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During extreme conditions, the transport of the wave-averaged suspended sediment concentrations in the inner surf zone affects dune erosion. Although large-scale laboratory experiments have provided insight in what drives these sediment concentrations, corresponding field data are lacking. To fill this gap, novel field observations of suspended sediment concentrations are compared to drivers that govern sediment suspension during storm conditions known from literature. A total of 128 time intervals of 20 min are analysed, spread over 10 different high water events with different hydrodynamic conditions. For each time interval, the wave-averaged (i.e. 20 min mean) suspended sediment concentration is computed and compared to three suspension drivers. The studied drivers are (1) bed shear due to near bed velocities that originate from mean currents in combination with wave-induced orbital flow, (2) the horizontal pressure gradients under steep wave fronts that increase the forces on the bed material, and (3) bore-induced turbulence that is generated at the free surface and reaches the bed. The derived bore-induced turbulence generates the greatest correlation with the mean suspended sediment concentrations (r = 0.74, p = 4.47E-23). Samples that deviate from this correlation correspond to time intervals with lower values of derived bore turbulence, less wave energy saturation in the inner surf zone, and stronger mean currents. The correlation with the mean suspended sediment concentrations increases when the shear stress originating from mean currents is used for these time intervals (r = 0.83, p = 1.63E-33). For time intervals during which more energetic conditions persist and the wave energy is saturated in the nearshore, bore turbulence was the dominant mechanism in stirring up sediment. The outcome of this study suggests that, based on the events analysed, dune erosion models may achieve more accurate results if computations of suspended sediment concentrations include a bore-induced turbulence term, or if already included, properly address the relative importance of bore-induced turbulence when compared to bed shearing. • A dune erosion field experiment was conducted to study drivers of wave-averaged suspended sediment concentrations. • The studied drivers are (1) flow-induced bed shearing, (2) horizontal pressure gradients under wave fronts, and (3) bore-induced turbulence. • The variability in bore-induced turbulence generated the greatest correlation with the variability in mean suspended sediment concentrations. • When more energetic conditions persisted and wave energy was saturated in the inner surf zone, bore turbulence appeared the dominant driver. [ABSTRACT FROM AUTHOR]

• Human interventions affect the dynamics of meandering channels. • Unusual inner bank erosion and outer bank deposition occurred due to upstream damming. • Altered flow-sediment regimes and channel boundary drive the unusual meander dynamics. Human activities, such as reservoir construction and bank revetment, significantly alter downstream flow and sediment regimes and river channel changes, impacting river ecosystem services. However, our understanding of how intense human activities affect morphodynamics of meandering channels in big river systems remains incomplete due to the lack of high-resolution in-situ data. Here, we use comprehensive data encompassing hydrology and sediment, historical channel maps, and high-resolution river bathymetry to investigate the evolution of meandering bends in the Middle Yangtze River (MYR) across three distinct phases: the natural period (1490–1975), the bank revetment period (1975–2002), and the post-dam period (2003–2018). The study revealed that, in the absence of human intervention, the meandering channels of the MYR naturally experienced inner bank deposition and outer bank erosion, largely governed by curvature-induced secondary flow patterns in flow and sediment transport mode. In 1975–2002, outer-bank revetments reduced erodibility, stabilizing outer banks, while inner banks continued to experience lateral and vertical deposition, causing a narrower and deeper channel hydraulic geometry. Conversely, meandering bends had exhibited an unusual pattern of 'outer bank deposition and inner bank erosion' in 2003–2018. Channel morphological changes characterized by channel incision and widening were driven by changes from erodible bank boundaries to solidified bank boundaries, substantial reduction in suspended sediment concentration, and an altered and extended effective flow range (10,000–25,000 m3/s). Our findings highlight that human interventions such as damming and bank revetments can alter the conventional erosion–deposition morphodynamics of meandering bends in large river systems, carrying vital implications for sustainable river management in the Anthropocene. [ABSTRACT FROM AUTHOR]

Meretrix meretrix (M. meretrix) are commonly found on tidal flats along the global coastlines. They are believed to potentially affect the sedimentary processes and thus morphological dynamics on the tidal flat. Their effects on sediment erosion and deposition, however, are not well quantitatively understood. To fill this gap, we conducted an integrated synchronous field investigation of hydrodynamic, sediment properties, and macrobenthos at two nearby tidal flats, one with abundant M. meretrix and the other without. In addition, seasonal comparison between summer and winter for the M. meretrix abundant site, where there was much less M. meretrix in winter than in summer, was conducted to further examine the influence of M. meretrix on critical value for the initiation of sediment entrainment. The results show that the critical shear stress for erosion (τ e) in the M. meretrix abundant site was lower than the bare tidal flat by ~23%. Differently, for the critical shear stress for deposition (τ d), the value at the M. meretrix abundant site was greater than that at the bare tidal flat by ~30%. Overall, we concluded that the existence of M. meretrix tends to enhance both the erodibility of the sea bed and the deposition of suspended sediment in the water column. It is suggested that the effect of macrobenthos on sediment erosion/deposition should not be neglected when predicting long-term morphological changes of an intertidal flat. [ABSTRACT FROM AUTHOR]

Intensive plantation management can affect catchment conditions, especially in large clear-cut areas that expose soil thereby encouraging sediment transport to streams. Harvesting strategies are needed to reduce these effects while enabling commercial logging. In this study, we examined the effects of harvested areas in suspended sediment production by selecting three catchments covered by Eucalyptus spp. forests with 15%, 60% and 88% harvested areas (hereafter H 15 , H 60 and H 88 , respectively) and monitoring suspended sediment during two years. We compared two approaches of estimating annual suspended sediment: weekly grab samples vs. weekly grab samples + bottle traps. Proportion harvest and suspended sediment yields were directly related on an annual basis. Such differences were more notable for H 15 and H 88 ; H 60 had intermediate values. Annual suspended sediment yields ranged from 3.0 to 208.2 kg ha−1 year−1, and in addition to harvest proportion, presence of buffer riparian forest possibly reduced concentrations of suspended sediments in streams. The use of weekly grab samples underestimated TSS yields. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Contour currents with different physical natures observed over a drift-moat system • High SSC on the drift due to long-range sediment transport by contour currents • High SSC in the moat due to moat wall erosion by tidal-induced secondary flows • Formation of drifts forced by upslope sediment transport of tidal currents Contourite drifts are ubiquitous sedimentary features in the world′s oceans, and their formation are usually ascribed to sedimentation from contour currents. However, in-situ observations of contour currents and their associated sedimentary processes were inadequate. Here, we present mooring observation results from a drift-moat contourite system in the South China Sea to gain insight into its sediment dynamics and formation mechanism. We found that quasi-persistent contour currents develop in the moat, on and below the drift, yet subject to diverse physical oceanographic processes. High suspended sediment concentrations observed on the drift mainly occur in winter, induced by high levels of sediments transported by contour currents from Taiwan. In the moat, however, high suspended sediment concentrations are mostly caused by erosion of the moat wall during periods of strong tidal currents and low shear variance. Such results underscore the complexity of current patterns and sedimentary processes across various topographic units in the drift-moat contourite system. A novel formation mechanism of the contourite drift is thereby proposed, wherein sediment transport by contour currents brings materials for constructing the drift, while its formation is driven by near-critical reflection and upslope transport of sediments by tidal currents. [ABSTRACT FROM AUTHOR]

• 24,918 Landsat images focused on the lower Yellow River were used to monitor SSC during the period 1997–2020. • The proposed HGAR method significantly outperforms other retrieval methods in terms of retrieval accuracy. • HGAR is a reliable method for SSC retrieval and can be used for long-term monitoring of SSCs. Monitoring suspended sediment concentrations (SSCs) of channel waters is essential for evaluating important issues such as erosion, sediment transport and deposition, reservoir siltation, and water pollution throughout watersheds. Remote sensing technology provides a new approach to large-scale SSC monitoring, but the accuracy of existing retrieval methods based on remote sensing technology still needs to be improved for complex environments. This study proposes a new hyperparameter and globally adaptive retrieval (HGAR) method for river SSC retrieval that combines a remote sensing technique and machine learning methods. The HGAR method uses the light gradient-boosting machine method as the basic model for SSC retrieval, and the tree-structured Parzen estimator method, coefficient of determination, and residual prediction deviation are combined to optimize the basic model's hyperparameters. The experiment was conducted in the lower Yellow River, where 24,918 Landsat images from 1997 to 2020 were acquired using Google Earth Engine, and 1,772 monthly cloud-free images were obtained in the end. The sequential backward floating selection method was adopted to determine the optimal modeling features. Two regression and three machine learning methods were compared with the proposed method. The results demonstrate that the proposed HGAR method significantly outperforms other retrieval methods in terms of retrieval accuracy (as evidenced by a correlation coefficient of 0.626 and a Nash-Sutcliffe efficiency coefficient of 0.613), generalizability, and robustness. Finally, the model explanation results show that the HGAR method can successfully capture the key information for SSC retrieval and has higher flexibility than traditional statistical models. In addition, we found that the overall fit and the fit of local extreme values are inconsistent in the lower Yellow River, and the proposed improved accuracy indicator balances the two aspects well. In conclusion, the proposed HGAR method can be used effectively to estimate channel SSC and is expected to provide technical support for long-term and large-scale monitoring of the channel surface SSC. [ABSTRACT FROM AUTHOR]

• Combined numerical model and GOCI to improve the ability of sediment flux (SF) estimation. • Multi-timescale SFs at typical cross-sections in YRE are estimated in 2013 and 2015. • Locally morphological changes are further estimated, showing erosions in 2013 and 2015. Sediment flux (SF) in the estuary is vital to the coastal and estuarine environment, especially the morphodynamical and ecological processes. However, its quantitative estimation with high accuracy is difficult because it is controlled by complex mechanisms and multiple processes. This study corrects the seasonal variations of the simulated suspended sediment concentration (SSC) by using GOCI-derived surface SSC and calculates the variations of SFs at the main cross-sections in and out of the Yangtze River Estuary (YRE). The results show that in 2013, 159 Mt and 143 Mt of sediments passed through Xuliujing hydrological station in YRE and estuarine mouth section, respectively. In the inner estuary, the significant seasonal variations of sediment transport are noted that the most seaward transport happens in summer (43.8%) and the least occurs in winter (7.3%). In the outer estuary, the southward transport towards Hangzhou Bay is the most critical pathway, accounting for 109.0% of total transport at mouth section, and is prevalent in autumn and winter. With considerations of sand mining and land reclamation, obviously erosions appear in the whole estuary during both 2013 and 2015. With stronger wind conditions in 2013, severer erosion (161 Mt) happens in outer estuary than that in 2015 (86 Mt). By combining the GOCI-derived surface SSC and the numerical model results, this study can better represent high-frequency hydro- and sediment-dynamical processes to calculate the annual, seasonal, and vertical SFs with improved accuracy. Hence this method may provide a viable way to infer locally averaged morphological changes. [ABSTRACT FROM AUTHOR]

Highlights • Two crucial periods for suspended sediment transport were June and November/December. • Analysis of 236 floods highlighted their intermittency and did not show relationships. • Medium-term continuous time series are necessary to assess range of variations of SSF. Abstract In mountainous catchments, soil erosion and sediment transport are highly variable throughout time and their quantification remains a major challenge for the scientific community. Understanding the temporal patterns and the main controls of sediment yields in these environments requires a long term monitoring of rainfall, runoff and sediment flux. This paper analyses this type of data collected during 7 years (2007–2014), at the outlet of the Galabre River, a 20 km2 watershed, in south eastern France, representative of meso-scale Mediterranean mountainous catchments. This study is based on a hybrid approach using continuous turbidity records and automated total suspended solid sampling to quantify the instantaneous suspended sediment concentrations (SSC), sediment fluxes, event loads and yields. The total suspended sediment yield was 4661 Mg km−2 and was observed during flood events. The two crucial periods for suspended sediment transport at the outlet were June and November/December (63% of the total). The analysis of suspended sediment transport dynamics observed during 236 flood events highlighted their intermittency and did not show any clear relationship between rainfall, discharge and SSC. The most efficient floods were characterised by counter-clockwise hysteresis relationships between SSC and discharges. The floods with complex hysteresis were the more productive in the long term, during this measuring period exceeding a decade. Nevertheless, the current research outlines the need to obtain medium-term (five years) continuous time series to assess the range of variations of suspended sediment fluxes and to outline clearly the seasonality of suspended sediment yields. Results suggest the occurrence of a temporal dis-connectivity in meso-scale catchments over short time-scales between the meteorological forcing and the sediment yields estimated at the outlet. These findings have important methodological impacts for modelling and operational implications for watershed management. [ABSTRACT FROM AUTHOR]

In the Geum River, a representative altered estuary, in-situ mooring and erosion experiments were conducted to reveal the effects of human-controlled discharge on benthic sediment disturbances. The strong discharge through the estuarine dam increased the current velocities within the benthic boundary layer (BBL) up to 79% and 153% during spring and neap tides, respectively. During the discharge period, the suspended sediment concentration in BBL was five times higher than that during the non-discharge period. During the flood phase, a critical shear stress for erosion (τ ce) was in the range of 0.1278 to 0.1391 Pa. Immediately after the ebb phase with strong discharge, τ ce increased to 0.1848 Pa, and the erosion rate (E) decreased from 33.73 to 14.81 mg m−2 s−1. The repetition of human-controlled discharge removed the erodible sediments within BBL, exposing the underlying consolidated sediment bed with low E and high τ ce. The results suggest that an altered estuary is vulnerable to benthic sediment erosion under combined natural and anthropogenic forcings. [Display omitted] • Human-controlled discharge disturbed benthic sediment transport and velocity structures. • Altered estuary is vulnerable to sediment erosion under anthropogenic forcings. • Discharge removed sediments, exposing consolidated sediment with low erodibility. • Erosion experiments present direct evidence on benthic sediment resuspension. [ABSTRACT FROM AUTHOR]

Field work combining in-situ mooring and erosion experiments was conducted in the intertidal flat of Asan Bay to reveal the relationship between sediment erodibility and external forcing and the contribution of local erosion to sediment transport. A total of 25 tidal cycles occurred during the mooring period with 6-h submergence and 5.7-h air exposure. The erosion rate (E) for sediment bed during air exposure was 0.007 g m−2 s−1, which was 36% of E (0.019 g m−2 s−1) during submergence. Although the sediment bed was influenced by consolidation during air exposure, the erodibility of the submerged bed was closely associated with the unconsolidated deposits of sediments newly supplied from tidal channel and bed shear stress (τ cw) induced by current-wave interactions. In particular, τ cw could be enhanced by strong winds, which depended on the ratio (H s / h) of significant wave height and water level, directly disturbing the sediment bed. Under weak winds (H s / h < 0.06), the newly deposited sediments with high erodibility increased the bed elevation. A small amount of the sediment bed was eroded (E : 0.006 g m−2 s−1), as a floc erosion, with a slight decrease in suspended sediment concentration (SSC T). This increased the contribution (57.2%) of eroded sediments to SSC T. Under strong winds (H s / h > 0.06) with enhanced τ cw , meanwhile, the erodible sediment in the bed was depleted accompanied by a decrease in bed elevation. A large amount of sediment bed was eroded (E : 0.025 g m−2 s−1), as a surface erosion, resulting in the rapid increase in SSC T and the enhanced seaward sediment flux. The sediments eroded from the bed were supplied to water column accounting for 86.8% of SSC T. This suggests that seaward sediment transport under strong winds could be caused by surface erosion shifting from floc erosion in the intertidal flat. [Display omitted] • In-situ erodibility of submerged bed was unaffected by consolidation in exposure. • Bed erosion type was shifted between floc and surface erosions depending on winds. • Surface erosion by strong wind increased fraction of eroded sediment in suspension. • Seaward exported sediments were mostly originated from bed under strong wind. [ABSTRACT FROM AUTHOR]

• High-turbidity events are triggered by wind waves with wind speeds of > 7 m s−1. • Sediment erosion and deposition are synchronous during HTEs. • Synchronism causes a near-lakebed turbid water layer and sustains the lutocline. High-turbidity events (HTEs) frequently occur in shallow lakes and can deeply influence lake ecosystems. However, the processes of sediment erosion and deposition are not fully understood. To investigate these processes, two investigative campaigns that integrate bed sediment measurements, sediment settling experiments, in-situ observations, or a hydrodynamics-sediment model were conducted to quantitatively study wind-induced HTEs in Lake Taihu, China. Cohesive sediments were massively entrained from the lakebed by wind waves when the wind speed exceeded its critical value of 7 m s−1, as estimated by water depth, triggering HTEs with turbidity waves of > 100 nephelometric turbidity units. The suspended sediment concentration was the net sediment flux of erosion (average: 5.9 mg m−2 s−1) and deposition (average: 5.5 mg m−2 s−1), which occurred synchronously for most of the HTEs and resulted in high temporal variation in suspended sediment concentration. This synchronism was determined by the critical erosional stress of lakebed sediments, which was spatially heterogeneous (0.017–0.055 N m−2) in a large lake. Equations for erosion and deposition processes were derived following the investigative campaigns and used to develop a cohesive sediment transport model for simulating HTEs in Lake Taihu. Simulations indicate that the synchronism of sediment erosion and deposition led to a near-lakebed turbid water layer during an HTE, which sustained the sediment lutocline in Lake Taihu. Further investigation should be conducted on the role of the near-lakebed turbid water layer during endogenous pollution in large eutrophic lakes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Total volume and peak discharge are the most important drivers of sediment transport. • Antecedent moisture condition is correlated only with the initial discharge of floods. • Hysteresis loops between SSC and Q are analyzed with the hysteresis index (HI). • Negative HI are predominant indicating delayed SS transport and distant SS sources. • In the catchment soil erosion from hillslopes is the dominant process. This study aimed to evaluate the drivers of suspended sediment (SS) transport by analyzing the flood events recorded from July 2010 to June 2011 in the Celone River basin (Apulia, S-E Italy). High-resolution data of rainfall, streamflow (Q), and measurements of suspended sediment concentrations (SSC) were used to carry out the multivariate analysis. Among the initial 18 variables, the Principal Component Analysis revealed that total volume (m3), peak discharge (Qmax, m3/s), and the flood duration were the most important factors influencing SS transport. Total rainfall and total kinetic energy recorded in the gauging station located in the lowland were also important factors, whereas the same rainfall variables recorded in the remote mountainous area of the basin had a minor influence on SS transport. Antecedent moisture conditions were significantly correlated only with the initial discharge of the flood. Hysteresis loops between SSC and Q were analyzed for each flood event by using the hysteresis index (HI). Results showed that this catchment was dominated by anticlockwise loops (negative values of HI) representative of delayed SS transport and of distant SS source areas in terms of the gauging station. These results also suggested that soil erosion from hillslopes was the dominant process compared with channel and bank erosion and that there was no exhaustion of sediment availability in the basin. [ABSTRACT FROM AUTHOR]

• • Thorough analysis of WSRS-induced impacts on the river channel and delta. • • The natural hydrological cycle process has been altered by the artificial floods. • • Reservoirs regulation scheme altered the erosion–deposition regime of the riverbed. • • New light is shed on saving the global sinking deltas. The water and sediment regulation schemes (WSRS) orientated by dams have profoundly adjusted the hydrological process and geomorphological evolution of the lower Yellow River and delta. Two decades since the implementation of WSRS, the observed multidisciplinary datasets allowed us to systematically evaluate the impacts of this unprecedented engineering effort on the river-coastal system. The sediment fluxes transported to the sea showed a notable rebounded and coarsened process due to the erosion of the riverbed during the WSRS periods. The average median grain size of suspended sediment increased from 17.7 μm in the 1990 s to 26 μm in 2002–2009. The natural rhythm of hydrological process is fundamentally altered by WSRS, about 50% and 30% of annual sediments and water delivered to the sea for only 20 days. The water discharge system is more temporally dynamic and complex with higher dimensionality after the operation of WSRS. The erosion pattern has been a dominant feature in all the channel segments downstream the Xiaolangdi Reservoir, with an average total erosion volume of 1.02 × 108 m3/a after the WSRS. However, the erosion efficiency of the lower river showed a decreased trend, due to the riverbed had formed a coarse armored substrate for the continued scouring since 2002. The YRD has changed from the pattern of erosion to progradation for the increase of sediment supply, and the average growth rate of subaerial delta was about 6.89 km2/a during 2003–2014. The lessons learned from the operation of WSRS may provide a valuable reference for the management of global large river systems. [ABSTRACT FROM AUTHOR]

Monitoring turbidity and Surface Suspended Sediment Concentration (SSSC) of inland waters is essential to address several important issues: erosion, sediment transport and deposition throughout watersheds, reservoir siltation, water pollution, human health risks, etc. This is especially important in regions with limited conventional monitoring capacities such as West Africa. In this study, we explore the use of Moderate Resolution Imaging Spectroradiometer data (MODIS, MOD09Q1 and MYD09Q1 products, red (R) and near infrared (NIR) bands) to monitor turbidity and SSSC for the Bagre Reservoir in Burkina Faso. High values ​​of these parameters associated with high spatial and temporal variability potentially challenge the methodologies developed so far for less turbid waters. Field measurements (turbidity, SSSC, radiometry) are used to evaluate different radiometric indices. The NIR/R ratio is found to be the most suited to retrieve SSSC and turbidity for both in-situ spectoradiometer measurements and satellite reflectance from MODIS. The spatio temporal variability of MODIS NIR/R together with rainfall estimated by the Tropical Rainforest Measuring Mission (TRMM) and altimetry data from Jason-2 is analyzed over the Bagre Reservoir for the 2000–2015 period. It is found that rain events of the early rainy season (February-March) through mid-rainy season (August) are decisive in triggering turbidity increase. Sediment transport is observed in the reservoir from upstream to downstream between June and September. Furthermore, a significant increase of 19% in turbidity values is observed between 2000 and 2015, mainly for the July to December period. It is especially well marked for August, with the central and downstream areas showing the largest increase. The most probable hypothesis to explain this evolution is a change in land use, and particularly an increase in the amount of bare soils, which enhances particle transport by runoff. [ABSTRACT FROM AUTHOR]

The Paraná River is one of the world's largest fluvial systems due to its discharge. During the last 30 years, water discharge has averaged 18,389 m3 s−1 downstream of the Paraguay-Paraná confluence, where its most important tributaries, the Paraguay and the upper Paraná rivers contribute 22% and 78% of its total discharge, respectively. However, the sedimentological dynamics of this system behaves peculiarly due to the influence of the Bermejo River, a tributary of the Paraguay River. Even though the contribution of the Bermejo River discharge represents only 2% of the Paraná River discharge, its input of suspended sediments is significant due to the erosive processes in the upper Bermejo basin. Most earlier studies have primarily focused on the contributions and dynamics of the wash load (silt and clay) from the Bermejo River through the Paraguay River to the Paraná River, and neglected the relevance of fine and very fine sands (coarser than 63 μm). These sediment fractions play a key role in bed sediment composition, roughness, and bed forms, ultimately modifying the flow resistance and the morphodynamic processes, among other environmental and biological parameters. This study seeks to quantify the suspended sediment contribution of the main tributaries of the middle Paraná River during the last three decades. In particular, water discharge, sediment transport and grain size data measured at gage stations located at the Paraguay River upper reach, the Bermejo River, and the upper and middle reaches of the Paraná River are analyzed. Focus is placed on the coarse suspended sediment fraction. Additionally, the authors collected sediment samples at different river cross-sections and water discharges. The temporal analysis revealed the dynamic behavior of the sediments along the system. The results show different behaviors of the wash load and suspended sand transport provided by the Bermejo River. Along the middle Paraná reach, results suggest a significant suspended coarse fraction deposition during the highest sediment input period. Bed sediments, in turn, are re-suspended during the months with low contributions from the Bermejo and/or during the high water levels stages of the Paraná. This sediment dynamics produces a complex pattern of coarse sediment transport in the Paraná River at its middle reach, also modifying the sedimentological characteristics of the river bed. • 95% of suspended sand of the middle Paraná river are provided by the Bermejo river. • 93% of wash load of the middle Paraná river are provided by the Bermejo river. • Sediment deposition and resuspension occurs along the hydrological year. • Sediment load from Bermejo have a strong impact in Paraná river morphodynamic. [ABSTRACT FROM AUTHOR]

Spatially and temporally variable suspended sediment transport from upstream sources was investigated in the West River (unofficial name) at the Cape Bounty Arctic Watershed Observatory (CBAWO) on Melville Island, Nunavut (74°55′ N, 109°35′ W), a river with nearly a decade of hydrological and sediment transport research in the Canadian Arctic and subject to recent permafrost disturbances, such as soil skin flows on slopes, massive ground ice melt in the channel, and substantial climate change. During the 2012 season, a survey was undertaken during the nival period to identify areas of the river where the flow was isolated from the channel bed by snow and where it progressively reached the bed. During the nival period, and throughout the rest of the season, suspended sediment transport data were collected from a primary outlet station and six upstream locations to identify the sources and sinks of sediment in the various reaches of the West River. An inferred sediment budget approach was used to identify the storage and release dynamics in each reach. Nival event-scale hysteresis and seasonal diurnal hysteresis patterns for 2012 were primarily anticlockwise, suggesting that sources of sediment were not readily available for transport during peak flows but became available as discharge waned. Analysis of diurnal hysteresis relationships for the years 2004–2012 (excluding 2011) signals a shift in daily sediment-discharge hysteresis from primarily clockwise to anticlockwise following an episode of permafrost disturbance and enhanced erosion in 2007. Consistent sediment storage in the upper catchment from this disturbance is interpreted to have contributed to the shift to anticlockwise daily hysteresis. Results provide insights into the fluvial and geomorphological response to changes in sediment availability in Arctic rivers and how these changes in turn affect sediment transport in these environments. [ABSTRACT FROM AUTHOR]

The long-distance transport of Yellow River sediments has formed an omega-shaped ('Ω') distal muddy deposit in the Yellow Sea. Numerous studies have investigated the sediment dynamics and sedimentary evolution of the deposit, but several key questions remain unanswered due to insufficient observations. To reveal the mechanisms of sediment dynamics and quantify sediment transport and deposition processes, this study collected field datasets in the depocenter of the muddy deposit off the Shandong Peninsula. Bottom mounted tripods were deployed from August 18 to 27, 2017, and from February 23 to March 2, 2018, during which two strong wind events with speeds of over 10.8 m/s occurred. The results showed that near-bed suspended sediment concentration responded directly to varying hydrodynamic conditions, and significant differences in suspended sediment concentration between two wind events could be ascribed to a number of factors (e.g., tidal current, wave periods, wind stress, turbulence). The harmonic analysis demonstrated that suspended sediment variations during the spring tide were directed mainly by resuspension, while resuspension and advection contributed equally at neap tide. The variations in background suspended sediment concentration can be ascribed to the residual current. Furthermore, the sediment transport pattern is similar to the pattern of water circulation. Generally, the along-shore suspended sediment flux is about one order of magnitude higher than the cross-shore flux. In summer, the suspended sediment was transported mainly downcoast. In winter, sediment was transported downcoast during wavy periods and upcoast during calm periods. Advection dominated sediment flux in most cases, except during wavy periods when local resuspension increased significantly, and the contribution of resuspension term to along-shore flux was up to 87%. Meanwhile, cross-shore flux also increased significantly under strong winds, which was simultaneously modulated by downcoast and offshore winds. After statistical analysis, we found that offshore winds controlled the cross-shore sediment transport in winter. Using parameterized calculation and statistical analysis, the average accumulation rate of the study site was estimated to be 0.6 cm/yr. During calm periods, lower background sediment concentration in summer led to lower deposition rates than in winter. In addition, the frequent strong wind events in winter cause extremely high erosion rates. This study provides new perspectives on quantitative variations in suspended sediment transport and regional erosion/deposition from synoptic to seasonal variations in the distal mud deposit. • In-situ observations at the bottom boundary layer were conducted in summer and winter on the muddy deposit off the Shandong Peninsula. • The advection dominates sediment flux in most cases, except for during wind gusts when local resuspension increases significantly. • Combining parameterized method and observational data, the accumulation rate is estimated. [ABSTRACT FROM AUTHOR]

• SWAT hydrological model has high potential in the assessment of watershed changes. • Land use changes caused by forest fires affect hydrological response of watershed. • Significant increase in surface runoff and sediment load in the post-fire scenario. • Sediment yield increased by 6.5 times with the highest fire spatial distribution. • Forest fire scenarios help to limit hydrological impacts of fire on sediment load. Forest fires profoundly affect the nature of watershed responses to precipitation, increases in runoff rate and volume, and post-fire sediment discharge. A post-fire watershed assessment to identify potential trouble spots for soil erosion and flooding can help land managers for decision-making on deploy mitigation, remediation measures, and restoration action plans. Predicting the potential impact of fires on runoff and soil erosion requires distributed hydrological modeling methods. This study used the Soil and Water Assessment Tool (SWAT), a rainfall-runoff model, to investigate the hydrological consequences of forest fires and their impact on sediment load under different burnt scenarios. For the pre-fire (baseline) scenario, the watershed is calibrated by using the measured discharge and suspended sediment concentration data from the weather station during the time step to estimate post-fire changes at the sub-catchment scale. The total water and sediment yield for the selected sub-catchment in the post-fire scenario with the highest spatial distribution of forest fire, due to the excessive surface runoff (an increase of 14.5%) increased significantly, resulted in 6.5 times increase in sediment yield. The results obtained from the study indicate a significant increase in sediment transport into the stream in the post-fire scenario. A large volume of soil losses occurred during the time step. In contrast, due to removing trees and vegetation from the ground, less evapotranspiration and infiltration occurred in selected sub-catchment areas after forest fires. In terms of watershed management, understanding the consequences of forest fires on hydrological services will be an effective method for sediment budget control. Therefore, applying the rainfall-runoff and erosion models for the watershed with developing plausible forest fire scenarios can be a productive method to deal with the threats and hydrological risks such as soil erosion and sediment transfer to the downstream environment. [ABSTRACT FROM AUTHOR]

The flow routing module in several large-scale erosion and sediment transport models generally adopts simplifications that ignore important physical aspects of river dynamics. In this study we compare for the first time the results generated by a large-scale erosion and sediment transport model, using two different flow routing approaches: a combined Saint-Venant and Muskingum-Cunge method and the Inertial flow routing. For this assessment, simulations are performed with the MGB-SED model. We evaluate sediment characteristics such as suspended sediment load and concentration, floodplain effects, and the flux of suspended sediment within the Madeira River basin. The simulation with the inertial approach presents satisfactory results, similar to those achieved with the combined Saint-Venant approach for lowland rivers and the Muskingum-Cunge method for steeper rivers. Also, Inertial module is capable to represent the complex processes of the basin, but with easier preprocessing and numerical features, thus promising expanded capabilities for large-scale simulations. • Evaluation of the relative weights of the Saint-Venant equation terms. • Large-scale sediment model using inertial flow routing method. • The average percentage that is represented by the advective inertial term is 0.15%. • Similar results were achieved with full Saint-Venant equations for lowland rivers. [ABSTRACT FROM AUTHOR]

Abstract: A computational investigation is presented of mono-, bi-, and polydisperse lock-exchange turbidity currents interacting with complex bottom topography. Simulation results obtained with the software TURBINS are compared with laboratory experiments of other authors. Several features of the flow, such as deposit profiles, front location, suspended mass, and runout length, are discussed. For a monodisperse lock-exchange current propagating over a flat surface, we investigate the influence of the boundary conditions at the streamwise and top boundaries, and we generally find good agreement with corresponding laboratory experiments. However, we note some differences with a second set of experimental data for polydisperse turbidity currents over flat surfaces. A comparison with experimental data for bidisperse currents with varying mass fractions of coarse and fine particles yields good agreement for all cases except those where the current consists almost exclusively of fine particles. For polydisperse currents over a two-dimensional bottom topography, significant discrepancies are observed. Possible reasons are discussed, including erosion and bed load transport. Finally, we investigate the influence of a three-dimensional Gaussian bump on the deposit pattern of a bidisperse current. [Copyright &y& Elsevier]

Abstract: Understanding the dynamics of sediment fluxes is a key issue to constrain modern erosion rates in mountain belts and determine the still debated level of control exerted by precipitation, topography and tectonics. The well defined monsoon seasonality in the Himalayas, together with active tectonics and strong relief provide an ideal environment to assess these possible interactions. For this purpose, we present a new compilation of daily suspended sediment data for 12 stations of the major rivers of the Nepal Himalayas. We analyze the relationships of sediment transport with daily river discharge and precipitation data as well as with morphometric parameters. We show that suspended sediment concentrations vary systematically through the seasons and asynchronously to river discharge displaying a hysteresis effect. This clockwise hysteresis effect disappears when suspended sediment fluxes are directly compared with direct storm discharge. Therefore we attribute the hysteresis effect to groundwater dilution rather than a sediment supply limitation. We infer a rating model to calculate erosion rates directly from long river discharge chronicles. We show that, when normalized by drainage area and mean sediment flux, all rivers exhibit the same trend. This similarity implies that all river basins have the same erosion behavior, independent of location, size and catchment characteristics. Erosion rates calculated from suspended sediment fluxes range between 0.1 and 2.8mm/yr. The erosion rates of the three main basins of Nepal are in the range 0.9–1.5mm/yr, Erosion rates in the Higher Himalayas are relatively low (<0.5mm/yr, except for Kali Gandaki), while in the Lesser Himalayas they range from 0.2 to 2mm/yr. We propose that material transport in the rivers depends on hillslope sediment supply, which is, in turn, controlled by those rainfalls producing direct runoff. In other words, the rivers in the Nepal Himalayas are supply-limited and the hillsopes as a contributing source are transport-limited. We also show that erosion processes are not as much controlled by infrequently occurring extreme precipitation events, than by moderate ones with a high recurrence interval. [Copyright &y& Elsevier]

Abstract: Appropriate descriptions of turbulence are important in predicting sediment transport and seabed evolution. We use here a three-dimensional model to investigate the impacts of sediment-induced stratification, erosion parameterization, and turbulence closures on sediment transport and morphological simulations. The model is implemented in the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS), which couples a hydrodynamic model to the General Ocean Turbulence Model (GOTM) and to a sediment transport model. This sediment transport model calculates both suspended sediment concentrations and bed evolution. A large number of turbulence closures can be tested and we focus on the methods used to calculate the turbulent length scale and the stability functions. Different modelling scenarios are assessed against experimental data of velocity profiles, suspended sediment concentrations, and trench migration in a laboratory flume. Numerical results show that the processes investigated have little impact on the flow velocity profiles, in spite of some differences on the bed shear stress. The only exception is the one-equation turbulence closure, which cannot reproduce velocity profiles appropriately. Sediment-induced stratification, erosion parameterization, and turbulence closures can all have significant impacts on the suspended sediment concentration and the bed evolution. Model-data comparisons are found to be particularly sensitive to the method used to calculate the turbulent length scale. [Copyright &y& Elsevier]

Abstract: This paper summarizes process-oriented field and numerical studies undertaken on the river plume in the partially-mixed Changjiang River estuary. Both estuarine circulation and tidal asymmetry are of great importance to the fine sediment processes. Mean suspended sediment concentration (C̄) and bottom shear stress are the dominant physical parameters controlling the flocculation and settling velocities (w s ) of mud flocs in suspension. Two important physical processes are revealed by acoustic imaging, i.e. (i) the near-bed impulsive resuspension and (ii) the transport processes driven by fine sediment-induced plumes during a spring tide. A turbidity maximum, associated with a suspended sediment front, is observed. Its formation is caused mainly by tidal asymmetry, near-bed periodic tidal resuspension and turbulence suppression by suspension/salinity stratifications. A conceptual sketch of the turbidity maximum is cautiously proposed for the Changjiang River estuary. Four different settling velocity equations, taking flocculation into account, have different effects on the modeled concentration profiles of fine sediment: apparently, Cao and Wang (1994, pp. 252–253) would be the best for spring tide and Thorn (1982, Fig. 3/page 66) for neap tide. Both tidal acceleration and tidal deceleration have strong effects on the concentration profiles of fine sediment within the Changjiang River estuary. [Copyright &y& Elsevier]

Summary: Erosion and suspended sediment transport dynamics were studied in the open water season (April–November) of three consecutive years in a drained peatland forest. Discharge and suspended solids were monitored continuously and sediment properties surveyed with individual samples. Sediment transport dynamics were studied using statistical methods and plotted as hysteresis, duration and effective discharge plots. Sediment rating curves for averaged daily data for months and total season were established to seek empirical sediment yield predictive model(s). The discharge patterns in the study catchment were dominated by peak runoff events resulting from snowmelt and intensive rainfall. Fluctuations in suspended sediment concentrations (SSC) were associated with discharge fluctuations. Sediment transport varied markedly during the study months and years, with organic sediment playing an important role. The present study demonstrates sediment transport processes and reveals the underlying mechanics operating in forested peatland areas. These include inter-storm sediment storage, bank collapse and the role of peak runoff rate on erosion in peak flow events. Sediment availability in drainage network channels also played a major role in erosion and SSC. The results indicate that summer runoff peaks can be a dominant element controlling annual sediment yield, partly contradicting previous studies in drained peatland areas identifying spring snowmelt as the dominant element. Sediment yield prediction with the empirical sediment-transport rating curve gave good regressions for some data, but simple regression models were not adequate to provide accurate annual predictions. [Copyright &y& Elsevier]

Abstract: Field measurements of fluid velocities and suspended sediment concentrations were used to investigate the relative role of coherent vortices (related to wave breaking) in suspended sediment dynamics. The measurements were obtained from a barred (intermediate-type) beach and the instrument rig was exposed to a range of wave types during the experiment; including shoaling waves and both spilling and plunging breakers. The time scale of the observed breaker vortices was <<5Hz and thus in the frequency range of wave orbital motion. Coherent breaker vortices were separated from wave orbital motions and incoherent higher-frequency turbulence using a threshold magnitude for the vertical velocity component. Plunging breakers displayed the largest root-mean-square (RMS) and maximum vertical velocities; the latter reaching approximately 1m s− 1. These measurements were made at an elevation of 0.15m above the bed. Given the observed scale of the breaker vortices and the phase match between suspended sediment concentrations and fluid velocities, the turbulence injected into the water column by the plunging breakers played a significant role in suspending bed sediment. On the other hand the role of coherent vortex structures in suspending sediment under spilling breakers and shoaling waves is more limited. RMS vertical velocities under the spilling breakers and shoaling waves in this experiment were respectively a factor 2 and 4 smaller than for plunging breakers. Different phase relationships were observed between the horizontal fluid velocity and vortex-induced sediment suspension for each of the wave types, which may contribute to an explanation of net offshore and onshore sediment transport observed during episodes of beach erosion and recovery, respectively. [Copyright &y& Elsevier]

Abstract: The impact of unusual events on the sediment dynamics in rivers is discussed in this paper. The increase in the number of extreme precipitation events and other unusual weather events in Norway strongly suggests that weather conditions are changing. It is difficult to monitor sediment transport during large magnitude floods. It is however well known that they may deliver substantial amounts of sediment. The suspended sediment load in the upper Atna river during the springflood in 1995 was 44 times the mean load measured during the preceding years. The recurrence interval of this flood was estimated to be 100–200 years. The conditions during the occurrence of a particular flood event may also be of considerable importance and measurements during rainfall on frozen ground have indicated unusually high runoff and erosion rates. The seasonal distribution of runoff in several parts of Norway has changed in recent years and higher winter temperatures have produced an increase in the frequency of flood events. A very long lasting flood caused by a prolonged period of rain occurred in the Vikka stream during September to December 2000. The availability of sediment increased with the increasing soil moisture content in the area. As the ground became saturated, more active slope processes caused erosion rates to increase markedly. The combined effects of climate change and human impact on sediment transport in rivers appear to enhance downstream sediment delivery. Flood protection works along river channels prevent sediment from being deposited on the floodplain. River channels that have been lowered in order to reduce groundwater levels in agricultural floodplain areas will experience the same effect. During the last decade extensive ecological changes have taken place in the coastal areas of southern Norway as 90% of the sugar kelp forest has been lost. This change has been attributed to an apparent increase in sediment delivery to the sea along with a rise in sea temperatures. [Copyright &y& Elsevier]

Abstract: Turbidity currents may feature active sediment transport and rapid bed deformation, such as those responsible for the erosion of many submarine canyons. Yet previous mathematical models are built upon simplified governing equations and involve steady flow and weak sediment transport assumptions, which are not in complete accordance with rigorous conservation laws. It so far remains unknown if these could have considerable impacts on the evolution of turbidity currents. Here a fully coupled modeling study is presented to gain new insights into the evolution of turbidity currents. The recent analysis of the multiple time scales of subaerial sediment-laden flows over erodible bed [Cao Z, Li Y, Yue Z. Multiple time scales of alluvial rivers carrying suspended sediment and their implications for mathematical modeling. Adv Water Resour 2007;30(4):715–29] is extended to subaqueous turbidity currents to complement the fully coupled modeling. Results from numerical simulations show the ability of the present coupled model to reproduce self-accelerating turbidity currents. Comparison among the fully and partially coupled and decoupled models along with the analysis of the relative time scale of bed deformation explicitly demonstrate that fully coupled modeling is essential for refined resolution of those turbidity currents featuring active sediment transport and rapid bed deformation, and existing models based on simplified conservation laws need to be reformulated. [Copyright &y& Elsevier]

Abstract: Shelf-to-canyon suspended sediment transport during major storms was studied at the southwestern end of the Gulf of Lions. Waves, near-bottom currents, temperature and water turbidity were measured on the inner shelf at 28-m water depth and in the Cap de Creus submarine canyon head at 300m depth from November 2003 to March 2004. Two major storm events producing waves H s>6m coming from the E–SE sector took place, the first on 3–4 December 2003 (max H s: 8.4m) and the second on 20–22 February 2004 (max H s: 7m). During these events, shelf water flowed downcanyon producing strong near-bottom currents on the canyon head due to storm-induced downwelling, which was enhanced by dense shelf water cascading in February 2004. These processes generated different pulses of downcanyon suspended sediment transport. During the peak of both storms, the highest waves and the increasing near-bottom currents resuspended sediment on the canyon head and the adjacent outer shelf causing the first downcanyon sediment transport pulses. The December event ended just after these first pulses, when the induced downwelling finished suddenly due to restoration of shelf water stratification. This event was too short to allow the sediment resuspended on the shallow shelf to reach the canyon head. In contrast, the February event, reinforced by dense shelf water cascading, was long enough to transfer resuspended sediment from shallow shelf areas to the canyon head in two different pulses at the end of the event. The downcanyon transport during these last two pulses was one order of magnitude higher than those during the December event and during the first pulses of the February event and accounted for more than half of the total downcanyon sediment transport during the fall 2003 and winter 2004 period. Major storm events, especially during winter vertical mixing periods, produce major episodes of shelf-to-canyon sediment transport at the southwestern end of the Gulf of Lions. Hydrographic structure and storm duration are important factors controlling off-shelf sediment transport during these events. [Copyright &y& Elsevier]

Abstract: At high bed shear stress sheet flows often occur in coastal waters in which high-concentration bedload sediments are transported in a thin layer near the bed. This paper firstly constructs a theoretical model (partial differential equations, PDEs) for the intense transport of non-cohesive bedload sediments by unidirectional currents and then seeks a special solution to the PDEs to determine the thickness of the bedload particle–water mixture, which could serve as the “reference height” that is often invoked in numerical computation and simulation of suspended sediment transport in turbulent flows. Moreover, a modified formula is presented to determine the “reference concentration”. Using a “uch” approach the present study derives a 1D formula for predicting bedload transport rate in sheet flows driven by asymmetric waves, with the help of a novel formula for evaluating wave friction factor. The new bedload formula can generically take into account slope angle (positive and negative), wash load concentration in the driving water flow and other factors that affect bedload transport rate. It compares well with measured data in a large-scale wave flume [Dohmen-Janssen, C.M., Hanes, D.M., 2002. Sheet flow dynamics under monochromatic non-breaking waves. Journal of Geophysical Research, 107(C10), 1301–1321], a large-scale oscillatory water tunnel [ Hassan, W.N., Ribberink, J.S., 2005. Transport processes of uniform and mixed sands in oscillatory sheet flow. Coastal Engineering, 52, 745–770] and in a swash zone of natural beach [Masselink, G., Hughes, M.G., 1998. Field investigation of sediment transport in the swash zone. Continental Shelf Research, 18, 1179–1199]. [Copyright &y& Elsevier]

Abstract: The sedimentary processes acting over an intertidal flat (Hythe, UK) located in Southampton Water, Hampshire, UK are investigated on the basis of hydrodynamic, morphological and sediment transport field measurements. Bed level changes, patterns of suspended sediment transport and shell movement over the tidal flats were examined in order to identify sediment transport pathways and salt marsh–mudflat morphological changes. Overall, sediment transport patterns at Hythe can be described in terms of suspended sediment and bedload-shell transport. The hydrodynamic complexity of the tidal flow over the flats determines the patterns of suspended sediments transport. During the young flood phase, tidal currents present a SW orientation (shoreward). About 1 h into the flood, a change occurs and the currents start flowing in a SE direction (estuary mouthward). This veering of the tidal current controls the hydrodynamic pattern over the mudflat inducing sediment transport towards the estuary mouth. Conversely, shell tracer experiment showed a net landward movement. Shells are transported over the mudflat, deposited at the base of the cliff, and eventually transported over the salt marsh where they form extensive chernier deposits. Shell transport rates can reach up to 0.7 m/tide over the upper mudflat. Shell movement over the salt marsh (on cheniers) occurred only during storms (up to 3 m in a storm event). Shell-induced erosion can become an important parameter on morphological changes of a coastal area. Shell transport and deposition over the salt marsh surface can contribute to vegetation deterioration, as shell deposits migrate over the marsh surface. As a result, the seaward limit of the salt marsh showed deteriorated vegetation, which leads to scouring and consequent surface lowering. In terms of bed level changes, no seasonal pattern was observed. A relationship between mudflat bed erosion and cliff retreat is suggested. During periods of high cliff erosion there was a tendency for the mudflats to be stable and, conversely, mudflat bed erosion was greatest when cliff retreat rates were lowest. Hence, morphological characteristics of Hythe intertidal area appear to be controlled by a combination of prevailing hydrodynamic conditions and shell transport over the salt marsh. [Copyright &y& Elsevier]

Abstract: Flow, sediment transport and bed deformation in alluvial rivers normally exhibit multiple time scales. Enhanced knowledge of the time scales can facilitate better approaches to the understanding of the fluvial processes. Yet prior studies of the time scales are based upon the concept of sediment transport capacity at low concentrations, which however is not generally applicable. This paper presents new formulations of the time scales of fluvial flow, suspended sediment transport and bed deformation, under the framework of shallow water hydrodynamics, non-capacity sediment transport and the theory of characteristics for the hyperbolic governing equations. The time scale of bed deformation in relation to that of flow depth is demonstrated to delimit the applicability region of mathematical river models, and the time scale of suspended sediment transport relative to that of the pertinent flow information is analyzed to address if the concept of sediment transport capacity is applicable. For shallow flows with high sediment concentrations, bed deformation may considerably affect the flow and a fully coupled model is normally required. In contrast, for deep flows at low sediment concentrations, a decoupled model is mostly justified. This pilot study of the time scales delivers a new theoretical basis, on which the interaction between flow, suspended sediment transport and bed deformation can be potentially better characterized. [Copyright &y& Elsevier]

Abstract: Intensity and spatio-temporal variability of fluvial sediment transfers and mechanical fluvial denudation were analyzed in the periglacial Latnjavagge catchment (9km2; 950–1440m a.s.l.; 68.20N, 18.30E) in Arctic-oceanic northernmost Swedish Lapland. The present-day rates of fluvial sediment transfer are low. The mean annual mechanical fluvial denudation rate at the inlet of lake Latnjajaure, as calculated after five years of process monitoring (2000–2004), and excluding a “rare rainfall event” which caused 3.2 times higher suspended sediment transport during one day as compared to the total mean annual suspended sediment transport, is 2.3t km−2 yr−1. In years without “rare rainfall events”, most of the total annual sediment load is transported in a few days during annual snowmelt runoff. In the calculation of longer-term sediment budgets, rare rainfall events like the July 20th–21st, 2004 event have to be considered as essential components. Reliable estimation of the recurrence intervals of such events is problematic. The pattern of ice patches and snow fields within the valley, the steepness of streams and channels and the location of areas showing slushflow activity are the major factors controlling spatial variability of mechanical fluvial denudation in the drainage basin. The five lakes in Latnjavagge, especially lake Latnjajaure, are significant sediment traps and ground below 1300m a.s.l. is protected by a very stable and closed vegetation cover and rhizosphere across the entire lower catchment. [Copyright &y& Elsevier]

Abstract: We have measured 238U–234U–230Th radioactive disequilibria in five size fractions of colloids and suspended sediments for four rivers from the Murray–Darling River basin (SE Australia). Continuous compositional trends of composition are observed for (234U/238U) and (230Th/238U) activity ratios over the range of size fractions studied. They are explained by the variable contribution of two components: detrital alumino-silicates and organic matter. Using relationships between activity ratios and the loss-on-ignition, it is possible to estimate the U-series isotopic composition of both detrital and organic end-members, which provide the best estimate for the composition of the true detrital phase (i.e. controlled only by the removal of elements through weathering) and the true dissolved phase (i.e. colloid-free), respectively. When performing a single filtration at 0.2 μm, it appears that size fractions > and <0.2 μm underestimate the disequilibrium in both the true detrital and dissolved phases, respectively. We show that erosion does not currently operate in steady state in the Murray–Darling basin and catchment soils are currently being degraded. This could be a consequence of the intensification of agriculture and deforestation over the past 100 yr. The residence time of sediments in the different sub-basins is calculated by computing the composition of the detrital phase with a continuous weathering model. It yields 11±2 kyr for the Darling River basin, only 2–3±1 kyr for the Murray River and 7±2 kyr for the Goulburn River. These values are correlated with the age of changes in river dynamics, in turn probably controlled by climate fluctuation, and indicate the age of the modern river system for each sub-basin. [Copyright &y& Elsevier]

Abstract: Based on data from the middle Yellow River, a model of erosion and sediment yield is proposed to describe coupled eolian and fluvial processes in a transitional zone from arid to sub-humid climates, and to explain rapid erosion and a high sediment yield in the zone. In the study area, wind action predominates from March to June, which erodes weathered bedrock and transports eolian sand to gullies, river channels and floodplains. In the following summer, especially from July to September, rainstorm runoff in gullies and river channels transports large quantities of fine loessic material, in the form of hyperconcentrated flow. As a result, most of the previously stored eolian sand and material supplied by mass-wasting of loess can be transported to the major tributaries and the main stream of the Yellow River, resulting in the high specific sediment yield. There exists an optimal grain size composition which maximizes suspended sediment concentration in the study area, resulted from the combined wind–water processes. [Copyright &y& Elsevier]

Abstract: The erosion behaviour of various fine-grained sediment deposits has been investigated in laboratory experiments. This work mainly focused on tests using sewer sediment in which strong biochemical reactions were observed during the deposit formation period. A small number of initial tests were conducted in which the deposits were made from mixtures of “clean” mineral and organic sediments. The erosion behaviour observed in these tests was compared with the erosion characteristics for sediments taken from deposits in a sewer. The impact of the biological processes on physical properties such as bulk density, water content, deposit structure and the erosive behaviour as a function of bed shear stress are quantified and discussed. Based on these observations it is believed that bio-processes weaken the strength of the in-pipe sediment deposits. A significantly weaker sediment surface layer was observed during deposition under quiescent oxygen-rich conditions. This resulted in a deposit with low shear strength which may be a cause of a first foul flush of suspended sediment when flow rates were increased. Comparison between tests with sewer sediments and the artificial representative surrogates suggested that the deposits of the later did not correctly simulate the depositional development and the resultant erosion patterns observed with the more bio-active sewer sediment. [Copyright &y& Elsevier]

Abstract: The latest Holocene sedimentary record of a cohesive channel and subtidal shoal in the lower Hudson River Estuary was examined to elucidate natural (sea-level rise, sediment transport) and anthropogenic (bulkheading, dredging) influences on the recent morphodynamic evolution of the system. To characterize the seafloor and shallow subbottom, ∼100 km of high-resolution seismic reflection profiles (chirp) were collected within a 20-km reach of the estuary and correlated with sediment lithologies provided by eight vibracores recovered along seismic lines. Sediment geochronology with 137Cs and 14C was used to estimate intermediate and long-term sedimentation rates, respectively, and historical bathymetric data were analyzed to identify regional patterns of accretion and erosion, and to quantify changes in channel geometry and sediment volume. The shoal lithosome originated around 4 ka presumably with decelerating eustatic sea level rise during the latest Holocene. Long-term sedimentation rates on the shoal (2.3–2.6 mm/yr) are higher than in the channel (2 mm/yr) owing to hydrodynamic conditions that preferentially sequester suspended sediment on the western side of the estuary. As a result, the shoal accretes oblique to the principal axis of tidal transport, and more rapidly than the channel to produce an asymmetric cross-section. Shoal deposits consist of tidally bedded muds and are stratified by minor erosion surfaces that seismic profiles reveal to extend for 10s of meters to kilometers. The frequency and continuity of these surfaces suggest that the surficial shoal is catastrophically stripped on decadal-centennial time scales by elevated tidal flows; tidal erosion maintains the shoal at a uniform depth below sea level and prevents it from transitioning to an intertidal environment. Consequently, the long-term sedimentation rate approximates the rate of sea-level rise in the lower estuary (1–3 mm/yr). After the mid 1800s, the natural geometry of the lower Hudson River Estuary changed rapidly in response to engineering works that forced the channel to self-deepen. Analysis of historical bathymetric data indicates that the channel lost an estimated 3×106 tons of sediment between ca. 1939 and 2002 (50,000 tons/yr average) by subaqueous erosion, increasing in depth by as much as 4 m in places. Erosion appears to have been concurrent with systematic bulkheading of the shoreline after ca. 1865, which decreased the estuary surface area by ∼19% overall. Evidently, self-deepening of the channel is a morphodynamic adjustment to reestablish equilibrium cross-sectional area, yet the state of this change locally and elsewhere in the estuary is unknown. Subaqueous erosion documented in this study is a significant source of sediment with implications to the sediment budget and environmental quality of the Hudson River Estuary. [Copyright &y& Elsevier]

Abstract: The processes responsible for sediment transport and morphological change in the intertidal zone of natural beaches are not well known. Consequently, factors determining whether the intertidal beach erodes/accretes or remains stable in the face of significant wave impact, and the mechanisms behind the elusive concept of ‘equilibrium beach slope’ are poorly understood. A field experiment was designed to measure suspended sediment transport in the swash and inner surf zone through successive tidal cycles in the intertidal zone at Egmond Beach, The Netherlands, using a stack of fiberoptic backscatter sensors (UFOBS-7). The experimental period comprised three large storm events, including an extreme storm with offshore significant wave heights in excess of 7 m. Surveys spanning a >1 km long section of the beach as well as observations from an ARGUS video camera system showed that gently sloping shoreline salients (megacusps) were highly stable in position and displayed only minor slope adjustments through the storm period, whereas steeply sloping embayments were eroded significantly. The sediment transport measurements at a shoreline salient indicated that the subdued net beach response was because offshore sediment transport occurring under surf zone conditions at high tide was compensated by onshore sediment transport at low tide when swash zone processes dominated. Such temporally varying, tidally modulated sediment transport rates and directions are suggested to be able to maintain a quasi-equilibrium intertidal beach slope and the results indicate that a negative feedback existed between initial beach slope and net sediment transport patterns. [Copyright &y& Elsevier]

Abstract: A series of sand bed experiments was carried out in the Large Wave Flume in Hannover, Germany as a component of the SISTEX99 experiment. The experiments focussed on the dynamic sediment response due to wave group forcing over a flat sand bed in order to improve understanding of cross-shore sediment transport mechanisms and determine sediment concentrations, fluxes and net transport rates under these conditions. Sediment concentrations were measured within the sheet flow layer (thickness in the order of 10 grain diameters) and in the suspension region (thickness in the order of centimetres). Within the sheet flow layer, the concentrations are highly coherent with the instantaneous near-bed velocities due to each wave within the wave group. However, in the suspension layer concentrations respond much more slowly to changes in near-bed velocity. At several centimetres above the bed, the suspended sediment concentrations vary on the time scale of the wave group, with a time delay relative to the peak wave within the wave group. The thickness of the sheet flow changes with time. It is strongly coherent with the wave forcing, and is not influenced by the history or sequence of the waves within the group. The velocity of the sediment was also measured within the sheet flow layer some of the time (during the larger wave crests of the group), and the velocity of the fluid was measured at several cm above the sheet flow layer. The grain velocity and concentration estimates can be combined to estimate the sediment flux. The estimates were found to be consistent with previous measurements under monochromatic waves. Under these conditions, without any significant mean current, the sediment flux within the sheet flow layer was found to greatly exceed the sediment flux in the suspension layer. As a result, net transport rates under wave groups are similar to those under monochromatic waves. [Copyright &y& Elsevier]

Abstract: We develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach, and we investigate the morphodynamical role that such transport may play. Although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment, we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse; additionally, settling lag effects may promote a weak onshore movement of sediment. We quantify both effects in terms of the properties of the sediment and of the swash event, and comment on the relationship between our findings and recent field studies of swash zone sediment transport. [Copyright &y& Elsevier]

Boat traffic and resulting wakes are among the major human-mediated stressors on coastal ecosystems. Modulation of sediment transport by wakes and tides in an intertidal waterway with boat traffic is studied here. The hypothesis that boat wakes cause significant increases in sediment transport in intertidal settings is tested. Field observations of tides, currents, boat wakes and turbidity were collected on a transect within the Atlantic Intracoastal Waterway in Northeast Florida, USA. Hydrodynamic and sediment processes were evaluated by analyzing this field data set. A daily average of 60 wake events of varying energies were identified in the observations using time-frequency analysis methods. Due to differences in sediment suspension in response to each wake and unpredictable evolution of the bed state, decomposition of the effects of each individual wake on sediment is not possible. Therefore, the sediment dynamics during the periods of boat activity were compared in their entirety with the sediment dynamics during the periods of boat inactivity. Throughout the experiment, all periods of boat activity had consistently greater suspended sediment concentration near the bed compared to their preceding and succeeding periods of boat inactivity. In the first eight days of the experiment where tidal forcing was relatively similar between boat activity and inactivity periods, sediment transport rates were estimated as 0.048 m3/m/hr and 0.043 m3/m/hr during boat activity and inactivity, respectively, indicating a 12% increase in sediment transport due to boat traffic. A larger increase in sediment transport rates during boat activity compared to boat inactivity occurred over the last three days of the experiment. Volumes of sediment transported in low-tide, mid-tide and high-tide during boat activity were greater than their low-tide, mid-tide and high-tide counterparts during boat inactivity. Therefore, the results confirm the earlier mentioned hypothesis. • Boat traffic increased sediment transport rate by 12%. • Sediment transport in low-tide, mid-tide, and high-tide during boat activity were greater than their low-tide, mid-tide, and high-tide counterparts during boat inactivity. • Boat wakes must be considered to manage wetland stability in high-traffic estuaries. [ABSTRACT FROM AUTHOR]

Morphological evolution of large river deltas is highly vulnerable to extreme storm events due to insufficient sediment supply. As an abandoned delta lobe, the coasts along the northern Yellow River Delta (YRD) and Gudong Oil Field have recently suffered serious erosion due to extreme storm events and become increasingly vulnerable. In this study, a well validated and tested Delft 3D module by the observing hydrodynamic and sediment data to simulate the hydrodynamics and seabed erosion during a storm event in the littoral area of YRD. Observed wave, current and sediment data under both fair-weather and storm conditions were collected in the study area and used to validate the model. The results indicated that the model can reproduce well the hydrodynamic and sediment transport processes. A series of numerical experiments were carried out to examine the hydrodynamic changes and sediment transports. In the numerical experiment of normal condition, there is hardly any sediment transport off the YRD. The numerical experiment of storm condition showed that storms enhanced tidal residual currents, weakened tidal shear front, and significant wave heights up to 2 m, considerably intensified the sediment resuspension and dispersal. The local sediment resuspension due to the increased wave-induced bottom stress promoted the sediment plume to expand to the central area of Laizhou Bay, which seemed to provide sediment source for offshore and southward transport. During the storm, the active nearshore sediment resuspension provided sediment source for offshore and southward transport. The intensive dynamics and sediment transport under storm conditions caused significant changes in seabed erosion and siltation. The main erosion occurred off the Gudong and northern YRD, while the main siltation appeared in the central area of Laizhou Bay. No significant recovery after a storm and frequent strong winds have an accumulative effect on the erosion, which is very likely to dominate the erosive states of the YRD coast in the future. • Storm-induced energetic hydrodynamic forces intensify sediment resuspension and dispersal significantly. • Wave-induced bottom stress promotes sediment plume and enhances local resuspension. • Storms increase suspended sediment concentration and offshore sediment transport. • Storm-induced accumulative effect on seabed scour tends to cause long-term erosion. [ABSTRACT FROM AUTHOR]

• First validation of a daily large-scale sediment model using remote-sensing data. • Remotely-sensed reflectance can help sediment dynamics modeling in ungauged basins. • Better spatiotemporal sediment patterns using surrogate observations. Sediment models are important for estimating soil erosion, sediment transport, and deposition at different scales and for disparate scenarios; however, the availability of in-situ measurements may not be sufficient for the appropriate evaluation of model performance. For this reason, this study investigated how surrogate data (water quality [WQ] and remote sensing) could be used as a proxy for suspended sediment concentration (SSC) in order to evaluate the performance of a large-scale erosion and sediment transport model. To achieve this, the daily SSC was simulated, using the Large Scale Sediment Model (MGB-SED), a semi-distributed and conceptual model in which the Modified Universal Soil Loss Equation (MUSLE) is used to estimate sediment yield and an advection-diffusion equation is used to route suspended loads along rivers. Four experiments were performed that compared simulated SSC against: (1) in-situ SSC; (2) turbidity; (3) total suspended solids (TSS); and (4) surface spectral reflectance (SSR). Correlation analysis showed that r -values above 0.5 were found in 62%, 91%, 89% and 83% of the SSC, turbidity, TSS and SSR stations, respectively. Spatially, the model was evaluated in smaller drainage areas, using WQ data. Temporally, the number of SSR observations was greater than the number of in-situ measurements, allowing a better analysis of the temporal dynamics of the simulated SSC. Also, the SSR data improved the spatial coverage and could be employed for even large-scale, ungauged basins. These results bring a new perspective to the application of sediment models in poorly or ungauged basins, since surrogate data can improve the spatial and temporal suspended sediment coverage when compared to traditional SSC measurements, which is a common issue in large-scale sediment modeling. [ABSTRACT FROM AUTHOR]

• Mud samples in the LD estuary were measured using U-GEMS, and average τ ce of 0.26 N/m2 was obtained. • The simultaneous paradigm with τ ce of 0.26 N/m2 well explained the measured SSCs during the dry season. • The simultaneous paradigm with τ ce of 0.15 N/m2 agreed better with observations during the wet season. • The simultaneous deposition paradigm was better for SSC modelling during both the wet and dry seasons. Suspended sediment and the surficial sediment in most estuaries throughout the world consist of fine particles. Modelling cohesive sediment transport is an important way to explore the morphological evolution of estuaries where cohesive sediment is dominant. Various values for critical shear stress and deposition paradigms for cohesive sediment transport were evaluated here by analysis of field samples combined with numerical simulation in the Lingdingyang (LD) estuary in China. A UMCES-Gust Erosion Microcosm System (U-GEMS) experiment using field samples suggests that the experimental average value of critical shear stress for erosion (τ ce) is 0.26 N/m2. Two conflicting paradigms, i.e. mutually exclusive versus simultaneous erosion and deposition, are commonly used for cohesive sediment transport. Simulations of tidal currents and sediment transport during the wet season of 2007 and dry season of 2016 in the LD estuary were conducted under these two paradigms using the TELEMAC-2D hydrodynamic module and the sediment module SISYPHE in the TELEMAC model. Model verification under these two paradigms was carried out, and the τ ce parameters in the TELEMAC model were revised based on a U-GEMS experiment. The results showed the following. (1) The simulation results of the model in the LD estuary were satisfactory when an experimental average τ ce value of 0.26 N/m2 was used. (2) The simultaneous paradigm using a τ ce value of 0.26 N/m2 well explained the changes in the field-observed depth-averaged suspended sediment concentrations under all tidal regimes during the dry season, whereas the simultaneous paradigm using a τ ce of 0.15 N/m2 was more similar to observations in the LD estuary during the wet season. [ABSTRACT FROM AUTHOR]