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The Zhejiang-Fujian (Zhe-Min) coastal muddy area plays a crucial role in facilitating sediment exchange through a cross-front. The mud depocenter off the Zhe-Min coastal area is a source of suspended sediment that can be transported to the continental shelf of the East China Sea (ECS). Although the front of the inner shelf of the ECS has been extensively reported, the cross-front material transport off the coastal area of Zhe-Min in summer has not been well studied, especially using measured data. To reveal how the front controls the transport of suspended sediment, this study focuses on the impact of fronts on the dispersion of suspended sediment off the coastal area of Fujian Province in different seasons. The results indicate that the front acts as a barrier, inhibiting the dispersion of suspended sediment into the sea. The high-concentration suspended sediment is mainly found to the northwest of the front, with an average SSC of 8.5 mg/L in winter and 3.1 mg/L in summer. The suspended sediment concentration (SSC) follows a V-shaped distribution along the cross-isobath transects, with lower SSC observed at the 50-m isobath compared with the shallow water area and the deep water area. The SSC at the front was the lowest, with an average concentration of 2.3 mg/L in winter and 1.9 mg/L in summer. The front is crucial for the development of the Zhe-Min coastal muddy area. The winter monsoon is strong, resulting in a sufficient supply of suspended sediments in the muddy area and a high transport flux of suspended sediments in the nearshore. The front hinders the dispersion of high-concentrated sediment from the nearshore to the offshore, resulting in the deposition of fine-grained sediments in the nearshore and the formation of an inner shelf muddy sedimentary zone. The findings of this study will help improve our understanding of the sediment source-to-sink processes in the ECS and land–sea interactions. • The front acts as a barrier, inhibiting the dispersion of suspended sediment from the nearshore into the sea. • The distribution of SSC follows a V-shaped pattern along the cross-isobath transects. • The front is crucial for the development of the Zhe-Min coastal muddy area. • This study improves our understanding of the formation and evolution of the ECS shelf muddy area. [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]

Suspended sediment concentration (SSC) is one of the fundamental topics in sediment study. The parameterization of the SSC profile of silty sediments is still under-researched. This study focuses on the mean SSC profile for silty sediments under non-breaking wave-dominant conditions. First, inspired by a 1DV model, different types of the distribution of mean eddy viscosity were proposed, i.e., a toe-type distribution over flat bed and a constant-toe type distribution over rippled bed. Then, the time-averaged diffusion equation for suspended sediment transport was analytically solved, and expressions for the mean SSC profiles were derived. The expressions involve several basic physical processes, including the effects of bed forms, stratification, hindered settling and mobile bed. Verification using a number of experimental datasets showed that the proposed expressions can properly calculate the mean SSC for silt and are applicable for sand as well. In conclusion, this research provides an approach to estimate the mean SSC for silty sediments under wave-dominant conditions, which is expected to be applicable for engineering practice and numerical modelling. • Formulations for mean SSC (suspended sediment concentration) profile of silty sediments were derived. • Several essential physical processes were considered in the formulations. • The SSC profiles over rippled bed and hydrodynamically plane bed were simulated. [ABSTRACT FROM AUTHOR]

In situ measurements and ship-based resuspension experiments using annular flumes are used to determine sediment stability and critical erosion thresholds for four sites with significantly different sediment characteristics, located in the Celtic Sea at water depths of 100 m. Seasonal and spatial variability of sediment characteristics and erodability is examined, and found to be the result of changes in percentage of organic carbon in the surface sediments (R2 = 0.82) and bulk density (R2 = 0.73) respectively when individual characteristic bed parameters are considered. Principal component analysis and linear regression analysis are used to determine a predictive model for erosion threshold in the Celtic Sea (R2 = 0.99), based on grain size, sorting, kurtosis, bulk density, porosity, percentage fines, organic carbon content and chlorophyll a concentration. Physical sediment characteristics were found to be more significant controls of bed stability than biological factors. Local hydrodynamic conditions are used to determine the likelihood and frequency of resuspension given these critical erosion thresholds. Resuspension is driven by tidal currents, and is common year-round, leading to a constant re-working of bed sediments in particular at the muddier sites. This is confirmed by in situ measurements of suspended sediment concentration. • Bed erodibility in the Celtic Sea a function of organic carbon and bulk density. • Predicting erosion threshold requires emphasis on physical sediment characteristics. • Bed sediments re-worked year round by tidal resuspension, enhanced by winter waves. [ABSTRACT FROM AUTHOR]

Sediment transport over Sandy Point dredge pit in the northern Gulf of Mexico during a cold front event in November 2014 was examined using a finely resolved numerical model. The Delft3D model was used to perform numerical experiments that simulate the effect of wind-generated waves, wind-driven currents, river discharge, and tides on sediment dynamics in Sandy Point dredge pit. The hydrodynamics and sediment models were validated and calibrated using field data of current, wave, water level, and suspended sediment concentration. Two potential sources of sediment were examined: fluvial sediment from the Mississippi River and resuspended sediments from the seabed. Results showed that during a cold front, shear stress from wave motions played a significant role in the resuspension of sediments in Sandy Point dredge pit. The maximum cold front-related wave impact on sediment resuspension could increase near-bed sediment concentration in Sandy Point dredge pit by 20–50 times. In addition, the results suggest that the primary source of sediment for Sandy Point dredge pit during a cold front was resuspension from the ambient seabed due to increased bottom shear stress by wind-induced waves and strong southward wind-driven currents. Currents dispersed sediments from the Mississippi River passes and inhibited riverine sediment supply from Sandy Point dredge pit. Results also showed that cold fronts contribute 16%–24% of the annual sedimentation in Sandy Point dredge pit. • A coupled wave-current-sediment model was used to study the sandy dredged pit. • The combined effect of waves and currents on sedimentation was assessed. • The reverse bottom current inside the pit was identified. • Bottom boundary layer was significantly affected by waves. • Sediment accumulation occurs mostly on the north of the pit. [ABSTRACT FROM AUTHOR]

A model is proposed to determine the sediment transport rate generated by the combined action of sea waves and tidal currents, the latter being modelled as a sequence of steady currents because of the large values of the Keulegan-Carpenter number of the tidal flows, which allow to neglect inertial effects in their modelling. The hydrodynamic module solves Reynolds-averaged momentum equations by introducing a two-equation turbulence model, which considers also the flow in the region closest to the sea bottom and enforces the no-slip condition and the vanishing of the turbulent kinetic energy at the bottom without the need to assume the existence of a logarithmic velocity profile and to fix the normal derivative of the turbulent kinetic energy close to the sea bed. Hence, the evaluation of the velocity profile in the near-bed region turns out to be accurate. The sediment transport module determines the sediment concentration and sediment transport for a mixture of non-cohesive and cohesive sediments. To validate the model, its predictions are compared with laboratory measurements and field data collected over rippled beds at two different tidal estuaries. Then, results are obtained for values of the parameters chosen to mimic a site close to Punta Umbría (Huelva, Spain) and considering different hydrodynamic conditions and different sediment mixtures. The influence of the waves on the suspended sediment concentration is lower for the cohesive fraction than for the non-cohesive fraction. For all the sediment mixtures, it turns out that the cohesive fraction is well mixed over the whole water depth, meanwhile the concentration of the non-cohesive fraction has significant values only near the bottom, thus showing that an accurate description of turbulence dynamics in the buffer layer and viscous sublayer (if it exists) is important to quantify the sediment transport rate. • Sediment transport module that reproduces the concentration of cohesive fraction is presented. • Tidal current is modelled as a sequence of steady-currents due to the large values of the Keulegan-Carpenter number. • Menter's turbulence model to predict the turbulence structure both in the wave bottom boundary layer and in the core region. • Turbulence dynamics description in the buffer layer and viscous sublayer is important to quantify the sediment transport. • Applicable to any type of sediment mixture. [ABSTRACT FROM AUTHOR]

The Lower Mekong Delta Coastal Zone (LMDCZ) is emblematic of the coastal erosion problem facing many tropical deltas. Over the last 3500 years, large river sediment fluxes expanded the delta seaward, and waves and currents formed the Ca Mau Peninsula to the southwest. Since the middle of the 20th century, the LMDCZ is affected by various human activities that include reduction of river fluxes due to damming and sand mining, land subsidence due to groundwater extraction, and reduction of protective coastal mangroves in favor of agriculture and aquaculture. Coastal erosion is observed along many sections of the delta, with a rate of up to 50 m per year in some areas. However, the role of human activities remains difficult to assess because of its complexity. The present modeling study is designed to sort out the contribution of natural hydrodynamic redistribution of sediments from man-induced erosion. The modeling system used is based on CROCO, forced by global reanalyses at the boundaries and at the surface, including wave statistics (required by the sediment transport model). Tides and realistic river forcing are also included. Calibration and validation relies on a combination of in situ and remotely-sensed observations, and laboratory experiments. Once validated, coastal dynamics are investigated by performing sensitivity experiments for both the hydro- and sediment dynamics. The results suggest that while wind is the main factor driving the coastal currents, the sediment dynamics is essentially the result of re-suspension due to wave-induced bed shear stress. The suspended sediments are then redistributed by coastal currents that are not limited to the nearshore zone. Strong seasonality of the process is observed with the northeast winter monsoon being the season of strongest re-suspension and sediment redistribution. The annual sediment budget is characterized by important local disequilibrium, with alongshore patterns that are in agreement with the observed shoreline evolution. The effect of a decrease in river sediment supply is difficult to evaluate because the estuarine zone is still in accretion, apart from the particular case of Go Cong shores. Far from the estuarine zone, subsidence is an additional strong candidate to explain erosion in areas that should naturally be accreting. Synthesizing these results, the study proposes a first attempt at a "taxonomy and geography" of processes along the coastal Mekong delta that can explain the recent observations of shoreline changes and help design protection measures. [ABSTRACT FROM AUTHOR]

The role of small scale single turbulent events in the vertical mixing of near bed suspended sediments was explored in a shallow shelf sea environment. High frequency velocity and suspended sediment concentration (SSC; calibrated from the backscatter intensity) were collected using an Acoustic Doppler Velocimeter (ADV). Using quadrant analysis, the despiked velocity time series was divided into turbulent events and small background fluctuations. Reynolds stress and Turbulent Kinetic Energy (TKE) calculated from all velocity samples, were compared to the same turbulent statistics calculated only from velocity samples classified as turbulent events ( Re events and TK E events ). The comparison showed that Re events and TKE events was increased 3 and 1.6 times, respectively, when small background fluctuations were removed and that the correlation with SSC for TKE could be improved through removal of the latter. The correlation between instantaneous vertical turbulent flux ( w ′ ) and SSC fluctuations ( SSC ′ ) exhibits a tidal pattern with the maximum correlation at peak ebb and flood currents, when strong turbulent events appear. Individual turbulent events were characterized by type, strength, duration and length. Cumulative vertical turbulent sediment fluxes and average SSC associated with individual turbulent events were calculated. Over the tidal cycle, ejections and sweeps were the most dominant events, transporting 50% and 36% of the cumulative vertical turbulent event sediment flux, respectively. Although the contribution of outward interactions to the vertical turbulent event sediment flux was low (11%), single outward interaction events were capable of inducing similar SSC ′ as sweep events. The results suggest that on time scales of tens of minutes to hours, TKE may be appropriate to quantify turbulence in sediment transport studies, but that event characteristics, particular the upward turbulent flux need to be accounted for when considering sediment transport on process time scales. [ABSTRACT FROM AUTHOR]

The Gulf of Alaska is a biologically productive ocean region surrounded by coastal mountains with high seasonal runoff from rivers and glaciers. In this complex environment, we measured the concentrations and size distributions of 2.5 µm–27 mm marine particles using the Laser in situ Scattering and Transmissometry device (LISST-DEEP) and the Underwater Vision Profiler 5 (UVP) during summer 2015. We analyzed the spatial distribution of particles across a wide range of size classes to determine the probable drivers. Spatially, total particle concentrations surpassed 1000 µl/l nearshore in the northeasternmost entrances and in the outflow of Cook Inlet, as well as offshore past the shelf break. These dual maxima suggest high lithogenic inputs nearshore and high biological production at and beyond the shelf break. Most large particles (> 0.5 mm) imaged by the UVP were detrital aggregates. In nearshore surface waters near river inputs, size distributions revealed small size classes (< 100 µm) to be most influential. At the shelf break, size distributions revealed a dual peak in both small (< 100 µm) and very large (> 2 mm) size classes. This study highlights the importance of lithogenic inputs from a mountainous margin to the coastal ocean and their potential to enhance sinking of biological material produced at the shelf break. [ABSTRACT FROM AUTHOR]

Recent studies suggest that tidal forcing can be as important as gravitational circulation in maintaining an estuarine turbidity maximum (ETM). It is further postulated that a long-term mass balance between the import and export of sediment in an estuary may require episodic large river discharges or ‘freshets’ to flush sediment out of the ETM towards the open sea. In this study, we use a 2-month data set from a mooring in a tidal river that drains into a large drowned-river-valley estuary (Kaipara Harbour, New Zealand) to investigate interactions between tidal-current asymmetry and gravitational circulation. During baseflow river discharge and on spring tides, suspended-sediment transport was directed up-channel (landwards), driven by tidal pumping due to tidal-current asymmetry. During neap tides, the suspended-sediment flux was approximately zero. The data suggest that the bed was not locally erodible and that bed sediments at the site were being supplied by an ETM. The ETM only migrated far enough down channel to be observed at the mooring site during spring tides when the tidal excursion was longer. Suspended sediments were effectively trapped and recycled within the ETM. During and after two freshets, high river discharge displaced saline water from the tidal river, water-column stratification strengthened and the surface and bed current speeds increased. As a result, the advective component of the down-channel directed suspended-sediment flux increased. This provided a transport pathway for sediment out of the otherwise tidally pumped, flood-dominant system. We conclude that largest export of sediments out of the tidal river would potentially occur when a large freshet coincides with an apogean spring tide. [ABSTRACT FROM AUTHOR]

A 3D sediment transport model based on the modified environmental fluid dynamics code (EFDC) and the nearshore waves simulation model (SWAN) is developed to study the change of suspended sediment concentration and bottom shear stress under the actions of pure current and wave-current. After being validated by the field measured data, the proposed sediment transport model is applied in the Oujiang River Estuary, China. The results show that the ratios of both bottom shear stress and suspended sediment concentration of pure current to those of wave-current show a gradually increase from shallow nearshore water to deep open sea. The results also show that the proportion of wave contributions on bottom shear stress and sediment concentration are above 60%, approximately 20-30% and less than 10% for the water depth of less than 5 m, 5-10 m and more than 20 m, respectively. For the waters among islands, the proportion of wave contribution to bottom shear stress and sediment concentration is reduced to 10-20% for -5 m water depth and this is more obvious for the waves of large amplitude. The bottom stress and suspended sediment concentration between islands are mainly controlled by tidal current, and the effect of wave is not significant. [ABSTRACT FROM AUTHOR]

Particular attention was focused on modeling the spectral scattering properties of phytoplankton ( b ph ( λ )) and non-algal particles (detrital organic and inorganic sediments b NAP ( λ )) from absorption and attenuation measurements in near-shore and lagoon waters. The absorption line height ( a LH (676)) measured above a linear background between 648 nm and 714 nm in particulate and dissolved organic matter absorption spectra ( a p ( λ )) is a spectral feature that is primarily associated with the chlorophyll with significantly less pigment package effect compared to the blue peak, and hence it is solely attributed to the phytoplankton absorption ( a ph ). The correlation of a ph ( λ ) with b ph ( λ ) in terms of the spectral shape and the relation of a LH (676) with chlorophyll concentration hold the key to derive b ph (648) from the a LH (676) measurements. b NAP (648) values are then determined by subtracting the b ph (648) from b p (648), allowing the power-law model to derive the b NAP ( λ ). In-situ determination of b ph ( λ ) is subsequently achieved by subtracting the featureless b NAP ( λ ) from b p ( λ ) provided by the ac-s sensor. These data form the basis for the development of models for independent estimates of b ph ( λ ) and b NAP ( λ ) based on the measurements of a LH and suspended sediment concentration or turbidity. The validity of this method was demonstrated in a wide variety of samples from coastal and inland environments. Comparison of the modeled and measured spectral variations of b ph ( λ) showed the mean relative percent difference between these two data to be within 20%. b NAP ( λ) predictions also had an error a few percent and the correlation coefficient close to unity. When comparing the modeled b ph ( λ) with laboratory culture data, the results were exceptionally good although discrepancies in size and refractive index of cells of monospecific lab culture samples and natural assemblages due to the simultaneous presence of different species. The proposed approach and models are highly instrumental in investigating the scattering properties of phytoplankton and non-living constituents, and will provide new tools for improving our current understanding of particle dynamics, advancing biogeochemical and ecosystem modeling, and assessing phytoplankton blooms and sediment plumes within inland and coastal environments. [ABSTRACT FROM AUTHOR]

Observations of suspended sediment size and concentration, flow and acoustic backscatter intensity collected on the Seine Estuary (France) are used to study the acoustic response in cohesive-sediment dominated environments. Estimates of suspended sediment concentration based on optical backscatter sensors and water samples are used to calibrate the acoustic backscatter intensity. The vertical structure of suspended sediment concentration is then estimated from acoustic backscatter information. To our knowledge, this is the first field application of the recently proposed model of acoustic scattering by flocculating suspensions based on the variation of particle density (floc-scattering model). The estimates of sediment concentration reproduce well the observations under different tidal (neap/spring) conditions, confirming the applicability of the new model in the field when detailed particle size measurements are available. When particle size measurements are not available, using estimated floc sizes based on the turbulence intensities may provide reasonable SSC profiles. During spring tide events (associated with strong currents, small flocs and large concentrations), the performances of the new floc-scattering model and the previous models given for solid particle-scattering are comparable. The floc-scattering model increases the quality of the SSC estimates especially during low-energy conditions characterized with larger flocs. [ABSTRACT FROM AUTHOR]

An 11-tidal-cycle record time series of current, wave, suspended-sediment, and bed-level characteristics was analyzed to identify physical and sedimentary processes on the tidal flat of Jiangsu Coast, China. A tripod observation system was placed near the transition between mid and upper tidal flat south of a newly constructed harbor for hydrodynamic and sediment dynamic measurements from 27 Apr 2013 to 3 May 2013. The observations confirm the stable longshore northward (ebb direction) current s with residual velocities ~59.2° anti-clockwise from the offshore direction. This phenomenon can be attributed to the effects of headland (the Harbor) induced tidal eddies based on comparable frictional length scale and the headland length scale. Benthic fluid mud layers occurred in 2 of 11 tidal cycles, with the conditions of strong waves during the flood phase. The fine sediment was resuspended by the waves and currents from the lower area, transported upward and concentrated at the observation station, resulting in the formation of a fluid mud layer with thickness of ~15 cm and SSC of ~8 kg/m 3 at 10 cm asb. Once formed, the fluid mud layer dramatically modified the flow structure, showing a large reduction of current speed from 20 cm asb to 10 cm asb, when the gradient Richardson number was around the critical value of 0.25, inferring that sufficient turbulence from waves and currents exists to maintain fluid mud suspension. The fluid mud processes appear to occur episodically and may play an important role of sediment dynamics on the tidal flat. [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]

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]

The influences of environmental gradients on the spatio-temporal variability of phytoplankton (Chlorophyll-a) in the macrotidal Chikugo River Estuary were studied during a two-week period of September 2010. Vertical profiles of salinity, turbidity, and light intensity were measured at 18 stations separated by a 1-km interval. Water samples for the determination of suspended sediment concentration (SSC), concentration of Chlorophyll-a (Chl-a) and Pheophytin-a (Pheo-a) were collected from the surface layer at all stations. The estuarine water column was vertically well mixed with high SSC (100–2000 mg L −1 ) during spring tide and the photic depth (z p ) was less than 0.2 m. The mixing depth (z m ) was more than 10 times the photic depth for the major part of the estuary. The estuary gradually changed to partially mixed with decrease in SSC (≤400 mg L −1 ) during the intermediate tide. The estuary became stratified with low SSC (20–50 mg L −1 ) during neap tide and the z p reached 4 m. The z m was less than 0.5 times the z p for the whole estuary. Light attenuation was dominated by SSC and the z p varied according to semidiurnal and semilunar tidal cycle. The z p : z m ratio did not show any relationship with Chl-a in the Chikugo river estuary. This is because the Chl-a concentration reached maximum two to three days after the neap tide. The peak concentration of Chl-a was located near the low salinity region and that of Pheo-a was located in the Estuarine Turbidity Maximum (ETM) zone. The Pheo-a concentration reached maximum during the spring tide. A good relation between z p : z m ratio and Pheo-a indicates that the increase in Pheo-a was caused by the light limitation due to suspended sediment and the responses of the Pheo-a on the light condition was instantaneous. These phenomena were remarkably found in the interface between freshwater and saltwater. Light availability driven by mixing and ETM process during semidiurnal and semilunar tidal cycle is the controlling factor of the phytoplankton dynamics in the Chikugo River Estuary. [ABSTRACT FROM AUTHOR]

A laboratory experiment was carried out to study sediment transport dynamics occurring in the swash zone of a coarse-sandy beach built in a large-scale wave flume. Hydro- and morpho-dynamic as well as sediment transport data were collected using sensors mounted on a scaffold rig deployed in the lower swash zone close to the moving bed. The high resolution of near-bed data permitted quantitative evaluation of suspended and sheet flow contributions to the total sediment transport. Although sheet flow sediment fluxes were higher than suspended fluxes, the vertically integrated suspended sediment load overcame the sheet flow load during uprush and it was on the same order of magnitude during backwash. The observed cumulative sediment transport was generally larger than the morphological changes occurring shoreward of the rig location implying either an underestimation of the offshore sediment transport or an overestimation of the onshore fluxes obtained from concentration and velocity profile data. Low correlations were found between net swash profile changes and runup parameters suggesting that local hydrodynamic parameters provide little or no predictability of accretion and erosion of an upper beach which is near equilibrium. The balance between erosion and deposition induced by individual swash events brought a dynamic equilibrium with small differences between the profiles measured at the start and at the end of the run. [ABSTRACT FROM AUTHOR]

Fine-grained sediments supplied to the Ocean by the Amazon River and their transport under the influence of continental and oceanic forcing drives the geomorphic change along the 1500 km-long coast northward to the Orinoco River delta. The aim of this study is to give an encompassing view of the sediment dynamics in the shallow coastal waters from the Amazon River mouth to the Capes region (northern part of the Amapa region of Brazil and eastern part of French Guiana), where large mud banks are formed. Mud banks are the overarching features in the dynamics of the Amazon-Orinoco coast. They start migrating northward in the Capes region. Suspended Particulate Matter (SPM) concentrations were calculated from satellite products (MODIS Aqua and Terra) acquired over the period 2000–2013. The Census-X11 decomposition method used to discriminate short-term, seasonal and long-term time components of the SPM variability has rendered possible a robust analysis of the impact of continental and oceanic forcing. Continental forcing agents considered are the Amazon River water discharge, SPM concentration and sediment discharge. Oceanic forcing comprises modelled data of wind speed and direction, wave height and direction, and currents. A 150 km-long area of accretion is detected at Cabo Norte that may be linked with a reported increase in the river's sediment discharge concurrent with the satellite data study period. We also assess the rate of mud bank migration north of Cabo Norte, and highlight its variability. Although we confirm a 2 km y −1 migration rate, in agreement with other authors, we show that this velocity may be up to 5 km y −1 along the Cabo Orange region, and we highlight the effect of water discharge by major rivers debouching on this coastal mud belt in modulating such rates. Finally, we propose a refined sediment transport pattern map of the region based on our results and of previous studies in the area such as the AMASSEDS programme, and discuss the relationship between sediment transport and accumulation patterns and the coastal geomorphology of this region. [ABSTRACT FROM AUTHOR]

The processes of sediment entrainment. transport and deposition over bedforms are highly dynamic and temporally and spatially variable. However, most measurements of these processes tend to be collected in a vertical line at one spatial location above the bed; one dimensional in the vertical 1D-V. Such measurements capture the temporal signature, and, to a lesser degree, the spatial variability when bedforms migrate, and they have contributed greatly to our understanding of sediment transport processes. It is generally acknowledged, however, that such 1D-V systems provide a limited description of the spatially three dimensional processes occurring at the turbulent and intra-wave time scales. It would undoubtedly facilitate the interpretation of fundamental sediment processes above bedforms if other spatial dimensions could be simultaneously interrogated. To this end a multi-frequency acoustic array lias been developed to measure suspended sediments and bedforms over a horizontal transect of the bed in the vertical providing two dimensional observations in the vertical and lwrizontal, 2D-HV. This new acoustic instrument, the BASS I; Bedform And Suspended Sediment Imager, has been deployed in the River Dee tidal estuary in the UK. The design of the BASS1 and results from the deployment are presented and its performance assessed against more conventional instrumentation. Measurements and images of 2D-HV suspended sediments and bedforms are provided to illustrate the capability anp future use of the BASSI for the investigation of sediment transport processes. [ABSTRACT FROM AUTHOR]

Surface partial pressure of CO 2 ( p CO 2 ) and pertinent parameters (i.e., pH, total alkalinity, dissolved oxygen, chlorophyll a) were investigated in the southern Yellow Sea (SYS) and the East China Sea (ECS) basing on two surveys conducted in June and August of 2013. The results suggested carbonate chemistry dynamics and related controlling factors were provided with significant temporal and spatial variations in different subregions of these two continental shelf seas. The western of SYS (SYSW) was CO 2 -undersaturated both in June and August, with the average F CO 2 −1.88 mmol m −2 d −1 and −3.72 mmol m −2 d −1 , respectively. The phytoplankton initiated CO 2 -absorption and the suspended sediment induced CO 2 -emission jointly controlled the air–sea CO 2 exchange there. The center of SYS (SYSC) also behaved as an obvious CO 2 sink (−1.57 mmol m −2 d −1 and −3.99 mmol m −2 d −1 in June and August, respectively), probably due to elevated TA/DIC ratio and the subsequent effects of spring bloom. As for the Yangtze River estuary (YRE), it changed from an obvious CO 2 sink (−1.28 mmol m −2 d −1 ) in June into a very weak CO 2 source (0.04 mmol m −2 d −1 ) in August. This change was probably associated with the rising of seawater temperature and monthly variation of Yangtze River discharge. The inner shelf of ECS (ECSS) experienced obvious air–sea CO 2 flux changes during from June (−8.88 mmol m −2 d −1 ) to August (−0.36 mmol m −2 d −1 ) as well. Biological DIC consumption in the upper layer and DIC regenerated from respiration in the subsurface jointly controlled this p CO 2 variation. As a whole, the SYS and ECS acted as an obvious CO 2 sink during summer and could absorb atmospheric CO 2 with the average air–sea flux ( F CO 2 ) −2.68 mmol m −2 d −1 . The summary of air–sea CO 2 flux in the ECS and SYS during recent two decades indicated the ECS served as quite a stable CO 2 sink, whereas the SYS experienced obvious change. Discharge of Yangtze River and anthropogenic nutrients loading could profoundly affect the variations of p CO 2 and F CO 2 in future. [ABSTRACT FROM AUTHOR]

To understand the variations of vertical settling flux in a spring-neap tidal cycle in strong tidal environments, an anchored vessel with a Hydro-Bios Multi-Sediment Trap and a Nortek Acoustic Doppler Velocimeter (ADV) was deployed in the sub-tidal flat in Luoyuan Bay, a typical semi-enclosed embayment, from January 16 to 31, 2010 (from spring to neap to spring again). The observed results reveal that there is a strong relationship between the Signal-Noise Ratio (SNR) recorded by the ADV and the synchronous suspended sediment concentration (SSC) obtained by the filtrated method. The time-series of SSC and settling velocity were then estimated. The measured results indicated that the maximum tidal range during the observation was 7.03 m, which occurred during the spring tide, and the minimum value during the neap tide was 3.58 m. The near-bottom (1.1 m above the bed) current speed, SSC, bed shear stress, and settling velocity decreased from spring to neap tide, and the maximum values were 0.556 m/s, 53.40 mg/L, 0.806 N/m 2 and 0.26 mm/s, respectively. The horizontal flux varied from 0.04 g/m 2 s to 21.77 g/m 2 s; the horizontal fluxes over a tidal cycle decreased from spring to neap tide, and the net horizontal flux of suspended sediment was 880.66 kg/m 2 with a net transport direction of 292° during the entire observation time. The daily vertical settling fluxes, calculated based on mass balance, varied from 17.03 g/m 2 d to 56.86 g/m 2 d, which were lower than those obtained by the sediment trap (18.50–332.80 g/m 2 d). According to the analyzed results of the hydrodynamic data, when the current speed exceeds 0.20 m/s, the flow can penetrate the whole sediment trap and the bottom quiescent layer no longer exists. The horizontal flux plays an important role in the trap collection efficiency in strong tidal environments, which can lead to overestimation and a maximum value of 585% during the spring tide. A constant settling velocity (mean value during the observation) may underestimate the daily settling fluxes by approximately 22.28–51.80% during the neap tide and overestimate the fluxes by approximately 19.61–30.86% during the spring tide. [ABSTRACT FROM AUTHOR]

A new method is introduced for estimating suspended sediment concentration and grain size from acoustic backscatter observations, incorporating techniques from linearized statistical inverse theory and data assimilation. A series of laboratory experiments with a sediment-laden jet were conducted for the purposes of demonstrating the method. The inversion results show improvements in stability compared to existing methods, in cases with highly attenuating suspensions. These improvements are due to the use of statistical regularizing assumptions, which act to mitigate issues associated with poor conditioning and nonlinearity in the inverse problem. The new method is also more computationally efficient than existing methods, owing to the use of linearization. Matlab code is provided implementing the new method, see Appendix A . [ABSTRACT FROM AUTHOR]

Two surveys were conducted on the East China Sea inner shelf before and after the passage of Typhoon Morakot in 2009. The typhoon-induced variations in the size distributions of suspended matters were studied based on the data collected by a Laser In Situ Scattering Transmissometer (LISST). A comparison of the measurements from the two surveys revealed significant changes in seafloor sediment grain size, suspended matter volume concentration and size distribution due to Typhoon Morakot. The mean seafloor sediment grain size increased generally, while the sorting coefficient decreased after the typhoon. Before the typhoon, suspended matter size was generally >100 μm, which was significantly reduced to between 20–50 μm after the typhoon. The single-grain fraction with sizes <36 μm and microflocs with sizes between 36–133 μm significantly increased in volume concentrations and percentage after the typhoon. On the other hand, the volume concentration of macroflocs (with sizes >133 μm) were largely reduced from >40% before the typhoon to <20% after the typhoon in the entire water body. Our analyzes suggest that the dynamic process of the typhoon caused the seafloor sediment resuspension, which significantly increased the suspended matter volume concentration in addition to the increase of terrigenous materials due to high-intensity rainfall accompanying the typhoon. The typhoon process also decreased the suspended matter size and macrofloc (>133 μm) concentration by strong disturbance of water column and the temporary demise of plankton under heavy cloudy condition. [ABSTRACT FROM AUTHOR]

The vertical distribution of longshore sediment transport was measured on sandy macrotidal barred beaches of Northern France under low to moderate wave energy conditions, using streamer traps collecting sand at different elevations above the bed. Longshore sediment flux measurements and wave and current data were collected at several locations along cross-shore transects in order to analyse the relation between the vertical patterns of suspended sand transport and the forcing hydrodynamics across the bar-trough topography. Suspended sediment fluxes generally showed a typical upward decrease in longshore transport, revealing that near-bed transport represents the major transport mode on these macrotidal beaches, notably over the bars where the highest rates of sediment transport were measured. Conversely to previous studies in which the shape of the vertical distribution was either independent of the location in the surf zone or which showed an increase in suspended transport over intertidal bars, our results revealed a strong upward decrease in longshore sediment transport over bars, especially under higher wave energy conditions, whereas more uniform vertical distributions were observed in troughs. These differences in the vertical distribution of longshore sediment flux can be explained by spatially variable wave breaking and surf zone processes over the bar-trough topography and by the distribution of small-scale bedforms across the intertidal zone, which influence sand resuspension processes and control the shape of the vertical profiles of sediment transport. Larger longshore sediment fluxes over bars can be explained by the action of breaking waves that are responsible for increased sediment remobilization, but the dominance of spilling breakers on the studied beaches likely results in significant turbulence dissipation, leading to limited sand resuspension in the water column. Comparatively, landward propagating surf bores over bars favour an increase in sediment concentration at higher elevations above the bottom in the adjacent trough. [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]

Distribution of suspended sediment in the Bohai Sea and its seasonal variability were investigated based on the datasets obtained from four cruises carried out in different seasons in 2010 and 2012. The results indicate that the spatial distribution of suspended sediment in the Bohai Sea was dominated by the river input and coastal resuspension that depends on the type of local surface sediment and hydrodynamics. The suspended sediment was mostly concentrated in the southern Bohai Sea particularly around the Yellow River Delta in the summer season as impacted by the river plume but confined within a very limited area near the river mouth, whereas in winter–spring seasons sediment concentration became much higher as a result of active coastal resuspension induced by energetic wave actions in the shallow water. High sediment concentration was found in Liaodong Bay in winter–spring seasons when dynamics become strong but decrease significantly in summer seasons. The sediment concentration in the southern Bohai Strait was much higher than that in the northern part, suggesting evident sediment export to the Yellow Sea particularly in the winter–spring seasons. Strong seasonal variability of suspended sediment distribution in the Bohai Sea was consistent with the monsoon activity and associated wave actions and coastal currents that are varying seasonally. The dominance of seasonal monsoon signal and associated wave dynamics make the subaqueous Yellow River delta to be a major sink for the terrestrial sediment in the summer seasons, but transiting to a primary source in winter–spring seasons for sediment redistribution in the Bohai Sea and sediment export to the Yellow Sea. The seasonal patterns of suspended sediment distribution in the Bohai Sea and the dominance of monsoon activities may provide a good reference to understanding the sediment transport in the China Shelf Seas where sediment resuspension and coastal circulation are evidently driven by monsoon. [ABSTRACT FROM AUTHOR]

The vertical distribution of suspended sediment in continental shelf waters has significant implications for water quality, aquatic ecology, and sediment transport. Nevertheless, there have been relatively few systematic field studies aimed at determining whether a general vertical trend in suspended sediment concentration (SSC) exists, or how any such vertical trend can be expressed mathematically. In this study, based on 402 individual SSC profiles measured hourly during 16 dual-tide voyages at 8 stations in the outer Yangtze Estuary, we found that SSC followed an average depth profile that was smoothly concave-up. This average profile, and the relationship between SSC and height above the seabed, was exponential ( R 2 >0.99). In comparison, the traditional Rouse equation based on hydrodynamics describes the measured average SSC profile poorly, in that the greater the distance from the near-bed height (where the reference SSC is taken), the greater the deviation of the simulated SSC from the measured SSC. However, in this study, a new approach was developed to overcome this flaw in the Rouse equation, which divides the equation into two parts. One part uses a reference SSC from a near-bed level, and an upwards decreasing coefficient, in the same way as the conventional Rouse equation. Conversely, the other part uses a reference SSC from at the water surface, and a downwards decreasing coefficient. Our modified hydrodynamics-based equation expresses the measured SSC well, with an R 2 between the simulated and measured SSCs exceeding 0.99. According to the average SSC profiles, the near-bed SSC was 2.8 times greater than the SSC at the water surface (close to the value of 3 suggested for modeling studies in the absence of empirical data), and the depth-averaged SSC was 1.8 times greater than the SSC at the water surface. We also found that the average SSC profile showed a uniform (from water surface to seabed) decline in SSC (25%) in response to the dramatic decline in the suspended sediment load supplied by the Yangtze River over the past three decades. However, the shape and vertical ratio of the average SSC profile have changed little, which suggests that the general form of the SSC profile is determined mainly by local hydrodynamics and sediment properties, and not by fluvial sediment supply. [ABSTRACT FROM AUTHOR]

The development of a theoretical description of how sound interacts with flocculating sediments has been lacking and this deficiency has impeded sound being used to extract quantitative suspended sediment parameters in suspensions containing flocs. As a step towards theoretically examining this problem a relatively simple heuristic approach has been adopted to provide a description of the interaction of sound with suspensions that undergo flocculation. A model is presented for the interpretation of acoustic scattering from suspensions of fine sediments as they transition from primary particles, through an intermediate regime, to the case where low density flocs dominate the acoustic scattering. The approach is based on modified spherical elastic solid and elastic fluid scatterers and a combination of both. To evaluate the model the variation of density and compressional velocity within the flocs as they form and grow in size is required. The density can be estimated from previous studies; however, the velocity is unknown and is formulated here using a fluid mixture approach. Uncertainties in these parameters can have a significant effect on the predicted scattering characteristics and are therefore investigated in the present study. Furthermore, to assess the proposed model, outputs are compared with recently published laboratory observations of acoustic scattering by flocculating cohesive suspensions. [ABSTRACT FROM AUTHOR]

The effect of the joint action ofM2andM4tidal flow, residual flow and spatial settling lag on the lateral entrapment of sediment is examined in tidally dominated estuaries with an idealized model that assumes along-estuary uniform conditions. Approximate solutions are obtained for arbitrary cross-channel bed profiles by scaling and perturbation analysis. The hydrodynamics include externally drivenM2tidal flow, externally and internally drivenM4tidal flow and residual flow driven by horizontal density gradient, river discharge and nonlinear advection. The sediment concentration includes a mean component, anM2component driven by bed erosion and anM2component driven by both bed erosion and inertial terms. Sediment availability is calculated by imposing a morphodynamic equilibrium condition. The model is applied to a transect in the James River estuary where data of flow and suspended sediment concentration are available. Two types of sediment are separately considered, viz., fine silt and coarse silt. Residual advective transport of sediment by the lateral flow induces trapping of sediment over the left shoal (looking landward). Model results also show that the incorporation ofM4tidal flow and spatial settling lag leads to a second sediment trapping region over the right shoal. Model results are qualitatively in good agreement with the observations. [ABSTRACT FROM AUTHOR]

A series of experiments were conducted to examine the effect of mud floc growth on the acoustic back-scatter signal recorded by a Nortek Vector acoustic Doppler velocimeter (ADV). Several studies have shown that calibration equations can be developed to link the backscatter strength with average suspended sediment concentration (SSC) when the sediment particle size distribution remains constant. However, when mud is present, the process of flocculation can alter the suspended particle size distribution. Past studies have shown that it is still unclear as to the degree of dependence of the calibration equation on changes in floc size. Part of the ambiguity lies in the fact that flocs can be porous and rather loosely packed and therefore will not scatter sound waves as a solid particle would. In addition, direct, detailed measurements of floc size have not accompanied experiments examining the dependence of ADV backscatter and suspended sediment concentration. In this set of experiments, direct measurement of the floc size distribution is made with time in a mixing chamber using a floc camera system. A Vector ADV and an OBS are also placed within the tank to measure acoustic backscatter and SSC as the flocs change size with time; concentration in the experiments ranges from 15 to 90mg/l. Results showed that the growth of mud flocs did influence the SNR recorded by the Vector ADV, and that the sensitivity of the SNR signal to changes in floc size was higher for flocs with diameters less than ≈ 80 μ m (it kr=1 at a diameter of 80μm). The response of SNR to changes in floc size and SSC was modeled with a modified sonar equation. If properly calibrated, the model was able to capture the functional behavior of SNR with changes in floc size and concentration. Values of the calibration coefficients showed that while changes in floc diameter up to about 80μm did alter the SNR, the change was less than what would be expected from a similar change in the size of solid scatterers. [ABSTRACT FROM AUTHOR]

Retrieval of the inherent optical properties and estimation of the constituents׳ concentrations from satellite ocean colour data in turbid and eutrophic waters are important as these products provide innovative opportunities for the study of biological and biogeochemical properties in such optically complex waters. This paper intends to develop models to retrieve absorption coefficients of phytoplankton, suspended sediments and coloured dissolved organic matter and describe vertical profiles of chlorophyll and suspended sediments from satellite ocean colour data. These models make use of the relationships between remote sensing reflectance ratios Rrs (555)/Rrs (443) and Rrs (620)/Rrs (490) versus aph (443) and aph (555), and acdom (443), and ad (443) to derive the model parameters. Validation with the in-situ data obtained from coastal waters around India and other regional waters (e.g., NASA bio-Optical Marine Algorithm Data-Set, NOMAD) shows that the new models are more accurate in terms of producing the spectral absorption coefficients (aph, ad, acdom across the entire visible wavelengths 400-700nm) in a wide variety of waters. Further comparison with existing models shows advantage of the new models that have important implications for remote sensing of turbid coastal and eutrophic waters. The retrieved absorption coefficients of phytoplankton and suspended sediments (non-algal matter) are also found to relate better to chlorophyll and total suspended sediments. Taking advantages of this, we derive models to determine and describe the vertical profiles of chlorophyll and suspended sediment concentrations along the depth. The model parameters are derived empirically. These new parameterizations show potential in estimating the vertical profiles of chlorophyll and suspended sediments with good accuracy. These results suggest robustness and suitability of the new models for studying the ecologically important components of optically complex turbid and eutrophic waters using remote sensing data. [ABSTRACT FROM AUTHOR]

Abstract: Sediment trapping by the halocline of a river plume was investigated over a spring-neap tidal cycle in the 2010 dry season in the Pearl River Estuary. Benthic tripod observations and concurrent shipboard measurements were conducted to examine mean and turbulent flows, and sediment distributions. The field observations showed that suspended particles are apparently concentrated on the halocline of the river plume, forming a patchy high-concentration suspension with larger floc sizes. This sediment trapping occurred only on the neap tide when the estuary was highly stratified. An estimation of the gradient Richardson number indicates that stratification suppression is dominant below the halocline, whereas shear-induced instability occurs above the halocline. The turbulent kinetic energy balance demonstrates that the buoyancy flux dominates over viscous dissipation in turbulence destruction. Therefore, the trapping of suspended sediment with large floc sizes on the halocline is induced by both salinity stratification and buoyancy-induced instability. This finding can explain the role of salinity stratification in the mechanism for estuarine turbidity maxima and long-distance transportation of suspended sediment. [Copyright &y& Elsevier]

The Rouse profile has been traditionally used to represent the vertical distribution of suspended sand in a marine benthic boundary layer. Yet it is one of the biggest unknowns in estuarine morphodynamics, largely due to uncertainties of the ratio of the sediment fall velocity to bed friction on which the Rouse exponent (R=w s/βku ⁎) is based. A field campaign was carried out at three different locations in the Oka estuary, northern Spain, in order to examine these uncertainties. Each location differed in grain size and flow condition thus offering a wide range of settings. The first survey was inside the estuary (wave sheltered, flood tide dominated and relatively broad estuary section), the second was at the distal ebb delta (ebb tide dominated and narrow estuary section), and the third was over the wave exposed proximal ebb delta (wave/flood tidal current combined flows and open sea). The aim of this study is to evaluate the applicability of the Rouse (1937) theory for the distribution of sand in suspension throughout a turbulent benthic boundary layer. A modified version of a Helley–Smith sampler was used to trap sand and measure the vertical distribution of sand in the water column. As well, a 1200 ADCP was used to measure flow velocity and backscatter together with an ADV (turbulence). The sand traps were found to have a sampling efficiency of 44%. The grain size at all stations was finer near the surface and coarser near the bed. The sand transport inside the estuary (Station 1) is inwards dominant. By contrast, the sand concentration during the ebb tide was ten times higher than during the flood tide at Station 2 and even higher at Station 3, which suggests that the sand transport over the ebb delta is seawards. The average Rouse parameters for Stations 1, 2, and 3 are 0.48±0.035, 0.78±0.23, and 0.46±0.06 respectively, which correspond to a coefficient of proportionality of the movability number, (χ) of 4 (Van Rijn, 1993). These differ from previous findings of Villatoro et al. (2010) and Amos et al. (2010b). [ABSTRACT FROM AUTHOR]

Abstract: For over two decades, coastal marine scientists studying boundary layer sediment transport processes have been using, and developing, the application of sound for high temporal–spatial resolution measurements of suspended particle size and concentration profiles. To extract the suspended sediment parameters from the acoustic data requires an understanding of the interaction of sound with a suspension of sediments and an inversion methodology. This understanding is distributed around journals in a number of scientific fields and there is no single article that succinctly draws together the different components. In the present work the aim is to provide an overview on the acoustic approach to measuring suspended sediment parameters and assess its application in the study of non-cohesive inorganic suspended sediment transport processes. [Copyright &y& Elsevier]

Abstract: In situ data set in the Bohai Sea of China was collected to test a previous model for surface water inorganic suspended particle size developed by Bowers et al. Based on this, a simple empirical model was then established for estimating median particle size in the Bohai Sea. The median inorganic suspended particle size was retrieved from ratio of green (560nm) to red (665nm) band. The model produced retrieval of particle sizes which are in good agreement with in situ measurements with the average percent difference of 27.0% (N=40, R 2=0.55) and root mean squared deviation of 4.311μm. This model was quite insensitive to input noises. Then the model was applied to MERIS Level 2 data and MODIS Level 3 data (monthly climatology) to analyze the spatio-temporal pattern and seasonal variability of inorganic suspended particle size in the Bohai Sea. The size of inorganic suspended particles was expected to be related to water turbulence. Wind was idendified as an important influencing factor of particle size distribution. There was an onshore to offshore gradient in inorganic suspended particle size in the Bohai Sea. A significant seasonal cycle exits in particle sizes (large in summer and small in winter). More independent dataset was needed for further research. [Copyright &y& Elsevier]

This paper assesses the fine sediment fluxes in the Caravelas estuarine system (Bahia, Brazil, 17o45'S and 039o12'W). The estuary reaches the ocean at the shore across from the Abrolhos Bank, the largest tropical reef habitat in the South Atlantic. The Caravelas estuarine system is composed of several meandering channels, which are connected to the ocean by a double inlet system. These two openings – the Caravelas and Nova Viçosa estuaries – are connected by a narrow, 30km long channel. The Caravelas estuary does not receive significant continental input, while the Nova Viçosa estuary receives the contribution of the Peruíbe River, which drains an area of approximately 5000km2. To understand the fine sediment dynamics and net transport, observations of tides, currents, salinity and suspended sediment concentration (SSC) were recorded in 13-h tidal surveys (spring and neap tide) and with 20-day long CTDs/ADCP moorings at the Caravelas estuary and in the interconnection channel. The SSC dynamic in the Caravelas estuary is primarily driven by advection, with SSC originating in the inlet and inner shelf area. Residual water and sediment transport are up-estuary in the Caravelas estuary and toward the Caravelas estuary in the interconnection channel. The residual transport showed pronounced synodical modulation and was stronger during spring tide. The Caravelas estuary function as a trap for inner shelf materials and fine sediments delivered by the Peruípe River at Nova Viçosa. [ABSTRACT FROM AUTHOR]

The Río de la Plata is one of the largest and most turbid estuaries of the world, carrying a total of 160 million tonsy−1 of suspended sediments. The knowledge of their spatial distribution and their scales of variability is fundamental for management and scientific reasons, but has been limited by the scarcity of observations. During 2009 and 2010, in-situ data (CTD and turbidity profiles, and water and bottom sediment samples) were collected at 26 sites during six repeated cruises and from three fixed instruments deployed in the frame of the FREPLATA/FFEM experiment. In this paper we complement the analysis of this in-situ data base with 10 years of daily intermediate resolution (1km) MODIS-Aqua observations processed for surface suspended matter using the IFREMER algorithm for coastal turbid waters. The aim of this work is to provide a comprehensive characterization of the annual mean suspended matter concentration distribution, to study its variability on seasonal time scale and to identify the involved physical mechanisms. The comparison between the statistics of the direct and remote sensed data is satisfactory, showing a good agreement in the magnitude and spatial distribution of the mean suspended sediments concentration, its standard deviation, so as the seasonal variability. Our data show that all along the year the concentration of surface suspended matter maximizes along the southern coast of the upper and intermediate estuary and at the tips of Samborombón Bay. This fact is linked in part with the higher solid discharge of the Paraná River – flowing along the southern coast – compared to the Uruguay River which flows following the northern coast. The former receives most of the sediments load to the Río de la Plata from the Bermejo River. The observed mean pattern is also related to the stronger tidal currents along the southern coast of the estuary and at the tips of Samborombón Bay, which act re-suspending sediments near the bottom. Then, wind waves during storms enhance vertical mixing, increasing the surface concentration. The concentration of suspended sediments rapidly falls seawards the Barra del Indio shoal, in the area of the salt wedge. In the outer estuary, suspended matter concentration is also strongly associated to the wind-forced motion of the freshwater plume. Suspended matter concentration exhibits a maximum in winter and a minimum in summer, that cannot be fully explained in terms of the seasonal cycle of the solid discharge of the tributaries, but seems to be related to a raise in the frequency of the storms in winter, increasing the frequency of strong winds and higher wind waves, and the associated re-suspension and mixing. [ABSTRACT FROM AUTHOR]

Abstract: Rain falling at or near low tide is capable of eroding and transporting cohesive sediment from intertidal areas. Given that metals adsorb strongly to silt- and clay-sized particles, it is conceivable that low-tide rainfall may also liberate previously-deposited metals from storage in intertidal sediment. To investigate the potential for rainfall as an agent of remobilization, this study tested the hypothesis that suspended sediment in a tidal creek during low tide rainfall events contains different suites of adsorbed metals than during wind-only events and fair weather days. Water samples were collected during low-tide rain events in winter and wind resuspension events in summer. The concentrations of suspended sediment, particulate organic carbon and nitrogen, and the total adsorbed concentration (gL−1) of most metals were higher for a low-tide rainfall event than during wind-only and fair-weather conditions. Metal contents (gg−1) were also greater during the rain event for most metals. Principal components analysis and relationships between metal content and suspended sediment concentration suggest that rainfall during low tide can mobilize a different source of sediment than wind–wave resuspension and regular tidal action. The metal content of bulk sediment samples from around the study area could not be matched satisfactorily to the suspended sediment in any of the events. This implies that bulk sediment composition should not be used to extrapolate to suspended sediment composition in terms of adsorbed metal content. [Copyright &y& Elsevier]

Abstract: Intermittent features of turbulence and sediment suspension were investigated in a large-scale laboratory flume, under erosive and accretive conditions with measured free surface elevation, fluid velocity, and sediment concentration across the surf zone. Intermittent events of turbulence and sediment suspension occurred for a small portion of the time series but contained a significant amount of motions in these events. Comparison of intermittency statistics with previous studies conducted under different experimental conditions showed similar results, indicating that intermittency is a general aspect of turbulence and sediment suspension in the surf zone, including the bar crest, the bar trough, and the inner surf zone. The relationship of these intermittent turbulence and suspension events was examined with conditional probabilities. Here, it was found that only 20–35% of the turbulent events were associated with sediment suspension events, implying that much of the intermittent turbulent motion may act to dissipate wave energy rather than suspend sediments. On the other hand, 50–65% of the sediment suspension events were associated with turbulent events, implying that intermittent turbulent motion is one of the fundamental mechanisms for the initiation of sediment suspension in the surf zone. The sediment suspension events that were uncorrelated with turbulent events were mostly induced by strong offshore low-frequency motion, suggesting that advection plays a key role. The vertical structures of intermittency showed that the fraction of intermittent events for both turbulence and sediment concentration were vertically uniform and quantitatively similar each other, although their thresholds varied vertically. The motion contained in the intermittent suspension events increased toward the bed, while it was vertically uniform in the intermittent turbulent events. Finally, it was found that the intermittent sediment suspension events play an important role in each bathymetric change. [Copyright &y& Elsevier]

Abstract: Many estuaries in high latitude regions are subjected to seasonally ice-covered conditions. However, ice effects on estuarine variability have received limited scientific attention and remain poorly understood. In this paper, an 11-month mooring record is used to examine seasonal variation of estuarine hydrodynamics in the Nelson River estuary (NRE), Hudson Bay (HB), in northern Canada. We show that ice cover strongly affects tidal amplitudes, velocities and phases in the NRE. In the mid-winter, the M 2 tidal amplitude and consequently the tidal range are significantly reduced due to under-ice friction in HB, while conversely the M 2 tidal velocity is amplified due to reduction of cross-section of the channel by formation of fast ice. A stronger surface seaward residual flow observed in the winter indicates that the formation of fast ice could also enhance the residual circulation. Suspended sediment concentration in the river mouth is reduced, also possibly due to the formation of fast ice that protects shallow nearshore shoals from erosion. This study demonstrates the importance of ice effects on estuarine variability and the complexity of processes in a seasonally ice-covered estuary. [Copyright &y& Elsevier]

Abstract: Suspended sediment in the coastal zone is an important limiting factor for the growth and health of inshore coral reefs. The Great Barrier Reef (GBR) lagoon receives sediment from a number of tropical rivers and the physical and biological effects of riverine discharge and turbidity within the lagoon are of considerable scientific and public interest. Published data from two inshore regions of the GBR are reviewed herein to evaluate the relative influence of river plumes and wave resuspension on suspended sediment concentration (SSC) around coral communities over a range of timescales. Data from Cleveland Bay and from other sites near the mouth of the Tully River show that wave resuspension is the most dominant mechanism controlling SSC at inshore reefs. At many nearshore areas today fine-grained bed sediment is abundant, consistent with millennial-scale geological evidence of sediment dispersal prior to European settlement and catchment impacts. Flocculation, particle settling and dilution occurs within the river plume, and riverine sediment concentrations at reefs directly attributable to individual flood inputs is significantly reduced, suggesting that the plume component is a relatively small contribution to the total suspended sediment mass balance over inter-annual timescales. Resuspension events can generate higher ambient SSC than that measured in flood waters (e.g. Tully River). In addition, while visually spectacular, satellite and aerial images offer limited quantitative information of total sediment load carried by hypopycnal plumes, as many of these plumes may contain algal blooms but relatively low concentrations of suspended sediment (ca. <5mg/l). Nonetheless, the cumulative effect of sediment-laden plumes may be a vector for other adsorbed contaminants of potential ecological concern, but coral smothering by hypopycnal plumes alone appears an unlikely impact particularly at inner- and middle-shelf reefs exposed to high wave energy and resuspension. Terrigenous sediment dispersal and turbidity within the GBR is governed by physical processes common to many continental shelves globally. Despite the examples examined in detail herein, the role of frequency, magnitude and duration in determining the impact or exposure of corals to elevated SSCs is poorly constrained by limited quantitative measurements during events, and our ability to place these into a broader temporal context. More high-quality observational data, at meaningful length-scales, can only enhance our ability to disentangle potential behavioural shifts in environmental responses. [Copyright &y& Elsevier]

Abstract: Using a detailed set of hydrodynamic and suspended-sediment observations, we developed data-driven algorithms based on Boosted Regression Trees and Artificial Neural Networks to predict suspended-sediment reference (near-bed) concentration using water depth, wave-orbital semi-excursion, wave period and bed-sediment grainsize as inputs. With one exception, the response of the data-driven algorithms was physically sound; the exception was the response to water depth. Outside of the range covered by the data, predictor performance could not be assessed and is not necessarily reliable. Boosted Regression Trees provide the best predictor of suspended-sediment reference concentration and have a clear explanatory power. Artificial Neural Networks provide slightly poorer predictions. Although the response of the latter is more difficult to interpret, they can be more easily included in numerical models simulating larger (in space) and longer (in time) morphodynamic behavior. Within the range of variability provided by the measurements, these algorithms outperform conventional process-based predictors. [Copyright &y& Elsevier]

Abstract: The use of an Ultrasonic Velocity Profiler (UVP) to obtain phase-averaged velocity and turbulent Reynolds stress profiles inside an oscillatory boundary layer flow is described in detail and possible error sources are summarized. Since the instrument also reports the acoustic backscatter, a novel application of the same ultrasound profilers to obtain phase-averaged suspended sediment concentration profiles and the errors involved in this technique are carefully discussed. The experiments were performed in the Large Oscillatory Water-Sediment Tunnel (LOWST), which has been a recent addition to the experimental facilities of the Ven Te Chow Hydrosystems Laboratory at the University of Illinois at Urbana-Champaign. The results showed that for the selected transducer frequency and flow, the instrument ability to characterize turbulence is compromised by the presence of Doppler noise and the size of the sampling volume. Regarding the suspended sediment estimation, it was found that the calibration obtained using water samples yielded good results, allowing for the study of the suspended sediment evolution along the oscillation. [Copyright &y& Elsevier]

Abstract: Measurements of suspended sediment concentration profiles in aquatic environments may be made by remote sensing acoustic backscatter (ABS) instruments. These typically operate at MHz frequencies and narrow beamwidths (1–2°). The backscatter equation for these instruments is not in a closed form. It may be solved by iteration. A direct general solution has previously been presented by recasting into the form of a Bernoulli equation [. Journal of the Acoustical Society of America 104 (2), 820–830 (Pt. 1)]. It is shown that the direct solution is also enabled by recasting as a Riccati equation. The direct solution obtained by the Riccati formulation has the same form as given previously, but its derivation clarifies inconsistencies in previous work which have disguised its potential usefulness. [Copyright &y& Elsevier]

Abstract: Measurements are presented from a multi-frequency acoustic backscatter study of aqueous suspensions of sand sized particles having different and mixed mineralogical compositions. Seven different mineral sands are examined: quartz, crushed shell fragments, aragonite, muscovite mica, olivine, zircon, and magnetite. For each of these sands, measurements of the normalised total scattering cross section and backscatter form function were obtained. These measurements show some significant differences in the acoustic scattering properties between the different mineral sands. If the composition is erroneously assumed to be quartz when inverting the acoustic backscatter data collected from these different mineral sands, relatively poor estimates of mean size and suspended sediment concentration are obtained. To overcome this problem, the scattering measurements are used to construct a generic scattering description by normalising the scattering properties by grain density and averaging over the different minerals examined. This generic scattering description is evaluated by testing its application to the inversion of the acoustic backscatter data obtained from the seven different mineral sands, as well as two different mixtures each containing multiple mineral sands spanning size distributions typical of those encountered in the marine environment. These inversion results show close agreement to independent estimates of suspended sediment concentration and mean size. [Copyright &y& Elsevier]

Abstract: In the last five years, horizontal acoustic Doppler current profilers have come onto the market as an instrument designed to measure real-time horizontal current profiles from a permanent fixed mount. The focus of this paper is on the feasibility of using these commercial instruments to measure suspended sediment fluxes in rivers. Measurements are presented from a study site that was equipped with an optical turbidity meter and three horizontal ADCPs operating at 300kHz, 600kHz and 1200kHz between November 2009 and June 2010. Laser grain size measurements showed the primary particles of the suspended sediment to be predominantly silts with some clay and occasionally some fine sand. Measurements of sediment attenuation by the three horizontal ADCPs are presented for two high concentration events during which concentrations reached 2.5 and 8kg/m3, respectively. Very clear linear relationships are seen between sediment attenuation and particle concentration and the sediment attenuation is consistent with the theory for viscous absorption by fine sediments. Using the relationship between attenuation and concentration, we are able to reconstruct the concentration time series for events during which the turbidity data are unavailable. Our findings show that, when properly positioned, horizontal ADCPs can provide suitable measurements of sediment transport during extreme river flow conditions such as floods, at least for predominantly silt-sized particles. This ability is of primary interest for river survey applications since the long term sediment transfer is believed to be driven by these intense events. [Copyright &y& Elsevier]

Abstract: This work presents a detailed analysis of suspended sediment concentration measured in the inner surf and swash zone under large-scale wave flume conditions. Controlled hydrodynamic conditions tested in the laboratory corresponded to highly energetic (erosive) conditions. Hydrodynamic, bottom evolution and suspended sediment concentration (SSC) data were acquired at several locations within the inner surf and the swash zone. A limited number of hydrodynamic type of events have been identified to induce important suspended sediment concentrations. These hydrodynamic conditions include incident broken wave, wave capture, weak and strong wave backwash interactions or pure backwash events. The acquired data showed the variability of the suspended sediment concentration pattern depending on the cross-shore location from which measurements were taken. This suspension mechanism also varied depending on the time series characteristic. There was a clear predominance of incident wave/bore as a forcing term in the surf zone, whilst the SSC measured in the swash zone showed that wave-swash interaction controls the most significant events. Finally, the importance of a wave-by-wave analysis is highlighted in this study. It was observed that despite the fact that most of the time series induce profile accretion in the mid and upper swash area, only one or two swash events are able to erode extensive parts of the beach and change the final output of the entire time record from accretion to erosion. [Copyright &y& Elsevier]