Atlantic Coast of the USA, with a focus on the persistent shoreline shape, at the western half of this 50-km-long barrier island, that has been hypothesized to be linked to the sand deposits at the shoreface.

A checklist of dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) associated with the Vypin-Kadamakkudy Barrier Island System, Kerala, India

Barrier islands are one of the most dynamic ecosystems that are constantly changing with waves, wind, tidal energies, and so on. These islands are placed parallel to the shore with gently sloping coastal plains and a moderate tidal range supported by estuaries and wetlands. They act as a natural barrier to protect the land from high tides and support diverse taxa. Dung beetles are ecologically important organisms that facilitate various services influencing the total stability of that ecosystem. They can be considered as a focal taxon, and their conservation and protection keep the ecosystem clean and healthy. The present study is a preliminary study on the dung beetles from a tropical barrier island system; the Vypin-Kadamakkudy Barrier Island System; located in the Kerala part of the south Indian coast. The study accounted for 29 dung beetle species of eight genera under three tribes. The heavily populated island system is marked by two new reports to Kerala, namely, Catharsius pithecius Fabricius, 1775 and Digitonthophagus bonasus (Fabricius, 1775). Four species reported are already categorized as rare in the South Western Ghats.

A PATH TOWARDS HOLISTIC COASTAL ZONE MANAGEMENT IN TEXAS LEVERAGING SIGNIFICANT INVESTMENTS IN DATA COLLECTION, PLANNING, AND IMPLEMENTATION

The Gulf of Mexico shorelines of Texas are in a largely regressive state due to an amalgamation of factors including but not limited to: sea level rise, subsidence, littoral drift, and riverine supply disruptions. In some areas the erosion rate is several meters annually, leading to significant loss of coastal barrier island area. The bulk of the coastal barrier systems in Texas is undeveloped. However, barrier island loss is no longer able to go unnoticed as there is ever-growing recognition of their intrinsic value to coastal habitat and economies and their role in coastal storm resilience. Projects with significant merit and sediment needs are being identified for funding, which could result in a firstcome- first-serve extraction of the easily available and less costly sediment resources. Without proper management, the complexity and cost of future projects will naturally escalate, leading to a reduction in investments due to lower returns. The following questions need to be addressed: how can lower returns be avoided to incentivize investment and maximize coastal restoration efforts in Texas? And what can be done to galvanize support for beneficial use (BU) placement of beach-quality dredge material to minimize its removal from the littoral system? What can be done now to inform and leverage the existing and future knowledge so that management decisions lead to better outcomes for the environment and Texas constituents? A well thought out and executed plan maximizing returns and coastal resilience will enable other regions to more easily replicate the success.

Agricultural economic concept toward earthquake and tsunami in Simeulue Island

The agricultural economic concept comprises research and education, smallholder and rural development, project planning and administration, as well as the formulation, planning, and analysis of macro-level policies. This study was out to explain the agricultural economic theory behind project management and planning on Simeulue Island. This study used an ethnographic approach and a qualitative paradigm. The information was gathered through audio-visual recordings, in-depth interviews with Simeuluenese, and other sources. Gathering information from Simeuluense about characteristic plants that have promise as food resources, especially the major food, was the first step in developing an agricultural economic framework. The next step is to determine the connection between Simeulue island’s readiness for mitigation and the agricultural economic idea. The concept is then categorized by making an effort to grow and cultivate a typical plant. Moreover, food processing for food preservation is to be developed for the food resource. As an agricultural concept, sustainability and food security are essential regarding preservation in facing mitigation, especially for a disaster such as an earthquake or tsunami of an island which needs much time to have aid from overseas to survive on the barrier island.

THE EFFECT OF WAVE OBLIQUITY ON DUNE EROSION: A FIELD EXPERIMENT

Storm conditions can lead to excessive dune erosion with potential floods as a consequence. Barrier islands and low-lying countries protected by dunes are especially vulnerable to dune erosion. To properly assess the risks these areas face, a clear understanding of the physical processes during dune erosion is required. One of such processes is the effect of wave obliquity on sediment transport in the surf zone. Classic dune erosion models assume that dune erosion volumes decrease under oblique wave attack, because the time-averaged cross-shore undertow decreases in magnitude and with that offshore directed sediment transport decreases (Steetzel, 1993). More recent process-based erosion models predict an increase in erosion quantities, because the generated longshore currents increase surf zone sediment concentrations, and with that offshore directed sediment transport increases (Den Heijer, 2013). The main objective of this study is to analyse the effect of wave obliquity on dune erosion through a field experiment, by quantifying the effect of the decreasing undertow but increasing alongshore current on sediment concentrations in the surf zone.

CASE STUDY OF INTEGRATED COASTAL ZONE MANAGEMENT IN IVORY COAST: STABILIZATION OF A MIGRATING TIDAL INLET BY SOFT PROTECTION MEASURES

The village of Lahou Kpanda (Grand Lahou, Côte d'Ivoire), located to the immediate west of the mouth of the Bandama River, on the barrier island of the Tagba lagoon, is highly vulnerable to coastal erosion. It is directly threatened by the migration of the river mouth, which has been occurring at an average speed of 160 m/year over the last 10 years, as well as by the risks of flooding and coastal flooding which the effects of climate change will exacerbate further. This article presents the study, beginning in 2019 and financed by the WACA programme, which contributed to the choice and dimensioning of a sustainable solution for stabilization of the Grand-Lahou sandy barrier island.

Unprecedented Historical Erosion of US Gulf Coast: A Consequence of Accelerated Sea‐Level Rise?

AbstractMost of the US Gulf Coast is composed of barrier islands, peninsulas, chenier plains, and mainland beaches that are the main line of defense for wetlands, estuaries, and urban and industrial centers from rising sea level and severe storms. These wave‐dominated shorelines are currently experiencing widespread erosion. Using newly acquired and existing results from 13 sites spanning south Florida to south Texas, we compare shoreline migration rates during the late Holocene (∼−4000 to 1850 CE) with historical changes since the mid‐19th century. The records show an overall trend of seaward growth during the late Holocene followed by landward migration or a decrease in the rate of growth during historical time. Diminishing offshore sand supply, human alteration of rivers and coastal sand transport, and severe storms have contributed to this change in shoreline trajectory, but their influence has been mostly limited in extent. The most likely cause of this reversal from coastal stability and growth to widespread shoreline retreat is the dramatic historical increase in the rate of sea‐level rise over the past century.

Advances in Morphodynamic Modeling of Coastal Barriers: A Review

Advances in Morphodynamic Modeling of Coastal Barriers: A Review

REINFORCING ECOSYSTEM ENGINEERS WITH ENHANCED VEGETATION AND AN ARTIFICIAL REEF ALONG THE US RHODE ISLAND COASTAL BARRIER SYSTEMS

Beach barrier systems (BBS) act as “ecosystem engi-neers” (EE), protecting the mainland and back bays from direct wave impact and reducing storm surge and flow passing through their inlets. BBS naturally adapt to slowly evolving wave climates by regressing or transgressing. However, observations show that BBS have been destabilized during past periods of fast changes in sea level or wave climate, potentially leading to drowning of the barrier. In this respect, current predictions of large changes in future Sea Level Rise (SLR) and wave climate, combined with anthropogenic effects, are concerning as these could challenge the natural adaptability of BBS. This raises the following questions: (1) can the future protective ability of local EE be predicted? (2) can the added benefits of implementing selected Nature Based Solutions (NbS) to enhance this natural protective ability be quantified, as well as their potentially negative feedback effects? In this study, these questions are considered for the south shore of Rhode Island (RI) through numerical modeling, in part based on earlier regional storm hazard assessment (Grilli et al., 2020). Specifically, here, as part of a NOAA project (“Effects of Sea-Level Rise 2021, Coastal Resilience” program), we assess the efficiency of NbS in changing climate conditions, while integrating local concerns, observed trends, and supporting local ecosystem and people’s way of life.

Assessing the morphodynamic response of a New England beach-barrier system to an artificial reef

As a result of climate change and the ensuing accelerating sea level rise, the Ninigret Trustom Pond beach barrier system, located along the southern shore of Rhode Island, USA, has become increasingly vulnerable to tropical storms, hurricanes, and Nor’easters affecting the region. In this work, we explore the ability of a segmented artificial reef (AR) to protect the Ninigret Trustom Pond beach barrier system, by reducing the incident wave energy and ultimately the beach erosion. A set of nine AR concepts are selected, which are predicted to be accretive based on Ranasinghe et al.’s (2010) design criterion (RVB), extended by van der Baan (2013) to apply to segmented submerged breakwaters. The effectiveness of each concept is then assessed through numerical simulations, for both average wave climate conditions and storm events, with and without sea level rise, using the 2D morphodynamic model XBeach. The AR concepts are evaluated based on their ability to reduce coastal erosion during the storm events, including with a near future sea level rise of 0.31 m (scenario based on local prediction by 2050 relative to 2020 following the intermediate NOAA scenario) , while ensuring a slightly accretive behavior in average wave conditions. The reduction of the coastal erosion during the storm events is quantified by comparing the subaerial eroded volume at the site, with or without sea level rise, when implementing each of the nine pre-selected AR concepts. While all concepts are found to protect the shoreline during storm events, including with the 0.31 m sea level rise scenario, four of the nine AR concepts, pre-selected to be accretive based on the RVB criterion, are found to be erosive in average conditions. Assuming a given submergence level, the distance to the shoreline and the AR lateral confinement ratio, LC, (gap width to length ratio of the segments) are the main controlling parameter.

Golf course living leads to a diet shift for American alligators.

Human-driven land use change can fundamentally alter ecological communities, especially the diversity and abundance of large-bodied predators. Yet, despite the important roles large-bodied predators play in structuring communities through feeding, there have been only a few investigations of how the feeding patterns of large-bodied predators change in human-dominated landscapes. One group of large-bodied predators that has been largely overlooked in the context of land use change is the crocodilians. To help fill these gaps, we studied the feeding patterns of juvenile American alligators (Alligator mississippiensis) on neighboring barrier islands on the southeast coast of Georgia, USA. Jekyll Island has multiple golf courses and substantial amounts of human activity, while Sapelo Island does not have any golf courses and a much smaller amount of human activity. We found that juvenile alligator populations on both islands ate the same types of prey but in vastly different quantities. Sapelo Island alligators primarily consumed crustaceans while alligators that lived on Jekyll Island's golf courses ate mostly insects/arachnids. Furthermore, the Jekyll Island alligators exhibited a much more generalist feeding pattern (individuals mostly ate the same types of prey in the same quantities) than the more specialized Sapelo Island alligators (diets were more varied across individuals). The most likely explanation for our results is that alligators living on golf courses have different habitat use patterns and have access to different prey communities relative to alligators in more natural habitats. Thus, land use change can strongly alter the feeding patterns of large-bodied predators and, as a result, may affect their body condition, exposure to human-made chemicals, and role within ecological communities.

Transgression Related Holocene Coastal Glendonites from Historic Sites

This study examines the occurrence of glendonite along coastlines since 1825, which have been previously referred to under different names such as Pseudogaylussite, Fundylite, and Kool Hoot across eleven sites. By utilising element ratios and 14C radiometric dating techniques, we establish a more accurate chronology for these varied sites ranging from 10 to 1 thousand years before the present (Ky BP). Sites include tidal flats, coastal barrier islands, and Wadden Sea environments. While some sites still exist, others are only known through publications and museum collections. Our research expands upon previous findings by presenting petrographic evidence that correlates with glendonite formation. Through the examination of the Olenitsa site on the Kola Peninsula, we demonstrate that marine bioclasts enclosed within concretions surrounding glendonites provide temporal context, suggesting that these outcrops were formed during a single event under changing conditions. Notably, certain sediment structures at selected sites indicate the occurrence of cold-water ice-raft storm events and the presence of drop stones. Furthermore, our paper explores the association of historic coastal sites with the formation of ikaite, highlighting the limitations of relying solely on geochemistry and isotopic analysis for interpretation. Intriguingly, we observe that pseudomorphs are abundant in specific areas but absent in adjacent regions with similar environmental, physical, and chemical conditions. No apparent connection is found between volcanic dust cloud-induced cold spells and glendonite. The distribution of coastal glendonites is more likely related to periods of climatic cooling through other means. We show that radiometric dating with 14C provides an indication of age, but the results can be erroneous due to the inclusion of older carbon sources in the analysis. The oldest locations discussed in this study are Kool Hoot (Alaska) and the river Clyde (Scotland), and the youngest glendonites discussed are from the Bay of Fundy in Canada. Occurrences from the Wadden Sea are intermediate in age and sit between the other two groups. The age of the Olenitsa site on the Russian Kola Peninsula is uncertain and still debated. We show that measuring the ratio of Mg/Ca can indicate how much the recrystallised ikaite preserved as calcite is influenced by diagenetic pore waters.

Hydraulic head fluctuations in an intermediate depth coastal surface aquifer

Tides and storm surges are important drivers of groundwater circulation and fluxes in coastal aquifers. However, few field studies have characterized the response of the coastal aquifer to both forcings. Here, three years of hydraulic head observations in a roughly 20-m deep barrier island surface aquifer are used to investigate the inland propagation of fluctuations driven by ocean water-level changes owing to diurnal and semi-diurnal tides and storm-induced surge and wave-driven setup. Similar to prior observations, the observed rate of amplitude attenuation of the hydraulic head fluctuations is higher than the inland increase in phase lag for the tidally-driven head fluctuations. Additionally, tidal hydraulic head fluctuations deeper in the aquifer lead those nearer the surface of the aquifer. In contrast, storm surges with periods of several days have similar rates of amplitude attenuation and inland increase in phase lags, and hydraulic head fluctuations are roughly depth uniform. A nonlinear, intermediate aquifer-depth theory (not previously compared with field observations) describes the inland and vertical changes of tidal amplitudes and phase lags, and collapses to the linear solution for long period fluctuations, consistent with the storm surge observations. The diffusivity estimated by fitting intermediate depth solutions to the observed tidal amplitude attenuation and rate of inland phase lag is consistent with the aquifer properties, providing a method to characterize aquifers using coastal head observations. Numerical model simulations neglecting capillary effects, hysteresis, and vertical layering (which can cause discrepancies between amplitude attenuation and phase lag evolution) are similar to the observations and support the importance of the depth of the aquifer relative to the wavelength of the hydraulic head fluctuations.

Incised valleys on the Algarve inner shelf, northern Gulf of Cadiz margin: Stratigraphic architecture and controlling factors in a low fluvial supply setting

A network of cross-shelf paleovalleys has been recognized over the paleo-inner shelf off the Gilão-Almargem Estuary, a small fluvial drainage system that presently receives minor sediment supply in the eastern Algarve shelf, northern margin of the Gulf of Cadiz (SW Iberian Peninsula). This study is aimed at determining the driving controls that triggered substantially different paleohydrological conditions and sedimentary dynamics of ancient fluvial systems in this margin. We focus on evidences of secondary controls on valley genesis and evolution, superimposed to primary glacio-eustatic control such as antecedent geology, low fluvial supply and changing hydrodynamic regimes. The architecture and spatial distribution of these paleovalleys were interpreted based on a grid of seismic profiles with different resolutions. Likewise, a sediment core obtained in a distal position of the paleovalley system provided information about sedimentary processes during the most recent stage of valley infilling. The chronostratigraphic framework was constructed based on regional seismic horizons defined in previous studies and complemented with two AMS 14C dates obtained from bivalve shells.The inner shelf paleovalley system is composed of several incised valley features which exhibit a remarkable similar internal architecture. These inner valley features exhibit two major incision phases (from oldest to youngest; IP 2 and IP 1) that are thought to constitute a simple paleovalley system formed during the last glacial cycle. The origins of the incision are considered to be different. The older one is related to fluvial incision during the sea-level fall leading into the Last Glacial Maximum, whereas the recent one is interpreted as the result of tidal scour during the postglacial transgression. Their corresponding infillings are interpreted, respectively, as estuarine bay-fill deposits and estuary-mouth sands. Overlying the paleovalley infilling, a distinctive reflective unit is in agreement with the generation of coastal barriers and related depositional systems.The formation of the paleo-inner-shelf paleovalley system was strongly conditioned by antecedent geology, which strongly limited the generation of wide incised valleys and determined the amount of incision landward of a well-defined break of slope. Its postglacial infilling was mainly estuarine in nature, likely involving the development of a dendritic system, with numerous barriers interrupted by tidal inlets and channels in a mixed estuarine system with low fluvial supply.

Twenty-Year Record of Salt Marsh Elevation Dynamics in Response to Sea-Level Rise and Storm-Driven Barrier Island Geomorphic Processes: Fire Island, NY, USA

Twenty-Year Record of Salt Marsh Elevation Dynamics in Response to Sea-Level Rise and Storm-Driven Barrier Island Geomorphic Processes: Fire Island, NY, USA

Spatial and temporal variations of seabed sediment characteristics in the inner Louisiana shelf

Although many studies have been performed in the northern Gulf of Mexico, there have been a paucity of high-resolution sediment data collected from seabed. New multicores were collected repeatedly at 4 fixed stations in the inner Louisiana shelf on March 12, 2021, July 7, 2021, November 20, 2021, and March 5, 2022, respectively, to study detailed spatial and temporal variations of surficial sediment. Being a very high sediment accumulation zone, Raccoon Island dredge pit and its nearby shelf were selected as our study area and additional six vibracores were collected inside and outside the pit for comparison. This study area is about 140 km west of the modern Mississippi Delta and 70 km southeast of the Atchafalaya Delta. A total of 624 samples from both vibracores and multicores were analyzed for this study. Spatially, our results show that sediment near Ship Shoal was the coarsest and sediment deposited in the pit was the finest. The organic matter was highest inside the pit and lowest near Ship Shoal. The carbonate content was the lowest near Ship Shoal. Temporally, surficial sediments were generally coarser in July and November of 2021 and finer in March of 2021 and March of 2022. Although the Mississippi and Atchafalaya Rivers supply a large amount of sediment during spring season, it takes time for the river-derived sediment to be delivered into the study area. Hurricanes Delta, Zeta and Ida passed this area and greatly impacted sediment transport in the years 2021 and 2022. The comparatively coarser sediment in July and November of 2021 were likely related to the resuspension of some coarse sediment by these hurricane events. Besides the river supply, Ship Shoal and barrier islands are nearby localized sandy sources and inner Louisiana shelf is a widespread mud source. This spatial heterogeneity of surficial sediment interplays with the timing of Mississippi and Atchafalaya River flood season and hurricanes and together dictates the sediment texture. This research on a filled-up dredge pit can benefit future evaluation of the safety of existing oil infrastructure and the feasibility of building new pipelines and platforms after dredging activities. Our results also shed light on the study of river- and hurricane-impacted sediment transport in muddy and mixed-texture passive continental margins around the world.

Flood vulnerability under sea level rise for a coastal community located in a backbarrier environment, Portugal

Sea level rise will be a major threat to coastal communities within the next century due to the intensity and severity of the floods it can cause. A new methodology considering water infiltration, slope, and hydraulic connectivity was developed to assess the potential inundation extension associated with different total water level and sea level rise scenarios on sandy coasts. This methodology was applied for the current conditions as well as 2050 and 2100 scenarios of storm surge and high tide levels with return periods of 1 year and 100 years. The study area is Culatra village, located on the lagoon side of a barrier island in southern Portugal. The effects of shoreline evolution after the construction of a harbor and associated beach nourishment were also evaluated within the inundation scenarios. The results show that, within the study area, total water level variations caused by sea level rise have a greater influence on the inundation extension than shoreline retreat. The village appears to be safe for the current and 2050 total water level scenarios with a 1-year return period but would be highly affected by 100-year return periods, especially from 2050 onwards. This novel approach represents an improvement on more common flood mapping methods such as the bathtub approach and can be easily applied to other backbarrier environments under sea level rise or facing coastal erosion.

Physics-based modeling of climate change impact on hurricane-induced coastal erosion hazards

Coastal erosion is an adverse impact of extreme water levels during major hurricanes. A warmer climate is expected to increase storm surge and wave hazards due to hurricane climatology change (HCC) and sea level rise (SLR). We conduct physics-based morphodynamic modeling to quantify the regional impacts of HCC and SLR on erosion hazards to sandy beaches and dunes along the barrier islands of New Jersey in the United States. Under the RCP8.5 scenario, we find a substantial increase in erosion hazards from the late-20th-century to late-21st-century. The regionally averaged 100-year eroded volume of beach-dune systems would increase by 58 and 84%, respectively, under the HCC and HCC + SLR scenarios. Our projections show a large spatial variability in future changes to erosion hazards, suggesting that, in addition to HCC and SLR, the morphological characteristics of beach-dune systems play an important role in the impacts of climate change on coastal erosion.