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Observation and Numerical Modeling of Sediment Transport in Coastal Areas

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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Oceans and Coastal Zones".

Deadline for manuscript submissions: closed (30 January 2020) | Viewed by 51371

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Special Issue Editors

Prof. Dr. Kehui Xu

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Department of Oceanography & Coastal Sciences, Louisiana State University, Baton Rouge, LA, USA
Interests: geological oceanography; coastal morphodynamics; observation and numerical modeling of sediment transport along bottom boundary layer; sedimentary geology; coastal processes
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Dr. Joseph Carlin

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Guest Editor

Department of Geological Sciences, California State University, Fullerton, CA, USA
Interests: coastal sedimentology; terrestrial sediment flux to marine environments; coastal geomorphology; sediment deposition and remobilization; event deposition; coastal processes; stratigraphy

Prof. Dr. Houjie Wang

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Guest Editor

Key Laboratory of Submarine Geosciences and Exploration Technology, Ocean University of China, Shandong, China
Interests: coastal sediment dynamics; land-sea interactions in context of global change; estuarine and coastal processes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The objective of this Special Issue is to improve our knowledge of the observation and modeling of sediment tranport in various coastal areas. We encourage submissions based on the studies of sediment delivery, transport, and depositional processes in multiple coastal environments in continental margins, including shelves, estuaries, deltas, bays, barrier islands, and others. We would like to gather a series of publications that highlight recent new findings on various aspects of morphodynamics, sediment dynamics, non-cohesive and cohesive sediment transport, sedimentary geology, sequence startigraphy, geological oceanography, subsidence and land loss, sediment management, sediment-related human activities, coastal restoration, and beyond. Studies may derive from field observations, laboratory experiments, and model studies across a wide range of timescales. This Special Issue should be of interest to coastal scientists, engineers, stakeholders, resource managers, and decision makers.

Prof. Dr. Kehui Xu
Prof. Dr. Joseph Carlin
Prof. Dr. Houjie Wang
Guest Editors

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Keywords

Sediment tranport
Coastal processes
Estuaires and deltas
Continental shelves
Bottom boundary layer
Cohesive and noncohesive sediment processes

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Published Papers (12 papers)

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22 pages, 7231 KiB

Open AccessArticle

The Impact of Biophysical Processes on Sediment Transport in the Wax Lake Delta (Louisiana, USA)

by Courtney Elliton, Kehui Xu and Victor H. Rivera-Monroy

Water 2020, 12(7), 2072; https://doi.org/10.3390/w12072072 - 21 Jul 2020

Cited by 10 | Viewed by 3569

Abstract

Sediment transport in coastal regions is regulated by the interaction of river discharge, wind, waves, and tides, yet the role of vegetation in this interaction is not well understood. Here, we evaluated these variables using multiple acoustic and optical sensors deployed for 30–60 days in spring and summer/fall 2015 at upstream and downstream stations in Mike Island, a deltaic island within the Wax Lake Delta, LA, USA. During a flooding stage, semidiurnal and diurnal tidal impact was minimal on an adjacent river channel, but significant in Mike Island where vegetation biomass was low and wave influence was greater downstream. During summer/fall, a “vegetated channel” constricted the water flow, decreasing current speeds from ~13 cm/s upstream to nearly zero downstream. Synchrony between the upstream and downstream water levels in spring (R² = 0.91) decreased in summer/fall (R² = 0.84) due to dense vegetation, which also reduced the wave heights from 3–20 cm (spring) to nearly 0 cm (summer/fall). Spatial and temporal differences in total inorganic nitrogen and orthophosphate concentrations in the overlying and sediment porewater were evident as result of vegetation growth and expansion during summer/fall. This study provides key hourly/daily data and information needed to improve the parameterization of biophysical models in coastal wetland restoration projects. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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19 pages, 12817 KiB

Open AccessFeature PaperArticle

Periodic Oscillation of Sediment Transport Influenced by Winter Synoptic Events, Bohai Strait, China

by Haiqin Duan, Jingping Xu, Xiao Wu, Houjie Wang, Zhiqiang Liu and Chenghao Wang

Water 2020, 12(4), 986; https://doi.org/10.3390/w12040986 - 31 Mar 2020

Cited by 7 | Viewed by 3332

Abstract

Instruments on two bottom-mount platforms deployed in the Bohai Strait during a cruise from January 6–13, 2018 recorded an intense northerly wind event. The responses of hydrodynamic and hydrographical characteristics in Bohai Sea and Yellow Sea to the wind event were analyzed aided by the wind, wave, sea surface suspended sediment concentration and sea surface height datasets from open sources. It is shown that the strong wind event had a significant impact on the redistribution of sea surface height, regional wave conditions, regional circulations and the accompanying sediment transport pattern. Specifically, the sediment transport through the Bohai Strait may be divided into two chronological phases related to the wind event: (1) the enhanced sediment transport phase during the buildup and peak of the wind event when both the Northern Shandong Coastal Current and regional suspended sediment concentration were sharply increased; and (2) the relaxation phase when the northerly wind subsided or even reversed, accompanied by the enhanced Yellow Sea Warm Current with lowered suspended sediment concentration. Such results at synoptic scale would improve our capability of quantifying sediment exchange between the Bohai and Yellow sea, through the Bohai Strait and provide valuable reference for the study of other similar environments worldwide. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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27 pages, 3873 KiB

Open AccessArticle

Streamflow Decline in the Yellow River along with Socioeconomic Development: Past and Future

by Shi Lun Yang, Benwei Shi, Jiqing Fan, Xiangxin Luo, Qing Tian, Haifei Yang, Shenliang Chen, Yingxin Zhang, Saisai Zhang, Xuefa Shi and Houjie Wang

Water 2020, 12(3), 823; https://doi.org/10.3390/w12030823 - 14 Mar 2020

Cited by 15 | Viewed by 4171

Abstract

Human society and ecosystems worldwide are increasinAagly threatened by water shortages. Despite numerous studies of climatic impacts on water availability, little is known about the influences of socioeconomic development on streamflow and water sustainability. Here, we show that the streamflow from the Yellow River to the sea has decreased by more than 80% in total over the last 60 years due to increased water consumption by agricultural, industrial and urban developments (76% of the streamflow decrease, similarly hereinafter), decreased precipitation (13%), reservoir construction (6%) and revegetation (5%). We predict that if the past trends in streamflow will continue, year-round dry-up in the lower Yellow River will commence in the late 2020s or early 2030s, unless effective countermeasures such as water diversion from the Yangtze River are taken. These results suggest that streamflow in semiarid basins is highly vulnerable to human impacts and that streamflow decline would in turn hinder further socioeconomic development and endanger river-sea ecosystems. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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13 pages, 2834 KiB

Open AccessArticle

Recent Spatio-Temporal Variations of Suspended Sediment Concentrations in the Yangtze Estuary

by Haifei Yang, Bochang Li, Chaoyang Zhang, Hongjie Qiao, Yuting Liu, Junfang Bi, Zhilin Zhang and Fengnian Zhou

Water 2020, 12(3), 818; https://doi.org/10.3390/w12030818 - 14 Mar 2020

Cited by 14 | Viewed by 4121

Abstract

Water and sediment are two of the most essential elements in estuaries. Their product, suspended sediment concentration (SSC), is involved in hydrology, geomorphology and ecology. This study was focused on the spatial and temporal variations of SSC in the Yangtze Estuary under new situations after the closure of ~50,000 dams in the Yangtze basin, including the Three Gorges Dam (TGD) in 2003. It was found that the SSC first exhibited an increasing and then a decreasing trend longitudinally from Xuliujing Station to the outer estuary with the Turbidity Maximum Zone located in the mouth bar area. Vertically, the SSC in the bottom layers averaged 0.96 kg/m³, about 2.4 times larger than the surface layers (0.40 kg/m³). During spring tides, the SSCs were always higher than those in neap tides, which was fit for the cognition law. As for the seasonal variations in the North Branch and mouth bar area, the SSCs in the dry season were higher than those in the flood season, while in the upper reach of the South Branch and outer estuary, the seasonal variation of SSCs reversed. This phenomenon primarily reflected the competition of riverine sediment flux and local resuspended sediment flux by wind-induced waves. As for the interannual changes, the SSCs demonstrated overall fluctuant downward trends, determined by riverine sediment flux and influenced by waves. This study revealed the new situation of SSC and can be a reference for other related researches in the Yangtze Estuary. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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18 pages, 32267 KiB

Open AccessArticle

Impact of Sea Ice on the Hydrodynamics and Suspended Sediment Concentration in the Coastal Waters of Qinhuangdao, China

by Man Jiang, Chongguang Pang, Zhiliang Liu and Jingbo Jiang

Water 2020, 12(2), 611; https://doi.org/10.3390/w12020611 - 24 Feb 2020

Cited by 1 | Viewed by 3244

Abstract

The influence of sea ice on the hydrodynamics, sediment resuspension, and suspended sediment concentration (SSC) in the coastal area of Qinhuangdao was systematically investigated using 45-day in situ measurements at two stations (with ice at station M1 and without ice at station M2) in the Bohai Sea in the winter of 2018. It was found that the daily fluctuations of temperature and salinity at M1 are more significant than those at M2. During a typical seawater icing event on January 28, the temperature and salinity of the bottom water at M1 were decreased by 1.77 °C and increased by 0.4 psu, respectively. Moreover, due to the shielding effect of the sea ice, the residual current was much less affected by the wind at M1 than at M2. For the vertical distribution of current velocity, it changed from a traditional logarithmic type under ice-free conditions to parabolic type under ice-covered conditions due to the larger drag coefficient of the water body on the solid ice surface. For the SSC and turbidity at the bottom layer, the average values were 4.9 μL/L and 8.6 NTU at M1, respectively, approximately half of those at M2. The smaller SSC and turbidity at M1 can be attributed to the lower near-bottom turbulent kinetic energy (TKE). At M2, however, the larger SSC is closely related to the strong wind forcing, which could induce higher TKE without sea ice cover, and hence stronger turbulent resuspension. The seabed sediment analysis results showed that in the study area, fine sand is most likely to resuspend, while cohesive particles would resuspend only under strong hydrodynamic conditions. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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18 pages, 4672 KiB

Open AccessArticle

Future Response of the Wadden Sea Tidal Basins to Relative Sea-Level rise—An Aggregated Modelling Approach

by Quirijn J. Lodder, Zheng B. Wang, Edwin P.L. Elias, Ad J.F. van der Spek, Harry de Looff and Ian H. Townend

Water 2019, 11(10), 2198; https://doi.org/10.3390/w11102198 - 22 Oct 2019

Cited by 26 | Viewed by 6340

Abstract

Climate change, and especially the associated acceleration of sea-level rise, forms a serious threat to the Wadden Sea. The Wadden Sea contains the world’s largest coherent intertidal flat area and it is known that these flats can drown when the rate of sea-level rise exceeds a critical limit. As a result, the intertidal flats would then be permanently inundated, seriously affecting the ecological functioning of the system. The determination of this critical limit and the modelling of the transient process of how a tidal basin responds to accelerated sea-level rise is of critical importance. In this contribution we revisit the modelling of the response of the Wadden Sea tidal basins to sea-level rise using a basin scale morphological model (aggregated scale morphological interaction between tidal basin and adjacent coast, ASMITA). Analysis using this aggregated scale model shows that the critical rate of sea-level rise is not merely influenced by the morphological equilibrium and the morphological time scale, but also depends on the grain size distribution of sediment in the tidal inlet system. As sea-level rises, there is a lag in the morphological response, which means that the basin will be deeper than the systems morphological equilibrium. However, so long as the rate of sea-level rise is constant and below a critical limit, this offset becomes constant and a dynamic equilibrium is established. This equilibrium deviation as well as the time needed to achieve the dynamic equilibrium increase non-linearly with increasing rates of sea-level rise. As a result, the response of a tidal basin to relatively fast sea-level rise is similar, no matter if the sea-level rise rate is just below, equal or above the critical limit. A tidal basin will experience a long process of ‘drowning’ when sea-level rise rate exceeds about 80% of the critical limit. The insights from the present study can be used to improve morphodynamic modelling of tidal basin response to accelerating sea-level rise and are useful for sustainable management of tidal inlet systems. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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26 pages, 7274 KiB

Open AccessArticle

An Integrated Approach for Constraining Depositional Zones in a Tide-Influenced River: Insights from the Gorai River, Southwest Bangladesh

by Edwin J. Bomer, Carol A. Wilson and Dilip K. Datta

Water 2019, 11(10), 2047; https://doi.org/10.3390/w11102047 - 30 Sep 2019

Cited by 13 | Viewed by 4005

Abstract

The tidal to fluvial transition (TFT) of estuaries and coastal rivers is one of the most complex environments on Earth with respect to the transportation and deposition of sediment, owing in large part to competing fluvial and marine processes. While there have been recent advances in the stratigraphic understanding of the TFT, it is still unclear whether these findings are site-specific or representative of mixed tidal-fluvial systems worldwide. Yet, research from this depositional domain holds profound societal and economic importance. For instance, understanding the underlying stratigraphic architecture of channel margins is critical for assessing geomorphic change for fluvio-deltaic settings, which are generally vulnerable to lateral channel migration and resultant erosion. Findings would also benefit paleo-geographic reconstructions of ancient tide-influenced successions and provide an analog for hydrocarbon reservoir models. In the Ganges-Brahmaputra Delta of Bangladesh, the Gorai River is one of two Ganges distributaries actively connected to the Bay of Bengal. With fluvial input from the Ganges and meso-scale (2–4 m range) tides at the coast, the Gorai exhibits a variety of hydrodynamic regimes across its 350-km reach, providing a unique opportunity to investigate along-channel depositional patterns across the TFT. This study integrates multiple datasets—core sedimentology, river channel bathymetry, and remote sensing—to provide a process-based framework for determining the relative position of sedimentary deposits within the tidal-fluvial continuum of the Gorai River. The results of this investigation reveal coincident, abrupt shifts in river channel morphology and sediment character, suggesting the occurrence of backwater-induced mass extraction of relatively coarse sediments (i.e., fine sand). Despite being situated in an energetic tidal environment, evidence of tidal cyclicity in cored sediments is relatively rare, and the bulk stratigraphy appears strongly overprinted by irregularly spaced cm- to dm-scale sediment packages, likely derived from monsoonal flood pulses. Such findings differ from previously-studied mixed tidal-fluvial systems and underscore the site-specific complexities associated with this depositional domain. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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18 pages, 11679 KiB

Open AccessFeature PaperArticle

Sediment Identification Using Machine Learning Classifiers in a Mixed-Texture Dredge Pit of Louisiana Shelf for Coastal Restoration

by Haoran Liu, Kehui Xu, Bin Li, Ya Han and Guandong Li

Water 2019, 11(6), 1257; https://doi.org/10.3390/w11061257 - 15 Jun 2019

Cited by 21 | Viewed by 5273

Abstract

Machine learning classifiers have been rarely used for the identification of seafloor sediment types in the rapidly changing dredge pits for coastal restoration. Our study uses multiple machine learning classifiers to identify the sediment types of the Caminada dredge pit in the eastern part of the submarine sandy Ship Shoal of the Louisiana inner shelf of the United States (USA), and compares the performance of multiple supervised classification methods. High-resolution bathymetry and backscatter data, as well as 58 sediment grab samples were collected in the Caminada pit in August 2018, about two years after dredging. Two primary features (bathymetry and backscatter) and four secondary features were selected in the machine learning models. Three supervised classifications were tested in the study area: Decision Trees, Random Forest, and Regularized Logistic Regression. The models were trained using three different combinations of features: (1) all six features, (2) only bathymetry and backscatter features, and (3) a subset of selected features. The best performing model was the Random Forest method, but its performance was relatively poor when dealing with a few mixed (sand and mud) surficial sediment samples. The model provides a new and efficient method to predict the change of sediment distribution inside the Caminada pit over time, and is more reliable when predicting mixed bed with rough pit bottoms. Our results can be used to better understand the impacts on biological communities by (1) direct defaunation after initial sand excavation, (2) later mud accumulation in topographic lows, and (3) other geological and physical processes. In the future, the deposition and redistribution of mud inside the Caminada pit will continue, likely impacting benthos and water quality. Backscatter, roughness derived from bathymetry, rugosity derived from backscatter, and bathymetry (in the importance order from high to low) were identified as the most effective predictors of sediment texture for mineral resources management. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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11 pages, 17452 KiB

Open AccessArticle

Typhoon Soudelor (2015) Induced Offshore Movement of Sand Dunes and Geomorphological Change: Fujian Coast, China

by Haidong Li, Yunhai Li, Binxin Zheng, Guicai Zhong, Hannv Zhang, Hengbo Wang and Lei Qiao

Water 2019, 11(6), 1191; https://doi.org/10.3390/w11061191 - 7 Jun 2019

Cited by 6 | Viewed by 4085

Abstract

Typhoons play a significant role in the marine sedimentary dynamic process and thus could significantly change the submarine geomorphology in their influence area. In this study, a high-resolution sub-bottom profiler and a side-scan sonar were used to detect the submarine geomorphology of the southeast coastal area of Nanri Island in the Taiwan Strait before and after Typhoon Soudelor—three times in 2015. The results show that the typhoon induced seaward movement of the sand dunes up to several tens of meters, resulting in significant changes in both the shape of the sand dunes and the scale of the exposed bedrocks. The typhoon also changed the submarine geomorphology, including the smoothing of anchor traces of fishing boats and the formation of relatively small sand dunes (groups). A comparison of the results of different surveys shows that the submarine geomorphology that was changed by Typhoon Soudelor could not recover within a short period of time. The wind field simulations of the typhoon process showed that the storm wave caused by the strong wind stress of the typhoon was a key dynamic factor for changing the submarine geomorphology. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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16 pages, 5327 KiB

Open AccessArticle

The Influence of Temperature on the Bulk Settling of Cohesive Sediment in Still Water with the Lattice Boltzmann Method

by Guang-quan Qiao, Jin-feng Zhang, Qing-he Zhang, Xi Feng, Yong-chang Lu and Wei-bing Feng

Water 2019, 11(5), 945; https://doi.org/10.3390/w11050945 - 5 May 2019

Cited by 3 | Viewed by 3194

Abstract

Flocculation is very common and significant for cohesive sediment in coastal areas, and the influence of temperature on it cannot be neglected. The Lattice Boltzmann Method (LBM), combined with the extended Derjaguin‒Landau‒Verwey‒Overbeek (XDLVO) theory, which considers the micro-interaction forces between particles, was applied to simulate the settling and flocculation processes of cohesive sediment under various temperature conditions. The floc size, floc volume, suspended sediment concentration (SSC), and settling velocities were analyzed. The analyses revealed that with increasing temperature, both the mean floc diameter and floc volume grew, while the maximum floc diameter initially increased and then slightly decreased with its peak at 10 °C. During settling, the SSC change rate was exponentially related to the SSC, with an optimal fitting index of 0.3. The LBM sediment settling velocity was also compared with some formulas and physical model tests; the comparison results consistently demonstrated that the LBM was reasonable for modeling the bulk settling of cohesive sediment. Further discussions illustrated that the cohesive sediment is more difficult to flocculate at low temperatures due to the low aggregation frequency, while at high temperatures, some large flocs broke easily due to the effect of the short-distance force and macro force. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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28 pages, 12006 KiB

Open AccessArticle

A Two Decadal (1993–2012) Numerical Assessment of Sediment Dynamics in the Northern Gulf of Mexico

by Zhengchen Zang, Z. George Xue, Kehui Xu, Samuel J. Bentley, Qin Chen, Eurico J. D’Sa and Qian Ge

Water 2019, 11(5), 938; https://doi.org/10.3390/w11050938 - 4 May 2019

Cited by 19 | Viewed by 5066

Abstract

We adapted the coupled ocean-sediment transport model to the northern Gulf of Mexico to examine sediment dynamics on seasonal-to-decadal time scales as well as its response to decreased fluvial inputs from the Mississippi-Atchafalaya River. Sediment transport on the shelf exhibited contrasting conditions in a year, with strong westward transport in spring, fall, and winter, and relatively weak eastward transport in summer. Sedimentation rate varied from almost zero on the open shelf to more than 10 cm/year near river mouths. A phase shift in river discharge was detected in 1999 and was associated with the El Niño-Southern Oscillation (ENSO) event, after which, water and sediment fluxes decreased by ~20% and ~40%, respectively. Two sensitivity tests were carried out to examine the response of sediment dynamics to high and low river discharge, respectively. With a decreased fluvial supply, sediment flux and sedimentation rate were largely reduced in areas proximal to the deltas, which might accelerate the land loss in down-coast bays and estuaries. The results of two sensitivity tests indicated the decreased river discharge would largely affect sediment balance in waters around the delta. The impact from decreased fluvial input was minimum on the sandy shoals ~100 km west of the Mississippi Delta, where deposition of fluvial sediments was highly affected by winds. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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17 pages, 6181 KiB

Open AccessCase Report

Effect of Wave, Current, and Lutocline on Sediment Resuspension in Yellow River Delta-Front

by Bowen Li, Yonggang Jia, J. Paul Liu, Xiaolei Liu and Zhenhao Wang

Water 2020, 12(3), 845; https://doi.org/10.3390/w12030845 - 17 Mar 2020

Cited by 9 | Viewed by 3962

Abstract

Historically, the Yellow River in China discharges > 1 × 10⁹ ton/yr sediment to the sea, and has formed a large delta in the western Bohai Sea. Its river mouth is characterized by an extremely high suspended sediment concentration (SSC), up to 50 g/L. However, the hydrodynamic factors controlling the high suspended sediments in the Yellow River estuary are not well understood. Here, we conducted two hydrodynamic observations and SSC measurements in the winter and spring low-flow seasons of 2014–2015 and 2016–2017 under five sea conditions, including calm-rippled, smooth-wavelet, slight, moderate, and rough, in the Yellow River Delta-front during the observation period. Under calm-rippled conditions, the contribution of currents to the total resuspended sediment concentration (RSC) was 77.7%–100.0%. During the smooth-wavelet and slight periods, the currents’ contribution decreased as low as 30% and 3.0% of the total RSC, respectively. Under moderate and rough-sea conditions, waves accounted for at least 70% and 85% of the total RSC, respectively. The results indicate that 20 cm-thick lutoclines were created after a significant increase in the wave height to a peak value followed by a decrease. When the SSC is over 3 g/L and hydrodynamic conditions could not break the lutoclines, the flocculent settling of suspended sediment changes to hindered settling in the Yellow River Delta. Under hindered settling, the settling velocity decreases, and the resuspended sediments remains in the lutoclines and their lower water layers. This study reveals different controlling factors for the high SSC near a river-influenced delta, and helps us get a better understanding of a delta’s resuspension and settling mechanisms. Full article

(This article belongs to the Special Issue Observation and Numerical Modeling of Sediment Transport in Coastal Areas)

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