Barrier Island Research Articles

Nearly five decades of changing shoreline mobility along the densely developed Lagos barrier-lagoon coast of Nigeria: A remote sensing approach

Lagos is the old capital and largest port city in Nigeria. There are increased ecological and environmental problems around this coastal area with fast-growing industrialization and a population of 14 million in 2020. In this study, we utilized satellite images to study the shoreline evolution of Lagos Lagoon Barrier coast, Nigeria from 1973 to 2019. The Lagos Lagoon Barrier coast is divided into three sections: Section I (Marginal Lagos), section II (Eko Atlantic City), and section III (Lekki peninsula). Section I coast was stable compared to other sections with around 77% of the section experiencing erosion with the averaging rate of −1.73 m/yr, and the remaining 23% accreting at the rate of +0.57 m/yr throughout the study period. Around 92% of Section II was eroded at the rate of −3.59 m/yr, and 8% of this section accreting at the rate of +4.46 m/yr from 1973 to 2008, with a serious erosion rate of −11.79 m/yr from 1986 to 1999. After the Eko Atlantic City project from 2008 to 2019, Section II experienced advancement up to +92.16 m/yr (53%) and a retreat of up to −6.50 m/yr (47%). Along section III, erosion dominates with around 90% of this section being eroded at the averaging rate of −3.55 m/yr with only 10% accreting at the averaging rate of +1.10 m/yr for the study period. Along the westernmost edge of section III, intense erosion up to +7.10 m/yr dominates and continues eastward of Victoria Island from 2012 to 2019. Furthermore, we recorded shoreline erosion up to −11 m/yr along the Ibeju-Lekki axis and Lagos Free Trade Zone (eastern fringe of section III) from 1999 to 2012.Extrapolating the responsible factors for the shoreline fluctuations along the Lagos Lagoon Barrier coast, this study has identified a combined impact of sea-level rise, limited sediment supplied by longshore current from adjacent rivers due to construction of dams along the several tributaries in the Bight of Benin, hard coastal engineering procedure such as the Eko Atlantic City (section II) and Lekki deep seaport projects, and intensified population along the coastline to have contributed to the erosion feature observed along the study area. Moreover, this study has revealed that Eko Atlantic City may have contributed to the eroding coast along section III. Our final deduction shows that section I is dominated by natural shoreline change patterns and therefore primarily responded to the effect of sea-level rise. Section III is influenced by both natural and human forces while section II is influenced by human intervention through coastal protection as a result of reverse-engineering the effect of climate change and sea-level rise. Conclusively, this study has recommended that current coastal management policies and plans in Lagos State need to be reconsidered and revised to ensure the sustainable use of the coastal zone.

Controls on coastal flooding in the southern Baltic Sea revealed from the late Holocene sedimentary records

Climate change and related sea-level rise pose significant threats to lowland coasts. However, the role of key controlling factors responsible for the frequency and landward extent of extreme storm surges is not yet fully understood. Here, we present a high-resolution sedimentary record of extreme storm surge flooding from the non-tidal southern Baltic Sea, spanning two periods: 3.6–2.9 ka BP and 0.7 ka BP until present. Sediments from coastal wetland, including sandy event layers, were analyzed by sedimentological (grain size, loss-on-ignition, micromorphology), geochronological (14C), geochemical (XRF), mineralogical (heavy minerals) and micropaleontological (diatoms) methods. The results show that both periods were characterized by high-frequency of storm surge flooding, in order of 1.3–4.2 events per century. These periods correlate with phases of enhanced storminess in northwest Europe and took place during both rising and fluctuating sea levels. The study shows that the frequency and landward extent of coastal inundation, largely depended on the development of natural barriers (e.g. beach ridges and aeolian foredunes). Thus, in the context of the future coastal storm-surge hazard, the protection of existing coastal barriers and their morphology is essential.

Coastal Microbial Communities Disrupted During the 2018 Hurricane Season in Outer Banks, North Carolina.

Hurricane frequencies and intensities are expected to increase under warming climate scenarios, increasing potential to disrupt microbial communities from steady-state conditions and alter ecosystem function. This study shows the impact of hurricane season on microbial community dynamics within the barrier island system of Outer Banks, North Carolina. We found that the passage of two sequential energetic hurricanes in 2018 (Florence and Michael) were correlated with shifts in total and active (DNA and RNA) portions of bacterial communities but not in archaeal communities, and within surface waters but not within the sediment. These microbial community shifts were distinct from non-hurricane season conditions, suggesting significant implications for nutrient cycling in nearshore and offshore environments. Hurricane-influenced marine sites in the coastal North Atlantic region had lower microbial community evenness and Shannon diversity, in addition to increased relative abundance of copiotrophic microbes compared to non-hurricane conditions. The abundance of functional genes associated with carbon and nitrogen cycling pathways were also correlated with the storm season, potentially shifting microbial communities at offshore sites from autotroph-dominated to heterotroph-dominated and leading to impacts on local carbon budgets. Understanding the geographic- and system-dependent responses of coastal microbial communities to extreme storm disturbances is critical for predicting impacts to nutrient cycling and ecosystem stability in current and future climate scenarios.

Review and direct evidence of transgressive aeolian sand sheet and dunefield initiation

AbstractThe multiple hypotheses which exist to explain the initiation of transgressive aeolian sand sheets and dunefields, are reviewed and discussed. Direct evidence supporting many of these hypotheses is largely lacking. In South Australia, the Younghusband Peninsula coastal barrier extends ~180 km and predominantly comprises transgressive and parabolic dunefields. The 42 Mile Crossing area on the barrier is undergoing significant erosion at variable rates of 0.5 to 5.0 m/yr, and a new transgressive aeolian sand sheet has rapidly developed in ~1 year and is extending landwards at an average rate of 13 m/yr. This research provides unequivocal evidence that large‐scale shoreline and dunefield erosion does lead to the development of a new transgressive aeolian sand sheet (and eventual dunefield) phase thereby demonstrating an initiation mechanism that is likely linked to future sea level rise and climate change. We also show that the initiation process, and, in particular, the subsequent rate of sand sheet transgression occurs at an incredibly rapid rate (+100 m in 8 years).Plain Language SummaryCoastal sand dunes border many of the world's coastlines and are highly adapted to local climate and conditions. How coastal dunes transition from predominantly vegetated and stable systems to wind‐blown sand sheets and dunefields transgressing prior terrain is a research area of pressing relevance due to forecasts of sea level rise and climate change. The factors or triggers that are considered to initiate transgressive aeolian sand sheets and dunefields are reviewed. The formation and evolution of a new transgressive aeolian sand sheet phase triggered by large‐scale shoreline erosion in South Australia is presented. According to the results from historical and satellite images, local shoreline erosion began in the late 1970s and has continued at highly variable rates. We show that once the foredune was removed, the high scarp created by wave erosion of the relict, vegetated transgressive dunefield destabilized and was then eroded by wind processes leading to the rapid development of a transgressive aeolian sand sheet. The initiation and evolution of the sand sheet provides an excellent example of how dunefields might respond to future sea level rise and climate change.

Nature versus Humans in Coastal Environmental Change: Assessing the Impacts of Hurricanes Zeta and Ida in the Context of Beach Nourishment Projects in the Mississippi River Delta

Hurricanes are one of the most devastating earth surface processes. In 2020 and 2021, Hurricanes Zeta and Ida pounded the Mississippi River Delta in two consecutive years, devastated South Louisiana, and raised tremendous concerns for scientists and stakeholders around the world. This study presents a high-resolution spatial-temporal analysis incorporating planialtimetric data acquired via LIDAR, drone, and satellite to investigate the shoreline dynamics near Port Fourchon, Louisiana, the eye of Ida at landfall, before and after the beach nourishment project and recent hurricane landfalls. The remote sensing analysis shows that the volume of the ~2 km studied beachfront was reduced by 240,858 m3 after consecutive landfalls of Hurricanes Zeta and Ida in 2020 and 2021, while 82,915 m3 of overwash fans were transported to the backbarrier areas. Overall, the studied beach front lost almost 40% of its volume in 2019, while the average dune crest height was reduced by over 1 m and the shoreline retreated ~60 m after the two hurricane strikes. Our spatial-temporal dataset suggests that the Louisiana Coastal Protection and Restoration Authority’s (CPRA’s) beach nourishment effort successfully stabilized the beach barrier at Port Fourchon during the hurricane-quiescent years but was not adequate to protect the shoreline at the Mississippi River Delta from intense hurricane landfalls. Our study supports the conclusion that, in the absence of further human intervention, Bay Champagne will likely disappear completely into the Gulf of Mexico within the next 40 years.

Investigation of Barrier Island Highway and Marsh Vulnerability to Bay-Side Flooding and Erosion

Coastal highways along narrow barrier islands are vulnerable to flooding due to ocean and bay-side events, which create hazardous travel conditions and may restrict access to surrounding communities. This study investigates the vulnerability of a segment of highway passing through the Pea Island National Wildlife Refuge in the Outer Banks, North Carolina, USA. Publicly available data, computational modeling, and field observations of shoreline change are synthesized to develop fragility models for roadway flooding and marsh conditions. At 99% significance, peak daily water levels and significant wave heights at nearby monitoring stations are determined as significant predictors of roadway closure due to flooding. Computational investigations of bay-side storms identify peak water levels and the buffer distance between the estuarine shoreline and the roadway as significant predictors of roadway transect flooding. To assess the vulnerability of the marsh in the buffer area, a classification scheme is proposed and used to evaluate marsh conditions due to long-term and episodic (storm) stressors. Marsh vulnerability is found to be predicted by the long-term erosion rate and distance from the shoreline to the 5 m depth contour of the nearby flood tidal channel. The results indicate the importance of erosion mitigation and marsh conservation to enhance the resilience of coastal transportation infrastructure.

Island area and historical geomorphological dynamics shape multifaceted diversity of barrier island floras

The influence of island dynamics and characteristics on taxonomic diversity, particularly species richness, are well studied. Yet, our knowledge on the influence of island dynamics and characteristics on other facets of diversity, namely functional and phylogenetic diversity, is limited, constraining our understanding of assembly processes on islands (e.g. biogeographic history, dispersal and environmental filtering and species interactions). Using barrier islands, a highly dynamic and so far, understudied island type, we investigate how multiple facets of vascular plant diversity (functional, phylogenetic and taxonomic diversity) are shaped by island geomorphology, modern and historic area, and habitat heterogeneity. In line with our expectation, historical dynamics in island geomorphology affected phylogenetic and taxonomic diversity via habitat heterogeneity. However, island area was the best predictor across all facets of diversity. Specifically, larger islands had higher functional and phylogenetic diversity than expected by chance while most of the smaller islands had lower diversity. The influence of area on functional diversity acted via habitat heterogeneity, with habitat heterogeneity influencing negatively functional diversity. Our results suggest that larger islands accumulate functionally and phylogenetically unique species. Further, results for functional diversity pointed towards potential area–heterogeneity trade‐offs, with these trade‐offs likely resulting from increased interspecific competition favoring a specific set of trait values (of stronger competitors), particularly on smaller islands. Together, these results demonstrate that going beyond taxonomic diversity contributes to identifying underlying processes shaping diversity–area relationships.

Satellite tagging and flipper tag recoveries reveal migration patterns and foraging distribution of loggerhead sea turtles (Caretta caretta) from eastern Australia

Marine turtles encounter different threats during various life-history stages. Therefore, understanding their movements and spatial distribution is crucial for effectively managing these long-lived migratory organisms. This study combines satellite telemetry data with long-term capture-mark-recapture data derived from flipper tag studies to determine distribution patterns of endangered loggerhead turtles (Caretta caretta) during post-nesting migrations from different eastern Australian nesting sites. Individuals from the K’gari-Fraser Island and Great Barrier Reef island rookeries typically migrated northward, whereas individuals from mainland rookeries migrated equally northward and southward. Despite this difference in foraging distribution, loggerheads from the different rookeries did not differ substantially in their migration duration or distance travelled. The foraging distribution identified from successful satellite tag deployments represented 50% of the foraging distribution identified from a large long-term flipper tag recovery database. However, these satellite telemetry results have identified new migration and foraging habitats not previously recognised for loggerhead turtles nesting in eastern Australia. Additionally, they support the conclusion from a past study using flipper tag recovery data that the mainland nesting turtles migrate to different foraging grounds than the turtles nesting on Great Barrier Reef islands. Collectively, the two data sources provide valuable data on the migration route, habitat distribution and ecological range for a threatened genetic stock of loggerhead turtles.

Morphostratigraphy of barrier spits and beach ridges at the east margin of Salgada Lagoon (Southeast Brazil)

At wave-dominated coasts, it is common the presence of coastal barriers that can be of different typologies and whose dynamics can influence the formation of lagoon systems. Along southeastern and south Brazil the dynamics involving barrier-lagoon evolution is related to wave and aeolian process associated with sea-level behavior. For a better understanding about the relationship regarding to coastal process, barriers, and lagoons the application of geophysical techniques enables to identify morphostratigraphic characteristics improving the acknowledgment of the main processes forming these morphologies. In this study, a 1.4 km long common-offset GPR profile, in cross-shore direction, was surveyed in order to obtain the internal depositional architecture of the sandy coastal barrier to the east of Salgada lagoon, located in the wave-dominated Paraiba do Sul river delta, in southeastern Brazil. The GPR allows to describe morphostratigraphic characteristics imprinted by sediment dynamics and how it is related to the lagoon system formation. Eight radarfacies were identified, grouped according to the coastal barrier pattern, divided in barrier spit and beach ridge, and sediment transport characteristics. Five radarfacies comprise the barrier spit environment and three the beach ridge environment. The barrier spit environment radarfacies showed different characteristics of the portions of the spit sequence (initial, medium or distal), and along with its subsurface imaging angle (parallel, oblique or transversal to the spit growth direction) providing highly detailed data regarding those barrier types. This recognition allowed the interpretation of a previous spit, approximately 3 m deep, located under another one that overlapped it. Also, spit accretion records were found, which occur due to the seaward exposure to high-angle wave action. Meanwhile, the beach ridge environment radarfacies revealed the typical pattern of progradation due to swash processes, and also the occurrence of berm ridge accretion and overtopping/overwashing processes. The integrated analyses using the subsurface data indicated that the evolution of the targeted coastal barriers and the lagoon can be divided into four stages. The first stage is the most landward barrier spits growth, where Salgada lagoon was beginning its closing process. This is followed by the second stage with the continuity of barrier spits growth but with changes in spits orientation. The third stage represents an erosive phase, with a major erosive truncation that probably eroded a significant area of the spits. At the last stage suggested there was a subsequent accumulation phase, marked by the formation beach ridges. Besides that, it is also important to recognize that the development of coastal barriers of different types at the site showed an alignment variability of paleocoastlines. While barrier spits revealed variation in their orientation, beach ridges have kept their alignment more constant. This fact occurred independently of erosive episodes. Furthermore, the GPR profile acquisition strategy made it possible to investigate the spit from different perspectives, which helped with the interpretation of deeper radarfacies.

Global coastal geomorphology – integrating earth observation and geospatial data

Coastal geomorphic classification identifying the type of depositional environment, is an important indicator for coastal state and vulnerability, e.g., beach, bedrock and wetland (tidal flat and estuarine/delta/back-barrier depression). Accurate and current maps of these geomorphology classes from local (100 m-1 km) to global (105 km) scales are important for a range of objectives in the coastal zone. Previous methods to create coastal geomorphic maps relied heavily on manual efforts and expert opinions. However, these approaches are labour intensive and impractical for consistent application at a global scale, while still including local details. Existing global coastal geomorphology datasets are a compilation of different local-scale datasets, with varying spatial, categorical resolutions and accuracies. The recent availability of “big” and “open” data as well as increased processing capabilities resulted in the use of satellite images and digital elevation models to identify sandy beach and cliff separately. In our work, these raster data were processed on Google Earth Engine, combined with shape descriptors of coastline vectors and then fitted into machine learning models to classify the intertidal coastal geomorphology into bedrock, beach or wetland classes on the global scale (from 56° S to 60° N, excluding coral reef/fringing reef and fjord dominated coasts). A unique attribute of this new method was the incorporation of shape descriptors extracted from shoreline vector data, which substantially improved the classification accuracy. Using existing data from European Union (EU), the United States of America (US) and Australia for training and testing, the model achieved averaged 85% accuracy for testing datasets in these continents and 84% accuracy for 10,000 independent global validation samples beyond these continents. Successful classification was achieved for coasts dominated by a single geomorphology class, as well as more complex environments, such as headland bay and barrier island systems, where multiple classes appear next to each other. The model had relatively less confidence in coasts with sandy cliffs, tall canopy cover and engineered structures. Complete statistics from this study covering 56° S to 60° N showed 36.8% (142,845 km) wetland, 26.7% (103,762 km) beach and 36.5% (141,579 km) bedrock. Beach and bedrock geomorphic classes were commonly detected at mid-latitudes (30o to 60o N/S), while wetland dominated tropical latitudes (0o to 30o N/S). The output dataset can be used for different coastal management purposes. The accuracy and categorical resolution of the classification can be further improved with the development of Earth Observation Big Data in the future.

An Integrated GIS Method – The Influence of Human Activities on Shoreline Change in Western Indian Small Island States: A Two Centuries Analysis of Urban West Unguja - Zanzibar Shoreline

Purpose: Urban areas have a high impact on shoreline changes that are more influenced by human activities rather than natural factors, together with hard structural mitigation and management, which are more practiced compared to other areas. This paper describes shoreline changes of small islands specifically; the shoreline of Urban West of Unguja Island in Zanzibar United Republic of Tanzania. This island has been changed for 174 years in different stages due to human activities including; reclamation of Darajani creek, port expansion at Malindi, Mtoni beach nourishment, sewer and stormwater channeling at Kilimani, construction of walls, groins, jetties, etc. 
 Methodology: The study uses an integrated method to analyze and detect changes using a sketch plan survey map of 1846 and 1892, a topographic map of 1907 and 1987, an aerial photo of 2004, Landsat images, and google images of 2019 and 2020. These maps were carefully georeferenced with latitude and longitudes, digitized using ArcGIS and demarcated along the study area supported with ground truth observation to analyze the coastal shoreline changes.
 Findings: The results show that the area experiences more accretion rather than retreat, integrated analysis and projections of the overall accretion and retreat for 174 years is 1,527,693.85 m2 (1.53 km2) and -936,135.48 m2 ( -0.94 km) receptively. The average accretion of land from 1846 to 2020 is 8,779.85m2/yr. (0.0088 km2/yr.) and retreat is -5,380.09m2/yr. (-0.0054 km2/yr.). A major accretion was observed and detected during the early 1900s to late 1987 which were major land transformation while other minor development activities were between 2010 to 2020. Sea walls, groins, beach nourishment, mangroves, barrier islands, and islets are major management practices of the shoreline which show a positive impact.
 Recommendations: The study finds it more appropriate to use multi datasets as an integrated method to analyze long-term coastal shoreline changes especially when there is limited data.

Following the Sand Grains

When longshore transport systems encounter tidal inlets, complex mechanisms are involved in bypassing sand to downdrift barriers. Here, this process is examined at Plum Island Sound and Essex Inlets, Massachusetts, USA. One major finding from this study is that sand is transferred along the coast—especially at tidal inlets—by parcels, in discrete steps, and over decadal-scale periods. The southerly orientation of the main-ebb channel at Plum Island Sound, coupled with the landward migration of bars from the ebb delta to the central portion of the downdrift Castle Neck barrier island, have formed a beach protuberance. During the constructional phase, sand is sequestered at the protuberance and the spit-end of the barrier becomes sediment starved, leading to shoreline retreat and a broadening of the spit platform at the mouth to Essex Bay (downdrift side of Castle Neck). Storm-induced sand transport from erosion of the spit and across the spit platform is washed into Essex Bay, filling channels and enlarging flood deltas. This study illustrates the pathways and processes of sand transfer along the shoreline of a barrier-island/tidal-inlet system and provides an important example of the processes that future hydrodynamic and sediment-transport modeling should strive to replicate.

Holocene deposits at the lower shoreface and inner shelf of the Dutch coast

To further detail insights into the composition and distribution of Holocene and late Pleistocene deposits at the surface and in the shallow subsurface of the lower shoreface of the Dutch coast, vibrocores were collected in three coastal sections. The study areas Noordwijk, Terschelling and Ameland Inlet represent contrasting settings: closed Holland coast vs. segmented Wadden coast (Noordwijk – Terschelling) and lower shoreface of a barrier island vs. lower shoreface of an ebb-tidal delta (Terschelling – Ameland Inlet).Six different depositional environments were distinguished: 1. the active layer, 2. seabed deposits, 3. lower-shoreface deposits, 4. ebb-delta channel deposits, 5. tidal channel deposits, and 6. alluvial (river) channel deposits. The several dm-thick active layer forms the mobile top of the seabed-, lower-shoreface- and ebb-delta channel deposits. Ebb-delta channel deposits (probably grading into terminal-lobe deposits) are restricted to the Terschelling and Ameland Inlet areas, fluvial deposits to the Noordwijk site. The front of the Ameland Inlet ebb-tidal delta is steep and consists of material supplied by the main ebb channel. These ebb-delta channel deposits are reworked by waves and currents, they grade seawards into seabed deposits. The low-gradient shoreface of the Terschelling site consists of a thin active layer on top of ebb-delta channel deposits. At the Noordwijk site fluvial deposits with incised bodies of tidal channel sand underlie a steep shoreface and a ridge-swale topography farther offshore.The ebb-delta channel deposits at the shoreface of Terschelling are similar to those at the front of the ebb-tidal delta of Ameland Inlet. Moreover, the tidal channel deposits that are common in the Noordwijk area, occur in only one core at Terschelling. This indicates that the deposits underlying the shoreface of Terschelling were formed in the ebb-tidal delta of a precursor of Ameland Inlet and not in the transgressive setting of a retreating barrier island. These deposits were possibly formed as part of the ebb delta of the Middelzee, a large medieval predecessor of the Ameland tidal basin, this needs to be confirmed by dating.Reworking of the shoreface of the prograded Subboreal beach barriers at Noordwijk at water depths of 12.5–13.5 m produced a 1.1-m-thick series of fining-upwards storm beds, including the active layer. At the shoreface of Terschelling storm beds are missing at these depths and only an active layer 0.2 m thick occurs. This suggests that the largest part of reworked sediment at Terschelling is carried off, which implies large-scale erosion of the shoreface. This needs further investigation.

Range expansion of the invasive portunid crab Charybdis japonica in New Zealand

ABSTRACT Charybdis japonica, a large invasive portunid, has been recorded in New Zealand since its detection in the Waitematā Harbour in 2000. In this study, the distribution, invasion history, abundance and population structure were investigated for C. japonica across the North Island of New Zealand. This was done using various distribution data available, trapping across several sites and interviews with commercial fishermen. Charybdis japonica was detected in the previously uninvaded Tauranga, Ohiwa, Hokianga, Manukau Harbours and Great Barrier Island. The rate of spread for C. japonica is continuous, with harbours or estuaries hundreds of kilometres apart having detections every two to three years. Population abundances reported by commercial fishermen constantly increased, with no signs of stabilisation or decrease. Catches were male-biased, with female abundance varying seasonally. Several possible pathways and vectors may be responsible for this spread, including shipping and aquaculture, on top of dispersal of larvae by currents across the North Island. Further research is required to determine population sources, with findings providing important information for invasive species monitoring and management.

Thresholds in Road Network Functioning on US Atlantic and Gulf Barrier Islands

AbstractBarrier islands predominate the Atlantic and Gulf coastlines of the USA, where population and infrastructure growth exceed national trends. Forward‐looking models of barrier island dynamics often include feedbacks with real estate markets and management practices aimed at mitigating damage to buildings from natural hazards. However, such models thus far do not account for networks of infrastructure, such as roads, and how the functioning of infrastructure networks might influence management strategies. Understanding infrastructure networks on barrier islands is an essential step toward improved insight into the future dynamics of human‐altered barriers. Here, we examine thresholds in the functioning of 72 US Atlantic and Gulf Coast barrier islands. We use digital elevation models to assign an elevation to each intersection in each road network. From each road network we sequentially remove intersections, starting from the lowest elevation. We use the maxima of the second giant connected component to identify a specific intersection—and corresponding elevation—at which functioning of the network fails, and we match the elevation of each critical intersection to local annual exceedance probabilities for extreme high‐water levels. We find a range of failure thresholds for barrier island road network functioning, and also find that no single metric—absolute elevation, annual exceedance probability, or a quantitative metric of robustness—sufficiently ranks the susceptibility of barrier road networks to failure. Future work can incorporate thresholds for road network into forward‐looking models of barrier island dynamics that include hazard‐mitigation practices for protecting infrastructure.

Back-barrier evolution and along-strike variations in infilling of the Kosi Bay lake system, South Africa

This study examines both the inlet dynamics, recorded in the back-barrier stratigraphy of Kosi Bay, and the competing effects of waterbody segmentation on along-strike changes in the character and nature of an incised valley fill at Kosi Bay, South Africa. The Kosi Bay system comprises four interconnected lakes (Lake Makhawulani, Lake Mpungwini, Lake Nhlange and Lake Amanzimnyama) subject to varying degrees of marine influence. Formerly, the system's only connection to the ocean was through the Bhanga Nek palaeo-inlet. The location of this system behind a continuous coastal barrier predisposes it to excellent archives of environmental change related to changing sea-level and sediment supply. In this context, two cores were extracted from the system (KB2 and KB4), together with over 150 km of seismic reflection profiling, as well as AMS radiocarbon analyses and legacy data in order to present a new stratigraphic evolution model for this back-barrier system. A total of 5 seismic units were imaged (Units A-E). A major unconformity surface (SB), characterised by broad u-shaped incised valleys, incises the underlying unconsolidated sandy acoustic basement (Unit A). Unit B forms as thickly developed central basin deposits, partially infilling the incised valleys. Two forms of prograding spits are evident -Unit C1 progrades from the palaeo-highs of the valley interfluves into the nearest available accommodation space and Unit C2 progrades from the margins of the system into the basin. These are separated by an erosional surface (T-RS) formed by migrating tidal channels as sea-level rose and marine waters entered the system during the Holocene. Unit C2 spits are in turn associated with slump deposits formed on the steepest part of the margins (Unit D) that were dated to 2900 ± 165 cal. BP. The unusual depth of Surface T-RS is attributed to (1) limited sediment supply during sea-level rise, (2) the presence of easily erodible fine sediments in which this surface erodes and (3) a larger tidal prism when the Bhanga Nek inlet was still open and system segmentation by Units C2 and D had not yet occurred. Unit E caps the stratigraphy and is interpreted as lacustrine fines with a thin layer of acoustically transparent material (gyttja) on top. The deposition of Unit E signifies the closure of the system to the ocean and the overall shift from an estuarine/lagoon environment to a lacustrine one. Recalibrated AMS dates place the system closure to between 3160 and 2900 cal. BP, coeval with the formation of the prograding marginal spits and waterbody segmentation (Unit C2). Along-strike variation in the timing of the basin infilling, attributed to changes to the inlet functioning coupled to the segmentation of the waterbody, is characteristic of this area. At 1450 cal. BP, a new tidal inlet formed to the north of Lake Makhawulani, where impounded waters were diverted via a low point in the back-barrier coastal dune cordon. The formation of this inlet suggests a prolonged period of back-barrier flooding until a low point in the barrier was breached during the Holocene sea-level highstand of 1.5 m. Such inlet development and along-strike back flooding of incised valleys is an unusual attribute of coastal waterbodies of South Africa.

Nearshore bathymetric changes along the Alaska Beaufort Sea coast and possible physical drivers

Erosion rates along Alaska's Beaufort Sea coast, among the highest in the world, are negatively impacting communities, industrial and military infrastructure, and wildlife habitat. Decreasing maximal winter ice extent and increasing summer open water duration and extent in the Beaufort Sea may be making the coast more vulnerable to destructive storm waves than during recent, colder, icier decades. Previous studies of Beaufort Sea coastal change have been limited to subaerial analyses of the shoreline. Here we describe nearshore seafloor change by comparing post-World War II (WWII) (1945-53) bathymetry data to recently acquired (1985–2018) bathymetry data and relate the observed seafloor change to adjacent shoreline change near Utqiagvik, within Stefansson Sound, and immediately west of Barter Island and Kaktovik. Within the Utqiagvik region, seabed erosion was generally highest (>1.0 m of loss) offshore of Point Barrow and along the eastern end of the Tapkaluk Islands, while there were lesser amounts of deposition (<0.5 m of gain) within the protected waters of Elson Lagoon. Sedimentation was generally highest offshore of Point Barrow, in a region of converging currents, and on the landward side of the barrier islands and spits fronting Elson Lagoon, which is likely related to a regional trend of westerly sediment transport and landward migration of the barrier islands. Within Stefansson Sound, perhaps the most notable changes from post-WWII bathymetry data compared to recent data are a switch from mixed, low erosion and deposition in 1997 to low deposition (<0.5 m) in 2018 east of the Boulder Patch, a switch from low erosion in 1997 to neutral depth change in 2018 in the channel between the north and south Boulder Patch areas, and higher deposition from 1997 to 2018 landward of the rapidly retreating barrier islands along the Sound's northern border. At Barter Island, high erosion near north-facing shorelines and high deposition near west-facing shorelines generally matched shoreline changes. One of our goals is to identify possible processes responsible for the depth changes we quantified. Using simple metrics that relate sediment characteristics with modeled waves and non-wave induced currents, we show that sediment resuspension and transport by both wave and non-wave driven currents likely contribute to the overall patterns of change within the ∼13 m isobath along the open coast, and that the influence of wave action affecting sediment transport is expanding seaward.

A Survey of Global Mixed-Energy and Wave-Dominated Barrier Island Distribution and Development

Fenster, M.S.; Hughes, C.P., and Stutz, M.L., 2022. A survey of global mixed-energy and wave-dominated barrier island distribution and development. Journal of Coastal Research, 38(4), 795–806. Coconut Creek (Florida), ISSN 0749-0208. This study quantifies the length, percentage, and type of development found on global mixed-energy and wave-dominated coastal plain and deltaic barrier islands. Google Earth photographic imagery from 2015–2017 was used to measure the lengths of individual islands, identify infrastructure types 300 m landward of the shoreline, and measure the alongshore extent of each island's land uses. The United States Geological Survey's land-use classification scheme enabled categorization and quantification of predominant structure types. The results from this study showed that, of the 1444 mixed-energy and wave-dominated barrier islands located within 53 countries around the world: (1) 832 (approximately 59%) of those barriers islands have some type of development; (2) approximately 16% of the total length of shorelines (approximately 1,793 km/11,249 km) are developed; (3) wave-dominated barriers (approximately 17%) are more developed than mixed-energy (approximately 14%) barriers; (4) coastal plain (approximately 21%) settings have double the development than deltaic settings; (5) the U.S. contains approximately 66% of all developed global barrier island shorelines and the highest percent development of mixed-energy (New Jersey approximately 67%) and wave-dominated (Florida approximately 62%) coastal plain barrier islands in the world; and (6) high-density, residential dwellings dominate development type and comprise an average 14% of the world's barrier island shorelines. Finally, development percentage and/or land use type do not appear to depend on or correlate with hydrodynamic or geologic setting and coastal processes and geology do not influence development type. Instead, site specific or regional factors most likely dictate the percentage and type of development.

Impacts of Hurricane Matthew on adjacent developed and undeveloped barrier islands in southeastern North Carolina

High-magnitude storms such as hurricanes can cause significant and potentially long-lasting morphological coastal change, particularly along low-lying barrier islands. This study investigated the impacts of Hurricane Matthew (2016) on neighboring undeveloped Masonboro Island reserve and engineered/nourished Wrightsville Beach barrier islands, located in southeast North Carolina. Using a combination of high-resolution pre- and post-storm RTK–GPS beach surveys, coupled with direct observations, storm surge and wave runup calculations and aerial imagery, a range of contrasting storm-induced coastal changes and impact regimes were identified across the two adjacent barriers. Storm impacts were especially pronounced across low-lying undeveloped central/southern Masonboro Island, which was dominated by significant overwash processes, leading to landward directed barrier crest migration. In contrast, only short-lived and minor collision with the dune base was observed at Wrightsville Beach, were storm impacts were dominated by a swash storm regime resulting in significant beach erosion. Field- and aerial based observations match well with modeled extreme water level estimates. This study offers a real-time example of how geomorphologically different neighboring islands respond to specific storm events, and how storm impact regime type and duration helps explain differences in barrier responses. Similar storm impacts are likely at other locations with comparable barrier island settings and differing coastal management approaches.

Genesis of a coastal aquifer in the coastal plain of the Pelotas Basin, southern Brazil: Implications for stratigraphic evolution

In the coastal plain of the Pelotas Basin, southernmost Brazil, a granular aquifer close to 70 m deep, formed by coarse and angular sediments, caught the attention of drillers, who gave it the suggestive nickname of “Coarse Salt” (“Sal Grosso”). Despite being almost unknown in geological and stratigraphic terms, the aquifer has been increasingly used to supply the growing coastal population. Considering that stratigraphic knowledge is essential for the management of groundwater resources, we sought to understand the configuration of this aquifer and investigate its genesis based on drilling samples from 29 groundwater wells and through 19 vertical electrical soundings. The sedimentary record investigated has an approximate thickness of 100 m, and is formed by three units, interpreted as: alluvial (where the aquifer is located), marine and coastal barriers. The analysis of the sediments that make up the Coarse Salt (Sal Grosso) aquifer led to the interpretation that the investigated region represents the distal (fluvial) portion of an alluvial system. Spatially, the aquifer constitutes an elongated feature in the NW-SE direction, perpendicular to the current coastline. The geometry and sedimentology led to the interpretation of a paleochannel, responsible for the transport of sediments from the granitoid rocks of the Sul-Riograndense Shield, associated with the paleodrainage system of the Jacuí River. A greater stratigraphic variability present in wells closer to the continent, with intercalation of continental and marine deposits, indicated the position of a coastline, prior to the formation of the coastal barrier unit, which is the predominant depositional system in the actual coastal plain. The stratigraphic analysis resulted in the paleogeographic model corresponding to a complete depositional sequence, indicating that the Coarse Salt (Sal Grosso) aquifer was formed during a lowstand. Later, a marine transgression allowed the deposition of a thick bundle of muddy sediments, which constitutes an important protection to the aquifer. Afterwards, the coastline started to prograde, with the development of the barrier-lagoon systems in a highstand/falling stage systems tracts context. The understanding of stratigraphy generates framework for decision-making that enable better management of this groundwater resource.