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Total suspended solids (TSS) can be a useful indicator of environmental change in nearshore coastal environments. Understanding the mechanisms of TSS variations in response to environmental drivers is of broad interest for ecology and geomorphology. The Yellow River Delta (YRD) in China is a fragile coastal region that has been affected by human activities and climate change. Here, we investigated TSS along the YRD shoreline over two decades with time‐series satellite data (2002–2020). We observed that TSS concentration decreased significantly in nearshore waters (5‐m isobath) surrounding the YRD, especially in the LaiZhou Bay. During the same time period, wave height (WH) along the deltaic shoreline and sediment load from the Yellow River have decreased, while sea surface height (SSH) has displayed a positive trend. Our results indicate that WH and SSH play a major role in sediment resuspension and dispersion, while the YSD mildly affected TSS variability along the coast. Monthly bed shear stress triggered by waves was then computed using WH, wave period (WP), and SSH. Bed shear stress and TSS displayed a positive correlation. We concluded that seasonal oscillations in SSH in conjunction with wind waves are responsible for TSS variability in the shallow waters in front of the YRD. [ABSTRACT FROM AUTHOR]

In the fragile mining areas of western China, the contradiction between coal mining and water resource protection coexists prominently. Facing this issue, it is necessary to understand the dynamic relationship between mining-induced shear stress and groundwater seepage, as well as the fracture morphology of the overlying strata. In this study, the seepage characteristics of rough fractures within the rock mass are thoroughly investigated, with an emphasis on studying the effects of shear stress and seepage erosion. This research is carried out through seepage experiments and 3D fracture morphology scanning, and the research results are mainly as follows: (a) Rocks with higher shear strengths show less fluctuation in changes in fracture morphology and seepage velocity. (b) The permeability of sandstone and concrete fractures is inversely proportional to the shear stress. The layering of coal greatly limits seepage through the fractures and the permeability of coal is about one-tenth of the permeability of sandstone and concrete under the same conditions. (c) The mechanism of erosion damage to the rock by water-force coupling is the result of the shear and extrusion generated by rock fractures and the transport of rock particles. Changes in fracture erosion and seepage characteristics brought about by the damage will mutually promote and intensify the erosive effect of water force. (d) The degree of change in fracture morphology (fracture damage) under the same conditions is coal > concrete > sandstone. There are differences in the response of different types of rock to the shear stress–seepage erosion, but all show obvious changes in fracture damage and seepage characteristics. [ABSTRACT FROM AUTHOR]

Reclamation projects generally change the hydrodynamics and thus affect the topography of the seabed, which is the main threat to the safety of marine engineering. The Caofeidian Reclamation Project, the largest reclamation project in China to date, involved the reclamation of coastal regions of the Hebei Province. However, the project also created several issues and flaws due to the size of the reclaimed area. Through the comparative analysis in the Caofeidian sea area of multi-phase bathymetric topography, shallow stratigraphic changes, and numerical simulation of sediment dynamics, the characteristics of surface sediments and spatial distribution of erodibility were summarized. New marine geological hazards were discovered, such as submarine landslides and erosion depressions. It was concluded that after the reclamation of the Caofeidian, the south of the deep trough was still in an erosion state, and the erosion rate increased slightly. The shear stress formed by strong tidal currents in the deep trough was greater than the critical erosion shear stress of surface sediments, which caused the erosion transport of sediments. It was the primary dynamic mechanism leading to the long-term erosion state of the deep trough. • The characteristics of surface sediments and spatial distribution of erodibility were summarized. • New marine geological hazards were discovered near the Caofeidian Reclamation Project. • The south of the deep trough was still in an erosion state, and the erosion rate increased slightly. [ABSTRACT FROM AUTHOR]

The unmanned underwater tracked bulldozer (UUTB) is an indispensable equipment for dredging and cleaning obstacles on the river bed in the flood season. The investigation on the interaction properties between the UUTB tracks and sediments provides foundation for the evaluation of operation performance when it works on the inland river bed. Based on the current worldwide research, the sediments mixed by sand, bentonite and water with sand content 0%, 10% and 20% were configured in this study to replace the real sediments on the inland river bed in China. The current pressure-sinkage model and shear stress-shear displacement model were discussed. Three different tracks were tested for the pressure-sinkage and the shear stress-shear displacement on the platform. The relationship between pressure and sinkage under sand content 0%, 10% and 20% are revealed based on the experimental results. The modulus of cohesive deformation and friction deformation of the sediments under said sand content are presented. The curves of shear stress and shear displacement are also obtained, which demonstrates the properties between the tracks and configured sediments under sand content 0%, 10% and 20%. The relationship between the tractive force and slip ratio with three different tracks under said sand content is also presented based on the quantitative analysis, which provides reference for the dynamics control and performance evaluation of UUTB on the inland river bed. [ABSTRACT FROM AUTHOR]

Poyang Lake, the largest freshwater lake in China, is distinguished by complicated suspended sediment (SS) dynamics. Apart from lake currents, wind is an important form of natural disturbance in driving SS transport. Combining field data, laboratory experiments, and numerical simulations, we gained valuable insight into wind impacts on SS dynamics in Poyang Lake. (1) Lake current patterns exert great influence on the level of wind impacts. Due to reduced sediment carrying capacity, SS under weak current suffers from stronger wind influence than under strong currents. (2) Wind speed determines the degree of wind impact, not only affecting horizontal SS transport, but also regulating vertical dynamics. Winds exceeding critical intensity can enhance horizontal transport through both surface drift and Stokes drift at different water depths, triggering sediment suspension to feed the loads in overlying water. (3) Wind impact is influenced by lake morphology. The broad water surface in the central lake permits formation of continuous waves, leading to the largest SS fluctuation, from -10.05 mg·L-1 to +20.17 mg·L-1, while average variation in the south and north part of the lake is only -6.59 mg·L-1 to þ10.36 mg·L-1. (4) SS in four reserves are characterized by notable wind impact, while in the other two reserves SS show no obvious departure from values without wind. [ABSTRACT FROM AUTHOR]

The disturbance of the water-sediment interface by wind-driven currents and waves plays a critical role in sediment resuspension and internal nutrient release in large, shallow lakes. This study analyzed the effects of the interactions between wind-induced currents an1d waves on the driving mechanism of sediment resuspension in Lake Taihu, the third largest freshwater lake in China, using acoustic and optic techniques to collect long-term, high-frequency, synchronous in situ measurements of wind, currents, waves, and suspended solid concentrations (SSCs). The results suggested that water turbidity started to increase at wind speeds of approximately 4 m/s and significantly increased when wind speeds exceeded 6 m/s. In most cases, wind-induced waves were the main energy source for changes in turbidity. Wave-generated shear stress contributed more than 95% to sediment resuspension and that only in weak wind conditions (<4 m/s) did the lake bottom shear stresses generated by currents and waves contributed equally. The relationship between SSC and bottom shear stress generated by wave was established by fitting the observed results. The processes of sediment dynamics were divided into four stages (A through D) according to three shear-stress thresholds. In stage A, SSC remained stable (about 45 mg/L) and τ was less than 0.02 N/m. In stage B, the sediment bed was starting to be activated (SSC 45∼60 mg/L) and τ was in the range of 0.02∼0.07 N/m. In stage C, a medium amount of sediment was suspended (SSC 60∼150 mg/L) and τ ranged from 0.07 to 0.3 N/m. In stage D, large amount of sediment was suspended (SSC 150∼300 mg/L) and τ was larger than 0.3 N/m. The findings of this paper reveal the driving mechanism of sediment resuspension, which may further help to evaluate internal nutrient release in large shallow Lake Taihu. [ABSTRACT FROM AUTHOR]

The dynamics of sediment erosion and deposition have been investigated in the Baisha Bay, China featured by a sandy bed. The wave elements, tide level, velocity and direction of the currents, seabed height change were measured by the underwater anti-subsidence in-situ tripod in December 2013. During the observations, the tripod installed with steel clump weights and needle-like piles can keep itself from subsiding vertically and moving horizontally. Both the observation results and shear stress analysis show that the contribution of waves to sediment erosion and deposition surpasses that of currents. On the whole, the seabed height change (approximately 1 millimeter [mm]) caused by currents is about one order smaller than that (0.8 centimeter [cm] to 2.2 cm) caused by high waves. The maximum wave-induced shear stress can reach up to 1.56 Pascal (Pa) and the mean wave-induced shear stress is approximately 10 times greater than mean current-induced shear stress. Even so, the influence of currents on sediment erosion and deposition cannot be arbitrarily ignored. Besides, the waves are responsible for sediment erosion and deposition only during episodic high waves and currents constantly cause sediment erosion and deposition. Despite the difference in deposition amount, the episodic high waves lead to sediment deposition with centimeter scale during the observation. While the sediments are eroded during flood tidal currents and deposited during ebb tidal currents with millimeter scale. [ABSTRACT FROM AUTHOR]

The influence of overlying hydrodynamics on the exchange behaviour and fluxes of heavy metals at the sediment-water interface (SWI) is poorly understood. In the study, metals exchange behaviour and exchange rate at the SWI under resuspended and undisturbed scenario were investigated The results showed that dissolved Cr, Cu, Zn, and Pb concentrations increased rapidly to attain maximum values between 0.3 and 0.5 N·m -2 after the sediment resuspended. Following the quick release, metals concentrations gradually decreased and remained at relatively low levels, especially for Cu and Zn. Meanwhile, Cu, Zn, and Pb had higher potential remobilization potential in the undisturbed case. Calculating with the hydrodynamics in the Modaomen, the metals efflux under the resuspension scenario could reach 0.55 to 4130.83 mg·m -2 ·yr -1 , which were 1-3 orders of magnitudes higher than the undisturbed case. Whether or not resuspension events occurred, estuarine sediments were source of heavy metals, especially in the weakly mixed zone., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This study was conducted to investigate the flow restructure and resistance in vegetal flow under wind shear action in shallow lakes. A special racetrack-style flume with two sets of driving devices installed on the top was designed to simulate the wind-driven current. Two typical types of live vegetation, Vallisneria natans and Acorus calamus of Taihu Lake in China, were planted in the system. The results revealed that the velocity distribution of vegetal flow under wind action differed from that in open channels. The velocity distribution can be described as logarithmic-curve shaped and contained a compensation current in the lower layer. The area within the effective height of vegetation in which the velocity was obviously affected comprised an effective friction region. When compared with V. natans, A. calamus displayed better resisting capacity. Based on measured data, a new empirical relationship between drag coefficient and wind speed was presented, which indicated the resistance ability of vegetation under different intensities of wind action. Variations in the equivalent roughness coefficient were also discussed. [ABSTRACT FROM AUTHOR]

ABSTRACT A case study of typhoon-induced sediment resuspension and its effects on some indicators of water quality (dissolved oxygen, pH and turbidity) and nutrient release in the large shallow eutrophic Lake Taihu, the third largest freshwater lake in China, was documented, and its effect on the algal biomass was investigated. Typhoon Morakot that swept from the west of Lake Taihu in August 2009 led to a number of changes in the lake ecosystem: (1) intensive winds produced large seiches, strong waves and large wave-induced shear stress; (2) typhoon Morakot led to increased suspended solids and nutrients in the water column. Post-typhoon concentrations of suspended solid, total phosphorus, total nitrogen, soluble reactive phosphorus (SRP). NO3-N and NH4-N were 4, 2, 1·5, 2·5, 3·5 and 1·5 times those observed in the pre-typhoon water column, respectively; and (3) during typhoon Morakot, there was no obvious stratification between the surface and bottom of the water column in chlorophyll a (Chl a), the post-typhoon Chl a concentration throughout the water column increased with a maximum daily mean of 87·8 µg l−1, and the algal bloom recurred. Typhoon-induced sediment resuspension could lead to both nutrient and light limitations for algal growth, whereas after the typhoon had passed, water column conditions (water temperature, solar radiation, light penetration and nutrient availability) favoured the growth and production of algae. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Sediment dynamics have an important influence on the morphological evolution of tidal wetlands, which consist of mudflats and salt marshes. To understand the nature of sediment behavior under combined current–wave action at an exposed tidal wetland, we measured the waves, currents, water depths, bed-level changes, and sediment properties at a mudflat–salt marsh transition on the Yangtze Delta, China, during five consecutive tides under onshore winds of ~8m/s, and calculated the bed shear stresses due to currents (τ c ), waves (τ w ), combined current–wave action (τ cw ), and the critical shear stress for erosion of the bottom sediment (τ ce ). The bed shear stresses under combined current–wave action (τ cw ) were approximately five times higher on the mudflat (up to 1.11N/m2; average 0.27N/m2) than on the salt marsh (up to 0.14N/m2; average, 0.06N/m2). On the mudflat, τ cw was larger than the critical erosion shear stress (τ ce =0.103N/m2) for 70% of the period of submergence, whereas τ cw was always lower than τ ce at the salt marsh site (τ ce =0.116N/m2). This result indicates that the sediment dynamics on the mudflat were dominated by erosion, whereas at the salt marsh they were governed by deposition, which is in agreement with the observed bed-level change during the study period (−3.3mm/tide on the mudflat and 3.0mm/tide on the salt marsh). A comparison of τ cw values calculated using the models for bed shear stresses under combined current–wave action indicates that both models are applicable to the present case and effectively predict the bottom shear stress under combined current–wave action. Overall, we conclude that τ cw in combination with τ ce is useful in assessing the hydrodynamic mechanisms that underlie the morphological evolution of exposed tidal wetlands. [Copyright &y& Elsevier]

Dams intercept the river flow and reduce the water input of downstream lakes, which leads to the decreased water level and deteriorated water environment. Environmental water releases are becoming regular ways to maintain ecological water demand of lakes. This study was carried out to describe how natural submerged flexible vegetation altered velocity and generated turbulence under different water releases discharge scenarios. Natural Ceratophyllum demersum L. was collected from a large shallow lake, Baiyangdian Lake, China. Two vegetation densities were set in this flume experiments. The flow velocity was measured using particle image velocimetry (PIV) techniques and used to study the mean flow features (velocity and Reynolds stress) and distributions of vegetative drag and development length. The observed velocity profiles presented vertical stratification. The greatest gradient of velocity and shear stress appeared around the top of the canopy. The canopy drag of submerged flexible vegetation presented a parabolic vertical distribution, and smaller drag was generated by larger flows under the same density. The initial adjustment length of water flow was linearly correlated with the deflected height of flexible vegetation and was little affected by the vegetation density in the two studied densities. The most intense turbulence in the vegetation canopy appeared at its top, where the largest shear stress was also observed. Strong canopy-scale vortices on the top of the canopy were produced and penetrated closer to the bed in the cases of denser vegetation under small discharges (Cases 3.1–3.5); penetration was also restricted by canopy drag and was unable to reach the bed. • Drag of natural flexible vegetation canopy was vertically parabolic. • Initial adjustment length of flow was linear with the deflected height of vegetation. • The diffusion near the bed dominated the mass and momentum exchange within the vegetation canopy. [ABSTRACT FROM AUTHOR]

Background and Aims: The association between carotid wall shear stress (WSS) and cerebral small vessel disease has yet to be fully elucidated. The major purpose of this study was to investigate this association in older subjects., Methods: Common carotid artery WSS, endothelial function, white matter hyperintensities (WMH), lacunes, and microbleeds were assessed in 1396 older adults. Participants were followed-up for an average of 69.7 months., Results: Mean (M) and peak (P) WSS and changes in endothelial function were independently associated with changes in WMH volume and fraction, lacune counts, and microbleed counts (all p < 0.05). The risks of new-incident Fazekas scale ≥2 [hazard ratio (HR) with 95% confidence interval (CI): 2.141 (1.469-3.119), p = 0.005 and 1.731 (1.197-2.505), p = 0.004, respectively], lacunes [HR (95% CI): 2.034 (1.369-3.022), p < 0.001 and 1.693 (1.151-2.490), p = 0.003, respectively], and microbleeds [HR (95% CI): 2.311 (1.509-3.541), p < 0.001 and 2.208 (1.299-3.751), p < 0.001, respectively] were significantly higher in the lowest quartile group than in the higher quartile group, as classified by either MWSS or PWSS, after adjustment for confounders., Conclusions: Low carotid WSS is an independent risk factor for the progression of cerebral small vessel disease in older adults., (Copyright © 2019 The Authors. Published by Elsevier B.V. All rights reserved.)