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We employed idealized numerical experiments using Delft3D to investigate how the interactions of coalescing buoyant river plumes with mangrove vegetation affect sediment transport and deposition in the coastal zone. Our model system, based on the Firth of Thames in the North Island of New Zealand, is designed to represent two mangrove-lined rivers debouching into a coastal bay. Sediment transport patterns into the three adjacent mangrove forest regions (central, western, and eastern) were assessed by quantifying the sediment fluxes over a tidal cycle. The interactions between the buoyant river plumes resulted in a coalesced river plume that flowed along the central mangrove forest between the rivers. The dominant contributors to the total sediment transport into the mangrove forests varied with both the total and the relative flows through the two rivers. When both rivers were forced with their respective flows at the 50th percentile of observed flow, the analysis of sediment transport fluxes along the central forest revealed sediment deposition inside the mangrove forests lining the river mouth nearly four times greater than in the intermediate regions along the central forest; consistent with satellite imagery of the Firth of Thames. Winds of 5 m s−1 modify the overall sediment transport patterns by deflecting the river plume in the direction of the wind. The magnitude of sediment flux is the highest (nearly 80% compared to the no-wind scenario) in the case of an easterly wind scenario as the alongshore transport is enhanced by Coriolis deflection and wind direction aligned with the alongshore flows of the larger plume. • Plume-to-plume interactions result in a coalesced river plume. • Sediment plume bulge of one river inhibits along-shore sediment transport of the other. • The presence of winds altered sediment transport patterns. [ABSTRACT FROM AUTHOR]

Variability in supply of terrestrial sediments to the coastal zone impacts sediment transport processes and ecological dependencies. This study investigated surface sediment distribution and transportation within a 2020 km2 shallow embayment following a period of flood induced sediment supply. Extensive field sampling of 221 common sites between 2015 and the 2019 follow-up survey presented, identified significant reduction in fine sediment fractions, evident through a 367 km2 decrease in surface mud coverage. Wind-wave sediment transport processes controlled the spatial distribution of fine sediments, exporting 23 million tonnes of mud from the shallow sedimentation zones. In a broader context, sensitive benthic habitats such as seagrass meadows exhibited signs habitat recolonisation coinciding with areas of reduced mud content. Despite these promising short-term outlooks, the developed fine sediment budget suggests ongoing terrestrial sedimentation will exhaust key sediment sinks within Moreton Bay, effectively reducing the system's ability to buffer future sedimentation events. • Significant reduction in surface mud within subtropical embayment. • Rapid reduction in sediment supply consistent with climate oscillations. • Wind-wave resuspension controlling surface mud recovery. • Moreton Bayshows some level of resilience to extreme flood events. [ABSTRACT FROM AUTHOR]

The process of flocculation in dredge plumes was investigated by field measurements using Laser In-Situ Scattering and Transmissometry (LISST), Optical Back Scatter (OBS) sensors and an Acoustic Current Doppler Profiler (ADCP) during dredging campaigns in Port Curtis, Queensland (Australia). Suspended sediment characteristics differed significantly between natural ambient suspended sediment and sediment suspended by dredging as well as between sediment suspended by mechanical and hydraulic dredgers. LISST measurements enabled distinction of the suspended sediment by origin and showed that the majority of sediment particles naturally in suspension were aggregated flocs made up of multiple smaller particles. Primary particles in natural suspended sediment had a median particle size (d 50) of 8 to 14 μm, while in-situ flocs had a d 50 of 52 to 99 μm. There were both microflocs and macroflocs present in the natural suspended sediment, with the microflocs being dominant (representing 67%–80% of the flocs). Mechanical dredging resulted in the release of individual particles, microflocs and macroflocs, with the potential for a comparable percentage of macroflocs as in natural suspended sediment (11%–27% compared to 20%–33% in natural suspended sediment). Macroflocs released by mechanical dredging were likely to have originated from the seabed. During overflow from the hopper, the suspended sediment released from the hydraulic dredger had smaller flocs compared to the natural suspended sediment, with a reduction in the d 50 of in-situ flocs from 91 to 67 μm and a reduction in the proportion of macroflocs from 32% to 24%. These results indicate that larger macroflocs present on the seabed had been broken up by the hydraulic dredging, with most of the suspended sediment remaining in the form of smaller microflocs, suggesting that the flocs were not completely disaggregated by the shear-stress generated during hydraulic dredging. Ongoing aggregation of suspended sediment was shown to occur in the sediment suspended by both dredging methods within 20–25 min of the plumes being generated. This study demonstrates the importance of considering flocculation in predictive dredge plume modelling studies to prevent significantly underestimating the settling velocity and substantially over-estimating the extent and intensity of dredge plumes if flocculation is not accounted for. • Flocculation occurs in plumes generated by both mechanical and hydraulic dredging • Flocs released by mechanical dredging were comparable to natural flocs • Flocs from hydraulic dredging were smaller than natural flocs • Ongoing aggregation of flocs occurred in the plume for both dredge types [ABSTRACT FROM AUTHOR]

Cross-front transport is a vital process in the offshore transport of terrestrial materials. The factors influencing cross-front transport are multifaceted and exhibit regional variability. As important factors regulating material transport patterns in the shelf seas of eastern China, the East Asian Winter Monsoon (EAWM) and Kuroshio current (including its branches) vary on multiple time scales, yet their role in controlling offshore transport is not fully understood. In this paper, cross-front offshore transport in the North Yellow Sea is chosen to investigate the aforementioned issue using numerical simulation. By excluding other potential processes for offshore transport, frontal instability is identified as the primary mechanism for offshore transport, which is triggered by winter storms (bursts of the EAWM); hence, the intensity of offshore transport is highly associated with the strength of winter storms on synoptic scales. However, on the inter-annual scale, the intensity of offshore transport is more likely regulated by the strength of the Kuroshio current, and a warming Kuroshio facilitates offshore transport. Although the role of each factor in controlling the intensity of offshore transport is delineated, the interactive effects of the EAWM and Kuroshio current on offshore transport are quite intricate, and how to quantitatively estimate their roles on multiple time scales remains a challenge using modelling. The results obtained from this study can be applied to analyse cross-front transport throughout the eastern China seas and bear significant implications for future studies on pollutant diffusion, nutrient distribution, and sediment transport in the coastal area. • Cross-front transport around the Shandong Peninsula was revealed using a numerical model. • EAWM and Kuroshio affect the strength of cross-front transport on different time scales. • With global warming, the temperature of Kuroshio might gradually become the primary control of cross-front transport. [ABSTRACT FROM AUTHOR]

Estuarine dams are constructed in estuaries for reasons such as freshwater, flood control, and navigation. By changing tidal and river properties, estuarine dams can change the circulation and sediment transport in estuaries. Previous studies have investigated the along-channel changes in flow and sediment transport, however across-channel changes due to an estuarine dam are not well understood. To increase our understanding, this study analyzed an idealized estuary using the COAWST numerical modeling system. Models of strongly stratified, partially mixed, periodically stratified, and well-mixed estuaries were run for one year. Then, the models were subject to the construction of an estuarine dam and run for another year. For each estuarine type, scenarios with an estuarine dam at x = 20, 55, and 90 km from the mouth and freshwater discharge intervals of Δt = 0.5, 3, and 7 days were investigated, and the scenarios were compared. The results indicated that the river-dominated and tide-dominated estuaries behaved differently. In river-dominated estuaries, the residual circulation tended to be inflow in the channel and outflow over the shoals due to the estuarine exchange flow, and the secondary circulation was bottom divergent due to differential advection. The exchange flow and secondary circulation were found to weaken with longer discharge interval. The sediment fluxes in the channel were dominant, and, despite the weaker exchange flow, were found to be greater and directed seaward due to strong dam discharge for long discharge intervals. In tide-dominated estuaries, the residual circulation tended to be inflow over the shoals and outflow in the channel due to the tide-induced circulation, and the secondary flow was bottom convergent due to differential advection resulting from Stokes return flow. As the estuarine dam was located nearer to the mouth, the tide-induced circulation was replaced with exchange flow, and the secondary flow became bottom divergent. The sediment fluxes in the channel were dominant in this case as well, and were determined by tidal asymmetry from the interaction of the tides with the residual current, becoming directed landward as the seaward tide-induced circulation decreased with the estuarine dam near the mouth. With respect to bed level change, gradients in along-channel sediment fluxes were found to contribute most to bed level change near the mouth and estuarine dam, whereas gradients in across-channel sediment fluxes contributed most to deposition on the estuarine shoals. This study demonstrates that estuarine dam location and discharge interval can alter estuarine transverse variability and improves our understanding compared to previous analyses based solely on along-channel processes. • River-dominated estuaries exhibited inflow in channel, outflow over shoals. • Tide-dominated estuaries exhibited inflow over shoals, outflow in channel. • Estuarine dams near mouth with large discharge interval reduced these circulations. • Tide-dominated estuaries switched from tide-induced circulation to exchange flow. • Lateral sediment fluxes contributed to shoal deposition. [ABSTRACT FROM AUTHOR]

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. • A new phase-averaged morphodynamic model is developed to represent cross-shore sediment transport and beach morphology. • The model is calibrated based on comprehensive measurements to ensure good representation of all physical processes. • Model validation demonstrate the effectiveness of the model parameters for the related sediment transport processes. • Wave asymmetry and breaking turbulence to the near bed sediment onshore transport and resuspension is very important. • Detailed modelling of near bed process to include breaking turbulence to the sediment transport predictions is required. [ABSTRACT FROM AUTHOR]

Estuarine turbidity maxima (ETMs) are of sedimentological, geomorphological and ecological significance. In this study, a well-validated and process-based sediment transport model was used to investigate the response of ETM dynamics in the Yangtze Estuary (YE) to construction of the Three Gorges Dam (TGD) and morphological evolution of the YE. The model results demonstrated that the ETM dynamics change in the upper estuary was controlled by the TGD construction. After the TGD construction, the ETM area decreased by 22% (from 1116 to 874 km2) and the ETM center location moved landward 7 km during the flood season. The estuarine morphological evolution played a key role in the ETM dynamics change of the mid-lower estuary. The ETM area decreased by 55% (from 1478 to 658 km2) and 15% (from 658 to 562 km2) due to the estuarine morphological evolution from 1998 to 2010 and from 2010 to 2018, respectively. Meanwhile, the ETM center location moved landward 38 km and 7 km during the periods 1998–2010 and 2010–2018, respectively. Overall, both the TGD construction and estuarine morphological evolution induced decreased suspended sediment concentrations in the estuary. Furthermore, the effect of TGD construction was dominant in the upper estuary, whereas the effect of estuarine morphological evolution became dominant in the mid-lower estuary. These findings provide implications for management of the YE and other similar estuaries. • Estuarine turbidity maximum (ETM) decreased by 22% and moved landward 7 km after Three Gorges Dam (TGD) construction. • Estuarine morphological evolution induced ETM to decrease by 15–55% and move landward 7–38 km. • TGD construction and morphological evolution dominated ETM changes in upper and mid-lower estuaries, respectively. [ABSTRACT FROM AUTHOR]

Sediment transport and depositional processes in the Southwest Atlantic Inner Shelf are strongly influenced by the contribution from Río de la Plata and Patos Lagoon fluvial systems. Understanding the behavior of erosive and depositional processes and bed evolution in the region is of utmost importance to address the impacts of anthropogenic activities, climate change and for navigation security. Therefore, this work aims to improve the understanding of such processes, and their temporal and spatial scales of variability. We employed the SISYPHE morphodynamic model coupled with the TELEMAC-3D hydrodynamic model to simulate the resulting depositional and erosional fluxes and the bottom evolution during a period of 8 years (2005–2012). Results indicate that during this period, depositional fluxes mostly exceeded erosional fluxes in the south of the Patos Lagoon mouth, resulting in predominantly positive bottom evolution. On the other hand, erosional fluxes exceeded depositional fluxes to the north of the Patos Lagoon mouth, resulting in predominantly negative bottom evolution. Widespread positive values of bottom evolution are observed along the northern and southern coasts off the Río de la Plata mouth, indicating a general dominance of sediment deposition over erosion. A wavelet analysis showed that fluvial discharge influences the variability of depositional process on an interannual time scale, whereas the synoptic variability is influenced by wind action. Moreover, positive ENSO periods (El Niño) are related to increased depositional fluxes, and decreased depositional fluxes during the negative phase (La Niña), with pronounced effects off Río de la Plata. • The study area presented predominantly positive bottom evolution. • Erosional fluxes exceeded depositional fluxes north of the Patos Lagoon mouth. • Positive values of bottom evolution are observed along coasts off the Río de la Plata mouth. • The fluvial discharge influences the deposition process on interannual time scale, while the wind action is related to the synoptic time scale variability. • The ENSO effect can increase the depositional fluxes during El Niño and decrease during the Niña. [ABSTRACT FROM AUTHOR]

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. • Estuarine modeling was conducted to study suspended sediment dynamics. • ETM excursion occurs for high and low river. • Decomposing sediment fluxes reveals ETM mechanisms. • River discharge and tidal pumping play roles on ETM formations. [ABSTRACT FROM AUTHOR]

Typhoons frequently occur in the East China Sea, which significantly affect the material transport, marine hydrodynamics, and sedimentary environment of coastal currents in a relatively short time scale. Based on the in-situ observation and satellite remote sensing data, this paper analyzes the influence of five typhoons on the coastal currents of East China Sea in 2019 during different seasons. The typhoons Lekima and Mitag, which passed directly, greatly influenced the coastal current, resulting in the disappearance of the tide signal, and stimulated the current to generate new periodic signals of 3–6 days and 1–3 days, respectively. Typically, the wind of Lekima changed the flow field of the East China Sea Coastal Current (ECSCC) from northeastward to southwestward in summer in a short period, and the southwestward volume transport of the ocean current was 4 times that during periods without typhoon occurrence. The remaining water levels of the Haimen, Jiantao, and Damutu tidal level stations showed maximum water level increases during the observation period, whose values were 1.89, 1.26, and 0.90 m, respectively. Mitag only caused a northeastward current transport during autumn, and the water levels of tidal level stations along the coast increased by more than 0.5 m. However, weak and distant typhoons (Danas, Lingling, and Tapah) caused relatively small changes in ocean currents, along with the corresponding change in water transport and deposition. The results show that local wind accompanying typhoons is the main factor affecting the evolution (destruction and reconstruction) of the coastal current system. Therefore, the evolution of the ECSCC under different typhoons can provide a more comprehensive understanding of the impact of typhoons with different paths and intensities on the coastal current. [Display omitted] • The destruction and reconstruction of coastal current by typhoons was studied. • The coastal current system was destroyed by typhoons passing directly through. • The tide signal of coastal current disappeared and a new signal established. • Water level and sediment transport dramatic varied during typhoons. [ABSTRACT FROM AUTHOR]

Knowledge of sediment transport pathways is important for coastal management as well as for offshore infrastructure such as wind farms and other renewable energy installations. Here a three-way coupled model of tides, waves and sediment dynamics is presented, which extends the approach of Davies and Robins (2017) for the prediction of the locally-varying seabed roughness k s resulting from the interaction between the flow (tides and waves) and the bed sediment (grain size mixture) subject to wave-current interaction (WCI) at the seabed. The model was applied to the North Wales coastal area, with particular emphasis on an extensive shore-connected sand bank (Constable Bank), the stability of which was investigated through the study of residual sediment circulation patterns. Multi-beam (MBES) and seabed rig (AWAC) observations have allowed validation of the predicted k s and hydrodynamics, respectively. With due allowance for the supply of mobile sediment, the agreement between predicted k s and observed bedform height was generally good. The model has been used to determine residual velocities and sediment pathways, both with and without wave effects included. Wave influence and WCI are predominant in nearshore areas, affecting the magnitude and direction of the residual fluxes. A key modelling outcome offshore is a clockwise residual circulation pattern for water and sediment around the end of Constable Bank, set within a generally eastward net drift of sediment in the wider study area. • Sediment pathways predicted using a novel 3-way-coupled tide-wave-sediment model. • Coastal area flow modelled with temporally/spatially varying bed roughness. • Implementation in Telemac of wave-current interaction at the seabed. • Comparison between MBES-observed and Telemac-predicted physical bed roughness. • Residual flow and transport predicted highlighting a shore-connected sandbank. [ABSTRACT FROM AUTHOR]

In the present article two flocculation models, given in [5] (LG model) and [36] (S model) are compared. Both models give the time evolution d L / d t where L is the size of a particle undergoing flocculation, and t is the time. The LG model is based on logistic growth theory, whereas the S model is based on the theory originally derived by Smoluchowski. Both models have the advantage of easy implementation in, for instance, large-scale sediment transport numerical models. However, it is found that they do not obey the same kinetics. A series of laboratory experiments is presented where the flocculation of a mineral clay by polyelectrolyte is studied as a function of clay concentration and shear rate. From modelling these experiments, it is found that the LG model reproduces the time dependence of the floc sizes found experimentally, whereas the S model does not. It is shown that the LG model can be used to model the data over the whole range of clay concentration and shear investigated. Based on the study presented in this article, it was found that the average floc growth in time for the clay type and conditions applied in the experiments could be modelled by: d L / d t = 40 × 1 0 − 4 G 0. 75 × [ e x p (− 2 × 1 0 − 4 G 0. 75 t) ] / [ 1 + 20 e x p (− 2 × 1 0 − 4 G 0. 75 t) ] L. • Logistic growth theory is compared with Smoluchowski-based theory. • The models do not have the same kinetics. • Only logistic growth theory agrees with experiments. • Logistic growth theory models data for all clay concentrations. • Logistic growth theory models data for all shears investigated. [ABSTRACT FROM AUTHOR]

The South Yellow Sea (SYS) is strongly influenced by large amounts of sediment input from surrounding rivers, but the dispersal patterns of these sediments, especially how they accumulate in the central Yellow Sea mud (CYSM) region, have not been well illustrated. Here, we present a detailed temporal variation record of the clay mineral compositions from core YSC-10 of the northern SYS near the western margin of the CYSM, trying to investigate sediment provenance and to discuss transport processes occurring during the Holocene. The clay mineral assemblages of core YSC-10 mainly consist predominantly of illite (68 ± 3%), followed by chlorite (15 ± 2%) and kaolinite (10 ± 2%), with scarce amounts of smectite (6 ± 3%). Combined with published data, our results suggest that the fine sediments of core YSC-10 are most likely a mixing product of the Huanghe (Yellow River), Changjiang (Yangtze River) and Korean Peninsula small river sediments, with notable temporal changes. During 8.4–6.4 ka, the Huanghe sediments from the Bohai Sea flowed directly into the SYS and played major roles in the sedimentation therein. In addition, as the modern ocean circulation pattern was formed ∼6 ka, the ocean front developed along the Shandong Peninsula coastal area of the SYS, which would have prevented the dispersal of the Huanghe sediments to the CYSM. The Changjiang sediments delivered by the diluted water replaced those from the Huanghe as the main source of the CYSM during the period of 6.4–4.2 ka. After 4.2 ka, the coastal shear front weakened and moved seawards due to the weakening and eastward shift of the Yellow Sea Warm Current (YSWC) in winter and the weakening and shrinking of the Yellow Sea Cold Water Mass (YSCWM) in summer. The Huanghe sediments seem to have increased and fluctuated frequently to core YSC-10 since then. Our study thus highlights that the coastal shear front may have played an important role in the source-to-sink processes of the SYS. • Clay mineral assemblages of core YSC-10 which near the western margin of the CYSM since the Holocene. • The source and transport mechanism of clay minerals of core YSC-10 in different time periods since Holocene. • The oceanic front played critical role in the source to sink processes of the SYS. [ABSTRACT FROM AUTHOR]

Predicting net suspended sediment fluxes in coastal regions is important for promoting good water quality, maritime transport and marine industries. Aggregation and disaggregation of suspended particulate matter responding to spatial and temporal variations in turbulence can control particle size and hence settling speed; little is currently known about how this influences the net suspended sediment flux. A tidal strait, in which the flux is confined to be in one of two directions, makes a good site for observing the effect of changes in particle size on the suspended sediment flux. The Menai Strait in North Wales is a narrow tidal strait in which the flow speeds increase to a maximum in the narrowest central region, the Swellies. Observations at sites on either side of the Swellies show that the median size of suspended particles varies with the speed of the tidal current, but also depends on the direction of the flow, with the smallest particles seen when the current is flowing out of the Swellies. The implication (supported by model results) is that the strong currents in the centre of the strait tear up flocs into small pieces which are then carried out towards both ends of the strait by the tide. Averaged over a tidal cycle, there is a net flux of larger particles into the Swellies and a net flux of small particles out. These results are relevant to the formation of isolated turbidity maxima around a region of strong turbulence. • We present observations of current velocity, suspended particle concentration and size at two locations in a tidal strait. • The size of the particles varies over a tidal cycle and is smallest when the flow is directed from the centre of the strait towards the observing site. • There is a net flux (averaged over a tide) of larger particles from both ends of the strait towards the centre and a net flux of small particles in the opposite direction. • A simple model of suspended particle transport in a tidal strait has been constructed to help interpret these observations. [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]

Erosion rates along Alaska's Beaufort Sea coast, among the highest in the world, are negatively impacting communities, industrial and military infrastructure, and wildlife habitat. Decreasing maximal winter ice extent and increasing summer open water duration and extent in the Beaufort Sea may be making the coast more vulnerable to destructive storm waves than during recent, colder, icier decades. Previous studies of Beaufort Sea coastal change have been limited to subaerial analyses of the shoreline. Here we describe nearshore seafloor change by comparing post-World War II (WWII) (1945-53) bathymetry data to recently acquired (1985–2018) bathymetry data and relate the observed seafloor change to adjacent shoreline change near Utqiagvik, within Stefansson Sound, and immediately west of Barter Island and Kaktovik. Within the Utqiagvik region, seabed erosion was generally highest (>1.0 m of loss) offshore of Point Barrow and along the eastern end of the Tapkaluk Islands, while there were lesser amounts of deposition (<0.5 m of gain) within the protected waters of Elson Lagoon. Sedimentation was generally highest offshore of Point Barrow, in a region of converging currents, and on the landward side of the barrier islands and spits fronting Elson Lagoon, which is likely related to a regional trend of westerly sediment transport and landward migration of the barrier islands. Within Stefansson Sound, perhaps the most notable changes from post-WWII bathymetry data compared to recent data are a switch from mixed, low erosion and deposition in 1997 to low deposition (<0.5 m) in 2018 east of the Boulder Patch, a switch from low erosion in 1997 to neutral depth change in 2018 in the channel between the north and south Boulder Patch areas, and higher deposition from 1997 to 2018 landward of the rapidly retreating barrier islands along the Sound's northern border. At Barter Island, high erosion near north-facing shorelines and high deposition near west-facing shorelines generally matched shoreline changes. One of our goals is to identify possible processes responsible for the depth changes we quantified. Using simple metrics that relate sediment characteristics with modeled waves and non-wave induced currents, we show that sediment resuspension and transport by both wave and non-wave driven currents likely contribute to the overall patterns of change within the ∼13 m isobath along the open coast, and that the influence of wave action affecting sediment transport is expanding seaward. • Patterns of decadal-scale changes in shoreline positions and bathymetry indicate possible linkages within the nearshore. • Depth changes are additionally driven by sediment resuspension and transport by both wave and non-wave driven currents. • Wave action affecting sediment transport expanded seaward and deepened by as much as 15 cm/yr between 1979 and 2019. [ABSTRACT FROM AUTHOR]

Net wave-induced sheet-flow sediment transport rate, Q net , can be produced by two co-existing effects: nonlinear waveshape and wave propagation, which alter the intra-wave boundary layer flow and sediment concentration. A intriguing question is whether the two effects can be simply added (the additivity hypothesis). This paper addresses this question based on simulations of a one-phase numerical model for sheet-flow sediment transport and examinations of the governing equations for boundary layer flow and sediment concentration. The additivity for the mean velocity (or streaming) is first demonstrated under typical field conditions. The main reason is that the two driving forces, i.e., momentum transfer produced by wave propagation and intra-wave asymmetry of flow turbulence produced by nonlinear waveshape, do not affect each other. The net sediment flux is separated into wave- and current-related components. Since the mean concentration profile is determined by the first-order process, the 'current'-related flux produced by the two effects, following the mean velocity, can be superimposed. After examining the leading Fourier components, the wave-related flux is also found to follow the additivity hypothesis. The findings are confirmed by numerical experiments. The implication of this work is that a practical formula for Q net can be designed with two separate components for nonlinear-waveshape and wave-propagation effects. • Simulations were conducted to study the effects of wave propagation and nonlinear waveshape on net sheet-flow transport rate. • The boundary layer streaming due to the two effects can be simply added. • The two effects produce net transport rates without much mutual interaction. [ABSTRACT FROM AUTHOR]

Typhoon Mangkhut, in 2018, was one of the worst typhoons in recent history that has made landfall in the Pearl River Estuary (PRE) China. It swept along the coast of Guangdong Province, causing severe damage to many areas and affecting more than one million people. To study the hydrodynamics and sediment dynamics in different sub-regions of the PRE during the typhoon, we implemented a 3D wave-current-sediment coupled ocean model based on the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM). A series of numerical experiments were conducted to study the variation in suspended sediment concentration (SSC) under different external forcing mechanisms, including tides, waves, river discharges and strong winds. Moderate Resolution Imaging Spectroradiometer (MODIS) images, collected after the typhoon landed, were used to assess the simulation results. We found that in the area where the water depth was shallower than 20 m, the increased total suspended sediment concentration was dominated by the regional erosion of fine sediment which was caused by near-bottom wave orbital velocity and bottom shear stress, especially at the four western outlets and along the western coast of the PRE. For the deeper coastal zone, at depths between 20 and 30 m offshore of the western coast, the high total SSC resulted from the contribution of fine sediment transported from the upper and middle estuaries by southwestward advection. A small amount of sand eroded and migrated locally, owing to the corresponding increase in the bottom shear stress. The variation in SSC during the typhoon had a time lag compared with other dynamic conditions, resulting in a maximum 1 h delayed response after the typhoon made landfall. Based on the results of the sensitivity experiments under the same typhoon conditions, we found that, as a result of wave-enhanced bottom shear stress, the SSC values associated with wave-current interaction were significantly higher, by as much as 1.5 and 1.3 times those of simulations without the waves at the surface and near-bottom layers, respectively. This indicated that the sediment resuspension induced by waves was important during typhoon landfall. However, the strong wind-induced current was weakened owing to the joint effect of wave radiation stress and enhanced bottom stress; thus, considering wave effects, the magnitude of the resulting sediment transport rate was smaller than that without considering wave effects, especially in shallow waters. During the approach, landfall and retreat of Typhoon Mangkhut, Lingding Bay experienced two transitions from a slight state of sediment loss to a relatively high state of sediment gain, followed by an even greater state of sediment loss. During an M 2 tidal cycle after Typhoon Mangkhut made landfall, the net seaward suspended load sediment transport in Lingding Bay reached 0.37 megatonnes. For the typhoon period covering three M 2 tidal cycles, the overall state of suspended load sediment transport in Lingding Bay was sediment loss, with the magnitude of sediment loss on the west side being larger than that of sediment gain on the east side. The magnitude of the overall sediment loss in Lingding Bay would be enlarged unrealistically by approximately 73% if the wave effects were excluded. In each period, the extent of sediment transport between the two sides of the bay was strengthened by the wave-current interaction under typhoon conditions. We determined that the net effect of wave-current interaction and strong wind-induced currents under typhoon conditions was a key factor for erosion, which resulted in SSC-influenced areas being approximately 8.7 and 4.4 times as large as those under normal weather conditions for the surface and near-bottom layers, respectively. The turbidity maximum moved from the West Shoal of Lingding Bay under normal weather to the Modaomen Estuary, which was the most affected area during the typhoon when wave effects were considered. We also showed that the relative location of the typhoon path with respect to the estuary had a more significant effect on erosion than the intensity of the typhoon. ● A 3D wave-current-sediment coupled ocean model was set up and validated to simulate sediment transport during Typhoon Mangkhut. ● Waves were primarily responsible for resuspension of both fine sediment and sand during the event. ● Strong wind-induced currents were weakened owing to the joint effect of wave radiation stress and enhanced bottom stress. ● Turbidity maximum moved westward along the path of the typhoon. [ABSTRACT FROM AUTHOR]

Although many studies have been carried out on the mud wedge in the inner shelf of the East China Sea (ECS), the sediment sources and seismic textures of the mud wedge are still unclear and remain controversial. Therefore, this study utilizes grain size and clay mineral analyses of surficial sediment samples and high-resolution sub-bottom seismic profile interpretation to identify the provenance and texture of these mud wedge sediments. The results show that sediment sources on the inner shelf of the East China Sea are mixed by the Yangtze River, small mountainous rivers along the Zhejiang-Fujian, and western Taiwan coasts. The sediments derived from the Ou and Min rivers are mainly concentrated in the shallowest shelf area within a water depth of 20 m which is located north of the Min River Estuary. Their contribution to the estuaries and coastal areas reflects the different sediment transport patterns of the two small mountainous rivers. The thickness of the Holocene mud wedge between Hangzhou Bay and Taizhou Bay is greater than 20 m at a water depth of approximately 10 m. The cause of this phenomenon is possibly related to the presence of the Zhoushan Islands, which are distributed along the Zhejiang coast and appear to effectively trap sediments from the Yangtze River, facilitating sediment accumulation. The findings of this study will help improve our understanding of the sediment transport and deposition mechanism of deposition on the inner shelf of the East China Sea. • We produced grain size and clay mineral analyses and high-resolution sub-bottom seismic profile interpretation. • Sediments derived from small mountainous rivers are mainly concentrated in the shallowest shelf area. • The thickness of the Holocene mud wedge is locally greater than 20 m in the shallowest shelf area. [ABSTRACT FROM AUTHOR]

Pollen and spores of terrestrial plants found in marine sediments are excellent proxies for paleovegetation and paleoclimate reconstructions of surrounding areas. Ascertaining the pollen transport mechanism from terrestrial to oceanic environments is crucial for the interpretation of pollen data from marine sediments. In this study, we present the distribution of suspended sediments and pollen from 59 surface ocean water samples collected during September and October of 2013, in the northern South China Sea (SCS). The results suggest that there is a difference between the transmission mechanisms of suspended sediment and pollen/spores. Suspended sediment (silt, coarse sand, and gravel) settle quickly in nearshore and continental shelf waters due to their density. Alternately, small, light-weight pollen grains can be carried over long distances in a marine setting. The density of suspended sediment has a high correlation with the concentrations of Pinus , evergreen Quercus , Poaceae and Cyperaceae pollen as well as fern spores (e.g., Dicranopteris), but no correlation with total pollen concentration. This finding will broaden the understanding of the relationships between suspended sediments and pollen in the northern SCS and help to better interpret pollen records extracted from marine sediment cores from the SCS. • 59 sea surface water pollen samples in the northern South China Sea were investigated. • Close relationship between the densities of suspended sediment and the percentages of Pinus , evergreen Quercus , Poaceae and Cyperaceae pollen and spores. • Relatively low values of Pinus , Podocarpus and the evergreen Quercus pollen seem to be correlated with the flowering season. [ABSTRACT FROM AUTHOR]

Sand waves are rhythmic bedforms existing in shallow seas and typically induced by the interaction of currents and topography. In this study, a physically-modified spectral model for simulating small-scale sand wave migration is proposed by integrating non-linear spectral analysis, typhoon wind field and sediment transport theory. We introduce a power-average velocity to modify the spectral analysis, which gives explicit physical meanings to the morphological method and improves its stability and reliability. Then, the effects of typical and extreme weather are decoupled and the short-term migration caused by typhoons is removed from the total migration. Results show that a single typhoon will cause large sand wave migration, but the migration caused by multiple typhoons in a long period of time will cancel each other out in the measured data. Moreover, the bilateral reverse migration trend of one-group sand waves in a small scale (∼3 km) is captured, which is consistent with field data and previous researches. Compared with existing researches, the proposed model is able to identify the influences of extreme conditions on sand wave migration and provide a feasible and high efficiency way to predict sand wave migration when the available hydrodynamic data is limited. • A physically-modified spectral model for prediction of sand wave migration is proposed. • The model integrates the non-linear spectral model, typhoon and sedimentation transport theory. • The bilateral reverse migration trend of one-group small-scale sand waves is simulated. • The proposed model provide a feasible way with limited hydrodynamic data. [ABSTRACT FROM AUTHOR]

Sediment is needed for coastal restoration in Louisiana and is often excavated offshore from mud-capped and sandy dredge pits. To better understand the post-dredging effects on hydrodynamics, sediment transport, and water quality, two tripods were deployed at sandy Caminada pit and mud-capped Sandy Point pit in summer 2018 and 2019, respectively, and profiling data were collected during a total of 34 casts in 2018 and 2019. The results reveal similarities and differences between pit and adjacent waters and are used to compare two pits. Tropical storm events were observed during each deployment which provided insight concerning the effects these storms have on dredge pits. Water masses inside Caminada pit were relatively stable and sluggish which resulted from the pit's deep depth and location. Sandy Point dredge pit was highly impacted by the Mississippi River plume due to its proximity, which effectively stratified the water column in summer 2019, affecting ventilation near the seabed. Strong winds, taller waves, higher shear stresses, elevated turbidity and increased dissolved oxygen were generally found during the passages of tropical storms over both pits. Comparing with outside tripod station, the inside station of Caminada pit experienced a longer duration of low dissolved oxygen in bottom waters. Water mass movements and oxygen consumption from resuspension of pit bottom are likely key mechanisms driving oxygen dynamics. Our results provide observational data for future studies on post-dredging morphologic change, marine communities, and oxygen dynamics of dredge pits on the Louisiana shelf and other coastal dredge areas worldwide. • Tripod time series analysis of dredge pits in Gulf of Mexico. • Less variable bottom water masses in a dredge pit compared to adjacent seafloor. • Bottom DO conditions are complex, controlled by physical, biogeochemical processes. • Dredge pit location impacts variability of water column. [ABSTRACT FROM AUTHOR]

The paper presents a two-dimensional model, based on the Lagrangian description of sand grain dynamics, for the estimation of mean velocities of sediment particles driven by the oscillatory motion of water generated by non-linear gravitational surface waves of the Stokes type. The model was verified against experimental results obtained in a wave flume, by comparing its predictions with the sediment velocities measured by applying a PIV (particle image velocimetry) technique. The model was used to calculate near-bed sediment transport velocities generated by surface waves of the parameters encountered in real sea conditions, with the purpose to investigate the effect of the wave velocity skewness on the near-bed sediment net transport rates. The results of numerical simulations, carried out for a range of wave parameters and sand grain sizes, showed that normalized sediment transport velocities vary approximately linearly with an index defining the wave skewness, and are practically independent of sediment grain diameters. Based on the laboratory measurements, also approximate formulae relating a bed ripple asymmetry index with the surface wave skewness index were derived. • Surface wave velocity skewness effect on sediment transport rates is investigated. • Lagrangian model for individual sand grains driven by hydrodynamic forces is proposed. • Results illustrate the variation of sand transport rates with increasing wave skewness. • It is shown that sand grain size has little effect on sand transport rates. • Formula connecting wave skewness with bed ripple asymmetry is derived. [ABSTRACT FROM AUTHOR]

In this paper, an improved numerical scheme is developed to estimate the initial conditions (ICs) based on a three-dimensional suspended sediment transport model (3D SSTM) with adjoint data assimilation, and the method is then applied to Hangzhou Bay as an example. Specifically, the ICs are estimated by assimilating artificial observations in twin experiments and suspended sediment concentrations (SSCs) retrieved from the Geostationary Ocean Color Imager (GOCI) in practical experiments. In the twin experiments, the sensitivity of the estimated ICs to several influential factors is discussed. The results demonstrate that the conjugate descent algorithm of Fletcher is proven to be better than the steepest descent, finite memory BFGS, and five other conjugate gradient algorithms in estimating the ICs; the estimated ICs are sensitive to initial guess values, and appropriate initial values are necessary for improving the efficiency of convergence and obtaining good results. Additionally, the errors of observations can significantly influence the estimated results. In contrast, the estimated results are not very sensitive to cloud coverage, errors in the background flow field, and length of the assimilation time window. In practical experiments, according to the conclusions of twin experiments, an improved 3D SSTM with the adjoint method is developed for Hangzhou Bay, and the surface GOCI-retrieved SSCs during typical neap and spring tidal cycles are assimilated to estimate the practical ICs. The experimental results imply that with the present estimation method, more accurate ICs can be obtained, which indicates that the adjoint method is effective in the estimation of the ICs in SSTMs. Furthermore, this study verifies that accurate ICs are critical for the numerical modeling of SSCs on the tidal cycle scale. This study is not only useful for further improving the accuracy of ICs in SSTMs but also suggestive for the initialization schemes of other matter transport models. • Initial conditions are critical for simulating suspended sediment concentrations over tidal cycles. • The adjoint method is effective in estimating initial conditions. • Data assimilation can compensate for information in areas of missing satellite data. [ABSTRACT FROM AUTHOR]

Ripples and small-scale bedforms are ubiquitous in shallow water environments under the combined action of currents and waves. Small scale processes linked to their formation and migration are interconnected with sediment transport at larger scales (e.g. tens of metres to kilometres), both resulting in and being affected by large scale sediment transport and geomorphological evolution. The lower shoreface provides a key link between coasts and continental shelves, but the contribution of ripples and small-scale bedforms to sediment transport in this region has yet to be fully addressed. This work presents a study of sediment dynamic processes on the lower shoreface in the presence of small-scale bedforms. Observations were made during the winter of 2017 on the lower shoreface of Perranporth Beach, which is in the south west of the UK and exposed to Atlantic waves. The analysis of morphological expressions and the variability of ripples under waves, currents and wave-current conditions are assessed. Ripple morphology and associated dynamics are analysed for their potential contribution to the exchange of sediment between the lower and the upper shoreface. In the present study it was observed that even though ripples were evolving depending on the wave-current forcing, little ripple migration was observed due to low wave skewness. The implication is that ripple migration and bedload transport are only a small contribution to onshore sediment transport under low to moderate energy conditions. However, during more energetic conditions, ripples were washed out and the wave skewness increased, resulting in onshore sediment transport under a sheet flow regime. This suggests that ripple formation and migration can have little impact on the cross-shore supply of sediment from the lower shoreface to the upper shoreface and that more energetic wave conditions are required to significantly transport sediment towards the beach. • High-resolution observations on the seabed reveal 2D and 3D wave vortex ripples in a macrotidal sandy lower shoreface. • The morphological ripple transitions provide assessment of sediment transport regime thresholds. • The hypothesis of ross-shore sediment supplied from the lower to the upper shoreface through ripple migration is not supported. [ABSTRACT FROM AUTHOR]

While the role of shore-parallel transport is extensively documented, its contribution to source-to-sink and provenance studies is often overshadowed by tectonic variations, sediment influx, and sea-level change. To isolate the sedimentary contribution of shore-parallel transport, this study examines the central Levant continental margin (easternmost Mediterranean), where the other three factors are well constrained. New high-resolution multibeam and seismic reflection data collected in a dedicated cruise aboard the RV Bat Galim are used for analyzing current-indicating morphologies formed since the Last Glacial Maximum (LGM). Results show six different current indicators, which attest to the ongoing shore-parallel Levant Jet System (LJS) flow. Throughout the post-LGM transgression and coastal retreat, the LJS shifted landward to flow over the submerged shelf and upper slope. This shift, along with periodic/seasonal alterations in the flow intensity, regulated the sediment transport, distribution and erosion, along and across the margin, during the lowstand, transgression, and highstand conditions. This case study emphasizes the central role of shore-parallel currents in regulating the sedimentary budget. It provides a reference case for continental margins where the shore-parallel role is obscured by more dominant tectonic-eustatic-sedimentation factors. • New high-resolution multibeam and Chirp data from the central Levant continental margin (easternmost Mediterranean). • The tectonic, eustatic, and sedimentation factors are well constrained in the study area. • The study examines the shore-parallel sediment transport role in shelf build-up. • Shore-parallel currents regulate sediment transport, distribution, and erosion, along and across the margin. [ABSTRACT FROM AUTHOR]