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

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

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

The Nam Dinh Coast is a constituent part of the dynamic coastline, belonging to the Red River Delta. It is bounded to the north and south by the Red and Day Rivers, with Ninh Co and So Rivers located in the middle. This coast has been undergoing severe erosion during the last hundred years. Over this period, vital agricultural area along the coastline has vanished into the sea and families have been forced to abandon their houses due to the erosive action of waves. Numerous studies were conducted to identify the major causes governing the erosion problems, and several hypotheses have been proposed. In the present work, remote sensing data analysis techniques with both optical and synthetic aperture radar (SAR) were employed to examine the hypothesis that land subsidence is contributing to the erosion along the Nam Dinh Coast. The results revealed that the high lateral erosion rates observed at sandy beaches between estuaries are approximately -6 m/yr in the south and -10 m/yr in the north of the So River. Meanwhile, sediments transported from the rivers accumulate mainly around the estuaries, leading to rapid accretions of approximately +93, +4, and +46 m/yr for Day, Ha Lan (So River), and Ba Lat (Red River), respectively. Simultaneously, land is sinking and uplifting at highly uneven rates, with a few sections subsiding 10 times faster than the overall spatial average. Uplifting observed in southern areas ranges from +1.2 to +1.9 mm/yr. In contrast, subsidence was identified in the northern parts, with mean rates varying from -0.1 to -12.3 mm/yr. Based on the Bruun Rule, the combined effects of land subsidence and relative sea level rise (SLR) could explain approximately 66% of the observed rate of erosion in the northern part of Ha Lan. Findings from surface deformation data contribute to a deeper insight into coastal erosion in Nam Dinh. • The erosion mechanism in the Nam Dinh Coast is not yet fully understood. • Combined use of SAR and optical images is applied to detect subsidence and to discuss its effect on coastal erosion. • Land is sinking and uplifting at highly uneven rates, varying from -21 to +2.5 mm/yr. • Combined effects of land subsidence and relative sea level rise contribute to 66% of the erosion. [ABSTRACT FROM AUTHOR]

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