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Abstract The battering of bedrock by bedload collisions is the primary mechanism by which bedrock rivers erode and landscapes evolve. The energy imparted via impacts acts to detach bedrock via the growth and intersection of surface fractures. We present impact experiments designed to test the influence of particle impact energy on bedrock erosion rates. We found that erosional efficiency increased with increasing impact energy. Notably, these increases in efficiency are not captured by a widely‐used mechanistic bedrock erosion model. Observed increases in erosional efficiency were linked with enhanced elastic energy dissipation captured by differences in the coefficient of restitution. We suggest that this increase in energy dissipation is indicative of enhanced crack extension for high velocity impacts. Our experiments indicate a clear energy‐dependence for bedrock detachment processes that is not yet captured by bedrock incision models but may be integrated into long‐term erosion rates and landscape evolution.

In the last few years, the exploitation of deep-sea regions for minerals extraction raised international attention as an economically viable source for the mining industry. However, most of these minerals are found close to sensitive ecosystems that can be harmed by mining activities. Given the potential impact, there is a need for the establishment of best practices towards the adoption of preventive strategies for the sustainable management and exploitation of deep-sea environments. To accomplish this objective, numerical models have proven to be reliable tools to support decision-making. In the present study, a high-resolution eddy-resolving ocean numerical model was configured and integrated with a semi-Lagrangian model aiming to map the transport of rock-fragments associated with mining activities. The model was applied to an area rich in polymetallic sulphides at the Northern Mid-Atlantic Ridge (NMAR). Model results showed that local topography and circulation dynamics played an important role for the dispersion and settling of the rock-fragments. In the presence of local submesoscale processes, the residence time do not follow the neutral relation H/vs. It was demonstrated that, depending on the local hydrodynamics, rock-fragments released at sub-surface depth can impact wider areas, with a predicted impact on pelagic and benthic organisms.

The availability of LiDAR data (including open-source data), combined with specialized algorithms, allows the use of these data to automatically detect landforms, vegetation and other objects. LiDAR point clouds have been frequently applied for the detection and evaluation of living trees but never for root plates of uprooted trees. However, tree uprooting is one of the most important biotic-abiotic interactions in temperate forests. This process leads to the formation of root plates, i.e., microrelief forms consisting of undecomposed tree root systems and the attached soil and rock particles. Root plates are involved in biotransport, i.e., the movement of soil and rock material by living organisms. The objective of this study was to develop an automatic method for root plate detection and volume (and thus biotransport) estimation based on LiDAR data. The study area included three Norway spruce-dominated plots located in two national parks in the Polish Carpathians. For validation, the author mapped the root plates using a GNSS receiver and measured their dimensions. We created the differential model presenting the height of root plates, fallen trunks, and dense understory vegetation by interpolating the last returns with a normalized height

We investigated wind-wave and suspended-sediment dynamics in Little Holland Tract and Liberty Island, two subsided former agricultural tracts in the Cache Slough complex in the northern Sacramento-San Joaquin Delta which were restored to tidal shallows to improve habitat. Turbidity, and thus suspended-sediment concentration (SSC), is important to habitat quality because some species of native fishes, including the Delta Smelt, are found preferentially in more turbid waters. Data from October 2015 to August 2016 show that average SSC was greater within Little Holland Tract than in the primary breach that connects the basin to surrounding channels: approximately twice as great at a shallower station farther from the breach and 15% greater at a deeper station closer to the breach. Suspended-sediment concentration within Little Holland Tract was directly related to wave shear stress and inversely related to water depth, based on linear regression. We used measurements of suspended-sediment flux (SSF) through the largest levee breaches to assess whether the enhanced SSC within Little Holland Tract is exported to surrounding waters, thus potentially increasing turbidity over a wider region. Cumulatively, sediment is exported through the Little Holland Tract breaches in winter and imported in summer, consistent with regional patterns in sediment flux, indicating that wind-wave re-suspension within the basin does not control sediment flux from Little Holland Tract on seasonal time-scales. Some sediment was exported during wind-wave events, and results show that sediment export is greater when primary breaches are located downwind of the basin rather than upwind.

The new navigation channel for large vessels entering the Hau River through the Kenh Tat and Quan Chanh Bo channels was announced in January 2016. The navigation channel route through Dinh An estuary in Soc Trang province to Can Tho port was not deeply concerned by the agency because of the sedimentation phenomenon, which was very serious and complicated. Only small vessels of 1,000-2,000 DWT can pass through the Dinh An estuary navigation channel, whereas large vessels pass through the Kenh Tat and Quan Chanh Bo channels. However, the new navigation channel entering the Hau River is also seriously sedimented, especially in the Cua Dai An area, where the tributary route starts from the Hau River through the Quan Chanh Bo channel and the estuary area in the Duyen Hai harbor basin. These are two important bottlenecks that drastically reduce the throughput capacity of this new navigation channel. This paper proposed five options for the spatial arrangement of works to stabilize and protect the channel through the Dinh An estuary. A MIKE 21 couple mode was used to simulate hydrodynamic and sediment transport in the study area, and the impact of these options on the characteristics, including water level, flow velocity, and bottom topographic change, was analyzed and evaluated. Based on these results, an optimal solution was suggested.

Land use is one of the most important variables impacting river basin water and land resource planning and management. Sediment transport in streams is an important issue in the assessment of sediment deposition in dam reservoirs and its impact on operational activities. Evaluation of sediment yield contributes to decision-makers for effective water management and protection of the dam body and its elements. In this study, land use cover changes, in particular in forest areas, agricultural areas, arable lands, permanent crops, heterogeneous agricultural areas, and pastures in the Çakıt and Körkün sub-basins of the Seyhan River basin were examined between 1990 and 2018 using CORINE land use cover (CLC) data. The effect of land use/land cover (LULC) modifications on sediment yield was studied using suspended sediment observation data and CLC data. It was determined that the forest area in the Çakıt sub-basin drainage area increased between 1990 and 2018, and decreased in the Körkün sub-basin. It was determined that the increase in forest area in the Çakıt sub-basin drainage region until 2018 helped to reduce sediment movement. The regression values between forest area and suspended sediment concentration in Çakıt and Körkün sub-basins were found to be 0.9521 and 0.4431, respectively. HIGHLIGHTS Investigation of land use changes in river basins.; Assessment of sediment transport in river basins.; Investigation of the impact of land use changes on sediment yield.;

This study aimed to comprehensively investigate the influence of substrate level difference and material composition on dam break wave evolution over two different erodible beds. Utilizing the Volume of Fluid (VOF) method, we tracked free surface advection and reproduced wave evolution using experimental data from the literature. For model validation, a comprehensive sensitivity analysis encompassed mesh resolution, turbulence simulation methods, and bed load transport equations. The implementation of Large Eddy Simulation (LES), non-equilibrium sediment flux, and van Rijn’s (1984) bed load formula yielded higher accuracy compared to alternative approaches. The findings emphasize the significant effect of substrate level difference and material composition on dam break morphodynamic characteristics. Decreasing substrate level disparity led to reduced flow velocity, wavefront progression, free surface height, substrate erosion, and other pertinent parameters. Initial air entrapment proved substantial at the wavefront, illustrating pronounced air-water interaction along the bottom interface. The Shields parameter experienced a one-third reduction as substrate level difference quadrupled, with the highest near-bed concentration observed at the wavefront. This research provides fresh insights into the complex interplay of factors governing dam break wave propagation and morphological changes, advancing our comprehension of this intricate phenomenon.

The intricate calculation of bed sediment load (BSL), which is influenced by hydraulic, hydrological, and sedimentary factors, is vital for informed decision-making in water resource management. Machine learning models, which are gaining popularity due to their accessibility and ability to reveal complex relationships, play a significant role in tackling these challenges. The efficacy of gene expression programming (GEP) models, support vector machines (SVMs), multi-layer perceptron (MLP), and multivariate adaptive regression splines (MARS) has been assessed through measured data of number 540 obtained from six rivers, namely Oak Creek, Nahal Yatir, Sagehen Creek, Elbow River, Jacoby River, and Goodwin Creek from 1954 to 1992. The assessment of model performance has been conducted utilizing root mean square error (RMSE), R2, Nash–Sutcliffe coefficient (NSE), and developed discrepancy ratio (DDR) as indices. Following data normalization within the range of 0–1, the data models underwent training and testing processes with a partition ratio of 80% for training and 20% for testing. Four dimensionless parameters, denoted as Fr = U/√gy, U/U*, Se, and ω = τU/γs√gyDs3, were employed as inputs in the models. The outcomes indicate that they exhibit superior performance compared to other methods, as evidenced by the following metrics in predicting BSL during the test stage: RMSE = 1.4088, NSE = 0.73054, R2 = 0.8729, and maximum QDDR(max) = 1.9564. HIGHLIGHTS The present work proposes BSL prediction using field data from six rivers.; Four machine learning models including SVM, GEP, MLP and MARS are employed to forecast BSL.; A variety of inputs is implemented for each MLMs to find optimum output.; Statistical indices are used to opt for superior MLMs for BSL prediction.;

Predicting and estimating sediment yield from the catchment is crucial for the effective management of water resources and controlling soil erosion. Until now, Universal Soil Loss Equations (USLE) and their modifications are appreciated and commonly applied among many methods. The idea of this work is to use the ESDAC database (a web platform hosting a series of pan-European and global datasets on soil erosion) to build the modified form of the USLE for the Zagożdzonka catchment, a small agricultural area located in central Poland. The calculated sediment yield is compared with the one determined based on the reservoir survey. Conducted analyses show that the average annual suspended sediment yield from the study catchment estimated using the MUSLE equation accounts for 201 Mg and is close to that determined based on the reservoir survey, i.e., 248 Mg. However, MUSLE, with the initially proposed parameters, will overpredict sediment transport at the study site. The ESDAC database may support local studies concerning soil erosion and sediment transport. The research is helpful for policymakers, planners, and engineers.

Despite modern advances in the study of rivers globally, there remains a plethora of work to be done especially in the area of fluvial sedimentology of some present-day river systems. Previous studies on fluvial sedimentology of the sediments of the river Ethiope (in southern Nigeria) are meagre. Grain size analytical methods are indispensable to infer siliciclastic sediments' hydrodynamic conditions, transportation mode(s), and sedimentary environments. Twenty-eight samples (n=28) of the river Ethiope sediments were selected and studied using granulometric analyses (mechanical sieving and pebble morphometric methods). The granulometric analyses results revealed that the obtained sediments were comprised of 82.75% sand, 9.33% gravel, and 7.92% mud. A ternary diagram of sand-gravel-mud shows the sediments are mainly gravelly sand, with few indicating slightly gravelly sand, gravelly muddy sand, muddy sand, and sandy gravel. The grain size statistical analysis shows that the river Ethiope sediments consist of medium to coarse, poorly-sorted to moderately well-sorted, strongly coarse skewed to strongly fine skewed, and very platykurtic to extremely leptokurtic sands. The pebble morphometric analysis revealed that the pebbles range in shape from bladed (B) 22%, compact-bladed (CB) 17%, compact (C) 16%, compact-platy (CP) 16%, compact-elongated (CE) 12%, platy (P) 5%, to elongated (E) 5%. The integration of bivariate plots, ternary diagrams, and C-M patterns plotted for the sediments of the river Ethiope indicated a fluvial environment with sediments characterised by low to moderately high energy that transport sediments of different sizes and grades through saltation, traction, and suspension modes. This study also confirms that sediment transport modes such as saltation, traction, and suspension typify river environments. In general, the existing sedimentologic models derived from grain size analysis of sediments and pebble morphometric methods obtained from modern-day rivers can be applied to better understand transport modes, sedimentary processes, and palaeoenvironments of their ancient counterparts.

Estimating ecological environmental flow in tidal rivers is one of the major challenges for sustainable water resource management in estuaries and river basins. This paper presents an ecological environmental flow framework that was developed to accommodate highly dynamic medium tidal estuaries found along the Yellow Sea coast of China. The framework not only proposes a method of water quality-based ecological flow for tidal gate-controlled rivers but also proposes a method of water demand for scouring and silting to protect ports in coastal viscous sediment environments. The framework integrates the instream water requirements of water quality, sediment and basic ecological flow, and considers the temporal and spatial variation differences for the environmental flow requirements of tidal rivers. This study emphasizes the significance and necessity of continuous monitoring of ecological data in determining the environmental flow of tidal rivers. The output of this study could provide vital references for decision-making and management of the water resource allocation and ecological protection in tidal rivers. HIGHLIGHTS This study develops an ecological environmental flow framework for highly dynamic medium tidal estuaries.; This study suggests a method of water quality-based ecological flow for tidal gate-controlled rivers.; This study proposes a method of water demand for scouring and silting.;

Understanding the material properties and physical conditions of basal ice is crucial for a comprehensive understanding of Antarctic ice‐sheet dynamics. Yet, direct data are sparse and difficult to acquire. Here, we employ ultra‐wideband radar to map high‐backscatter zones near the glacier bed within East Antarctica's Jutulstraumen drainage basin. Our backscatter analysis reveals that the basal ice in an area of ∼10,000 km2 is composed of along‐flow oriented sediment‐laden basal ice units connected to the basal substrate, extending up to several hundred meters thick. Three‐dimensional thermomechanical modeling supports that these units form via basal freeze‐on of subglacial water that originated from further upstream. Our findings suggest that basal freeze‐on, and the entrainment and transport of subglacial material play a significant role in an accurate representation of material, physical, and rheological properties of the Antarctic ice sheet's basal ice, ultimately enhancing the accuracy and reliability of ice‐sheet modeling. Plain Language Summary: We investigate the lowermost portion of the ice column of the Antarctic ice sheet, known as basal ice. This part holds crucial information about how the ice sheet behaves when it flows. Using the principle of echo‐location, we use radar technology to scan the ice in East Antarctica's Jutulstraumen drainage basin. We discover that a significant portion of the basal ice in this region is filled with sediment and can be several hundred meters thick. To better understand how this distinctive type of ice forms, we used a mathematical model that suggested that these ice units likely form when water underneath the ice is transported and refreezes at particular locations. Our findings highlight the importance of these freezing and mixing of materials from beneath the ice. Understanding where these ice units are located provides important information for ice‐flow models to ultimately better understand how the Antarctic ice sheet behaves in the future. Key Points: We have identified high‐scattering basal ice in Jutulstraumen Glacier's onset region using radar, reaching several hundred meters from the bedBackscatter analysis suggests that the basal ice units contain unstratified point scatters and cause little radio‐glaciological loss3D thermo‐mechanical modeling implies that freeze‐on of basal meltwater generated upstream likely initially formed the basal ice units [ABSTRACT FROM AUTHOR]

The occurrence and level of polycyclic aromatic hydrocarbons (PAHs) in mangrove sediment from Ifiekporo Creek in Warri, Delta State, Nigeria, were assessed in this study. The extraction of PAHs from the sediment samples was achieved using the PAH analytical test method (USEPA 8270). This method measures the individual concentrations of extractable PAHs in samples. The PAHs were quantified within the C11-C22 subgroup. The basic GC parameters for the analysis of polyaromatic hydrocarbons were analysed using a gas chromatography‒mass selective detector (GC‒MSD). The individual PAH concentrations in the mangrove sediment samples ranged from 850 µg/kg−1 to 3470 µg/kg−1. PAH source apportionment employing isomeric ratios and multivariate statistics indicated both pyrogenic and petrogenic source inputs in the sediment samples. The order of PAH homology in the sediment was 3-ring > 2-ring > 4-ring. The sediment samples were mostly dominated by LMW PAHs. The results of the ecological risk assessment in the study area indicate that there is low ecological risk associated with PAH exposure in sediment. These results provide data on the concentrations and compositional patterns of PAHs, which is useful for understanding the effects, sources, fates, and transport of PAHs in sediment in the study area, as well as for providing relevant information for environmental quality management and forensic studies. [ABSTRACT FROM AUTHOR]

The aim of this research was to analyze the impact of implemented erosion control works (ECW) on soil erosion intensity in the watershed of the Ćelije reservoir (Rasina River) in the period between 1968 and 2022. The Erosion Potential Method was used to calculate the annual gross erosion (W), sediment transport (G), and erosion coefficient (Z) in the study area. As a result of the performed ECW there was a general decreasing trend in the intensity of soil erosion processes in the last 54 years. The specific annual gross erosion was 1189.12 m3/km−2/year−1 in 1968, while in 2022 it was 554.20 m3/km−2/year−1. The specific sediment transport was 540.18 m3/km−2/year−1 in 1968 and 253.55 m3/km−2/year−1 in 2022. Due to the changes in the intensity of erosion processes, the specific annual gross erosion decreased by 634.92 m3/km−2/year−1 and the specific sediment transport decreased by 286.63 m3/km−2/year−1. The erosion coefficient was reduced from Z = 0.62 to Z = 0.35. A dependence between the slope of siltation and the natural bed slope was defined. The results show a significant correlation between erosion intensity and performed ECW, providing a basis for future watershed management and defining a strategy for soil erosion control in the Ćelije reservoir watershed. [ABSTRACT FROM AUTHOR]

Predicting morphological adjustments in alluvial meandering streams remains a challenging task due to the complex nature of the governing inter-related dynamic flow and sediment transport processes. This difficulty is increased in streams with irregular single-channel planform geometries, such as skewed meanders, where the meander apex is shifted in either the up-valley or down-valley direction relative to the meander centroid. Research in confined bank flume experiments has shown that the geometry difference affects flow characteristics and streambed development. The present study extends upon these findings by being the first to investigate the effects of skewness orientation in a wide-channel flume with a fully unconfined bed and banks. Three experiments were completed with an up-valley skewed, a down-valley skewed, and a non-skewed symmetrical channel, using well-sorted coarse sand and no sediment feed. The results had some variabilities in erosion and magnitude of morphological developments due to initial experimental conditions, but our analysis of the bedform positioning showed notable similarities and differences between the geometries. Bedforms typically formed upstream of the apex, with differences in their stream-wise direction extents. This research highlights how channel width-to-depth ratio and bank erodibility significantly impact river evolution, offering new insights into the dynamics of skewed meandering river channels. This study is a novel step towards a better understanding of skewed meandering rivers in unconfined alluvial channels and highlights opportunities for further research. [ABSTRACT FROM AUTHOR]

In this study, a swash-zone model, using Larson and Wamsley formula (LW07), was combined into the Telemac-2D model system to examine the performance of modeling swash-zone processes through comparisons with field observation data. The experimental site was the Haeundae Beach in South Korea where Typhoon Phanfone occurred in October 2014, and bathymetric surveys were performed before and after the typhoon. Hydrodynamic data were also measured to validate the modeled data. The performance of LW07 was tested by running the model in two modes, with and without LW07. First, the model was run to simulate the shoreline response to an imaginary coastal breakwater. The result showed a clear discrepancy between the two modes as the sediments were considerably cumulated behind the breakwater in the case with the swash-zone formula (LW07) in the wide range along the shoreline behind the breakwater, indicating that the sediments more actively and rapidly responded to the shadowing by the breakwater with LW07. The model was also run for a realistic case from August to October 2014, which included the typhoon's period during 2–6 October. The results showed that the morphological changes at both ends of the beach in the swash zone were simulated with higher accuracy with LW07, supporting the effectiveness of LW07 in simulating the short-term morphological changes induced by the typhoon attack. In particular, the successful simulation of the sand accumulation at the end sides of the beach's swash zone indicates that LW07 was effective in estimating not only the cross-shore transport but also longshore transport, which was likely due to the characteristics of LW07 that calculated sand transport in both directions. The enhanced modeling performance with LW07 was likely due to the adjustment of the sediment transport rate to the instantaneous changes in the local beach slope, which could successfully control the erosion/accretion process in the swash zone more realistically. [ABSTRACT FROM AUTHOR]

The Inner Mongolia section of the Yellow River is a primary alluvial segment of the main channel. The variations in water and sediment not only alter the cross-sectional morphology and flow capacity of the river but also impact the scheduling of upstream cascade reservoirs. Based on runoff and sediment load data and topographic information from typical hydrological stations, the characteristics of runoff and sediment load variations and the evolutionary pattern of siltation in the Inner Mongolia River section were analyzed via trend analysis methods, Mann–Kendall test methods, the sediment load transport rate method, and the water level–flow relationship. The results showed that the water and sediment loads at the hydrological stations in the Inner Mongolia River section significantly changed from the 1960s to after 2000, with runoff decreasing by approximately 22% to 32% and the sediment load decreasing by approximately 65% to 73%. Sedimentation in the river section generally increased, and the average annual siltation amount reached 0.144 billion t. The joint utilization of the Longyangxia and Liujiaxia reservoirs in 1987 was the main reason for the rapid increase in siltation, and siltation in the Inner Mongolia River section was slightly reduced after 2005. In addition, the critical sediment load coefficients of the Bayangaole–Sanhuhekou and Sanhuhekou–Toudaoguai River sections were 0.0073 and 0.0051 kg·s/m6, respectively, from 1952 to 1968, and 0.0053 and 0.0037 kg·s/m6, respectively, from 1969 to 2020. This study could provide technical support for river flood control and reservoir water sediment regulation in Inner Mongolia. [ABSTRACT FROM AUTHOR]

This study applies the WaTEM/SEDEM model, a watershed-scale model based on the Universal Soil Loss Equation (USLE), to enhance sustainable watershed management by identifying high-erosion-risk areas for targeted mitigation at various scales. It focuses on identifying potential errors in using statewide or worldwide land use data layers derived from remote-sensing algorithms and inaccuracies in the spatial distribution of cropland and soil types resulting in misinterpretation of sediment yields. These model limitations emphasize the need for field validation and precise input data, particularly stream data, to improve the reliability of these models. The study examines hydrologic rainfall-runoff processes in Tennessee's 182 km2 Oostanaula catchment using various data sources, including the National Land Cover Database (NLCD), the European Space Agency WorldCover dataset (ESA), and manual field surveys. Three modeling scenarios were evaluated, with and without stream topology corrections, using the WaTEM/SEDEM model. It details the global data used, the methodology of the field survey, the simulation and validation of data, and the critical point identification. Significant discrepancies in long-term sediment transport predictions were found, depending on the land use data source. This study addresses watershed model validity and potential errors and recommendations for the use of globally available data. [ABSTRACT FROM AUTHOR]

Sediment fluxes to the seafloor govern the fate of elements and compounds in the ocean and serve as a prerequisite for research on elemental cycling, benthic processes and sediment management strategies. To quantify these fluxes over seafloor areas, it is necessary to scale up sediment mass accumulation rates (MAR) obtained from multiple sample stations. Conventional methods for spatial upscaling involve averaging of data or spatial interpolation. However, these approaches may not be sufficiently precise to account for spatial variations of MAR, leading to poorly constrained regional sediment budgets. Here, we utilize a machine learning approach to scale up porosity and 210Pb data from 145 and 65 stations, respectively, in the Skagerrak. The models predict the spatial distributions by considering several predictor variables that are assumed to control porosity and 210Pb rain rates. The spatial distribution of MAR is based on the predicted porosity and existing sedimentation rate data. Our findings reveal highest MAR and 210Pb rain rates to occur in two parallel belt structures that align with the general circulation pattern in the Skagerrak. While high 210Pb rain rates occur in intermediate water depths, the belt of high MAR is situated closer to the coastlines due to lower porosities at shallow water depths. Based on the spatial distributions, we calculate a total MAR of 34.7 Mt yr-1 and a 210Pb rain rate of 4.7 · 1014 dpm yr-1. By comparing atmospheric to total 210Pb rain rates, we further estimate that 24% of the 210Pb originates from the local atmospheric input, with the remaining 76% being transported laterally into the Skagerrak. The updated MAR in the Skagerrak is combined with literature data on other major sediment sources and sinks to present a tentative sediment budget for the North Sea, which reveals an imbalance with sediment outputs exceeding the inputs. Substantial uncertainties in the revised Skagerrak MAR and the literature data might close this imbalance. However, we further hypothesize that previous estimates of suspended sediment inputs into the North Sea might have been underestimated, considering recently revised and elevated estimates on coastal erosion rates in the surrounding region of the North Sea. [ABSTRACT FROM AUTHOR]

Sediment grains are progressively rounded during their transport down a river. For more than a century, Earth scientists have used the roundness of pebbles within modern sediment, and of clasts within conglomerates, as a key metric to constrain the sediment's transport history and source area(s). However, the current practices of assessment of pebble roundness are mainly qualitative and based on time-consuming manual measurement methods. This qualitative judgement provides the transport history only in a broad sense, such as classifying distance as "near" or "far". In this study, we propose a new model that quantifies the relationship between roundness and the transport distance. We demonstrate that this model can be applied to the clasts of multiple lithologies including modern sediment, as well as conglomerates, deposited by ancient river systems. We present field data from two Himalayan catchments in Nepal. We use the normalized isoperimetric ratio (IRn), which relates a pebble's area (A) to its perimeter (P), to quantify roundness. The maximum analytical value for IRn is 1, and IRn is expected to increase with transport distance. We propose a non-linear roundness model based on our field data, whereby the difference between a grain's IRn and the maximum value of 1 decays exponentially with transport distance, mirroring Sternberg's model of mass loss or size reduction by abrasion. This roundness model predicts an asymptotic behaviour for IRn , and the distance over which IRn approaches the asymptote is controlled by a rounding coefficient. Our field data suggest that the roundness coefficient for granite pebbles is 9 times that of quartzite pebbles. Using this model, we reconstruct the transport history of a Pliocene paleo-river deposit preserved at the base of the Kathmandu intermontane basin. These results, along with other sedimentary evidence, imply that the paleo-river was much longer than the length of the Kathmandu Basin and that it must have lost its headwaters through drainage capture. We further explore the extreme rounding of clasts from Miocene conglomerate of the Siwalik zone and find evidence of sediment recycling. [ABSTRACT FROM AUTHOR]

Fluvial discharge is a principal driver of suspended sediment (SS) transport in the Central Himalayan region, Nepal. The study examines the relationship between specific discharge at three hydrometric stations along the main Kali Gandaki (KG) River, four hydrometric stations on its tributaries with rainfalls across the entire basin and its sub basins, in relation to SS transport at a hydropower reservoir. Over the period of 2006–2017, the average monthly rainfall in June (388.39 ± 84.24 mm), July (674.91 ± 105.24 mm), August (571.81 ± 110.77 mm), and September (356.50 ± 104.39 mm) yielded an average of 2.469 ± 1.641, 12.952 ± 4.932, 12.629 ± 7.937, and 4.406 ± 2.363 megatons (Mt) of SS loads, respectively, flowing from the KG catchment into the hill-side dam reservoir. Results indicated that approximately 97% of SS was transported during the monsoon season (June–September). This corresponds to an estimated annual weathering rate in the basin of 4390 tons/km2/year, equivalent to 1.66 mm/year. Notably, both the specific direct runoff discharge and the monsoonal daily erosion rate during major rainfall events (> 30 mm/day) exhibited an upward linear trend with the basin's rainfall. [ABSTRACT FROM AUTHOR]

A high‐resolution wave model is crucial for accurate modeling of sediment and organic material transports, but its computational costs hinder direct coupling to an ecosystem model. We developed a machine learning model using long short‐term memory to simulate large‐scale, high‐resolution waves. Trained with numerical wave model (NWM) outputs and wind data from nine locations, our model successfully replicates NWM results for daily mean significant wave height and period in Chesapeake Bay with identical spatial resolution. Compared to the NWM, the data‐driven model has root‐mean‐square errors below 6 cm for daily mean significant wave height and 1 s for the wave period in the bay. It demonstrates excellent model skills and can accurately forecast daily mean significant wave height and period at NOAA wave stations comparable to NWMs. Using minimal wind data and having a short runtime, our data‐driven model shows promise as an alternative for wave forecasting and coupling with sediment and ecological models. Plain Language Summary: Accurately modeling sediment and organic transport necessitates the use of a high‐resolution numerical wave model (NWM). However, the computational expenses of running an NWM within an ecosystem model pose significant challenges. We conducted a study using a machine learning approach based on long short‐term memory to replicate the results of an NWM. The data‐driven wave model (DWM) was trained with the NWM outputs and wind data from nine locations. The trained DWM can replicate the NWM results of daily mean significant wave height and period in Chesapeake Bay with identical spatial resolution and the same predictive skill with a root‐mean‐square error of less than 6 cm and 1 s, respectively for the model domain. The model successfully forecasted daily mean significant wave height and period at NOAA wave stations, showing great forward prediction capability. Notably, the DWM only relied on a minimal amount of wind data from selected locations and had a short runtime. These findings indicate that machine learning is promising as an alternative approach to NWM for wave forecasting. Moreover, it can serve as an alternative wave model and be coupled to ecological models for simulating sediment transport, light attenuation, and resuspension of organic materials. Key Points: A machine learning‐based wave model reproduces the numerical wave model (NWM) results at the same spatial resolution with good accuracyThe data‐driven model, trained on daily significant wave height and period using NWM outputs, has comparable wave prediction skillThe fast‐running data wave model, driven by wind data from nine locations, can forecast waves and couple with sediment and ecological models [ABSTRACT FROM AUTHOR]

Feedbacks between sediment and plants in the submersed aquatic vegetation (SAV) beds of the Susquehanna Flats help modulate sediment delivery into the upper Chesapeake Bay from its major tributary (Susquehanna River). Recent modeling work has shown that SAV can steer the river plume, directly controlling sediment transport and fate. However, transport mechanisms likely differ between flood and non‐flood conditions and depend on event timing. An opportunity to evaluate these insights in the field occurred with several flood events in summer 2018. Sediment and biomass samples were collected after the flood in the large, continuous main SAV bed of the Flats and in smaller patches to the west of the main bed to evaluate the effect of SAV bed size (width). Sediment characteristics (grain size, organic content) and deposition rates were compared to previous observations during non‐flood conditions in the main bed in 2014–2015 and in the smaller patches in 2019. Overall, sediment deposition rates could be predicted by an empirical model including sediment load, vegetation biomass, and SAV bed width, reflecting the role of vegetation in steering the Susquehanna River plume and modulating sediment input to the upper Chesapeake Bay. Understanding spatiotemporal patterns of sedimentation is essential for realistic estimates of sediment and nutrient (especially nitrogen and carbon) storage in freshwater SAV systems, which have not received as much attention as their saltwater counterparts. [ABSTRACT FROM AUTHOR]

Relocating levees further back from river channels to increase river–floodplain connection can reduce flood stages and provide a host of co‐benefits. Modeling case studies show the significant potential of large levee setbacks for reducing flood stages; however, the difficulty of comparing between these case studies limits our understanding of how the hydraulic effects of setbacks vary in different settings. We filled this research gap by systematically modeling the hydraulic effects of setbacks across a range of river and flood conditions. We used unsteady, 1D Hydrologic Engineering Center‐River Analysis System models to quantify changes in flood stage, channel velocity, and sediment transport capacity for various setback sizes with different river slopes, widths, floodplain roughness, and flood sizes (peak flows) and durations. Setbacks reduce flood stages within the setback, as well as up‐ and downstream. Channel velocity and sediment transport capacity both increased upstream and decreased within the setback. Channel slope, flood size, and flood duration had the largest influence on hydraulic changes. There are diminishing returns in hydraulic effects with increasing setback size. These results can help guide the design and prioritization of levee setback projects and help set reasonable expectations for the scale of changes to flood hydraulics relative to the size of the reconnected floodplain. [ABSTRACT FROM AUTHOR]

The accumulation of pollutants in the sediment along surface water may negatively affect riparian zones and increase ecological risk. This article investigates the effects of metal sediments on riparian soil via field monitoring and ICP-OES analysis. To this end, pollution levels, seasonal changes, and potential sources of the pollutants were determined for the Melen River watershed, Turkey. The ecological statuses (contamination factor, enrichment factor, index of geo-accumulation, pollution index, modified pollution index, and potential and modified ecological risk indexes) of the watershed were also analyzed. Although no significant seasonal differences in the metal sediments were observed, their spatial distribution in the sediments and riparian soils varied markedly. Cr (11.4 to 136), Co (7.7 to 21.52), Cu (11.4 to 76.6), and Ni (14.06 to 128.2) recorded as mg/kg significantly increased from the upstream to the downstream. The metals possessing the highest risk in the sediment and riparian soil regarding the river health were Cu, Co, and Ni. The risk values were found to be heavily polluted (PI > 3 and MPI > 10), and the risk indexes were above the "desired environment without the risk". The risk index was found to be more than 50, and the modified risk indexes exceeded 200 at many points. The transportation of pollutants in surface water became evident in the sediment, resulting in adverse effects on the riparian zone and the ecological system. [ABSTRACT FROM AUTHOR]

Excessive sedimentation in sand-laden rivers significantly hinders the normal operation and overall effectiveness of reservoirs. This is observed particularly in plain-type sand-laden reservoirs where weak hydraulic conditions in the reservoir area contribute to sediment deposition. Water–sediment regulation is essential in reducing sedimentation and prolonging the lifespan of such reservoirs. Taking the plain-type reservoir of the primary stream of the Yellow River—Haibowan Reservoir as an example, based on a two-dimensional shallow water equation, a two-dimensional mathematical model of water and sediment in the reservoir area is established, the corresponding boundary conditions are improved, and the reliability of the model is verified. Under the premise of ensuring the flood control safety of the reservoir dam, considering the impact on the power generation of the reservoir and the downstream river, and maintaining the long-term large effective storage capacity of the reservoir as the basic principle, the water–sediment regulation scheme is proposed. A two-dimensional kinetic model of sediment transport and representative water–sediment series are employed to simulate the erosion and sedimentation processes in the reservoir under different schemes. The optimisation and comparison of multiple schemes reveal that the sediment-flushing scheme, which lowers the water level to 1072 m above sea level when the inflow discharge is 1500–2760 m3/s and inflow sediment concentration is 5–10 kg/m3, can yield an effective reservoir capacity of 97 million m3 and an average annual hydropower generation of 389.5 million kWh after 15 years of operation. This scheme outperforms the existing sediment-flushing scheme and is recommended as an optimised approach for water–sediment regulation in reservoirs. The results of this study provide technical support for the application of water–sediment regulation in the Haibowan Reservoir and may be useful in the exploration and management of water–sediment regulation for plain-type reservoirs on sand-laden rivers. [ABSTRACT FROM AUTHOR]

The present knowledge of plunging hyperpycnal river plumes is mainly based on two‐dimensional (confined) laboratory experiments. Several hypotheses on three‐dimensional (unconfined) flow processes have been made, but not tested in situ. In this field study, the dominant three‐dimensional hydro‐sedimentary processes related to unconfined plunging were elucidated by synchronizing autonomous time‐lapse camera images with boat‐towed acoustic Doppler current profiler measurements. It was found that the flow field complies with two‐dimensional conceptualizations along the plume centerline. Perpendicular to the centerline, the plume slumped laterally due to its density excess and simultaneously converged laterally due to its vertical divergence. This combination led to a narrowing of the plume near the surface, resulting in a sediment‐rich triangle‐shaped pattern on the surface near the inflow, and a rather stable width near the bed. The formation of secondary flow cells transporting riverine water and suspended particulate matter (SPM) away from the plume near the bed, up toward the surface and back toward the plume near the surface, was revealed. An increase of the average SPM concentration and the SPM flux in the main flow direction indicates net sediment erosion under the investigated conditions of high discharge and sediment load. This suggests transient storage of sediment during conditions of lower discharge and sediment load, and high morphological activity in the plunging area. These findings allowed extending a classical conceptual plunging model to laterally unconfined sediment‐laden plunging inflows for conditions of well‐mixed ambient water in the plunging region and inflow densimetric Froude numbers exceeding 1, common in nature. Plain Language Summary: When higher density river water flows into a lower density lake or reservoir, the river water forms a plume that dives down (referred to as plunging) toward the bottom of the lake or reservoir and flows along its bottom as an underwater current. Previously, the processes related to plunging were poorly understood in typical lake settings. In this study, these processes were investigated by combining camera images of the lake surface and measurements along a grid of both the currents and sediment concentration of the Rhône River plume entering Lake Geneva (Switzerland). Previously predicted processes occurring in the river plume, including plunging along its axis and a combination of lateral collapsing and contracting motions, were confirmed to exist. Other processes, including two swirling flows transporting river water and sediment back toward the surface, were revealed. These contribute to the spreading and mixing of river water and sediment in different ways from those measured in laboratory representations of reservoirs. Furthermore, the plunging river water eroded the lake bed near the river mouth during the measurements. The results from this study lead to a better understanding of plunging flows in lakes and allow for improved modeling and better predictions of such flows. Key Points: Dominant three‐dimensional hydro‐sedimentary processes related to laterally unconfined river plume plunging were revealed by field measurementsThese processes include lateral secondary flow cells spreading over the local depth, sediment transport, and flow‐bed interactionsThe new findings allowed extending a classical conceptual plunging model to laterally unconfined sediment‐laden inflows [ABSTRACT FROM AUTHOR]

The spatial distribution of sediments on the seafloor reflects the various dynamic processes involved in the marine realm. To analyze sediment transport patterns in the North Aegean Sea, 323 surficial samples were obtained and studied. The granulometry data revealed a diverse range of grain sizes of surficial sediments, ranging from purely sandy to clay. The predominant size classes were silt and muddy sand, followed by sandy silt and mud. However, there were very few samples that fell within the clay classes. The sorting coefficient ranged from 0.21 to 5.48, while skewness ranged from −1.09 to 1.29. The sediment transport patterns were analyzed based on the grain-size parameters (mean, sorting, and skewness). The results showed the variability of flow parameters involved in sediment distribution. River influx and longshore drift near the shoreline are the most significant factors affecting sediment transport. At the open sea, sediment distribution is mainly controlled by general water circulation patterns, especially by the outflow of low-salinity waters from the Black Sea through the Dardanelles and the Marmara Sea. The heterogeneity of sediment textural parameters across the study area suggests that seafloor sediments are further reworked in areas where water masses are highly energetic. It can be concluded that open sea water circulation controls sediment distribution patterns at the open shelf, while close to the coast, river discharge plays a key role. [ABSTRACT FROM AUTHOR]

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

Sandy beaches high in recreation value make up 16% of the over 4000 km long shoreline of Estonia. The shore processes associated with climate change have remarkably accelerated over recent decades. Many sandy shores have suffered from strong erosion, including an excellent former beach at Valgeranna. The jetties, which were built in the 1860s to protect the navigation channel of Port Pärnu from clogging, have prevented natural sediment transport along the coast from south to north. At the same time, the sandy beach in Pärnu is expanding, and part of the sand accumulates with strong storms also in between the jetties, reducing the width of the shipping channel. The channel needs regular dredging, but, so far, the dredged sediment has been taken far away to the open sea and accumulated on the seabed. The current paper addresses the possibilities of using that sand for beach restoration in destructed and eroded areas. An overview of the applied methods and measurements during field studies is given. The results of modelling the processes of wave activity and sediment transport are discussed. The recycling of shore sediments is an important measure in sustainable coastal zone management. Different options and scenarios are analysed in order to find the most reasonable ways to bring sand back onto beaches and stabilize natural processes. Support from the state by working out respective laws and regulations would be motivating as well. [ABSTRACT FROM AUTHOR]

The construction of check dams is a common practice around the world where the aim is to reduce the damage by flooding events through mountain streams. However, quantifying the effectiveness of such engineering structures has remained very challenging and requires well-selected case studies, since the outcome of such an evaluation depends on site-specific geometric, geologic and climatic conditions. Conventionally, the check dams' effectiveness has been estimated using information about how the bedload sediment flux in the stream changes after the check dams are constructed. A permanent lowering of the bedload flux not only points to a success in reducing the probability of sediment transport occurrence but also implies that the sediment input through the system is likely to decrease. Here, we applied a method for data acquisition and two different equations (Meyer-Peter–Müller and Recking approach) to estimate and compare the sediment transport in a mountain stream in Switzerland under engineered and non-engineered conditions. Whereas the first equation is derived from a classical approach that is based on flume experiment data with a slope of less than 0.02 m m -1 , the second equation (Recking) has been derived based on a bedload field dataset comprising active mountain streams under steeper conditions. We selected the Guerbe (Gürbe) River situated in the Swiss Alps as a case study, which has been engineered since the end of the 19th century. This has resulted in more than 110 check dams along a ca. 5 km reach where sediment has continuously been supplied from adjacent hillslopes, primarily by landsliding. We measured the riverbed grain size, topographic gradients and river widths within selected segments along this reach. Additionally, a gauging station downstream of the reach engineered with check dams yielded information to calibrate the hydroclimatic situation for the study reach, thus offering ideal conditions for our catchment-scale experiment. Using the acquired data and the dataset about historical runoff covering the time interval between 2009 and 2021 and considering the current engineered conditions, we estimated a mean annual volume of transported bedload which ranges from 900 to 6000 m 3 yr -1. We then envisaged possible channel geometries before the check dams were constructed. We inferred (1) higher energy gradients which we averaged over the length of several check dams and which we considered a proxy for the steeper river slope under natural conditions; (2) channel widths that are smaller than those measured today, thereby anticipating that the channel was more confined in the past; and (3) larger grain size percentiles, which we consider to be similar to the values measured from preserved landslides in the region. Using such potential non-engineered scenarios as constraints, the two equations both point towards a larger sediment flux compared to the engineered state, although the results of these equations differed significantly in magnitude. Whereas the Recking approach returned estimates where the bedload sediment flux is ca. 10 times larger in comparison with the current situation, the use of the Meyer-Peter–Müller equation predicts an increase of ca. 100 times in bedload fluxes for a state without check dams. These results suggest that the check dams in the Guerbe River are highly efficient not only in regulating sediment transport by decreasing the probability of high sediment flux occurrence during torrential conditions but also in stabilizing the channel bed by avoiding incision. The most likely consequence is a stabilization of the terrain around such structures by reducing the activation of landslides. [ABSTRACT FROM AUTHOR]

Shorelines face growing threats due to climate change and diminishing sand supply. Coastal headlands, common rocky features along coastlines, are crucial in shaping hydrodynamics and sediment transport. Yet, the influence of future climate conditions, including sea‐level rise (SLR) and intensified storm energy on complex shorelines with headlands has remained relatively unexplored. In this study, we model changes in hydrodynamics and headland bypassing under different SLR and higher storm wave scenarios. Our findings reveal the formation of circulation cells on both sides of a headland, where wave energy converges around the headland zone. Future climate conditions result in larger storm waves on the beach. However, SLR enhances nearshore currents through a landward shifting of the circulation cells, while higher storm waves intensify offshore flow currents due to the seaward movement of the cells. This effect, in turn, increases the potential for headland sediment bypassing. Plain Language Summary: Coastal headlands, prominent rocky features along open coastlines, play a crucial role in protecting nearby beaches from strong waves and erosion. They also affect how sand is exchanged between different beaches. We use a model to explore how future climate conditions including sea‐level rise (SLR) and larger storm waves influence coastal waves, littoral currents, and the transport of sand around headlands. Our findings reveal that headlands converge wave energy forming circulation flow cells. SLR results in stronger nearshore currents, driven by the landward movement of the rotating flow cells. In contrast, larger storm waves can move the rotating flow cells seaward, thereby increasing offshore current strength and the potential for sand transport around the headland. Understanding how coastal waves, flow and sediment transport change under future climate conditions will help determine coastal resilience. Key Points: The formation of circulation cells and wave energy convergence around headlands during storms reduce bottom shear stress at the beachSea‐level rise increases wave heights, currents, and bed shear stress in the nearshore because of landward shifting of the circulation cellsHigher storm waves expand the surf zone, shift circulation cells seaward, and enhance potential headland sediment bypassing [ABSTRACT FROM AUTHOR]

Export production, which is defined as the export of organic matter fixed by photosynthesis, is crucial for sustaining oceanic carbon uptake. The export route in the open ocean is the sinking of biogenic particles through the bottom of the euphotic layer. In contrast, the export routes in the shelf seas are the sinking of biogenic particles to the sediment and the horizontal transport of biogenic particles across the boundary of the shelf seas to the open ocean. The biogenic particles in the shelf seas are supported bymultisource nutrients including riverine and oceanic ones. Their exports depend on the hydrodynamic conditions and biogeochemical processes responsible for different sources of nutrients. Here, a unique physical-biological coupled model with a tracking approach is applied to evaluate the export production supported by multisource dissolved inorganic nitrogen (DIN) over the East China Sea. The total export production is 6.83 kmol N s-1 (=17.16 Tg C yr-1), which is slightly lower than the reported atmospheric CO2 absorption. Approximately 80% of particulate organic nitrogen (PON) is exported via off-shelf transport, and the remaining 20% is buried in the sediment. The PON supported by DIN from rivers accounts for 8% of export production, with an e-ratio (export production/primary production) of 0.09. In comparison, that from the Kuroshio accounts for 64%, with an e-ratio of 0.22. This suggests that offshore areas here are more efficient in exporting local production than nearshore ones, largely supported by oceanic nutrients. [ABSTRACT FROM AUTHOR]

Despite the environmental significance and ecological importance of cohesive sediment (<63 μm), improved knowledge of how effective particle size distributions (EPSDs) change due to flocculation under different conditions of shear stress and bed configuration is required to better understand in situ transport and storage properties and refine existing sediment transport models. Here, a rotating annular flume was used to (i) evaluate EPSDs under different shear stress and bed types (plane-impermeable and -porous gravel bed) for deposition and erosion experiments; (ii) assess flocculation processes with EPSDs; and (iii) compare flume and field EPSDs observations with respect to measured shear stress. While deposition experiments over the impermeable bed led to an EPSD equilibrium in all shear conditions (constant EPSD percentiles), the ingress experiment over the gravel bed resulted in varying EPSDs, and no equilibrium was observed. During the erosion experiment, deposited flocs became coarser due to bed consolidation, and no particle breakage was observed once particles were resuspended. The ingress experiment showed high efficiency in entrapping suspended particles (~95% of initial suspended sediment), and no exfiltration or resuspension was recorded. Flocculation ratios calculated using EPSDs showed negative correlations with shear stress, indicating that increasing flow energy promoted flocculation for flume and field observations. Our results showed that both suspended and bed sediments can flocculate into coarser flocs that, in turn, are preferentially ingressed and stored in the substrate when in suspension. These findings have important implications regarding legacy impacts, as substrate-stored particles can potentially extend the effects of upstream landscape disturbances. [ABSTRACT FROM AUTHOR]

The process of removing water from sewage sludge is particularly important due to its high content in the raw sludge. This translates into problems with the transport and storage of sediments. Additionally, high water content reduces the calorific value of the sludge. The methods for selecting the appropriate parameters for sewage sludge conditioning and filtration, based on the experimental data presented in this work, may allow for the optimization of sludge dewatering lines in small and large sewage treatment plants. The optimization of the dewatering process has a significant impact on the environmental and economic benefits, which consequently results in a decrease in the power costs of the devices used, flocculants, and sludge processing, and, above all, it contributes to the reduction in the negative impact on the environment. The use of mineral substances in the preparation of sewage sludge improves the effects of its dewatering in the pressure filtration process, as expressed in the obtained values of the final hydration and process efficiency. The use of polyelectrolytes alone significantly improves the effects of sewage sludge dewatering. In this work, the polyelectrolytes were supported by the addition of cement or zeolite. The conditioning of sewage sludge in combined methods using C-494 polyelectrolyte and minerals made it possible to reduce the compressibility coefficient to the range of 0.24–0.47 and, at the same time, to achieve the best results of sludge dewatering in the filtration process. The lowest hydration of 74.9% was achieved when polyelectrolyte and cement were added to the sludge, and this hydration was 6.5 percentage points lower compared to that of the non-filtered sludge. [ABSTRACT FROM AUTHOR]

The 2021 Navalacruz wildfire occurred in a mountainous area in the Sistema Central (Spain). Despite having an average low severity index (dNBR), the loss of vegetation cover associated with the fire was responsible for a high rate of sedimentation in the rivers and streams. Additionally, the burned area affected up to 60 cultural heritage sites, including archaeological and ethnological sites, and damage ranged from burnt pieces of wood to the burial of archaeological sites. In the present work, we document and analyze the post-fire evolution in several rivers and streams. This is based on a field survey of infiltration rates, hydrodynamic modeling, and the study of channel morphological changes. Our analysis revealed how the first post-fire rains caused the mobilization and transport of ashes. This created hydrophobicity in the soils, resulting in large amounts of materials being transported to rivers and streams by subsequent medium- and low-magnitude storms. A hydrological and hydraulic model of the study catchments under pre- and post-fire conditions suggests that these trends are a consequence of a post-fire increase in flow rates for similar rainfall scenarios. In this respect, our estimates point at a significant increase in sediment transport capacities associated with this post-fire increase in flow rates. The combination of locally steep slopes with high-severity fire patches, and a considerable regolith (derived from pre-fire weathering), resulted in a series of cascading responses, such as an exacerbated supply of sand to the drainage network and the triggering of debris flows, followed by erosion and entrenchment. [ABSTRACT FROM AUTHOR]

Effects of bed material and downstream flow depth on bed evolution in a right-angled channel confluence were studied through laboratory experiments. Velocity field, water surface elevation, and bed profile were measured intermittently until the flow attained equilibrium. Sediment discharges at various locations of the confluence were estimated from bed levels. Six prominent bedforms were identified, and their characteristics were quantified. The sediment discharges from different channels were initially high but decreased to approximately zero as the flow attained equilibrium. Downstream flow depth influenced overall sediment transport in the system, including the main features of bed morphology. Overall erosion in the confluence reduced as the particle size of the bed material increased. In addition, the maximum scour depth occurred at the confluence edge, and, due to the sharp corner of the confluence, its location did not change with time. Results from the present experimental study can help validate numerical models and assist in the design of a right-angled confluence. This study is related to the hydraulics of man-made confluences with mobile beds and can be useful in the following practical applications. More accurate numerical models to predict maximum scour, bed morphodynamics, and sediment transport in man-made confluences can be developed using the detailed bed profile measurements at different time instants presented in this study. Note that available numerical models use sediment discharge formulas (e.g., Meyer-Peter-Muller, Van Rijn), which are for sediment flows in straight channels. The interplay between the three-dimensional flow field, developed bed shear stress, and sediment discharge can be explored. In addition, A man-made confluence with the mobile bed can be designed with findings from the present study. The bedforms corresponding to equilibrium flow depend on discharge ratio, confluence angle, flow conditions at the exit channel, and bed material characteristics. The major bedforms can be incorporated into the confluence geometry. [ABSTRACT FROM AUTHOR]

Following the eruption of the Taal Volcano in January 2020 and its continuous signs of unrest in the preceding years, this study delves into the investigation of sediment transport in the Pasig River, Philippines. The historical data of total suspended solids (TSS) and arsenic indicated a notable increase starting from the year 2020. The field measurements were conducted in February and March of 2022, two years after the eruption. Due to the observed homogeneity in the river's mixing, a refined 1D sediment transport model was developed. In this study, HEC-RAS modeling software was employed. The calibration process using the Laursen transport function yielded an impressive R2 value of 0.9989 for the post-eruption model. This predictive accuracy underscores the robustness of the developed model. The study's scope was further expanded by creating a model for February 2020, incorporating water quality data gathered by the Pasig River Coordinating and Management Office. The model simulation results showed peak TSS values of 120.63 mg/L and 225.15 mg/L in February 2022 and February 2020, respectively. The results of the study highlight the probable impact of geological events on sediment dynamics within the Pasig River, which could help manage and sustain ongoing river improvements. [ABSTRACT FROM AUTHOR]

An integrated current–wave–sediment model is developed for coastal and estuary applications. The new model aims to improve the existing ones in both the physical process representation and the numerical techniques. Two areas of improvements are emphasized: the numerical procedure and a new general sediment sub-model. The numerical procedure adopts the one-model one-mesh approach to improve the model accuracy, efficiency and user friendliness. One model is developed which includes three major sub-models: current flow, wave dynamics and sediment transport. The three are tightly coupled during the solution process by exchanging data among sub-models within the same time step. Further, one unstructured geophysical mesh is adopted for all three sub-models and the mesh allows the most flexible polygonal shapes with an arbitrary number of sides. The current flow sub-model is an extension of the existing river hydraulic model (SRH-2D), the wave sub-model follows the third-generation theory implemented in SWAN which solves the multi-frequency multi-direction wave action balance equation and the sediment sub-model is a new development adopting a general multi-size non-equilibrium sediment transport formulation but tailored for coastal applications. In this paper, the theory, the governing equations and the numerical methods are presented; the new model is then verified and validated using selected experimental cases. It is shown that the new model may predict the current–wave–sediment dynamics well. In addition, model sensitivity results are also discussed to shed light on future needs. [ABSTRACT FROM AUTHOR]

Despite the reliability and flexibility of hydropower, the operation of hydroelectric power plants may have significant impacts on the downstream river system, including its water stage, sediment transport, and water temperature, ultimately affecting the ecology. To address these challenges, there is a need to identify water scheduling patterns that improve both hydropower economics and the environment relative to current operations. This paper presents a new methodology to explore promising operational criteria/rules that can achieve such improvements. Typical environmental impact statements and relicensing processes generally perform detailed site-specific analyses of a few alternatives that focus on reservoir water release operating rules and their associated environmental impacts. In contrast, the methodology presented in this article uses a widely applicable approach that explores a much larger solution space. This large set of potential alternatives can be represented in a multidimensional space for which one axis represents the economic value and the other axis quantify individual environmental impacts (e.g., sediment transport and fish growth), and they are explored via two approaches: a Monte Carlo simulation that identifies "win–win" alternatives and a multi-objective optimization problem that identifies Pareto-optimal alternatives. [ABSTRACT FROM AUTHOR]

Riparian vegetation plays a fundamental role in alluvial channel evolution by modifying flow and sedimentation dynamics. To elucidate the roles of sediment supply, flow‐dependent transport capacity, and morphodynamic feedbacks on the evolution of emergent vegetation patches over a single hydrograph, we conducted two experiments with different reach‐scale sediment supplies: a high‐supply experiment (HSE) and low‐supply experiment (LSE). We measured flow velocities, bedload transport, and topographic changes around a full‐scale patch of live emergent willows in an outdoor laboratory flume. Erosion occurred in the patch‐adjacent channel areas irrespective of the sediment supply, whereas deposition within the patch interior was suppressed in the LSE and enhanced in the HSE. The magnitude of patch deposition in each experiment was controlled by the local sediment supply to the patch and local sediment mobility during each discharge in the hydrograph. The local sediment supply was affected by bed morphodynamics at the patch head, which modulated the reach‐scale sediment supply by redistributing the bedload in the channel. Sediment mobility within the patch was flow‐dependent and a function of velocity and turbulent kinetic energy. For different discharges, the velocity in the patch changed proportionally with the freestream velocity; however, the turbulent kinetic energy was more sensitive, being elevated compared with the freestream during high flows and inhibited at low flows. Therefore, deposition and erosion within vegetation patches are not simply functions of the reach‐scale sediment supply or patch flow characteristics, as is often assumed, but additionally depend on the local sediment supply to the patch interior. Plain Language Summary: Riparian vegetation in rivers and deltas is considered a primary cause of sediment deposition and channel stabilization. However, in the laboratory, we identified the physical mechanisms influencing sediment deposition and erosion and their change over a natural flow regime to illustrate that the same full‐sized willow patch can either enhance or reduce sediment deposition within the patch interior relative to the same channel without vegetation. The amount of sediment deposited in the vegetation patch depended on the velocity and turbulent kinetic energy of the water, which changed as the flow decreased. Additionally, the presence of a single vegetation patch fundamentally changed the character of the channel from depositional to erosional near the patch, indicating that more erosion occurred in adjacent channels than deposition within the patch. Deposition and erosion of the bed were also influenced by the amount of sediment supplied to the channel from upstream. This reach‐scale sediment supply was modified by a sediment mound that formed at the upstream end of the patch during high sediment supply to the channel. The mound redistributed the sediment transport within the channel and vegetation patch, revealing another physical mechanism influencing the spatial and temporal variability of bedload transport in vegetated channels. Key Points: Relative to the open depositional channel located upstream, a single vegetation patch caused channel erosion that lowered the median bed elevations by up to 640%The same vegetation patch can both inhibit and enhance interior sediment deposition depending on the flow‐dependent transport capacity and local sediment supplyMorphodynamic bed changes modulated the reach‐scale sediment supply in and around the patch by spatially redistributing bedload within the channel [ABSTRACT FROM AUTHOR]

Recent climate change has caused an increase in warming-driven erosion and sediment transport processes on the Tibetan Plateau (TP). Yet a lack of measurements hinders our understanding of basin-scale sediment dynamics and associated spatiotemporal changes. Here, using satellite-based estimates of suspended sediment, we reconstruct the quantitative history and patterns of erosion and sediment transport in major headwater basins from 1986 to 2021. Out of 13 warming-affected headwater regions, 63% of the rivers have experienced significant increases in sediment flux. Despite such intensified erosion, we find that 30% of the total suspended sediment flux has been temporarily deposited within rivers. Our findings reveal a pronounced spatiotemporal heterogeneity within and across basins. The recurrent fluctuations in erosion-deposition patterns within river channels not only result in the underestimation of erosion magnitude but also drive continuous transformations in valley morphology, thereby endangering local ecosystems, landscape stability, and infrastructure project safety. Climate change intensifies erosion and sediment transport in rivers of the Tibetan Plateau. Satellite data unveil unprecedented patterns of sediment deposition in rivers. Pronounced spatiotemporal heterogeneities within and across basins are found. [ABSTRACT FROM AUTHOR]

The spatiotemporal variations in suspended sediment concentration (SSC) in the lower reaches of the Yellow River exhibit significant variability and are influenced by reservoir operations. Understanding the spatiotemporal distribution characteristics of SSC in water holds crucial implications for environmental protection and reservoir operation management. Based on daily-scale SSC monitoring data from four hydrological stations in the lower Yellow River, this study established an SSC remote sensing model applicable to Landsat series satellite data. The independent variable of the model, Rrs(NIR)/(Rrs(G) + Rrs(R) + Rrs(SWIR)), demonstrated sensitivity to water bodies with different SSC values. Distinctive spatiotemporal characteristics in sediment transport were observed across the lower Yellow River. Spatially, the SSC values in the Sanmenxia and Xiaolangdi reservoirs were notably lower than those in other river sections, averaging 1008.42 ± 602.83 mg/L and 1177.89 ± 627.95 mg/L, respectively. Over time, the majority of the river sections (96%) exhibited decreasing trends in SSC during 1984–2022, particularly in the downstream Xiaolangdi reservoir, with average SSC values of 4265.58 ± 1101.77 mg/L in the 1980s and 1840.80 ± 2255.15 mg/L in the 2020s. Seasonal variations in SSC were prominent, with higher summer concentrations, averaging 5536.43 ± 2188.77 mg/L (2020s summer) and 814.11 ± 158.27 mg/L (2020s winter). Reductions in SSC during 1984–2022 primarily occurred in summer, weakening its seasonal variability in the lower Yellow River. Water discharge emerged as a critical factor influencing suspended sediment transport, with SSC increasing in high-water-flow months. Following the construction of the Xiaolangdi reservoir, the relationship between SSC and water discharge at different stations underwent notable alterations. This study enhances our understanding of the spatiotemporal dynamics of suspended sediment transport in the lower Yellow River, providing valuable insights for utilizing long-term Landsat series data in the dynamic monitoring of river sediment transport. [ABSTRACT FROM AUTHOR]

Pulau Baai Port, located strategically in the Indian Ocean and considered a vital maritime hub in Indonesia, grapples with persistent challenges related to abrasion and sedimentation, which negatively impact its maritime infrastructure. One of the affected components is the exposed gas pipeline installation along the port's coastline. The sedimentation rate along Pulau Baai's coastline is alarming, ranging from 600,000 to 800,000 m3/year, resulting in coastal abrasion at a rate of up to 20 m/year. This study focuses on three scenarios using MIKE 21, including a baseline without alternatives, shore protection alternatives, and jetty protection alternatives. A comprehensive dataset, incorporating bathymetric maps, wave patterns, current data, and sediment characteristics, supports the analysis of coastal dynamics, emphasizing the urgency for intervention. The research introduces the novelty of analyzing coastal abrasion through the exposure of underground pipelines, establishing a relationship between impacting factors such as wave height, tides, sedimentation, and coastal abrasion. Mitigation alternatives, particularly alternative model-2 with jetty protection, are recommended based on a thorough evaluation of the model performance and actual measurements. The results show that Pulau Baai's sediment, primarily sandy, experiences substantial abrasion and coastline changes, notably in alternatives-2 and -3. The study anticipates potential sedimentation in certain sections of the subsea exposed pipelines in the absence of shore protection. The outcomes of this research provide a foundational guide for informed decision making and strategies to ensure the sustainable functionality of maritime infrastructure in Pulau Baai and similar coastal regions. [ABSTRACT FROM AUTHOR]

One of the most important processes for mass movement in coastal areas is sediment transport; it plays a significant role in coastal morphology changes. This manuscript focuses on the distribution and variation in surface-suspended sediments in the North Passage of the Yangtze Estuary. Field data on surface-suspended sediment concentration (SSSC) and suspended particle size (SPS) were collected at fifteen hydrological sites over a period of three years, from 2016 to 2018. The main objective was to analyze the spatial and temporal patterns of sediment and particle size and their potential impact on the estuary. Results indicate that extreme weather events have an influence on the hydrological conditions and sediment dynamics of the area. The intensity and range of SSSC variation in the North Passage seem to be determined by the magnitude of the current velocity, while the sediment load significantly impacted the sediment distribution pattern. This study demonstrates that surface sediment dynamics can be used as a basis for understanding the spatiotemporal variation in estuarine turbidity maximum (ETM) in the North Passage of the Yangtze Estuary. [ABSTRACT FROM AUTHOR]

One of the challenges in using Manning’s equation lies in accurately determining Manning’s roughness coefficient, especially due to sediment transport. The condition of sediment transport within a specific section of a river can be in equilibrium, meaning that the amount of sediment entering and exiting the segment is balanced or it can be in non-equilibrium, where there is an imbalance between the sediment entering and leaving the segment. Experiments were carried out in the laboratory to simulate both transport conditions, one involving sediment feeding (equilibrium condition) and the other without sediment feeding (non-equilibrium condition). A total of 180 mean velocity profiles were measured using an acoustic doppler velocimeter (ADV) in fixed and movable bed flows. The present experiment was combined with theoretical approaches to evaluate Manning’s coefficient in open channels under sediment transport-flow conditions and reach conclusive results. The shape of the velocity profile, u/U, for flows over a movable bed with sediment feeding is “slender” compared to those without sediment feeding. The presence of sediment transport affects the shape of the velocity profile, especially in the inner region, influencing Manning's roughness coefficient. This coefficient can be determined from two-point velocity measurements at z/H = 0.1 and 0.2 for fixed and movable bed flows with and without sediment feeding, respectively. On average, sediment feeding increases the coefficient by 19% compared to the non-sediment feeding case. [ABSTRACT FROM AUTHOR]

The presence of a late Quaternary ice sheet/ice shelf over the East Siberian Sea has been proposed in several papers. Here, we further document its duration/resilience based on the sedimentary, bulk mineralogical, and geochemical (organic matter content and its stable isotopic composition, U‐Th series) properties of a core raised from the southernmost Mendeleev Ridge. The chronostratigraphy of the studied core was mainly built from the 230Th excess (230Thxs) distribution and decay downcore. At the core‐top, peaking 230Thxs values during the early MIS 3 and mid‐MIS 1 encompassing an MIS 2 hiatus were observed. As documented in several papers, these peaks suggest seasonally open ice conditions over proximal continental shelves. Below, the interval spanning MIS 4 and possibly MIS 5d records major ice‐rafting events illustrated by overall high coarse‐fraction contents. Underlying MIS 5e, down to MIS 11, the sediment depicts relatively low sand (1.7±2.5 dw%), high clay (33.5±4.7 dw%), and very low organic carbon (0.10±0.06 dw%) contents, and low δ13Corg values (−24.3±0.9‰). This section is interpreted as recording fine sediment transport by deep currents and/or meltwater plumes below a resilient ice cover, only interrupted by a few short‐duration events. These events include (i) detrital carbonate pulses assigned to deglacial events along the NW Laurentide Ice Sheet margin (Termination (T) III), and (ii) intervals with some planktonic foraminifer occurrences, likely relating to their advection from open areas of the Arctic Ocean (MIS 5e, 9 and 11). All Terminations, but TII and the early MIS 3, show peaking Mn/Al values linked to the submergence of Arctic shelves under a rising sea level. We conclude that the resilient ice cover, likely an ice shelf, has been present over the southern Mendeleev Ridge during most of the interval after the Mid‐Pleistocene Transition and was favoured by the low summer insolation of the MIS 14 to 10 interval. [ABSTRACT FROM AUTHOR]

Floods are among the most common natural disasters responsible for severe damages and human losses. Numerically produced data, managed by user-friendly tools for geographically referenced data, have been adopted to increase preparedness and reduce vulnerabilities. This paper describes the locally sensed and numerically produced data that characterize a flood event that occurred in February 2016 in the Portuguese Águeda River, referred to as Agueda.2016Flood for short. The data were managed through the RiverCure portal, a collaborative web platform connected to a validated shallow-water model featuring modelled dynamic bed geometries and sediment transport. The dataset provides a synthesis of topo-bathymetric, hydrometric and numerically produced data from a calibrated hydrodynamic model. Due to the lack of measured hydrometric data near the city, the numerically produced data are crucial for a complete description of the flood event. The Agueda.2016Flood dataset constitutes a complete validation test for flood forecasting models and a tool to better mitigate floods in this river and in similar rivers. Thus, Agueda.2016Flood is a relevant dataset for Águeda River stakeholders as well as for the community of flood modellers, as it provides a well-documented validation event for forecasting tools. The dataset can be accessed at 10.4211/hs.937927473a3a4e66a07a2e2fdd9d581e (Ricardo et al., 2024). [ABSTRACT FROM AUTHOR]

The grain size 2 mm is the conventional border between sand and gravel. This size is used extensively, and generally without much physical justification, to discriminate between such features as sedimentary deposit type (clast-supported versus matrix-supported), river type (gravel bed versus sand bed), and sediment transport relation (gravel versus sand). Here we inquire as to whether this 2 mm boundary is simply a social construct upon which the research community has decided to agree or whether there is some underlying physics. We use dimensionless arguments to show the following for typical conditions on Earth, i.e., natural clasts (e.g., granitic or limestone) in 20 ∘ C water. As grain size ranges from 1 to 5 mm (a narrow band including 2 mm), sediment suspension becomes vanishingly small at normal flood conditions in alluvial rivers. We refer to this range as pea gravel. We further show that bedload movement of a clast in the pea gravel range with, for example, a size of 4 mm moving over a bed of 0.4 mm particles has an enhanced relative mobility compared to a clast with a size of 40 mm moving over a bed of the same 4 mm particles. With this in mind, we use 2 mm here as shorthand for the narrow pea gravel range of 1–5 mm over which transport behavior is distinct from both coarser and finer material. The use of viscosity allows the delineation of a generalized dimensionless bed grain size discriminator between "sand-like" and "gravel-like" rivers. The discriminator is applicable to sediment transport on Titan (ice clasts in flowing methane/ethane liquid at reduced gravity) and Mars (mafic clasts in flowing water at reduced gravity), as well as Earth. [ABSTRACT FROM AUTHOR]

River bifurcations are constituent components of multi-thread fluvial systems, playing a crucial role in their morphodynamic evolution and the partitioning of water and sediment. Although many studies have been directed at exploring bifurcation dynamics, the conditions under which avulsions occur, resulting in the complete abandonment of one branch, are still not well understood. To address this knowledge gap, we develop a novel 1D numerical model based on existing nodal point relations for sediment partitioning, which allows for the simulation of the morphodynamic evolution of a free bifurcation. Model results show that when the discharge asymmetry is so high that the shoaling branch does not transport sediments (partial avulsion conditions) the dominant branch undergoes significant degradation, leading to a higher inlet step between the bifurcates and further amplifying the discharge asymmetry. The degree of asymmetry is found to increase with the length of the downstream channels to the point that when they are sufficiently long, the shoaling branch is completely abandoned (full avulsion conditions). To complement our numerical findings, we also formulate a new analytical model that is able to reproduce the essential characteristics of the partial avulsion equilibrium, which enables us to identify the key parameters that control the transition between different configurations. In summary, this research sheds light on the fundamental processes that drive avulsion through the abandonment of river bifurcations. The insights gained from this study provide a foundation for further investigations and may offer valuable information for the design of sustainable river restoration projects. [ABSTRACT FROM AUTHOR]