Suspended Sediment Transport Research Articles

A trapping capacity constraint model for sediment transport in vegetative filter strips (VFS) on sloping surfaces

AbstractMost current modelling practices for sediment trapping in vegetative filter strips (VFS) assumed a constant sediment trapping efficiency of VFS, while, in practice, it was found to decrease greatly with the increasing trapped sediment amount in VFS (decreasing sediment trapping capacity of VFS). To account for this impact, a widely used VFS sediment transport module was modified to consider the changing sediment trapping capacity of VFS, which was expressed by a power‐law relationship with the inflow discharge, sediment concentration, slope gradient, and antecedent deposition amount. An integrated model that coupled a slope infiltration‐runoff module and the modified sediment transport module was then developed to simulate hydrology and suspended sediment transport in VFS on sloping surface. The model is calibrated and validated by 18 VFS experiments with different inflow, sediment, and slope conditions from Luo et al. (Science of the Total Environment, 725, 138361, 2020). Good agreements between observed and simulated runoff and sediment transport processes were found for nearly all cases. Due to the impact of changing sediment trapping capacity of VFS, the trapped sediment amount and the sediment transport rate of outflow varies greatly in space and time. With the increase of inflow discharge, sediment concentration, and slope gradient, the overall sediment trapping efficiency of VFS tends to decrease greatly and then remains almost unchanged. The comparison between proposed model and original physically based model shows that neglecting the impacts of changing sediment trapping capacity of VFS would lead to a constant and overly large sediment trapping efficiency of VFS, especially on steep slopes. Moreover, comparing with the empirical expression, the model with well‐founded theory can provide higher fidelity and more detailed results. Thus, the modelling framework is expected to provide a more effective approach for VFS assessment and maintenance in local or watershed scale.

Development, calibration and validation of a phase-averaged model for cross-shore sediment transport and morphodynamics on a barred beach

Simulating cross-shore sediment transport and associated sandbar migration is still a challenging task for phase-averaged coastal morphological models. Numerical studies have mostly relied on beach morphology prediction for calibration and validation, without examining in much detail the underlying hydrodynamics, sediment concentrations and transport rates. This paper reports on a new three-dimensional coastal morphodynamic model based on the hydrodynamic model of Zheng et al. (2017), combined with an advection-diffusion type suspended sediment transport model and the extended SANTOSS near-bed sediment transport formula of Van der A et al. (2013), to represent the key cross-shore transport mechanisms. The model is are calibrated based on comprehensive measurements from a large-scale laboratory experiment involving regular plunging breaking waves over an evolving sandbar, covering detailed comparisons on hydrodynamics, sediment suspension, transport rates, and bed level evolution. Separate validation using large scale wave flume experiments were also conducted to confirm the model's performance on different conditions. Good agreements are obtained between measurements and model results, which demonstrates the model's ability to reproduce cross-shore sediment transport processes under breaking waves correctly, given that the appropriate parameterizations for intra-wave processes are included. Model results also reveal the onshore near-bed transport is related to wave-induced near-bed streaming, wave skewness and asymmetry, and bed slope effects at different locations across the beach surface. Wave breaking-induced turbulence enhances the near-bed transport within the bed boundary layer which needs to be taken into account in order to achieve good model prediction skills.

Some recent finite volume schemes for one and two layers shallow water equations with variable density

We propose a class of finite volume algorithms that are both simple and efficient for solving numerically the shallow water equations with varying densities; shallow water flows in single and two layers are considered. In these flow regimes, variable horizontal or vertical density is taken into account. The shallow water equations for the hydraulic variables are coupled with a suspended sediment transport equation for the concentration variable to construct the model. To approximate the numerical solution of the models under consideration, a generalized Rusanov method is proposed; this method avoids solving Riemann problems during the time integration process, and it is simple and accurate. The proposed method is divided into two stages: predictor and corrector; the presented finite volume approach is well balanced, conservative, and simple. Non‐oscillatory and suitable for shallow water equations when Riemann problems are challenging to solve. Several test problems for single‐layer and two‐layer shallow water flows are applied to the proposed method. The numerical results show that the proposed finite volume approach has high resolution and that it is capable of simulating shallow water equations with variable density in flow regimes with strong shocks accurately.

Cross‐shore suspended sediment transport in a macro‐tidal and low‐sloping upper shoreface

AbstractThe driving mechanisms of sediment transport across the upper shoreface have been poorly examined to date because of the scarcity of field measurements beyond the intertidal area, which is mainly due to instrumentation difficulties. Here, we investigate the cross‐shore suspended sediment transport from synchronized time series of bottom pressure, current velocity and suspended sediment concentration measured by 13 m water depth, in a macro‐tidal and low‐sloping shoreface, under storm waves and fair weather conditions. Depending on the tidal phase and the incoming wave height, the measuring structure was alternatively located in the shoaling zone and in the outer surf zone. The analysis of field observations first revealed that steady currents dominate suspended transport, with a notable contribution of the wave‐driven return current under storm wave conditions. Cross‐spectral analysis further indicates that short waves globally induce an offshore‐directed transport under energetic conditions associated with a crest‐to‐trough phase lag effect. The contribution of infragravity (IG) waves, which reaches as much as 20% of the total transport, shows contrasting directions depending on whether IG waves are bound to the short wave groups or propagate as free waves.

A Study on the Influence of Submergence Ratio on the Transport of Suspended Sediment in a Partially Vegetated Channel Flow

AbstractRiparian or aquatic vegetation thrives with seasons. The understanding of canopies' Submergence‐Ratio (SR = stem height/water depth) influence on suspended sediment transport is still limited. Thus, Large Eddy Simulations coupled with the Discrete Phase Method are used to investigate the particles' three‐dimensional distribution in a partially vegetated straight channel. The spanwise distribution of particles are quantified by the probability density function (PDF), showing a non‐uniformity of particles in time as quantified by the PDF variance. We found that (a) with SR rising, the particles' depletion effects exerted by the vegetation‐side mixing layer is improved along the interface between vegetated and vegetation‐side bare channel region. However, the SR has little effect on the variance of the particles' PDF in the spanwise direction when the mixing layer is fully developed. (b) During the developing stage of the over‐canopy mixing layer, submerged vegetation with higher SR gains a stronger upwards (vertical) entrainment capability. The case (SR = 60%) has a higher sediment concentration than other cases in the fully developed vertical mixing layer region over canopy. (c) The vertical suspension of particles in the vegetation‐side bare channel region is analyzed. Particles migrating from the vegetated region are entrained into the vegetation‐side bare channel region by turbulent structures. Nevertheless, the vertical concentration profile is more uniform in the vegetated region than in the vegetation‐side bare channel at the same streamwise location. The cases SR = 40% and 60% still have higher sediment concentration than other cases in the vegetation‐side bare channel's upper region.

Near‐Bed Sediment Transport Processes During Onshore Bar Migration in Large‐Scale Experiments: Comparison With Offshore Bar Migration

AbstractDetailed information on nearshore sediment transport processes during onshore bar migration were obtained from large‐scale laboratory experiments with bichromatic wave groups on a relatively steep initial beach slope (1:15). Detailed measurements of velocity and sand concentration near the bed from shoaling up to the outer breaking zone including suspended sediment and sheet flow transport are presented. The analysis focuses on onshore migration under an accretive wave condition but comparison to an erosive condition highlights important differences. Decomposition shows that total transport mainly results from a balance of short wave‐related, bedload onshore transport and current‐related, suspended offshore transport. When comparing the accretive to the more energetic erosive condition, the balance shifts toward onshore transport, and onshore migration, because the short wave‐related transport does not decrease as much as the current‐related transport. This is related to the effects of skewness and asymmetry combined with less sediment suspension in the water column and undertow magnitude under the accretive condition. Transports from streaming in the wave boundary layer and from infragravity waves become visible but only play a subordinate role. Identified priorities for numerical model development include parametrization of wave nonlinearity effects and better description of wave breaking and its influences on sediment suspension.

Numerical study of the water-sediment regulation scheme (WSRS) impact on suspended sediment transport in the Yellow River Estuary

IntroductionThe transport of suspended sediment plays an important role in regulating erosion-accretion in estuaries. The Yellow River, the second longest river in China, which has a large amount of sediment and contributes sediment to the Yellow River Estuary (YRE) every year. The water and sediment discharge patterns in the lower reaches of the Yellow River have experienced significant changes over recent decades. In particular, the water-sediment regulation scheme (WSRS) of the Xiaolangdi Reservoir transports large amounts of water and sediment to the YRE within a very short time, causing dramatic changes in the spatiotemporal estuarine sediment dynamics.MethodsIn this study, we presented a coupled numerical model based on FVCOM-SWAVE-SED that considered the highly dynamic sediment variations in the YRE. The sediment distribution and erosion-accretion patterns in the YRE during the WSRS in 2013 were analyzed by the high-resolution model.ResultsThe sediment entering the YRE spread with freshwater, forming a high sediment concentration zone near the river mouth, where most of the sediments were deposited. The sediment dispersal distance was limited by the tidal shear frontal (TSF), and the southeast outspread length of the sediment was slightly larger than the northwest spread. Outside of the YRE, the areas with high flow currents exhibited high erosion. We examined the effects of the main external driving forces (such as waves, tides, and runoff) on the sediment distribution and showed that runoff, tides, and waves were the key factors affecting the sediment distribution of the YRE.ResultsThis study shows that WSRS effectively changes the sediment distribution and erosion condition in the YRE and provides a data for researches on changes in estuarine ecosystems.

A new method for measurement and calculation of unit width suspended sediment transport rate

Abstract The unit width suspended sediment transport rate is the basis for calculating river sediment flux, which provides an important measure of river hydrology and morpho-dynamics. By integrating the vertical distribution of the suspended sediment concentration and logarithmic flow velocity, the formula for unit width suspended sediment transport rate is presented. Based on this formula, the calculation of the near-bed relative transport rate missing in field measurement is given. Moreover, a new stratified water sampling device is invented for suspended sediment transport rate measurement by the six-point method at Mengsheng hydrological station in the Lancang River basin. Results of 24 sets of measurements show that the near-bed relative sediment transport rate ranges from 3.4 to 10.7% and is significantly positively correlated with the suspension index. The unit width suspended sediment transport rate measured by the traditional depth integrating method is on average 15.0% smaller than that calculated by the theoretical formula, which can be a reference for correcting the sediment transport rate based on the traditional method. This work provides a new device and a new method for the measurement and calculation of the unit width transport rate of suspended sediment, which has theoretical and practical significance.

Suspended sediment dynamics and influencing factors during typhoons in Hangzhou Bay, China

Hangzhou Bay is located in China on the south side of the Changjiang Estuary and is vulnerable to extreme weather, such as typhoons in the summer and autumn. In this study, a three dimensional suspended sediment numerical model was developed that considers the dynamic factors of advection, mixing, wave, and sediment-induced stratification to simulate and analyze the effect of typhoons on water and sediment transport in Hangzhou Bay. The model validations show that the model can sufficiently reproduce the variability of the suspended sediment concentration (SSC) during typhoon conditions. The simulation results show that the high SSC in the bottom layer was mainly distributed in the leading edge of the south coast, and generally exceeded 10 kg·m−3. During typhoons, the water and suspended sediment transport in Hangzhou Bay presented a pattern of "north-landward and south-seaward" circulation, which promoted the convergence of suspended sediment in the center part of the bay. During Typhoon Rumbia in 2018, the water and sediment flux across the section from Nanhui Cape to Qiqu Archipelago (NQ section) increased by 18.13% and 265.75%, respectively, compared with those before the typhoon. The wave-induced bottom shear stress during typhoons has a very significant impact on the bottom SSC. The sensitivity experiments show that the wave-induced bottom shear stress greatly promotes the sediment resuspension during typhoons, which indirectly makes the sediment-induced stratification stronger than the direct effect of waves on the vertical mixing. The strong winds brought by typhoons mainly enhanced the vertical mixing, which has a stronger effect on surface SSC than waves. The suppression of vertical mixing by sediment-induced stratification during typhoons should not be ignored, especially for high turbidity coastal waters, such as Hangzhou Bay.

PAPEL DA VEGETAÇÃO COMO INDUTOR A SEDIMENTAÇÃO EM CANAL ARTIFICIAL DE TERRA

The biogeomorphic role of vegetation has been explored in different contexts with advances in the understanding of sedimentation and hydrodynamic changes in channels and riparian zones. However, it is yet to be better established regarding their role in small earth-derived canals water gullies, the development of these issues, and canal users. This study verified whether vegetation development has more prominent role as reducer of the transport of suspended sediments along the artificial channel than the natural river system, focusing on the role of vegetation as a filter of the sedimentary load. We understand that vegetation should be addressed as part of the channel management process, providing users with favorable turbidity indices and lower risks of structures breaking, as well as the formation of extenders of fluvial and riparian habitats in the rainy season. Keywords: biogeomorphic succession; anthropogeomorphology; artificial open channels; sedimentation; hydrogeomorphology.

Impacts of tidal flat reclamation on suspended sediment dynamics in the tidal-dominated Wenzhou Coast, China

Reclamation of tidal flats is one of the engineering measures of expanding land area and developing the economy in coastal areas; however, this process disturbs the natural processes of the tidal flat system. Taking the flood-tidal dominant Oufei tidal flat at the Wenzhou coast as a study area, the influences of tidal flat reclamation on tidal and suspended sediment dynamics were comprehensively investigated via numerical modeling. Before the reclamation, the Eulerian residual current flows alongshore and the residual sediment transport on-shore in the tidal flat area. The reclamation reduces the tidal flat area, shifting the M4 co-phase line toward the coast and squeezing the flood-dominated area. Consequently, the tidal current is weakened and the suspended sediment concentration (SSC) is reduced, but the residual sediment transport change insignificantly. The residual sediment transport in the Feiyunjiang Estuary is controlled by the tidal pumping effect. The upper estuary shows a net sediment transport landward, while a seaward transport is observed in the lower estuary, which further splits into two circulation outside the estuary. The south Oufei dike construction interferes the northern sediment circulation, resulting in the alteration of local SSC and enhancing landward sediment transport inside the estuary. The methodology and understandings arising from this study could be a good reference for the analysis of suspended sediment transport under tidal flat reclamation effects at other sites.

Suspended sediment transport and turbidity maximum in a macro-tidal estuary with mountain streams: A case study of the Oujiang Estuary

Macro-tidal estuaries with mountain streams are typical estuarine systems in southeastern China. Suspended sediment transport and turbidity maxima are sensitive to changes in the tidal and fluvial regimes of estuaries. To improve our understanding of river-ocean interactions and thus improve estuarine forecasts for biogeochemical processes, we developed a high-resolution hydrodynamic and sediment transport coupled model to investigate the suspended sediment transport and estuarine turbidity maximum (ETM) in the Oujiang Estuary. This estuary is characterized as a macro-tidal estuarine system with a large tidal range and drastic fluctuations in freshwater and sediment discharge. The results led to the following conclusions: (1) the ETM occurred during spring tides due to strong tidal resuspension. In contrast, it was not formed during the neap tide because of weak bottom shear stress. The ETM moves upstream to Yanmen during low river discharge and migrates downstream to the river mouth during high river discharge, causing sediment deposition in the nearshore region. (2) Owing to the characteristics of mountain streams and upstream anthropogenic reservoirs, the ETM is strengthened during low river discharge (∼100 m3 s−1) even during the wet season, which supplements the fact that the ETM is more prevalent during the dry season and withers during the wet season. The suspended sediment forming the ETM mainly originates from shallow offshore shoals owing to tidal resuspension. Owing to the weak vertical exchange flow near the river mouth, the ETM is related to the exchange flow during the low water flow. (3) The ETM excursion shows semi-diurnal variability with different transport distance for high and low river discharges. Tidal pumping dominates the suspended sediment flux in the core of the ETM, which is mainly maintained by two components of the Euler and Stokes fluxes as the tidal energy depletes during the flood tide.

Non-Fickian transport models for characterising the sediment suspension in unsteady flows

Non-Fickian transport of suspended sediment has been observed at field and laboratory scales. Such as turbulent bursting, resulting in complex dynamics for the sediment particles movement. The erosion and deposition of sediment have an impact on the hydraulic engineering and environment. This study makes an attempt to develop the variable-order fractional advection-diffusion equation (VOFADE) and variable-order Hausdorff fractal derivative advection-diffusion equation (VOHADE) models to describe the vertical distribution of suspended sediment in unsteady turbulent flows. From a classical viewpoint, the distribution of the concentration in sediment-laden flows is determined based on Fick?s first law. However, the vertical diffusion of suspended particles exhibits the non-locality/space scale dependency and history memory/time scale dependency properties due to turbulent bursting. Moreover, previous literatures have indicated that turbulence structure changes with the water depth. Hereby, we employ the space-dependent VOFADE and VOHADE models to describe the vertical diffusion of suspended sediment in unsteady flows, and further test its applicability with the experimental data. Numerical simulation results confirm that the VOFADE and VOHADE models give a better agreement with the experimental data and can well characterise the space-dependent anomalous transport. Hence, the models proposed by this study may help to provide a powerful mathematical physical model in the quantification of suspended sediment transport.

Suspended Sediment Transport Dynamics In River Musa, Niger State - Nigeria

Energy circumstances frequently affect how suspended sediment behaves in rivers; for example, sediment is retained during low flow and transferred at high discharge. However, the mixing and directing of water and sediment from various sources can also have an impact on the timing of the maximum sediment movement. In this study, the movement of suspended sediment, river bed material, and flow characteristics of the Musa River were examined. Besides, the study is aimed at studying the suspended sediment laden water transported by the River Musa, as there is no consistent, reliable data collection of sediment inflow into Nigerian rivers to aid water resources planning and management. Several techniques adopted for estimating the rates of sedimentation are highly laborious, expensive, and time-consuming, although these challenges are made easier by the availability of some sediment and flow rating curves. The rate of sediment carried by the River Musa during this study was estimated using the direct sediment sampling data approach.The average sediment concentration estimates conveyed by River Musa during the study period was 0.1337 mg/l which is low and may increase if the catchment area's upstream is subjected to more urbanization, agricultural, and animal grazing activities. Besides, discharge rates were measured, and the riverbed material transported classified.

Detecting the drivers of suspended sediment transport in an intermittent river: An event-based analysis

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.

Improve the Accuracy in Numerical Modeling of Suspended Sediment Concentrations in the Hangzhou Bay by Assimilating Remote Sensing Data Utilizing Combined Techniques of Adjoint Data Assimilation and the Penalty Function Method

Suspended sediment dynamics play an important role in controlling nearshore and estuarine geomorphology and the associated ecological environments. Modeling the transport of suspended sediment is a complicated and challenging research topic. The goal of this study is to improve the accuracy of modeling the suspended sediment concentrations (SSCs) with newly developed techniques. Based on a three-dimensional suspended cohesive sediment transport model, the transport of suspended sediment and SSCs are simulated by assimilating SSCs retrieved from the Geostationary Ocean Color Imager (GOCI) with the adjoint data assimilation in the Hangzhou Bay, a typical strong tidal estuary along the coast of the East China Sea. To improve the effect of the data assimilation, the penalty function method, in which the reasonable constraints of the estimated model parameters are added to the cost function as penalty terms, will be introduced for the first time into the adjoint data assimilation in the SSCs modeling. In twin experiments, the prescribed spatially varying settling velocity is estimated by assimilating the synthetic SSC observations, and the results show that the penalty function method can further improve the effect of data assimilation and parameter estimation, regardless of synthetic SSC observations being contaminated by random artificial errors. In practical experiments, the spatially varying settling velocity is firstly estimated by assimilating the actual GOCI-retrieved SSCs. The results demonstrate that the simulated results can be improved by the adjoint data assimilation, and the penalty function method can additionally reduce the mean absolute error (MAE) between the independent check observations and the corresponding simulated SSCs from 1.44 × 10−1 kg/m3 to 1.30 × 10−1 kg/m3. To pursue greater simulation accuracy, the spatially varying settling velocity, resuspension rate, critical shear stress and initial conditions are simultaneously estimated by assimilating the actual GOCI-retrieved SSCs to simulate the SSCs in the Hangzhou Bay. When the adjoint data assimilation and the penalty function method are simultaneously used, the MAE between the independent check observations and the corresponding simulated SSCs is just 9.90 × 10−2 kg/m3, which is substantially less than that when only the settling velocity is estimated. The MAE is also considerably less than that when the four model parameters are estimated to be without using the penalty function method. This study indicates that the adjoint data assimilation can effectively improve the SSC simulation accuracy, and the penalty function method can limit the variation range of the estimated model parameters to further improve the effect of data assimilation and parameter estimation.

A modified approach to determine mean sediment load and related discharge indices for suspended sediment transport

Discharge indices, viz., half-load discharge (Q1/2), and functional-equivalent discharge (Qfed), can be used to quantify the effectiveness of flow distribution in sediment transport through a river network. Q1/2 represents the flow below and above which half of the total long-term sediment load is transported, while Qfed indicates a uniform flow that replicates the total magnitude of the sediment load transported by the complete discharge distribution. In Magnitude Frequency Analysis (MFA), these indices are computed based on the estimate of mean sediment load (μS) transported through a river network. Conventionally, the analytical expression for μS was derived by assuming the discharges to be lognormally (LN) or Gamma (G) distributed. However, the assumption of discharge distribution is location specific and hence LN or G distributed discharge may not be valid for all catchments. Thus, it is necessary to assess the uncertainty in the estimate of μS and thereby the estimates of Q1/2 and Qfed when the discharge data do not follow either LN or G distribution. In this study, a modified approach is proposed to determine μS and related Q1/2 and Qfed for the general distribution of discharge datasets. The Proposed Approach (PA) includes the transformation of discharge data by applying the Box-Cox transformation followed by the estimation of μS, Q1/2, and Qfed. Furthermore, an analytical expression is derived for the solution of μS under the proposed framework. A simulation experiment is performed to establish the effectiveness of PA over the conventional (LN or G -based) approaches. Results indicated that PA provides reliable estimates of μS, Q1/2, and Qfed. The utility of the PA is demonstrated through its application to suspended sediment transport in four South Indian rivers.

Bedload Estimation: Case of Wadi El-Hammam in the North-West of Algeria

In Algeria, only the transport of suspended sediment is measured, the rate of bedload in the global transport of solids is estimated, approximately. Measures of bed load transport in the field are very costly, due to flow disturbances. As a result, evaluations of this type of sediment transport are difficult to carry out in the absence of databases. In this article, we tried to quantify this mode of transport at the wadi El-Hammam using the formula of Meyer-Peter and Müller. Formula that seems best adapted to the physical characteristics and flow conditions of the wadi studied. The results obtained show that the calculated bedload ratio is between 0.6 and 28 % of the suspension. The quantities transported annually are very large and irregular as they vary from 2.3 to 32 Mg.km-2.year-1, characterising the Mediterranean mountains and semi-arid environments. A good correlation was found between the daily bedload flow and the liquid flow, the obtained model Qs = aQb, can be easily used to estimate the bedload transport at the Hacine hydrometric station, located at the output and without data concerning this phenomenon. Keywords: Bed load transport; Fergoug; Meyer–Peter and Müller formula; Suspension; Wadi El-Hammam.

Coastal plumes contribution to the suspended sediment transport in the Southwest Atlantic inner continental shelf

Global coastal zones are constantly changing due to the actions of various physical forces. Recent studies show that the supply of suspended sediment of continental origin plays an important role in these changes. Once in the coastal region, this sediment significantly influences the sedimentation process on the inner shelf. Thus, understanding the transport and destination of these suspended sediments is crucial to interpret the morphodynamic evolution of the seabed and biogeochemical processes in the ocean. The Southwest Atlantic Shelf is the largest continental shelf in the Southern Hemisphere and one of the most important in biological production, because of the great continental contribution exercised by both Río de la Plata and Patos Lagoon. Studies in the region showed that these effluents are significantly affected by the El Niño–Southern Oscillation (ENSO) effect, which can interfere with the availability of suspended material inserted into the coastal region. Despite the great efforts of several authors to understand these changes and their interactions with the environment, some questions remain unanswered. Thus, this work aims to fill this gap by answering questions related to the contribution of suspended sediment of continental origin and its behaviour on the Southwest Atlantic Inner Shelf. The behaviour of suspended sediment was investigated in two distinct periods using the hydro-morphodynamic model TELEMAC-3D: one representing normal years, that is, without the effect of ENSO (2005–2006) and the other experiencing the effect of ENSO (2008–2009).The model was calibrated and validated using field data for both studied periods. R esults were based on statistical analysis, such as wavelet and empirical orthogonal function (EOF) analysis, in addition to time series analysis. Results showed that the Southwest Atlantic Inner Shelf is mainly influenced by the fluvial discharge of Río de la Plata and Patos Lagoon, and by the local wind. Río de la Plata is the largest exporter of suspended sediment in the region, with an approximate rate of 1.2 × 108 tons.year-1 in neutral (normal) years and 3.0 × 108 tons.year-1 in years under the influence of ENSO. The Patos Lagoon, on the other hand, exports approximately 1.25 × 107 tons.year-1 in the period without the ENSO effect and 1.35 × 107 tons.year-1 in the period influenced by ENSO. Results also showed that the fluvial discharge interacts with the suspended sediment in seasonal to interannual scales, while the wind contributes to the concentration of suspended sediment on synoptic scales. Still on the wind regime, results show that the local wind regime gains importance particularly when the suspended sediment reaches the coastal region.

Sedimentation and Erosion Patterns of the Lena River Anabranching Channel

Lena River is one of the largest “pristine” undammed river systems in the World. In the middle and low (including delta) 1500 km course of the Lena main stem river forms complex anabranching patterns which are affected by continuous permafrost, degradation of the frozen ground and changes in vegetation (taiga and tundra). This study provides a high-resolution assessment of sediment behavior along this reach. Comprehensive hydrological field studies along the anabranching channel located in the middle, low and delta courses of the Lena River were performed from 2016 to 2022 including acoustic Doppler current profiler (ADCP) discharge measurements and sediment transport estimates by gravimetric analyses of sediment concentration data and surrogate measurements (optical by turbidity meters and acoustic by ADCP techniques). These data were used to construct regional relationships between suspended sediment concentrations (SSC, mg/L), turbidity (T, NTU) and backscatter intensity (BI, dB) values applicable for the conditions of the Lena River. Further, field data sets were used to calibrate the seasonal relationships between Landsat reflectance intensities and field surface sediment concentration data. Robust empirical models were derived between the field surface sediment concentration and surface reflectance data for various hydrological seasons. Based on the integration of in situ monitoring and remote sensing data we revealed significant discrepancies in the spatial and seasonal patterns of the suspended sediment transport between various anabranching reaches of the river system. In the middle course of the Lena River, due to inundation of vegetated banks and islands, a downward decrease in sediment concentrations is observed along the anabranching channel during peak flows. Bed and lateral scour during low water seasons effects average increase in sediment load along the anabranching channels, even though a significant (up to 30%) decline in SSC occurs within the particular reaches of the main channel. Deposition patterns are typical for the secondary channels. The anabranching channel that was influenced by the largest tributaries (Aldan and Viluy) is characterized by the sediment plumes which dominate the spatial and temporal sediment distribution. Finally, in the distributary system of the Lena delta, sediment transport is mostly increased downwards, predominantly under higher discharges and along main distributary channels due to permafrost-dominated bank degradation.