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• 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]

• 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]

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]

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]

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]