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Laboratory experiments and particle-resolved simulations are employed to investigate the settling dynamics of a pair of rigidly connected spherical particles of unequal size. They yield a detailed picture of the transient evolution and the terminal values of the aggregate's orientation angle and its settling and drift velocities as functions of the aspect ratio and the Galileo number $Ga$ , which denotes the ratio of buoyancy and viscous forces acting on the aggregate. At low to moderate values of $Ga$ , the aggregate's orientation and velocity converge to their terminal values monotonically, whereas for higher $Ga$ -values the aggregate tends to undergo a more complex motion. If the aggregate assumes an asymmetric terminal orientation, it displays a non-zero terminal drift velocity. For diameter ratios much larger than one and small $Ga$ , the terminal orientation of the aggregate becomes approximately vertical, whereas when $Ga$ is sufficiently large for flow separation to occur, the aggregate orients itself such that the smaller sphere is located at the separation line. Empirical scaling laws are obtained for the terminal settling velocity and orientation angle as functions of the aspect ratio and $Ga$ for diameter ratios from 1 to 4 and particle-to-fluid density ratios from 1.3 to 5. An analysis of the accompanying flow field shows the formation of vortical structures exhibiting complex topologies in the aggregate's wake, and indicates the formation of a horizontal pressure gradient across the larger sphere, which represents the main reason for the emergence of the drift velocity.

We investigate how luminescence signals imprinted on fluvial sediments vary depending on the depositional environment and vary through time in the same river. We collected sediment samples from four geomorphically distinct locations on the modern floodplain and modern point bar on the Buffalo River in northwest Arkansas, USA, in order to determine if different depositional environments are associated with distinct bleaching characteristics in the sediments. Our analysis revealed that all samples from different depositional environments yielded ages consistent with modern deposition. The samples collected from the floodplain and bar head contained a higher proportion of grains with residual doses, indicative of incomplete bleaching during transport, while samples from the mid‐bar and bar tail appeared well bleached. Our results are particularly intriguing for two significant reasons. First, they highlight distinct equivalent dose distributions in different depositional environments. Second, they shed light on an intriguing relationship: despite generally well‐bleached modern floodplain samples, ancient sediments from corresponding terraces displayed equivalent dose (De) distributions that suggest partial bleaching in some cases. This research contributes to the growing body of work that seeks to establish a relationship between luminescence properties and sediment transport processes and offers valuable insight into how luminescence signals vary locally in modern fluvial deposits, which can help guide the interpretation of older fluvial deposits. [ABSTRACT FROM AUTHOR]

ABSTRACT The lower Nama Group in southern Namibia contains trace fossils and soft‐bodied and biomineralized macro‐organisms from the terminal Ediacaran Period (ca 550 to 539 Ma), offering insights into early metazoan evolution. Interpretation of the fossilized Nama Group organisms as being preserved in, or very close to, the environments in which they originally lived has yielded insights into organism feeding habits, reproduction and life histories. Sedimentological evidence presented here reveals that typical ‘Nama‐type’ Ediacaran macro‐fossils (Cloudina, Ernietta, Pteridinium and Rangea) in the Dabis and Zaris formations of the Witputz Sub‐basin seldom preserve organisms in life position in their original palaeoenvironments. Both soft‐bodied and biomineralizing organisms were transported in sediment gravity flows (debris flows, turbidity flows and transitional debris flow‐turbidity flow ‘hybrid’ event beds) or combined flow (hummocky cross‐strata) to their terminal environment of deposition in shoreface and offshore shelf settings. Transport has placed studied beds and their associated macro‐organisms in depositional settings detached from the original life habitat, with macro‐organisms sourced from shallower‐water, up‐slope environments. Integrated sedimentological and palaeontological data indicate that the Nama Group may not provide a high‐fidelity record of original Nama ecosystems. Individual macro‐organisms are clasts within beds, and can be horizontal, imbricated or chaotic in orientation. Transport can blend different communities at various scales (bed, outcrop and basin), complicating interpretations of life habitats, species interactions and taxon‐specific ecology, such as feeding behaviour and life position of organisms. Recognition of organism transport also impacts datasets used for comparing global Ediacaran fossil assemblages, with implications for tracking spatial and temporal patterns in early animal evolution. [ABSTRACT FROM AUTHOR]

Predicting the nearshore sediment transport and shifts in coastlines in view of climate change is important for planning and management of coastal infrastructure and requires an accurate prediction of the regional wave climate as well as an in-depth understanding of the complex morphology surrounding the area of interest. Recently, hybrid shoreline evolution models are being used to inform coastal management. These models typically apply the one-line theory to estimate changes in shoreline morphology based on littoral drift gradients calculated from a 2DH coupled wave, flow, and sediment transport model. As per the one-line theory, the calculated littoral drift is uniformly distributed over the active coastal profile. A key challenge facing the application of hybrid models is that they fail to consider complex morphologies when updating the shorelines for several scenarios. This is mainly due to the scarcity of field datasets on beach behavior and nearshore morphological change that extends up to the local depth of closure, leading to assumptions in this value in overall shoreline shift predictions. In this study, we propose an improved hybrid model for shoreline shift predictions in an open sandy beach system impacted by human interventions and changes in wave climate. Three main conclusions are derived from this study. First, the optimal boundary conditions for modeling shoreline evolution need to vary according to local coastal geomorphology and processes. Second, specifying boundary conditions within physically realistic ranges does not guarantee reliable shoreline evolution predictions. Third, hybrid 2D/one-line models have limited applicability in simple planform morphologies where the active beach profile is subject to direct impacts due to wave action and/or human interventions, plausibly due to the one-line theory assumption of a constant time-averaged coastal profile. These findings provide insightful information into the drivers of shoreline evolution around sandy beaches, which have practical implications for advancing the shoreline evolution models. [ABSTRACT FROM AUTHOR]

Within the framework of safeguarding Egypt’s coastal lowlands, which face escalating susceptibility to both climate change and human interventions, this study aims to provide a comprehensive analysis of sediment transport dynamics and their implications, with Damietta serving as a case study. To achieve this, a thorough review of the existing literature on sediment transport dynamics was conducted. MIKE21 Shoreline Morphology (MIKE21 SM) model was employed to simulate longshore sediment transport (LST) dynamics both before and after the construction of Damietta Port (DP). Analysis of the model output revealed that the model underestimated the infl uence of waves, primarily originating from the Northwest, on shaping the LST pattern. The results indicate that the construction of DP led to a reduction in average gross longshore sediment transport (GLST) and average net longshore sediment transport (NLST) by 18%, decreasing from 1.1 to 0.9 106 x m³ /year, and 42%, decreasing from 0.73 to 0.42 x 106 m3/year, respectively. Additionally, the average monthly GLST and NLST reductions were 17% and 37%, respectively, compared to pre-construction conditions. Consequently, this research underscores the importance of continuous monitoring of sediment transport to ensure shoreline stability and protect surrounding ecological systems. This recommendation is vital for managing and mitigating the impacts of ongoing and future coastal interventions. [ABSTRACT FROM AUTHOR]

In this study, an acoustic Doppler current profiler (ADCP) operating at 600 kHz was installed on an ocean data buoy in the Qigu waters, Taiwan, to gather real-time sound echo intensity data. These data were then correlated with turbidity measurements obtained by a turbidimeter mounted on the buoy's mooring line at a water depth of 13 m. The data buoy operated from 6 June to 16 August 2017. During this period, turbidity measurements were recorded from 6 to 21 June 2017. This study established a calibration between the sound echo intensity measured by the ADCP and the turbidity measured using the turbidimeter; a strong linear correlation was discovered between these two variables. This correlation enabled the conversion of echo intensity data into a continuous time series of turbidity measurements, facilitating real-time and long-term monitoring of coastal water turbidity through the deployment of a buoy equipped with an ADCP. The relationships between turbidity and environmental factors such as rainfall, tides, current speeds, and wave activity over an extended period were then investigated. The results revealed that stronger tides and currents in the Qigu waters often lead to higher turbidity, suggesting that these two factors are the primary driving forces for sediment transport in the Qigu waters. Additionally, sampling of water in the Qigu area revealed sediment particles of size ranging from 2 to 120 μm. [ABSTRACT FROM AUTHOR]

This study investigates the morphological evolution of river particles and their mechanical behavior during sediment transport. River particles exhibit distinct shape differences between upstream and downstream sections, with particles becoming progressively rounded downstream. The rounding process is quantitatively described using morphological indices. The analysis reveals upstream particles are more angular, while downstream particles become increasingly rounded due to erosion and abrasion, modeled by a unified abrasion function. The Loop subdivision method effectively simulates this gradual rounding process. Additionally, the Discrete Element Method (DEM) calculates the natural angle of repose for particles with varying erosion levels, showing angles ranging from 38.2° for angular particles to 34.4° for rounded particles, closely matching field observations. The numerical results effectively demonstrate the interlocking effect caused by particle morphology. This research enhances the understanding of sediment transport dynamics and provides a robust framework for modeling particle shape evolution. [ABSTRACT FROM AUTHOR]

This study introduces the fractional stochastic diffusion particle tracking model (FSD-PTM), a novel Lagrangian particle tracking model (PTM) designed to simulate stochastic suspended sediment transport by incorporating fractional Brownian motion (FBM). This FBM-based approach introduces memory into particle movements, particularly when particles are influenced by coherent turbulent structures near boundaries, such as ejection and sweep events. These coherent structures exhibit consistent motion over time, leading to correlated increments in particle movements. In scenarios unaffected by coherent structures, the FBM reverts to the Wiener process, preserving the independent increments. The FSD-PTM is applied to a steady, incompressible, fully developed two-dimensional open channel flow, and Monte Carlo simulations yield ensemble statistics results, including mean, variance, skewness of particle positions, particle velocity, and concentrations. These simulation results validate the FSD-PTM against experimental data, demonstrating its superior performance when considering correlated increments. Without such consideration, concentration profiles generated by previous PTMs fail to reach long-term equilibrium. A key innovation of the FSD-PTM is its integration of correlated motion directly within the governing stochastic differential equation (SDE), eliminating the need for additional terms. This model's flexibility also allows for the incorporation of various particle dynamic models, enhancing its utility for sediment transport analysis. The FSD-PTM represents a substantial advancement in modeling stochastic suspended sediment transport, particularly when particles' movements exhibit correlations due to surrounding turbulence. [ABSTRACT FROM AUTHOR]

The stratigraphic principle of superposition assumes that sediments at surface are youngest. And yet, patches of older preserved landscapes continue to be identified in the regions formerly covered by the Laurentide Ice Sheet. Two gravel pits, at the edge of the western Hudson Bay Lowland near the geographic centre of the North American Ice Sheet Complex, reveal additional patches where older glacial and nonglacial sediment is preserved. These sites expose 1–4 m of a darker, highly overconsolidated, clayier till, and 0–2 m of a lighter, less consolidated, sandier till over glaciofluvial and post-glacial gravels and sands; the waning stages of deposition occurred at 214 ± 22 ka (1σ minimum age model quartz grain optical age estimates, n = 2). This was during the latter end of the cool Marine Isotope Stage (MIS) 7-d (within 1σ range) or near the end of MIS-8 (within 2σ range). Next followed a warmer period similar to, or warmer than, present day with higher precipitation; inferred from pollen and macrofossils deposited in nonglacial low-energy floodplain or pond sediments. Our study highlights the need to accurately date Quaternary sediments, given that the shallowest nonglacial sediments at both gravel pits were deposited during an old (MIS 7) interglacial; there is likely no record of the youngest interglacial (MIS 5). Preservation of older sediment also means that in Quaternary stratigraphy, disjoint regional nonglacial "organic marker beds" should not automatically be considered correlative. Identification of similar "old" patches, together with till stratigraphy and composition, is essential to accurately model glacial sediment transport over time. [ABSTRACT FROM AUTHOR]

This paper introduces a continuous finite element model to simulate fluid flow-bedform interaction problems. The approach utilizes a non-oscillatory finite element algorithm to compute the fluid dynamics by solving the complete Navier–Stokes equations. Additionally, it addresses the evolution of the fluid–bedform interface as a consequence of spatially non-balanced sediment fluxes through the solution of a conservation equation for the erodible layer thickness. A sign preservation algorithm is particularly relevant for landform tracking because a positive definite thickness of the erodible sediment layer is essential to model the interaction between evolving cohesionless sediment layers and rigid beds. The fluid/terrain interface is explicitly captured through a surface tracking methodology. First, new nodes fitting the interface are incorporated into the finite element mesh; then, elements beneath this interface are deactivated, while intersected elements are restructured to get a mesh composed exclusively of tetrahedral elements. Numerical experiments demonstrate capabilities of the method by exploring relevant problems related with civil engineering, such as the evolution of trenches and the scour of a submerged pile. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to obtain a preliminary understanding on the sources of debris flow sediments and the characteristics of organic carbon (OC) transported by debris flow events. Methods: Samples from debris flow and debris flow deposits as well as potential sources in the catchment were collected. For the collected samples, we measured grain size compositions, OC concentrations and properties such as C:N ratio, stable C isotopic composition and OC components derived from nuclear magnetic resonance (NMR) spectroscopy. Results: As inferred from OC concentrations, C:N ratios and δ13C values, we found that OC in debris flow sediments and bare land soils are mainly petrogenic OC, while OC in forest, cropland and grassland soils contained a large fraction of biospheric OC. Fine particles were found to be preferentially transported in debris flow, and the particle selectivity decreased with increasing debris flow erosion intensity. However, no selectivity was observed for OC contained in debris flow, which is different from the widely observed preferential mobilization of OC in sediments by surface erosion. Conclusions: Our results show that sediments in debris flow are mainly sourced from bare lands. The fact that there are no significant differences in the petrogenic OC concentrations in various size fractions of debris flow sediment sources leads to no selectivity of OC in debris flow despite of selectivity of sediment particles. [ABSTRACT FROM AUTHOR]

Bedforms are complex and varied features on riverbeds created by the interaction between flow and sediment particles. Bedform evolution is crucial for understanding sediment transport, bed resistance, and the ecological environment of rivers. In this study, a series of movable-bed dune experiments were conducted utilizing advanced 3D topographic laser scanning technology to precisely measure the 2D and 3D dune bedforms under various conditions. This enabled the detailed analysis of the bedform parameters, including the dune length and height, the crest height, and the trough depth. Furthermore, this study examined the relationship between bed resistance and dune morphology and investigated how the intensity of bedload transport affects bed resistance. The findings indicate that bedload mass transport on the riverbed significantly contributes to increased bed resistance. Given the limitations of the traditional bedload transport rate formulas for dune bedforms, this research introduces a new formula derived from the experimental data. The accuracy of this formula was confirmed using the nonlinear least squares method. Our study enhances the accuracy of sediment transport predictions and provides scientific support for river management and engineering practices. [ABSTRACT FROM AUTHOR]

Understanding the changes of sediment concentration in rivers, especially under heavy rains, is of great significance to accurately evaluate the effectiveness of soil and water conservation measures in the Loess Hilly Area. On July 26, 2017, an extremely heavy rain (maximum rain intensity of 66.6 mm/h, the highest rainfall of 256.8 mm in 10 h, and a return period of 100 years) occurred over the 821 km2 Xiaoli River watershed in the Wuding River watershed. In order to understand the sediment concentration during the heavy rain event, 10 dam‐controlled catchments in the center of the rainstorm (3 in the Xiaoli River watershed and 7 in its adjacent watersheds) without drainage and damage were selected. All the retained runoff and sediment in the check dams were measured by the cross‐sectional survey according to the flood marks left by the heavy rain. Combined with the observed runoff and sediment transport data by the hydrological station at the outlet of the Xiaoli River watershed as well as the deposited sediment investigated in the watershed during the heavy rain event, the change of sediment concentration and the role of check dam were analyzed. Results showed that under heavy rain, all the sediment concentrations of runoff in the dam‐controlled catchments ranged from 344 to 552 kg/m3, suggesting that the sediment retaining effect of slope measures (woodland, grassland, and terrace) is limited and cannot prevent the occurrence of hyperconcentrated flows. The gully measures (check dams) in the Xiaoli River watershed can hold a large amount of sediment under heavy rain and make the runoff no longer a hyperconcentrated flow at the watershed outlet. In order to control the transport of hyperconcentrated flows to the downstream, more attention should be paid to the construction of check dams while carrying out vegetation ecological construction in the Loess Hilly Area. [ABSTRACT FROM AUTHOR]

Soil erosion is a global environmental issue, and sediment transport capacity (Tc) is critical for developing soil erosion models. This study conducted flume drainage experiments at six flow discharges (0.15, 0.25, 0.35, 0.45, 0.55, and 0.65 L s−1) and eight slope gradients (1.5, 3.0, 4.5, 6.0, 7.5, 9.0, 10.5, and 12.0°) to investigate how the Tc of gentle slopes in the northeastern hilly region of China and water erosion factors are related and to establish a Tc model of overland flow. The study demonstrated a power–law relationship between Tc, flow discharge, and slope gradient, as evidenced by a high coefficient of determination (R2; 0.94) and Nash–Sutcliffe efficiency (NSE; 0.92) values. Additionally, there was a positive correlation between Tc and average flow velocity, with R2 and NSE values of 0.86 and 0.84, respectively. Among the hydrodynamic parameters tested, the average flow velocity was determined to be the most effective Tc predictor, surpassing stream power (R2 > 0.7, NSE > 0.7), shear stress (R2 > 0.6, NSE > 0.6), and unit stream power (R2 < 0.5, NSE < 0.5). These findings lay the foundation for developing process‐based sediment transport models for gentle slopes in the northeastern hilly regions of China. [ABSTRACT FROM AUTHOR]

Reservoirs deliver vital ecological services, including water storage and drainage. However, these functions are increasingly compromised by the dual pressures of climate change and human activities. Among the most pressing concerns is reservoir sedimentation, highlighting the urgency of investigating hydrodynamic sediment scouring. This study focuses on the plain reservoirs of Liaoning Province, using the Shifo Temple Reservoir as a case study. An optimized sediment scouring scheme was developed based on the reservoir's hydrodynamic characteristics to improve water and sediment management. A coupled hydrodynamic and sediment transport (ST) model was constructed to simulate runoff dynamics and sediment distribution within the Liao he River Basin, while the MIKE21 model was applied to simulate the interaction between the hydrodynamics and sediment transport. The study analyzed groundwater dynamics across different runoff scenarios, seasons, and representative years, offering a scientific foundation for optimizing water and sediment allocation strategies. The results demonstrated a strong correlation between simulated and observed data during validation, confirming the accuracy of the hydrodynamic simulations. Utilizing the coupled HD and ST modules, the study proposed a sediment transfer scheme. The analysis revealed that flow rates between 165 and 190 m3/s significantly enhance sediment scouring in the long term (2029–2039) compared to the short term (2024–2029), effectively reducing sedimentation, minimizing deposition length, and lowering silt removal costs. The findings offer critical insights for predicting reservoir evolution and conducting risk assessments, thereby contributing to the sustainable management and ecological restoration of water systems in Liaoning Province. [ABSTRACT FROM AUTHOR]

The rapid development of coastal structures on sandy coastlines raises concerns about their impacts on the shoreline's evolution and the sediment transport dynamics. This study utilized a numerical modeling approach to simulate the multi-year response of Haikou Bay's coastline to various nearshore structures, including piers and a large artificial island. The LITLINE module of the MIKE21 (v2020) software was employed to analyze the sediment transport patterns across three distinct coastal segments. The simulation results indicated that the sediment transport directions varied significantly: from west to east in the western segment, from east to west in the middle segment, and convergence toward the center in the eastern segment, divided by a construction trestle. The net sediment transport rates were quantified as 2000 m3/year for the western segment, 8000 m3/year for the middle segment, and 13,000 m3/year (west) and 10,000 m3/year (east) for the eastern segment. Due to the conflicting sediment transport directions on each side of the breakwater, noticeable deposition occurred on both sides. The presence of the artificial island created notable deposition in its wave shadow area, while the overall impact on the shoreline changes diminished over time. These findings underscore the significant influence of human activities, particularly coastal structures, on the natural evolution of shorelines. [ABSTRACT FROM AUTHOR]

In this paper, the hydrographic data, empirical formulas and numerical modelling were used to investigate the longshore sediment transport (LST) rate in the Genaveh port to calculate the sediment accumulation in the harbour basin under the development plan. The Genaveh port is located on the northern coast of the Persian Gulf. Based on the field sediment collection, the type of sediment in this area is fine sand and silty sand. The empirical formulas, LITPACK, and MIKE21-FM were utilised to calculate the LST rate in the region, bathymetric changes in front of the port, and the sediment accumulation in the harbour basin, respectively. The results indicated that the main direction of non-cohesive sediment is from the northwest to the southeast in the region. Moreover, due to the existence of Dareh Gap River, the location of the harbour basin's mouth is important in reducing sediment accumulation in the harbour basin. [ABSTRACT FROM AUTHOR]

The Soil and Water Assessment Tool Plus (SWAT+) model depends on the Modified Universal Soil Loss Equation (MUSLE), which in turn depends on the peak runoff rate for the estimation of soil loss from a catchment. The SWAT+ model generates a random number for each day in the process of peak runoff rate estimation from the catchment. On the other hand, the model provides calibration parameters like the peak rate adjustment factor for sediment routing in the tributary channels and main channels. There is uncertainty that how likely the SWAT+ model estimates the actual peak runoff rates. An improved MUSLE does not depend on the peak runoff rate, and, therefore, it minimizes uncertainty related to the peak runoff rate when estimating soil loss from the catchment in the SWAT+ environment. On the other hand, the effect of the topographic factor of the MUSLE or improved MUSLE on soil erosion and sediment transport is not explicitly explained. Therefore, we modify the source code of the SWAT+ model for sediment yield estimation by replacing the improved MUSLE and the best-fitted equations of the topographic factor in the source code. The modified SWAT+ model showed better performance than the original SWAT+ model. [ABSTRACT FROM AUTHOR]

In the surfzone, breaking‐wave generated eddies and vortices transport material along the coast and offshore to the continental shelf, providing a pathway from land to the ocean. Here, surfzone vorticity is investigated with unique field observations obtained during a wide range of wave and bathymetric conditions on an Atlantic Ocean beach. Small spatial‐scale [O(10 m)] vorticity estimated with a 5 m diameter ring of 14 current meters deployed in ∼2 m water depth increased as the directional spread of the wave field increased. Large spatial‐scale [O(100 m)] vorticity calculated from remote sensing estimates of currents across the surfzone along 200 m of the shoreline increased as alongshore bathymetric variability (channels, bars, bumps, holes) increased. For all bathymetric conditions, large‐scale vorticity in the inner surfzone was more energetic than in the outer surfzone. Plain Language Summary: Circular, rotating flow features, such as eddies, swirls, and vortices mix and disperse material throughout the ocean. Here, circular flow features that can transport sediments, pollutants, and biota from the shore to the continental shelf were investigated using field observations from a 5 m diameter ring of current meters in 2 m depth and from tracking naturally occurring ocean foam visible in optical images of the surfzone (where waves break) spanning 200 m of the coast. The observations show that small‐scale flow patterns become more energetic as ocean waves arrive from a wider range of directions and that large‐scale flow features become more energetic as the seafloor becomes more nonuniform (including holes and channels). Key Points: Surfzone vorticity is estimated for the first time with unique field observations within, across, and along the surfzoneIn situ observations show that small‐scale vorticity injected by breaking waves increases with wave directional spreadRemotely sensed observations show large‐spatial scale vorticity increases as bathymetry becomes more alongshore inhomogeneous [ABSTRACT FROM AUTHOR]

Fluvial cross strata are fundamental sedimentary structures that record past flow and sediment transport conditions. Bedform preservation can be significantly influenced by the presence of larger‐scale topographic features that cause spatial gradients in flow. However, our understanding of the controls on cross strata preservation in the presence of a morphodynamic hierarchy is limited. Here, using high‐resolution bathymetry from a physical experiment, we quantify bedform evolution and cross strata preservation in a zone of flow expansion and deceleration. Results show that the size and celerity of superimposed bedforms decreases along the host‐bedform lee slope, leading to a systematic downstream increase in the sediment accumulation rate relative to bedform celerity. This increase in local bedform climb angle results in the preservation of a larger fraction of formative bedforms. Our results highlight the need to revise current paleohydraulic reconstruction models, and demonstrates that fluvial morphodynamic hierarchy is a fundamental determinant of sedimentary strata. Plain Language Summary: Dune evolution in rivers creates inclined layers of sediment, called cross strata, that are an integral part of the rock record on Earth and Mars. The thickness distribution of cross strata is the primary means of estimating ancient flow and sediment transport conditions. Dunes exist with larger‐scale features, such as bars and larger dunes, in rivers, where a train of dunes responds to flow steering by larger‐scale features through changes in dune size and speed. However, we currently lack data to assess the influence of larger‐scale features on dune evolution and cross strata. Here, we studied dune evolution on the lee side (downstream facing slope) of a larger bedform in an experimental channel, where flow expands and slows down. Using high‐resolution data, we show that the dune size and speed decrease with downstream distance along the host‐bedform lee side. The rate of sediment build‐up relative to dune speed increases downstream, which leads to the preservation of a larger fraction of dunes in cross strata. Results suggest that cross strata preserved in the presence of larger‐scale features are common in the rock record, and we need to revise our current models for estimating past flow conditions from cross strata. Key Points: We characterize bedform evolution and cross strata preservation in a zone of flow expansion and deceleration in a physical experimentBedform size and celerity decrease along the host‐bedform lee slope, causing an increase in aggradation rate relative to bedform celerityA larger fraction of the formative bedforms is preserved as cross strata than typically assumed by paleohydraulic reconstruction models [ABSTRACT FROM AUTHOR]

Background: Gravity-driven depositional processes play a pivotal role in shaping the geomorphology of subaqueous deltas worldwide, particularly by eroding the seafloor, leading to the formation of rugged submarine channels (SCs) and triggering various subaqueous geohazards. A comprehensive understanding of SCs is crucial for elucidating these depositional mechanisms and mitigating the risks associated with submarine geohazards. Although SCs in the Huanghe delta front have been previously identified, often described as seafloor gullies or subsurface "disturbed strata," most studies have primarily concentrated on their engineering geological properties. However, there has been limited research on the scale, morphology, and development of these SCs, especially those that are buried within the stratigraphy. Methods: This study integrates high-resolution sub-bottom data, sediment core analyses, and historical bathymetric data to investigate the morphology, distribution, and formation mechanisms of SCs in the Huanghe subaqueous delta. Results: The SCs, both buried and exposed, are widespread along the middle and upper delta front, predominantly located at or near the landward flank of sediment gravity flow (SGF) -related accumulations. The buried SCs are characterized by cut-and-fill structures with transparent to semi-transparent fills, indicating rapid infilling processes as SGF energy dissipates. These buried channels were preserved within different sets of delta front deposits formed during 1855-1964 CE, 1964-1976 CE, and 1976-2007 CE, with the latter two periods separated by a significant lobe-switching event in 1976 CE. This event, combined with prevailing southeastward sediment transport and erosional regimes, appears to have controlled the preservation of SCs along the delta front: SCs in the Diaokou Lobe's delta front (pre-1976) suffered significant erosion, leaving only one set of channel (erosional remnants) preserved, while the SCs in the Qingshuigou Lobe's delta front (post-1976) are characterized by well-preserved, multi-phase channels at different horizons. The cross-section morphology of the SCs reveal three primary types: symmetrical, asymmetrical, and composite, corresponding respectively to (1) idealized SGF incision, (2) uneven incision intensity on either side of the SCs, and (3) the merging of two or more symmetrical/asymmetrical SCs. Conclusions: We describe in detail the morphology, distribution and development of SCs in the modern Huanghe subaqueous delta. These findings provide insights into the formation and distribution of SCs in other shallow marine settings, particularly in delta front areas, and potentially offer information for disaster prevention and engineering development in such regions. [ABSTRACT FROM AUTHOR]

A comprehensive modeling framework utilizing hydrodynamic and sediment transport models (MIKE Hydro River, MIKE 21 FM, MIKE 21C) was applied to the 33.57 km stretch of the Banshadhara River from Banshadhara bridge, Gunupur to Kashinagar town. Daily discharge, water levels, and sediment data from 2013 to 2022 of Gunupur and Kashinagar gauge stations was used as model input, and calibration–validation of models. Additionally, satellite remote sensing data used for determined Manning's roughness (n) values as well compared the model outputs. Calibration procedures ensured high accuracy, with MIKE Hydro River achieving 98.3% agreement between observed and simulated water levels. 1D sediment transport model showing significant variability in total bed load values ranging from 0.3 to 3.83 m^3/s. The Wilcock & Crowe gravel bed load formula accurately predicted bed load transport within the expected magnitude, albeit tending to overestimate transport, indicative of supply-limited conditions. 2D MIKE 21 FM simulations highlighted flow dynamics, with rapid flood arrival at Kashinagar and varying current speeds along the river, especially at bends. MIKE 21C, focused on the central portion, indicated erosion processes at river bends with high discharge. Sediment transport model accuracy was approximately 86.7%, capturing general trends despite occasional discrepancies. Over a 10-year simulation, erosion trends and potential river course shifting were observed, particularly near bends. The analysis provides valuable insights for river management, flood risk mitigation, water resource management, infrastructure planning, and environmental preservation in the Banshadhara River basin and similar environments. Article Highlights: Accurate modeling predicts river erosion and possible course shifts, vital for flood risk planning. Sediment transport varies widely, indicating complex riverbed dynamics impacting river management. Study offers insights into managing river ecosystems, infrastructure, and environmental preservation. [ABSTRACT FROM AUTHOR]

Floods are the most common and costly disasters worldwide, while spatial flood risk assessment is still challenging due to fewer observations and method limitations. In this study, the flood risk zonation in the Nile districts of the Damietta branch, Egypt, is delineated and assessed by integrating remote sensing with a geographic information system, and an analytical hierarchy process (AHP). Twelve thematic layers (elevation, slope, normalized difference vegetation index, topographic wetness index, modified normalized difference water index, topographic positioning index, stream power index, modified Fournier index, drainage density, distance to the river, sediment transport index, and lithology) are used for producing flood susceptibility zonation (FSZ) and six parameters (total population, distance to hospital, land use/land cover, population density, road density, and distance to road) are utilized for producing flood vulnerability zonation. Multicollinearity analysis is applied to identify highly correlated independent variables. Sensitivity studies have been used to assess the effectiveness of the AHP model. The results indicate that the high and very high flood risk classes cover 21.40% and 8.26% of the area, respectively. In 14.07%, 27.01%, and 29.26% of the research area, respectively, flood risk zones classified as very low, low, and moderate are found. Finally, FSZ is validated using the receiver operating characteristics curve and area under curve (AUC) analysis. A higher AUC value (0.741) in the validation findings demonstrated the validity of this AHP approach. The results of this study will help planners, hydrologists, and managers of water resources manage areas that are susceptible to flooding and reduce potential harm. [ABSTRACT FROM AUTHOR]

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

A one-dimensional numerical overland flow model based on the cascade plane theory was developed to estimate rainfall-induced runoff and soil erosion on converging and diverging plane surfaces. The model includes three components: (i) soil infiltration using Horton's infiltration equation, (ii) overland flow using the kinematic wave approximation of the one-dimensional Saint-Venant shallow water equations for a cascade of planes, and (iii) soil erosion based on the sediment transport continuity equation. The model's performance was evaluated by comparing numerical results with laboratory data from experiments using a rainfall simulator and a soil flume. Four independent experiments were conducted on converging and diverging surfaces under varying slope and rainfall conditions. Overall, the numerically simulated hydrographs and sediment graphs closely matched the laboratory results, showing the efficiency of the model for the tested controlled laboratory conditions. The model was then used to numerically explore the impact of different plane soil surface geometries on runoff and soil loss. Seven geometries were studied: one rectangular, three diverging, and three converging. A constant soil surface area, the rainfall intensity, and the slope gradient were maintained in all simulations. Results showed that increasing convergence angles led to a higher peak and total soil loss, while decreasing divergence angles reduced them. [ABSTRACT FROM AUTHOR]

Sediment transport is a geophysical phenomenon characterized by the displacement of sediment particles in both the horizontal and vertical directions due to various forces. Most of the sediment transport equations currently used include only parameters related to the horizontal direction. This study measured both instantaneous longitudinal and vertical parameters, i.e., velocities and forces, and found that the magnitude and direction of the vertical force play an important role in sediment incipient motion. An innovative experimental system was developed to investigate the effect of vertical force on incipient motion in rapidly varying flows. A quadrant analysis of the instantaneous measured forces on the critical shear stress was performed. The research revealed that upward positive vertical forces enhance particle mobility, whereas downward negative vertical forces increase particle stability. Novel equations have been developed to represent the influence of vertical forces on sediment transport. A comprehensive critical Shields stress for sediment transport was proposed, extending the Classic Shields diagram to encompass the incipient motion in highly unsteady flows. [ABSTRACT FROM AUTHOR]

Background: The July flood 2021 at the mountain front of the Eifel-Ardennes Mountains and their foreland resulted in the flooding of the lignite mining area of Inden in Germany. The mining activities resulted in large-scale anthropogenic changes to the relief and fluvial system, leading to a landscape that is no longer adjusted to the recent process-response system. This paper concentrates on the Inde River, where lignite mining led to the relocation of a 5-km-long river section. The flood event resulted in the temporary avulsion of the Inde River into the former channel and, ultimately, in the flooding of the open-cast lignite mine Inden. Results: The flooding of the open-cast lignite mine Inden led to headwall erosion and enormous sediment mobilisation, mobilising more than half a million cubic metres of sediment within a few hours, forming a 700-m-long deeply incised channel cut. Thereby, the underlying bedrock, near-subsurface man-made structures, and former river channels influence the erosional processes to different degrees. Surface erosion is likely to be the decisive process, and subsurface erosion is likely to play a secondary role. In both cases, former channels and mill ditches were likely impacting the course of erosional processes. Conclusions: During high flood events open-cast mining sites in floodplains are endangered by enormous erosion and sediment transport within a short period of time (several hours). Understanding such complex erosion and depositional processes in open-cast mining areas could provide a blueprint for geomorphological processes and hazards in these anthropogenically shaped fluvial landscapes. Further, information on historic impact in the area is crucial to estimate potential risks. [ABSTRACT FROM AUTHOR]

Fluvial sediment dynamics in mountain rivers are changing rapidly in a degrading cryosphere, raising the potential for erosive rainfall and runoff and detrimental effects on downstream areas. Hence, we need to understand better what characterises and drives episodic pulses of water and suspended solids in rivers. Here, we infer different types of such sediment-discharge events from 959 automatically detected events based on 16 metrics derived from 15 min time series of streamflow and suspended sediment concentrations from Vent–Rofental in the high Ötztal Alps, Austria. We use principal component analysis to extract uncorrelated event characteristics and cluster event types with a Gaussian mixture model. We interpret the thus inferred event types with catchment metrics describing antecedent conditions, hydrometeorological forcing, and fraction of catchment area with freezing temperatures and snow cover. We find event magnitude, hysteresis, and event shape complexity to be the main factors characterising the overall event regime. The most important characteristics distinguishing the event types are suspended sediment and streamflow magnitude and complexity of the hydro- and sedigraphs. Sediment-discharge hysteresis is less relevant for discerning event types. We derive four event types that we attribute to (1) compound rainfall–melt extremes, (2) glacier and seasonal snowmelt, (3) freeze–thaw-modulated snowmelt and precipitation events, and (4) late-season glacier melt. Glacier and snowmelt events driven by warm conditions and high insolation were the most frequent and contributed some 40 % to annual suspended sediment yield on average; compound rainfall–melt extremes were the rarest but contributed the second-highest proportion (26 %). Our approach represents a reproducible method for objectively estimating the variety of event-scale suspended sediment transport conditions in mountain rivers, which can provide insights into the contribution of different drivers to annual sediment yields in current and future regimes. Our findings highlight the importance of both meltwater and rainfall–runoff as drivers of high-magnitude suspended sediment fluxes in mountain rivers. [ABSTRACT FROM AUTHOR]

Morphometric analysis of previously unresearched tributary junction fans (TJFs) of the Spiti valley cold desert, India, was conducted to understand the factors influencing their development. An integrated remote sensing and field approach was employed, including the development of multi-method morphometric indices viz. fan conicality (FCI), sweep angle (SA), fan width-to-length ratio (W/L), feeder stream-order and valley floor width-to-height ratio (Vf). Such TJFs, which are the most suitable cultivation and settlement sites in this region, were found to be largely polygenic and planimetrically confined, with many being multi-staged in terms of their development. The results of morphometric analyses reveal that the TJFs are relatively smaller but steeper than their counterparts in other settings, with high relative topographic confinement causing the construction of smaller and steeper fans. The competence of the feeder stream, along with associated processes, notably influences fan morphology using differential sediment transporting capacity. TJFs created by more competent streams are less steep, more influenced by topographic confinement and more vulnerable to truncation by the trunk stream. Furthermore, tectonically induced base-level fall and resultant downcutting in confined environments have caused the formation of truncated, multi-staged and entrenched fans and are primarily responsible for coupling between TJF catchments and trunk stream in the study area. [ABSTRACT FROM AUTHOR]

Introduction: The thickness of ground substrate in shallow mountainous areas is a crucial indicator for substrate investigations and a key factor in evaluating substrate quality and function. Reliable data acquisition methods are essential for effective investigation. Methods: This study utilizes six machine learning algorithms -Gradient Boosting Machine (GB), Random Forest (RF), AdaBoost Regressor (AB), Neural Network (NN), Support Vector Machine (SVM), and k-Nearest Neighbors (kNN) -to predict ground substrate thickness. Grid search optimization was employed to finetune model parameters. The models' performances were evaluated using four metrics: mean squared error (MSE), root mean squared error (RMSE), mean absolute error (MAE), and the coefficient of determination (R2). The optimal parameter combinations for each model were then used to calculate the spatial distribution of ground substrate thickness in the study area. Results: The results indicate that after parameter optimization, all models showed significant reductions in the MSE, RMSE, and MAE, while R2 values increased substantially. Under optimal parameters, the RF model achieved an MSE of 1,589, RMSE of 39.8, MAE of 26.5, and an R2 of 0.63, with a Pearson correlation coefficient of 0.80, outperforming the other models. Therefore, parameter tuning is a necessary step in using machine learning models to predict ground substrate thickness, and the performance of all six models improved significantly after tuning. Overall, ensemble learning models provided better predictive performance than other machine learning models, with the RF model demonstrating the best accuracy and robustness. Discussion: Moreover, further attention is required on the characteristics of sample data and environmental variables in machine learning-based predictions. [ABSTRACT FROM AUTHOR]

The river flow transports sediment, resulting in the formation of alternating sandbars in the riverbed. The underlying physics is characterized by the interaction between flow and river geometry, necessitating an understanding of their inseparable relationship. However, the dynamics of river flow with alternating sandbars are hard to understand due to the difficulty of measuring flow depth and riverbed geometry during floods with current technology. This study implements an innovative approach utilizing physics-informed neural networks (PINNs) to estimate important hydraulic variables in rivers that are difficult to measure directly. The method uses sparse yet obtainable flow velocity and water level data. The governing equations of motion, continuity, and the constant discharge condition based on the mass conservation principle are integrated into the neural network as physical constraints. This approach enables the completion of sparse velocity fields and the inversion of flow depth, riverbed elevation, and roughness coefficients without requiring direct training data for these variables. Validation was performed using model experiment data and numerical simulations derived from these experiments. Results indicate that the accuracy of the estimations is relatively robust to the number of training data points, provided their spatial resolution is finer than the wavelength of the sandbars. The inclusion of mass conservation as a redundant constraint significantly improved the convergence and accuracy of the model. This PINNs-based approach, using measurable data, offers a new way to quantify complex river flows on alternating sandbars without significant updates to conventional methods, providing new insights into river physics. [ABSTRACT FROM AUTHOR]

In this numerical study, TELEMAC-3D and GAIA solvers were coupled to examine the three-dimensional (3D) flow and morphological changes in an alluvial channel due to sand mining. The 3D modeling approach enables a comprehensive analysis of the interactions between bed shear stress, velocity field, secondary flows, and turbulent kinetic energy that affect sediment transport processes near the mining pit. First, the numerical model was applied to two previous experimental studies on straight channels with mining and validated with their published data. Thereafter, model applications are demonstrated to a 180° curved channel with a mining pit at three different locations. The results indicate that the morphological changes in curved channels with a mining pit were relatively more asymmetrical in contrast to straight channels. The most severe bed degradation of 76.8% was observed at the outer bank downstream of the pit located at the end of 180° bend. The analysis of bed shear stress in the curved channel revealed higher values at the outer bank and lower values around the inner bank downstream of the pit location. Additionally, the presence of the mining pit had a significant impact on the structure and location of the secondary flow recirculation cell in the curved channel. The results indicate that turbulent kinetic energy increases significantly in the vicinity of the mining pit in both straight and curved channels. This increased turbulence due to bed topography may account for the enhanced secondary flow and sediment movement observed in the pit region. [ABSTRACT FROM AUTHOR]

Wave nonlinearity and free surface effects are recognized as important factors for sediment transport under nonlinear waves. Existing studies primarily focus on oscillatory water tunnel (OWT) instead of real waves for sediment transport due to the challenges in constructing real-scale wave tank. In contrast to OWT, the wave tank performs both wave nonlinearity and free surface effect on sediment transport. A numerical wave-sediment tank is developed for strong nonlinear wave propagation over sediment bed with low computational cost. The nonlinear wave is generated by defining the inlet boundary condition and absorbed by using a damping function, and the classical volume of fluid method is used to handle the free surface. The numerical tank further considers particle wake vortex effect and modifications in relative velocity of high sediment concentration, and incorporates phase lag, mass conservation, acceleration effect, and asymmetric wave boundary layer into near-bed sediment conditions. Therefore, the numerical tank avoids complex calculations for near-bed hyper-concentrated sediment in comparison with a two-phase model, i.e., the calculation of particle collision, friction, and detection of mobile bed surface. The numerical tank reasonably agrees with large-scale wave flume experiments and a two-phase model including free surface wave, and successfully performs sediment transport induced by strong nonlinear (second-order Cnoidal) wave. Compared to the OWT, the extra onshore streaming caused by free surface wave significantly enhances onshore sediment transport. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of sizing the spillway of a closed check dam. Check dams are structures designed to control the solid transport and morphology of mountain streams. Paradoxically, however, their spillways are typically sized in clear-water conditions. The paper first analyses the behaviour of a check dam under clear water and then under live-bed conditions which is by far the most frequent operating condition. The theoretical approach is based on the conservation equations of solid mass, total mass, momentum and energy of the flow. The results of the theory are then compared with the results of some experiments in a laboratory channel equipped with a closed circuit for solid and liquid flow rates. The comparison between experiments and theory shows the validity of the approach. As expected, in some conditions that are far from rare, the design made in the clear-water condition is not safe. [ABSTRACT FROM AUTHOR]

The seabed and the water column are tightly coupled in shallow coastal environments. Numerical models of seabed‐water interaction provide an alternative to observational studies that require concurrent measurements in both compartments, which are hard to obtain and rarely available. Here, we present a coupled model that includes water column biogeochemistry, seabed diagenesis, sediment transport and hydrodynamics. Our model includes realistic representations of biogeochemical reactions in both seabed and water column, and fluxes at their interface. The model was built on algorithms for seabed‐water exchange in the Regional Ocean Modeling System and expanded to include carbonate chemistry in seabed. The updated model was tested for two sites where benthic flux and porewater concentration measurements were available in the northern Gulf of Mexico hypoxic zone. The calibrated model reproduced the porewater concentration‐depth profiles and benthic fluxes of O2, dissolved inorganic carbon (DIC), TAlk, NO3 and NH4. We used the calibrated model to explore the role of benthic fluxes in acidifying bottom water during fair weather and resuspension periods. Under fair weather conditions, model results indicated that bio‐diffusion in sediment, labile material input and sediment porosity have a large control on the importance of benthic flux to bottom water acidification. During resuspension, the model indicated that bottom water acidification would be enhanced due to the sharp increase of the DIC/TAlk ratio of benthic fluxes. To conclude, our model reproduced the seabed‐water column exchange of biologically important solutes and can be used for quantifying the role of benthic fluxes in driving bottom water acidification over continental shelves. Plain Language Summary: In coastal environments where water is shallow, significant interactions occur between the seabed and the overlying water column. In the Northern Gulf of Mexico (NGoM) hypoxic zone, the seabed is believed to play an important role in the acidification of bottom ocean water. In this study we use a numerical model to understand how the seabed can affect bottom water acidification over the NGoM hypoxic zone. We found that during fair weather periods, mixing in the sediment bed due to biological activity, organic matter supply from the water column to the sediment, and the porosity of sediment itself can largely affect the role of the seabed in acidifying the bottom water. When the ocean condition is highly dynamic and resuspension occurs, the contribution of the seabed to bottom water acidification will likely be enhanced. Key Points: A coupled water column biogeochemical‐seabed diagenetic model is updated to include dissolved inorganic carbon (DIC) and TAlk for ocean acidificationThe modeled impact of benthic fluxes on bottom water acidification during quiescent periods is impacted by the intensity of bio‐diffusionResuspension enhances bottom water acidification by increasing the benthic flux DIC/TAlk ratio [ABSTRACT FROM AUTHOR]

Cable bacteria exhibit a unique metabolism involving long‐distance electron transport, significantly impacting elemental cycling in various sediments. These long filamentous bacteria are distributed circumglobally, suggesting an effective mode of dispersal. However, oxygen strongly inhibits their activity, posing a challenge to their dispersal through the water column. We investigated the effective dispersal of marine cable bacteria in a compartmentalised microcosm experiment. Cable bacteria were grown in natural 'source' sediment, and their metabolic activity was recorded in autoclaved 'destination' cores, which were only accessible through oxygenated seawater. Colonisation occurred over weeks, and destination cores contained only one cable bacterium strain. Filament 'snippets' (fragments with a median size of ~15 cells) accumulated in the microcosm water, with about 30% of snippets attached to sediment particles. Snippet release was also observed in situ in a salt marsh creek. This provides a model for the dispersal of cable bacteria through oxygenated water: snippets are formed by filament breakage in the sediment, released into the overlying water and transported with sediment particles that likely offer protection. These insights are informative for broader theories on microbial community assembly and prokaryotic biogeography in marine sediments. [ABSTRACT FROM AUTHOR]

Tidal flats are valuable ecosystems that depend on complex biogeomorphic processes between organisms and sediment transport. Climate change has led to a rise in extreme weather events, such as storms. This, in turn, has increased sediment dynamics and created risks for the benthic communities inhabiting tidal flats. However, replicating sediment disturbances caused by extreme weather is difficult. To overcome this, we used the plow rake to enhance the natural tidal currents and wave conditions to simulate intensified sediment dynamics. The raking disturbance was repeated on two intertidal zones with different inundation frequencies and wind fetch levels to simulate the increasing frequency of storm impact on sediments due to climate change. We compared the measurements of sediment dynamics and macrofauna between plots that were raked and the control plots that were only influenced by natural hydrodynamics. Results showed that tidal flat sediments experienced erosion by 10–20 mm after six times biweekly raking treatments, depending on the site‐specific hydrodynamic conditions. Sediment dynamics served as a helpful tool for monitoring the species distribution regarding mobility traits: the high dynamic exposed sites were inhabited by mobile species, while the low dynamic sheltered sites were characterized by less‐mobile species. Moreover, the raking treatment decreased the abundance of species with immobile traits, yet the species composition did not experience significant change. Overall, the present findings indicate that tidal flats with low sediment dynamics and immobile macrofauna are at higher risk of declining abundance under intensified sediment disturbances than areas with high sediment dynamics and mobile macrofauna. [ABSTRACT FROM AUTHOR]

During the Late Paleozoic–Early Mesozoic Era, the sediment transport system and tectonic regime in the southeastern margin of the South China Block (SESCB) all changed, significantly affected by the Paleo-Pacific subduction. However, controversy exists about the Paleo-Pacific subduction's initiation time. This study uses detrital zircon U-Pb ages to discuss the Late Triassic source-to-sink system in the SESCB. It provides some references for the Paleo-Pacific subduction process based on crucial age information and zircons' trace elements. The paleogeography and similarity of detrital zircon age distribution indicate that three sinks were found in the SESCB during the Late Triassic: 1. the Yangchun-Kaiping-Gaoming area, comprising major age ranges of 260–220, 460–400, and 1 200–800 Ma, which might be sourced from the Yunkai terrane; 2. the Jiexi-Kanshi-Nanjing area, characterized by the significant age component of 2 000–1 800 Ma, which corresponded to the Wuyi terrane; 3. the Xinan area, consisting of significant age groups of 290–250 and 380–320 Ma, which might be sourced from the magmatic rocks formed by the Huinan Movement and Paleo-Pacific subduction. Note that 290–250 Ma zircons were widely distributed in the Upper Triassic strata, and their trace elements suggested the existence of a magmatic arc near the SESCB during the 290–250 Ma. Thus, we propose that the Paleo-Pacific subduction might have begun in the Early Permian. [ABSTRACT FROM AUTHOR]

Enzyme-induced carbonate precipitation (EICP), which precipitates calcium carbonate within the soil matrix to cement the granular grains, presents a promising bio-mediated approach for scour countermeasures. This study explores the erosion performance of bio-cemented sand in a closed-conduit flume system, investigating the effectiveness of EICP in mitigating scour and reducing erodibility. Various parameters such as curing duration, cementation degrees and urease activities are examined to understand their influence on erosion behaviors. Furthermore, the study incorporates the analysis of calcium carbonate content and crystal microstructure to provide a better understanding on the EICP mechanism in scour mitigation. These results highlight the critical role of the interaction between calcium carbonate content and crystal features in determining the effectiveness of erodibility reduction. As the precipitated amount increases, the cemented soil exhibits enhanced hydraulic erosion resistance, with the erosion mode shifting from particle erosion and aggregated detachment to chunk fracture. In other words, the mode of sediment transport essentially is affected by the variations in crystal size, crystal quantities and deposited morphology. Two predictive formulas for threshold Shields parameter and erosion rate are also developed. Notably, the cemented soil could maintain its stability under an elevated flow of 4 m/s under an EICP treatment with 1 M of urea and calcium chloride, and a curing duration of 24 h. These findings are anticipated to serve as a valuable theoretical foundation for engineering applications. [ABSTRACT FROM AUTHOR]

Although the Carpathian Mts. area is considered as extremely prone to surface erosion which results in capacity loss of the dammed reservoirs, a lack of data to follow details of this process is perceivable. The research of the selected sediment fractions transport tracking was conducted using the capabilities of the digital platform—Macromodel DNS (Discharge‐Nutrient‐Sea) for the catchment with drinking water reservoir in the Polish part of Western Carpathian. The continuity of sediment transport simulation in two hydrologically different elements of the catchment—the river and the reservoir—was possible due to consolidation of two models in the platform—SWAT (Soil & Water Assessment Tool) and AdH/PTM (Adaptive Hydraulics Model/Particle Tracking Model). The result of those modules' integration was a database for tracking the individual sediment fractions delivered to the reservoir and deposited in specific reservoir zones. The implementation of climate and land use change scenarios allowed additionally to analyse the estimation of those processes in the future. The simulation outcomes consist of daily flows and monthly sediment loads at the reservoir inflow and the individual sediment particle fractions deposition location inside of the reservoir. [ABSTRACT FROM AUTHOR]

ABSTRACT Present day submarine canyons are active conduits for the transfer of large volumes of sediment, carbon and pollutants from continents to oceans. However, the evolution of submarine canyons over geological timescales remains poorly understood due to their erosional nature and low preservation potential. The Late Cretaceous Punta Baja Formation represents a well‐preserved submarine canyon‐fill that evolved on a tectonically‐active ocean‐facing margin. Exposures provide kilometre‐scale continuous strike and dip sections of the 120 m thick and 1.2 km wide feature. An inherited tectonic fabric influenced the location and orientation of canyon incision into fluvial bedrock. The stratigraphic evolution of the Punta Baja submarine canyon is reconstructed from incision to fill, which shows that it remained an active sediment conduit throughout the time represented by the preserved fill. The depositional architecture of the north–south oriented erosionally confined canyon‐fill is asymmetrical, with sub‐vertically stacked channel‐fills to the west, and an overbank confined by the canyon margin to the east. Sedimentary process interactions led to depositional patterns that are considered distinct to submarine canyon fills. Dynamic topography generated by mass‐wasting processes captured sediment and drove knickpoint development, an autogenic mechanism that modifies sediment delivery to the ocean floor. Widespread upstream dipping surfaces in channel‐fills are interpreted as the stratigraphic expression of upstream migrating supercritical‐flow bedforms, which played an important role in sediment storage and transport in the canyon. The steep relief and internal topography of canyons leads to complicated and characteristic confined overbank flow behaviour and depositional patterns. This study provides insight into how processes that are observed in modern canyons are selectively preserved through the lifetime of the canyon and construct or destroy stratigraphy on geological timescales. [ABSTRACT FROM AUTHOR]

Depth of closure (DOC), the point in a beach profile where surface wave action no longer impacts the sediment on the seabed, is used in several coastal engineering application (e.g., beach fill in beach nourishment project, placement of dredged materials). Measurement of DOC requires long term measurements on the evolution of coastal profile data which is not readily available for many locations around the world. Empirical formulation relating the DOC with statistical properties of wave height and period and other drivers of coastal profile are often used to compute DOC for wide range of applications. In this study, empirical formulation and associated uncertainty of standard models used to calculate DOC are revisited. These models are evaluated and compared using local wave data and recalibrated to improve local efficacy. Recalibrated models are then applied to climate change models to project future DOC and examine coastal retreat along the coast of Louisiana. [ABSTRACT FROM AUTHOR]

The Paleogene paleotopography of the western United States, which may grant insight into Farallon subduction dynamics and North American Cordillera orogenic processes, can be constrained by reconstructing drainage networks through sediment provenance studies. In the northern Sierra Nevada, the provenance of SW-directed, Paleogene paleochannel deposits is controversial; prior studies favor either sources proximal to the deposits or distal source areas in central Nevada. These different hypothesized source areas would have contrasting implications for the paleotopography of the Sierra Nevada and western Basin and Range. We conducted a new provenance analysis of paleochannel deposits in the Sierra Nevada and western Nevada using new and compiled detrital zircon U-Pb age data from across the preserved paleochannel network, together with compiled bedrock geochronologic ages of potential sediment source areas for the paleochannel deposits. The geochronology compilation of potential source areas reveals systematic longitudinal variations in bedrock ages within the study area. Jurassic ages are present primarily in the western Sierra Nevada batholith, Cretaceous ages are dominant in the eastern Sierra Nevada batholith, and Eocene ages are present only in north-central Nevada. The distribution of potential source ages allows confident inference of sediment provenance from detrital zircon U-Pb ages. The distributions of detrital zircon U-Pb ages in the paleochannel deposits can be categorized into three distinct types. The first type, found in the vicinity of Malakoff Diggins State Historic Park (SHP) and further northwest, is dominated by Jurassic, Paleozoic, and Precambrian ages reflecting derivation from local sources in the western Sierra Nevada, and also contains scattered Eocene ages. The lack of Late Cretaceous ages in these samples, despite the presence of Late Cretaceous plutons in close proximity to the east, suggests small sediment source areas with fluvial transport of zircon grains no farther than 50 km. The few Eocene ages in these samples likely reflect volcanic air fall, consistent with an overlying tuff at one sample site that is interpreted to have its volcanic source to the north, outside the paleochannel network. The second zircon age distribution type, from samples south of Malakoff Diggins SHP, includes Cretaceous and Jurassic ages representative of exposed bedrock across the entire width of the Sierra Nevada batholith but no Eocene ages. This combination of ages suggests a sediment source area that encompassed the entire batholith but did not include north-central Nevada. The third zircon age distribution type, from samples to the northeast of Malakoff Diggins SHP, contains Jurassic, Cretaceous, and Eocene ages consistent with fluvial derivation of sediment from the entire width of the Sierran batholith as well as from north-central Nevada. This third type only occurs in fluvial deposits interbedded with Oligocene ignimbrite tuffs, whereas samples older than the Oligocene tuffs belong to zircon age distribution types 1 or 2. Thus, prior to the emplacement of Oligocene ignimbrites, there is no evidence of fluvial transport of sand-sized sediment from north-central Nevada sources to Sierran paleochannel deposits. The lack of pre-Oligocene fluvial transport across the Sierra Nevada may reflect either a Paleogene drainage divide that separated the Sierra Nevada from north-central Nevada or a large-scale knick zone with a low-gradient upstream reach that trapped sand and larger sediment. The first arrival of fluvially transported Eocene zircon grains following Oligocene ignimbrite emplacement suggests that ignimbrite volcanism, and related hinterland uplift, established or promoted sediment transport from north-central Nevada across the Sierra Nevada by driving drainage reorganization or steepening existing channels. Our provenance analysis broadly confirms previous paleochannel network reconstructions, especially for the Ancestral Yuba River, and thus validates the use of paleochannel deposits as a datum by which to infer post-Paleogene tilting of the northern Sierra Nevada. Azimuthal trends in Ancestral Yuba River paleochannel gradient suggest ~0.6° SW-directed, post-Paleogene tilting of the northern Sierra Nevada, which would have resulted in ~1 km of uplift of the range crest. Such a magnitude is consistent with Eocene–Oligocene stable isotope paleoelevation estimates. [ABSTRACT FROM AUTHOR]

In the Tsitsa River catchment of the Eastern Cape Province, South Africa, concerns regarding the sedimentation of a proposed large, multipurpose, in-channel water storage scheme prompted investigations of sub-catchment suspended sediment loads and yields. Confluence-based fingerprinting and source apportionment was undertaken to explore whether this simple approach could identify relative sub-catchment contributions to downstream sediment loads, supplementing modelling and direct sampling. In November 2018, fine sediment sequestered in bed substrates was sampled above and below confluences, using a resuspension technique. The < 63 µm sample fraction underwent analysis of mineral magnetic properties, gamma emitting radionuclide activities and geochemistry to identify suitable tracers. Conservatism and range tests were used to select different combinations of composite fingerprints at seven confluences. Bivariate source apportionment using an unmixing model showed that the approach could be used as a preliminary means of determining relative sub-catchment sediment contributions. Catchment characteristics such as geology and land cover, as well as land tenure and management, were considered as explanatory factors for the difference in sediment contributions. The results for most sub-catchments were broadly similar to those from other studies. Shortcomings of this approach included the reliance on a single sampling effort, and uncertainty associated with sub-catchment sediment transport and residence times. [ABSTRACT FROM AUTHOR]

Before the increase in anthropogenic activities, the global coastal ocean was a net autotrophic system. From human activity and the evolution of the earth, changes have been generated in its continents, oceans, atmosphere and life. Transport of sediments and bioelements to the coastal zone has been drastically altered, and there is debate about whether this zone is autotrophic or heterotrophic. This work carried out an exploratory study of five sandy beaches in the central coastal area of the state of Veracruz, three urban beaches on a gradient of anthropogenic activities in the Metropolitan Zone of Veracruz (ZMV) and two natural, non-urbanized beaches far from the ZMV to determine the concentrations and biochemical characteristics of the heterotrophic bacterial groups found in samples of surface marine sediments during two contrasting seasons in the region: dry season and rainy season. The presence of heterotrophic bacteria reflected the degree of anthropogenic disturbance that each beach presents, with a tendency to concentrate mainly on those close to urban centers. On the other hand, the anthropogenic disturbance gradient did not influence the diversity of biochemical characteristics of heterotrophic bacteria. [ABSTRACT FROM AUTHOR]

[Objective The aims of this study are to analyze the response of farmland surface runoff and sediment loss to rainfall patterns under different planting modes, to explore the laws of farmland surface runoff and sediment transport in the Poyang Lake plain area under new circumstances, and to provide scientific basis for preventing and controlling farmland surface soil erosion, [Methods] 64 rainfall events were classified using K-means clustering method, and combined with monitoring data such as runoff and sediment production in runoff plots, the impact of surface runoff and sediment losses in different rainfall types of farmlands under three planting modes were analyzed. Results] (1) The duration, rainfall and maximum rainfall intensity of 30 minutes were taken as the rainfall characteristic indicators. The rainfall could be divided into 4 types (type A: 'medium duration, small rainfall and light rainfall intensity', type B: 'short duration, small rainfall and medium rainfall intensity', type C: 'long duration, heavy rainfall and medium rainfall intensity', and type D: short duration, medium rainfall and heavy rainfall intensity'). (2) The variation of runoff and rainfall of each planting mode was basically the same, and the runoff was also more when the rainfall was larger. In each month dry farming mode produced the most runoff, (3) No matter what type of rainfall, the runoff and sediment losses of dry farming mode were the highest. Under the types A and C. the runoff and sediment yields of water farming mode were the lowest. Under the type B. the runoff reduction effect of water and dry rotation mode was the best. (4) There were significant differences in the total runoff and sediment loss under different planting modes, and the performance followed the order: dry farming mode paddy upland rotation mode paddy farming mode. [Conclusion In conclusion. compared with the dry farming model, the water farming model has certain advantages in reducing runoff and sediment, especially when dealing with type A and type C. the effect of runoff and sediment reduction is more obvious. [ABSTRACT FROM AUTHOR]

Water-reactive polymer grouts can be injected directly into contaminated sediment zones where a portion of the contaminated pore water may participate in grout polymerization and contaminants may be immobilized in the grout matrix. This study evaluated the effectiveness of injecting a water-reactive polymer grout into frozen soil for immobilizing iodide by incorporation into grouted soil monoliths. Iodide was used as a model sediment contaminant. Soil freezing is a unique method used in subsurface remediation and was investigated because it may limit the amount of contaminated water displaced and mobilized during pressure grouting. In addition, joint use of grouting and soil freezing has the potential to broadly impact other remediation challenges, for example, treatment of collapsible soil and soil in water-active areas. Variables analyzed were freezing, moisture content, iodide concentration, and accumulated pressure due to carbon dioxide gas generated during polymerization. Iodide mobilization, iodide leaching as cumulative fraction leached (CFL), effective diffusivity (D), and leachability index (LI) were evaluated. Iodide mobilized during polymer injection into frozen sands was 37.9%±12.9% which indicated that soil freezing did not prevent iodide from being mobilized when injecting the liquid polymer. Lowering the moisture content from 5% to 1.6% by weight, to align reacted water with the introduced polymer, resulted in a decrease in the mobilization of iodide to only 0.23%±0.06%. This is the lowest reported result for contaminant displacement from liquid reaction additions known to the authors. All grouted samples leached less and more slowly than the ungrouted (control) samples. Grouting reduced effective iodide diffusivity by more than 96% and the LI of the grouted soil monoliths was greater than 6.0, which meets the criteria for materials intended for shallow burial with radioisotopes. These results demonstrate that polymer grouting of sands can be used to immobilize and slow the subsurface transport of sediment contaminants. [ABSTRACT FROM AUTHOR]

The morphology of alluvial fans provides valuable information about changes in tectonic, climate, base level, and drainage basin characteristics. This study aims to evaluate the relationship between active tectonics and morphometric characteristics of alluvial fans in the less studied southern region of the Joghatay mountain, northeast Iran. The study area includes 13 alluvial fans and their corresponding catchment basins in a region with semi-arid climate. Morphometric characteristics of alluvial fans and their corresponding drainage basin including fan area, fan slope, sweep angle, fan toe length, fan radius, basin area, basin slope, fan's width-to-length ratio, asymmetry factor, and basin shape were measured. Our results revealed a negative relationship between the slope of alluvial fans and their corresponding basin area. The weak correlation between the drainage basin area and the fans area may be attributed to the lithology and active tectonics in the study area. The small sweep angle values of the studied alluvial fans can be attributed to the activity of thrust faults and presence of an uplifting anticline that resulted in formation of elongated alluvial fans in our study area. Analysis of the relationship between the morphometric characteristics of the fans and their corresponding basins indicated a negative correlation, which can be attributed to the sediment transport efficiency of the basins. [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]