Search

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]

The Saint-Venant-Exner system is widely used in industrial codes to model the transport of bed sediments. In practice, most of the methods used for its numerical resolution suffer from significant stability problems due to the fact that they are mainly guaranteed by separation techniques which allow weak coupling between hydraulic and morphodynamic software. The search for an adequate alternative method to this problem is a focus towards which several approaches converge. Recently, many authors have proposed acceptable methods but they are not so trivial to implement in an industrial context and some do not take into account all aspects such as mobile steady states. In this work, we derive a well-balanced scheme that takes into account all stable states, to approach weak solutions of the sediment transport model in shallow waters. We demonstrate that it captures exactly all regular steady solutions with non-evanescent velocities, retains water level positivity and is able to degenerate to a classical shallow water model when the sedimentary transport flow is null. A number of numerical test cases are also presented to illustrate these properties. [ABSTRACT FROM AUTHOR]

Mangrove‐saltmarsh ecotones are experiencing rapid alterations due to climate change and human activities, however, the ecological and morphological implications of these shifts remain largely unknown. This study systematically explores how interspecific interactions and herbivory influence the dominant wetland species, as well as the resultant morphological evolution and landscape configuration. To achieve this, we develop a new eco‐morphodynamic model that integrates hydrodynamics, sediment transport, bed‐level change, and vegetation dynamics. The novelty of the current model lies in newly incorporated modules to simulate biotic interactions between mangroves and saltmarshes, enabling exploration of eco‐morphodynamic feedback in mangrove‐saltmarsh ecotones in response to tidal flows and species interactions. Our results show that vertical growth rates of coexisting vegetation species are dominant factors in determining wetland dominance. When mangroves and saltmarshes exhibit comparable growth rates, mangroves typically become the dominant wetland species. Conversely, if mangroves grow more slowly than saltmarshes, they are unable to outcompete saltmarshes. Additionally, herbivory can fundamentally alter wetland dominance depending on herbivore food preferences. Our simulations further underline that saltmarsh‐dominated wetlands develop channel networks more extensively and rapidly than mangrove‐dominated systems. This pattern is also observed during species invasions, with invading saltmarshes extending channel networks, while invading mangroves inhibit ongoing network expansion. This study highlights the pivotal roles of relative growth properties and herbivory in driving ecotone development in respect to wetland dominance and channel network development at the intertidal scale. Plain Language Summary: In coastal areas where mangrove trees and saltmarsh grasses exist together, climate change and human activities significantly impact wetland development. This study uses a novel computer model to explore how different plants interact, how plant‐eating animals influence plant distribution and how these factors affect the shape of coastal landscapes. Our findings reveal that mangrove trees with growth rates similar to saltmarsh grasses can outcompete saltmarshes and become the dominant wetland species. Additionally, animals that eat plants play a crucial role in determining which plants survive, with their effects highly dependent on their feeding preferences. Wetlands dominated by saltmarshes tend to develop deeper channels. This occurs because saltmarshes spread slowly and grow in patches, which changes water flow and promotes erosion in areas without vegetation. Conversely, wetlands where mangroves are taking over typically feature fewer and shallower channels. Overall, our study suggests that the growth rates of different plants and the presence of plant‐eating animals are essential in shaping these coastal environments. Key Points: A new eco‐morphodynamic model is developed accounting for facilitation, competition and predation in mangrove‐saltmarsh ecotonesEcotone dynamics at intertidal scale are determined by herbivory and the relative growth properties between mangroves and saltmarshesTidal networks in saltmarsh‐dominant ecotones are formed more rapidly and extensively with deeper channels [ABSTRACT FROM AUTHOR]

National Capital Integrated Coastal Development (NCICD) aims to protect Jakarta from flooding. This project includes a coastal reservoir (CR) development plan at the Cisadane Estuary, Tangerang Regency, Indonesia. CR planning must consider the sedimentation process. With numerical modelling of sediment transport, the sedimentation pattern of bed load and suspended load sediments will be known. This study used the MIKE21/3 Integrated Models software that is coupled with Flow Model (FM) and Mud Transport (MT) for one year (August 1, 2020 - July 31, 2021). The validation result of surface elevation shows that the modelling results are valid with NRMSD 93.35%. Based on the simulation results, suspended sediment concentration in the west monsoon is higher than in the east. The sediment concentration around the coastal reservoir at the bottom layer of the water is slightly higher than the surface layer. There is an increase in the maximum bed thickness of 1.2 m in the northeast corner of CR. There is a reduction in the bottom thickness of about 0.5 m on the west side of the CR embankment. The results of this study can be used to develop the most optimal CR design to minimise the environmental impacts. [ABSTRACT FROM AUTHOR]

Grade control structure (GCS) can be used to reduce erosion in river beds. They decrease the river bed scour by changing the flow regime and reducing its velocity. It is required to maintain the stability of these structures against the scour hole that generates downstream of them, so investigating the scour hole characteristics downstream of the GCS is inevitable. In the present research, the equilibrium scour holes downstream of GCS were investigated under three discharges (q=0.00467, 0.00583, 0.00700 m3/s.m) and two different sedimentation conditions (d50=0.082, 1.6 mm). The results show that in the constant GCS geometry and finer sediment, the maximum scour depth (ds) and maximum scour hole length (ls) increase. In the same sedimentary conditions and different geometry, when the slope of the GCS downstream face varied from 90° to 60°, ds increases, but ls decreases. Also, the hydraulic jump forms on the scour hole at high flow intensity, which has an essential influence on the geometry of the equilibrium scour hole. Comparison of ds/Hc between the present study and Ben Meftah and Mossa (2020) has R2=0.891 and RE=10.66%, which reveals acceptable compatibility between the present study results and previous ones. [ABSTRACT FROM AUTHOR]

The aim of this study is to identify the main pollutants and evaluate the mechanisms of sediment transport from land to sea. This goal is justified by environmental pollution in the area associated with dredging and port activities. The objective is planned to be achieved by investigating the geochemical behavior of major and trace elements in fourteen surface sediment samples collected along the Moroccan Atlantic coast, from the mouth of the Lukkous River to the coast between the cities of Larache and Moulay Bousselam. k0-standardization method of neutron activation analysis using neutrons of the Moroccan Triga Mark II research reactor at the National Centre for Nuclear Energy, Science and Technology, has been used for analysis of collected sediment samples. The enrichment factor analysis revealed high levels of arsenic and chlorine, along with significant calcium enrichment, were found along the Atlantic coast. The enrichment factors (FE) for arsenic and chlorine are in the range of 20 < FE < 40, and for calcium, the FE is in the range of 5 < FE < 20. Conversely, some elements exhibited little to no enrichment, suggesting a crustal origin. PCA helped in synthesizing these findings, providing a clearer understanding of the spatial variations in sediment composition based on their multi-elemental signatures. The research examines surface sediments along the Moroccan Atlantic coast, revealing current contamination levels and geochemical behavior. These findings, applicable to similar coastal environments, are crucial for monitoring and managing sediment quality, especially in areas affected by erosion. Additionally, dredging and port activities in this region significantly disturb the sediments, resuspending contaminants and altering sediment composition, which further exacerbates pollution issues. This study offers a comprehensive geochemical characterization of coastal sediments in Morocco, enhancing understanding of sediment contamination and geochemical processes, with implications for environmental protection and sustainable marine resource management. [ABSTRACT FROM AUTHOR]

Coastal restoration projects are significantly important in coastal ecosystems as wetland losses accelerate. This study investigates tidal hydrodynamics and the potential impacts of a waterway opening on an existing roadway to restore and revitalise salt marshes in a small estuarine system in Virginia, USA. A depth-integrated, discontinuous Galerkin shallow-water equations model (DG-SWEM) is applied for astronomic tide simulation. The model employs a high-resolution unstructured mesh with a minimum element size of less than one meter and resolves complex tidal flows in the entire barrier island system, including the existing culvert gate and canal system. Compared to the existing system, the water exchange increased dramatically (flushing time also dramatically decreased) under the opened scenarios regardless of the opening width (22.9-, 30.5-, and 38.1-m width). By increasing the opening width, peak velocity through the proposed opening decreased 30–40%, and the maximum shear stress was reduced by more than half. The high-resolution model represented complex tidal flows, including eddies, and assisted in striking a balance of water-exchange capability, opening stability, and minimising their potential erosions for the opening design. Besides, erosion and sediment transport potentials for suspended sediments were estimated using bed shear stress and a Lagrangian particle tracking module. Such proxy modelling approach allows for the impact assessment of civil engineering and ecological waterworks in complex and highly damped tidal flow areas and is readily transferrable to other like systems (e.g. causeway construction, causeway cutting, biota passageways, and inlet modification). [ABSTRACT FROM AUTHOR]

The direct extraction of clear water from a sandy river is a difficult task and can only be achieved through specific engineering measures. This paper proposes an artificial percolation riverbed structure for extracting clean water from sandy rivers, using a numerical simulation to study the flow field distribution characteristics of the structure under clean water conditions. The main conclusions are as follows: When the percolation vortex tube opening rate is 1.4%, the vortex tube with or without opening the percolation hole has little influence on the distribution characteristics of the flow field in the artificial riverbed, and the purpose of water extraction can be achieved while constructing a helical flow field. The axial flow velocity and circumferential flow velocity of the vortex tube cross-section under different Reynolds numbers show the distribution of a low-flow velocity close to the center of the vortex tube, and a high-flow velocity close to the vortex tube side-wall area. The average axial flow velocity and average circumferential flow velocity of the vortex tube show a trend of increasing and then decreasing distribution along the axial axis of the vortex tube in the direction of the sediment transport flume. The mean axial flow velocity of the vortex tube along the axis of the vortex tube toward the sediment transport flume and the mean circumferential flow velocity both show a distribution trend of increasing and then decreasing. At the junction of the vortex tube and the sediment transport flume, there are obvious pressure changes, and the pressure changes drastically under the same horizontal line. Along the direction of the bottom line of the vortex tube, the pressure at the vortex tube is obviously greater than that at the sediment transport flume. The vortex of the artificial percolation riverbed is mainly concentrated in the vicinity of the vortex tube, and the maximum value of the vortex intensity generally occurs at the junction of the vortex tube and the sediment transport flume. With the increase in the Reynolds number, the vortex intensity has an overall increasing trend, and the distribution of the vortex is more complex. This study helps to elucidate the distribution characteristics of the flow field in the artificial percolation riverbed, and it provides a reference basis for the future study of the flow field of artificial percolation riverbeds of sandy rivers. [ABSTRACT FROM AUTHOR]

This study comprehensively explores the intricate hydrodynamic and geomorphological processes that affect the Sulina Channel and bar area. It employs advanced hydrodynamic, wave, and sediment transport models to simulate the influence of marine currents, waves, and shipping traffic on sediment transport and deposition patterns, providing valuable insights for maintaining navigable conditions in the Sulina Channel. It is shown that sediment deposition is highly dynamic, particularly in the Sulina bar area, where rapid sediment recolonization occurs within one to two months after dredging. The simulation indicates that vessels with drafts of 11.5 m cause notable erosion. In comparison, drafts of 7 m have a minimal impact on sediment transport, emphasizing the importance of managing vessel drafts to mitigate sediment disturbances. This research highlights and quantifies the siltation phenomenon from the Black Sea to the mouth of the Sulina Channel, effectively addressing the challenges posed by natural and anthropogenic factors to ensure the Channel's sustainability and operational efficiency. [ABSTRACT FROM AUTHOR]

Local scour around offshore wind turbine foundations presents a considerable challenge due to its potential influence on structural stability, driven by hydrodynamic forces. While research has made strides in comprehending scouring mechanisms, notable complexities persist, specifically with newer foundation types. Addressing these limitations is vital for advancing our understanding of scour mechanisms and for improving mitigation strategies in offshore wind energy development. This review synthesizes current findings on local scour across various offshore foundations, encompassing field observations, data-driven approaches, turbulence-sediment interactions, scour evolution processes, influencing factors, and numerical model advancements. The objective is to enrich our understanding of local scour mechanisms. In addition, future research directions are outlined, including the development of robust artificial intelligence models for accurate predictions, the exploration of vortex structure characteristics, and the refinement of numerical models to strengthen prediction capabilities while minimizing computational efforts. [ABSTRACT FROM AUTHOR]

Ice formation is generally considered to exclude many particles and most solutes and thus be relatively pure compared to ambient waters. Because river ice forms by a combination of thermal and mechanical processes, some level of sediment entrainment in the ice column is likely, though reports of sediment in river ice are limited. We observed high and sporadic levels of silt and sand in ice of the Kuskokwim and Tanana rivers (Alaska, the United States) during routine field studies. These observations led us to make a more comprehensive survey of sediment entrainment in river ice of the Kuskokwim and Yukon rivers and several of their tributaries. We collected and subsampled 48 ice cores from 19 different river locations in March 2023, which included concurrent measurements of water turbidity, velocity, and depth. Approximately 60% of cores contained detectable levels of sediment, averaging 438 mg/L with median concentrations exceeding 1000 mg/L in three cores from the Yukon and Kuskokwim main stems. Many cores had even higher concentrations at certain intervals, with seven cores having subsamples exceeding 2000 mg/L; these were often located in the middle or lower portion of the ice column. Jumble ice, formed mechanically by frazil‐pan jamming during freeze‐up, was generally the best predictor of higher sediment entrainment, and these locations often had higher under‐ice velocities and depths. Our observation of high and widespread sediment entrainment in northern river ice, particularly in jumble‐ice fields, may have implications for sediment transport regimes, ice strength and transportation safety, and how rivers break up in the springtime. [ABSTRACT FROM AUTHOR]

Shallow floodplains play a crucial role in river basins by providing essential ecological, hydrological, and geomorphic functions. During floods, intricate hydrodynamic conditions arise as flow exits and re-enters the river channel, interacting with the shallow vegetation. The influence and mechanism of shoal vegetation on channel hydrodynamics, bed topography, and sediment transport remain poorly understood. This study employs numerical simulations to address this gap, focusing on the Xiaolangdi–Taochengpu river section downstream of the Yellow River. Sinusoidal-derived curves are applied to represent the meandering river channel to simulate the river's evolutionary process at a true scale. The study simulated the conditions of bare and vegetated shallow areas using rigid water-supported vegetation with the same diameter but varying spacing. The riverbed substrate was composed of non-cohesive sand and gravel. The analysis examined alterations in in-channel sediments, bed morphology, and bed heterogeneity in relation to variations in vegetation density. Findings indicated a positive correlation between vegetation density and bed heterogeneity, implying that the ecological complexity of river habitats can be enhanced under natural hydrological conditions in shallow plain vegetation and riparian diffuse flow. Therefore, for biological river restoration, vegetation planting in shallow plain regions can provide greater effectiveness. [ABSTRACT FROM AUTHOR]

Gravel transport in subaerial environments occurs through different flows that are conveniently classified as debris flows, debris floods and water flows based on their distinct morpho‐sedimentary dynamics and different implications for geomorphic hazard. Because distinctive features allowing gravelly sedimentary bodies to be ascribed to related genetic process are still a matter of discussion, this study aims to establish whether imbrication fabric represents a sedimentological fingerprint potentially applicable towards a more robust genetic classification of gravels. We analysed the fabric of 1007 imbricated clasts from modern and ancient deposits. Our results highlight statistically significant differences between imbrication fabrics in gravels deposited by different flows. Particles imbricated by water flows are typified by low imbrication angles (median of 35°) and elongated clasts oriented perpendicular to the flow. In contrast, debris‐flow gravels exhibit high imbrication angles (median of 65°) and elongated clasts oriented parallel to the flow. Debris‐flood deposits display elongated clasts both parallel and transverse to the main flow and intermediate values of imbrication angle (median of 47°). We propose that imbrication angles result from the combination of stability‐driven selection—a process acting under tractional transport and promoting the remobilization of high‐angle imbrication fabrics—and shear‐stress‐driven overriding—a mechanism leading to the formation of the higher imbrication angles—with the first dominating in water flows and the latter being effective in mass transport processes. The progressive change in imbrication fabrics from fluid‐gravity to sediment‐gravity flow deposits offers easily quantifiable sedimentological evidence to help in distinguishing genetic processes that contribute to the accumulation of gravels in alluvial and colluvial settings. Analysis of imbrication fabric can add valuable information, particularly as regards the classification of (1) coarse deposits in stratigraphic records and (2) modern debris flood deposits. [ABSTRACT FROM AUTHOR]

Severe fire on steep slopes increases stormwater runoff and the occurrence of runoff‐initiated debris flows. Predicting locations of debris flows and their downstream effects on trunk streams requires watershed‐scale high‐resolution topographic data. Intense precipitation in July and September 2013 following the June 2011 Las Conchas Fire in the Jemez Mountains, New Mexico, led to widespread debris flows in the watershed of Rito de los Frijoles. We differenced lidar Digital Elevation Models (DEMs) collected in 2010 and 2016 to map subwatersheds experiencing debris flows and changes in elevation of the trunk stream. Debris flow occurrence was well predicted by previous assessments of debris‐flow hazard; debris flows occurred in 7 of 9 sub‐basins where the debris‐flow hazard was above 60% for the 25‐year rainfall event, and in 0 of 21 basins where debris flow hazard was less than 60%. Debris flows resulted in fan deposition at the confluence with the trunk stream followed by transport during three documented floods. The bed of the 22 km trunk stream increased in elevation by a mean of 0.29 m, but the local change in thalweg elevation was controlled by inputs of water and sediment and longitudinal variation in gradient. Downstream of the mouths of tributaries with debris flows, the thalweg of the trunk stream rose as much as 2 m. Downstream of the mouths of tributaries without debris flows the thalweg of the main stem degraded by as much as 2 m, mobilizing sediment that was then deposited further downstream where the gradient of the trunk stream decreases. In conclusion, the transport of sediment generated by debris flows was predictably related to spatial variation in sediment supply, discharge and gradient. [ABSTRACT FROM AUTHOR]

Geomorphological evolution is one of the main factors that increases flood damage in small or medium rivers located in upstream river reaches. These types of flood damage have been increasing at knickpoints where the riverbed slope and river width change abruptly and are likely to cause non‐equilibrium conditions for sediment transport during floods. Therefore, it is important to understand the non‐equilibrium morphological response at the knickpoint and the resulting new dynamic equilibrium state under given external forces. The effects of two‐dimensional (2D) morphological features on the dynamic equilibrium riverbed profile, however, have not been specifically studied because the methods currently in use for calculating equilibrium profiles are based on zero‐ or one‐dimensional (0D or 1D) modeling. Here, we perform numerical calculations using the 2D morphodynamic model iRIC‐Nays2DH to clarify the dynamic equilibrium profile and the process of reaching a dynamic equilibrium state. We also use an existing 1D model to show the 2D effect in the dynamic equilibrium state. To understand this, we set up three channels: slope transition point, width transition point, and both the slope and width transition point. 1D results show a constant slope profile in channels with constant width and upward‐convex profiles in channels with width expansion at the equilibrium state, owing to the adjustment of the difference in sediment transport volume in the two reaches with different widths by changing the slopes. In contrast, the 2D results show that the alternate bars create a small autogenic knickpoint even in the straight channel and significantly dampen sediment deposition at the width expansion point, as seen in the 1D model result. This was because the bars' shape increased the volume of sediment transport because the shape of the bars concentrated flow. These results suggest that 2D morphological features, such as fluvial bars, play a significant role in the equilibrium riverbed profile. [ABSTRACT FROM AUTHOR]

Copyright of Ingeniería del Agua is the property of Universidad Politecnica de Valencia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Analyzing the processes and influencing factors of accretion or erosion in estuaries and tidal basins is important for coastal conservation and utilization, planning, and ecosystem maintenance. This study analyzed the process of topographic changes in Taizhou Bay, China over the past five decades by comparing bathymetric datasets from different years. The coastlines were extracted via remote sensing image interpretation, and the coastal reclamation process was analyzed. The results revealed that this bay experienced slow siltation from 1963 to 2004, which mainly occurred on mudflats and shore slopes. It turned into a feature dominated by erosion between 2004 and 2013, and erosion increased between 2013 and 2019. Coastal reclamation has occurred during every 10-year period since the 1960s. Reclamation occupied a portion of the intertidal flat, decreased the tidal prism, and changed tidal asymmetry, causing net sediment to be transported into the bay and accumulate on the intertidal flat and upper part of the subaqueous shore. The drastic reduction in sediment supply caused by the Three Gorges Dam may have been responsible for erosion from 2004 to 2019. A negative feedback process exists between tidal flat expansion and coastal reclamation. The compensatory expansion of the tidal flat is a much slower process than the advance of reclamation. [ABSTRACT FROM AUTHOR]

This paper studies hydrodynamic and morphodynamic field measurements of two storms with dune erosion in the swash‐dune collision regime. It analyses (a) the behavior and change of the total dune profile over the course of both storms (b) the erosion rate at the dune base, (c) the slumping frequency, and (d) the volumes of individual slumps. The erosion rate at the dune base shows a strong positive correlation with the square of the total water levels that were exceeded for 2% of the time, recorded approximately 5–6 m in front of the dune face (r = 0.91). Individual slumping events occurred when nearly all sediments from previous slumps at the dune base were transported away from the dune. A strong positive correlation was found between the time between two consecutive slumps, and the volume of the first slump divided by the mean erosion rate between the two slumps (r = 0.90). As a consequence, smaller slumps were followed more rapidly by a new slump than larger slumps, under identical erosion rates. The majority of the slumping events occurred after the last wave impact before a slumping event, when the instantaneous water level in front of the dune was still retreating. No clear process based on the incident hydrodynamics could be identified that determined the size of individual slumps. Overall, the results of this study suggest that the morphodynamic behavior of the upper dune face and dune crest is primarily steered by the erosion at the dune base. Plain Language Summary: At sandy coastlines, dunes often act as the primary sea defense against storms. During storms, an elevated water level temporarily submerges the beach, enabling waves to collide with the dune. In time, the dune becomes unstable and slumps of sediment periodically slide down the dune and drop at the dune base. Here, waves transport the sediment away, leaving room for a new slump to drop down. This paper analyses data from a field experiment and examines the speed with which sediment at the dune base eroded away. It studies when and what caused a slump to fall down, and what determined the size of slumps. The erosion speed with which sediments are transported away from the dune increased when the elevation difference between the incident water levels and the dune toe increased. The size of the previous slumps and the erosion speed of the slumped sediments at the dune base determined when a new slump dropped down. No clear explanation for the size of slumps could be found following from this study. Overall, the results of this study suggest that the erosion speed of the slumped sediments at the dune base steers the behavior of the upper dune. Key Points: Field measurements of dune erosion rates and slumping volumes during two storms are related to hydrodynamic forcingsMeasured erosion rates at the dune base show strong correlations with the water level at the dune baseThe timing of slumps was related to the size of previous slumps and the erosion rates at the dune base [ABSTRACT FROM AUTHOR]

The survival of salt marshes, especially facing future sea‐level rise, requires sediment supply. Sediment can be supplied to salt marshes via two routes: through marsh creeks and over marsh edges. However, the conditions of tides and waves that facilitate sediment import through these two routes remain unclear. To understand when and how sediment is imported into salt marshes, 2‐month measurements were conducted to monitor tides, waves, and suspended sediment concentration (SSC) in Paulina Saltmarsh, a meso‐macrotidal system. The results show that the marsh creek tends to import sediment during neap tides with waves. A tidal cycle with a small tidal range result in weaker flow in the marsh creek during ebb tides, reducing the export of sediment. Waves enhance sediment supply to the marsh creek by eroding mudflats. However, strong waves can directly resuspend sediment in marsh creeks during spring tides when the water level is above the marsh canopy, enhancing sediment export through creeks. Net sediment import over marsh edges requires the opposite tidal and wave conditions: spring tides with weak waves. Spring tides provide stronger hydrodynamics, facilitating sediment import over the marsh edge. Increased SSC during the ebb phase can occur with strong waves over the marsh edge, resulting in net sediment export. Therefore, the net import or export of sediment, through the creek and over the marsh edge, depends on the combination of tidal and wave conditions. These conditions can vary between estuaries and even individual marshes. Understanding these conditions is crucial for better management of salt marshes. Plain Language Summary: The future of salt marshes greatly depends on receiving enough sediment, especially in the face of rising sea‐level. This sediment can reach salt marshes via two routes: through marsh channels or over the seaside boundary of the marsh. It is not fully understood under what tidal and wave conditions sediment can be supplied to salt marshes, either through marsh channels or over the marsh boundary. Therefore, 2‐month data sets on hydrodynamics and sediment dynamics were collected in Paulina Saltmarsh to investigate the optimal conditions of tides and waves for importing sediment into salt marshes. We found that sediment supply along marsh channels and over the marsh boundary requires contrasting tidal and wave conditions. Strong waves and small tidal ranges are favorable conditions for marsh channels to bring sediment into salt marshes. Conversely, sediment tends to be brought into salt marshes during tidal cycles with large tidal ranges and weak waves. This work highlights when and how sediment can be transported into the marsh, contributing to better salt marsh management. Key Points: Tidal ranges determine the direction of residual sediment flux in the marsh creek, while wave intensity determines the magnitudeWave intensity determines the direction of residual sediment flux over the marsh edge, whereas tidal ranges determine the magnitudeUnlike mudflats, waves cause erosion in marsh creeks only during tides with large tidal ranges [ABSTRACT FROM AUTHOR]

The determination of critical shear stresses is fundamental to bedload sediment transport prediction in gravel‐bed rivers. Due to the heterogeneous shape and arrangement of the individual clasts in a riverbed, critical shear stresses typically show a large spatial variability, which is not adequately captured by the reach‐averaged description followed in common studies. In this regard, there is a general paucity of field data on this spatial variability of the critical shear stress, largely due to the lack of a standardized measurement method. In an attempt to fill this gap, we propose a field‐based workflow to estimate the frequency distribution of dimensionless critical shear stress (also named critical Shields number), which is based on the measurement of a series of variables related to the position, orientation and resistance to motion of individual clasts in a gravel‐bed river, combined with a probabilistic approximation to drag and lift coefficients. Following this workflow, the patch‐scale variability of particle incipient‐motion conditions was determined in a gravel bar of the Upper Cinca River, Spain. The results are consistent with what is known about sediment entrainment in gravel‐bed rivers. We consider this method to have great potential to advance our understanding of particle initiation of motion in gravel‐bed rivers as it provides valuable systematic field information. Plain Language Summary: Predicting the flow conditions required to entrain sediment in gravel‐bed rivers is essential for fluvial ecology, flood risk assessment, river restoration and sustainable river management, among many other issues. In this regard, sediment entrainment conditions exhibit large spatial variability due to the heterogeneous shape, weight and arrangement of individual grains in a gravel bed. Our ability to model and quantify bedload transport is limited by this variability and exacerbated by the lack of standardized protocols for characterizing it in the field. In this context, this work builds on existing theory to propose a field‐based workflow for characterizing the variability in the forces required to move gravel in a river bed. This field‐based workflow opens the door to the collection of field data that will allow progress in our understanding of bedload transport in natural rivers. Key Points: Critical shear stress is a key parameter to understand bedload transport. It is often described by section‐ or reach‐averaged values in field studiesWe propose a field‐based workflow to characterize the spatial variability in critical Shields stress in gravel‐bed riversThis workflow allowed us to approximate the critical Shields frequency distribution in two 1 m2 patches of the Cinca River (NE Iberian Peninsula) [ABSTRACT FROM AUTHOR]

Sediment erosion, transport, and deposition by glaciers and ice sheets play crucial roles in shaping landscapes, provide important nutrients to downstream ecosystems, and preserve key indicators of past climate conditions in the geologic record. While previous work has quantified sediment fluxes from subglacial meltwater, we also observe sediment entrained within basal ice, transported by the flow of the glacier itself. However, the formation and evolution of these debris‐rich ice layers remains poorly understood and rarely represented in landscape evolution models. Here, we identify a characteristic sequence of basal ice layers at Mendenhall Glacier, Alaska. We develop a numerical model of frozen fringe and regelation processes that describes the co‐evolution of this sequence and explore the sensitivity of the model to key properties of the subglacial sedimentary system, using the Instructed Glacier Model to parameterize ice dynamics. Then, we run numerical simulations over the spatial extent of Mendenhall Glacier, showing that the sediment transport model can predict the observed basal ice stratigraphy at the glacier's terminus. From the model results, we estimate basal ice layers transport between 23,300 m3 ${\mathrm{m}}^{3}$a−1 ${\mathrm{a}}^{-1}$ and 39,800 m3 ${\mathrm{m}}^{3}$a−1 ${\mathrm{a}}^{-1}$ of sediment, mostly entrained in the lowermost ice layers nearest to the bed, maximized by high effective pressures and slow, convergent flow fields. Overall, our results highlight the role of basal sediment entrainment in delivering eroded material to the glacier terminus and indicate that this process should not be ignored in broader models of landscape evolution. Plain Language Summary: Glaciers shape landscapes by eroding mountain ranges and moving the eroded sediment downstream to the lakes, fjords, and other ecosystems near the terminus. To quantify this supply of sediment, and thus understand the evolution of high alpine landscapes, we often use numerical models to simulate the processes of erosion and transport. Previous work has focused on the role of meltwater channels underneath glaciers to transport sediment, analogous to how rivers move sediment across much of Earth's surface, but we also know from field observations that a portion of the underlying sediment is picked up and incorporated into the ice itself. Here, we develop a new model to simulate where and how sediment is incorporated into ice beneath the glacier, and how those debris‐rich ice layers are modified as the glacier flows downstream. We use this model to predict the total amount of sediment reaching a glacier's snout, as well as the spatial distribution and thickness of the debris‐rich ice. Our results show that the amount of sediment transported in glacier ice likely represents a significant component of the total amount of sediment eroded or transported by the glacier, and thus should not be ignored in broader models of landscape evolution. Key Points: We develop a model of sediment entrainment beneath an alpine glacier to predict sediment fluxes and basal ice stratigraphy at the terminusThe model explains the co‐occurrence of solid, debris‐rich ice layers and overlying dispersed basal ice facies observed at glacier marginsAt a case study, we find sediment can be entrained up to 5 m in basal ice, maximized at high effective pressure and slow, convergent flow [ABSTRACT FROM AUTHOR]

Coastal hydrodynamics and morphodynamics integrate the effects of small‐scale fluid‐sediment interactions; yet, these small‐scale processes are not well understood. To investigate sediment trapping by turbulent coherent structures or vortices, the transport of coarse sand over ripples was analyzed in a small‐oscillatory flow tunnel with phase‐separated Particle Image and Tracking Velocimetry. Results from one of the first direct measurements of vortex‐trapped sand grains under oscillatory flows are presented. The vortices mobilized sand grains along the ripple slopes just prior to flow reversal and transported the suspended sediment grains. During several flow cycles, some sand grains were temporarily trapped in the vortex, prescribing semi‐circular trajectories off‐center from the vortex core in quadrants of the vortex that were closest to the ripple slope, as illustrated by Nielsen (1992, https://doi.org/10.1142/1269). Comparisons of the horizontal sediment grain velocity with the horizontal fluid velocity yielded a linear relationship with a slope of 0.87. The vertical grain velocities also varied linearly with the vertical fluid velocity with a slope of approximately 1 and an offset of −0.08 m s−1 ${\mathrm{s}}^{-1}$. The offset is close to the still water settling velocity for coarse sand grains, as hypothesized during vortex trapping. Additionally, estimates of the off‐center distance, between the centers of the semi‐circular sediment paths and vortex cores, compared well with the ratio of the settling velocity to the radian frequency of the vortex yielding a linear regression slope of 0.99. Improved understanding of vortex trapping effects on sediment dynamics may decrease uncertainty in model predictions of large‐scale coastal hydrodynamics and sediment transport. Plain Language Summary: Large‐scale coastal processes integrate the effects of small‐scale fluid‐sediment interactions; yet, these small‐scale processes are not well understood. Nielsen (1992, https://doi.org/10.1142/1269) hypothesized that suspended sand grains over ripples could get caught in a vortex under certain hydrodynamic conditions, in a process called vortex trapping. In this article, we present results from one of the first direct measurements of vortex‐trapped sand grains under oscillatory flows. Vortices along the ripple slope mobilized sand grains prior to flow reversal and transported the suspended grains. During several flow cycles, some sand grains were temporarily trapped in the vortex and moved along semi‐circular paths off‐center from the vortex core in sections of the vortex that were closest to the ripple slope, as illustrated by Nielsen (1992, https://doi.org/10.1142/1269). Comparisons of the sediment grain velocity with the fluid velocity yielded a linear relationship. Additionally, the distance between the center of the semi‐circular sediment paths and the center of the vortex cores agreed with the theory. Improved understanding of the effects of vortex trapping on sediment dynamics may decrease uncertainty in the predictions of large‐scale coastal hydrodynamics and sediment transport models, which do not typically account for this small‐scale process. Key Points: Observations of vortex‐trapped grains suggest delayed settling of advected grains, as well as delayed advection of grains mobilized from the bedQuantitative comparisons of vortex‐trapped sand grains compared well with theoretical formulations by Nielsen (1992, https://doi.org/10.1142/1269) for a forced vortexImproved understanding of vortex trapping effects on sediment dynamics may decrease uncertainty in large‐scale coastal model predictions [ABSTRACT FROM AUTHOR]

Gobi's (gravel deserts) are one of the largest dust sources in northern China. Previous studies indicated that sand transport processes above the surface differed between Gobi and sand surfaces. However, the sand transport rate and related dust emission processes above Gobi (gravel) surfaces are still poorly understood. In this field study, we quantified this transport to provide important support for parameterizing Aeolian sediment transport models and clarifying the relationship between dust emission and transport. Threshold wind velocity can reach 0.38 ± 0.04 (mean ± SD) m s−1 above Gobi surfaces. Compared to the most commonly used sand‐transport models, we found that the Lettau and Lettau sediment transport model can be used to calculate horizontal sediment transport above a Gobi surface. The relationship between the vertical sediment transport (Fs) and shear velocity could be expressed using a power function. Although the horizontal sand transport and vertical flux (Q and Fs, respectively) above Gobi surfaces can be expressed similarly to previous results (i.e., using similar equation forms), the equation coefficients were much larger for the Gobi surface than for a shifting sand surface; that is, sediment transport was higher above the Gobi surface. This difference resulted from the larger sand transport rate and saltation height above the Gobi surface, and the larger transport and higher saltation height were related to the larger sand transport height and higher content of coarse sand transported above the Gobi surface. Plain Language Summary: Sediment transport by the wind is a major erosion process in the world's arid and semiarid regions but also occurs on other planets. This transport causes the formation and evolution of sand dunes and produces dust storms. Therefore, it is important to accurately quantify Aeolian sediment transport to support the design of measures to prevent or mitigate desertification and to predict dust storm occurrence and severity. Previous studies have shown that sediment transport above gravel (Gobi) surfaces differs from transport above a mobile sand surface. However, the relationships between sand transport and dust emission above a Gobi surface are poorly understood. In this study, we measured sediment transport by the wind above Gobi surfaces in the field, and found higher sand transport rates and higher saltation (hopping of particles) heights above the Gobi surfaces than above a mobile sand surface. The change of the transport rate with height could be expressed as a Gaussian peak function. The observed sediment transport results from the nature of the gravel surface and soil crusts, which cause higher saltation above a Gobi surface than above mobile sand. We parameterized the coefficient values for previous transport models, which will support efforts to improve sand transport models. Key Points: Horizontal sediment transport followed the Lettau and Lettau's (1978) equationThe saltation height above the Gobi surface is higher than the sand surfaceCoarse and fine materials were both transported above the Gobi surface [ABSTRACT FROM AUTHOR]

Longshore sediment transport (LST) is essential for shaping sandy shorelines. Many shorelines are complex and indented, containing headlands, offshore islands and tombolos. Tombolos often form between islands and the mainland; however, the conditions for LST across tombolos are unclear. This question is important because tombolos are often reinforced with anthropogenic infrastructure, potentially causing sediment starvation of downdrift beaches. Along many shorelines, the return to a tombolo's natural condition has been proposed to promote sediment connectivity and counteract erosion. Nevertheless, the implications of such restorations remain uncertain. In this study, we employ the Delft3D wave‐current model to investigate hydrodynamics and sediment dynamics across a tombolo, examining its role as a connector between adjacent beaches. Contrary to expectations, our simulations show only diminutive longshore currents from the updrift beach across the tombolo unless offshore wave heights exceed 8 m. Instead, predominant currents crossing the tombolo originate from offshore of the island, driven by storm‐induced water level differences and circulation cells on both sides of the tombolo. The offshore island shelters the downdrift domain, resulting in higher wave energy and dissipation updrift of the tombolo. Further, increasing wave height or wave approach angle not only intensifies water level differences but also relocates circulation cells, enhancing total sediment transport from the updrift beach across the tombolo. However, in general, the deposition of sediment from the updrift side of the domain does not compensate for the sediment loss on the downdrift beach. We conclude that LST across tombolos is limited and occurs only under extreme wave conditions. Plain Language Summary: Longshore transport, the movement of sand and fine gravel along the shoreline driven by waves and tides, plays a crucial role in building and maintaining stable and healthy beaches. Here, we focus on the potential impact of the removal of a road that obstructs water flow and sediment transport across a tombolo. Contrary to our expectations, removal of the road does not result in longshore currents across the tombolo unless the wave heights are very large. Instead, we observe water movement from the offshore of the island's updrift side toward the downdrift beach. This unexpected pattern is attributed to storm‐driven water level differences bet side of the island. Additionally, storms generate circulating current patterns on both sides of the island, influencing the direction of water movement. Further investigation reveals that larger waves, particularly those moving more parallel to the beach, amplify the water level difference and alter the location of the rotating currents. Extremely large waves produce longshore currents across the tombolo, which increase the amount of sediment transferred from the updrift to the downdrift domain. However, this addition of sediment from the updrift domain does not fully compensate for sediment loss from the downdrift beach during storms. Key Points: The position, magnitude, and size of circulation cells on both sides of a tombolo vary with storm surge, wave height, and wave directionCirculation cells and storm‐driven water level differences determine sediment transport across the tomboloLongshore sediment transport across the tombolo is negligible except during extreme storms [ABSTRACT FROM AUTHOR]

A new, non‐dimensional ripple reset parameter and a stochastic point process model is used to estimate the likelihood of propagating ocean waves to form ripples on sandy seabeds. The ripple reset parameter is a function only of water depth, significant wave height, and mean grain size. Ripple formation is estimated by the magnitude of an intensity function based on a time series of the ripple reset parameter. The point process model is trained with a time series of observed waves and ripple change, and is then applied to predict the probability that a ripple field with a different geometry will form within a given time interval from another time series of wave data. The model is trained and tested with four field deployments at three field sites to determine its skill in predicting the ripple formation (a) at one field site over one time period after being trained with observations from the same site over a different time period, and (b) at one field site after being trained with observations from another field site. Results show that while the model is sufficient at predicting ripple formation in both scenarios, it is sensitive to the quality and quantity of the training data. Increasing the amount of training data greatly improves model performance. Employing a stochastic model based on a simple ripple reset parameter reduces tunable model parameters and provides a prediction of the probability for ripple formation given only a water depth, grain size, and time series of wave heights. Plain Language Summary: Ripples are small, hill‐like mounds of sand that are formed by water in the ocean moving back and forth by waves. Sand ripples can cause an increase of sand movement on the seafloor, can cause ocean instrumentation to respond unexpectedly, and can bury and expose objects. Understanding when they form is important for scientists to measure and predict ocean dynamics. If the average height of the waves, the water depth, and the sand grain diameter is known, we can predict whether or not the waves will form ripples with mathematical equations. Previously, the equations to predict ripple formation required a lot of difficult to obtain ocean information. We developed an equation and model to quickly and easily predict the likelihood of ripples forming by waves in a specific size sand and water depth. Key Points: A ripple reset parameter based on wave height, water depth, and grain size is presentedA stochastic model based on the ripple reset parameter can predict the probability of ripple formationThe model accurately predicted ripple resets at three different field sites without calibration [ABSTRACT FROM AUTHOR]

Segmented barrier islands can be found in regions with small tidal ranges. In contrast to tidally dominated barriers, where inlet dynamics are thought to control island length scales, the controls on barrier island length scales in wave‐dominated environments have not been quantified. These microtidal barriers typically have a curved shoreline, suggesting the influence of wave‐driven alongshore sediment transport. Microtidal barriers are also typically hydrodynamically isolated from one another, as weak tidal flows limit interactions between adjoining barriers. To better understand the controls on and scales of barrier segmentation in the relative absence of tides, here we develop a theoretical framework to estimate the alongshore length scales at which a barrier will either breach or heal following a disturbance in the barrier morphology. The non‐dimensional framework compares the timescales of overwash (advective) and alongshore sediment transport (diffusive) processes along barrier island chains. We then apply this framework to modern barrier islands in the microtidal Gulf of Mexico using wave hindcast data and the lengths, widths, heights, and lagoon depths measured from remotely sensed geospatial data and topobathymetric data. We find that most of these barriers are currently longer than their critical length scale, often as a result of coastal restoration efforts. Our critical length scale analysis suggests that most of the Gulf of Mexico barriers are vulnerable to segmentation despite coastal restoration efforts intended to protect fisheries and the mainland coasts. Plain Language Summary: Barrier islands provide valuable protection for mainland communities, marine fisheries, and coastal ecology. Restoration efforts are frequently enacted to preserve barrier islands, particularly after storm‐induced breaches segment a barrier into two or more shorter islands. Stable barrier island length scales have been predicted in environments with large tides, where barriers are separated by inlets; however, the characteristic stable length of barriers has not been quantified for environments with small tidal ranges. In these micro‐tidal environments, barriers are primarily shaped by two mechanisms of sediment transport: (a) overwash, which moves sediment from the nearshore environment on top of and behind barriers and (b) wave‐driven alongshore sediment transport, which smooths the shoreline. Here, we present a theoretical framework to evaluate the ability of barrier islands to heal when breached, based on a comparison of timescales for barrier rollover by overwash and shoreline smoothing through alongshore sediment transport. We then apply this analysis to barrier islands in the Gulf of Mexico, finding that many of these barriers are overly long, which suggests that they are vulnerable to segmentation despite (or perhaps due to) coastal restoration. Key Points: We assess the vulnerability of micro‐tidal barriers to segmentation by comparing the timescales of island rollover and alongshore diffusionThe comparison defines a critical length scale over which barriers should be vulnerable to segmenting into smaller islandsMany Gulf of Mexico islands are longer than predicted critical length scales—these long islands tend to be anthropogenically modified [ABSTRACT FROM AUTHOR]

Stream sediment transport results from a convolution of climate, weather, geology, topography, biology, and human influence. In addition to providing water and food security for rural dryland communities, sand dams—small weirs designed to trap only the coarse fractions of transported sediments in seasonal and ephemeral streams—highlight many complexities of geomorphological dynamics. Sand dams store water in interstitial riverbed pores and the size of deposited sediment particles largely determines the recoverability of stored water: Fine materials limit transmission and provide lower volumetric yield. In this study, we seek to identify a practical method for evaluating the theoretical effect of staged sand dam crest construction on key sediment‐trapping processes for a proposed dam site. We argue that the Rouse number provides a useful criterion for identifying regimes where the target material grades are trapped. These ideas were tested using sediment data collected in Kenya and US Army Corps of Engineers River Analysis System numerical simulations to evaluate the sensitivity of sedimentation processes to crest height. We show that constructing sand dams in stages results in more targeted trapping of coarse material. Sedimentation is shown to be more sensitive to variation in crest height than the flood hydrograph, especially when a dam's crest height is small. By introducing a method to assess the necessity and inform design of staged crest construction based on local flow dynamics, this study offers a framework for optimising sand dam performance in data‐scarce environments. This approach provides a means to balance construction costs with expected benefits, enhancing the sustainability and functionality of sand dams in arid and semi‐arid regions. [ABSTRACT FROM AUTHOR]

Acoustic backscatter data were collected in the shallow nearshore environment under breaking and non‐breaking waves, using a multi‐frequency sonar at 0.5, 1.0, and 2.0 MHz. The data are used to develop and test an acoustic inverse model for measuring suspended sediment concentration (SSC) in the presence of bubbles generated by breaking waves. The model leverages the contrasting frequency dependence of acoustic scattering by bubbles and sand, to simultaneously estimate SSC and bubble void fraction. Validation against in situ sediment measurements shows the acoustic technique can recover sediment concentration with good accuracy in both breaking and non‐breaking waves, unlike existing algorithms which only perform well in non‐breaking waves. Finally, data from the experiment are used to validate existing theories for suspended sediment dynamics under breaking waves, for which few previous data sets exist. Plain Language Summary: The surfzone is the energetic region of the coast where waves break, causing strong currents, mixing, and sediment transport. An understanding of fundamental sediment transport processes in the surfzone is essential to coastal engineering applications, for example, mitigating coastal erosion and flooding. However, theories for nearshore sediment transport suffer from a lack of direct field validation, owing to inadequate measurement techniques. The measurement challenges are many, including the need to detect sediment concentrations within centimeters of a moving seabed. Here, we introduce and validate a multi‐frequency sonar technique capable of obtaining the necessary measurements, including in bubbly flow under breaking waves where field data are arguably most critical. The method is validated with field data collected at Duck, NC. Results from the experiment are used to test existing theories for the vertical distribution of suspended sediment. The data show wave breaking has a strong influence on sediment vertical mixing, with implications for sediment transport predictions. Key Points: Novel observations of mobile sediment in the energetic nearshore zoneNew acoustic remote sensing technique for detecting sediments under breaking wavesField validation of models for near‐bed sediment concentration and vertical mixing, in breaking and non‐breaking waves [ABSTRACT FROM AUTHOR]

We report on a laboratory study of wave‐swash interactions, which occur in the very nearshore environment of a beach when the shallow swash flow of a breaking wave interacts with a subsequent wave. Wave‐swash interactions have been observed in the field, hypothesized to be important for nearshore transport processes, and categorized into different qualitative types, but quantitative descriptions of their dynamics have remained elusive. Using consecutive solitary waves with different wave heights and separations, we generate a wide variety of wave‐swash interactions with large flow velocities and vertical accelerations. We find that wave‐swash interactions can be quantitatively characterized in terms of two dimensionless parameters. The first of them corresponds to the wave height ratio for consecutive waves, and the second is a dimensionless measure of the time separation between consecutive wave crests. Using measurements of bed pressure and free‐surface displacement, we estimate the total vertical accelerations and focus on the peak upward‐directed acceleration. We find that wave‐swash interactions can generate vertical accelerations that can easily exceed gravity, despite occurring in very shallow water depths. The large vertical accelerations are upward‐directed and are quickly followed by onshore‐directed horizontal velocities. Together, our findings suggest that wave‐swash interactions are capable of inducing large material suspension events of sediment or solutes in sediment pores, and transporting them onshore. While the data are from a single location making it difficult to generalize the findings across the swash zone, the results clearly demonstrate the importance of large vertical accelerations in wave‐swash interactions. Plain Language Summary: Waves arriving at a beach create fast shallow flows that are responsible for moving large amounts of sediment. Here, we consider how the flow due to one wave interacts with the next wave to arrive in idealized wave tank experiments. We find that in such interactions, flows moving in opposite directions can collide and create large, but short‐lived peaks in upward‐directed flow and acceleration. These peaks in flow and acceleration are likely to drive movement of material such as sediment and dissolved constituents in ways that are currently not taken into account. Key Points: Wave‐swash interactions can be characterized by the ratio of consecutive wave heights and the dimensionless time separation between themLarge upward‐directed vertical accelerations that often exceed gravity are observed for certain wave‐swash interactionsDuring large upward‐directed vertical accelerations, the flow velocity is upward‐ and onshore‐directed [ABSTRACT FROM AUTHOR]

Floodplain encroachment by embankments heightens flood risk. This is exacerbated by climate change and land‐use modifications. This paper assesses the impact of embankments on sediment transport, channel geometry, conveyance capacity, and flood inundation of a reach of the Nakkhu River, Nepal. Using the CAESAR‐Lisflood landscape evolution model based on a 2‐m digital elevation model, we simulate four flood scenarios with and without embankments and sediment transport: a historical 25‐year return period flood event used to design the embankments, 50‐year, 100‐year, and 1000‐year return period flood events forecast using the Generalized Logistic Model (using data from 1992 to 2017). Our results indicate that flow confinement by embankments reduces inundation by 99% (from 22.5 to 0.3 ha) for the historical 25‐year flood discharge of 42.23 m3/s ${\mathrm{m}}^{3}/\mathrm{s}$ and by 15% (from 28.8 to 24.4 ha) for the 1000‐year return period flood discharge of 95 m3/s ${\mathrm{m}}^{3}\mathrm{/}\mathrm{s}$ (similar to a 25‐year maximum mid‐future). The presence of embankments increases downstream sediment transport by more than 32% for all flood scenarios considered. Inclusion of sediment transport leads to a fivefold increase in predicted inundation area for a 25‐year maximum mid‐future flood compared to the no‐sediment case in the embanked channel. Changes in channel geometry due to sedimentation significantly reduce conveyance capacity increasing overtopping flood risk, particularly where the channel is sinuous or located on flat terrain. Our results indicate that sediment erosion in outer meanders may threaten embankment stability by promoting undercuts. It is recommended that sediment transport effects be factored into embankment design and floodplain planning. Plain Language Summary: Our research explores the impact of flood protection embankments being constructed along the Nakkhu River in the Kathmandu Valley, Nepal, in a region that is experiencing rapid urban growth. Using advanced computer simulations, we study how these embankments influence the erosion and deposition of sediment in the river, and hence impact flood risk. Our findings indicate that the construction of embankments increases sediment transport, and alters the geometry of the river increasing downstream flood risk during extreme flood events. This is particularly the case for embankments designed to follow natural, meandering river courses. We recommend incorporating sediment transport analysis into the planning and design of embankments and developments in floodplain areas to reduce the risk of flooding. Our study indicates that embankment construction by itself may not always be a sustainable long‐term flood‐protection measure for rivers carrying high sediment loads. Key Points: Inclusion of sediment processes is very important in predicting the effect of embankments on river flood riskFor the embanked Nakkhu, predicted inundation is fivefold larger for 25‐year maximum mid‐future event when sediment transport is includedSedimentation reduces channel capacity for flat terrain and large meanders; erosion at outer meanders threatens Nakkhu embankment stability [ABSTRACT FROM AUTHOR]

The development of sustainable river management strategies requires knowledge of the effect of vegetation on hydrodynamics and sediment transport. To date, the complex physical processes involving the combined effects of leafy flexible vegetation and mobile bedforms are not completely understood. Most sediment transport models have been developed for bare bed conditions so that their performance in the presence of leafy flexible vegetation remains unclear. On the other hand, recently developed models consider vegetated conditions but they typically account only for the presence of rigid cylinders and in some cases scour at their base. For this purpose, laboratory experiments were conducted with mobile dune bed conditions and artificial flexible plants with varying Leaf Area Index to investigate the effect of flexible vegetation on bed morphology and sediment transport. Sediment transport rates and bedform characteristics such as height, wavelength and celerity, were measured in specifically designed experimental runs. The collected data show that the presence of leafy vegetation alters bed morphology, tending to reduce the average dune wavelength and leading to the formation of complex 3D geometries. Bed‐shear‐stress‐based models for predicting sediment transport were verified to be valid under conditions of low vegetation roughness density. On the contrary, the collected data emphasize that the measured bed‐load transport rate increased in the presence of leafy flexible vegetation with higher frontal area. Recent bed‐load models for vegetated channels provide a better interpretation for dense leafy vegetation but are less effective when predominant effects related to dunes are present. Key Points: Near‐bed leaves decrease the average dune wavelength and influence their tridimensionality, challenging common bedform stability diagramsClassical bed‐load transport models proved effective in scenarios with limited frontal vegetation area and in the absence of foliageThe presence of leafy vegetation leads to higher bed‐load transport than predicted by classical sediment transport models [ABSTRACT FROM AUTHOR]

Naumure Multipurpose Project (NMP) featuring a 169 m high Concrete Face Rock Filled Dam (CFRD) is the proposed reservoir project in the West Rapti River with an installed capacity of 218.34 MW. Most of the rivers in Nepal carry significant sediment loads that will consequently catalyze reservoir sedimentation. This phenomenon prevails as the primary factor in reducing reservoirs useful life, making ineffective for both flood control and hydroelectricity generation. Ultimately, such process of sedimentation has adverse impacts on projects economic feasibility and long-term sustainability. Therefore, the objective of this research was to examine the expected sediment deposition pattern in the NMP reservoir throughout its operational period by employing 1D HEC-RAS model to simulate the sedimentation process. The model was simulated for 10, 20, 30, 40 and 50 years. Yang's equation as a sediment transport function, Active layer as a bed sorting method and Toffaleti as a fall velocity method were best suited for the river reach. The delta deposition was formed between 11 km and 22 km upstream of the dam region in the Jhimruk river, with the sediment deposition depth reaching peaks of about 23 m, 38 m, 39 m, 41 m and 49 m in 10, 20, 30, 40 and 50 years, respectively. Similarly, the delta deposition was formed between 13 km and 33 km upstream of dam region in the Madi river, with the sediment deposition depth reaching peaks of about 47 m, 62 m, 60 m, 68 m and 75 m in 10, 20, 30, 40 and 50 years respectively. Headcutting of delta deposition occurred between 20 and 30 year due to high flood during low stage of reservoir. Furthermore, the study revealed that about 6.22%, 11.61%, 15.94%, 22.96% and 25.65% of the storage capacity of NMP reservoir will be depleted in 10, 20, 30, 40 and 50 years respectively. [ABSTRACT FROM AUTHOR]

Rates of land surface processes provide insights into climatic and tectonic influences on topography. Bedrock incision rates are estimated by dating perched landforms such as strath terraces, assuming a constant bedrock incision rate from terrace abandonment to the next terrace level or present river level. These estimates express biases from the stochastic nature of sediment and water discharge in controlling river incision as well as from using a mobile channel elevation as a reference frame, leading to different incision rates when calculated over different timeframes. We introduce a 1‐D model incorporating fluvial mechanics, tectonics, sediment, and climate variability to predict these biases and assess their sensitivity to climate and tectonics. Findings suggest biases intensify under highly variable climates and slow rock uplift, with climate periodicity being a primary control for our modeled scenarios. Our model provides a mechanism to improve river incision measurement uncertainty, impacting paleoclimate and tectonic geomorphology reconstructions. Plain Language Summary: Geomorphologists often measure how fast rivers erode bedrock over time by dating river terraces that have been uplifted to be higher than the elevation of the modern river channel. This helps us learn how landscapes evolve and about what past climates were like over long timescales. But this method is complicated by the fact that rivers do not erode rocks at a steady rate and the elevation of the channel surface above which we measure terrace height changes over time. We present a numerical model that predicts how these terraces develop under different climates and rates of rock uplift. Model results imply that measurements of long‐term river incision are most susceptible to temporal bias in regions experiencing highly variable paleo‐climate and slow rock uplift. Our model helps us make better measurements of river erosion and understand how climate and rock uplift shape landscapes. Key Points: We present a numerical model that reproduces biases in rates of river incision measured from strath terracesWe find that these measurement biases are the strongest when climates are highly variable and rock uplift is slowUnderstanding bedrock incision measurement biases allows for bias correction in field studies and improves data comparability [ABSTRACT FROM AUTHOR]

The origin of the Amazon River is formed at the confluence of the Marañón and Ucayali rivers. Remote sensing and detailed hydrodynamics, sediment transport and bed morphology analysis under different hydrological conditions have been applied to understand the control mechanisms of the modern confluence, thus informing about ancient confluences. Results showed that: 1) meandering‐meandering confluences existed when bifurcated meandering channels from the Marañón River joined the meandering Ucayali River, 2) far‐field scale provided the boundary conditions for the near‐field scale processes. In the case of the Marañón River, the spatial frequency and displacement of incoming anabranching structures to the confluence location set the boundary conditions for the near‐field scale. In the case of the Ucayali River, the incoming hydrodynamics and bed morphology are governed by far‐field processes such as the occurrence of cutoffs, 3) high intensity secondary flows at large rivers were observed at far‐ and near‐field scales, where previous studies have reported that secondary flows are weak or nonexistence or mainly found downstream of confluences. Finally, 4) even though the Marañón River is larger compared with the Ucayali River, the confluence hydrogeomorphology is governed by the Ucayali River because of more developed and stronger secondary flows. [ABSTRACT FROM AUTHOR]

This study assesses the effectiveness of a distributed physically based hydrological model (MARINE) to investigate erosion estimation during flash floods compared with other widely used empirical models derived from the Universal Soil Loss Equation (USLE) like Revised Universal Soil Loss Equation (RUSLE) and Modified Universal Soil Loss Equation (MUSLE). It is carried out on a small catchment in south‐eastern France, the Claduègne catchment. To compare the erosion volumes simulated by the three models, MARINE, MUSLE and RUSLE, a sensitivity analysis on the model parameters is carried out. According to physics‐based simulations, flood events fall into two categories: those dominated by raindrop erosion and those dominated by shear stress erosion. The results show that the erosion simulated by the three methods are comparable, except for events dominated by raindrop erosion suggesting that further research is needed to improve raindrop erosion within MARINE. Simulations from the MARINE model provide access to the spatio‐temporal variability of erosion dynamics during the event and can also be used to produce erosion/deposition maps, which are useful for environmental decision‐makers and planners in identifying areas at risk from erosion and deposition hazards. [ABSTRACT FROM AUTHOR]

Understanding the effects of human disturbance on the bedload transport regime of anthropised rivers is a topic of growing importance, as such information is of interest for adequate river diagnosis, correct implementation of restoration measures and appropriate design of post‐action monitoring programs. However, such assessments are complex, especially in sites where multiple factors simultaneously influence the bedload transport regime, so that it is difficult to establish simple causal relationships between human disturbances and changes in the sediment transport regime, notably on bedload. To overcome this, there is a need for rigorous hypothesis‐driven approaches to assess the isolated effects of each driver. With this in mind, we have characterised the dynamics of bedload transport in the Upper Garonne (Central Pyrenees, Spain‐France), a river impacted by sediment retention, flow diversion and mining that influence its morphological conditions and transport regime. We assessed the effects of (1) surface grain size distribution, (2) river morphology, (3) sediment supply and (4) flow diversion on the bedload transport regime. Four sites with different degrees of river anthropisation were selected. After defining hypotheses on the most likely bedload transport conditions for each site, we proposed a set of discriminating criteria to test these hypotheses, based on temporal within‐site and spatial between‐site comparisons of coarse particle tracking measurements over four years. The results of this research showed that the hydrosedimentary regime of the Garonne is controlled by a complex combination of drivers such as valley physiography, which exerts a first‐order control on differences in reach‐scale bedforms and bedload dynamics; and human disturbances which contribute to a reduction in sediment supply through changes in land cover and hydropower dams, or to changes in hydrology (i.e., flow competence) due to water diversion and abstraction. [ABSTRACT FROM AUTHOR]

Quantifying suspended sediment concentration‐runoff (SSC‐Q) hysteresis can help to understand the source and transport mechanism of sediment. Due to the unique lithology, shallow soil, high infiltration capacity, complex geomorphology and heterogeneous landscape of karst watersheds in southwestern China, SSC‐Q hysteresis patterns remain unclear in this region. In the present study, the hysteresis index (HI) was used to quantify the SSC‐Q hysteresis pattern. The effects of rainfall and runoff on the HI were also evaluated from 2014 to 2019 in the Mahuangtian (2.26 km2) and Muzhaihe (0.09 km2) karst watersheds. The results showed that the clockwise loops accounted for more than 60% of the total hysteresis patterns in the two karst watersheds. In contrast, the counter‐clockwise and figure‐eight loops occupied no more than 30% and 10% of the total hysteresis patterns, respectively. These differences in the hysteresis patterns probably resulted from the spatial distribution of sediment sources and hydrological connectivity. The HI was significantly affected by the maximum discharge in the Mahuangtian watershed (P < 0.05) and by the flashiness index in the Muzhaihe watershed. This may be attributed to their different 3D hydrogeological structure, lithology and watershed size. This study can facilitate a better understanding of suspended sediment dynamics and provide important guidance for accurately implementing soil and water conservation strategies in karst areas. [ABSTRACT FROM AUTHOR]

In North‐West Europe and throughout the world, dune systems are increasingly stabilised by vegetation, due to both human intervention and changes in climate. Blowouts are erosional hollows produced by wind erosion in vegetated or semi‐vegetated dune systems. Where active blowouts are present in vegetated dunes, they provide a source of dynamism and sediment in an otherwise fixed environment. The transition from a fixed vegetated dune to an active blowout is poorly understood, however, and anthropogenic attempts to reactivate areas of bare sand in dunes are often unsuccessful. In this study, we measured topographic change at a monthly resolution in the deflation basins of one bowl and one trough blowout over a 23‐month period in Ainsdale Sand Dunes National Nature Reserve, North‐West England. Our results show that monthly surface change in the blowouts did not correlate strongly with the transport capacity of winds measured at a meteorological station 10 km south of the site. Precipitation was found to have a moderate negative correlation with all indices of surface change, that is, the more it rained the less the surface changed. Inter‐annual (23 months) patterns of topographic change in the bowl and trough blowouts were distinctly different. In the deflation basin of the bowl blowout erosion predominantly took place on the erosional walls facing into the prevailing winds, while minimal change occurred on the erosional walls facing away from the prevailing wind direction. This produced a moderate negative correlation between surface change and slope, that is, the steeper the slope, the more erosion occurred. In the trough blowout, erosion took place in the centre of the deflation basin and minimal change was measured on the easternmost erosional wall, which faced the prevailing winds. Patterns of monthly topographic change were highly variable and demonstrated that changes in the direction of above‐threshold winds can cause blowout walls and floors to 'flip' from erosional to depositional surfaces. These findings highlight the variability and complexity of surface change in blowouts and demonstrate that patterns vary because of landform morphology and climatic conditions. [ABSTRACT FROM AUTHOR]

Deltas are reliant on upstream fluvial sediment sources for their survival. In the Rhine basin, the suspended sediment transport governs the supply of fines to the delta, a supply that has been dwindling for several decades. We investigate the changes in suspended sediment (SS) fluxes along the main Rhine branch and its tributaries since 1997 and link these to past and ongoing human activities in the basin. We demonstrate that the spatial pattern in the temporal change can allow us to discount and determine specific mechanisms of SS delivery, transport and trapping that are causing the recent decline. A clear spatial trend in the temporal change emerges: there is an increasing loss of SS from the upper basin towards the delta apex. For the last two decades, this is contributed to the introduction of retention basins, which increase the trapping of overbank fines during high flow. However, the declining sediment flux to the delta extends further in the past (at least since 1950); thus, we also examine potential historical mechanisms, which are different from the short‐term explanation. The longer term decline can be explained by the compound effects of dam construction and the decreasing fine sediment uptake by the river from its channel bed. The Rhine River has demonstrated incision in response to normalization works (finalized in the early 1920s). The incision rates declined over the second half of the 20th century corresponding to a declining SS supply from the bed to the delta apex. The importance of the channel bed as a source contributing to the total SS in human‐affected rivers and the contribution of fines through varying channel bed incision has not yet been identified or considered in global river basin studies. However, it may become increasingly relevant as more rivers are urbanized and controlled for flood protection purposes in the face of climate change. [ABSTRACT FROM AUTHOR]

The article in the Journal of Fluid Mechanics delves into the settling dynamics of two connected spheres through experiments and simulations, examining orientation angles, settling velocities, and drift velocities based on aspect ratio and Galileo number. The research sheds light on the intricate motion of the aggregate at varying parameters, emphasizing the formation of vortices in its wake. The study aims to deepen comprehension of environmental transport processes and engineering applications involving particle aggregates, offering empirical scaling laws for predicting settling behavior. [Extracted from the article]

In rivers, the addition of finer sediment to a coarser riverbed is known to increase the mobility of the coarser fraction. Two mechanisms have been suggested for this: a geometric mechanism whereby smaller sizes smooth the bed, increasing near-bed velocity and thus mobility of the larger sizes, and a viscous mechanism whereby a transitionally smooth turbulent boundary layer forms, rendering the coarser grains more mobile. Here, we report on experiments using two sediment mixtures to better understand these proposed mechanisms. In Mixture 1, we used 0.5 and 5 mm grains, and in Mixture 2, we used 2 and 20 mm grains. If the entrainment of coarse gravel by finer sediment is a purely geometric effect, then the addition of finer material should produce the same effect on the mobility of the coarser material for both mixtures because they have the same size ratio. We show that addition of finer material has a different effect on the two mixtures. We observed an increase in the mobility of the coarse fraction for both mixtures, but the increase in coarse fraction mobility for Mixture 1 was almost twice that for Mixture 2. Our experiments show that in addition to the geometric effect, enhancement of coarse gravel transport by finer sediment is also driven by a viscous effect. [ABSTRACT FROM AUTHOR]

Integrating coastal topographic and bathymetric data for creating regional seamless topobathymetric digital elevation models of the land/water interface presents a complex challenge due to the spatial and temporal gaps in data acquisitions. The Coastal National Elevation Database (CoNED) Applications Project develops topographic (land elevation) and bathymetric (water depth) regional scale digital elevation models by integrating multiple sourced disparate topographic and bathymetric data models. These integrated regional models are broadly used in coastal and climate science applications, such as sediment transport, storm impact, and sea-level rise modeling. However, CoNED's current integration method does not address the occurrence of measurable vertical discrepancies between adjacent near-shore topographic and bathymetric data sources, which often create artificial barriers and sinks along their intersections. To tackle this issue, the CoNED project has developed an additional step in its integration process that collectively assesses the input data to define how to transition between these disparate datasets. This new step defines two zones: a micro blending zone for near-shore transitions and a macro blending zone for the transition between high-resolution (3 m or less) to moderate-resolution (between 3 m and 10 m) bathymetric datasets. These zones and input data sources are reduced to a multidimensional array of zeros and ones. This array is compiled into a 16-bit integer representing a vertical assessment for each pixel. This assessed value provides the means for dynamic pixel-level blending between disparate datasets by leveraging the 16-bit binary notation. Sample site RMSE assessments demonstrate improved accuracy, with values decreasing from 0.203–0.241 using the previous method to 0.126–0.147 using the new method. This paper introduces CoNED's unique approach of using binary code to improve the integration of coastal topobathymetric data. [ABSTRACT FROM AUTHOR]

Iron‐rich, ferruginous waters were the dominant geochemical regime for most of Earth's history. Modern ferruginous waters are found in stratified, sulfur‐poor lakes, and serve as crucial analogs for biogeochemical cycling throughout Earth's past. Here we present the first depth‐resolved data of physical structure, nutrients and trace elements from Lake Poso (Indonesia), a deep oligotrophic ancient lake. Lake Poso is ferruginous, with anoxia below ~ 90 m depth, placing it among the world's largest ferruginous lakes. Physical stratification is weaker than other tropical anoxic lakes, indicating sensitivity for paleoclimate reconstructions. Trace elements and nutrients are predominantly shaped by the oxic–anoxic transition. Manganese– and Fe oxyhydroxide–driven biogeochemical cycling occurs at distinct depth horizons, with Co and Ni controlled by Mn and showing shallow release in anoxic waters, while V, Cr, P, and As are controlled by Fe, with release in surface sediments and diffusive transport. Chromium is nonquantitatively removed in anoxic waters, in contrast to widespread assumptions in Cr‐based paleoreconstructions. Oxycline U and Se removal corresponds to a local N minimum, suggesting biological reduction and/or uptake. These first ferruginous water Se data also show removal in sediments, indicating sediment signals reflect multiple removal processes and informing Se‐based paleoreconstructions, while the absence of sediment U removal contrasts other anoxic basins. A comparison with other ferruginous lakes demonstrates how local influences drive deviations from expectations in other systems, and highlight common, generalizable ferruginous basin features. Therefore, these data will guide research in ferruginous settings across space and time, and improve paleoreconstructions from ferruginous sediment records. [ABSTRACT FROM AUTHOR]

Logjams create an upstream backwater of deepened, slower water, locally reducing bed shear stress. We compared hydraulic impact of logjam series across 37 geomorphically diverse reaches of mountain streams observed over 11 years in the US Southern Rockies. To enable reach‐scale comparison of logjam structure and spacing, we identified the modeled best‐fit effective resistance coefficient minimizing difference between outflow exiting a 1D channel with logjams present, and the same model channel with elevated channel resistance. Effective resistance increased with ratio of jam upstream depth to depth without a logjam, ratio of backwater length to average spacing, and decreased for randomly distributed jams due to close spacing, which reduced backwater impact. An analytic approximation and boundaries for region of relative spacing with steepest increase in effective resistance are provided. Our results can assist in targeting interventions to areas where hydraulic impact is greatest, providing value for money in nature‐based solution design. Plain Language Summary: In a river channel, logjams created by wood pieces create upstream backwater regions with slower, deepened water. By creating a backwater, logjams increase heterogeneity of habitat and sediment transport and increase connection between river channel and floodplain. We compared logjams in 37 reaches of mountain streams in the US Southern Rockies. The sites studied had high variation in logjam density, channel steepness, channel width, and floodplain width. To compare between reaches and identify the ability of logjam backwaters to slow water within a river channel, we found an effective channel resistance coefficient that produced similar model output as a reach containing a series of logjams. The effective resistance increased with ratio of jam upstream depth to flow depth without a logjam, and ratio of backwater length to average spacing. The highest rate of increase in effective resistance with more logjams in the river reach occurs for an intermediate range of inter‐jam spacing relative to backwater length. Engineered logjam and wood addition projects could target this range to provide the most benefit per intervention. Key Points: We compared the hydraulic impact of logjams, identified by effective resistance, across 37 reaches and 11 years in the Colorado RockiesEffective resistance increases with decreasing stream power, analytically linked to dependence on jam structure and spacingObserved random jam distribution reduces effective resistance compared to uniform distribution, due to backwater truncation [ABSTRACT FROM AUTHOR]

Sediment residence time (SRT) is a key parameter of the Earth's surface system, bridging the realms of sediment transport, biogeochemical cycles, sedimentary archives, and watershed management. SRT in mountainous catchments includes the time particles have spent in the subsurface weathering zone, which has been challenging to measure thus limiting our understanding of the magnitude and controlling factors of SRT in steep terrains. In this study, we apply the 234U/238U activity ratio, (234U/238U), which reveals particle comminution age, to estimate SRTs in 32 catchments (drainage area of 6.79–143.67 km2) draining an active mountain range at the eastern margin of the Tibetan Plateau. The uranium comminution age allows us to account for the time that particles have spent in the weathering zone. The sampled catchments span a range of erosional, topographic, climatic and lithologic conditions, providing a unique opportunity to explore the controlling factors on SRTs. We measured the (234U/238U) of the 20–25 µm size fraction of the collected riverbed sediment samples and used the results to calculate particle comminution ages, which are used to approximate SRTs of fine sediment in the catchment. We then investigated the relationships between estimated SRTs and denudation rates, topography, climate, and lithology to assess controls on SRTs. The estimated SRTs range from 5.0 to 149.2 ka, and exhibit strong negative correlations with the 10Be-derived denudation rates and metrics for landscape steepness (relief, gradient, and channel steepness), with weak-to-moderate correlations with climatic and lithologic conditions. By combining the SRTs and denudation rates and assuming a steady-state weathering zone, we estimate a catchment-average comminution depth of 1.98 to 28.7 m, comparable to the depth of weathering zone estimated from modeling studies. Considering a topographic steady-state where denudation rates are in equilibrium with uplift rates, our results suggest that tectonic uplift exerts a primary control on the SRT in active mountain ranges, such that faster uplift rates shorten SRTs. Our findings suggest that tectonic uplift could regulate the temporal duration of chemical weathering by limiting the SRTs of fresh minerals in mountainous regions, sustaining a 'kinetically-limited' weathering scenario. [ABSTRACT FROM AUTHOR]

Submarine fan reservoirs are important accumulation zones for oil, gas, and natural gas hydrates, offering significant potential for hydrocarbon exploration. During the deposition period of the Sanya Formation in the southern part of the Changchang Sag of the Qiongdongnan Basin, a large submarine fan developed. However, the internal structure, source-sink system, and formation mechanism of this fan remain poorly understood, posing significant challenges to exploration in this area. This paper examines the source-to-sink sedimentary processes and deposition of submarine fans, using the Changchang Sag, in the Qiongdongnan Basin in the Northern South China Sea, as an example, which will provide valuable general guidance for deep water oil and gas exploration. Based on the theories of seismic stratigraphy and seismic sedimentology, this paper utilizes techniques such as seismic facies analysis, seismic attribute optimization, paleogeomorphology reconstruction, and source-to-sink sedimentary systemanalysis to analyze the 3D seismic data of the study area. Research indicates that the Sanya Formation in the Changchang Sag of the Qiongdongnan Basin comprises three depositional units: submarine fan, feeder channel, and Semi-deep marine to deep marine mudstone. The submarine fan is a fan formed by the coupling and convergence of submarine fans sourced from the southwest and southeast. Internally, it is divided into three sub-facies: the proximal fan of the sand-rich submarine fan, the main body of the sand-rich submarine fan lobes, and the distal lobes of the sand-rich submarine fan. The submarine fan sourced from the southwest extends nearly north-south and is primarily fed by sediment transported through three large, banded ancient valleys. The sedimentary filling is characterized by three-phase progradation. The submarine fan sourced from the southeast extends nearly east-west and is primarily fed by sediment transported through a single large, banded ancient valley. The sedimentary filling is characterized by two-phase lateral accumulation. During the deposition period of the Sanya Formation, certain areas of the southern uplift belt were exposed for extended periods and subjected to weathering and erosion. Sediments are transported to large ancient valleys through small supply channels. A large number of sediments were transported to the southern slope of the Changchang sag through the provenance channel system such as large ancient valleys and slope belts and deposited in the center of the sag. These make up a complete system of large ancient uplifts and submarine fan source-to-sink sedimentary systems. The sedimentary model is a lobed submarine fan controlled by semi-restricted ancient valleys and expansive basins. [ABSTRACT FROM AUTHOR]

Channel networks have been widely used to model sediment transport and accumulation. Extracting channel networks in the check dam region from digital elevation models on the Loess Plateau can facilitate effective decision‐making and planning for soil and water conservation. Three methods are generally used to ensure the continuity of channel networks by removing check dams as hydrological barriers: filtering, filling and breaching. However, these methods may still cause disruption and displacement of the channel network owing to the existence of check dams. This study presents the development of an integrated method (improved regional growth and linear feature detection [iRG‐LFD]) for extracting natural continuous channel networks and locating check dams. First, a proposed improved region growth method based on channel and check dam terrain features was used to extract the complete channel network. Subsequently, the line segment detector for extracting straight lines was then improved to separate lines with different slopes. Finally, by combining the channel network and line segment detector results, a cross model was proposed for extracting check dams of different sizes. The experimental results for the Wangmaogou and Zhoutungou catchments showed minimal errors when the proposed method was used to extract the channel network, and F1‐scores of 86.67% and 86.95% were obtained for the predicted check dam samples in the two catchments, respectively. The results indicate that this method can be effectively used to extract continuous natural channel networks and accurately identify check dams and can thus be used to design soil and water conservation measures. [ABSTRACT FROM AUTHOR]

This study focuses on evaluating the sediment mobility and transport patterns in two Himalayan rivers (Aglar and Paligad Rivers) during monsoon and non‐monsoon flows. The virtual velocity approach involving the measurements of the bed proportional mobility (Y), active layer depth (ds), displacement length and virtual velocity of mobilized grains was employed. Both local (0.5 m subsections) and wetted cross‐sectional average parameters were used. While using local parameters the total annual bed material transport was estimated to be 67 100 (±20 400 t) and 18 400 t (±6000 t) in the Aglar and Paligad Rivers, respectively. Of this, nearly 60% of transport occurred during the monsoon and the overall contribution of partial transport (PT) remained low (<6%). However, based on cross‐section average parameters, total transport was estimated to be 42 300 (±15 800 t) and 12 200 t (±4700 t), in Aglar and Paligad, respectively, with nearly 79% and 68% occurring during the monsoon. Moreover, the contribution of PT increased to nearly 18% and 29% for the Aglar and Paligad Rivers, respectively. Additionally, the dependence of PT on Y and full transport on ds results in an abrupt shift in transport rates at the transition from partial to full transport, causing discontinuity in transport curves. Therefore, a unified function was proposed to represent the extent of transport for both partial and full transport, yielding continuous transport curves. These findings are particularly relevant for efficient river management as the region houses several hydropower plants and is highly vulnerable to climate change. [ABSTRACT FROM AUTHOR]

The construction of large reservoirs has modified the process of water and sediment transport downstream, resulting in changes in the morphology of the river cross-section. Changes in water and sand transport and cross-sectional morphology are reflected in the rating curve at the cross-section. This study analyzed the variations in the rating curve at the Huayuankou (HYK) section and their influencing factors, and conducted water level predictions based on this relationship. The findings revealed that while the annual mean water level has shown a declining tendency over the past 20 years, the annual mean discharge has shown a constant pattern. The rating curve at this stretch narrowed from a rope-loop type curve in its natural condition to a more stable single curve as a result of the construction of the dam upstream of the HYK section. The effect of pre-flood section morphology and the water–sediment process on the scattering degree of the rating curve is inverse; increasing roughness and hydraulic radius decreases scattering degree, while increasing sand content and sand transport rate increases scattering degree. Using the measured data from 2020 as an example, the feasibility of predicting cross-sectional water levels using the rating curve was verified. The prediction results were accurate when the flow was between 1000 and 2800 m3/s; However, when the flow was between 2800 and 4000 m3/s, the forecast results were typically slightly lower than the measured values. Overall, the method demonstrates good predictive accuracy. Insight from the method can be used to predict water levels to better inform decision making about water resources management, and flood emergency response in the lower Yellow River. [ABSTRACT FROM AUTHOR]