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Nearshore sandbars are dynamic features that characterize shallow morphobathymetry and vary over a wide range of geometries and temporal lifespans. Nearshore sandbars influence beach geometry by altering the energy of incoming waves; thus, monitoring the evolution of sandbars is a fundamental approach in effective coastal planning. Due to several natural and technical limitations related to shallow seafloor mapping, there is a significant gap in the availability of high-resolution, shallow bathymetric data for monitoring the dynamic behaviour of nearshore sandbars effectively. This study introduces a novel image-processing technique that produces time series of pseudo-bathymetric data by utilizing multi-temporal (monthly) drone imagery, and it provides an assessment of local morphodynamics at a sandy beach in the southeast Mediterranean. The technique is called standardized-ratio bathymetric index (SRBI), and it transforms natural-colour drone imagery to pseudo-bathymetric data by applying an empirical formula used for satellite-derived bathymetry. This technique correlates well with laser altimetry depth measurements; however, it does not require in situ depth data for implementation. The resulting pseudo-bathymetric data allows for extracting cross-shore profiles and delineating the sandbar crest with 4 m horizontal accuracy. Stacking of temporal profiles allowed for the quantification of the sandbar's crest and trough changes at different alongshore sections. The main findings suggest that the nearshore crescentic sandbar at Episkopi Beach (north Crete) shows strong seasonality regarding net offshore migration that is promoted by enhanced wave action during winter months. In addition, the crescentic sandbar is susceptible to morphology arrestment during prolonged weeks of low wave action. The average migration rate during winter is 10 m.month−1, with some sections exhibiting a maximum of 60 m.month−1. This study (a) offers a novel remote-sensing approach, suitable for nearshore seafloor monitoring with low computational complexity, (b) reveals sandbar geometry and temporal change in superior detail compared to other observational methods, and (c) advances knowledge about nearshore sandbar monitoring in the Mediterranean region. [ABSTRACT FROM AUTHOR]

The loss of biodiversity in freshwater environments is becoming an increasing problem globally. As a result, many tools have been developed and improved to reduce this decline. However, there is still a need for the identification and evaluation of precise restoration measures to improve habitats and preserve sentinel freshwater species, such as brown trout. This paper provides an up‐to‐date viewpoint about the life history, habitat characteristics, suitability conditions, and metapopulation dynamic modelling of brown trout, aiming to identify and discuss gaps and propose possible improvements based on collating and reinterpreting literature data. Results suggest that habitat suitability curves for environmental and hydraulic variables possess some degree of universality, for spawning habitat, fry, juvenile and adult trout. Further, an improved method to estimate the amount of suitable area by including the role of stream obstacles (i.e., macro‐roughness with characteristic size in the order of the mean water depth) is proposed and discussed. This approach can be integrated into advanced metapopulation models and will allow experts to evaluate the best measures towards restoring and preserving freshwater riverine environments. [ABSTRACT FROM AUTHOR]

Experimental floods have been increasingly used as a promising practice to rehabilitate river ecosystems downstream of dams; however, the morphological and habitat dynamics they determine under different sediment supply conditions still poses relevant research and management questions. This study investigates the morphological and fish mesohabitat dynamics following an experimental flood, in two river reaches subject to different sediment supply regimes. We chose the lower Spöl River (Switzerland) as a relevant case study, subject to an experimental flood program for several years. Downstream of the dam, a tributary supplies large amounts of sediment to the Spöl dividing the study area into two homogeneous reaches with different sediment availability but similar flow conditions during the experimental flood. We analyzed and quantified the changes in morphology and fish habitat suitability for the Brown Trout (Salmo trutta) at the mesoscale in these two reaches caused by the 2021 experimental flood, which lasted 11 h and had a peak magnitude corresponding to a 1‐year return interval in the pre‐dam flow regime. We found almost no correlation between changes in the channel morphology and in habitat suitability for this event. In the upstream reach, located immediately downstream of the dam, we observed a narrower channel with a regular longitudinal sequence featuring nearly immobile coarse rapids, interspersed with more dynamic, finer riffles. Here, reach‐scale morphodynamics and the shifts of the mesohabitat mosaic and the suitable habitats were below 10%. Conversely, the downstream reach, characterised by a wider channel and much higher sediment supply of well‐sorted, finer bed material, was dominated by alternate bar instability and migration at the reach scale, which caused a 45% shift in its pre‐flood habitat mosaic. Nevertheless, in the same reach, the overall suitability of habitats remained relatively unchanged. We attributed these different dynamics to two main factors: (i) more prolonged bedload mobility conditions and (ii) the occurrence of bar migration in the downstream reach compared to the upstream one. This study (i) underscores the critical importance of considering sediment supply from downstream tributaries when designing and monitoring the effects of experimental floods, (ii) supports the use of morphodynamic models in the related planning and monitoring phases and (iii) shows the relevance of integrating morphodynamics and eco‐hydraulic analysis to support the implementation of such flow restoration programs. [ABSTRACT FROM AUTHOR]

Purpose: The nearshore area of many sandy beaches exhibits morphological patterns which are rhythmic along the coast. Most studies on submerged sandy bedforms have focused on their morphodynamics in the deeper part of the nearshore due to operational limitations when performing bathymetric measurements. Along part of the macrotidal Belgian west coast, a remarkable field of coast-normal submerged dunes is found in a very shallow area that partly emerges at low tide. Methods: For the first time, the morphology, volumetric budgets and evolutionary trend of these large transverse submerged dunes have been investigated using high resolution multibeam bathymetric surveys performed over an observation period of 9 years and returned at intervals from daily to a few years. Results: The morphological analysis indicates the presence of seven large transverse sharp-crested sandy dunes with a height of 1–2 m and a spacing up to 200 m, extending from the beach to 2.7 km offshore. Their morphodynamic patterns show a remarkable rhythmicity along the coast with a persistence over time. The large dunes are an integral part of the coastal system contributing to the long-term natural beach accretion. They migrate at a rate of 36 m yr−1 in the direction of the longshore sediment transport towards NE mostly driven by flood currents. The morphology of the large dunes is also controlled by storm-wave action depending on their depth below sea level. Storm-waves do not influence the dune mobility. Their morphology is forced by the bathymetric context as well as the presence of coastal engineering structures such as groynes. Conclusions: The morphodynamics and evolution of the large transverse dunes suggest complex morphosedimentary interactions of a shallow nearshore area, where a constant large natural sand supply interferes with strongly fluctuating coastal hydrodynamics. [ABSTRACT FROM AUTHOR]

Photosynthetic algae play a significant role in oceanic carbon capture. However, their performance is constantly challenged by fluctuations in environmental light conditions. While phototaxis is a common strategy to cope with such fluctuations, nonmotile species must adopt alternative mechanisms to avoid light-induced damage. Here, we show that the nonmotile, single-celled marine dinoflagellate Pyrocystis lunula contains a chloroplast network that undergoes strong deformation in response to strong light. By exposing cells to various physiologically relevant light conditions and applying temporal illumination sequences, we find that the light-induced network morphodynamics follows dynamic rules similar to temporal low-pass filtering.Wedevelop a mathematical formalism to model the light-regulated behavior, exposing the relevant timescales of the morphodynamic response. Moreover, confocal microscopy reveals that the unusual reticulated morphology exhibits properties similar to auxetic metamaterials, facilitating the rapid and drastic deformation necessary for the light-avoidance motion, confined by the cell wall. This mechanism reduces the effective chloroplast area under high light conditions, minimizing light absorption and preventing photodamage. Our findings demonstrate that the intricate connection between the chloroplasts topologically complex structure and active dynamics enables the dinoflagellate's dynamic adaptation to changing light environments, thereby supporting essential life-sustaining processes. [ABSTRACT FROM AUTHOR]

Uncovering fine‐grained phenotypes of live cell dynamics is pivotal for a comprehensive understanding of the heterogeneity in healthy and diseased biological processes. However, this endeavor poses significant technical challenges for unsupervised machine learning, requiring the extraction of features that not only faithfully preserve this heterogeneity but also effectively discriminate between established biological states, all while remaining interpretable. To tackle these challenges, a self‐training deep learning framework designed for fine‐grained and interpretable phenotyping is presented. This framework incorporates an unsupervised teacher model with interpretable features to facilitate feature learning in a student deep neural network (DNN). Significantly, an autoencoder‐based regularizer is designed to encourage the student DNN to maximize the heterogeneity associated with molecular perturbations. This method enables the acquisition of features with enhanced discriminatory power, while simultaneously preserving the heterogeneity associated with molecular perturbations. This study successfully delineated fine‐grained phenotypes within the heterogeneous protrusion dynamics of migrating epithelial cells, revealing specific responses to pharmacological perturbations. Remarkably, this framework adeptly captured a concise set of highly interpretable features uniquely linked to these fine‐grained phenotypes, each corresponding to specific temporal intervals crucial for their manifestation. This unique capability establishes it as a valuable tool for investigating diverse cellular dynamics and their heterogeneity. [ABSTRACT FROM AUTHOR]

Spatio-temporal assessment of the evolution and morphodynamics of the Brahmaputra River (BR) can contribute significantly in mitigating challenges offered by rapid urbanisation and climate change. The present remote sensing and geographic information system (RS and GIS) based analysis of the BR revealed an increased Braiding Intensity (BI) from 1976 to 2000, which declined in 2010, and re-emerged in 2020. The average maximum width of the river has generally widened over time and sandbar distribution has exhibited fluctuations. The overall active channel area increased by 1.5 times, and the sandbar area expanded by 1.2 times between 1976 and 2020. The interplay between braiding intensity and width reveals a positive relationship. The sandbar-water ratio reveals a significant prevalence of sandbars in the Brahmaputra River. Furthermore, the study highlights changes in the Bar Development Index (BDI), showing a significant increase in micro-bars and meso-bars but a decrease in macro-bars. With the approach of change detection, key factors observed within the river driving the changes are erosion, channel bifurcations, sandbar formation due to sediment deposition, and sandbar loss due to shifts in channel course. These characteristics are potentially influenced by high water and sediment influx, climate change, and anthropological activities. [ABSTRACT FROM AUTHOR]

According to fundamental concepts, the morphodynamic system of an accumulative sandy coast with underwater bars exhibits cyclic behavior across various time scales. This raises the question: which factor is more significant for the dynamics of a given coast—individual storms or seasonal changes in wave activity? While observations and studies addressing this issue have primarily been conducted on oceanic coasts, there is a lack of comparable data for fetch-limited areas. Monitoring of the bottom topography along the west coast of Vistula Spit (Baltic Sea) revealed a cyclic behavior in morphology, transitioning from a straightened external bar to its connection with the shore. Analysis of field measurement results indicated that seasonal variations in wave intensity do not significantly impact coastal relief. Furthermore, it was found that the complete cycle of underwater bar evolution lasts approximately two years, during which the coast profile maintains a stable shape at the stage of the straightened external bar. The identification of the primary factor influencing coastal evolution can be characterized by the Dean number (Ω), which combines wave parameters (wave height and period) with sediment fall velocity. Utilizing ERA5 wave reanalysis data, we compared the variability of Ω values on both annual and monthly scales. The analysis revealed that for the section of the coast under consideration, there is no clearly dominant evolutionary factor; rather, the coast is influenced approximately equally by individual storm events and seasonal fluctuations in wave energy. Modeling storm-induced bed profile deformations using the CROSS-PB model demonstrated that the position of the external underwater bar remains nearly constant even during intense and prolonged storms. It is concluded that under specific conditions—determined by a combination of sediment size, coastal slope, and wave regime characteristics—the coast can remain stable, exhibiting minimal response to relatively strong storms and seasonal variations in wave energy. Such coasts are characterized by an absence of a dominant evolutionary factor as indicated by fluctuations in the Dean parameter, allowing their morphodynamic cycles to span several seasons. This type of morphodynamics in coastal accumulative relief appears to be typical for conditions found in fetch-limited areas, such as regional and semi-closed seas. [ABSTRACT FROM AUTHOR]

Climate change and human activities pose significant threats to coastal environments. Here, we investigated the effects of storm surges and coastal urbanization on Caribbean sandy beaches, focusing on changes in morphodynamics and population parameters of the Atlantic ghost crab Ocypode quadrata. We measured beach slope, sediment size, and ghost crab populations in non-urbanized and urbanized beaches in St. Thomas, U.S. Virgin Islands, before, three days after, and five weeks after storm surges from Hurricane Lee (September 2023). Storm surges impacted beach morphodynamics, causing some beaches to become steeper with coarser sediment in the short term. Ghost crab burrow density declined in every beach immediately after the hurricane, with reductions of 50–98%. However, number of burrows rebounded to pre-hurricane levels within five weeks. Mean burrow width increased while burrow depth decreased immediately post-hurricane, but also returned to pre-storm levels after five weeks. Additionally, ghost crab burrows were clustered in the upper beach zones immediately post-hurricane but redistributed across the shore gradient after five weeks. Our results show that sandy beach ecosystems are strongly affected by storm surges associated with extreme events; however, they display high resilience and may return to their previous state within a few weeks. Nevertheless, given that the frequency of intense tropical cyclones is expected to increase in the near future, more intense and frequent storms could result in chronic perturbations rather than isolated events, which may compromise sandy beaches’ long-term resilience and sustainability. [ABSTRACT FROM AUTHOR]

Objectives: this study aims to identify the risks of material movement or what is known as morphodynamic risks and the explanation of their types, forms and ways to confront them in the area between the Mani Valley Basin and the Jabab Valley Basin north of the western Anbar Plateau according to the geographical vision. It also aims to shed light on the characteristics of the study area and its strategic depth represented by the fact that it represents the middle of the western part of Iraq and the northwestern part of Anbar Governorate.Methodology: The current study adopted the analytical-deductive approach to study the existing reality of the impact of morphodynamic risks in the area between the Mani Valley Basin and the Jabab Valley Basin north of the western Anbar Plateau, in addition to the field study for the year 2022.Results: Following the analysis of the data, the results showed that the impact of morphodynamic risks on land uses in the region represented by (agricultural use, urban use, and transportation). The results also showed that the highest area occupied by agricultural use amounted to (172) km2 and the lowest area occupied by urban use amounted to (14) km2, while transportation routes occupied an area extension of (337) km, as it was found that these uses exist to a large extent in the parts adjacent to the Euphrates River and their distance from the high and sloping parts and from the barren desert lands, which represent dangerous places that residents avoid and avoid establishing any activity in them.Conclusion: A model for morphodynamic risks was created through the layers entered in the GIS programs, and these layers are (rock material movement, morphometric, hydrological, water erosion), as it was found that the study area include (5) categories of risk degrees, which are (non-risk areas amounting to 89 –low-risk areas amounting to 203 - medium-risk areas amounting to 295 - hazardous areas amounting to 248 - high-risk areas amounting to 110) km2 of the study area

River sediment supply (Qs) and longshore sediment transport (LST) are recognized as two paramount controls on river delta morphodynamics and stratigraphy. We employed the Delft3D model to simulate the evolution of deltas from fluvial to wave‐dominated conditions, revealing the interplay between river‐ and wave‐driven sediment quantities. Wave‐influenced deltas may show alternating accumulation and retreat patterns driven by avulsions and wave‐induced sediment diffusion, posing coastal management challenges. Deltas with higher wave energy evolve under a fine balance between river supply and intense wave‐mediated sediment redistribution and are highly vulnerable under conditions of sediment reduction. Reducing Qs by ∼40%–70%, common in modern dammed rivers, can rapidly shift bypass from ∼0 to 1 (no bypass to complete bypass). This leads to accelerated diffusion and potential sediment loss in modern deltas. The study highlights the importance of accurately computing sediment quantities in real‐world deltas for improved management, especially under increasing anthropogenic and climatic pressures. Plain Language Summary: Ocean waves, like proficient sculptors, shape the meeting points of rivers and seas—where deltas are created. Under the power of ocean waves, the sediments transported by rivers are organized into distinct patterns. Using an advanced computer model, our research unveils how this interplay affects the physical form of these deltas and their functioning. In certain conditions, the sediment carried by waves can jump over the river mouth and move further along the coastline, contributing to stretching the delta and inducing erosion. Currently, river sediments are getting blocked behind river dams, depriving deltas of their sediment nourishment. As sediment supply decreases, powerful waves at the sea erode deltas more easily, endangering ecosystems, human communities and infrastructure. Because deltas are facing challenges from climate change and increased human activities, informed and innovative management strategies based on better knowledge of natural processes are needed to preserve these valuable coastal regions. Key Points: Deltas transition from avulsion‐dominated with localized depocenters to more diffuse and alongshore‐deflected wave‐dominated depocentersBypass increases and trapping decreases abruptly when longshore transport (LST) at the river mouth equals river sediment transport (Qs)LST under large‐scale blocking due to mouth bar and shoreface adjustment feeds wave‐dominated updrift beach ridge plains (strandplains) [ABSTRACT FROM AUTHOR]

We present new data of White Sea Coast dynamics within NE of the Gorlo Strait that were generated by satellite images, geomorphological and ground penetrating radar (GPR) profiling, aerial photography, and topographic surveys of coastal terraces and dunes. Our paleogeomorphological studies, supported by laboratory findings (diatom analysis and 14C dating), allowed us to reconstruct the morphodynamics of coastal and aeolian landforms. The obtained reconstruction enabled the evaluation of relative sea level (RSL) changes and the evolution of coastal landforms over the past ~ 3.7 cal ka BP. According to our research, sand was supplied to coastal zone and coastal dunes through scarp erosion (0.5–3.7 m/year) as well as from the shoreface, while the role of alluvial runoff is insignificant. The largest dune massifs were formed in the areas of longshore drift (from NE to SW) discharge. At the mouth of the Maida River, the barrier spit and foredune plain have been evolving from the end of the Holocene transgression (∼3.7–2.3 cal ka BP). The mean high water at this time was slightly higher (up to ∼2.5 m a.s.l.), and coastal processes were significantly more intense than current ones. Then, against a decrease in sea level and weakening sediment flows, the growth of the spit slowed. The ancient foredunes were stabilized by vegetation. Aeolian processes were activated ∼2.1 and after ∼0.8–0.7 cal ka BP. [ABSTRACT FROM AUTHOR]

We investigate whether geomorphic signatures of permafrost are embedded in planforms of river meanders, and we inquire as to how physical factors unique to permafrost environments are able to affect their dynamics. By exploiting satellite imagery, a data set of 19 freely‐meandering Arctic rivers is compared against an independent data set of 23 freely‐meandering streams flowing through temperate and tropical regions. Suitable dimensionless metrics are defined to characterize morphometric properties of meanders in terms of the spatio‐temporal distribution of curvature and channel width. Results show the absence of marked contrasts in the amplitude of bend‐curvature between the two data set. Differently, we find a permafrost signature in the channel width response, which manifests itself through larger values of the average bend‐width and by peaks of width fluctuations. Field data suggest that permafrost meanders tend to widen for increasing bend sinuosity, likely promoting a shift of their morphodynamic regime as final cutoff is approached. Plain Language Summary: One of the most striking impacts of climate warming in the Arctic region is permafrost thaw. Arctic rivers typically flow through perennially‐frozen floodplains, thus they are particularly susceptible to ground thawing. In order to understand the response of Arctic rivers to climate variability, basic knowledge about key differences with respect to non‐permafrost streams is needed. Despite recent studies which have emphasized the slower yearly movement rates distinguishing Arctic streams, we still do not understand whether permafrost‐affected rivers show distinctive features in their morphology due to specific physical mechanisms. By exploiting satellite imagery, we show that permafrost leaves a signature in the shape of meandering Arctic rivers. Specifically, their average bend‐width increases as sinuosity develops, while the amplitude of width oscillations is larger than that displayed by their non‐permafrost kin. Key Points: Permafrost is found to leave a morphological signature in the spatio‐temporal signal of channel width at the bend scalePermafrost meander bends show larger amplitude of width oscillations and widen as sinuosity increasesBend curvature as a standalone indicator does not provide evidence of any significant permafrost‐fingerprint [ABSTRACT FROM AUTHOR]

Introduction: Tidal marsh wetlands provide essential and valuable services to the wider interconnected marine and coastal environment, although the complex intertwined processes in morphological evolution remain insufficiently understood owing to synchronized data scarcity, limiting the development of numerical models and management strategies. Methods: This study investigated the hydrodynamic, biological, sediment and morphological processes on the Doulong tidal wetlands, Jiangsu, China, using a one-year field dataset that captured spatial and seasonal variations. Results and discussion: Our results indicate that biophysical interactions among multiple processes could result in some overlooked sedimentary behaviours and bio-morphological patterns in tidal marsh wetlands. Firstly, the dominance of alongshore currents caused a rapid alongshore expansion of saltmarsh patches, by which the marsh edge achieved seaward advancing, markedly different from the widely reported cross-shore expansion. Secondly, results showed that the particle size of sediment near the marsh edge coarsened when plants withered and then fined when plants grew, indicating that the seasonal variation trend of sediment grain size in saltmarshes was opposite to the trend of vegetation biomass. Thirdly, the interaction between vegetation and stranded marine debris formed banded debris zones within the saltmarsh, where debris bands could cause a biomass reduction of up to 58%, disrupting the commonlyobserved parabolic biomass-elevation relationship. Meanwhile, the seasonal variation of vegetation and hydrodynamics could alter the debris positions and hence result in the formation of multiple parallel debris bands. Overall, this study provides a synchronized dataset and elucidates specific bio-morphological relationships and processes that have thus far not been systematically documented, enhancing the comprehensive understanding of tidal marsh wetland evolution. [ABSTRACT FROM AUTHOR]

Meandering rivers are complex geomorphic systems that play an important role in the environment. They provide habitat for a variety of plants and animals, help to filter water, and reduce flooding. However, meandering rivers are also susceptible to changes in flow, sediment transport, and erosion. These changes can be caused by natural factors such as climate change and human activities such as dam construction and agriculture. Studying meandering rivers is important for understanding their dynamics and developing effective management strategies. However, traditional methods such as numerical and analytical modeling for studying meandering rivers are time-consuming and/or expensive. Machine learning algorithms can be used to overcome these challenges and provide a more efficient and comprehensive way to study meandering rivers. In this study, we used machine learning algorithms to study the migration rate of simulated meandering rivers using semi-analytical model to investigate the feasibility of employing this new method. We then used machine learning algorithms such as multi-layer perceptron, eXtreme Gradient Boost, gradient boosting regressor, and decision tree to predict the migration rate. The results show ML algorithms can be used for prediction of migration rate, which in turn can predict the planform position. [ABSTRACT FROM AUTHOR]

This research aims to investigate the morphodynamics of the Wulan River estuary in Demak Regency using the integration of multispectral remote sensing images and numerical modeling. In this study, PlanetScope for a manual-visual analysis of estuary morphodynamics and Sentinel-2 MSI Level 2A to obtain periodic total suspended solids (TSS) information for the east and west monsoon seasons. MIKE by DHI software used to develop hydrodynamic numerical modeling in order to characterize the current circulation and sediment transport model. Based on a marine cartography aspect, the obtained results illustrated that the climatological phenomenon of seasonal forcing plays a role in the development of the current circulation and indirectly influences the sediment transport. During the west season, the morphodynamics in the Wulan River estuary are much more massive and significant as compared to the east season. A projection of the deposition that results from the sediment transport is described in the bed-thickness change; this occurs in the western part of the Wulan River estuary during the east season, while the bed-thickness change occurs predominantly in the northern part during the west season (where there was previously a beach sandbar phenomenon). This was verified through multi-temporal satellite imagery that the deposition that occurs in the northern part of the Wulan River estuary during the west season is increasingly progressive and massive. [ABSTRACT FROM AUTHOR]

The protection against a storm event provided by nourishment to Costa da Caparica beaches near Lisbon, Portugal, is investigated numerically with a two-dimensional-horizontal morphodynamic model able to generate and propagate the longer infragravity waves. The beach has a groyne field and a multi-typology backshore. The nourishment of 106 m3 of sand was placed at the beach face and backshore. Pre- and post-nourishment topo-bathymetric surveys of the beach, which suffers from chronic erosion, were performed under a monitoring program. The morphodynamics of the pre- and post-nourished beach when exposed to a simulated historically damaging storm event and the post-storm morphologies were compared to evaluate the efficacy of the nourishment. Results indicate that the lower surface level of the beach face and backshore of the pre-nourished beach induces a larger erosion volume. The nourishment prevented the extreme retreat of the shoreline that occurred during the storm in the pre-nourished beach and reduced the storm-induced erosion volume by 20%, thus protecting the beach effectively against the storm. The beach backshore typology (seawall vs. dune) exerts differential influences on the sandy bottom. As a result, multi-typology backshores induce alongshore variability in cross-shore dynamics. The backshore seawalls exposed to direct wave action cause higher erosion volumes and a larger cross-shore extension of the active zone. The most vulnerable alongshore sectors of the beach were identified and related to the mechanisms responsible for the erosion phenomenon. These findings strengthen the importance of sand nourishment for the protection and sustainability of beaches, particularly those with a seawall at the backshore, where storm events cause higher erosion. [ABSTRACT FROM AUTHOR]

Proglacial forefields commonly include highly dynamic fluvial systems associated with the fundamental instability between topography, flow hydraulics and sediment transport. However, there is limited knowledge of how these systems respond to changing subglacial hydrology and sediment supply. We investigated this relationship using the first continuous field‐collected data sets for both suspended and bedload sediment export and proglacial river dynamics for an Alpine glacier forefield, the Glacier d'Otemma, Switzerland. The results show a strong sensitivity of fluvial morphodynamics to the balance between sediment transport capacity and supply. When subglacial bedload export rates exceeded fluvial transport capacity, we found bar construction leading to net forefield aggradation and surficial coarsening, especially on bar heads. This intensified braiding buffered the downstream transport of coarse sediment. When subglacial bedload export rates were lower than transport capacity, incision occurred, with reduced braiding intensity, net erosion and important amounts of bedload leaving the proglacial system. We found a net fining of surficial deposits except for very isolated coarsening patterns on bar heads. Thus, proglacial forefield morphodynamics are strongly conditioned by subglacial hydrology and sediment supply, but this conditioning is also influenced by the response of the forefield itself. Proglacial forefields have an important influence on the longitudinal connectivity of sediment flux in regions sensitive to climate change, such as recently deglaciated high mountain areas. The linkages we report between subglacial processes and river morphodynamics are critical for understanding the development of embryonic forefield ecosystems. Plain Language Summary: This study focuses on Alpine proglacial forefields, braided fluvial streams flowing in deglaciated terrains, and their geomorphic response to both sediment and water exported from retreating glaciers. This is achieved using the first continuous field‐collected data sets combining sediment flux quantifications at the glacier terminus and downstream changes of the river over time collected in the Glacier d'Otemma forefield (Switzerland). Results show that the fluvial landscape in recently deglaciated terrains changes rapidly, influenced by the balance between the amount of sediment being transported from under the glacier and the river's capacity to carry it. When the released amount of sediment matches the river's capacity, the deposition of coarser material dominates and the stream becomes more complex with increasing braiding intensity. However, when the river carries more sediment than supplied by the glacier, flow becomes more confined into fewer channels, promoting the erosion of previously deposited material, particularly for the coarser sediment fractions. The study emphasizes how both the river configuration and the landscape near a melting glacier depend on whether the river itself can transport the quantities of sediment delivered by the glacier. This balance can affect the downstream sediment flux from glaciered catchments and the development of ecosystems following climate change‐induced glacier retreat. Key Points: First study combining continuous subglacial sediment export rates and proglacial forefield geomorphic change at the melt season scaleStrong sensitivity of proglacial forefield morphodynamics to subglacial bedload export rates and fluvial transport capacityBar construction processes filter the downstream transport of bedload particles buffering the longitudinal connectivity of sediment flux [ABSTRACT FROM AUTHOR]

This study aims to investigate the hydrodynamic-morphological interactions on a microtidal intermediate-dissipative beach under low to moderate wave energy conditions using field measurements during two climatic seasons. The separate contributions of currents, sea-swell waves, and infragravity waves to high- and low-frequency sediment fluxes were analyzed. The infragravity wave energy was more relevant near the swash zone than in other areas. Although the currents are the primary suspended sediment transport mechanism, the results suggest that the waves are an important driver of sediment suspension from the seabed. The results indicate that Sea-Swell (SS) waves and cross-shore currents are the prevailing hydrodynamic factors in nearshore sediment transport, and the cross-shore suspended sediment transport rates are higher than those in alongshore transport. The submerged bar intensified during the wet season (1–4 November 2018) when the wave height intensities were lower, contrary to the dry season (24–25 March 2018). Significant accretion nearshore was identified (in the subaerial beach) during the wet season when the suspended sediments were greater, the SS-wave heights nearshore were lower, and sediment flux was directed onshore. A notorious erosion was distinguished during the dry season. The most representative volume changes occurred during the dry season (with high erosion), which is attributed to the high SS-wave energy. [ABSTRACT FROM AUTHOR]

This study examines the long-term impact of water management and navigation modifications on the hydromorphology of the lower Elbe River in Czechia. The research focuses on gravel-sand bars, which are remnants of the river's natural morphology. The analysis revealed a significant shift in the hydromorphological quality of the river, evaluated using a morphological quality index and historical data. The study analysed morphological and grain-size parameters of selected gravel-sand bars, as well as daily flow data. The results show a significant reduction in channel width and maximum average daily flows, leading to lower disturbance frequencies of the bars. The analysis suggests that close-to-natural processes affect the development of the bars but are influenced by artificial modifications. The findings indicate the need for restoration measures, which are discussed in this paper. [ABSTRACT FROM AUTHOR]

Plants in streams act as physical ecosystem engineers, both influencing and responding to hydrogeomorphic processes such as fine sediment retention. Instream vegetation may also influence propagule dispersal and retention, shaping plant community dynamics. These plant‐sediment interactions may result in synergistic feedback promoting hydrogeomorphic complexity and biogeomorphic succession. However, the role of aquatic plants (submerged or mostly submerged) in trapping propagules, fine sediment and organic matter in degraded lowland streams is uncertain. In this study, we sampled sediment (≤5 cm depth) from eight streams ranging in land use from rural to urban, including within patches of aquatic vegetation and unvegetated locations. We conducted a propagule bank trial to identify the abundance and diversity of propagules and analysed the particle size and organic matter composition of the samples. A total of 8,365 seedlings from 113 plant species were recorded with a range of hydrological tolerances. Aquatic plants retained 56% more propagules and 32% more species, and marginal vegetation retained 250% more propagules and 48% more species, than open channel locations (the least retentive location). Similar patterns were found for fine sediment and organic matter retention. Propagule bank communities were different across land‐use types but not sampling locations. The trapping effect of aquatic vegetation diminished as catchments became more urbanised. This study provides evidence that aquatic plants retain more propagules and species, and fine sediment and organic matter than vegetation‐free channel locations. Improving aquatic vegetation in streams may be an important early step in restoring hydrogeomorphic complexity and propagule retention, and the facilitation of biogeomorphic succession in degraded streams. Unfortunately, heavily urbanised streams with flashy flow regimes are unlikely to benefit from this function unless catchment‐scale hydrology is addressed. [ABSTRACT FROM AUTHOR]

The river morphology of a braided‐type river is rather complex. High sediment transport rates and frequently changing discharges are the cause of dynamic planform evolution. Over the past few decades, scientific attention has been directed toward understanding the coexistence of alternating bars and the consequent emergence of confluences and divergences, all of which interact intricately with the process of bank erosion. It is still rather challenging to estimate or predict the total sediment transport rate in this type of river, especially by considering various hydrologic data and climate effects. This study is focused on the reach of the Devoll River in Albania, located upstream of the Banja dam. Understanding the morphodynamics of this river reach holds significance due to the expanding delta upstream of the dam reservoir. The objectives of the two‐dimensional depth‐averaged approach of the present study are to investigate the temporal variation of braided intensity of Devoll River and the effect of using a discharge hydrograph from hydrologic data compared to the regulated one from the upstream dam on the morphodynamics and sediment transport of the river. After evaluating various parameters such as 11 different sediment transport functions, the best results were reached for a cell size of 5 × 5 m2, Manning roughness coefficient of 0.03, Meyer‐Peter and Müller's sediment function, Hayashi et al. (1980) hiding function, and Van Rijn bed roughness predictor in this study. In addition, the results of comparing satellite images and modeling the river from 2019 to 2023 show that the braided index decreased, and this can be due to the fact that the real scenario of the river has a regulated discharge compared to the non‐regulated discharge from hydrologic data, in the mentioned period. [ABSTRACT FROM AUTHOR]

Coastal erosion poses significant challenges to shoreline management, exacerbated by rising sea levels and changing climate patterns. This study investigates the influence of gap spacing between semicircular coastal defence structures on shoreline dynamics during storm events. The innovative design of these structures aims to induce a drift reversal of prevalent sediment transport while avoiding interruption of alongshore sediment drift, thus protecting the beach. Three different gap spacings, ranging from 152 m to 304 m, were analysed using the XBeach numerical model, focusing on storm morphodynamic behaviour. Methodologically, hydrodynamic and morphodynamic analyses were conducted to understand variations in significant wave heights adjacent to the structures, in accretion and erosion volumes, and changes in bed level under storm conditions. The study aims to elucidate the complex interaction between engineered coastal protection solutions and natural coastal processes, providing practical insights for coastal management practices. Results indicate that installing semicircular coastal defence structures influences sediment dynamics during storm events, effectively protecting stretches of the coast at risk. Optimal gap spacing between structures is crucial to mitigating coastal erosion and enhancing sediment accumulation, offering a sustainable shoreline protection approach. The findings underscore the importance of balanced location selection to optimize protection benefits while minimizing adverse morphological effects. Overall, this research contributes to advancing knowledge of hydro-morphological phenomena essential for effective coastal engineering and informs the design and implementation of more sustainable coastal protection strategies in the face of increasing coastal erosion and sea level rise challenges. [ABSTRACT FROM AUTHOR]

Context: Salt marsh landscapes at the land-sea interfaces exhibit contrasting spatiotemporal dynamics, resulting from varying physical constraints that limit new marsh establishment. The expansion of salt marsh landscapes towards the sea or their retreat towards the land is determined by patch-level changes, relying on the balance of power between the intrinsic biota traits and external physical disturbances. Objectives: Examine how marsh dynamics respond to physical constraints, and clarify the pathway from coupled physical processes involving hydrodynamic forces, sediment transport, and morphological changes to rapid patch evolution and landscape changes. Methods: We defined and distinguished four types of marsh changes based on patch proximities from five-month drone images in two typical marsh pioneer zones of the Yangtze Estuary, China: outlying expansion, edge expansion, infilling expansion, and retreat. Hydrodynamics and sediment transport were synchronously measured and compared near the two marsh edges, and morphological changes were generated by drone-derived digital elevation models (DEMs). Results: We identified distinct seasonal patterns of net marsh expansion at the accretion-prone site, that is: Net marsh expansion started from the outlying expansion in spring, followed by edge expansion in summer and infilling expansion in autumn. However, at the erosion-prone site that experienced high bed shear stress, low sediment availability and high seaward sediment transport, we only observed limited infilling and edge expansion in spring. This suggests that the potential for long-distance patch formation beyond the initial marsh edges is diminished in areas subjected to intensive physical disturbances. Conclusions: Patch evolution dynamics in response to site-specific physical constraints drive state differentiation of salt marsh landscape changes. Consequently, the heterogeneous evolution in salt marsh landscapes should be taken into account in restoration practice. [ABSTRACT FROM AUTHOR]

We present a method for learning spectrally descriptive edge weights for graphs. We generalize a previously known distance measure on graphs (graph diffusion distance [GDD]), thereby allowing it to be tuned to minimize an arbitrary loss function. Because all steps involved in calculating this modified GDD are differentiable, we demonstrate that it is possible for a small neural network model to learn edge weights which minimize loss. We apply this method to discriminate between graphs constructed from shoot apical meristem images of two genotypes of Arabidopsis thaliana specimens: wild-type and trm678 triple mutants with cell division phenotype. Training edge weights and kernel parameters with contrastive loss produce a learned distance metric with large margins between these graph categories. We demonstrate this by showing improved performance of a simple k -nearest-neighbour classifier on the learned distance matrix. We also demonstrate a further application of this method to biological image analysis. Once trained, we use our model to compute the distance between the biological graphs and a set of graphs output by a cell division simulator. Comparing simulated cell division graphs to biological ones allows us to identify simulation parameter regimes which characterize mutant versus wild-type Arabidopsis cells. We find that trm678 mutant cells are characterized by increased randomness of division planes and decreased ability to avoid previous vertices between cell walls.

Physics-based numerical models often depend on several parameters to close. Some of them can be expressed using established theoretical or empirical closure formulations. However, some others aggregate complex physical processes and are hence left as tuneable parameters, and can only be calibrated by trial and error. Yet, calibration data are not always available to do so, which prevents these models from being applied to wide ranges of laboratory or river flows. We hence propose a machine learning-based methodology to close any group of unclosed and correlated parameters, applied here to a two-phase/two-layer (2P2L) morphodynamical model. The methodology combines a numerical experiment with a known theoretical solution and machine learning. It is applied to the considered model to close two friction parameters for which generalizable and vastly acknowledged closure formulations lack in the literature. The resulting hybrid model, combining the original 2P2L model and the closure models, is tested against two laboratory dam break test cases. Despite excessive smoothness and underestimation of the concentration in sediment, the hybrid model performed similarly to other models from the literature requiring trial and error calibration and showed high stability and accuracy regarding the estimation of the water-sediment mixture's inertia. HIGHLIGHTS A methodology to close tuneable parameters applicable to many morphodynamical models.; Methodology based on machine learning and self-generated data from a numerical experiment with theoretical solution.; Presentation of a two-phase/two-layer model for unsteady flows highly laden with sediment, used as a proof of concept of the methodology.; New model's performance is similar to evenly complex models requiring trial and error to calibrate tuneable parameters.;

Many emergent, non-fundamental models of complex systems can be described naturally by the temporal evolution of spatial structures with some nontrivial discretized topology, such as a graph with suitable parameter vectors labeling its vertices. For example, the cytoskeleton of a single cell, such as the cortical microtubule network in a plant cell or the actin filaments in a synapse, comprises many interconnected polymers whose topology is naturally graph-like and dynamic. The same can be said for cells connected dynamically in a developing tissue. There is a mathematical framework suitable for expressing such emergent dynamics, stochastic parameterized graph grammars, composed of a collection of the graph- and parameter-altering rules, each of which has a time-evolution operator that suitably moves probability. These rule-level operators form an operator algebra, much like particle creation/annihilation operators or Lie group generators. Here, we present an explicit and constructive calculation, in terms of elementary basis operators and standard component notation, of what turns out to be a general combinatorial expression for the operator algebra that reduces products and, therefore, commutators of graph grammar rule operators to equivalent integer-weighted sums of such operators. We show how these results extend to dynamical graph grammars, which include rules that bear local differential equation dynamics for some continuous-valued parameters. Commutators of such time-evolution operators have analytic uses, including deriving efficient simulation algorithms and approximations and estimating their errors. The resulting formalism is complementary to spatial models in the form of partial differential equations or stochastic reaction-diffusion processes. We discuss the potential application of this framework to the remodeling dynamics of the microtubule cytoskeleton in cortical microtubule networks relevant to plant development and of the actin cytoskeleton in, for example, a growing or shrinking synaptic spine head. Both cytoskeletal systems underlie biological morphodynamics.

Numerical experiments have been carried out to model hydrodynamic and morphodynamic processes to explain the nature of the spatial distribution of Zostera marina (eelgrass) in the inner bays of Posyet Bay. Hydrodynamic modeling has been performed using the Delft3D flow model. The Simulating WAves Near shore (SWAN) spectral wave model has been used to simulate wind wave parameters (direction of propagation, wave length and height, and near-bottom orbital velocities). The restructuring of the bottom topography under the influence of wind waves and the hydrodynamic influence of tidal and wind currents has been calculated with the Delft3D software package. The results of numerical experiments showed that the dynamics of the coastal bottom topography is determined by the nature of sediment motion in the coastal zone under the combined influence of waves and currents. A comparison of the modeling results with data on the distribution of Zostera showed a high correlation with model simulations of erosion and accumulation in the coastal zone. [ABSTRACT FROM AUTHOR]

Introduction: Breast tumors often display an astonishing degree of spatial and temporal heterogeneity, which are associated with cancer progression, drug resistance, and relapse. Triple-negative breast cancer (TNBC) is a particularly aggressive and heterogeneous subtype for which targeted therapies are scarce. Consequently, patients with TNBC have a poorer overall prognosis compared to other breast cancer patients. Within heterogeneous tumors, individual clonal subpopulations may exhibit differences in their rates of growth and degrees of invasiveness. We hypothesized that such phenotypic heterogeneity at the single-cell level may accelerate tumor progression by enhancing the overall growth and invasion of the entire tumor. Methods: To test this hypothesis, we isolated and characterized clonal subpopulations with distinct morphologies and biomarker expression from the inherently heterogeneous 4T1 mouse mammary carcinoma cell line. We then leveraged a 3D microfluidic tumor model to reverse-engineer intratumoral heterogeneity and thus investigate how interactions between phenotypically distinct subpopulations affect tumor growth and invasion. Results: We found that the growth and invasion of multiclonal tumors were largely dictated by the presence of cells with epithelial and mesenchymal traits, respectively. The latter accelerated overall tumor invasion, even when these cells comprised less than 1% of the initial population. Consistently, tumor progression was delayed by selectively targeting the mesenchymal subpopulation. Discussion: This work reveals that highly invasive cells can dominate tumor phenotype and that specifically targeting these cells can slow the progression of heterogeneous tumors, which may help inform therapeutic approaches. [ABSTRACT FROM AUTHOR]

ABSTRACT On January 2022, the Carmo River (a tributary of the Doce River) was affected by an extreme hydrological event, with 50-yr return interval. This event was 50% higher than that associated to one of the largest tailing dam failures ever reported that took place in the Gualaxo do Norte River. This delivered to Doce River, through the Carmo River, in a Y-shaped confluence, the contaminated tailing slurry. In order to understand the role of tributaries in the recovery of the Doce River, 2D hydrodynamic and 2D sediment transport models were applied at the confluence of the Carmo River with the Piranga River. Our results, based on hydraulic modeling, remote sensing, and in-situ measurements, indicated that significant amounts of sediments were trapped on the riverbanks and stone banks, making this confluence an important site for the retention of contaminated sediments, influencing sediment budgets and downstream water quality. Therefore, this confluence deserves special attention from water engineering in order to prevent the sediments retained in this area from being transported downstream during extreme events in the coming years. These results can contribute to decision-making, to identify reaches with greater susceptibility to erosion and sediment deposition and to plan the restoration of these rivers.

The protection against a storm event provided by nourishment to Costa da Caparica beaches near Lisbon, Portugal, is investigated numerically with a two-dimensional-horizontal morphodynamic model able to generate and propagate the longer infragravity waves. The beach has a groyne field and a multi-typology backshore. The nourishment of 106 m3 of sand was placed at the beach face and backshore. Pre- and post-nourishment topo-bathymetric surveys of the beach, which suffers from chronic erosion, were performed under a monitoring program. The morphodynamics of the pre- and post-nourished beach when exposed to a simulated historically damaging storm event and the post-storm morphologies were compared to evaluate the efficacy of the nourishment. Results indicate that the lower surface level of the beach face and backshore of the pre-nourished beach induces a larger erosion volume. The nourishment prevented the extreme retreat of the shoreline that occurred during the storm in the pre-nourished beach and reduced the storm-induced erosion volume by 20%, thus protecting the beach effectively against the storm. The beach backshore typology (seawall vs. dune) exerts differential influences on the sandy bottom. As a result, multi-typology backshores induce alongshore variability in cross-shore dynamics. The backshore seawalls exposed to direct wave action cause higher erosion volumes and a larger cross-shore extension of the active zone. The most vulnerable alongshore sectors of the beach were identified and related to the mechanisms responsible for the erosion phenomenon. These findings strengthen the importance of sand nourishment for the protection and sustainability of beaches, particularly those with a seawall at the backshore, where storm events cause higher erosion.

Hidden and perilous rip currents are one of the primary factors leading to drownings of beach swimmers. By identifying the coastal areas with the highest likelihood of generating rip currents, it becomes possible to prevent fatalities and mitigate economic losses associated with these hazardous currents. Rip currents are characterized as streams of water moving towards the open sea, forming within the area where waves break, due to variations in wave-induced radiation stresses and pressure along the coastline. This study utilized nine different Machine Learning (ML) models, including M5 Model Tree (MT), Multivariate Adaptive Regression Spline (MARS), Gene Expression Programming (GEP), Evolutionary Polynomial Regression (EPR), Random Forest (RF), Support Vector Machine (SVM), Extreme Gradient Boosting (XGBoost), Adaptive Boosting (AdaBoost), and Stacked ML models, to estimate the Relative Tide Range (RTR) values for 50 southern beaches in China. Through this approach, we gathered a reliable dataset from prior research conducted on the southern coast of China. In this study, two parameters, namely dimensionless fall velocity parameter (Ω) and tide range (TR) are used to predict the vulnerability of rip current event. The results of the AI models were assessed by various statistical analyses (Correlation of Coefficient [R], Root Mean Square Error [RMSE], violin diagram, heatmap, and taylor diagram) for training and testing stages. Accordingly, the MARS model exhibited superior performance compared to other AI models in accurately predicting the RTR value. The outcomes substantiated the significant effectiveness and capability in estimating the RTR with high accuracy. Southern China coasts have relative high risk level of rip current, necessitating the attention and strategic management of this dangerous current by the beach managers.

Ramakrishnan, B.; Gavali, M., and Jeyaraj, S., 2024. Comprehensive analysis of siltation behavior in the navigation channel of Deendayal Port (India): Field observations, numerical modeling, and engineering solutions. Journal of Coastal Research, 40(1), 138–149. Charlotte (North Carolina), ISSN 0749-0208. Deendayal Port, formerly Kandla Port, is one of India's busiest ports, with a deep inland navigation channel that facilitates easy trade but has been plagued by siltation issues for decades because of the hydromorphodynamic characteristics of this region. This study aims to understand the siltation behavior in the port's navigation channel through field observations and numerical modeling and to suggest suitable engineering solutions. The in situ observations of tidal levels, currents, suspended sediment concentration, and multitemporal bathymetry datasets are used to calibrate a numerical model, developed using Delft3D, to estimate the hydromorphodynamics. As an engineering solution, porous barriers of different lengths and layouts are introduced in the numerical model to minimize siltation along the sides of the channel. It is observed that placing three porous barriers has reduced the siltation by 46 to 56% in the main navigation channel leading to the port. In practice, these porous barriers could be a silt curtain–type structure, which has successfully been adopted in several ports across the globe as an effective siltation stopper. [ABSTRACT FROM AUTHOR]

Aquifers on small islands are at risk of salinization due to low elevations and limited adaptive capacity, and present risks will be exacerbated by climate change. Most studies addressing small‐island saltwater intrusion (SWI) have focused on homogeneous sandy islands and one or two hydraulic disturbances. We herein investigate SWI dynamics in a layered, confined island aquifer in response to multiple environmental perturbations related to climate change, with two considered in tandem. Our field and modeling work is based on an island aquifer that provides the drinking water supply for an Indigenous community in Atlantic Canada. Observation well data and electrical resistivity profiles were used to calibrate a numerical model (HydroGeoSphere) of coupled groundwater flow and salt transport. The calibrated model was used to simulate the impacts of climate change including sea‐level rise (SLR), storm surge overtopping, changing aquifer recharge, and erosion. Simulated aquifer conditions were resilient to surges because the confining layer prevented deeper saltwater leaching. However, reduced recharge and erosion resulted in saltwater wedge migration of 170 and 110 m, respectively when considered individually, and up to 295 m (i.e., into the wellfield) when considered together. Despite the confining conditions, SLR resulted in wedge migration up to 55 m as the confining pressures were not sufficient to resist wedge movement. This is the first study to harness an integrated, surface‐subsurface hydrologic model to assess effects of coastal erosion and other hydroclimatic stressors on island aquifers, highlighting that climate change can drive extensive salinization of critical groundwater resources. Plain Language Summary: Due to their limited resources and adaptive capacity, small islands are highly vulnerable to climate change impacts, including saltwater intrusion. Freshwater needs on small islands are often sourced from small aquifers that are in delicate balance between conditions in the ocean, atmosphere, and land. In this study, we investigate the movement of saltwater into the freshwater aquifer of a small island that provides drinking water resources for an Indigenous First Nation. We consider climatic changes in the ocean (sea‐level rise (SLR), storm surges, and related coastal erosion) and atmosphere (changes to net precipitation) and associated impacts to the island's fresh groundwater resources. We use field data paired with a mathematical model and demonstrate that the pressurized conditions of the layered island aquifer make it more resilient to SLR than unconfined aquifers in sandy islands are. However, the aquifer's freshwater volume is susceptible to coastal erosion and reduced precipitation, particularly when these happen at the same time. Results point to coastal erosion as a potential widespread driver of freshwater loss along eroding portions of the global coastline. Key Points: A surface‐subsurface numerical model is used to investigate climate change impacts on island groundwater resources used for water supplyThe confined aquifer is resilient to storm surges which only salinize the unpumped surficial aquifer before being flushedCoastal erosion and recharge reductions result in the most saltwater intrusion and can work in tandem to threaten future water supply [ABSTRACT FROM AUTHOR]

The shallow-water and multilayer hydrostatic models have been commonly used to analyze the problems of a sediment-laden, plane open-channel flow. The models are adequate to solve a quasi-hydrostatic flow problem, but their accuracy deteriorates as the e ects of the vertical acceleration gain in significance. Herein, a higher-order numerical model for treating the problems of unsteady, plane open-channel flow over a movable bed is proposed. In this model, the flow hydrodynamics is governed by the depth-averaged Boussinesq-type equations, and the bed morphodynamics is determined by an Exner-type equation and additional equations describing the non-equilibrium transports of suspended load and bed load. A hybrid finite-volume and finite-di erence scheme was used to discretize and solve the governing equations, yielding solutions that are in satisfactory agreement with the experimental data. Overall, the results of the proposed model for the temporal free-surface profile and bed evolution were fairly adequate. For the two particular cases considered, however, the quality of its results was moderately a ected by the e ects of the three-dimensional characteristics of the dam-break flow and the sliding of the dike body due to sub-surface flow. The results of this investigation highlight the importance of including a higher-order Boussinesq-type correction for refining sediment transport computations. [ABSTRACT FROM AUTHOR]

The analysis of morphological changes in dynamic environments plays a crucial role in understanding their evolution. An example can be found on Algodoal/Maiandeua Island, on the Amazon coast. It has several ecosystems subject to rapid morpho-sedimentary changes due to river and sea flows in the Amazon Basin, mainly on its coastline, which is subject to erosion and sediment deposition processes. In addition, the island is experiencing an expansion of human occupation due to its tourism potential. This article aims to demonstrate how the coastline has evolved over 35 years in seven areas of the island. For this analysis, Landsat satellite images were captured in 1988, 2002, 2016, and 2023, processed using ArcGIS 10.5 software and the Digital Shoreline Analysis System extension v.5.1. The results indicated that the island presents different coastal processes. In the western sector, the island remains stable, with no erosion processes. In the northern sector, the coastline is in the process of accretion, although it also shows some erosional tendencies. In the east and southeast sectors, the island exhibits both accretional and erosional areas. In general, it was observed that coastal stability and accretion rates were more frequent, suggesting a reduced impact of coastal erosion. The limited human occupation along the island's coastline also contributes to a reduced risk of erosion. However, the island continues to be greatly influenced by oceanographic phenomena, especially coastal currents, and tides, which make it vulnerable to possible negative impacts in the future. [ABSTRACT FROM AUTHOR]

A morphodynamic approach to coastal evolution involves recognition of internal thresholds, feedbacks and boundary conditions and should underpin coastal management. The Holocene evolution of the Bega River estuary and Tathra Beach coastal barrier was examined integrating existing sediment cores and radiocarbon dating, airborne terrestrial and marine Lidar and OSL dating. Sediment coring reveals the Bega River estuary began infilling with fluvial sand once sea levels stabilised at or near their present elevation. Radiocarbon dating suggests a prograding fluvial delta reached the coast approximately 4000–2250 years BP. Barrier deposition commenced ~3200 years ago coinciding with the arrival of fluvial sand at the coast. Shoreline progradation of the Tathra barrier occurred at 0.15 m/year from ~3200 years to present forming a sequence of ~17 foredune ridges which were each active for an average of ~190 years. In the past ~500 years, a sand spit has restricted the entrance of the Bega River estuary to the northern end of the embayment. The infill of the Bega River estuary over the Holocene represents an internal morphodynamic threshold or tipping point, which then enabled coastal barrier deposition as fluvial sand reached the coast. The coastal system approaches another threshold as the Tathra embayment infills, and sediment may be transported northward out of the embayment. At Tathra Beach, the positive sediment budget which resulted in barrier progradation is approximately 0.55 m3/m/year. This signal is masked on the yearly to decadal scale by fluctuations in beach volume an order of magnitude greater (5–20 m3/m/year depending on the timeframe examined). Thus longer-term datasets of beach change or reconstructions from the geological record are needed to underpin management decisions which will impact shorelines decades or centuries into the future. [ABSTRACT FROM AUTHOR]

Due to the significant mismatch in timescales associated with morphological and hydrodynamic processes in coastal environments, modellers typically resort to various techniques for speeding up the bed evolution in morphodynamic simulations. In this paper, we propose a novel method that differs from existing ones in several aspects. For example, unlike previous approaches that apply a global measure (such as a constant acceleration factor that uniformly amplifies the bed evolution everywhere), we track and extrapolate local trends in morphological changes. The present algorithm requires the setting of four different parameters, values for which we set through an extensive calibration process. The proposed method is compared against the simple acceleration technique built into the popular software XBeach (wherein it is called morfac) for eight different beach profiles (including linear, Dean, and measured profiles). While the accuracy of both methods is generally similar, the proposed algorithm consistently shows a greater reduction in computational time relative to morfac, with our algorithm-accelerated simulations being on average 2.6 times faster than morfac. In light of these results, and considering the algorithm's potential for easy generalisation to address arbitrary coastal morphodynamic problems, we believe that this method represents an important addition to the toolbox available to the community interested in coastal modelling. [ABSTRACT FROM AUTHOR]

We use two‐dimensional physics‐based numerical modeling to study multi‐decadal evolution of vegetation and morphology under different flow regimes in real‐world gravel‐bed braided rivers. To assess model realism, we focus on two rivers in Canterbury (New Zealand) that, despite having been subjected to the introduction of similar invasive vegetation species in the last ∼100 years, show very different trajectories of vegetation presence due to their different flow regimes: the Lower Waitaki River and the Waimakariri River. The former, featuring a naturally damped flow regime—and having experienced further artificial flow damping due to hydropower generation from the 1930s, experienced vegetation encroachment; while the latter, featuring a flashy flow regime, retains an unvegetated braided planform. We propose an innovative calibration and validation procedure to determine an optimal setup of vegetation parameters that allows the model to robustly reproduce the trajectories of both rivers, thereby proving that the model responds sensibly to different hydrological conditions. Then, we isolate the impact of hydropower‐related flow regime modifications on vegetation encroachment in the Lower Waitaki by running the calibrated model with a natural flow regime that does not feature the effect of hydropower generation, and find that vegetation encroachment would have happened even without flow alteration, albeit to a milder degree. Finally, we apply to simulation results a conceptual framework based on a synthetic parameter that compares the relative strength of hydrological and vegetation controls, and discuss the use of this parameter as a predictor of vegetation presence across flow regimes. Plain Language Summary: We study how numerical models can predict the amount of vegetation that establishes on the gravelly bed of wide rivers. We focus on two rivers in New Zealand: the Waimakariri River, having frequent and intense floods, and the Lower Waitaki River, with less frequent and intense floods. This milder character of the Waitaki relates to the presence in the river catchment of three natural lakes that store flood flows and release them slowly, and to the additional storage of artificial hydropower reservoirs. Both rivers have been exposed to invasive vegetation that tends to spread on their beds; however, vegetation spread was significantly more pronounced in the Waitaki than in the Waimakariri. First, we find the parameter values that allow the model to reproduce the vegetation changes seen in both rivers. Then, we simulate the vegetation changes that would have happened in the Waitaki had the hydropower reservoirs not been built, finding there would still have been significant vegetation spread. Finally, we interpret the intensity of vegetation spread as depending on the frequency of floods and on the speed of vegetation growth: a higher vegetation presence is found if vegetation grows faster and if the floods are more spaced in time. Key Points: Calibration and validation on two rivers with same vegetation species but different hydrology ensures model's sensible response and realismNumerical modeling allows quantification of the impact of a hydropower scheme on vegetation encroachment in a braided riverThe ratio between inter‐flood period duration and vegetation growth timescale is a key control and predictor of vegetation presence [ABSTRACT FROM AUTHOR]

Alpine glaciers are rapidly retreating due to global warming and this has been associated with enhanced supply of subglacially derived sediment to downstream environments. We present the first high frequency quantitative record on how the signal of sediment exported from an Alpine glacier is filtered by its proglacial forefield. The data, covering two climatically distinct glacier melt seasons, show that the signal of subglacial bedload export is strongly filtered over short distances, unlike suspended load whose signal is less impacted. The reason is related to the interplay of short particle advection lengths with strong morphodynamic forcing. The subglacial sediment export signal is thus rapidly replaced by one combining (a) the local forcing by stream hydraulics and (b) the reworking of the proglacial braid plain itself. These findings have implications for estimating subglacial erosion rates, natural hazard mitigation, sediment management for hydropower plants and ecological succession related to rapid glacier retreat. Plain Language Summary: Alpine glaciers have been retreating at increasing rates since the early 20th century due to the current climate warming. As a consequence, new, powerful and rapidly changing rivers have developed in the newly emerged terrain in front of shrinking glaciers (i.e., proglacial forefields). These environments are known to be among the most rapidly changing landscapes on Earth. In this study we present the first combined high frequency quantitative data on sediment export from an Alpine glacier for two melt seasons with very different climatic conditions. Results show that the low potential transport distances of particles traveling on the river bed together with the continuously changing shape of these streams, rapidly modify the glacier‐dictated export signal (i.e., subglacial sediment evacuation rates in time). For sediment transported in suspension in the river, that loss of information is less evident. These findings are important for the understanding of how much, when, and which kind of sediment are delivered to the populated places downstream in the valleys, in order to mitigate natural hazards, but also for sediment management in hydropower plants and ecological succession in the context of rapid glacier retreat. The results are also key to improving estimation of glacial erosion rates. Key Points: Seismically inferred sediment transport anatomy reveals strong filtering of subglacial bedload export signal due to proglacial processesFiltering operates at a sub‐daily scale, and is due to the short advection lengths of bedload particles in the proglacial forefieldProglacial filtering is a key factor affecting (pro‐)glacial sediment transport dynamics, sediment connectivity and ecological succession [ABSTRACT FROM AUTHOR]

The expected increase in rates of sea level rise during the 21st century and beyond may cause barrier islands to drown. Barrier drowning occurs due to a sediment imbalance induced by sea level rise, causing inlets to open and expand. It is still unclear how fast barrier islands can drown. To gain insight into the morphodynamics of barrier systems subject to sea level rise, we here present results obtained with a novel barrier island exploratory model, BarrieR Inlet Environment‐Drowning, that considers inlet expansion beyond equilibrium size. We quantify how much of a barrier island chain is drowned by calculating the fraction of its length that is below mean sea level due to sea level rise. Results show that barrier drowning is mostly sensitive to the wave height and the rate of sea level rise. In the model, it takes 100s of years for barrier islands to start drowning in response to high rates of sea level rise (more than 5 mm/yr, for a typical coastal environment). This lag in barrier response is caused by a gradual decrease in the sand volume of the barrier. Higher rates of sea level rise cause earlier and more severe barrier drowning. Modeled barrier systems that face higher waves undergo more frequent inlet closures that lower the rate of drowning, but they also have a deeper shoreface that increases the rate of drowning. In model simulations, the latter process dominates over the former when sea level rise rates exceed 5 mm/yr. Model results fairly agree with available field data. Plain Language Summary: In extreme sea level rise scenarios (like those predicted during the 21st century and beyond) barrier islands may drown. Barrier drowning occurs due to a lack of sediment induced by sea level rise, which causes submergence of (parts of) the barrier chain. It remains difficult to predict when and under which conditions drowning may occur. In this study we investigated the dynamics of drowning barrier islands with an exploratory numerical model. A key finding from our model is that high rates of sea level rise (higher than 5 mm/yr), but also high waves (higher than 1.5 m) result in barrier drowning. However, even under model simulations with high rates of sea level rise, it takes a long time for the sand in the barrier island to erode. Barrier drowning and disappearance therefore might take 100s of years. The model results are consistent with available field data, but more observations are needed to achieve a full model verification. Key Points: Idealized morphological model simulations show that tidal inlets expand until barrier islands disappear under rapid sea level riseModeled barrier drowning lags sea level rise acceleration by 100s of yearsLag in modeled barrier drowning is explained by a decrease in the sand volume of the barrier [ABSTRACT FROM AUTHOR]