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Estuarine sediment transport is driven by the combined action of a multitude of influencing factors, including astronomical tides, waves dynamics, and river discharges. This study focuses on the effects of wave forces on sediment transport patterns in micro-tidal estuaries near Wanbao Beach, China. Numerical simulations are carried out using Delft3D. Modeling scenarios are configured using different wave characteristics, spanning from typical waves to those with a return period of 50 years. Results show that waves have a positive effect on landward sediment transport, resulting a larger active range of sediment. By comparing the spatial geomorphic variations under varying wave conditions, we find that modifications in significant wave height (Hs) primarily impact the position of erosion and deposition zones, whereas alterations in spectral peak period (Tp) predominantly influence the magnitude of these changes. The finding is further demonstrated by a comparison of residual currents under different wave intensities. Analysis of sediment transport rates in different transects indicates that the sediment transport rate is highest at the mouth transects and lowest at the alongshore transects. Moreover, variations in sediment transport rates exhibit distinctive patterns between the two outlet transects, even when subjected to identical wave conditions. The disparities are attributed to differences in runoff and the topographical features in proximity to the estuaries. Additionally, we find the sediment transport rate becomes insensitive to the variations in Hs when Hs is larger than a threshold value. The threshold decreases with increasing Tp. [ABSTRACT FROM AUTHOR]

Hyperpycnal flow deposits, one of the most important deep‐water gravity‐flow deposits in lacustrine basins, have become the research focus in recent years. However, the sedimentary characteristics and depositional model of hyperpycnal flow deposits in lacustrine basins remain unclear due to the differences of depositional settings between lacustrine and marine environments. Hyperpycnal flow deposits observed in the middle of the third member of the Shahejie Formation (Es3z) in the Bonan Sag, Bohai Bay Basin, Eastern China, provide a rare case study to reveal the characteristics and depositional model in lacustrine basins. For the first time, detailed core analysis, high‐resolution 3D seismic data, petrology and grain size analysis were used to unravel the characteristics and depositional model of hyperpycnal flow deposits in this study. Twelve lithofacies, six bed types and four bedsets (corresponding to feeder channel, distributary channel, levee and lobe) were recognized from detailed facies analysis. Plant fragment, an important identification mark for hyperpycnal flow deposits, can be classified into three types: completely broken plant fragments, partially broken plant fragments and complete leaves. The proximal part of the deposit develops a small amount of scattered and completely broken plant fragments in massive or spaced stratified pebbly sandstone and massive sandstone due to strong erosion of sustained high‐density turbidity current. The medial part of the deposit is dominated by laminated partially broken plant fragments in planar laminated or rippled sandstone due to suspended settling of sustained high‐density turbidity current and quasi‐steady low‐density turbidity current. Layered partially broken plant fragments with some complete leaves are common in the upper part mud rich division of hybrid event bed and laminated siltstone in the distal part of the deposit. The distribution pattern of hyperpycnites is controlled comprehensively by palaeogeomorphy and sediment supply. Palaeogullies determine the provenance direction of hyperpycnal flow. The formation of synsedimentary faults and troughs control the transport routing patterns. Local micro‐palaeogeomorphy and depression areas further restrict the distribution of sand bodies. During the early stage of deposition with insufficient sediment supply, sediments are transported to the deep basin along confined faulted troughs forming elongated sandy bodies. During the late stage of deposition with sufficient sediment supply, sediments are transported to the deep basin without confinement accumulating fan‐shaped sandy bodies. This study offers insight for enhancing the recognition criteria of hyperpycnites, as well as their depositional model in lacustrine basins. [ABSTRACT FROM AUTHOR]

• Hillslope erosion dynamic model integrating vegetation effect was established. • Unified baseline parameters were obtained across different land uses. • Effect of vegetation on soil detachment and sediment transport was revealed. • Contribution rates of vegetation to sediment reduction along slopes were quantified. Developing a process-based soil erosion model that comprehensively considers the effects of vegetation is complex but crucial for evaluating sediment reduction during vegetation restoration. Current understanding of the effect of vegetation on sediment reduction along hillslopes across different land uses is limited. In this paper, we developed a dynamic model of hillslope erosion that integrates the effects of vegetation on soil detachability and hydrodynamics (VED) based on the feedback mechanism between soil detachment and sediment transport. The VED was calibrated and validated with runoff plot data for woodland, grassland, and farmland in the Wuding, Yan, Jing and Wei Rivers of the Loess Plateau in China. Unified baseline parameters and decay coefficients of vegetation were obtained. The model validation results indicated that the coefficient of determination, Nash–Sutcliffe simulation efficiency and relative error ranged from 0.59 to 0.99, 0.56 to 0.90, and −45.99 % to 46.36 %, respectively. The decay coefficients for soil detachment capacity (Φ), sediment transport capacity (T c), and the sediment reduction effect of vegetation exhibited the following order: woodland > grassland > farmland. Compared with VED, existing process-based soil erosion models failed to effectively characterize the influence of vegetation on Φ and T c on the Loess Plateau, with differences of several orders of magnitude. The individual contributions of runoff, soil detachability, and hydrodynamics with vegetation impact on sediment yield were quantified by VED. The contribution rates of vegetation to sediment reduction decreased gradually with increasing slope length because the soil detachment capacity of bare slopes exceeded that of vegetated slopes, resulting in a faster increase in sediment yield. The contribution rates of vegetation to sediment reduction for woodland, grassland, and farmland with 20 %–60 % vegetation covers were 66.75 %–99.95 %, 57.43 %–99.63 %, and 27.91 %–88.63 % in the boundary conditions of this study, respectively. The results reveal the potential for integrating VED into other distributed watershed hydrological and sediment models to assess the effects of vegetation restoration on sediment reduction at a watershed scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • Distribution of vegetation avoided erosion in China increased by 12.89% in 1990–2020. • Greening of the surface has significantly prevented soil and water loss. • Spatial distribution roughly conforms to the division of the Hu Huanyong line. • Surface greening promotes a increase in vegetation avoided erosion efficiency. Global surface greening is very important to slow down regional warming, promote ecological balance and sustainable development, and China has made a significant contribution to this in the past 30 years, and effectively alleviated environmental problems such as land degradation, water shortage and air pollution by rapidly increasing vegetation coverage. Previous studies have shown that vegetation plays a positive role in alleviating soil erosion, but there is no quantitative description of runoff erosion and sediment transport under vegetation evolution with long time series and high resolution in China area. In this study, we use the RUSLE model and multi-source satellite remote sensing data to simulate overland soil erosion in China from 1990 to 2020 and analyze both the temporal and spatial variation of vegetation avoided erosion (VAE) and its correlation with multiple driving factors, such as Gross Primary Production (GPP). The results show that: 1)The distribution has increased by 12.89 % from 1990 to 2020, which is significant, and indicates that greening of the surface has significantly prevented soil and water loss;2)The spatial correlation strength of VAE-GPP in China is roughly in line with the division of the Hu Huanyong line (Hu-line), which is the result of the combined effect of vegetation distribution and human activities;3)The efficiency of VAE was significantly improved, especially the forest, accounting for about 76.50 % of the total, which was twice the sum of the other types. The research conclusion is of great significance to soil erosion prevention and control, soil ecological improvement, vegetation dynamic planning and regional sustainable development. [ABSTRACT FROM AUTHOR]

• It is essential to utilize diverse sources of observational data for the validation of long-term morphological simulations. • The multiple underlayer settings of the Delft3D model enable its acquisition of decadal bed layer stratigraphy. • Wind and waves sort sediment based on grain size, smoothing out morphological changes induced by tides. • Sea level rise significantly influences regions characterized by intricate morphological features. • Radial sand ridges form under a radial regime with low tidal ellipticity, abundant sand, and minor cohesive sediment. The tidal sand ridges in the southwestern Yellow Sea are unique in the world characterized by radial morphology, significantly higher elevation above low water level, and fine-grained sediment deposits. Using a numerical model, we examined the morphological evolution of the radial sand ridge system from 1979 to 2059. The model was calibrated and validated using hydrodynamic and sediment transport data, seabed topography, and grain size distributions from sediment cores. Our findings reveal that tidal force is the primary driver of the ridges' evolution, and they will continue to expand in response to sediment supply from the abandoned Yellow River delta and the Yangtze delta, with the latter contributing more. The ridges are mainly composed of fine sand and mud, with finer sediment dominating in the north and coarser sediment dominating in the south. Wind and waves sort sediment, depositing sand on ridges and fine sediment in channels, leading to erosion of higher elevated lands and filling of deep channels. Sea-level rise increases regional erosion, which has a large impact on areas with complex morphology. The 500-year morphological evolution of sand ridge systems, simulated through an idealized model, illustrated that the formation of radial sand ridges is dependent upon specific conditions such as the radial tidal regime, sufficient sediment sand, and the presence of cohesive sediment. This study deepens our understanding of the long-term prediction of coastal morphology and interpretation of seabed stratigraphy, and offers insights for effective coastal management. [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]

• Relatively small changes in rainfall at the event scale were observed. • Anthropogenic activities play a leading role in hydro-erosive responses variation. • Saturation-excess overland flow is increasingly occurring. • Reduced sediment connectivity resulted from the increasing disconnected areas. China's Loess Plateau remains one of the most serious water erosion areas on Earth, while runoff and sediments of the Yellow River continue to decrease due to soil and water conservation (SWC) measures. Besides, climate conditions are dynamic. A total of 197 rainfall-runoff events from 1965 to 2020 in the Huangfuchuan catchment, which were divided into 3 sub-periods (P0: 1965 – 1982 limited measures; P1: 1983–1998 only dams and P2: 1999–2020 dams and revegetation), were selected to reveal the differences and mechanisms of runoff generation and sediment dynamics. The results show that: 1) anthropogenic activities played a leading role in water and sediment reduction; 2) infiltration-excess overland flow during the first two periods was dominant mechanism, but the results imply a potential shift towards saturation-excess overland flow occurring more often during P2; 3) the studied system, in a highly erodible region, is transport-limited; 4) sediment connectivity is reduced noticeably at the catchment scale, in which the decrease in index of connectivity (IC) values mainly resulted from the increase in proportion of the most disconnected areas of the catchment, especially in P2. These findings can help towards a better understanding of the mechanisms behind the changes in sediment dynamics, which can be applied to develop and implement sustainable water and soil conservation planning in the local or other similar areas. Besides this knowledge is very important for improving hydrological and sedimentological models in order to forecast the effects of human induced changes. [ABSTRACT FROM AUTHOR]

The late Miocene is a time of strong environmental change in SW Asia. Himalayan foreland stable isotope data show a shift in the dominant vegetation of the flood plains away from trees and shrubs towards more C4 grasslands at a time when oceanic upwelling increased along the Oman margin. We present integrated geochemical and colour spectral records from International Ocean Discovery Program Site U1456 in the eastern Arabian Sea to reconstruct changing chemical weathering and erosion, as well as relative humidity during this climatic transition. Increasing hematite/goethite ratios derived from spectral data are consistent with long-term drying after c. 7.7 Ma. Times of dry conditions are largely associated with weaker chemical alteration measured by K/Rb and reduced coarse clastic flux, constrained by Si/Al and Zr/Al. A temporary phase of increased humidity from 6.3 to 5.95 Ma shows a reversal to stronger weathering and erosion. Wetter conditions can result in both more and less alteration due to the nonlinear relationship between weathering rates, precipitation and sediment transport times. Trends in relative aridity do not follow existing palaeoceanographic records and are not apparently linked to changes in Tibetan or Himalayan elevation, but more closely correlate with global cooling. An apparent opposing trend in the humidity evolution in the Indus compared to southern China, as tracked by spectrally estimated hematite/goethite, likely reflects differences in the topography in the Indus compared to the Pearl River drainage basins, as well as the generally wetter climate in southern China. [ABSTRACT FROM AUTHOR]

Bedforms like ripples are widely distributed in the coastal zone. They influence the bed roughness thus the estimation of bed shear stress and associated sediment transport. An echo sounder was mounted on a bottom-supported tripod intended to measure the erosion and deposition of seabed in the subaqueous Yellow River Delta, China. However, variations in bed elevation are found to be not the net erosion or deposition at the observation site, but the migration of silt ripples which were generated by waves and pushed back and forth or flattened off by the tidal currents. Ripple heights were observed to be within 0.1–0.7 cm and were used for testing the model of Nielsen (1981). The model overestimated the height of silt ripples as it was developed for sands, but the deviation can be well addressed by incorporating a linear modification (R 2 = 0.79). Alternatively, a new model specifically for silt ripple height was regressed from the field data with R 2 up to 0.78. The existence of silt ripples increases the bed shear stress by 4 times due to the additional bed roughness. A "fluffy layer" overlies the consolidated seabed, therefore, net seabed erosion occurs after the "fluffy layer" is resuspended. A representative critical bed shear stress for net seabed erosion in the study area was found to be 0.8 Pa. The echo sounder can be an alternative tool for observing silt ripples in coastal regions like the Yellow River Delta where the water is too turbid for underwater videos. The proposed model infers silt-ripple features from bed grain size and flow condition and provides a quick estimate for bed roughness improving the understanding on sediment transport. • A new model for silt ripple height is proposed based on field observation. • Bed shear stress is better estimated by incorporating bed roughness due to silt ripple. • Critical shear stress for erosion is inferred from field observations. • Echo sounder is used for observing silt ripples in turbid waters. • Ripple height is inferred from field-measured bed elevations. [ABSTRACT FROM AUTHOR]

Topographic relief and bedrock fractures caused by fault activity can accelerate surface erosion, suggesting that erosion rates increase with decreasing distance to the fault core. To test this hypothesis, we used 10Be cosmogenic nuclides to quantify catchment-wide erosion rates at various distances from a fault in the footwall of the Daqing Shan fault system, a 200-km-long active normal fault in Inner Mongolia, northern China. In addition, in order to examine the influence of topography and bedrock fractures on the surface erosion processes in the fault-weakened zone, their relationships with hillslope erosion, fluvial sediment grain size and transport efficiency, erosion rates, and erosion coefficients were studied. The resulting catchment-wide erosion rates ranged from 0.01 ± 0.00–0.13 ± 0.01 mm yr−1. These erosion rates and coefficients were unaffected by distance from the fault. The analysis of topography, bedrock fractures, and hillslope erosion yielded distinct hillslope erosion processes at different distances from the fault. Rapid mass wasting events, such as landslides, occurred at <15 km from the fault in steep, rocky hillslopes with abundant bedrock fractures. In contrast, at >15 km from the fault, hillslopes gradually become more gentle and soil-mantled. These spatial-slope configuration differences result in a decrease in sediment grain size delivered to river channels with increasing distance from the fault. Once sediments enter river channels, they impact fluvial transport capacity by influencing the initial motion threshold of sediment. Correlation analyses revealed that sediment transport efficiency in channels directly controls the catchment-averaged erosion rate and coefficient. This mechanism explains why the erosion rate remains insensitive to variations in topography and bedrock fractures in fault-weakened zones. • Study of patterns and controls on erosion rate across Daqing Shan fault zone. • Cosmogenic nuclide 10Be used to derive catchment-averaged erosion rate. • Erosion rates do not vary with distance from the fault. • Erosion rate remains insensitive to variations in topography and bedrock fractures. • Sediment transport efficiency in channels controls erosion rate. [ABSTRACT FROM AUTHOR]

• High-turbidity events are triggered by wind waves with wind speeds of > 7 m s−1. • Sediment erosion and deposition are synchronous during HTEs. • Synchronism causes a near-lakebed turbid water layer and sustains the lutocline. High-turbidity events (HTEs) frequently occur in shallow lakes and can deeply influence lake ecosystems. However, the processes of sediment erosion and deposition are not fully understood. To investigate these processes, two investigative campaigns that integrate bed sediment measurements, sediment settling experiments, in-situ observations, or a hydrodynamics-sediment model were conducted to quantitatively study wind-induced HTEs in Lake Taihu, China. Cohesive sediments were massively entrained from the lakebed by wind waves when the wind speed exceeded its critical value of 7 m s−1, as estimated by water depth, triggering HTEs with turbidity waves of > 100 nephelometric turbidity units. The suspended sediment concentration was the net sediment flux of erosion (average: 5.9 mg m−2 s−1) and deposition (average: 5.5 mg m−2 s−1), which occurred synchronously for most of the HTEs and resulted in high temporal variation in suspended sediment concentration. This synchronism was determined by the critical erosional stress of lakebed sediments, which was spatially heterogeneous (0.017–0.055 N m−2) in a large lake. Equations for erosion and deposition processes were derived following the investigative campaigns and used to develop a cohesive sediment transport model for simulating HTEs in Lake Taihu. Simulations indicate that the synchronism of sediment erosion and deposition led to a near-lakebed turbid water layer during an HTE, which sustained the sediment lutocline in Lake Taihu. Further investigation should be conducted on the role of the near-lakebed turbid water layer during endogenous pollution in large eutrophic lakes. [ABSTRACT FROM AUTHOR]

Silty coast, as a transitional state between muddy coast and sandy coast, possesses a considerable percentage of the overall coast in China. Huanghua-Binzhou coast in the southwest Bohai Bay in the northeastern China is a typical silty coast which is vulnerable to cold fronts when its seabed is prone to suffer suddenly drastic erosion and deposition due to the sediment there with relatively low incipient velocity and high settling velocity. In this study, a multi-sediment fraction model was established and two-way coupled with the wave-tide-surge model to investigate the responses of the sediment transport and morphodynamics of Huanghua-Binzhou coast to a cold front event during 10–13th Oct. 2003. The model results demonstrate that three sediment fractions, i.e. mud, silt and sand, showed different responses to the storm due to their different spatial percentages and distinct physical properties. The silt fraction, as the primary fraction, played a leading role in the suspension and transport of the total sediment, and showed a pattern of "deposition-erosion-deposition" in the cross-shore direction like the total morphological change. The fine sediment was transported westward and offshore during the storm, which indicated the sediment coarsening in the study area. The depth-induced wave modulation considerably enhanced the resuspension ability of the nearshore waves for sediment and thus played a critical role in intensifying the erosion. The Huanghua waterway siltation mainly resulted from the resuspension of the offshore sediment by the strong wind waves and its westward transport by the wind-induced currents during the storm. The construction of two long jetties in 2006 can significantly reduce the deposition in the waterway by 75%, and the additional large-scale construction in 2016 can further lessen the waterway siltation by intercepting the westward sediment transport and reduce the suspended sediment concentration by 30% by the land reclamation in the study area. • Silt played a leading role in sediment transport and morphological evolution during the cold front event. • Depth-induced wave modulation considerably enhanced nearshore sediment resuspension. • Offshore sediment resuspension and westward transport by strong wind-induced waves and currents caused waterway siltation. • The extended jetties in 2006 reduce deposition in the waterway by 75% under the action of the cold front event in 2003. [ABSTRACT FROM AUTHOR]

Global deltas are facing severe challenges under the impacts of riverine sediment decline and large estuarine projects. Comparing with abundant research on the Yangtze subaqueous delta, the shoals in shallow waters are poorly understood. The Hengsha Shoal, Yangtze Delta, China, expands during the past ∼65 years, with only slight changes during the pre-projects period and remarkable variations in the projects period. It's now half-surrounded by the Hengsha Reclamation Project and the Deep Waterway Project, both facilitating the recent expansion. The current vertical net rate of change in the study area is −2.2 cm/yr, suggesting an overall balance between sediment deposition and erosion. Spatially, the Hengsha Shoal is currently changing from horizontal expansion to vertical accretion. Considering the spatial patterns of erosion/deposition and residual currents and sediment, modern geomorphic changes in the Hengsha Shoal appear to be dominated by internal sediment transport from deep to shallow waters. Considering further possible changing conditions, the future evolution of this shoal and the resulting potential ecological impacts should be studied further. This case study demonstrates that sediment dynamics in semi-artificial shoals can be totally different from the subaqueous delta, highlighting the importance of human engineering in governing large deltas globally. • The Hengsha Shoal expands from slight changes to remarkable alterations. • This Shoal is currently changing from horizontal expansion to vertical accretion. • This study highlights the importance of engineering in governing deltas globally. [ABSTRACT FROM AUTHOR]

• New empirical formulae for estimating erosion-deposition in Luoshan-Hankou reach. • A functional chart differentiating erosion-deposition types of Luoshan-Hankou reach. • Diversion-afflux states for maximum and equilibrium erosion-deposition in the reach. It is not yet fully understood how water-sediment diversion and afflux along a mainstream reach of a river affect erosion-deposition in downstream reaches. This study focuses on the Luoshan-Hankou mainstream reach of the middle Yangtze River, China. The Luoshan-Hankou reach is vitally important for flood control, being located downstream of three diversion mouths and an afflux outlet along the Jingjiang reach. We establish empirical formulae for sediment transport rates at boundary cross-sections, and hence estimate the amount and proportion of erosion-deposition and its relative increase (termed erosion-deposition promotion) in the Luoshan-Hankou reach. We then propose critical net water supplies from Dongting Lake to Luoshan-Hankou reach based on maxima and equilibria of erosion-deposition and its promotion. It is found that net water supply partly drives erosion-deposition in the Luoshan-Hankou reach where maximal proportions of deposition and deposition-promotion may be approximated by 0.01 c -37.67 and 0.01 c -37.67 + c -1, in which c is a dimensionless parameter representing the erosion-deposition condition in Luoshan-Hankou reach for no water-sediment exchange. At Zhicheng hydrological station, the critical ratio of net water supply to overall water discharge is 0.418 c -33.33-1, and critical net water supply ratios for equilibria of erosion-deposition and its promotion are −1 (or c -33.33-1) and 0 (or (0.06 + 3.257 c 54.61)-1-1). A chart based on net water supply and c is devised representing four types of erosion–deposition and its promotion for the Luoshan-Hankou reach. Historical data over the past 65 years demonstrate that erosion-deposition and its promotion in the reach are respectively governed by c and net water supply; there is a remarkable shift from alternate erosion-deposition to monotonic erosion whilst the erosion-deposition effect remains consistent. The foregoing are in agreement with observed data, and comparable with data for the Jingjiang reach (affected by the three water-sediment diversion mouths). Satisfactory flood-control conditions in the convergence zone between the Yangtze mainstream and Dongting Lake accompanied by increasing erosion in the Luoshan-Hankou reach are predicted for the future. [ABSTRACT FROM AUTHOR]

• Under the action of concentrated flow, the change of surface runoff of karst gently sloping farmland is mainly controlled by the magnitude of concentrated flow. • Under the action of concentrated flow, the underground runoff of karst gentle slope farmland is significantly negatively correlated with the slope. • Concentrated flow can lead to severe soil erosion in karst gently sloping farmland. Exposed bedrock in karst areas considerably alters runoff paths causing partial runoff to converge into a concentrated flow, which is a potential source of soil erosion risk. However, research is lacking on how concentrated flow affects regional soil erosion. In this study, the surface and underground dual structure in karst areas was simulated in a steel tank. Combined with runoff plot monitoring, the runoff conversion process and erosion characteristics of gently sloping farmland in karst areas under different water discharge rates were examined through indoor concentrated flow discharge scouring tests, and the influence of concentrated flow changes on the runoff spatial distribution and sediment yield in gently sloping farmland was clarified. The results demonstrated the following: (i) there existed a significant positive correlation between surface runoff and the water discharge rate (p < 0.01); the partial correlation coefficient value reached 0.87. The higher the water discharge rate, the more surface runoff formation was facilitated. (ii) When the slope remained the same, the underground runoff was relatively high at 3 L/min. Given the same discharge, a significant negative correlation between underground runoff and slope was found (p < 0.05); the partial correlation coefficient value reached −0.71. (iii) In response to a water discharge rate of 5 L/min, surface soil erosion was serious, and the maximum sediment transport modulus was 174.088 g/min∙m2. A significant cubic function relationship existed between the scouring time and surface sediment yield. Overall, a critical flow rate occurred between 3 and 5 L/min, which controlled changes in surface runoff, subsurface runoff and surface sediment yield. Under highly concentrated flow, drastic soil erosion could occur. These results can provide a scientific basis for the control and prevention of concentrated flow-induced erosion in karst areas. [ABSTRACT FROM AUTHOR]

Eroded sediment is an important feature of permanent gully's development; however, obtaining the specific characteristics of the sediment transport in the gully can be difficult. Thus, a composite fingerprinting technique, incorporating uncertainty analysis, has been employed to investigate the mean relative contribution of sediment sources in permanent gullies. In this study, 31 tracers were measured at 62 different sampling sites from three layers of a gully wall [surface layer (SL), sandy soil layer (SSL), and semi-weathering rock layer (SWL)] and 36 sediment samples from the slumping deposit and alluvial fan of the gullies. The sediment source tracing procedure was therefore used to assess the relative contribution of each source. The mean relative contribution from the SL to the sediment of the slumping deposit is higher in the active gully (G1), and is relatively lower in the potentially stable (G2) and stable gullies (G3); thus there was no obvious gully bank retreat in G2 and G3. In different places of the G1 alluvial fan, the mean relative contribution of the SL, SSL and SWL ranged from 9–11, 36–43 and 46–55%, respectively. However, the sediment contribution of the SL increased in G2 and G3 due to the changes in the erosion type. The mean relative contributions of the SL were 33 ± 5 (G2) and 30 ± 3% (G3). These findings have important implications for the establishment of a scientific basis for permanent gully sediment transport management and control policies. [ABSTRACT FROM AUTHOR]

Understanding how subaqueous sediment gravity flows (SSGF) evolve in time and space, and how their deposits vary spatially, is a key research focus for gravity flow sedimentology. This study investigates depositional facies, depositional elements, and sediment transport processes of supercritical flows and hybrid event beds (HEBs) of the Lingshandao Formation in Lingshan Island, Eastern China. Three kinds of depositional elements were recognized: mass transport deposits (MTDs), channel-lobe transition zone (CLTZs), and lobe complexes. MTDs can be sub-divided into proximal and distal deposits. CLTZs are characterized by facies changes from massive coarse-grained pebbly sandstone to backset bedding sandstone in a down-slope direction, which are the deposits of supercritical turbidity currents. HEBs are common in both proximal and distal lobe settings. Tripartite structure in HEBs, which may be caused by up-slope substrate erosion, implies a relatively proximal origin compared with bipartite HEBs, perhaps caused by fluid fractionation in the research area. The succession is formed by a prograding lobe unit, followed by MTDs which are themselves overlain by deposits from a CLTZ. This vertical stacking pattern implies the potential longitudinal facies tract from CLTZ; to lobe complex deposits, is accompanied by emplacement of MTDs at the slope break. The flow types accompanied by sediment transport processes imply that erosion by supercritical turbidity currents associated with a hydraulic jump in the channel-lobe transition zone may be the main reason for mud-clasts and matrix addition to the flow. The large-scale addition of mud-clasts and suspended mud may dampen turbulence in proximal to medial lobe settings, and result in medium-to thick-bedded HEBs with common erosional features and tripartite structures. The remaining suspension flow (with abundant mud) may further transport down-dip and form medium-to thin-bedded HEBs with bipartite structures and rare mud-clasts. These findings may be applicable to other SSGF systems with supercritical flow deposits and hybrid event beds, emphasizing the downdip and lateral variation in depositional elements associated with gravity flow evolution. • CLTZs are characterised by bypass lags, backset bedding, cut-and-fill deposits, soft sediment deformation structures. • The erosion by supercritical turbidity currents caused mud matrix and clasts being added to the flow, and result in HEBs. • Vertical distribution represents the longitudinal sediment transport processes from CLTZ to lobe complex deposits. [ABSTRACT FROM AUTHOR]

Earthworms are ecological engineers that play an important role in hydrological processes and soil erosion by their burrowing and casting activities. Little is known, however, about the ecological function of the activities of an anecic species (Metaphire guillelmi) from the Loess Plateau in China where the soil is severely eroded. We conducted rain-simulation experiments on artificial slopes (mesocosms) filled with soil from Loess Plateau. Two rain intensities (90 and 120 mm h−1) and slope gradients (5° and 15°) were used to investigate the influences of earthworm activity on runoff and soil loss under multiple conditions. Data from 15 d of earthworm activity and 1 h of rain indicated that earthworm activity significantly reduced runoff but aggravated soil erosion. Runoff initiation time increased 2.7–3.1-fold, contributing to the promotion of water infiltration, and the amounts and rates of runoff were 35.8–61.6% and 35.1–60.8% lower under earthworm activity than the controls, respectively. Earthworms greatly influenced the physical and chemical properties of the soil, and these properties were strongly correlated with runoff initiation time and cumulative runoff. The surface casts produced by the earthworms on the soil surface were completely dispersed, increasing the cumulative sediment by a maximum of 169%. Both rain intensity and slope gradient greatly influence runoff and soil detachment, but with earthworm activity, slope gradient was more influential due to its superior contribution to sediment transport. This study quantified the effects of M. guillelmi on runoff and soil erosion and provides basic data for developing a more integrated control of soil erosion on the Loess Plateau. • The increase in infiltration related to earthworm activities decreases runoff. • Soil erosion is aggravated by the low stability of surface cast under intense rainfall. • Earthworm impact on soil loss is larger at lower rain intensity and steeper slope. [ABSTRACT FROM AUTHOR]

• An efficient 2D shallow water hydro-sediment-morphodynamic model is presented. • Morphodynamic processes under the impact of cascade movable weirs are studied. • Disparate morphological changes may result under different operation schemes. • An alternating operation scheme is proposed to constrain morphological changes. Cascade movable weirs have been increasingly widely used for river landscaping, water storage and ecological wellbeing. The weirs disturb the prior equilibrium in line with fluvial hydrology, sediment transport and geomorphology, and may lead to profound changes in the river, of which, however, the understanding has so far remained poor. Here, the first of its kind, a computational modelling study is presented on the morphodynamic processes under the impact of cascade hydraulic lifting dams, a type of movable weirs, as to the middle Fen River, China. A two-dimensional shallow water hydro-sediment-morphodynamic model is applied to resolve the fluvial processes, which is physically coupled and computationally efficient based on Finite Volume Method, unstructured mesh, local time stepping and parallel computing. Computational results show that the cascade dams alter the flow and sediment transport locally and on the reach scale in a distinct manner under different operation schemes, which in turn incur disparate morphological changes. Collapse of all the dams all year round would lead to net degradation in the study reach, with the floodplains aggrading and the main channel degrading. Operation of all the dams all year round may induce an overall aggradation both on the floodplains and in the main channel. If all the dams collapse in flood seasons and operate in dry seasons (CF), degradation occurs in the main channel whereas the floodplains experience aggradation, with a net degradation. When only the dams in the main channel operate all year round (OM), the floodplains degrade while the main channel aggrades, resulting in a net aggradation in the study reach. Either aggradation or degradation may prevail locally on floodplains, in main channel and individual subreaches. The present findings lead us to propose a complex operation scheme of annually alternating CF and OM to constrain significant morphological changes. [ABSTRACT FROM AUTHOR]

Summary: After the Yangtze River was closed by the Three Gorges Project (TGP) in 2003, erosion occurred from the dam site to the river mouth, especially in the middle and lower reaches of the Yangtze River. However, in some local areas of Chenglingji reach which holds the key position for flood management, there is actually deposition in contrast to the expected erosion. In this paper, a one dimensional mathematical model of the river network with sediment transport is used as the tool to simulate flow and fluvial processes. The calculation domain is from Yichang, which is downstream of the dam, to Hankou, the controlling node of flood management, 694km long in total. The model is calibrated based on the field data of hydrology and sediment transport during the period from October 2003 to October 2008. Then the model is utilized to simulate the erosion and deposition of the middle and lower reaches of the Yangtze River in the next two decades, and produce the results of a new river channel after river bed deformation occurs. The typical flood processes of 1954 and 1998 in the Yangtze River basin are used to check the flood management scheme for the research area, and results show that water storage of Three Gorges Reservoir (TGR) and a flood diversion program downstream of the Yangtze River should be taken into consideration. [Copyright &y& Elsevier]

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]

Abstract: We examined runoff and sediment transport associated with large-scale construction projects in Fujian Province, China. Six experimental plots, comprised of four plot types, were designed to mimic typical conditions immediately following disturbance. It was found that natural vegetative cover reduces both runoff and erosion by approximately 36 and 7457 times over bare ground, and 16 and 1801 times over typically planted grasses, respectively. The increase in erosion associated with the replacement of native vegetation with bare ground or grasses due to large-scale infrastructure projects in Fujian from 1999 to 2004, amounted to an estimated loss of 1.76×107 tonnes of top soil and 3.04×108 m3 of surface runoff from the province during the bare soil construction phase, and an additional 4.25×106 tonnes of top soil and 1.35×108 m3 of surface runoff from the province associated with the first year of operation for each project. This has implications for frequency and occurrence of landslides and other geographic hazards, the transport of chemicals into waterways, the transport of goods through shipping passages, and the fertility of land in Fujian. [Copyright &y& Elsevier]

Abstract: The largest plain in the North Vietnam has formed by the redundant sediment of the Red River system. Sediment supply is not equally distributed, causing erosion in some places. The paper analyzes the evolvement and physical mechanism of the erosion. The overlay of five recent topographical maps (1930, 1965, 1985, 1995, and 2001) shows that sediment redundantly deposits at some big river mouths (Ba Lat, Lach, and Day), leading to rapid accretion (up to 100m/y). Typical mechanism of delta propagation is forming and connecting sand bars in front of the mouths. Erosion coasts are distributed either between the river mouths (Hai Hau) or nearby them (Giao Long, Giao Phong, and Nghia Phuc). The evolvement of erosion is caused by wave-induced longshore southwestward sediment transport. Meanwhile sediment from the river mouths is not directed to deposit nearshore. The development of sand bars can intensively reduce the erosion rate nearby river mouths. Erosion in Hai Hau is accelerated by sea level rise and upstream dams. Sea dike stability is seriously threatened by erosion-induced lowering of beach profiles, sea level rise, typhoon, and storm surge. [Copyright &y& Elsevier]

The article reports on the survey of flow dynamics and sediment transport to assess secular denudation rates on Tianshan Qu mountain in China. It shows that the chemical weathering accounts for more than one third of the total denudation rate, noting that sediment transported as bed load cannot be neglected in the balance. It suggests that the resolution of the incompatibility has an important consequence to the understanding of the interplay between erosion and tectonics.

Abstract: This paper summarizes process-oriented field and numerical studies undertaken on the river plume in the partially-mixed Changjiang River estuary. Both estuarine circulation and tidal asymmetry are of great importance to the fine sediment processes. Mean suspended sediment concentration (C̄) and bottom shear stress are the dominant physical parameters controlling the flocculation and settling velocities (w s ) of mud flocs in suspension. Two important physical processes are revealed by acoustic imaging, i.e. (i) the near-bed impulsive resuspension and (ii) the transport processes driven by fine sediment-induced plumes during a spring tide. A turbidity maximum, associated with a suspended sediment front, is observed. Its formation is caused mainly by tidal asymmetry, near-bed periodic tidal resuspension and turbulence suppression by suspension/salinity stratifications. A conceptual sketch of the turbidity maximum is cautiously proposed for the Changjiang River estuary. Four different settling velocity equations, taking flocculation into account, have different effects on the modeled concentration profiles of fine sediment: apparently, Cao and Wang (1994, pp. 252–253) would be the best for spring tide and Thorn (1982, Fig. 3/page 66) for neap tide. Both tidal acceleration and tidal deceleration have strong effects on the concentration profiles of fine sediment within the Changjiang River estuary. [Copyright &y& Elsevier]

Abstract: In this study we applied 40Ar/39Ar dating methods to muscovite grains in sands from the modern Red and Yangtze Rivers in order to constrain palaeo and modern erosion patterns and sediment transport processes. Micas in the headwaters of the Red River and its southern Da River tributary are dominantly Cenozoic, while the northern Lo River tributary shows a typical 160–220Ma population. The lower reaches of the Red River comprise 53% of such Triassic grains, indicating that the Lo River is the most important net contributor to the modern delta. However, this contrasts with zircon U–Pb data indicating that the upper reaches of the Red River dominate that mineral group. We suggest that the mismatch reflects the rapid transport of mica relative to zircon in the river and the fact that the Red River is not in equilibrium. We hypothesize that the zircons were eroded >8ka under a regime of stronger monsoon that enhanced erosion in the northern drainage basin, while modern erosion is focused in the south, especially in the Song Chay Massif. Micas from the upper Yangtze River are resolvably older than those in the Red River (230–250Ma), so that this method could be used to test for drainage capture in palaeo-delta sediments. Micas in the modern Yangtze delta are generally much younger than those in the upper reaches and indicate that erosion in the Longmen Shan (Sichuan) and neighbouring regions is more important than the upper Yangtze in supplying sediment, reflecting the stronger monsoon rains in those areas. [Copyright &y& Elsevier]

Abstract: This paper presents a three-dimensional (3-D) numerical model to simulate morphological changes in alluvial channels due to bank erosion. A method for the simulation of bank erosion is established. This is incorporated into a 3-D mathematical model for turbulent flow and non-uniform, non-equilibrium sediment transport. This model is applied to simulate morphological changes in the Shishou bend of the middle Yangtze River in China, where serious bank erosions occurred during the last two decades. The double-layer sediment structure of the riverbank on the middle Yangtze River is taken into account in the bank erosion module. Both cohesive and non-cohesive bank material in the different layers are considered. The bank erosion module also includes other factors affecting the rate of bank erosion, such as the longitudinal length of failed bank, the thickness of each layer in the double-layer structure, and the erosion-resisting effect of cohesive material from the top layer of failed bank. A locally-adaptive grid system is proposed to efficiently simulate the lateral migration of alluvial channel due to bank erosion. The predictive capability of the 3-D model is examined by laboratory data. Simulated processes of bank erosion agree with field observations in the Shishou bend during the period of October 1996–October 1998, and the bank erosion module plays a significant role in simulating morphological changes of the study reach. In addition, the equivalent channel-forming discharge, which is defined as a constant discharge that can create the same amount of bank erosion in an alluvial channel as that created by natural runoff processes during the same period of time, is proposed to improve calculation efficiency for feasibility studies. [Copyright &y& Elsevier]

This note, using a three-dimensional model of river flow and sediment transport, examines the effect of the vertical resolution and the choice a nonequilibrium adaptation length Ls in predicting flow and sediment transport around groins in China’s Yongding River. The results show that a fine vertical grid and nonequilibrium sediment transport model provide good predictions, especially on the river bed profile with an obvious main channel and flood plain. [ABSTRACT FROM AUTHOR]

The modern Yellow River Delta is formed by fine-grained sediments through fast transportation and accumulation. Its coast is characterized by partially consolidated bed structure, high water content and weak erosion resistance. Despite recent advances in numerical morphodynamic modeling techniques, the current ability to predict long-term coastal changes at the Yellow River Delta is hampered by the lack of reliable data on the erosion resistance of the sediments deep in the bed. This paper describes a laboratory-based erosion study using a 30 m sediment core collected from the tidal flat on the northern coast of the Yellow River Delta in April 2004. The influence of various sediment properties such as bed stratification, grain composition, wet bulk density and water content on the measured erosion resistance has been analyzed in detail. The results reveal that there exist a definite negative relationship between the critical erosion shear stress and water content or median diameter, and also a clear positive relationship between the critical erosion shear stress and clay content. For the sediments of the same type, there was a positive relationship between the critical erosion shear stress and wet bulk density. It was also found that the erosion resistance changes considerably through depth with the lowest being near the surface and the highest at a depth of 9.1–13.5 m. The relationship between erosion rate and shear stress for erosion was shown to be dependent in a complex way on the grain distribution, sedimentation structure, wet bulk density and water content of the sediments. A number of distinct erosion behavior have been identified and although in most cases the erosion rate (ε) can be related linearly to the net bed shear stress (τ-τc), further study is needed to establish the erosion-stress relationship for the case where the erosion seems to show undulating behavior. [ABSTRACT FROM AUTHOR]

Sand extraction from the mid-lower Yangtze has increased rapidly since the 1980s, in contrast to a rapid decrease in sediment discharge from the Yangtze River into the sea. In-channel sand extraction poses great risks to flood protection, navigation channels and railway bridges. This paper reviews the recent history of in-channel sand extraction, discussing the present status and potential problems in legislation and management. It is concluded that the share of interests, the involvement of local criminal gangs and official corruption were the main difficulties for the ban on illegal sand extraction. It is proposed that the sites and amounts permitted for in-channel sand extraction should be re-evaluated under the new sediment budget after closure of the Three-Gorges Dam. It is necessary to explore the use of alternative materials in order to reduce the demand for natural sand while meeting the market needs for socio-economic development. [ABSTRACT FROM AUTHOR]

Yang's unit stream power formula is modified for the computation of total bed-material load in a sediment-laden river with a high concentration of fine suspended materials. Theoretical and laboratory studies indicate that modification can be made on the values of particle fall velocity, flow viscosity, and relative specific weight without any change of the coefficients used in Yang's original formula. Comparisons between computed results from the modified formula and field indicate that the modified formula can be used to compute total bed-material load in the Yellow River with accuracy. [ABSTRACT FROM AUTHOR]

• Mud samples in the LD estuary were measured using U-GEMS, and average τ ce of 0.26 N/m2 was obtained. • The simultaneous paradigm with τ ce of 0.26 N/m2 well explained the measured SSCs during the dry season. • The simultaneous paradigm with τ ce of 0.15 N/m2 agreed better with observations during the wet season. • The simultaneous deposition paradigm was better for SSC modelling during both the wet and dry seasons. Suspended sediment and the surficial sediment in most estuaries throughout the world consist of fine particles. Modelling cohesive sediment transport is an important way to explore the morphological evolution of estuaries where cohesive sediment is dominant. Various values for critical shear stress and deposition paradigms for cohesive sediment transport were evaluated here by analysis of field samples combined with numerical simulation in the Lingdingyang (LD) estuary in China. A UMCES-Gust Erosion Microcosm System (U-GEMS) experiment using field samples suggests that the experimental average value of critical shear stress for erosion (τ ce) is 0.26 N/m2. Two conflicting paradigms, i.e. mutually exclusive versus simultaneous erosion and deposition, are commonly used for cohesive sediment transport. Simulations of tidal currents and sediment transport during the wet season of 2007 and dry season of 2016 in the LD estuary were conducted under these two paradigms using the TELEMAC-2D hydrodynamic module and the sediment module SISYPHE in the TELEMAC model. Model verification under these two paradigms was carried out, and the τ ce parameters in the TELEMAC model were revised based on a U-GEMS experiment. The results showed the following. (1) The simulation results of the model in the LD estuary were satisfactory when an experimental average τ ce value of 0.26 N/m2 was used. (2) The simultaneous paradigm using a τ ce value of 0.26 N/m2 well explained the changes in the field-observed depth-averaged suspended sediment concentrations under all tidal regimes during the dry season, whereas the simultaneous paradigm using a τ ce of 0.15 N/m2 was more similar to observations in the LD estuary during the wet season. [ABSTRACT FROM AUTHOR]

The article discusses the research paper "Back Analysis of the Draining Process of the Tangjiashan Barrier Lake," by Zuyu Chen and colleagues. Topics discussed include the hyperbolic erosion model, uncertainties of dam breach modeling, and sediment transport models for surface erosion and breach evolution processes.

Xia, Junqiang, Zhengbing Wang, Yanping Wang, and Xin Yu, 2012. Comparison of Morphodynamic Models for the Lower Yellow River. Journal of the American Water Resources Association (JAWRA) 1-18. DOI: 10.1111/jawr.12002 Abstract: Significant channel adjustments often occur during flood seasons in the Lower Yellow River (LYR), and it is a challenging work to accurately simulate the morphodynamic processes in the LYR using numerical models. A comparison of two morphodynamic models (Delft3D and 2DLLCDM) for the LYR is presented herein to identify critical improvements for these models. The concepts of these models are first compared with each other. The models were then used to simulate the processes of flood routing, sediment transport, and morphological changes occurring in a braided reach of the LYR. The differences were investigated between the simulated results from these models and corresponding field measurements, and the results indicate that: (1) the hydrodynamic processes calculated by both models agree closely with the measurements if an appropriate Manning's roughness coefficient is used; (2) the concentrations of suspended load at the downstream boundary calculated by the models agree reasonably with the observed data; and (3) the predicted cross-sectional profiles obtained from these models do not correspond well with the measurements. Based on these findings, the weak aspects of the models are clarified, and three critical improvements are recommended, including: (1) the development of roughness predictor; (2) the refinement of graded sediment transport capacity formulation; and (3) the consideration of bank erosion module. These improvements need to be implemented in the future. [ABSTRACT FROM AUTHOR]