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Channel sandbars are extremely sensitive to basin‐wide natural processes and human activities, and their modifications considerably affect channel stability and river ecosystem health. However, quantitatively detecting the three‐dimensional dynamics of channel sandbars at a high spatial resolution over a large area remains challenging. In this study, we propose a semi‐automated process to address this challenge by extracting sandbar contours from Sentinel‐2 images in the Google Earth Engine (GEE) platform. We then generate contour datasets for each sandbar based on the spatial relationship between contours and water levels at nearby hydrological stations. Subsequently, digital elevation models (DEMs) are created for each sandbar using the contour dataset, and non‐linear relations between sandbar areas and water levels are fitted through polynomial curves of degrees 3–6 to calculate changes in sandbar volumes. Finally, we comprehensively analysed the driving mechanisms of sandbar changes in different sub‐reaches. Our findings reveal the area and volume of sandbars in three of the four sub‐reaches increased significantly between 2018 and 2019; however, these values decreased significantly and continuously between 2019 and 2022. Sandbars located downstream near the dam experienced more severe erosion compared to those farther downstream. Although the morphodynamic processes of each sub‐reach were different, extremely low rainfall in 2019–2020 and the operation of the Xayaburi Dam are significant global factors leading to the shrinkage of the sandbars. Furthermore, abnormal erosion with a change rate of −9.62% in area and −8.95% in volume was observed in the sub‐reach between Vientiane and Khong Chiam hydrological stations between 2018 and 2019, with the susceptibility of the channel to flow scour and anthropogenic sand mining being significant factors. Although the sediment replenishment from tributaries diminishes the impact of upstream dams and droughts on the reach farther downstream, the threat to channel stability due to excessive sand mining should be given high priority. Our study highlights how satellite remote sensing, specifically utilizing time series images with fine spatio‐temporal resolutions, effectively detects three‐dimensional variations in sandbars and river geomorphic changes. Additionally, it demonstrates the significant post‐dam alteration of erosion patterns and deposition dynamics within the sandbar region of the lower Mekong River. [ABSTRACT FROM AUTHOR]

Sandbars are an integral part of the alluvial river's geophysical system due to these rivers' wide sediment availability and varied transport capacity. The sandbars' evolution and translation considerably influence the stability of the riverbank. However, while designing the riverbank protection structures (RBPS), the impact of such sandbars is often overlooked, as the evolution of such bars is quite uncertain in terms of location, amplitude, and translation. This study evaluates the localized impact of sandbars on bank protection structures in two types of alluvial rivers: meandering (Ganges) and braided (Brahmaputra-Jamuna), utilizing time series satellite images, hydraulic characteristics, and numerical modeling. We found that sandbar development initiates width adjustment in both meandering and braided rivers when the ratio of width to depth surpasses 90. In the case of meandering rivers, riverbank erosion mostly occurs as a result of the presence of alternate bars or point bars. Sandbars in a meandering river (Ganges) can lead to an approximate 18% increase in flow depth. The depth-averaged velocity is anticipated to rise by approximately 29%, and the tractive force may increase by a factor of 1.6. On the other hand, the braided river (the Brahmaputra-Jamuna) underwent significant bank erosion due to the presence of both free unit and hybrid types of bars. In such rivers, the depth of the flow may experience a notable increase of 18%, while the depth-averaged velocity undergoes an approximate increase of 50%, and the tractive force has the potential to grow by a factor of 5.3. Consequently, we recommend allowing the natural evolution of sandbars while preserving the riverbank (where needed only) through RBPS, considering these additional loads. [ABSTRACT FROM AUTHOR]

The position and morphology of offshore sandbars are highly dependent on wave conditions; however, the mechanisms driving sand movement by water waves remain elusive to scientists and coastal engineers. This study presents a series of experiments conducted in a wave flume to investigate the impact of wave-induced pore pressure gradients on seabed instability around a sandbar, observed in the Benin Gulf of Guinea. The Froude-Darcy similitude principle was developed to ensure the similarity of hydrodynamics and seepage forces between the experiments and field conditions. Pore pressure gradients and free surface elevations were measured using three arrays of pore pressure transducers and eleven wave probes, respectively. The results indicate a rapid increase in both the horizontal pressure gradient and the maximum downward pressure gradient during the shoaling process. Conversely, the maximum upward pressure gradient decreases prior to wave breaking. Wave-induced pressure gradients significantly influence seabed instability and sediment transport. The effective weight of sand particles is reduced by up to 52% due to the upward pressure gradient during the shoaling process, and momentary liquefaction is triggered by the horizontal pressure gradient near the breaking point based on the liquefaction criterion. When liquefaction occurs, shear granular flow forms on the seabed surface. [ABSTRACT FROM AUTHOR]

Sandbars are commonly encountered in coastal environments, acting as natural protections during storm events. However, the sandbar response to waves and possible shear failure is poorly understood. In this research, a two–dimensional numerical model is settled to simulate the wave-induced sandbar soil dynamics and instability mechanism. The model, which is based upon the Reynolds-averaged Navier–Stokes (RANS) equations and Biot's consolidation theory, is validated using available experiments. Parametric studies are then conducted to appraise the impact of the wave parameters and soil properties on soil dynamics. Results indicate that the vertical distribution of the maximum vertical effective stress in the sandbar is different from that in the flat seabed, which decreases rapidly along the soil depth and then increases gradually. The impact of soil permeability and saturation on the vertical effective stress distribution around the sandbar also differ from that in the flat seabed. Unlike the flat seabed, the vertical distribution of shear stress in the sandbar increases with an increasing wave period. The sandbar soil shear failure potential is discussed based upon the Mohr–Coulomb criterion. Results show that the range of shear failure around the sandbar is wider and the depth is deeper when the wave trough arrives. [ABSTRACT FROM AUTHOR]

AbstractThis study assessed sandbar-topography changes in Nakdong River Estuary. The island shorelines in the study area, including Jinwoo Island, Shinja Island, and Doyo Sandbar, were analyzed using SPOT satellite images from 2006 to 2022. Shoreline analysis via ArcGIS revealed that Jinwoo Island is expanding at 6.46 m/year towards Nulcha Island. Shinja Island’s western side is expanding at 4.76 m/year, while the eastern side is retreating at 24.41 m/year. Doyo Sandbar’s southern shoreline is retreating at 14.69 m/year, with a gradual decrease in speed. Significant topographical changes indicate that the interlinked barrier islands are undergoing deposition and erosion, altering the shoreline. [ABSTRACT FROM AUTHOR]

In this study, we investigated the distribution and abundance of macrobenthos, particularly tanaids, in the Kadalundi Estuary, southwest coast of India, across three seasons. Tanaids were found to be the dominant macrobenthic group, with a strong preference for clayey mangrove habitats. The study highlights the vital role of mangroves in supporting macrobenthic communities and emphasizes the importance of conserving these habitats. Litterfall was identified as a crucial factor in nutrient cycling within the mangrove ecosystem. Sandbar formation near the estuary mouth poses a significant threat to mangrove ecosystems and associated fauna. This research contributes valuable insights for informed conservation strategies and ecosystem management. [ABSTRACT FROM AUTHOR]

To analyze the impacts of groins, sandbars, and channels on the three-dimensional features of rip currents, we conducted experimental investigations on the vertical distribution of rip currents under intersecting waves along barred beaches with channels. This study employed ADV flow velocity measurements at two distinct locations: within channel and on a sandbar. The results indicate that in nodal sections within channel and on a sandbar, the rip head region manifests surface flow characteristics, characterized by high velocities near water surface. In a rip neck location, the vertical distribution of rip currents on a sandbar exhibits greater variability, whereas within channel, the distribution is more homogeneous. The vertical distribution of rip currents in nodal sections within channel aligns with the logarithmic distribution law. The vertical distributions of the alongshore velocity of rip currents display a consistent pattern of higher at the top and lower at the bottom. However, this pattern varies slightly depending on the wave period. The presence of groins influences the fluctuation characteristics of the alongshore velocity of rip currents by regulating the nearshore circulation system. This results in the alongshore velocity of rip currents in channel pointing towards the groin. In contrast, the alongshore velocity of rip currents on sandbar, situated farther away from groin, exerts a weaker effect on the alongshore velocity of a rip current. [ABSTRACT FROM AUTHOR]

Since the late 1960s, the Qiantang Estuary has been narrowed on a large scale, significantly changing the water-sediment dynamics, riverbed evolution and their interaction processes. However, the tidal bore in response to the high-intensity human activities is not fully understood. Based on the measured data of topography, tide and tidal bore, combined with the mathematical model of tidal bore, the effects of large-scale contracted river for regulation on tide, river bed and tidal bore of Qiantang Estuary were studied. The results show that the distribution of shoal and channel was basically stable after the river was narrowed. With the increase of the ratio of river flow to tidal current, roughly bounded by Yanguan, the lower part of the tidal bore reaches was silted, the upper part was scoured, and the sandbar was moved downstream. The high tidal level rose along the estuary, the tidal range increased near the place where the tidal bore occurred and the upper part of the tidal bore reaches from Zhakou to Cangqian reach, and decreased from Cangqian to Yanguan reach. As a result, the occurrence point of the tidal bore and the maximum tidal bore position move downstream, the viewing positions of the tidal bore are fixed, the tidal bore scenery is abundant and stable, the tide bore arrival time is stable, the amplitude of the tidal bore height decreases, and the tidal bore height decreases from Cangqian to Yanguan reach. In order to protect the tidal bore, it is necessary to maintain a large tidal range and appropriate water depth in the tidal bore reach, and it is not suitable to carry out large-scale reclamation. [ABSTRACT FROM AUTHOR]

In this study, laboratory experiments were conducted to investigate the influence of changes in storm wave height and water level on beach response in a medium-scale wave flume. A schematic storm was simulated (rising, apex, and waning phases). A non-intrusive photogrammetric method was used to collect high-resolution and synchronous data regarding the free surface water elevation and bed level, from which shoreline location, sandbar position, cross-shore sediment transport rates, and nonlinear wave parameters were derived. The cross-shore sediment transport was in agreement with previous laboratory measurements, including the monotonous exchange from foreshore erosion to shoaling zone accretion in most stages of the storm simulation. The surf zone was the main region supplying sediment for beach morphology modification and sandbar generation. The degree of storm erosion was not completely determined by the largest wave height and water level or the cumulative wave power of the apex phase. The largest gradients of the wave parameter sequence change occurred in the rising phase, and this was the main factor generating efficient beachface erosion. It induced an increase in sandbar size, accompanied by the cross-shore motion of maximum velocity amplitude, more violent disturbances of wave nonlinearity, and increased surf zone erosion, with these factors increasing beach instability and leading to more severe storm erosion. The large wave height and water level resulted in shoreline retreat, with a more significant swash zone erosion under a higher runup. The offshore sediment transport turned toward the onshore direction as the original large sandbar deteriorated under the decreasing wave parameter sequence in the waning phase. [ABSTRACT FROM AUTHOR]

The position and morphology of offshore sandbars are highly dependent on wave conditions; however, the mechanisms driving sand movement by water waves remain elusive to scientists and coastal engineers. This study presents a series of experiments conducted in a wave flume to investigate the impact of wave-induced pore pressure gradients on seabed instability around a sandbar, observed in the Benin Gulf of Guinea. The Froude-Darcy similitude principle was developed to ensure the similarity of hydrodynamics and seepage forces between the experiments and field conditions. Pore pressure gradients and free surface elevations were measured using three arrays of pore pressure transducers and eleven wave probes, respectively. The results indicate a rapid increase in both the horizontal pressure gradient and the maximum downward pressure gradient during the shoaling process. Conversely, the maximum upward pressure gradient decreases prior to wave breaking. Wave-induced pressure gradients significantly influence seabed instability and sediment transport. The effective weight of sand particles is reduced by up to 52% due to the upward pressure gradient during the shoaling process, and momentary liquefaction is triggered by the horizontal pressure gradient near the breaking point based on the liquefaction criterion. When liquefaction occurs, shear granular flow forms on the seabed surface.

Sandbars are narrow ridges of sand formed by the river system in Bengal delta in eastern India. Some charlands or riverbeds of the Damodar River are situated along both its banks as well as in its central channel, offering habitats for both human populations and wildlife. Throughout its history, the river has been known as ‘Sorrow of Bengal’ owing to its frequent inundations and devastating impact. Since the partition of India in 1947, numerous sandbars have been colonized at various stages. Before partition, the area consisted of vast fields covered with bushes. This paper elaborates on the living conditions of marginalized people of Bangladesh and the local settlers who have inhabited the sandbars. They face a multitude of challenges, including safety concerns during storms, a lack of access to essential amenities like water, electricity, healthcare, education, and employment opportunities, as well as transportation difficulties. Sandbars are susceptible to flooding, necessitating frequent evacuations for the residents when massive floods occur. Additionally, these riverbeds are often geographically isolated from neighbouring landmasses. Despite these challenges, both refugees and local settlers have managed to adapt to life on these transient sandbars. The research also elucidates how communities often develop unique techniques and technologies to mitigate the challenges posed by the river. Finally, this study demonstrates that assessments of vulnerability and insecurity are arbitrary and insignificant; however, immediate survival is crucial. [ABSTRACT FROM AUTHOR]

Sandbars are commonly encountered in coastal environments, acting as natural protections during storm events. However, the sandbar response to waves and possible shear failure is poorly understood. In this research, a two–dimensional numerical model is settled to simulate the wave-induced sandbar soil dynamics and instability mechanism. The model, which is based upon the Reynolds-averaged Navier–Stokes (RANS) equations and Biot’s consolidation theory, is validated using available experiments. Parametric studies are then conducted to appraise the impact of the wave parameters and soil properties on soil dynamics. Results indicate that the vertical distribution of the maximum vertical effective stress in the sandbar is different from that in the flat seabed, which decreases rapidly along the soil depth and then increases gradually. The impact of soil permeability and saturation on the vertical effective stress distribution around the sandbar also differ from that in the flat seabed. Unlike the flat seabed, the vertical distribution of shear stress in the sandbar increases with an increasing wave period. The sandbar soil shear failure potential is discussed based upon the Mohr–Coulomb criterion. Results show that the range of shear failure around the sandbar is wider and the depth is deeper when the wave trough arrives.

An existing Boussinesq wave model, solved in a hybrid format of the finite-difference method (FDM) and finite-volume method (FVM), with good merits of stability and shock-capturing, was used as the wave driver to simulate the beach evolution under nearshore wave action. By coupling the boundary layer model, the sand transport model, and the terrain updating model, the beach evolution model is established. Based on the coupled model, the interaction process between sandbars and waves was simulated, reproducing the process of the original sand bars diminishing, new sandbars creating, and finally disappearing. At the same time, the formation and movement process of sand bars under solitary and regular waves are numerically simulated, in the breaking zone, the water bottom has a larger shear stress, which promotes the sediment activation, transport and erosion formation, and near the breaking point, the decrease of sand-carrying capacity is the main reason for the formation of sandbars, the numerical model can accurately describe the changes in the shoreline profile under wave action. [ABSTRACT FROM AUTHOR]

River turbulence is spatially variable due to interactions between morphology of rivers and physical mechanics of flowing water. Understanding the variation of turbulence in rivers is important for characterizing transport processes of soluble and particulate materials in these systems. We present an exploratory effort to understand ecologically relevant flow patterns using measurements of mean flow and turbulence in a highly engineered river channel around an island in the lower Missouri River. Specifically, the profiles of mean river velocities were investigated to examine the logarithmic relation and associated parameters, including shear velocity and bed roughness. Turbulence intensity and Reynolds shear stress were compared with classic open‐channel profiles and previously reported river data in the hydraulics literature. With the capability of pulse‐to‐pulse coherent Doppler velocity profiling in high spatial resolution, we estimated the profiles of turbulence dissipation rate using resolved one‐dimensional velocity spectra. These measurement data allow us to examine the validity of turbulence production‐dissipation balance and the classic open‐channel profiles of turbulence statistics, including turbulence intensity, Reynolds shear stress, dissipation rate, and eddy viscosity. The field data show a strong variation of turbulence profiles in close vicinity of the river island. In shallow water depths close to the island, turbulence is substantially enhanced in comparison with classic open‐channel profiles. Such turbulence enhancement is likely attributed to non‐uniformity of the flow structures. [ABSTRACT FROM AUTHOR]

Changes in coastal topography can affect the ecological environment and marine industries. In this study, we analyzed the patterns and causes of changes in shoreline and undersea topography in the Nakdong River estuary in the southeast of Republic of Korea using depth and shoreline surveys of the estuary, as well as data on discharge, suspended sediments, and precipitation in the Nakdong River basin. The results showed that erosion and sedimentation occurred repeatedly owing to complex factors such as the discharge of the estuary and invasion by open sea waves. However, no clear unilateral trend was observed. Unlike previous survey data, a large amount of erosion occurred in the second half of 2020. Previously, sedimentation was the main process, but erosion occurred rapidly, which was observed in the summer of 2020 when the erosion was three times higher than that in other periods owing to the severe rainy season and torrential rains for over a month. In addition, regarding the flow rate and force of the river water outflow, the amount of discharge increased rapidly, causing erosion. Moreover, a strong typhoon in the summer of 2020 affected the topography of the estuary. [ABSTRACT FROM AUTHOR]

To analyze the impacts of groins, sandbars, and channels on the three-dimensional features of rip currents, we conducted experimental investigations on the vertical distribution of rip currents under intersecting waves along barred beaches with channels. This study employed ADV flow velocity measurements at two distinct locations: within channel and on a sandbar. The results indicate that in nodal sections within channel and on a sandbar, the rip head region manifests surface flow characteristics, characterized by high velocities near water surface. In a rip neck location, the vertical distribution of rip currents on a sandbar exhibits greater variability, whereas within channel, the distribution is more homogeneous. The vertical distribution of rip currents in nodal sections within channel aligns with the logarithmic distribution law. The vertical distributions of the alongshore velocity of rip currents display a consistent pattern of higher at the top and lower at the bottom. However, this pattern varies slightly depending on the wave period. The presence of groins influences the fluctuation characteristics of the alongshore velocity of rip currents by regulating the nearshore circulation system. This results in the alongshore velocity of rip currents in channel pointing towards the groin. In contrast, the alongshore velocity of rip currents on sandbar, situated farther away from groin, exerts a weaker effect on the alongshore velocity of a rip current.

In this study, laboratory experiments were conducted to investigate the influence of changes in storm wave height and water level on beach response in a medium-scale wave flume. A schematic storm was simulated (rising, apex, and waning phases). A non-intrusive photogrammetric method was used to collect high-resolution and synchronous data regarding the free surface water elevation and bed level, from which shoreline location, sandbar position, cross-shore sediment transport rates, and nonlinear wave parameters were derived. The cross-shore sediment transport was in agreement with previous laboratory measurements, including the monotonous exchange from foreshore erosion to shoaling zone accretion in most stages of the storm simulation. The surf zone was the main region supplying sediment for beach morphology modification and sandbar generation. The degree of storm erosion was not completely determined by the largest wave height and water level or the cumulative wave power of the apex phase. The largest gradients of the wave parameter sequence change occurred in the rising phase, and this was the main factor generating efficient beachface erosion. It induced an increase in sandbar size, accompanied by the cross-shore motion of maximum velocity amplitude, more violent disturbances of wave nonlinearity, and increased surf zone erosion, with these factors increasing beach instability and leading to more severe storm erosion. The large wave height and water level resulted in shoreline retreat, with a more significant swash zone erosion under a higher runup. The offshore sediment transport turned toward the onshore direction as the original large sandbar deteriorated under the decreasing wave parameter sequence in the waning phase.

In recent years, flood damage was frequently occurring by the flow rate of rivers has increased due to heavy rains such as typhoons in Japan. Therefore, understanding the particle size distribution of riverbed materials was an important factor in river planning and sediment outflow forecasting. However, in many cases, the grain size considered in numerical calculations was only for the surface layer because collecting heavy sediment labor, and it has not been studied much in the depth direction. In this study, sediment was collected from multiple locations on the sandbar in the middle reaches of the Babamegawa River, which was a Class B River in Akita Prefecture. Then, the particle size analysis was performed in the cross-sectional and longitudinal directions. Sediment was collected twice to see the change in grain size before and after the flood. From the results, the D50 of the sediment collected after the flood tended to be larger than that of the sediment collected before the flood in both the cross-sectional and longitudinal directions. In the depth direction, it was confirmed a layer in which the particle size changes and a layer in which the particle size does not change. [ABSTRACT FROM AUTHOR]

Maintenance operations in regulated rivers are often implemented as preventive measure to maintain wide, smooth channels and to limit the risk of flooding. By clearing vegetation, removing roots and lowering sediment bar elevation, these works can recreate pioneer habitats and related plant communities. Using a before‐after‐control‐impact design with monitoring of riparian vegetation over 10 years, we evaluated the effects of fluvial maintenance works on plant richness and composition in an island complex located in a Nature Reserve along the Middle Loire River. Our results showed that artificial rejuvenation operations had a significant short‐term negative effect on richness. However, in the few years following the work, the riparian communities established on the rejuvenated island became more diverse, with a large proportion of annual plants, contributing to the increased species pool of the Nature Reserve. In addition, we found that temporal changes in species richness were strongly influenced by hydrological conditions, with a peak in biodiversity observed during prolonged summer low water. This highlights the importance of considering flow variations to more accurately assess the ecological benefit of restoration operations on riparian vegetation. Overall, as successional stages were more advanced at the island complex scale, fluvial maintenance works have allowed the recreation of sandy pioneer habitats exposed to flooding. These habitats have promoted the establishment of species‐rich communities without favoring the installation of invasive alien species. From this view, the maintenance works have increased the mosaic of habitats within the Nature Reserve and have restored environmental conditions favorable to early‐successional species. [ABSTRACT FROM AUTHOR]

Sandbars are commonly observed on sandy coasts, and they can prevent erosion on the beach face. Better prediction of sandbar evolution is necessary for coastal management and beach nourishment. In this study, a process-based morphodynamic model is used to reproduce the barred beach profile evolution in the Duck94 field experiments. The importance of the wave roller slope parameter in the model is revisited. Six idealized numerical experiments are set to investigate the effect of wave heights, wave periods and sea levels on sandbar migrations. By implementing two recent cross-shore varying roller slope formulas, the models achieved fair-to-good performances. It was found that the variations of sandbar morphological evolution are mainly controlled by the cross-shore varying roller slope. An increase in the wave height or a decrease in the wave period would lead to a more rapid and further-offshore migration of the sandbar. When the sea level variations are much smaller than the water depth over the sandbar, the effect of sea level changes on the sandbar migration is negligible, though a lower sea level would cause more erosion on the beach face. [ABSTRACT FROM AUTHOR]

Sharks, as apex predators, play an essential ecological role in shaping the marine food web and maintaining healthy and balanced marine ecosystems. Sharks are sensitive to environmental changes and anthropogenic pressure and demonstrate a clear and rapid response. This designates them a “keystone” or “sentinel” group that may describe the structure and function of the ecosystem. As a meta-organism, sharks offer selective niches (organs) for microorganisms that can provide benefits for their hosts. However, changes in the microbiota (due to physiological or environmental changes) can turn the symbiosis into a dysbiosis and may affect the physiology, immunity and ecology of the host. Although the importance of sharks within the ecosystem is well known, relatively few studies have focused on the microbiome aspect, especially with long-term sampling. Our study was conducted at a site of coastal development in Israel where a mixed-species shark aggregation (November–May) is observed. The aggregation includes two shark species, the dusky (Carcharhinus obscurus) and sandbar (Carcharhinus plumbeus) which segregate by sex (females and males, respectively). In order to characterize the bacterial profile and examine the physiological and ecological aspects, microbiome samples were collected from different organs (gills, skin, and cloaca) from both shark species over 3 years (sampling seasons: 2019, 2020, and 2021). The bacterial composition was significantly different between the shark individuals and the surrounding seawater and between the shark species. Additionally, differences were apparent between all the organs and the seawater, and between the skin and gills. The most dominant groups for both shark species were Flavobacteriaceae, Moraxellaceae, and Rhodobacteraceae. However, specific microbial biomarkers were also identified for each shark. An unexpected difference in the microbiome profile and diversity between the 2019–2020 and 2021 sampling seasons, revealed an increase in the potential pathogen Streptococcus. The fluctuations in the relative abundance of Streptococcus between the months of the third sampling season were also reflected in the seawater. Our study provides initial information on shark microbiome in the Eastern Mediterranean Sea. In addition, we demonstrated that these methods were also able to describe environmental episodes and the microbiome is a robust measure for long-term ecological research. [ABSTRACT FROM AUTHOR]

Sandbars are ubiquitous morphologic features found in the nearshore environment throughout the world, yet predictive capabilities of their evolution remain limited. In order to provide new insights on the relevant processes controlling sandbar morphodynamics, this study uses a 41‐year record of 637 monthly cross‐shore profiles from Duck, North Carolina, USA, to derive complex empirical orthogonal functions representative of the two dominant modes of sandbar migrations: offshore and onshore propagation. Interference of these two modes produces commonly observed sandbar states. While mild wave energies are traditionally assumed to drive onshore sandbar migration, the offshore mode is repeatedly seen to dominate sandbar migration in mild wave seasons following anomalously high late‐winter wave energy and when the inherited morphology is composed of a single bar or terrace, as opposed to a more common two‐bar state. A data‐derived conceptual model is presented synthesizing the effect of antecedent morphology and wave climate chronology on interannual trends in net offshore sandbar migration. Plain Language Summary: Sandbars commonly exist in shallow water just offshore of sandy coastal beaches. These features are thought to play an important role in protecting the beach from storm waves, but unfortunately there is limited skill in predicting how these sandbars form and move. An unparalleled 41‐year, monthly data set of nearshore sandbar behavior is used in this work to identify a repetitive pattern where emergence of new sandbars in the nearshore occurs when offshore migration occurs during mild wave seasons, which is contradictory to traditional conceptual models for nearshore morphology evolution. A new conceptual map is derived from the data that identifies common sandbar states and the migration direction that produces changes from one state to another, specifically highlighting that sandbar migration direction at the seasonal to yearly scale is strongly dependent on winter wave climates and the sandbar state at the beginning of mild wave seasons each spring. Key Points: Sandbar migrations in on‐ and offshore directions expressed as propagating modes derived from 41 years of surveysOffshore migrations are observed during mild wave conditions when a single‐bar or terraced beach profile is presentThe relative timing of large wave energy prior to extended periods of mild conditions enables offshore migrations [ABSTRACT FROM AUTHOR]

Bar and berm morphology characterize the seasonal beach evolution, and determine the protection against storm erosion as well as the touristic use of beaches. Thus, they are of particular interest for coastal management and engineering in the nearshore zone. This study used large-scale wave flume experiments to observe the transition from fully dissipative to fully reflective beach profile at a high level of detail. Starting from a post-storm profile generated under energetic waves, a very low energy wave condition caused dissipation of the outer and the inner bar, shoreline recovery, and berm accretion. Measurements revealed feedback between hydrodynamics and beach profile evolution with an onshore shift of the wave breaking location. As a result, the magnitude and cross-shore evolution of wave asymmetry-related bedload net onshore and suspended net offshore transport changed. The relative magnitudes of the two transport components and the way they shifted relative to each other caused the observed beach recovery. Additionally, a link between bar and berm morphology (surf-swash sand exchange) was observed. The shifting breakpoint enabled sustained, wave asymmetry-related onshore transport in the inner surf zone, feeding the berm accretion which occurred through advective swash zone processes including berm overwash. • Large-scale experiments of beach recovery and berm accretion. • Four morphological phases during transition from dissipative to reflective profile. • Shifting breakpoint controls transport processes and morphology. • Important roles of bedload, undertow, wave asymmetry and berm overwash. • Useful insights into surf and swash zone dynamics (sand exchange). [ABSTRACT FROM AUTHOR]

An existing Boussinesq wave model, solved in a hybrid format of the finite-difference method (FDM) and finite-volume method (FVM), with good merits of stability and shock-capturing, was used as the wave driver to simulate the beach evolution under nearshore wave action. By coupling the boundary layer model, the sand transport model, and the terrain updating model, the beach evolution model is established. Based on the coupled model, the interaction process between sandbars and waves was simulated, reproducing the process of the original sand bars diminishing, new sandbars creating, and finally disappearing. At the same time, the formation and movement process of sand bars under solitary and regular waves are numerically simulated, in the breaking zone, the water bottom has a larger shear stress, which promotes the sediment activation, transport and erosion formation, and near the breaking point, the decrease of sand-carrying capacity is the main reason for the formation of sandbars, the numerical model can accurately describe the changes in the shoreline profile under wave action.

Abstract Sandbars are ubiquitous morphologic features found in the nearshore environment throughout the world, yet predictive capabilities of their evolution remain limited. In order to provide new insights on the relevant processes controlling sandbar morphodynamics, this study uses a 41‐year record of 637 monthly cross‐shore profiles from Duck, North Carolina, USA, to derive complex empirical orthogonal functions representative of the two dominant modes of sandbar migrations: offshore and onshore propagation. Interference of these two modes produces commonly observed sandbar states. While mild wave energies are traditionally assumed to drive onshore sandbar migration, the offshore mode is repeatedly seen to dominate sandbar migration in mild wave seasons following anomalously high late‐winter wave energy and when the inherited morphology is composed of a single bar or terrace, as opposed to a more common two‐bar state. A data‐derived conceptual model is presented synthesizing the effect of antecedent morphology and wave climate chronology on interannual trends in net offshore sandbar migration.

Sharks, as apex predators, play an essential ecological role in shaping the marine food web and maintaining healthy and balanced marine ecosystems. Sharks are sensitive to environmental changes and anthropogenic pressure and demonstrate a clear and rapid response. This designates them a “keystone” or “sentinel” group that may describe the structure and function of the ecosystem. As a meta-organism, sharks offer selective niches (organs) for microorganisms that can provide benefits for their hosts. However, changes in the microbiota (due to physiological or environmental changes) can turn the symbiosis into a dysbiosis and may affect the physiology, immunity and ecology of the host. Although the importance of sharks within the ecosystem is well known, relatively few studies have focused on the microbiome aspect, especially with long-term sampling. Our study was conducted at a site of coastal development in Israel where a mixed-species shark aggregation (November–May) is observed. The aggregation includes two shark species, the dusky (Carcharhinus obscurus) and sandbar (Carcharhinus plumbeus) which segregate by sex (females and males, respectively). In order to characterize the bacterial profile and examine the physiological and ecological aspects, microbiome samples were collected from different organs (gills, skin, and cloaca) from both shark species over 3 years (sampling seasons: 2019, 2020, and 2021). The bacterial composition was significantly different between the shark individuals and the surrounding seawater and between the shark species. Additionally, differences were apparent between all the organs and the seawater, and between the skin and gills. The most dominant groups for both shark species were Flavobacteriaceae, Moraxellaceae, and Rhodobacteraceae. However, specific microbial biomarkers were also identified for each shark. An unexpected difference in the microbiome profile and diversity between the 2019–2020 and 2021 sampling seasons, revealed an increase in the potential pathogen Streptococcus. The fluctuations in the relative abundance of Streptococcus between the months of the third sampling season were also reflected in the seawater. Our study provides initial information on shark microbiome in the Eastern Mediterranean Sea. In addition, we demonstrated that these methods were also able to describe environmental episodes and the microbiome is a robust measure for long-term ecological research.

In a dynamic coastal environment, the morphology of a sandbar is anticipated to change regularly, particularly when there is a large annual sediment supply. The study explored the nature and magnitude of a developing sandbar’s morphological changes between 1972 and 2006 in Sonadia Island, Bangladesh, using five different satellite images. The sandbar’s changes across the shoreline were calculated using field survey data and manual-drawing outlines of overlaid maps. The study revealed continuous and rapid morphological changes of the sandbar along the Island’s shoreline. The net annual rate of shoreline displacement ranges between 3.94 m and 7.79 m during the period. These might directly result from the Island being exposed to huge wave and tidal action and excessive sediment supply around the Island. Transect 3 represents the sandbar’s head and appears to be the most active zone with the most significant annual shoreline displacement of 22.00 m. The sandbar’s far end around Transect 7 is more stable with a yearly shoreline displacement of 0.50 m. Changes were more drastic between 1999 and 2006 than between 1972 and 1999. These rapid changes after 1999 could indicate that the sandbar is becoming increasingly vulnerable to anthropogenic changes and the adverse effects of sea-level rise.

This study presents novel insights into hydrodynamics and sediment fluxes in large‐scale laboratory experiments with bichromatic wave groups on a relatively steep initial beach slope (1:15). An Acoustic Concentration and Velocity Profiler provided detailed information of velocity and sand concentration near the bed from shoaling up to the outer breaking zone including suspended sediment and sheet flow transport. The morphological evolution was characterized by offshore migration of the outer breaker bar. Decomposition of the total net transport revealed a balance of onshore‐directed, short wave‐related and offshore‐directed, current‐related net transport. The short wave‐related transport mainly occurred as bedload over small vertical extents. It was linked to characteristic intrawave sheet flow layer expansions during short wave crests. The current‐related transport rate featured lower maximum flux magnitudes but occurred over larger vertical extents. As a result, it was larger than the short wave‐related transport rate in all but one cross‐shore position, driving the bar's offshore migration. Net flux magnitudes of the infragravity component were comparatively low but played a nonnegligible role for total net transport rate in certain cross‐shore positions. Net infragravity flux profiles sometimes featured opposing directions over the vertical. The fluxes were linked to a standing infragravity wave pattern and to the correlation of the short wave envelope, controlling suspension, with the infragravity wave velocity. Plain Language Summary: Nearshore sandbars are seabed features that protect coastal infrastructure behind many sandy beaches around the world. In response to waves, they change in shape and distance to the beach. To improve understanding of their offshore movement, experiments representing natural conditions in a controlled laboratory setting were done. In this context, the underwater transport of sand was measured. The experiments featured groups of single short waves (less than 2.5 m long), which transported sand in different ways. Single short waves largely transported sand toward the beach, and in a very thin layer close to the seabed. Currents, caused by the short waves and their breaking, largely transported sand away from the beach, and over a much wider layer. Interactions between the single short waves in a group created longer waves. They transported sand partly toward and partly away from the beach. The currents transported sand more effectively than the single short waves, which explains the sandbar's offshore movement. The long waves transported less sand and only became important when transports from currents and short waves canceled each other out. This study provides useful information for better forecasting of sandbar movement, improving coastal protection. Key Points: Bar offshore migration resulted from balance of offshore‐directed, current‐related and onshore‐directed, short wave‐related transportsShort wave‐ (current‐) related transport dominant in sheet flow (suspended) layer. As they oppose, infragravity transport non‐negligibleThe presence/absence of time‐lags between concentration and hydrodynamics in the suspended/sheet flow layers affects transport direction [ABSTRACT FROM AUTHOR]

Exposed riverine sediments are unique riparian environments that exhibit high biodiversity and harbor many specialist species. Ground beetles are the most well studied inhabitants within these environments where they are often sampled using pitfall traps. In order to develop conservation measures for species occupying these habitats a logical first step is to refine sampling methods so that proper biodiversity assessments can be carried out. To that end, the effectiveness of two pitfall trap designs (standard trap vs. barrier trap) was evaluated. Over three sampling periods we collected 5,186 individuals represented by 43 species. Barrier traps proved to be superior, yielding significantly greater numbers of individuals (n = 3,456 vs. 1,730) than standard traps. Additionally, we collected more ground beetle species (37 vs. 30) in barrier traps than in standard pitfall traps. This study supports the rationale for deployment of more than one trap design to avoid deficiencies exhibited by a single type.

Sandbars are commonly observed on sandy coasts, and they can prevent erosion on the beach face. Better prediction of sandbar evolution is necessary for coastal management and beach nourishment. In this study, a process-based morphodynamic model is used to reproduce the barred beach profile evolution in the Duck94 field experiments. The importance of the wave roller slope parameter in the model is revisited. Six idealized numerical experiments are set to investigate the effect of wave heights, wave periods and sea levels on sandbar migrations. By implementing two recent cross-shore varying roller slope formulas, the models achieved fair-to-good performances. It was found that the variations of sandbar morphological evolution are mainly controlled by the cross-shore varying roller slope. An increase in the wave height or a decrease in the wave period would lead to a more rapid and further-offshore migration of the sandbar. When the sea level variations are much smaller than the water depth over the sandbar, the effect of sea level changes on the sandbar migration is negligible, though a lower sea level would cause more erosion on the beach face.

Rip currents have become one of the primary coastal hazards globally. In the present work, the dynamics of a multichannel rip system are revealed by a group of numerical simulations over truncated sandbar bathymetry under varying wave conditions. It is found that increasing wave height may disperse rip currents due to strong wave-current shear in opposite directions and the resulting microbreaking, which is contrary to the widely accepted proportional theory. The pump-feed phenomenon between adjacent channels shows that rip currents might be absent in small channels when water flows through neighboring broader pathways. Rip currents are indicated highly sensitive to wave direction and deflect into undulant alongshore currents around sandbars as waves deviate from normal incidence. The decay of rip currents with wave angle did not show a clear dependence on channel width, which was found in previous studies. Vortices usually appear near bar-channel edges and by sides of rip currents. The magnitude of the vortex is not explicitly related to the wave height but increases with the wave angle. The water setup shoreward by sandbars substantially increases with wave angle, while the surface depression over rip channels is less observed. This indicates a lower pressure differential to drive feeder flows toward the channels and explains why rip currents cannot persist when incident waves become slightly oblique. [ABSTRACT FROM AUTHOR]

A flood disaster was frequently happened resulting from local heavy rainfall in Japan. Many farmlands and housing were damaged terribly in 2017 and 2018. A high water level was observed in the Babamegawa River which was the largest Class B river. The embankment on the left bank at Babamegawa River was collapsed owing to scouring was caused by a sandbar at the downstream side. Like this, streamflow was greatly influenced by a sandbar, so it was important to understand the behavior of the sandbar. However, only one percent of rivers were conducted Periodic Vertical and Cross-sectional Survey while all Class A river were conducted measurement mainly because there were too many Class B river to measure. In this study, it was carried out that investigation using UAV to manage rivers easily. The Sandbar was taken the photographs from 150 m above the ground from September 2017 to November 2018 and The sandbars’ area, length, and width were calculated with SfM (Structure from Motion technique). These data were investigated sharply when the water level was decreased below ordinary. Moreover, it was important to remark the width of sandbar as a contraction of channel and loss of sandbar were needed to grasp for river management. It was found that the embankment was broken to slip by losing base performing the numerical calculation. [ABSTRACT FROM AUTHOR]

Exposed riverine sediments are unique riparian environments that exhibit high biodiversity and harbor many specialist species. Ground beetles are the most well studied inhabitants within these environments where they are often sampled using pitfall traps. In order to develop conservation measures for species occupying these habitats a logical first step is to refine sampling methods so that proper biodiversity assessments can be carried out. To that end, the effectiveness of two pitfall trap designs (standard trap vs. barrier trap) was evaluated. Over three sampling periods we collected 5,186 individuals represented by 43 species. Barrier traps proved to be superior, yielding significantly greater numbers of individuals (n = 3,456 vs. 1,730) than standard traps. Additionally, we collected more ground beetle species (37 vs. 30) in barrier traps than in standard pitfall traps. This study supports the rationale for deployment of more than one trap design to avoid deficiencies exhibited by a single type. [ABSTRACT FROM AUTHOR]

The Lower Ping River downstream from the Bhumibol Dam has suffered from the excessive sedimentation. Rapid growth sandbars occur along the 129 km of the downstream reach within the succession of weirs. Severe riverbank collapses can also be detected locally. The objective of this research is to assess riverbank accretion/erosion using remote sensing and GIS techniques. Comparison of the 2007 and 2017 satellite images shows that total emerged island bar area increases up to 5,702,557 m². The total riverbank erosion area is 1,150,943 m² whereas the total of accretion area is over 10,561,530 m². Digital Shoreline Analysis System (DSAS) software was used to determine the riverbank erosion/accretion rates. The DSAS output shows the average rate of erosion and accretion at 1.24 and 4.89 m/year. Rapid growth of sandbars is responsible for the shallowing and narrowing of river embankment leading to rapid overflow during flooding. The result from this study enables all authorities and stakeholders to recognize the specific locations, which have severely been affected by riverbank accretion and erosion. [ABSTRACT FROM AUTHOR]

The Sandbar Wildlife Management Area (SWMA) is on the northeast shore of Lake Champlain in Vermont. The wetlands of SWMA are bisected by US Rt. 2, an arterial highway with average daily traffi c (ADT) of 10,200. There are hundreds of acres of wetlands and forested upland on both sides of Rt. 2. Wildlife commonly crosses the highway, which results in a high incidence of roadkill. Northern leopard frogs (Rana pipiens) are a signifi cant portion of the roadkill. The Vermont Agency of Transportation (VTrans) in collaboration with the Vermont Agency of Natural Resources (VANR) installed silt fences as a barrier to keep animals off the highway. This is a short-term solution that also provided a test for the use of temporary fences to direct movement of animals. The long-term solution must include the installation of culverts and permanent fencing. A secondary benefi t of the project was to promote the needs for wildlife crossing in Vermont through media coverage of the project.

Cross-shore sediment transport is one of the effective factors in erosion and sedimentation, and affects dynamics of the beach profile in coastal areas. Furthermore, sandbar migration due to cross-shore sediment transport mostly effects beach nourishment, displacement of pollutions trapped in sediments, and organism and plants’ lives. In this manuscript, sandbar migration due to cross-shore sediment transport is studied and results have been compared to field data. Field data used here have been measured at the southern Caspian Sea, Noshahr coasts, Iran. During the measurement period, two high-energy events with significant wave height of approximately 1.4 m have been measured. All simulations have been done based on a one dimensional cross-shore transect. Wave transformation during propagation toward the coast has been modeled using the third generation model SWAN, and long-shore wave-induced current has been simulated by solving alongshore momentum equilibrium equation. To include the morphological change, the cross-shore sediment transport rate has been estimated using Bagnold [1966], Bowen [1980], and Bailard’s [1981] (BBB) energetic sediment transport model, and results has been compared to the model developed by Plant et al. [2001], which itself is an energetic model based on Bagnold [1966]. Finally, bathymetric changes has been forecasted by solving cross-shore mass conservation equation which indicated slight outperform of BBB rather than Plant et al. model in this study area.

Micro-estuaries in semi-arid areas, despite their small size (shallow depth of a few meters, length of a few kilometers, and a surface area of less than 1 km2) are important providers of ecosystem services. Despite their high abundance, tendency to suffer from eutrophication and vulnerability to other anthropogenic impacts, such systems are among the least studied water bodies in the world. In low tidal amplitude regions, micro-estuaries often have limited rate of sea-river water exchange, somewhat similar to fjord circulation, caused by a shallow sandbar forming at the coastline. The long-term study, we report here was inspired by the idea that, due to their small size and low discharges regime, relatively small interventions can have large effects on micro-estuaries. We used a stationary array of sensors and detailed monthly water sampling to characterize the Alexander estuary, a typical micro-estuary in the S.E. Mediterranean, and to identify the main stress factors in this aquatic ecosystem. The Alexander micro-estuary is stratified throughout the year with median bottom salinity of 18 PSU. Prolonged periods of hypoxia were identified as the main stress factor. Those were alleviated by breaching of the sandbar at the estuary mouth by sea-waves or stormwater runoff events (mostly during winter) that flush the anoxic bottom water. Analysis of naturally occurring sandbar breaches, and an artificial breach experiment indicate that the current oxygen consumption rate of the Alexander micro-estuary is too high to consider sandbar breaches as a remedy for the anoxia. Nevertheless, it demonstrates and provides the tools to assess the feasibility of small-scale interventions to control micro-estuaries hydrology and biogeochemistry.

Cheng, J. and Wang, P., 2019. Unusual beach changes induced by Hurricane Irma with a negative storm surge and poststorm recovery. Journal of Coastal Research, 35(6), 1185–1199. Coconut Creek (Florida), ISSN 0749-0208. The coast of west-central Florida, facing the Gulf of Mexico, experienced Hurricane Irma with a negative surge of 1.1 m and a highly oblique northerly approaching wave in September 2017. This unusual hydrodynamic condition provides an opportunity to investigate the effect of surge and incident wave direction on morphology changes. Beach profiles, spaced at 300 m apart, along a 15-km stretch of beach were surveyed 2 weeks prior to the passage of Hurricane Irma and 1 week after and continued for up to 5 months after the passage to obtain Irma-induced erosion as well as post-Irma recovery. Owing to the occurrence of negative surge, the profile volume of the dune field remained mostly stable. The majority of beach erosion occurred below mean sea level, with a considerable amount of sediment transported seaward of the depth of closure. This is opposite to the conservation of beach profile volume above depth of closure under several earlier storms with a positive surge. The alongshore variation of overall beach profile volume erosion demonstrates a southward decreasing trend, due to a southward decreasing wave height as controlled by the northerly incident wave. After the passage of Irma, minor beach volume recovery occurred during the calm period of the fall season. Opposite to the typical erosive beach in winter, the most substantial beach accretion and onshore bar movement were observed during the following peak winter season as beach/bar evolved toward equilibrium. The profile volume in the dry beach region experienced a complete recovery in the first 5 months after Hurricane Irma. Shoreline change is a valid proxy for beach volume change during both the erosive and the recovery phase of Irma. The systematically measured beach profiles provide a solid dataset to calibrate process-based models to study beach morphodynamics. [ABSTRACT FROM AUTHOR]

The variabilities of multiple bar system have been investigated in inter-annual time scale based on long-term field surveys. The field sites include Ishikawa Coast and Chirihama Coast facing the Sea of Japan. On both sites, large scale sandbar system has developed and the morphological variabilities are characterized by cyclic and systematic migration of multiple bars. On Ishikawa Coast, representative spatial patterns during individual cycle are analyzed to describe the three-dimensional morphological evolutions. Considerable changes in plan shape are observed such as quasi-regular crescentic patterns, parallel alignment of oblique bars, disconnection and realignment of bars. In contrast, bar migration on Chirihama Coast is quasi two-dimensional. The transition of the multiple sandbar systems is well reproduced by an empirical parametric model. [ABSTRACT FROM AUTHOR]

Abstract The 2011 flood, an approximately 500-yr flood on the Missouri River, built many large sandbars that have since been modified by eolian and fluvial processes. The '59-mile' segment of the Missouri National Recreational River, located between Yankton, South Dakota and Ponca, Nebraska, USA is a relatively free-flowing stretch of the river downstream of a major dam which has drastically reduced sediment loads since 1955. Critical sandbar habitat has gradually declined on this stretch of the river, presenting challenges to river management. Satellite and LiDAR imagery was used to measure changes in area, volume, and surface characteristics of sandbars over three years since the 2011 flood. The Portable in situ Wind Erosion Lab (PI-SWERL) was used to measure the potential for bare sandbars to emit dust. Our results suggest that eolian processes are important in the early evolution of sandbars, as the wind modifies the surface into dunes and gravel lags. Furthermore, sandbars are important local sources of dust until gravel lags stabilize the surface, limiting further eolian deflation. The lowering of sandbar surfaces by wind erosion makes them more susceptible to being overtopped by high water events. Fluvial erosion along the margins of the sandbars ultimately reduces their area over time. Vegetation growth further stabilizes sandbar surfaces. The rate of eolian and fluvial erosion ultimately depends on the position of the sandbars relative to the thalweg as well as wind direction. New sandbars are rarely built by fluvial processes on a regulated river like the Missouri, and are in a constant state of erosion and modification, ultimately limiting their longevity as quality habitat. Highlights • Eolian processes are important in the modification of sandbars following floods. • Sandbar surfaces stabilize with vegetation growth and gravel lag development. • LiDAR can help estimate proportion of eolian to fluvial erosion of sandbars. • Sandbars persist for several years but gradually erode on a regulated river. [ABSTRACT FROM AUTHOR]

A large‐scale laboratory experiment was conducted to evaluate cross‐shore sediment transport and bed response on a sandbar under erosive and accretive field‐scale wave conditions (total of 11 cases). Unprecedented vertical resolution of sediment concentration was achieved through the use of conductivity concentration profilers alongside miniature fiber optic backscatter profilers. Observations were made of intrawave (phase‐averaged) and wave‐averaged cross‐shore sediment flux profiles and transport rates in the lower half of the water column on the crest of a sandbar. The net sediment transport rate was partitioned into suspended sediment (SS) and bed load (BL) components to quantify the relative contributions of SS and BL to the total sediment transport rate. Net SS transport rates were greater than net BL transport rates for the positive (wave crest) half‐cycle in 6 of 11 cases, compared to 100% (11 of 11) for the negative (wave trough) half‐cycle. Net (wave‐averaged) BL transport rates were greater, in magnitude, than net SS transport rates for 7 of the 11 cases. The dominant mode of transport was determined from the ratio of net BL to net SS transport rate magnitudes. The net transport rate was negative (offshore‐directed) when SS dominated and positive (onshore‐directed) when BL dominated. Net BL transport rate correlated well with third moments of free‐stream velocity (r2 = 0.72), suggesting that energetics‐type quasi‐steady formulae may be suitable for predicting BL transport under the range of test conditions. Plain Language Summary: Sandbars are nearshore features found at many beaches around the world, constantly changing shape and migrating seaward or landward with ever‐changing environmental conditions. A large‐scale experiment was carried out under controlled conditions to better understand the processes responsible for sandbar morphology. The amount of sand transported on a sandbar crest, per wave (net), was determined through detailed measurements of waves, water velocity, and the volume fraction of sand in the water at many elevations in the water column. Sand transport occurred in two distinct layers, one very near the sand bed (bed load) and the other spanning the majority of the water depth (suspended load). Whether sand was transported seaward or landward, per wave, was governed by whether more sand was transported in the suspended or bed load layer, respectively. Ultimately, this study will lead to improved predictive capability of morphologic evolution models in this highly dynamic, economically important region of the beach. Key Points: Bed load and suspended load transport rates were measured on a sandbar crest under field‐scale wave forcingTotal net transport rate was offshore‐directed when suspended load dominated and onshore‐directed when bed load dominatedNet bed load transport rates were well correlated with third moments of free‐stream velocity [ABSTRACT FROM AUTHOR]

In its judgment of 2 February 2018 in the joined cases between Costa Rica and Nicaragua, the International Court of Justice held that Harbor Head Lagoon and the sandbar separating it from the Caribbean Sea belonged to Nicaragua, thereby creating an enclave on the Costa Rican coast. Despite this finding, the Court decided to disregard it when establishing the maritime delimitation. This article aims at showing that such a solution is incompatible with the United Nations Convention on the Law of the Sea as well as examining the options left to the Court to remedy the impracticality of the situation in accordance with the applicable law. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on 'sandbar' feature in a tide-dominated symmetrical funnel-shaped estuary using a hydro-morphodynamic model. A series of benchmark flows is simulated to demonstrate the capabilities of the model (e.g., well-balanced property, treating wet/dry fronts, shock-capturing ability), and the good quantitative accuracy. Afterwards, the model is applied for systematic numerical case studies. The main geometrical parameters, the upstream and boundary conditions are specified with reference to the Qiantang River Estuary (QRE), where a giant 'sandbar' is well known. It is shown that a maximum turbidity zone forms due to interactions of the riverine discharge and the tidal flow. Strong deposition occurs in the maximum turbidity zone, whereas erosion occurs otherwise. This results in a sandbar of comparable magnitude and position with the observed 'sandbar' in the QRE. As the sandbar grows, a slight increasing trend followed by a rapid decreasing trend for the difference between high and low water levels is established. A larger riverine discharge leads to a sandbar more closer to the seaside, but effect of the seasonal discharge variation is limited. Erodibility of bed and seaside sediment input mainly influence the height of the formed sandbar. [ABSTRACT FROM AUTHOR]

Modifications in river morphology are witnessed due to the hydrological fluctuations leading to braided rivers and sandbar developments. Understanding the hydrological alterations could offer crucial insight into the ecosystem's landscape pattern. To comprehend flood and drought in an agricultural ecosystem, we investigated the impact of short-term water level changes from 1999 to 2015. Numerical simulations were carried out on the fluctuant streamflow at different seasons in a braided river using a two-dimensional hydrodynamic model. The number of consecutive wet days (CWD), average wet days (AWD), consecutive dry days (CDD), and average dry days (ADD) were computed. The Standardized Streamflow Index (SSFI-4) was determined at a seasonal time scale, which is used to quantify the streamflow-based hydrological droughts. The calibration and validation of the hydrodynamic model was done with the measured velocity. To understand the planform geometry of the river, satellite images were derived for the historical period from 1976 to 80 till 2016–17. The Planform Index (PI) and Sinuosity Index (SI) were used to assess and classify the river into straight, braided and meander categories. Speedy modifications were observed across the longitudinal profile, with PFI varying between 3.72 and 42.8. Sandbars being an imperative asset for floodplain communities and dwellers, the effect of these fluctuations was studied in different landscape classes. We analyzed the changes in the spatial and temporal characteristics of dynamic landscape patterns between 2004 and 2014 at quinquennial and decadal scales. We found that a substantial-high water level from a 2010 flood led to a drastic change in the landscape pattern of the ecosystem. In addition, consecutive dry days witnessed over the sandbar regions affect the agriculture cropping patterns. Post flooding, the expansion of land under agriculture could be inferred from the fact that sediment was fertile and deposited after the flood recession; agriculture was dominantly practiced in the region. Overall, the study demonstrated that various hydrological components typically impact the spatial distribution characteristics of landscape patterns. • Riverine sandbars provide additional fertile land for agriculture and farming to meet food demand. • Modifications in river morphology were observed with PFI varying between 3.72 and 42.8 within short reaches. • Continuous dry days and wet days in cropping seasons could significantly impact the crop growth. • Increase in river braiding increased areas under cultivation. [ABSTRACT FROM AUTHOR]

Investigation of a beach and its wave conditions is highly requisite for understanding the physical processes in a coast. This study composes spatial and temporal correlation between beach and nearshore processes along the extensive sandy beach of Nagapattinam coast, southeast peninsular India. The data collection includes beach profile, wave data, and intertidal sediment samples for 2 years from January 2011 to January 2013. The field data revealed significant variability in beach and wave morphology during the northeast (NE) and southwest (SW) monsoon. However, the beach has been stabilized by the reworking of sediment distribution during the calm period. The changes in grain sorting and longshore sediment transport serve as a clear evidence of the sediment migration that persevered between foreshore and nearshore regions. The Empirical Orthogonal Function (EOF) analysis and Canonical Correlation Analysis (CCA) were utilized to investigate the spatial and temporal linkages between beach and nearshore criterions. The outcome of the multivariate analysis unveiled that the seasonal variations in the wave climate tends to influence the bar-berm sediment transition that is discerned in the coast. [ABSTRACT FROM AUTHOR]