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Vegetation-induced sedimentary structures (VISS) are bed features resulting from flow-vegetation feedback and turbulence induced by vegetation at riparian sites. Generally, these sedimentary structures commence at the individual plant level, but sediment accumulation over time may lead to the formation of fluvial islands. Additionally, riparian vegetation exposed to current may provoke local scouring. However, little research has been done on how the permeability of plants affects flow fields and sedimentary processes. Therefore, the main aim of the current study is to experimentally investigate patterns of local scour and deposition around artificial obstacles with six different levels of porosity, using a systematically designed flume experiment. Two experimental setups were implemented, with sediment transport occurring either as bed load or in suspension. Porosity, as a measure of the volume of porous space to bulk volume, was determined using optical porosity which was estimated from digital photographs. Furthermore, VISS of individual P. nigra shrubs were investigated at different seasonal stages (leafless and full foliage) at the Loire River, France, for comparison. Results show that increasing porosity caused a reduction in sediment deposition from suspension and locally scoured bed load sediment. A threshold value for optical porosity was determined, at which point a prolonged area of flow calm develops behind the barrier, promoting the accumulation of suspended sediment and suppressing local scour caused by bed load transport. An empirical model is presented, which assesses sediment erosion and deposition volumes at porous obstructions, considering (a) the flow-exposed surface area, (b) the obstruction's optical porosity, and (c) the intensity of the incoming flow. On the field scale, local scour holes were identified at P. nigra shrubs where flood-caused debris obstructions were stuck at their front, lowering the obstruction's porosity and encouraging local scour processes. [ABSTRACT FROM AUTHOR]

• The coupled 2D mophodynamic model considers effects of sediment concentration and bed deformation in the governing equations. • Unstructured meshes better conform with the irregular geometry of the natural rivers. • Channel adjustments play a significant role in sediment transport of alluvial rivers during a flood event. It is difficult to predict the detailed morphodynamic processes induced by heavily sediment-laden floods in alluvial rives, due to the complexity in topography and the significant channel evolution rates, especially in a braided reach of the Lower Yellow River (LYR). A two-dimensional morphodynamic model using a coupled solution approach was firstly developed, with the effects of sediment concentration and bed deformation being directly considered in the hydrodynamic governing equations. The finite volume method with the HLL-MUSCL scheme was adopted in the numerical solution, which can obtain second-order accuracy in space and time. In addition, unstructured meshes were used to accommodate the irregular boundaries. The proposed model was validated using measurements in the braided reach of the LYR during the flood events of 2020 and 2004, with general agreement obtained between the calculated and measured hydrographs of flow and sediment concentration. The highest accuracy was achieved in the simulation of discharge, with a Nash-Sutcliffe efficiency coefficient (NSE) of 0.92. The simulation accuracy in sediment concentration was improved by the coupled approach, with the relative error of the calculated peak value decreasing from 17 % to 9 %. In addition, transport characteristics of graded suspended sediments were well simulated, with the fine fraction being transported downstream and the medium fraction depositing in the study reach. Influences of channel adjustments on the sediment transport processes were investigated during a flood event. The results demonstrated that the incised channel in 2020 was characterized by a larger water depth and smaller velocity, as compared with the shallow channel in 2004. Consequently, the peak discharge decreased and the flood propagation time was extended under the 2020 topography, associated with the lower sediment discharge at the outlet due to the reduced sediment transport capacity. [ABSTRACT FROM AUTHOR]

Sediment control in watersheds requires information about soil erosion and sediment yield hotspot areas. Sediment connectivity is an emerging concept contributing to this field and structural sediment connectivity is a concept derived from sediment connectivity. Determining structural sediment connectivity in a watershed can yield a comprehensive image of sediment management possibilities applicable at the watershed scale. However, in most studies, the validity of extracted sediment connectivity maps has not been evaluated holistically. The current study is, therefore, designed to determine a valid structural sediment connectivity map and to use it to validate findings of sediment fingerprinting of the Idelo watershed in Zanjan province, Iran. Digital elevation model (DEM), slope, vegetation cover, and flow accumulative layers have been used in compiling the structural sediment connectivity map. Field observations were made to calculate the field connectivity index. The results showed that the mean structural sediment connectivity index of the target watershed is −6.18. Moreover, areas in the downslope section near the outlet and the narrow strips around the watershed boundaries have moderate to high structural connectivity. The results of field validation showed there is an acceptable agreement between the field connectivity index and the structural connectivity map. Also, these results confirmed previous findings of sediment fingerprinting in the study area. Based on the findings of the current study, determining the structural sediment connectivity index is an efficient method to make management and conservation decisions and control erosion and sediment in the watershed. [ABSTRACT FROM AUTHOR]

Annual sediment load transportation in the Indus River varies from 0.725 to 1.0 Mt/d and varies from 260 to 300 Mt/y. Sediment accumulation upstream of the inline structure (Guddu Barrage) has frequently increased. Consequently, the sediment accumulation reduces the intake canal supply, design withdrawals, and flood-carrying capacity of the Guddu Barrage. Furthermore, the Indus River changes its behavior, channel dimensions, pattern, and flooding frequency with respect to temporal and spatial morphology with braided high to low meanders. In the current study, the Hydrologic Engineering Center- River Analysis System (HEC-RAS) model, in combination with ArcGIS, were used to study sediment dynamics, analyze flood profile/water surface elevation, and assess erosion and deposition of sediment. In addition to this, a quasi-unsteady flow analysis method was used to simulate sediment transport from July to September 2010. It was found the invert change due to sediment transport maximum aggradation was 6.40 ft (1.950 m), and the maximum degradation was 30 ft (9.144 m), which further varies with the hydraulic conditions of the model. Cumulative mass bed change, sediment transport aggradation was 10.50 million tons (9.53 million t), and degradation was 3.7 million tons (3.3 million t). Moreover, it was found cumulative longitudinal mass change, sediment transport aggradation was 155 million tons (140.62 million t), and degradation was 10 million tons (9.07 million t). The cumulative mass inflow was 320 million tons (290.3 million t). Whereas the model revealed that the flood level upstream and downstream of the hydraulic structure was 264 ft (80.467 m) and 260.29 ft (79.34 m), respectively. Therefore, the HEC-RAS model accurately represents the sediment transport and water levels observed at a gated weir, which is an inline structure. [ABSTRACT FROM AUTHOR]

Soil erosion is a severe threat for ecosystems and anthropogenic infrastructure. Glaciers are retreating rapidly due to global warming and the receding ice leaves unvegetated depositions of sediment, which are prone to mobilisation during precipitation events. Vegetation is known to serve as erosion protection, but how above- and belowground plant traits, vegetation cover and plant diversity on community level are jointly affecting erosion is unclear. Additionally, soil microbial communities may have effects on slope stability by promoting plant growth and function. We measured sediment transport on 30 plots of 2 × 3 m size on proglacial slopes of the Gepatschferner glacier (Kaunertal, Austria) over three years in a natural pristine high alpine environment. Vegetation cover, species abundances and relevant above- and belowground traits were measured for each occurring plant species on community level. Path model analysis revealed that dense and species-rich plant cover characterized by specific plant growth strategies and trait diversity was best suited to decrease erosion. Vegetation properties were also closely linked to the composition of soil microbial communities characterised by next generation amplicon sequencing, which may facilitate soil formation and further enhance the plants' soil stabilising potential. Our study illustrates that erosion control may benefit from a high vegetation cover, which is facilitated by diverse plant communities with complementary morphological traits. These vegetation properties also affect soil microbiota, but their impact on slope protection in combination with the vegetation remains to be elucidated. Our findings may inform nature-based solutions against erosion such as revegetation of alpine slopes using specific seed mixtures. [ABSTRACT FROM AUTHOR]

In this article, we construct and analyze a second-order time-accurate, linear, decoupled fully-discrete discontinuous Galerkin (DG) pressure-projection numerical scheme for the hydrodynamic and sediment transport model. The proposed algorithm is based on DG method for spatial discretization, Crank-Nicolson (C-N) scheme for temporal discretization, linearly extrapolated scheme for the nonlinear term and coupling term and pressure-projection method for the Navier-Stokes equations. Moreover, we rigorously prove the unconditional stability and optimal error estimates of the proposed fully-discrete scheme. We make use of the techniques developed by Pietro et al. to prove the optimal error estimates for pressure rigorously. Finally, several numerical examples are performed to numerically demonstrate the accuracy, efficiency and applicability of the proposed scheme. [ABSTRACT FROM AUTHOR]

• An improved Eulerian method with the movable IBM is employed to study the deformation of the river bed. • A Simultaneous Bed Adjustment Method is proposed to consider the sand sliding on the riverbed in the DNS. • A Segment Plane Method is proposed to calculate the geometrical parameter of the complex riverbed. • The improved Eulerian method can capture both the development of the local scour and the flow structure in detail. An improved Eulerian method with a novel morphologic model is developed based on the direct numerical simulation (DNS) approach to study the local scour. A movable immersed boundary method is proposed to prescribe the geometry of the riverbed. Two techniques, namely the Simultaneous Bed Adjustment Method (SBAM) and (Segment Plane Method) SPM, are proposed to model the complex time changing geometry of the riverbed. The SBAM technique considers sand sliding in the model and the SPM is an algorithm calculating the geometrical parameter of the complex riverbed. A wind tunnel experiment obeying Reynolds similarity and measuring the pressure in a fixed scour hole is carried out to compare with the numerical results. The results show that the movable immersed boundary method performs well in capturing the local scour and qualitatively agrees with the experimental study in how the scour hole develops. The numerical results also show that the DNS can capture the formation of the local scour in details at the beginning and find that the Reynolds stress u'v' plays an important role in an erosion at the leading edge of the cylinder. Therefore, the newly improved Eulerian method is a valuable tool for DNS studies of local scour with the implementation of MPI. [ABSTRACT FROM AUTHOR]

Riparian buffers are commonly used to mitigate the negative effects of forestry operations near water, particularly sediment transport to streams. In Sweden, current practices typically involve 5-7 m wide riparian buffers along small streams. Historical forest management, which favored conifers up to the channel edge, has resulted in these narrow buffers having a simplified tree species composition and structure, making them prone to windthrow. While windthrow can contribute large wood (LW) to streams, windthrow also risks increasing sediment inputs if rootwads are exposed near stream edges. This disturbance affects sediment connectivity, or the movement of particles through the fluvial system, but the interaction between LW dynamics and sediment connectivity in small boreal streams is not well understood. We investigated sediment connectivity at the Trollberget Experimental Area in northern Sweden, where six 100 m stream reaches had either 5 m or 15 m wide riparian buffers. Pre-harvest and one-year post-harvest data on windthrow, hydrology, and sediment yields were collected. Forest harvesting increased sediment connectivity in the streams regardless of buffer width, indicating that buffers wider than 15 m are necessary to reduce sediment input impacts in small headwater streams. Windthrow affecting stream channels was more common in the 5 m buffers, leading to significantly higher deposition of very fine sediments (<250 μm) compared to the 15 m buffers. Coarse (>1 mm) and fine sediments (250 μm – 1 mm) were also higher in the 5 m buffers. We found that sediment connectivity in streams was closely linked to LW dynamics, negatively before harvest but positively after harvest. Before harvest, LW trapped sediment and prevented downstream transport, but after harvest, the increased sediment input overwhelmed this function. Our results highlight a trade-off between the recruitment of LW and minimizing sediment connectivity, two key objectives in riparian buffer management. • Riparian buffers are important to protect stream ecosystems when the adjacent forest is cut. • We applied 5 m and 15 m wide buffers and followed the impact on sediment connectivity. • Instream wood trapped sediments until harvest; windthrow disrupted this function. • All size fractions of sediment increased after harvest, regardless of buffer width. • Current buffer practices prevent providing both instream wood and sediment trapping. [ABSTRACT FROM AUTHOR]

Research into sediment provenance identification in Antarctica is emerging as a relevant field of study, providing a unique insight into understanding geomorphological processes in extreme climatic environments. This study focusses on the mechanisms of sediment redistribution in the catchment of the Korabelny Stream, located at the western end of the Bellingshausen Ice Dome on King George Island (Shetland Islands). The catchment area of the stream covers 2.83 km2, with 1.17 km2 under the glacier. Two main sediment sources have been identified: a) the glacierized part, extending along the glacier edge and represented by a complex of moraine deposits lacking protective vegetation cover, along with part of the catchment under the glacier; b) the periglacial part, occupying territory with permafrost and a thin loose cover unevenly protected by early successional vegetation. We combine a tracer-based fingerprinting technique, sediment delivery estimates based on sediment flow connectivity index and geomorphological mapping to quantify the sources contribution to sediment yield. The proportional contribution of the glacierized part was 60–66 % of the total sediment yield based on two independent methods, suggesting the reliability of the results. It is noteworthy that sediment transport from the glacierized part exceeds that from the periglacial part. However, a significant portion of the sediment is redeposited in temporary reservoirs formed along the glacier edge and Lake Mesyats, located in the central part of the Korabelny Stream catchment. The main factor determining sediment yield in the catchment is the water reserves in snow at the beginning of the ablation season. In years when water reserves in snow significantly exceed long-term average values, such as observed in the austral summer of 2014–2015 when study was conducted, sediment yield was low. This is attributed to the faster melting of ice on the glacier compared to snow, due to differences in albedo. • First time, assessed sediment sources in small Maritime Antarctica catchment. • Two independent methods used to determine proglacial and periglacial contributions. • Proglacial part contributes significantly more to sediment runoff. • The higher snow water reserves at ablation start the lower proglacial sediment runoff. [ABSTRACT FROM AUTHOR]

[Display omitted] • China's large river sediment loadings and runoff have not universally synchronously changed in the past 20 years. • There were 9/13 of large river systems showed downward trends of annual sediment loadings. • Lower reaches of the Yellow River had the maximum annual average sediment loadings. • Runoff volume accounted for over 30% of sediment loading variations among all river systems. • Afforestation plays a crucial role in reducing sediment in arid regions. Understanding the relationship between sediment loading and its environmental implications in river systems is crucial for water resource management and environmental protection. This study explored the spatiotemporal characteristics of sediment loading and their environmental relationships in seven large rivers in China, aiming to quantify the contributions of various factors to changes in sediment transport. Monitoring data spanning twenty-one years (2002 to 2022) on sediments, hydrology, and the environment collected by sixty-five stations were analysed. The multivariate statistical techniques employed included Spearman's correlation analysis, principal component analysis, and multivariate regression modeling. The results show that sediment transport in various river systems exhibited spatial heterogeneity, the maximum annual average sediment loadings (1.59 × 108 t/yr) occur in the lower reaches of the Yellow River, the middle reaches have the highest sediment concentration (41.54 kg/m3), followed by the downstream of the Yellow River (5.85 kg/m3). Sediment loading and runoff changes in the basins did not adhere universally to synchronous patterns. Eleven of the thirteen basins of these river systems showed upward trends in annual runoff volume, whereas nine basins showed downward trends in annual sediment loading. Runoff volume accounted for over 30 % explanatory of sediment loading variations in all seven large river systems, with the Yangtze, Huaihe, Qiantang, and Songhua rivers surpassing 60 % of the explanatory power. The Normalized Difference Vegetation Index of all watersheds showed an increasing trend, whereas the index of nine of the thirteen watersheds was correlated negatively with sediment transport. The influence of human activities on basin sediment transport was higher than that of natural resilience, whereas afforestation significantly reduced sediment in arid regions. This study provides insight into the temporal and spatial characteristics of sediment loadings and the driving effects of environmental factors, which has great significance for watershed environmental management. [ABSTRACT FROM AUTHOR]

Wave nonlinearity significantly influences wave attenuation and can cause sediment transport imbalances in vegetated zones, impacting shoreline stability and ecosystem-based coastal defences. Despite its importance, the parameterisation and mechanisms of wave nonlinearity evolution over flexible vegetation remain unclear. This study examines the mechanisms behind non-breaking wave nonlinearity evolution over flexible vegetation and provides parameterisation of wave nonlinearity, based on experimental data collected by Anderson and Smith (2014). The study derives a new set of empirical formulae for predicting wave nonlinearity in Spartina alterniflora, which considers Ursell number, relative vegetation width, vegetation submergence, and vegetation density. The predictions made using these formulae are in good agreement with the measurements. The results indicate a decrease in wave skewness across the span of vegetation, whereas wave asymmetry increases until it reaches a maximum before decreasing. The findings suggest a preferential dissipation of high harmonics compared to low harmonics in the vegetation zone. Additionally, bispectrum analysis reveals that vegetation enhances the difference interaction while suppressing the sum interaction between wave components. The findings enable improvements in our understanding of wave nonlinearity in vegetation, providing better predictive capabilities for wave attenuation and sediment transport, which are crucial for the design and optimization of coastal defence systems. • Non-breaking wave skewness keeps decreasing over the vegetation, while wave asymmetry initially rises to a maximum and then decreases. • Vegetation enhances the difference interaction while suppressing the sum interaction between wave components. • A new empirical formula for predicting non-breaking wave nonlinearity takes into account both vegetation properties and wave characteristics. [ABSTRACT FROM AUTHOR]

Process-based nearshore morphodynamic models are commonly used tools by coastal engineers and planners to predict the nearshore morphology change of sandy beaches across various spatiotemporal scales. Accurate modeling of the morphological response on medium and long time scales is imperative for quantitative assessments of coastal infrastructure over a project's intended life-span. However, most previous modeling applications have focused on single/sub-seasonal storm events and are often limited to an assessment of the subaerial beach (i.e. berm and dune). This not only leaves uncertainty concerning the quality of morphology predictions on extended (> weeks) time scales, but also the capacity of process-based models to emulate realistic nearshore sandbar dynamics and the corresponding exchange of sediment between the nearshore-beach system. To shed light on these meso-scale dynamics, CSHORE, a 1D phase-averaged, process-based nearshore morphodynamic model, was applied on an annual scale to a multi-barred, dissipative beach in Oysterville, WA, USA. Thousands of unique sediment transport and hydrodynamic parameter combinations were executed during model calibration. A large portion of these simulations displayed physically realistic sandbar dynamics, including the growth, decay, and migration of intertidal and subtidal sandbars. To explore the model mechanisms enabling realistic bar behavior, the binary and multinomial logistic regression model were used to quantify the relationship between model parameter selection and the probability of various categorical bar configurations occurring in the final predicted profile. The results indicate the most sensitive parameters associated with barred morphology, in this study, and support the use of separate sediment transport parameters for low and high wave energy conditions. The co-utilization of numerical and statistical modeling outlined in this publication is generalizable to future exploratory modeling and/or calibration routines concerned with categorical outcomes. • CSHORE is used to simulate annual scale nearshore and intertidal sandbar evolution. • Novel logistic regression methods inform model parameter influence on bar behavior. • Intertidal (subtidal) bars are most influenced by low (high) wave energy processes. • Low values of the breaker index favor barred morphology predictions. [ABSTRACT FROM AUTHOR]

Progressive coastal retreat has been an issue exacerbated in recent years due to climate change. Sand is eroded from beaches during the winter and partially recovered during summer by slow accretion processes. The development of new working with nature techniques that produce enhanced beach accretion could help recover most of the sand lost during winter and thus reduce the impact of climate change on beaches. The presence of bedforms contribute to increasing onshore sediment transport, but few studies have been performed to quantify their effect. In this study, the evolution and effect of artificially created bedforms on onshore sediment transport were analysed in prototype-scale laboratory experiments. The tested bedforms mimicked a beach ploughing of the intertidal area, with a wavelength of 1.6 m and height of 0.25 m, corresponding to the ploughing dimensions that a tractor can perform. Two tests were performed with the same initial morphology, medium sand (D 50 = 0.318 mm), sea state conditions (H s = 0.3 m, T p = 7 s) that produced accretion, and different water levels that represent two tidal states. The experimental flume was longitudinally split into two equal channels of 1 m wide, allowing the simultaneous simulation of a natural control geometry and a ploughed geometry, facilitating the comparison and assuring the very same sea conditions. The presence of ploughed bedforms produced two effects: (1) an acceleration of natural accretion rates reaching 40%, and (2) onshore sediment transport due to the migration of the bedforms. The acceleration of natural accretion was explained by the extra bottom roughness induced by the bedforms, which produced more wave dissipation through bottom friction and thus more accretive conditions. The ploughed height decreased exponentially as waves broke over the crest of the ridges, which almost disappeared after 2–3 h of wave action. As a result, the extra bottom roughness also decreased as time passed. Consequently, the nature-assisted beach enhancement technique of ploughing should be applied at each low tide to produce a cumulative effect. Plough bedforms migrated onshore at a rate of approximately 0.2 m/h during the first hour, mobilizing onshore up to 61 kg m−1 h−1 of sediment. Ripples appeared on the tops of the ridge crests and migrated faster onshore, contributing to the migration of the ploughed bedforms. These results demonstrated the importance of considering bedforms while studying accretion processes and the potential of ploughing as an innovative strategy of working with nature to enhance beach recovery. • Working with nature. • Ploughing the intertidal area of a beach enhances natural accretion. • Real scale laboratory experiments measuring sediment transport. • Mechanically ploughing increases hydraulic roughness and wave energy dissipation. • Onshore migration of bedforms help beach recovery. [ABSTRACT FROM AUTHOR]

Sediment supply downstream of dams through control techniques of reservoir sedimentation is attracting attention for promoting both sustainable water use and river ecosystem restoration. Sediment sluicing is a sediment control technique expected to recover natural sediment regimes because it allows sediment from an upstream reservoir to pass through a downstream dam during high flows. However, only a few studies have evaluated the restorative effects of sediment sluicing. We evaluated the restoration effects of sediment sluicing on macroinvertebrate assemblages in a dammed river using a before–after control–impact design. After sediment sluicing operations, the taxa richness of macroinvertebrates increased at sites downstream of the dam under free-flow conditions, where the reservoir was completely lotic and large amounts of sediment were transported. Meanwhile, there were few changes in macroinvertebrate richness and composition at sites downstream of the dam without sluicing operations and at the dam where sluicing was operational but did not achieve free flow. The increase in taxa richness was probably due to sediment supply from sluicing operations. As most taxa that increased in response to sluicing operations were grazers, sediment supply could provide benefits through indirect impacts via food resources. Negative impacts were observed on macroinvertebrates because of the first flush of excess sediment supply during the first sluicing; however, the extent of impact was spatiotemporally limited. Sluicing operation would be better than other sediment control techniques. This study suggests that sediment sluicing is an effective restoration method for not only macroinvertebrate assemblages but also for ecosystem functions. [Display omitted] • Sediment sluicing restores the natural sediment regimes in dammed streams and rivers. • Sediment supply through sluicing increased macroinvertebrate assemblage diversity. • Grazers were a group of macroinvertebrates that appeared after sediment sluicing. • Negative impacts of excess sediment supply due to the first flush were noticeable. • Sediment regime recovery improved structures and functions in riverine ecosystems. [ABSTRACT FROM AUTHOR]

Bioengineering approaches to slope stabilization involve biological and mechanical methods with low impact on the environment and landscape. Slope stabilization using vegetation patches or islands can greatly decrease runoff and soil erosion on an eroded lake shore. While vegetation islands showed promise for forest and grassland reclamation, they have rarely been used on eroded lake shores. A study was conducted to determine whether bioengineering using native vegetation islands and terraces could successfully revegetate and stabilize a severely eroded lake shore slope in the central aspen parkland, Alberta, Canada. Three gullies and three slopes were terraced using pressure treated planks, then transplanted with non-dormant (mid-August) and dormant (mid-October) 20 cm diameter vegetation islands in a soil amended with 25% (by volume) compost. Volumetric water content was significantly less in lower slope positions than upper slope positions, and sediment transport to lower slope positions was much reduced. After one year, both non-dormant and dormant transplanted islands survived and established on the terraced slope, under relatively inhospitable growing conditions. Although non-dormant islands had significantly lower vegetation mortality (10% or less) than dormant islands on both slopes and gullies, no differences in health and vigour were found by the end of the study. Overall plant species number on the site increased during the study. Graminoid species densities increased, while those of forbs, shrub and tree species declined in the transplanted vegetation islands. Non-dormant islands had greater graminoid density than dormant islands, where Poa pratensis was the dominant species in the islands. Bioengineering with vegetation islands and terraces can assist in trapping runoff and sediment, and accelerate establishment of a diversity of plant species and groups relative to traditional revegetation methods. • Eroded lakeshore slopes can be reclaimed with terraces and small vegetation islands. • Non-dormant and dormant transplanted islands survived on terraced lakeshore slopes. • Vegetation mortality was significantly lower with non-dormant than dormant islands. • Non-dormant islands had greater graminoid density than dormant islands. • Vegetation islands can trap runoff and sediment, and accelerate plant establishment. [ABSTRACT FROM AUTHOR]

Our coasts are facing a growing threat from rising sea levels and detrimental storm events. Nature-based solutions are gaining interest for their potential to provide multiple ecosystem services, including coastal protection. Seagrass can influence coastal sediment transport and wave propagation, however, whether seagrass can be used as an effective intervention for coastal protection is unclear. Using the Delft3D model, this study looks at how seagrass affects coastal hydrodynamics in a macrotidal bay, under idealised scenarios that simulate a rise in sea level and storm wave heights, emulating projected sea conditions under climate change. Through the use of a habitat suitability model, a seagrass patch in Morecambe Bay was simulated, based on a location within the bay that is most suitable for seagrass species Zostera marina. Hydrodynamic simulations were run for a number of scenarios for a domain with and without a seagrass patch. Scenarios included variable boundary wave heights, sea levels and vegetation parameters, to test the influence of seagrass in future climates. Results show that there is a reduction in mean and maximum wave height inside and behind the seagrass patch, with the largest changes in wave dissipation observed during higher boundary wave conditions. In these conditions the maximum wave height reduced by over a half within the patch. Simulations examining the influence of seagrass density and canopy height found that a lower density seagrass patch reduced maximum wave height more substantially than higher density patches. Although alternative hard engineered solutions are able to attenuate wave energy more effectively than seagrass, these results demonstrate seagrass could play an important role in conjunction with salt marsh restoration or existing hard engineering solutions, helping to mitigate the risk of flooding and erosion, whilst providing additional ecosystem services such as carbon sequestration and habitat provision. • Habitat suitability model locates site to test seagrass as a nature-based solution. • Simulations find seagrass to influence a reduction in significant wave height. • Potential for seagrass to be integrated into managed realignment plans. [ABSTRACT FROM AUTHOR]

The transport of microplastics (MPs) from urban environments to water resources via stormwater runoff poses significant concerns due to its adverse impacts on water safety and aquatic ecosystems. This study presents a modeling approach aimed at understanding the transport mechanisms of MPs in an urban residential setting, considering settling and buoyant MPs. To consider the effect of MP shapes, the settling velocity of various settling MPs in shapes of fibers, films, and fragments was calculated. Using an analogy of sediment transport, a Rouse number criterion was used to analyze the transport of MPs. For buoyant MPs, it was assumed that they transport as wash-load as soon as they float in the water and the travel time for them to reach the storm drain was determined. The calculation of settling velocity revealed the influence of shape on the settling velocity of MPs was particularly pronounced as the equivalent diameter of the MPs increased. The transport mechanism for the smallest settling MPs, irrespective of their shapes, density, and depth of flow, was wash-load. However, for larger MPs, the shape and size distribution of settling MPs, along with the depth of flow and slope significantly influenced their transport mechanisms compared to sediment particles. The influence of weathering on the MPs' transport mechanisms depended on their sizes and shapes. The site-specific characteristics, including slope and surface friction, significantly influenced the velocity of stormwater runoff and, consequently, the extent of MP transport during rain events. Moreover, an evaluation of the transport mechanism of settling MPs was conducted using the reported field data on MP abundance in road dust collected from residential and traffic sites. This study underscores the complexity of MP transport dynamics and provides a foundation for developing targeted strategies to mitigate MP pollution in urban environments. [Display omitted] • Microplastics' shape greatly affected settling velocity as their diameter and density increased. • For small MPs, regardless of shape, density, or flow depth, wash-load dominated. • Transport of larger sedimenting MPs depended on their size, shape, and flow depth. • Local features affect stormwater runoff depth and velocity, influencing MP transport dynamics. [ABSTRACT FROM AUTHOR]

Soil erosion rates after wildfire are strongly controlled by intrinsic properties such as topography, weather, climate, soil, and vegetation. These landscape and hydroclimatic properties are important in determining post-fire erosion rates; however, their influence on post-fire erosion and their interaction with the intensity of a wildfire remains uncertain. A key limitation in resolving this uncertainty is the lack of conceptual models and frameworks for organising data related to the geomorphic sensitivity of landscapes to wildfire. Our aim is to develop a framework for consolidating understanding of post-fire erosion in the context of hydroclimatic conditions which contribute to system states, for example soil and vegetation properties, and wildfire regime. The framework is developed around a simple conceptual model where the change in erosion due to wildfire is a product of change in runoff generation and sediment supply, which is strongly related to landscape net primary productivity (NPP). We hypothesised that geomorphic sensitivity to wildfire should vary as a unimodal humped relationship across a gradient of NPP, peaking at an intermediate level. To develop this framework and to test the hypothesis, we first review intrinsic soil and vegetation properties related to the supply and transport of sediment from burned and unburned hillslopes. Net primary productivity is systematically related to these intrinsic properties because it integrates many processes involved in soil and vegetation development. Empirical data indicate a trend in the change in surface runoff generation with NPP after wildfire, peaking at an NPP of approximately 15 Mg C ha−1 y−1. A simple model of fuel availability and soil heating are correlated with a similar "humped" trend in sediment supply. These results are consistent with our conceptual model, which indicates that sediment supply and runoff contribute towards a distinct peak in wildfire effects on erosion at an intermediate level of NPP. We propose that landscapes of intermediate NPP typically have the highest quantity of fuel available to burn, which cause large changes to the soil surface properties. Landscapes at intermediate NPP also tend to produce intrinsic soil and vegetation properties that promote erosion after wildfire. The interplay between these short and long-term landscape characteristics is strongest at intermediate levels of NPP. Our proposed biogeographic model of geomorphic sensitivity to wildfire was supported by erosion data from burned hillslope and zero-order catchments studies from a range fire-prone landscapes in Australia and North America. Our proposed conceptual model will help identify areas most vulnerable to post-fire erosion changes. [ABSTRACT FROM AUTHOR]

In this work, we consider biotic and abiotic reactive transport processes through marine sediment vertical profiles. The mathematical model is described by a multicomponent transport and formation of dissolved and solid sediment components with coupled nonlinear reaction terms. We present an efficient decoupled multiscale algorithm based on the implicit–explicit time approximation schemes, operator-splitting techniques, and multiscale finite element method. We start with a finite volume approximation by space on the fully resolved grid (fine grid). We present an implicit–explicit scheme (ImEx) for time approximation to construct the efficient numerical algorithm and localize the coupled nonlinear reaction part. The explicit time approximation is constructed for the slow, non-reactive transport subproblem. The nonlinear reaction part uses the implicit approximation. To overcome a more significant time step restriction induced by an explicit approximation of the diffusive part, we combine Operator Splitting with an implicit–explicit scheme for the non-reactive transport part (OS-ImEx). To reduce the size of the non-reactive transport system, we propose a multiscale lower-dimensional model for the non-reactive transport in marine sediment column. By combining the multiscale method with the Operator splitting scheme and implicit–explicit approximation for the non-reactive part, we obtain an efficient decoupled approach that localizes the nonlinear coupled reaction part and performs a faster solution of the non-reactive transport part. Numerical results are presented for one-dimensional and two-dimensional test problems to study the accuracy and efficiency of the proposed decoupled multiscale approach. [ABSTRACT FROM AUTHOR]

Foredunes provide many environmental and ecosystem services including protection from wave erosion and flooding hazards during storm events. While the impact of human interventions on the short-term evolution of coastal dunes is reasonably well understood, less is known about their contemporary influence on current wind and sediment dynamics several decades after implementation. The coastal dunes in Leucate (SE, France) have been anthropogenically constructed and are dominated by offshore wind conditions. Since their construction 20 years ago, a distinct variation in their longshore morphology has developed that is inherited from its original construction. The northern part of the dune has a symmetrical profile with a 28° degree stoss slope, 30° lee slope and a single crest. The southern part is asymmetric, with a gentler stoss slope (12°), 26° lee slope, and a double crest. To explore the potential geomorphic impacts of this distinct difference in morphology, several numerical simulations with varying wind speeds and direction were conducted. We used Computational Fluid Dynamics (CFD) to explore the spatial variations of the near surface wind flow, shear stress and aeolian sediment transport. show that for each scenario, near surface wind speed accelerated toward the dune crest on the windward slope of the dune. The maximum wind speed varied with incident wind direction, the highest speeds occurring when incident wind flow was perpendicular to the dune crest. The double crest in the southern section of the dune affected the wind flow by inducing two consecutive speeds-up zones, with a greater maximum wind speed than on the single crested dune. Wind flow separation was observed where a steep lee slope was present (single crested dune), and only during perpendicular winds. This suggests that the shape of the dune and the direction of the wind are key parameters rather than wind speed. The area affected by reversed separated flow was spatially limited and did not extend beyond the dune toe but was below the threshold for aeolian sediment transport. Elsewhere in the lee of the dune, the wind was only deflected by an order of 15° for the oblique winds (310 and 330°), and less than 10° for the perpendicular wind (290°) on the southern part. In these locations, the shear velocity exceeded the threshold, notably on the southern dune, which coincided with the formation of undulating aeolian deposits in the lee of vegetation on the dune crest. The spatial differences observed in wind flow and aeolian sediment transport processes on this human-made dune were directly inherited from differences in their construction two decades ago. These results demonstrate the importance of the constructed dune profile, due to its potential impact on the long-term evolution of the landscape and the sediment budget of the system. • Dune construction methods impact their morphology even after several decades. • A relatively small coastal dune can lead to airflow separation. • The pattern of wind flow perturbation depends on dune shape and wind direction. [ABSTRACT FROM AUTHOR]

The swash zone is an important region for the coastal morphodynamics. Often, model studies of the swash zone use depth-averaged models. These models typically assume a vertically uniform velocity and sand concentration for calculating the sand transport flux. However, this assumption is not always accurate in the swash zone. In order to investigate the vertical distribution of velocity and sand, we use a depth-resolving model that is able to capture these vertical variations. We simulate the flow and suspended sediment transport induced by bichromatic waves using a 2DV depth-resolving RANS model. Our verification of the model shows that special care needs to be taken to deal with bubbles in 2DV simulations. Furthermore, we show that turning off the (Wilcox, 2006, 2008) limiter for turbulence, increases the modelled turbulent kinetic energy that is induced by wave-breaking, resulting in improved predictions of sediment concentrations. Using the depth-resolving model, we show that the vertical distribution of velocity and sand is far from uniform in the swash zone. The results show that if one assumes vertically uniform depth-averaged velocities and concentrations, one can overpredict the sediment flux by 50%. • Air bubbles can stay unrealistically long near the bed in 2DV swash simulations. • Bubbles near the bed lead to lower shear stresses and lower sediment pick up. • Increased wave-breaking turbulence leads to increased onshore sand transport. • A model assuming a vertically uniform flux of sand can underpredict the flux by 50%. [ABSTRACT FROM AUTHOR]

The formation and evolution of coastal dunes result from a complex interplay of eco-morphodynamic processes. State-of-the-art models can simulate aeolian transports and morphological dune evolution under certain conditions. However, a model combining these processes for coastal engineering applications was not yet available. This study aims to develop a predictive tool for dune development to inform coastal management decisions and interventions. The aeolian sediment transport model AeoLiS is extended with functionalities that allow for simulations of coastal landforms. The added functionalities include the effect of topographic steering on wind shear, avalanching of steep slopes and vegetation processes in the form of growth and wind shear reduction. The model is validated by simulating four distinct coastal landforms; barchan-, parabolic-, embryo dunes and blowouts. Simulations, based on real-world conditions, replicate the landform formation, migration rates and seasonal variability. • Dune shaping processes are implemented into AeoLiS enabling landform simulations. • Four distinct landform types are simulated utilizing AeoLiS. • AeoLiS replicates accurate landform shapes and dynamics under real-world conditions. • Capabilities added to AeoLiS enable its use for a range of engineering applications. [ABSTRACT FROM AUTHOR]

We present the implementation of a new fully distributed multiclass soil erosion module. The model is based on a 2D finite volume solver (Iber+) for the 2D shallow water equations that computes the overland flow water depths and velocities. From these, the model evaluates the transport of sediment particles due to bed load and suspended load, including rainfall-driven and runoff-driven erosion processes, and using well-established physically-based formulations. The evolution of the mass of sediment particles in the soil layer is computed from a mass conservation equation for each sediment class. The solver is implemented using High Performance Computing techniques that take advantage of the computational capabilities of standard Graphical Processing Units, achieving speed-ups of two orders of magnitude relative to a sequential implementation on the CPU. We show the application and validation of the model at different spatial scales, ranging from laboratory experiments to meso-scale catchments. • A multiclass soil erosion module is implemented in a 2D shallow water model. • Sediment transport is modelled considering rainfall and runoff driven processes. • The GPU parallelization of the code enables its application to complex catchments. [ABSTRACT FROM AUTHOR]

The main purpose of the research was to develop appropriate tools for forecasting the effects of storms. The use of the high-resolution SWAN wave model powered by AROME wind fields to couple it with the SWANOneSed sediment transport model and a model using the Ruggiero formula, predicting the extent of the flooded shore, allowed the development of reliable tools for forecasting the effects of storms. Validation using qualitative analysis showed that the results obtained from the coupled SWANOneSed model are characterized by high consistency in intensification and direction of changes. The model using the Ruggiero formula obtained a high value of the correlation coefficient, i.e. 0.970 and 0.992 for the Satbałtyk-Xbeach model data, based on the Hunt&Mase formula, and the high-resolution Pleiades Neo satellite data, respectively. By combining models from the SWAN family, i.e. the SWAN and SWANOneSed wave model and a model using the Ruggiero formula, it was possible to obtain reliable and compatible tools enabling an uninterrupted and synchronized operational process of generating forecasts of storm effects. [Display omitted] • The coupling of the SWAN & SWANOneSed enables reliable and operational forecasting. • Measured & terrain surveyed data-fed model are consistent with other observed data. • Formula van Rijn reliably reproduces sediment transport in various types of coasts. • The Ruggiero formula is applicable in various parts of the Polish coast. [ABSTRACT FROM AUTHOR]

Large wood (LW) and log jams have important implications for sediment dynamics within river systems. Although many case studies explore this topic, far fewer synthesize these results at the reach and basin scales. In this paper, we present a conceptual model that relates valley setting and landscape history of forested, mountain streams to spatiotemporal patterns of sediment storage and transport via the formation and decay processes of logjams. This conceptual model explores the function of logjams as sediment transport moderators, significantly influencing sediment retention, channel morphology, and lateral and longitudinal connectivity. Detailed wood inventories, channel topographic surveys, and channel morphology from four case studies are used to illustrate the range of channel responses to logjam formation, evolution, and decay in different valley contexts. Valley setting is shown to influence logjam formation and dynamics by determining the mechanisms and timing of sediment and wood recruitment. In steep and narrow (and thus coupled, confined) reaches, colluvial processes are the dominant mechanisms of wood and sediment delivery, and logjams grow vertically as sediment is stored in a wedge behind the jam (longitudinal disconnectivity). In contrast, in unconfined reaches (decoupled hillslopes), wood and sediment recruitment occurs primarily through fluvial processes, and logjams grow laterally as the channel shifts across the valley bottom. These logjams have long lifespans, often over a century, and gradually release sediment as the logjam decomposes. Sediment deposits stabilized by riparian vegetation behind these structures may persist long after logjam decay. This conceptual model is a testable framework and practical tool that offers insight into wood-sediment interaction mechanisms within steep, forested basins. [ABSTRACT FROM AUTHOR]

This study reveals the morphological transformations of a deep-water channel system within the Rakhine Basin in the northeastern Bay of Bengal through a comprehensive analysis of high-resolution 3D seismic data integrated with drilling logs. Employing the "source-channel-sink" paradigm, this investigation examined the impact of various factors, including tectonic transformations, sediment influx, slope dynamics, climatic changes, and relative sea-level fluctuations, on the evolutionary trajectory of these channel systems. Applying precise time-slicing techniques integrating root-mean-square amplitude attributes, coherent amplitude attributes, and horizontal amplitudes on seismic profiles, this investigation recognized three distinct stages in the evolution of channel-levee complexes (CLCs): the Middle Miocene erosional deep-water channel-levee complex (CLC-1), the Pliocene erosional-depositional deep-water channel-levee complex (CLC-2), and the Pleistocene depositional deep-water channel-levee complex (CLC-3). Comparative analysis revealed that the CLC-3 exhibits unique characteristics, including shallower channel depth (D), wider channel width (W C), extensive U-shaped cross-sectional area (S), broader natural levee width (W L) and height (H), and the highest tortuosity coefficient (L C /L S) when contrasted with the other two CLCs. Furthermore, this study substantiated how tectonic processes, primarily the collision between the Indo-Eurasian plates, resulting in the Himalayan and Indo-Burma Range orogenies, have shaped the region's geological and climatic framework, thereby influencing monsoon circulation and precipitation patterns, which in turn augmented detrital material influx into the basin. Moreover, this tectonic collision has led to gradual changes in the slope gradient of the Rakhine Basin and its deep-water areas, impacting internal flow velocities and channel curvature, thus governing deep-water channel systems' development and spatial distribution. Also, episodic sea level fluctuations were identified as significant contributors to sediment transport from shelves to deep-water regions and sediment deposit reworking. Overall, this study underscores the role of tectonic changes after the Eocene in driving the evolutionary dynamics of the deep-water channel system within the Rakhine Basin, Myanmar. [Display omitted] • Indo-Eurasian plate collision shaped the deep-water channel systems in the Rakhine Basin. • 3D seismic data reveals three evolutionary stages in these deep-water channel systems. • Pleistocene depositional channel-levee complex exhibits unique physical characteristics. • Tectonically affected slope dynamics have directed the channels' evolutionary dynamics. • Episodic sea level fluctuations have also supported these morphological transformations. [ABSTRACT FROM AUTHOR]

We synthesize evidence suggesting a chain of global cause-effect relationships, linking population and economic development with cumulative effects on changes in landscape dynamics, including denudation and sediment transport/deposition. Temporal trends in global patterns of geomorphic processes or process combinations such as denudation, sedimentation, or frequency of geomorphic disasters, appear to reflect growing human pressure. Erosion rates, intensified by anthropogenic factors, are currently one to two orders of magnitude greater than prior to the 20th century, and are growing further. Per capita human transfer of Earth materials has increased tenfold. A considerable increase in the frequency of disasters related to geomorphic processes has also taken place in just over half a century, outpacing changes in other natural disasters. It is especially significant that the ratio between the frequency of geomorphic (implying water/land interaction, obviously influenced by climate change) disasters and frequency of purely climate-related disasters has increased more than ten-fold since the early 20th century. The changes described in geomorphic processes (global geomorphic change) appear to respond mainly to land surface modification, which reflects a "Great Geomorphic Acceleration" after the mid-twentieth century. However, these stressors, characteristic of the "Anthropocene", likely interact with climate change, increasing concerns about future implications for Earth surface dynamics and underscoring the need to not only reduce GHG emissions, but also improve land use practices, which modify the conditions of the terrain. [ABSTRACT FROM AUTHOR]

Floodplains are really important for the environment as they provide various functions for waterways, including ecological, hydrological, and geomorphic ones. During overbank flows, there are complex hydrodynamic conditions that occur as water interacts with the rough floodplain vegetation and drag forces due to the vegetation that changes the flow pattern. However, we still don't fully understand how floodplain vegetation influences channel-altering hydrodynamic forces and sediment transport. To address this, we conducted flume experiments and measured flow pattern and sediment transport under varied floodplain geometry and rigid and flexible conditions. For this purpose, a physical model was constructed in the laboratory, in which plastic rods with a diameter of 10 mm will be used as trees, and artificial grass will be grass vegetation. Thus, 36 experiments were conducted in which the sedimentation and hydraulic parameters of the flow were calculated by measuring the flow velocity, water surface, and sediment transport rate. The results show that in the floodplain with dense (rigid and flexible) vegetation, the friction coefficient (f) is even 1.5 times higher than in the floodplain without vegetation. The parameters such as flow velocity, bed shear stress and Darcy Weissbach friction coefficient increase in the vertical plane between the main channel and floodplains due to the difference in roughness between the main channel and floodplains. In addition, in the main channel, the flow resistance is almost constant and does not depend on the vegetation density. The Darcy-Weissbach friction coefficient is greatly increased in the presence of grass and tree vegetation on the floodplain, and the larger contribution of f is due to the grass vegetation. The results also showed the sediment transport rate has a direct relationship with the angle of divergence and density of vegetation and an inverse relationship with the relative depth of the flow. Therefore, as the sediment transport rate decreases in the diverging compound channel, the wavelength and height of the dunes increase. At smaller divergence angles, the dunes tend to the top of the zero line (the level of the sediments before the formation of the bed form). In the presence of vegetation, due to the increase in the roughness ratio of the floodplain to the main channel, the contribution of the main channel to the flow rate increases. As a result, the sediment transport rate increases. • The effect of rigid and flexible vegetation of floodplains on the flow pattern and transport of sediments was investigated. • The friction coefficient was 1.5 times higher than in the floodplain without vegetation in divergent compound channels. • In the main channel, the flow resistance is almost constant and does not depend on the vegetation density. • The sediment transport rate has a direct relationship with the angle of divergence and density of vegetation. [ABSTRACT FROM AUTHOR]

• Ecological model (SMM-YE) and hydrodynamic model (Delft3D) were coupled. • Model well simulated site-specific and interannual variations of vegetation dynamics. • High spatial heterogeneity of sedimentation pattern and marsh-edge scarp were captured. • Coupled model showed a superiority in simulating spatiotemporal biogeomorphology. A process-based ecological model (SMM-YE) was coupled with a hydrodynamic model (Delft3D) for understanding the biogeomorphology of coastal salt marsh in the Yangtze Estuary. The original SMM-YE mainly consists of modules for seed germination, propagule dispersal, seedling establishment, and biomass growth of marsh vegetation. Delft3D was used to simulate tidal movement, sediment transport, and geomorphological development. Against the field measurements (2014‒2019), the coupled model improved the simulation accuracy of the vegetation expansion pattern and deduced better the spatial heterogeneity of elevation change at the two study sites with different sedimentary regimes, compared to the original SMM-YE. Based on the interactions between vegetation and hydrological processes, the dynamics of marsh-edge scarp movement were also captured with a high match degree by using the coupled model. The model coupling biotic and abiotic processes revealed the simulation superiority in the spatiotemporal heterogeneity of tidal marsh biogeomorphology with high vegetation and hydro-sedimentary dynamics. [ABSTRACT FROM AUTHOR]

The Bohai Sea is the receiving basin of the Yellow River (Huanghe), one of the largest contributors of global terrestrial materials to the sea. An area of fine-grained sediment deposition extends northeast of the Yellow River and its formation mechanism is still unclear. A calibrated, high-resolution coupled model of the Bohai and Yellow Seas was used to investigate sediment transport pathways in the region under the influence of strong and varying winds in winter. Numerical results highlight the importance of storm events in modifying the regional sediment resuspension and transport. During winter, the prevailing winds are typically from the northeast and northwest, interspersed by relaxation periods with weak winds. Winds influenced the currents and sediment movement in the Bohai Sea through several processes: local wind waves and resuspension, coastal-trapped waves in the Bohai Sea, and remotely forced coastal-trapped waves in the Yellow Sea. During northwesterly winds, sediment off the Yellow River Delta was mainly transported eastward along the south coast of Bohai Sea and escaped the Bohai Sea through the southern Bohai Strait. When northeasterly winds prevailed, sediment transport split into three branches: westward into the Bohai Bay, northeastward to the central Bohai Sea, and eastward along the south coast of Bohai Sea. Modeling results driven by synoptic winds indicate a more complex sediment transport pattern than previously understood with monthly average wind forcing. These findings challenge the traditional view of predominantly eastward sediment transport during winter and help to explain the observed grain size distribution in the Bohai Sea, in particular the accumulation of fine-grained sediments northeast of the Yellow River. • Storms are important in modifying the regional sediment resuspension and transport. • Sediment movement in BS depends on local winds, its related CTWs and CTWs in YS. • The formation of muddy areas northeast of the YRD is related to the varied winds. [ABSTRACT FROM AUTHOR]

Chirp profiles collected on the southern Brazilian shelf were combined with sedimentological and hydrodynamic data to characterize shelf geomorphology, focusing on the development of outer shelf bedforms and their genetic links with major oceanic currents. Outer shelf sediment accumulations are interpreted as two scales of bedforms, such as dunes and sand ridges. In the São Paulo Bight, cuspate bedforms are bounded landward by a geomorphological scarp. The sector between Florianopolis and Mostardas also exhibits frequent asymmetric bedforms, whereas the inner- middle shelf is covered by semitransparent sheets. The southern Rio Grande Cone is characterized by stratified deposits covering vast outer shelf areas. Surficial sediment samples reveal a dominantly muddy composition and relatively high carbonate contents. Hydrodynamic data indicate a major influence of the Brazil Current over the São Paulo Bight. The prolific bedform outer-shelf environment is assumed to be mostly relict formed in a transgressive shallow-water setting. The sand ridges are believed to have evolved from a moribund stage characterized by morphological degradation to a relict stage, with preservation enhanced by fine-grained winnowing, coarse sediment armoring, and early cementation. Bedform migration seems to be occurring on the São Paulo Bight due to the presence of a nearly permanent meander of the Brazil Current. Over most of the inner shelf, the northward advection of sediments mainly led by the Brazilian Coastal Current has formed extensive fine-grained deposits. The occurrence of a relict shelf scarp may have conditioned the formation of the outer-shelf bedform environment. The vast spatial distribution of bedforms over most of the outer shelf seems comparable with other shelf areas, such as the south African shelf, dominated by the influence of unidirectional oceanic currents. Dune dimensions are lower on the Brazilian shelf, due to their relict character, the geomorphological configuration of the margin, and the scarcity of sand sources. • Outer shelf along the southern Brazilian margin covered by bedforms • Inner-to-middle shelf advection of fine sediments driven by Brazilian Coastal Current • Two scales bedforms (sand ridges and very large dunes) in a relict to moribund stage • Bedform preservation aided by fine-grained winnowing by the Brazil Current, armouring and cementation • Prolific bedform environment comparable with the south African shelf [ABSTRACT FROM AUTHOR]

Marsh creeks are perceived as important conduits for transporting water and sediment between mudflats and marshes. In order to advance the understanding of the transport mechanisms in creeks, the source and ultimate sink of sediment which moves between mudflats and marshes through creek channels need further investigation. Therefore, two field campaigns were conducted in two intertidal systems with varying sediment availability. The water depth, flow velocity, suspended sediment concentration, and bed level change were measured simultaneously in a marsh creek and on the adjacent mudflat in Chongming Island (China) and in Paulina Saltmarsh (the Netherlands). Paulina Saltmarsh is much smaller, more frequently flooded, and has lower sediment concentration than Chongming. These contrasting conditions allow for a comparison of transport mechanisms and functioning of the creek. Both systems first show that the high suspended sediment concentration (SSC) measured in marsh creeks is mainly the consequence of sediment advection rather than local erosion. In addition, erosion in marsh creeks is usually limited during ebb tides, reducing the export of sediment through these creeks. However, differences have been observed between two systems. The measured SSC was highly asymmetric between flood and ebb tides in Chongming. Large peaks in SSC during the flood period can be observed for most tidal cycles. The marsh creeks in Chongming therefore function as conduits for sediment import. Additionally, there are distinct overbank and underbank tides in Chongming. Sediment was trapped and retained in creeks during underbank tides, which can then be eroded and transported to the marsh during subsequent overbank tides. We also observed that mudflats in Chongming quickly recovered after erosion. These mechanisms have not been observed in Paulina Saltmarsh, where net sediment export via the marsh creek was observed due to a lack of abundant sediment in suspension during flood tides. Furthermore, the remaining bed surface of mudflats after an erosion event was stronger than before, limiting further erosion in Paulina Saltmarsh. These findings from the two systems indicate that the role of creeks in sediment import/export depends on the availability of sediment from mudflats, shedding light on nourishment strategies for salt marshes. • High SSC during flood tides in the studied marsh creeks is attributed to advection of sediment rather than local erosion. • Ebb tides were limited in suspended sediment by various mechanisms, reducing the export of sediment via marsh creeks. • Roles of marsh creeks in sediment delivery depend on the sediment supply from mudflats and hydrodynamic forcing in creeks. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the shallow water (SW) flow over the erodible layer using a fully coupled mathematical model in two-dimensional (2D) space. A well-balanced discontinuous Galerkin (DG) scheme is proposed for solving the SW equations with sediment transport and bed evolution. To achieve the well-balanced property of the numerical scheme easily, the nonlinear SW equations are first reformulated into a new form by introducing an auxiliary variable. Then the DG method is used to discretize the model, in which the FORCE flux is used. By choosing an appropriate value of the auxiliary variable, we can prove that the numerical method can accurately maintain the steady solution in still water, so it is indeed an equilibrium preserving scheme. The well-balanced property can be extended to any numerical flux which satisfies the consistency. Moreover, we investigate the impact on the numerical results if the appropriate value of auxiliary variable is slightly modified. The effectiveness of the numerical method is finally verified by numerical experiments. [ABSTRACT FROM AUTHOR]

• A new stochastic model is proposed for quantifying multiple uncertainties in modelling shallow water-sediment flows • A stochastic Galerkin framework with Haar wavelet expansion and an operator-splitting approach is used • The model reproduces typical shallow water flow-sediment-bed evolutions with multiple uncertainties The interactive processes of shallow water flow, sediment transport, and morphological evolution constitute a hierarchy of multi-physical problems of significant interests in a spectrum of engineering and science areas. To date, modelling shallow water hydro-sediment-morphodynamic (SHSM) processes is subject to multiple sources of uncertainty arising from input data and incomplete understanding of the underlying physics. A stochastic SHSM model with multiple uncertainties has yet to be developed as most SHSM models still concern deterministic problems and only one has been recently extended to a stochastic setting, but is restricted to a single source of uncertainty. Here we first present a new probabilistic SHSM model incorporating multiple uncertainties within the stochastic Galerkin framework using a multidimensional tensor product of Haar wavelet expansion to capture local, nonlinear variations in joint probability distributions and an operator-splitting-based method to ensure that the modelling system remains hyperbolic. Then, we verify the proposed model via benchmark probabilistic numerical tests with joint uncertainties introduced in initial and boundary conditions, matching established experiments of flow-sediment-bed evolutions driven by a sudden dam break and by a landslide dam failure and large-scale rapid flow-sediment-bed evolution in response to flash flood. The present work facilitates a promising modelling framework for quantifying multiple uncertainties in practical shallow water hydro-sediment-morphodynamic modelling applications. [ABSTRACT FROM AUTHOR]

Insight on wave regimes along the world's coastlines is important for virtually all coastal and nearshore marine activities, installations, planning and protection. Waves are pervasive and the dominant source of energy driving extreme sea levels, the transport of pollutants and sediments, erosion, and a major contributor to risks of flooding. We quantify the global spatio-temporal wave conditions along the world's coasts and evaluate the needs for coastal Earth Observation strategies, with the aim, notably, that the derived scales of change can contribute to optimisation of these strategies. A global dominant timescale of 30 days is found in coastal wave variability that is, on average, spatially correlated just over the synoptic 5 degrees' regional scale (≈ 550 km at the equator). This regional-scale dimension suggests that the timing and design of traditional field surveys and observations relevant to a vast array of coastal activities, and which may be expensive in terms of human resources, may be complemented by information gained from satellite Earth Observation that throws light on spatio-temporal scales of wave-energy change along the world's coastlines. [ABSTRACT FROM AUTHOR]

Since the seminal study by Bagnold in 1954, which was inspired by sand movement in the desert and sediment transport in rivers, researchers have continued to investigate inertial and collisional effects in flows of non-Brownian suspensions. This paper overviews several post-Bagnold experimental studies on neutrally-buoyant suspensions that focused on measuring the suspension effective viscosity for conditions in which the particle Reynolds number was greater than 1, Re p > 1. Similar to what was found with Bagnold's experiments, secondary flows and end-wall vortices impact the rheological measurements especially as the rotational speed is increased. Recent experiments using a specialized rheometer that decreases the effect of end vortices demonstrate that the inertial contribution to the effective viscosity increases with a Reynolds number based linearly on particle diameter, Re d. The magnitude of the increase, however, is modest with a doubling in the inertial viscosity as Re d increases from 1 to 500. Larger contributions from inertial and collisional stresses are expected for the flows originally considered by Bagnold — inertial flows involving particles denser than the surrounding fluid. [Display omitted] [ABSTRACT FROM AUTHOR]

Sediment budgeting within a landscape is useful in understanding landscape evolution, and hazard prediction and assessment. It has been observed that only a fraction of the total volume of sediment produced within the system gets exported, implying that a part of the total volume of sediment is stored within the system. This sediment mass gets arrested and stored in compartments within the system and is mobilised during extreme stochastic events. These sediment storage compartments are poorly connected with the channel network and hence, do not supply sediment at steady rates. We have evaluated sediment connectivity and conducted field validation within a 93 km2 mountainous river basin (Pranmati catchment) in the NW Himalayas. This assessment relies on the Index of Connectivity (IC), computed through two methods: one employing the original framework and the C-factor from RUSLE, and the other utilizing a multiple flowpath model that incorporates Manning's roughness coefficient. We developed a storage potential index (SPI) by modifying the basic framework of index of connectivity; SPI indicates the potential of a point on the hillslope to arrest sediment flux and store it. Based on the difference of normalised IC and SPI, we have developed a sediment evacuation susceptibility index (ESI S) that indicates the susceptibility of various parts of the hillslope to get evacuated. Using ESI S , a sediment evacuation susceptibility zonation map was prepared that delineates areas on the basis of their stability. Our study indicates that sediment flux gets arrested at the (1) junction of land use and land cover units that have contrasting sediment transporting capacity, (2) grassland/barren land pockets surrounded by forests, (3) croplands, and (4) landslide debris deposits. The parts of the hillslope in the vicinity of the channel network and areas around steep surfaces are highly susceptible to sediment evacuation. Gentle sloped surfaces away from the channel network are relatively stable. Landslide debris are highly stable units of sediment storage. • Sediment connectivity of a catchment was assessed using index of connectivity (IC). • The IC model was modified to identify potential sediment storage zones (SPI). • Sediment evacuation susceptibility index (ESI S) was formulated using IC and SPI. • Sediment evacuation hazard zonation map was prepared using ESI S. [ABSTRACT FROM AUTHOR]

Bioturbation in estuarine environments describes all sediment reworking processes implied in sediment transport. However, modelling at large spatial and temporal scales remains a challenge because of the need to consider the fauna at the community level, and because animal behaviour is highly seasonal with non-linear effects of macrofauna functional trait interactions. Bioturbation processes can be linked to the activity of organisms, based on the principle of energy ecology, linking the metabolic rate to the erodibility of a sediment colonised by benthic fauna. This study investigates this postulate by evaluating the erodibility parameters of a sediment subjected to: i) the bioturbation under seasonal temperature variations; ii) the synergistic bioturbation of different species. The experimental design consisted of: i) three temperature levels (winter, spring and summer), ii) three types of species duos (Cerastoderma edule and Macoma balthica ; Scrobicularia plana and Hediste diversicolor ; Corophium volutator and Peringia ulvae) at 4 different relative densities. Two successive experiments were carried out on the same individuals: measurement of oxygen consumption of fauna then measurement of the erodibility of the colonised sediment in a flume. The oxygen consumption confirmed that the metabolic rate is a good model of the fauna respiration, regardless of species. The erosion results indicated that the metabolic rate in the case of the fluff layer resuspension is an interesting descriptor for 1) the assessment of the bioturbation under variable temperatures and 2) the integration of the two different bioturbator species that could co-occur in the same habitat. In contrast, the effect of bioturbation on the mass sediment erosion threshold cannot be easily modelled by using the metabolic rate and the classification in functional groups is required. Bioturbation models of the fluff layer using metabolic rate is a promising tool for modelling the effects of faunal communities on sediment transport at the scale of an estuary and over the long term, even projected in the context of global warming. [Display omitted] • Temperature influences the effect of bioturbation on sediment erodibility by regulating physiological metabolism. • The erosion of the fluff layer is positively linked to the total metabolic rate, without consideration of the species. • The mass sediment erosion threshold is negatively impacted by some species, without consideration of their metabolic rate. [ABSTRACT FROM AUTHOR]

Beaches are important coastal features that provide vital ecosystem services; however, these systems are threatened by coastal erosion, sea-level rise, and coastal squeeze. Beach nourishments are a commonly applied coastal protection measure to mitigate erosion and flood risks while maintaining or enhancing recreational values. Nourishments vary in scale from mega-nourishments to small-scale nourishments, where the latter has typically been less studied due to the limited resources for monitoring. Meanwhile, with rising sea levels, the implementation of small-scale nourishments is expected to increase, and there is a need for more knowledge about the morphological evolution and technical lifetime of these interventions. In this study, the morphological responses of small-scale beach nourishment (total volume 20,000 m3 which amounts to 30 m3 added per m alongshore) are observed and quantified over various timescales, considering the initial adjustment, long-term development, and event-driven response. The investigated nourishment is implemented in a partly sheltered coastal embayment in the semi-enclosed Baltic Sea, which has a complex interaction between waves and water levels. Furthermore, the beach is surrounded by hard structures, a rock revetment at the back, and a harbor mole and a groin, influencing the longshore and cross-shore sediment transport. The results show that substantial reduction in subaerial volume can be attributed to specific events. In addition, we observed considerable spatial variation in the sediment re-distribution induced by hard structures and variability in the nearshore bathymetry. The lifetime of the beach nourishment is just over two years. The nourished material remains in the system at the end of the lifetime but is not available for beach recovery. Still, the added subaerial volume has eroded at the midsection, and the protective beach width has been reduced, leaving the rock revetment exposed with reduced protection for the hinterland. The energy conditions at the site are highly episodic, which impacts morphological evolution, and observations indicate that the development is event-driven. • Beach morphodynamics in a low-energy coastal embayment • Episodic wave activity and water level variations are influenced by basin effects. • Morphological response of a small-scale beach nourishment at different timescales • Beach nourishment performance during an extreme storm surge [ABSTRACT FROM AUTHOR]

Proglacial areas in the European Alps and other high-elevation mountains are currently undergoing rapid change due to global warming. Because of rising temperatures, glaciers and glacier forefields are subjected to increased melting and associated sediment export. This observation is increasingly important with respect to high-elevation geomorphological and ecological dynamics, emerging natural hazards and mitigation efforts, and hydropower plant management. It is therefore crucial to analyze the factors and feedback mechanisms governing sediment production, transport, and deposition in these rapidly changing areas. In this study, we investigated the sediment dynamics of a proglacial area located in the Eastern Italian Alps over the period 1969–2021 with the aims of: i) identifying the areas of sediment production; ii) quantifying volumes and rates of bedload sediment transport; and iii) determining the relative contribution of glacial export and fluvial erosion to the total sediment budget. We found that i) apart from glaciers, moraines and fluvial channels have been the most important sediment sources, albeit with substantial differences in terms of connectivity and thus supply rates; ii) the volumes and rates of sediment erosion varied by one order of magnitude (between tens and hundreds of mm per year), and were generally higher along the channel network; and iii) for a relatively shorter time interval between 2005 and 2021, the relative contribution of glacial bedload input with respect to the total sediment budget ranged between 34 % and 37 %, whereas 45 % to 59 % was derived from lateral fluvial erosion. Only a relatively small sediment volume was generated by net channel bed incision. These results imply that most of the sediment released from the proglacial area of the Sulden glacier is progressively transferred to the downstream sector of the channel network, with volumes that range between 931 and 1017 tons yr−1 km−2. These values are in the typical range of sediment export volumes from glaciated basins and highlight the high dynamicity of this region of the Alps. In general, our results confirm the complexity – in terms of spatial and temporal variability – of Alpine proglacial systems and highlight the need to systematically study these areas on a wide spatial and temporal scale, since the information provided by single locations or individual sectors of the sediment cascade, may not be adequate for understanding the dynamics acting in the entire proglacial regions. [Display omitted] • Proglacial areas change rapidly and supply sediment to the downstream valleys. • Moraines and channels are the most important sediment sources. • Glacial and fluvial erosion contribute between 35 % and 50 % to the sediment budget. • The proglacial area of the Sulden glacier is dominated by sediment transport. • In the Sulden region, sediment export may increase in the near future. [ABSTRACT FROM AUTHOR]

Concentrated Solar Power (CSP) plants are typically located in gravelly desert (Gobi) regions because of their level, steady land, and abundant sunlight. The Gobi region has many sand sources, and strong winds accelerate aeolian processes, leading to windblown sand and dust at CSP sites. Large-scale CSP plant heliostats and central building clusters affect Gobi surface aerodynamic roughness and flow field characteristics, leading to a distinct aeolian transportation mechanism compared with that of a natural Gobi surface. Field observations from the 100 MW large-scale Gobi central-tower CSP facility in Dunhuang, China, were used to study a typical aeolian transportation event to gain insight into windblown sand and dust movement in CSP plants. The plant experienced a 36 % reduction in wind friction velocity owing to the increased aerodynamic roughness compared to that in the external environment. The facility reduces the minimum wind friction velocity for sand particle initiation to 0.37 m s−1, which is 30 % lower than that over the typical Gobi surfaces, however, sand accumulation between the heliostats resulted in a 1.8 times higher sediment transport quantity than that transported externally. The blown sand mean saltation layer height in the plant was 0.09 m, similar to that of a sandy desert. The plant surface emits dust, causing PM10 levels to increase to 20,000 μg m−3. Large-scale CSP facilities should remove sand build-up and use windblown sand management methods, such as checkerboard sand barriers and sand-blocking fences, to minimize aeolian transport and dust concerns. • The friction wind velocity inside the Gobi CSP plant experiences a 36 % reduction. • The average saltation layer height inside the plant is 0.09 m, like that of a sandy desert. • Sediment transport quantity inside the plant is 1.8 times higher than that outside the plant. • The plant's surface emits dust, causing PM10 levels to rise to 20,000 μg m−3. • Windblown sand management methods are recommended to minimize aeolian transport. [ABSTRACT FROM AUTHOR]

The occurrence of extreme rainfall events over mountain catchments is likely to trigger mass failure processes on hillslopes and sediment transport within the channel network. Understanding the degree of linkage between the sediment sources and transfer pathways downstream is essential in those catchments where settlements are affected by hydro-geomorphic processes, in order to plan suitable interventions for risk mitigation. A recent storm (October 2020) named "Alex", estimated to be an extratropical cyclone with a more than 100-year return period, hit the Mediterranean Alps at the border between Italy and France, triggering deadly landslides and flooding processes. This work focuses on two adjacent mountain catchments located in the Liguria region (Italy) which share the same outlet, where a small village was damaged by high-magnitude sediment transport and deposition processes during the storm. In order to analyze sediment dynamics at the catchment scale leading to severe damage to the urban settlements at the outlet, an integrated approach was used. Very high resolution (0.5 m) satellite imagery was employed to map the mass failure processes on the hillslopes with a visual interpretation. This dataset was then compared with a map of the Index of Connectivity created using the SedInConnect 2.3 software to characterize the pre-event structural connectivity in both catchments. The integration of these two datasets permitted understanding that debris slides evolving into debris flows downstream supplied most of the sediments to the channel network. These processes concentrated mainly in a specific catchment where hillslopes have the highest connectivity with the valley bottom. This outcome provided a clear evidence that inventory maps developed soon after an extreme event, coupled with sediment connectivity datasets, can provide relevant information for future land management and risk mitigation strategies. These can be exploited to prioritize structural interventions in specific areas, to reduce the connectivity or disconnect inhabited areas from the hydro-geomorphic systems and avoid future damage. • We analyzed the geomorphic impact of a storm on two adjacent mountain catchments. • Debris slides turned into debris flows represented the principal sediment sources. • The Index of Connectivity allowed knowing the degree of linkage with valley bottoms. • Part of the mobilized sediments travelled up to the outlet damaging an urban center. • Inventory maps coupled with sediment connectivity represent relevant potentialities. [ABSTRACT FROM AUTHOR]

Existing prediction formulas for clear-water scour development are typically empirical fittings of lab-scale results. However, it is unreasonable to evaluate the in-situ clear-water scour process around a pile based on small-scale flume tests due to inherent scale effect. This study proposes a time-dependent model of clear-water scour development around a pile foundation under steady currents. A scaling expression of shear stress acting on sediment particles at the front of a circular pile is established based on the phenomenological theory of turbulence. By applying the sediment transport model of flat-bed to local scour around a circular pile, a physics-based ordinary differential equation for predicting the scour depth development is derived. The analytical solution of scour depth development is generally more consistent with the experimental data compared with previous models. The probability density function distribution of the proposed model's error mainly concentrates within the range of ±10%, which is significantly superior to previous models. The proposed model integrates all pertinent parameters that govern the scour process using fundamental principles, rendering it free from scale issues and applicable to prototype conditions. The present model is applied to evaluating clear-water scour development around typical prototype piles with diameters ranging from 2.0 m to 10.0 m. The predicted variations of equilibrium scour time with pile diameter, flow velocity and sediment particle size aligns closely with previous experimental observations. • A time-dependent model of clear-water scour development around a pile foundation is proposed based on the phenomenological theory of turbulence. • The derived analytical solution of scour depth development is more consistent with the experimental data compared with previous models. • The proposed model is free from scale issues and can be applied to prototype conditions. [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to investigate steady current scour around rectangular and square subsea caissons. The caissons, which are representative of subsea structures, have a submerged height ranging from 0.5 to several times their longest base dimension. The flow model used is based on the Reynolds Averaged Navier-Stokes equations, and the scour model simulates bed load and suspended load transport to predict the evolution of the seabed profile. The aim of this study is to investigate the mechanisms of local scour, specifically the contribution of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour. The model is validated through comparisons with experimental measurements, indicating reasonable agreement. Based on the numerical model results, the mechanisms of local scour around square and rectangular caissons are found to be qualitatively similar. If the flow is directed perpendicular to one of the caisson faces, both the horseshoe vortex and the local streamline contraction contribute to scour. The maximum scour depth is located at the two upstream corners of the caisson due to the combined effects of the horseshoe vortex and streamline contraction. When the flow approaches the caisson with a diagonal attack angle of 45°, the two upstream faces act like a streamlined wedge that splits the incoming flow. The study found that the horseshoe vortex almost disappears and the scour is primarily caused by the local velocity amplification at the two side corners. If the flow attack angle is 45°, the scour does not initiate near the upstream corner without the contribution from the horseshoe vortex. These findings are expected to serve as a valuable theoretical foundation for the design of scour protection. • Scour around subsea caissons is studied by fully three-dimensional simulations. • The contributions of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour are identified. [ABSTRACT FROM AUTHOR]

Scour around a circular monopile in coastal regions has been investigated extensively over the past decades, but the time development of scour depth around an offshore-wind monopile under large current–wave ratio still lacks a predictive model. By considering the conservation of sand volume and adopting the conventional exponential law for temporal variation, a semi-empirical model, which has three parameters, i.e., an equilibrium scour depth, a shape coefficient and a scour characteristic time scale, is developed for predicting the time development of scour depth around a monopile under live-bed conditions of combined wave–current flows. A series of laboratory experiments was conducted in current-only and wave–current flows to obtain data for model calibration and validation. Experimental results indicate that adding weak waves on current accelerates scour development, which is successfully captured by the proposed model through using the far-field bottom shear stress as a key model input. The overall model inaccuracy is within 25%, and the model's applicability is further confirmed by field measurements from an offshore wind farm in east China. This model can help to determine the timing of installing scour protection around offshore monopiles, especially for the circumstances with very strong local sediment transport (live-bed). • A new model for scour time development around a circular pile is proposed. • A set of scour tests was conducted in live-bed conditions for calibration and validation. • A field study was carried out for an offshore monopile wind farm in eastern China. [ABSTRACT FROM AUTHOR]

The beach slope β is a key component characterizing the coastal response to wave forcing. Here we investigate the rapid adaptation of the upper beach slope to a given wave forcing, for the case of a lower flat platform. Such types of morphology are found on coral and rocky reef beaches and low tide terrace environments. The influence of the lower platform on this rapid equilibrium beach state is shown to be significant depending on the breaking wave regime. In particular, the width of the platform and its water level can affect the wave dissipation along the inner surf and thus the wave structure entering the swash. This paper provides a classification of the beach slope equilibrium values as a function of the Dean number on a short time scale (individual wave action), based on both offshore and swash wave conditions. A decreasing trend of the beach slope with increasing offshore Dean number (Ω 0) is found for Ω 0 ≲ 2. 7. For Ω 0 ≳ 2. 7 it is observed that the beach slope gradient is strongly controlled by the surf zone dissipation and it becomes necessary to define the swash Dean number (Ω s w) to classify the slope. Finally, a semi-empirical formula for the beach slope evolution in the case of a low tide platform is introduced and tested on two natural low-tide terrace beaches. • Definition of rapid equilibrium beach face slope associated to individual wave action. • Distinction between swash and surf dominated beaches on LTT beaches using Dean number based on offshore or local swash flow characteristics (Ω 0 or Ω s w). • Swash-dominated beaches respond directly to offshore wave forcing. • In surf-dominated beaches the inner-surf zone cannot be disregarded. • A simplified model is proposed to predict the rapid evolution of the beach slope as a function of the swash Dean number Ω s w. [ABSTRACT FROM AUTHOR]

• T c of soils with varied particle size characteristics was contrasted. • Stream power were preferably recommended to predict T c for four soils. • Median particle size (D 50) and kurtosis (K g) were significantly correlated to T c. • The inclusion of D 50 and K g greatly improved the predictive accuracy of T c equations. The sediment transport capacity (T c) is essential for understanding soil erosion and creating soil erosion prediction models. Although many T c equations exist, they are not universally applicable to sloping farmland on the Loess Plateau. To tailor T c equations for this region, T c for four soils (Shenmu Inceptisol (SM I), Shenmu Entisol (SM E), Ansai Inceptisol (AS), and Yongshou Alfisol (YS)) from sloping farmland on the Loess Plateau was determined through flume tests with slopes ranging from 15.84 % to 38.39 % and flow discharges of 0.05 to 0.11 m2 min−1. Additionally, appropriate particle size characteristics were selected to distinguish the soil types. The results revealed that the T c of SM E exceeded that of YS, followed by SM I and AS in descending order. The T c of the four individual soils increased exponentially with flow discharge (Q) and slope (S). T c for individual soils could be satisfactorily predicted using power functions of mean velocity, shear stress (τ), stream power (ω), or effective stream power (R 2: 0.661–0.950, MAE : 0.020–0.110, RMSE : 0.023–0.151), with ω being identified as an optimal hydraulic parameter for simulating T c. In contrast, the unit stream power was a poor predictor of T c for individual soils (R 2: 0.403–0.700, MAE : 0.035–0.123, RMSE : 0.040–0.161). The median particle size (D 50), sorting coefficient, and kurtosis (K g) exhibited highly significant positive correlations with T c (P < 0.01). Finally, a quadratic power equation for Q , S , D 50 , and K g , along with two ternary power equations for ω (or τ), D 50 , and K g were newly constructed, all with satisfactory accuracies (R 2: 0.808–0.826, MAE : 0.061–0.063, RMSE : 0.086–0.090). The inclusion of σ and K g rectified the inaccuracies in predicting T c for all four soils using Q and S equations or ω (or τ). The results of this study offer valuable insights into the construction of the T c equations. [ABSTRACT FROM AUTHOR]

The morphodynamics of inlets and ebb-tidal deltas often exhibit cyclic behaviour, controlled by wave-tide interactions and the influence of these on sediment-bypassing processes. Variation in the form and timing of inlet dynamics can occur in response to changes in the key sediment transport processes and sediment supply, and particularly the relative dominance of differential wave direction driving alongshore sediment transport. This paper investigates the morphodynamics of the Deben ebb-tidal delta through multivariate analysis of multi-annual bathymetry and metocean parameters covering the period 1991 to 2023. Results show that sediment bypassing and associated morphological change in this ebb-tidal delta follows variable behaviour mid-cycle, leading to change in the morphology and configuration of the ebb-delta from cycle to cycle. In the most recent cycle (since 2003), delta volume followed a stepwise growth driven by sediment influx periods, evident primarily in the updrift shoal, followed by cross-shore redistribution. Interannual variability in wave climate was clustered into four groups that capture the relative balance between the dominant NE and SW forcing. Sediment influx periods are mostly associated with subdued SW and increased NE forcing, but the summer and winter NE wave climate play different roles on the up- and downdrift, and upper and lower components of the ebb-delta system. Tide level has increased in the last 33 years, which is strongly correlated with ebb-delta volume increase. Wave and tide conditions have discrete and independent effects on the ebb-tidal delta, whereas wave-tide interactions do not significantly change these underlying influences. • Differential within-cycle behaviour was found in multidecadal bypassing cycles. • Ebb-tidal delta volume has increased via a stepwise growth. • Sediment influx is related to reduced SW and increased NE wave forcing. • Wave and tide conditions have independent effects on the ebb-tidal delta. [ABSTRACT FROM AUTHOR]

Submarine canyons are primary conduits for turbidity currents transporting terrestrial sediments, nutrients, pollutants and organic carbon to the deep sea. The concavity in the longitudinal profile of these canyons (i.e. the downstream flattening rate along the profiles) influences the transport processes and results in variations in turbidite thickness, impacting the transfer and burial of particles. To better understand the controlling mechanisms of canyon concavity on the distribution of turbidite deposits, here we investigate the variation in sediment accumulation as a function of canyon concavity of 20 different modern submarine canyons, distributed on global continental margins. In order to effectively assess the isolated impact of the concavity of 20 different canyons, a series of two-dimensional, depth-resolved numerical simulations are conducted. Simulation results show that the highly concave profile (e.g. Surveyor and Horizon) tends to concentrate the turbidite deposits mainly at the slope break, while nearly straight profiles (e.g. Amazon and Congo) result in deposition focused at the canyon head. Moderately concave profiles with a smoother canyon floor (e.g. Norfolk-Washington and Mukluk) effectively facilitate the downstream transport of suspended sediments in turbidity currents. Furthermore, smooth and steep upper reaches of canyons commonly contribute to sediment bypass (i.e. Mukluk and Chirikof), while low slope angles lead to deposition at upper reaches (i.e. Bounty and Valencia). At lower reaches, the distribution of turbidite deposits is consistent with the occurrence of hydraulic jumps. Under the influence of different canyon concavities, three types of deposition patterns are inferred in this study, and verified by comparison with observed turbidite deposits on the modern or paleo-canyon floor. This study demonstrates a potential difference in sediment transport efficiency of submarine canyons with different concavities, which has potential consequences for sediment and organic carbon transport through submarine canyons. • The impact of submarine canyon concavity on turbidite deposition was assessed. • Distribution of turbidite deposits varies with changes in canyon concavity. • Three distinct deposition patterns were identified. • The recognized deposition patterns align well with the observed turbidite deposits. [ABSTRACT FROM AUTHOR]

While the impact of the spatio/temporal variability of grain size on morphological beach state is reasonably well understood, relatively little is known on its impact at a scale of days/months on aeolian sediment transport. This study focuses on five short intensive wind events during which aeolian sediment transport measurements, beach surface sampling and elevation change surveys were carried out for 1 to 3 days, over a 16-month period on a microtidal beach dominated by offshore winds. Monthly observations show a high temporal variability in beach grain size in relation to the decoupling between hydrodynamic and aeolian processes, from medium sand after a marine storm and inundation of the beach, to very coarse sand after several weeks of storm-force winds. During each wind event, topographic change on the beach ranged from zero, to 0.55 m. The time scale of coarsening depended on the initial beach grain size and could be very fast when the beach was composed of medium sand (e.g. 388 μm sand changed to coarse sand of 547 μm in 40 h). In contrast, it took one month to transition from a coarse median beach grain size of 883 μm to a very coarse one of 1323 μm. This variability in grain size results in dramatically different rates of sediment flux. For example, during average wind speeds of 10 to 14 m/s the sediment flux when the beach was composed of medium sized sand ranged between 21 and 154 kg/m/h compared to 0.4 to 50 kg/m/h when the beach was composed of coarse and very coarse sized grains. Overall, this study highlights the importance of beach grain size variability on aeolian sediment transport and shows that for similar incident wind and climatic conditions aeolian sediment transport rates vary dramatically. The study demonstrates the importance of taking care when using a constant median grain size in the calculation of long-term aeolian sand transport on beaches with heterogeneous spatial and temporal beach grain size variability. • Transport rates can be ten times greater on medium-sized beach than coarse one. • Offshore wind generate a grain size sorting, the finest sands are exported seaward. • Topographic variations of the beach depends on its grain size and sand supply. • The return of fine sediments depends on marine storms occurrence and intensities. [ABSTRACT FROM AUTHOR]