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• Numerical modeling approach to estimate time-varying river to riverbed travel times. • Advection-dispersion equation with time-dependent coefficients. • Tikhonov regularization is used to avoid spurious parameter fluctuations. • Substantially sub-daily flux transients in riverbed sediments of three urban rivers. Assessing solute transport in riverbed sediments is important for quantifying the effective reactivity of hyporheic sediments and the magnitude of exchange flows between rivers and their river beds. A typical approach of estimating transport in riverbed sediments is by measuring natural tracers such as fluctuations of temperature or electrical conductivity (EC) and fitting models to them that assume time-independent travel time distributions, implying steady-state flow. Here, we use a transport parameterization that is based on the advection–dispersion equation (ADE) with coefficients that continuously vary in time. The ADE is solved numerically and its solution is fitted to measured EC time series using Bayesian parameter inference. A continuous function of model parameters is constructed by smoothly interpolating between point values with different temporal resolution, and Tikhonov regularization is used to avoid spurious parameter fluctuations. The approach is tested using EC time series synchronously measured in river water and hyporheic porewater of two urban rivers in Germany and one urban river in South Australia. For all datasets the goodness of fit was improved by introducing a time-dependent EC offset. Estimated porewater velocities were highly transient in three out of the four datasets with values increasing by up to a factor of six over the course of a day. Flux transients were likely related to both variations of hydraulic gradients along and spatial shifting of flow paths. Comparison to stationary, non-parametric deconvolution indicated that transient flow may induce multimodality in stationary travel time distributions. Given the high temporal dynamics of transport in the streambed sediments of the three investigated urban rivers, we envision that the presented model is also a valuable tool to improve the assessment of reactive transport in riverbed sediments. [ABSTRACT FROM AUTHOR]

• Scale-specific controls of sediment load were identified in a seasonal inland river. • The combined method of MEMD and TDIC effectively address sediment transport process. • Predictions of sediment load using MEMD outperformed those made with the original dataset. Sediment transport is a multi-scale and non-linear process controlled by multiple variables. Given the intricate nature of sediment transport mechanisms and the overlap of different factors' effects on it at various time scales, unraveling the relationship between sediment load and its influencing factors is challenging. This study aimed to elucidate the multi-timescale effects of factors on monthly suspended sediment load in a seasonal inland river. In this study, monthly sediment loads measured by the depth-integrating method were obtained from the Tabu River Basin in northern China from 2007 to 2021, alongside data on four controlling factors: runoff, precipitation, water surface evaporation, and the normalized difference vegetation index (NDVI). The results showed that sediment load, runoff, and precipitation showed strong variability during 2007–2021, while water surface evaporation and NDVI exhibited moderate variability. Multivariate empirical mode decomposition (MEMD) decomposed the temporal patterns of sediment load and associated variables into five intrinsic mode functions (IMF) and a residue. IMF1 (4.7 months), IMF2 (9.0 months) and IMF3 (14.2 months) collectively explained 115.88 %, 91.73 %, 91.28 %, 107.69 %, and 106.09 % of the total variability in sediment load, runoff, precipitation, water surface evaporation, and NDVI, respectively. Subsequently, the time-dependent intrinsic correlation (TDIC) was utilized to illustrate the inherent relationships between sediment load and its controlling factors across various time scales. The associations between sediment load and the controlling factors changed significantly with the scale. Runoff was the dominant factor controlling sediment load at IMF1 (4.7 months), IMF2 (9.0 months), IMF3 (14.2 months), and IMF4 (25.1 months). Water surface evaporation controlled the sediment transport process at IMF5 (63.6 months). The prediction of sediment load on the measurement scale, using scale-specific controls analyzed with MEMD (R2 = 0.993), demonstrated superior performance compared to traditional multiple linear regression prediction (R2 = 0.748). This study will provide a theoretical basis for effective prevention and control of soil erosion and watershed management in inland river basins. [ABSTRACT FROM AUTHOR]

• Key aspects of the meandering flow dynamic include convective flow redistribution and cross-circulatory motion. • The above two flow mechanisms associates two different bed deformation patterns. • Decreasing B / h ratio enhances the sediment transport, activing meandering river migration. Meandering is one of the most common planforms of rivers, however, the ecological and fluvial integrity of meandering rivers are under challenges, resulting from increased anthropogenic pressure and extreme climate events. The present study elucidates the morphodynamics of meandering streams under variations of width-to-depth ratio (B / h) by delving into the two dynamic processes underlying within the flow, i.e. cross-circulatory motion and convective redistribution of the longitudinal flow velocity. Series of numerical simulations are performed in 70° sine-generated meandering streams under increasing flow depth that necessitates a wide range of B / h , characterizing flume experiments to large scale natural rivers. The radial flow structures and the early bed deformation patterns are computed and elucidated. Among the classical cross-circulatory flow patterns, outer bank cell occurs for flows having B / h < 9. Next, the different bed deformation patterns reveal the shift of significance in the driving forces of the bed deformation regarding different B / h ratio. At B / h = 100, bed deformation is dominated by the convective redistribution of the downstream velocity that causes longitudinal adjacent erosion–deposition zones. This implies downstream migration tendency of meander loops. At B / h = 12, the intensified cross-circulatory flow deflects the sediment trajectory, causing extra laterally adjacent erosion–deposition zones that necessitate the lateral expansion tendency of the loop. Decrement of B / h ratio (from 100 on ward) critically enhances the non-equilibrium transport of sediment that can lead to active fluvial evolution of meandering rivers. Overall, the results can be used to improve river management and restoration. [ABSTRACT FROM AUTHOR]

• A thermal infrared imaging observation system was established to measure overland flow velocities. • The system reached high precision (SD 0.004 m·s−1) high temporal and spatial resolutions (1/9 s, 2 mm). • This study provided a reliable way to measure shallow flow velocity to understand the mechanisms of soil erosion. Flow velocity is an important physical parameter in characterizing the hydraulics of water flow. The accurate measurement of overland flow velocities has great significance for understanding and modeling sediment transport and soil erosion. In this study, a Thermal Infrared Imaging Observation System (TIIOS) based on thermal infrared imaging techniques and computer vision recognition technology was established to measure overland flow velocities under controlled laboratory conditions. TIIOS has three subsystems including thermal tracer control, image acquisition and transmission, and image storage and processing. It can be used to dynamically monitor changes in shallow flow velocity by means of automatic control of thermal tracer, instantaneous image acquisition, image correction, noise removal and centroid determination. The observation precision was high with a standard deviation of 0.004 m·s−1 for flow velocity, a temporal resolution of 1/9th s, and a spatial resolution of 2 mm. The new system achieved higher accuracy compared to the traditional dye tracing and salt tracing techniques in observing the dynamic transport process of thermal tracer movement. The relative errors of the centroid velocity measured by the TIIOS ranged from −9.83 % to 6.40 %; whereas the relative errors of centroid velocity measured by salt tracer ranged from −21.36 % to 17.22 %. Measurements by the established TIIOS under different hydraulic conditions demonstrate that the relative errors of the centroid velocity are all smaller than those of the leading-edge velocity. This observational system provided a reliable way to measure shallow flow velocity for better understanding the mechanisms of water erosion processes and showed its potential to be used in field experiments under natural conditions. [ABSTRACT FROM AUTHOR]

• A novel self-contained hydrodynamic observation platform system was deployed to monitor flow and sediment with ultra-high-resolution in the Yarlung Tsangpo River. • Temporal-spectral analysis with ultra-high-resolution revealed the asynchronous variations of flow and sediment over nearly two months. • The varying behaviors of flow and sediment in different flood events was distinguished using ultra-high-resolution data. Traditional monitoring techniques of flow and sediment are inadequate for the sparsely populated, the rivers in the Qinghai-Tibetan Plateau region which are experiencing amplified climate change. Inspired by the Euchiloglanis fish, this study developed a unique self-contained hydrodynamic observation platform to withstand the high velocities of mountain rivers typically encountered in mountain rivers. The platform, equipped with sensors, was successfully deployed in the Yarlung Tsangpo River, collecting ultra-high-resolution data on flow and sediment over a period of nearly two months. Performance assessments showed that the median value of discharge per unit width measured and suspended sediment concentration by this system were basically consistent with those daily measurements from the hydrological station. Meanwhile, the superiority of the system was reflected in the more significant daily average change, especially at the flooding period. The data unveiled significant minute-level hydrological fluctuations and a complex interplay of factors affecting the river's flow and sediment transport. A wavelet coherence analysis revealed asynchrony changes in short-period flow and sediment variables. Persistent short-period and coherent long-period signals are significantly displayed during flood events. The platform promises future applications, such as automated benthic observations and replacing traditional 'lead-line' methods. Despite acknowledging system limitations of underwater attitude, burying tendency, and real-time data transmission capabilities, the study highlighted the crucial role of this system in understanding and managing river dynamics, particularly amid escalating environmental threats. [ABSTRACT FROM AUTHOR]

• Flume experiments were conducted to assess the impact of submerged flexible vegetation on regular wave attenuation and beach morphology. • The presence of vegetation prevented further erosion of the beach, resulting in a reduction of 7% to 63% in experiments. • The attenuation caused by vegetation results in the wave breaking point being closer to the shoreline on vegetated sand, leading to shoreline retreat. • A dimensionless equation was developed to characterize the behaviour of the cross-shore beach profile under the protection of flexible vegetation. Coastal protection methods are evolving from hard engineering techniques to natural enhancement approaches. Aquatic vegetation provides an environmentally friendly solution by effectively dissipating waves and resisting erosion. Laboratory flume experiments were conducted to investigate the effect of submerged flexible vegetation on the regular wave attenuation and cross-shore profiles on the artificial plane beach under varying hydraulic conditions. Variations in the waveform, wave spectrum, and wave height were analysed in the vegetation zone. Results show vegetation distorts the waveform and accelerates the attenuation process of the wave energy, and wave height evolution behaves differently from the theoretically obtained attenuation by Mendez and Losada (2004) due to the underestimating vegetation-induced attenuation and neglecting sediment-induced attenuation. Additionally, the formation process of the winter and summer profiles of the vegetated beach was analysed by the screenshots. Regenerated wave breaking becomes more apparent with increasing wave periods. The critical surf similarity parameter of the vegetated beaches was found to be lower than that of a smooth, impermeable slope because of the energy dissipation. Vegetation did not alter the type of the beach profiles, as compared to the final profiles and their characteristic parameters of the unvegetated beaches. Instead, it reduced the erosion depth and brought the eroded area closer to the shoreline. Dimensionless parameters were formulated to characterize the response of the cross-shore beach profile under the shelter of flexible vegetation, and an empirical equation about maximum erosion depth was developed within the scope of the experiment. [ABSTRACT FROM AUTHOR]

• Newly eroded sediment leads to decrease in resuspension age. • In areas where advection dominates, sediment suspension persists for a longer duration. • The vertical distribution of resuspension age is shaped by stratification. The concept of resuspension age was employed to assess the timescales of vertical sediment transport in the Changjiang Estuary (CJE) and its adjoining areas. Resuspension age refers to the duration elapsed since particles last made contact with the seabed. Energetic tidal current in the study area results in a significant amount of sediment being eroded into the water during spring tides, causing the resuspension age to consistently remain lower during spring tides compared to neap tides. Spatially, consistently low resuspension ages occur in the North Branch and turbidity maximum because suspended sediment in these areas primarily originates from local erosion. While advective sediment dominates in the HZB, leading to highest resuspension age there. During the wet season, the South Branch experiences an average resuspension age surpassing 10 days, primarily due to particles predominantly transported from the river. Sediments deposited on the seabed during the wet season become the primary source of suspended sediment after being eroded into the water column during the dry season, leading to a reduction in resuspension age. Likewise, the decrease in resuspension age in the Subei Coast during the dry season is closely associated with the appearance of sediment mass advected by the northern branch plume. When stratification occurs, the upward diffusion of sediment is impeded, constraining newly eroded sediment close to the bed. As a result, these sediments exhibit lower ages than those in the upper water column, where sediment transport is primarily dominated by horizontal advection. [ABSTRACT FROM AUTHOR]

• Decrease of suspended sediment transport in the Mediterranean over the last century. • Time series reconstruction using artificial intelligence. • Crucial role of climate change in the regulation of suspended sediment transport. • Secondary influences of the anthropic impact. The analysis of suspended sediment transport and of its variations over time is crucial for understanding environmental evolution and it is the key to future challenges caused by current global warming. The Mediterranean area is a hot spot for global changes, and the variation of precipitation amount and intensity will modify the environment of this region. In this work, we analyse the time series of suspended sediment transport of two rivers located in central Italy by using statistical and artificial intelligence techniques. Our study aims to re-analyze time series of suspended sediment transport, in order to demonstrate that climate change is responsible for the substantial decrease in the amount of sediment over the past century, in relation to the atmospheric teleconnections of the North Atlantic. Anthropic pressures like reforestation, land use change, and dam building have influenced the sediment transport capacity of rivers, causing a reduction of sediment concentration in water. These results are key factors to determine the future management of the Mediterranean areas, where the future scenarios predict a greater drop in yearly precipitation, and therefore a possible further decrease in the sediment transport capacity of the rivers, with major consequences for coastal and fluvial environments. [ABSTRACT FROM AUTHOR]

• Hydrological and erosive response at event scale for a recently burned catchment. • Comparison of two hydrological models, OpenLISEM and MOHID Land. • Parametrization based on variation in boundary conditions characterizing each event. • Models performance revealed the importance of subsurface flow at event scale. • Ash and sediment movement during large event needs different model parameterization. Wildfires are a source of instability for the natural water cycle in forested watersheds, endangering the water quantity and quality reaching downstream water bodies. The faster hydrological response of a burned area leads to increased runoff and transport of sediment and ash particles during and after rainfall events. Therefore, the use of an adequate spatiotemporal resolution in hydrological models is necessary to properly estimate post-fire impacts. Especially when addressing hydrological events such as flash floods and debris flows, which are highly unpredictable and are characterized by short duration and high impact outside the burned area. This study aims to compare the ability of two hydrological models to simulate the hydrological response and sediment transport during the first year after a fire to ultimately understand which one would best serve as a post-fire hydrological predicting tool at event scale. To achieve this goal, OpenLISEM, an event-based hydrological model, and MOHID Land, a continuous model with variable timestep, were compared. Driven by several limitations identified in previous modeling exercises at this scale during the calibration phase, this work performed a parametrization through the variation in boundary conditions characterizing each event. OpenLISEM and MOHID Land models exhibited similar capabilities in simulating runoff during the first post-fire year. However, the larger erosion input parameters required by MOHID Land increase the complexity of erosion prediction and increase equifinality. In addition, MOHID Land limited capacity to perform sensitivity and uncertainty analyses emerged as a major disadvantage, hindering the assessment of the reliability of the model's predictions. Despite its limitations for not integrating subsurface flow and base flow, OpenLISEM is the most suitable model for assessing post-fire impacts on runoff and sediment production at the event scale, because of its ease of implementation and its reduced computational requirements. [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]

• We used a tracer-based approach to quantify melt water proportions related to sediment transport at two contrasting Alpine proglacial streams. • Glacier melt was associated with higher bedload concentrations at the debris-covered glacier and much lower concentrations at the clean ice glacier. • Glacier size, presence of debris cover, and substrate were identified as the main drivers of melt dynamics and sediment transport at both glaciers. Subglacial sediments are a large component of the sediment budget of glacierized catchments but insights into the subglacial origin of sediments (bedload, in particular) linked to proglacial runoff dynamics remain scarce. In this study, we use a tracer-based approach to quantify meltwater proportions related to sediment transport at two proglacial streams, draining glaciers (named debris-covered and clean glacier) of different size, aspect and elevation range with contrasting distribution and thickness of debris cover and lithology of the subglacial sediments (i.e., metamorphic vs. sedimentary), in the Sulden/Solda catchment (Italian Alps). Results indicate that the glacier melt component (75 to 80 %) was associated with bedload concentrations of 1 to 10 kg m−3 at the debris-covered glacier and much lower concentrations of 0.01 to 1 kg m−3 at the clean ice glacier. At the seasonal scale, bedload and suspended sediment concentrations at both sites strongly varied with discharge. While daily bedload concentrations varied by up to two orders of magnitude obscured the seasonal development of bedload concentrations at both sites, a clear seasonality for suspended sediment concentrations was found. At the daily scale, the relationship of discharge, bedload, and suspended sediment was more complex because discharge and sediment transport did not always follow the daily variation of air temperature, or similar daily air temperatures resulted in different discharge and sediment transport responses and vice versa. Glacier size, presence of debris cover, and substrate were identified as the main drivers of meltwater dynamics and sediment transport at both glaciers. This study adds further insights into the interplay of meltwater contributions and sediment transport, which are essential to better assess the impact of climate warming on sediment supply in glacierized catchments. [ABSTRACT FROM AUTHOR]

• Analytically compared two approaches on the downstream variation of peak velocity. • Newly derived and evaluated a downstream hydraulic geometry relationships. • All the theoretical results were found to be well matched to those observed. • Especially, the downstream variation of peak velocity was found insignificant. This study compares three approaches to deriving the downstream hydraulic geometry (DHG) relationships: one by Leopold and Maddock (1953), a second by Huang and Nanson (2000), and the third in this study. The DHG relationships are the power function relationships between the downstream discharge and various variables, which include the flow velocity, channel width, channel depth, channel slope, and roughness coefficient. The DHG relationships can be described using a set of equations, including the continuity equation, flow velocity equation, and sediment transport equation. The derived relationships are then compared with the empirical results from previous studies worldwide, as well as those from two basins in Korea. As a result, first, all the theoretically derived exponents for peak velocity are found to be very small at around 0.1. This result supports the assumption that for a given rainfall event, the peak velocity in a basin remains unchanged. Simple regression analysis in this study also confirms that the change of peak flow velocity downstream is statistically insignificant. Through this, the assumption of a constant flow velocity within specific storm events may hold a certain degree of validity. Second, the range of the exponent for the channel width is found to be rather smaller at (0.4–0.6) than the those of the other two exponents. The range of the exponent for the channel depth is found to be (0.2–0.6), while that of the peak velocity to be (0.0–0.4). Possible reasons for this tendency have also been investigated in several studies, but have not yet been universally accepted. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stream power and soil clay content were used to model soil erosion rate. • Sediment sorting and transport were controlled by the soil properties. • A linear function was developed to quantify the sediment clay content. • The relative contributions of different transport mechanisms were quantified. Understanding the sediment sorting and transport processes is is crucial for enhancing the understanding of soil erosion mechanisms and improving soil erosion prediction. However, quantitative studies based on the coupling effects of both hydraulic parameters and soil properties are still lacking. In this study, five loessial soils with varying physicochemical properties were collected in the Loess Plateau of China, and simulated rainfall experiments were carried out in a metal box with a slope of 20 degrees under rainfall intensities of 1, 1.5, and 2 mm min−1. Runoff samples were collected to analyze the variation in erosion rates and effective particle size distribution of eroded sediments during the rainfall process. The results showed that the stream power was the optimal parameter to model the erosion rate, and a power function incorporating the clay content and stream power could well predict the erosion rate of different soils. The enrichment ratio indicated the enrichment of fine particles and depletion of coarse particles. And the sediment sorting degree increased with increasing soil clay content. The critical particle size for distinguishing different transport mechanisms varied among soils, with more than 55.46 % of the total sediment transported by suspension/saltation. A linear function and power function including the original soil particle size distribution and stream power were developed to quantify the sediment clay content and the relative contribution of different transport mechanisms. This study could be helpful to improve the soil erosion prediction model and provide basic guidelines for regional soil and water conservation. [ABSTRACT FROM AUTHOR]

• Human interventions affect the dynamics of meandering channels. • Unusual inner bank erosion and outer bank deposition occurred due to upstream damming. • Altered flow-sediment regimes and channel boundary drive the unusual meander dynamics. Human activities, such as reservoir construction and bank revetment, significantly alter downstream flow and sediment regimes and river channel changes, impacting river ecosystem services. However, our understanding of how intense human activities affect morphodynamics of meandering channels in big river systems remains incomplete due to the lack of high-resolution in-situ data. Here, we use comprehensive data encompassing hydrology and sediment, historical channel maps, and high-resolution river bathymetry to investigate the evolution of meandering bends in the Middle Yangtze River (MYR) across three distinct phases: the natural period (1490–1975), the bank revetment period (1975–2002), and the post-dam period (2003–2018). The study revealed that, in the absence of human intervention, the meandering channels of the MYR naturally experienced inner bank deposition and outer bank erosion, largely governed by curvature-induced secondary flow patterns in flow and sediment transport mode. In 1975–2002, outer-bank revetments reduced erodibility, stabilizing outer banks, while inner banks continued to experience lateral and vertical deposition, causing a narrower and deeper channel hydraulic geometry. Conversely, meandering bends had exhibited an unusual pattern of 'outer bank deposition and inner bank erosion' in 2003–2018. Channel morphological changes characterized by channel incision and widening were driven by changes from erodible bank boundaries to solidified bank boundaries, substantial reduction in suspended sediment concentration, and an altered and extended effective flow range (10,000–25,000 m3/s). Our findings highlight that human interventions such as damming and bank revetments can alter the conventional erosion–deposition morphodynamics of meandering bends in large river systems, carrying vital implications for sustainable river management in the Anthropocene. [ABSTRACT FROM AUTHOR]

• A new 2D meshless bedload sediment transport model is developed based on ESPH. • A formulation for calculating the time step size for an HLLC Riemann solver in a weakly coupled approach is proposed. • The simulated results based on the developed 2D ESPH-SW-BST model show good agreement with the measured results. • A particle configuration of eight interacting particles can yield more accurate predictions of erosion peaks in cases with significant lateral flow effects. A 2D Eulerian meshless bedload sediment transport model is developed using smoothed particle hydrodynamics (SPH) to simulate rapidly varied flows over mobile beds. In the developed model, we adopt a weakly coupled numerical approach to explicitly solve the governing equations, including 2D shallow water equations for fluid flow motion and the Exner equation for bed sediment movement at the same time step. A defined virtual bedload velocity in a weakly coupled approach is involved in the calculation of time step sizes. However, nonphysical virtual bedload velocities, which often occur in cases with nearly flat beds, require extremely small time step sizes. A formulation of the lower and upper bounds of information propagation speeds for an HLLC approximate Riemann solver is thus proposed to remedy the problem. Four case studies involving dam break flows in prismatic and erodible channels, knickpoint migration, dam erosion due to overtopping flow and dam-break flow in an erodible channel with an abrupt expansion are adopted to validate the developed model. In addition, to compare the performances of different particle interaction configurations under Cartesian uniform particle arrangements, four and eight interacting particles are obtained by changing the smoothing length. Against the measured results, the case of eight interacting particles shows more accurate predictions of erosion peaks along the measured cross-sections because the lateral flows are significant. The good agreement between the simulated and measured results shows that the developed 2D Eulerian SPH bedload sediment transport model with eight interacting particles is well suited for simulating complicated flow-induced bed erosion. [ABSTRACT FROM AUTHOR]

• Either climate data or streamflow data alone is not sufficient to accurately estimate SSL. • Gradient boosting models accurately predict SSL using hydro-climate data. • Hydrological metrics improve the accuracy SSL modeling during model calibration. • The prediction uncertainty of SSL increases with the basin's area. • Average ensemble modeling enhanced the accuracy of models in rivers. Machine learning (ML) models have the potential to improve the accuracy of Suspended Sediment Load (SSL) predictions. However, their ability to incorporate climate data to enhance SSL predictions remains underexplored. This study investigates the efficacy of ML models in modeling sediment transport using hydro-climate variables as input data. Boosted decision tree models, including Xgboost, LightGBM, and Catboost, were employed to estimate SSL using hydro-climate variables such as streamflow and precipitation, as well as maximum and minimum temperatures. The models were trained, optimized, and evaluated using either climate/streamflow data or a combination of both, encompassing 47 gauges across the contiguous United States (CONUS) between 1950 and 2022. The results demonstrate that streamflow data alone is insufficient for accurate SSL estimation in all rivers. Consequently, integrating climate data and streamflow data proved effective in predicting SSL at the daily scale across diverse climate zones with commendable accuracy. The models achieved an average Nash-Sutcliffe Efficiency (NSE) of > 0.66, Kling-Gupta Efficiency (KGE) of > 0.67, and Willmott Index (WI) of > 0.83 during the unseen (test) phase. These findings highlight the potential of ML models, particularly when combining climate data with streamflow, to enhance SSL predictions and improve our understanding of sediment transport dynamics. [ABSTRACT FROM AUTHOR]

• A strong signal of reduced winter conditions i.e. duration, snow accumulation and frost days. • Hydroclimatic regime shift alters the sediment flux seasonality in near future. • Thaw-seasons have important role controlling the annual sediment flux. Climate change alters high latitude hydrological cycle by diminishing the snow accumulation and spring flood magnitude, and by altering temperature and rainfall finally leading to hydroclimatic regime shift from snow-dominated to rain-dominated. These changes in temperature, precipitation patterns, and discharge strongly influence geomorphological processes in fluvial environments, leading to alterations in sediment transport, erosion, accumulation, and landscape changes. We conducted comprehensive analysis of hydroclimatic trends and shifts on boreal Oulanka River system, spanning over the past five decades. A strong signal of warming temperatures (+0.61 Celsius/decade), reduced winter conditions and warmer summers (+0.41 Celsius/decade) was detected. The spring flood magnitude diminished 7 %, but high discharge peaks (Q > annual p90m3/s) during other seasons increased 22 % together with 28 % increase of annual minimum discharge. Simultaneously, precipitation intensity increased during summer. The meander migration rate (mean 0.89 or 2.55 m/year) and bank erosion volume were interconnected to ground frost, high snow sum, high discharge, and high-water level during spring flood, but no significant long-term trends were observed. Our findings underscore that climate is the first-order control on fluvial geomorphology and emphasizes the complex interplay between various hydrological and climatic factors that shape the dynamics of river systems. Based on the results, we expect to see changes in the spatial–temporal distribution of high latitude rivers sediment flux in future. In addition, more attention should be addressed to the thaw seasons controlling the sediment transport, as majority of the observed shifts took place in these months. [ABSTRACT FROM AUTHOR]

• A threshold density for hydrodynamics between sparse and dense vegetation was found. • A secondary gyre that is generally missing in non-vegetated cavities was observed. • The mean retention time cannot be estimated with a single decay fit for all densities. • Vegetation further increases the macro-roughness function of lateral cavities. Large-Eddy Simulations (LES) were used to investigate the hydrodynamics and mass transfer between the flow in the main channel and a vegetated lateral cavity. Fourteen vegetation densities (0 to 10.65 %) were tested, revealing two distinct hydrodynamic patterns. For cavities with low vegetation density (a < 3.99 %), one primary gyre in contact with the interface between main channel and cavity with high velocity was formed; the thickness of the mixing layer grew longitudinally along the interface, and regions with high vorticity and turbulence kinetic energy appeared at the interface and inside the cavity. For cavities with high vegetation density (a > 3.99 %), two gyres in contact with the interface with low velocity were formed, the thickness of the mixing layer did not grow, and the vorticity and turbulence kinetic energy were low inside the cavity. The mass transport presented the same threshold value as the hydrodynamics (a = 3.99 %). For cavities with low vegetation density, a fast mass transfer occurred through the interface between the main channel and cavity and inside the cavity, while the opposite was observed for cavities with high vegetation density. Finally, the modelled hydrodynamics was used to infer possible sediment deposition patterns and flow resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Universal relations of key parameters in various flow conditions are determined. • An improved sediment transport capacity formula is established. • The improved formula shows the highest accuracy in simulating morphodynamic processes. The calculation of sediment transport capacity is of great importance in modelling of morphodynamic processes in alluvial rivers. Recently, worldwide fluvial sediment load is reducing especially in the Lower Yellow River (LYR), while the commonly used formulas of sediment transport capacity are specially developed for relatively high sediment-laden flow, which needs some improvement for the varying flow and sediment regime. The measurements during a long period (1956–2020) covering 4974 datasets in a quasi-equilibrium state were collected at seven hydrometric stations of the LYR, and the hydrodynamic variables related to suspended bed-material load were classified, in order to determine the critical parameters (K and M) in the widely used formula proposed by H.W. Zhang. The calculation relations were firstly developed between K and M and the comprehensive flow-sediment factor (STP), under various combinations of flow and sediment, which reduce the uncertainty related to modifying model input parameters. The improved formula was further applied to simulate the morphodynamic processes in the LYR. Results indicated that the improved formula presented the best accuracy in the simulation of morphodynamic processes induced by low or high incoming sediment amount, compared with the other two formulas. This improved formula can be directly applicable to the varying flow-sediment regime and achieves the accurate simulation of the hydrograph of low sediment concentration in the LYR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developing an integrated sediment source assessment index based on long series hydrologic signals. • Developing Karst Surface Characteristic Index based on karst desertification factors. • Karst Surface Characteristic Index is closely related to hydrological processes. • Clockwise hysteresis is the most frequent and efficient type of sediment transport. The source and transport processes of suspended sediment are issues that require further study. The complex relationship between the integrated surface characteristics and the mechanisms of sediment sources and transport in heterogeneous karst watersheds remains unclear. This study proposes a comprehensive assessment framework for sediment sources that combines the surface characteristics of karst watersheds, such as exposed rock and shallow topsoil in karst areas. Additionally, the Karst Surface Characteristic Index (KSCI) is developed to evaluate the potential supply capacity of sediment in karst watersheds. The hysteresis index (HI mid) is calculated using a long series of hydrological data to study runoff and sediment relationships in eight watersheds in the karst region of southern China. Results indicated that plan curvature, terrain relief, NDVI, and rock exposure contributed most to KSCI, with these four factors contributing 65%. The Q-SSC hysteresis analysis results based on 445 hydrological events showed that a clockwise hysteresis pattern was the most frequent and efficient pattern of sediment transport in the studied watershed (clockwise hysteresis pattern accounted for 72.3% of 445 hydrological events) owing to the limited sediment supply in the karst watersheds. The quantitative analysis results of HI mid and KSCI showed that HI mid was closely related to KSCI. With an increase in KSCI, a clockwise hysteresis pattern was more likely to appear, indicating that watershed characteristics exerted a significant influence on sediment transport velocity and efficiency. In terms of spatial distribution, near the outlet of the watershed or the river channel, high KSCI values were distributed, and clockwise hysteresis was more likely to occur. In contrast, at the far end of the watershed outlet or the river channel, high values of KSCI were distributed, and anticlockwise hysteresis was more likely to occur. Our findings further enrich the theory of soil erosion and the runoff-sediment relationship at the watershed scale in karst areas, and serve as valuable decision-making references for integrated water and soil sources management. [ABSTRACT FROM AUTHOR]

• An innovative framework was developed to couple water flow and solute transport at the surface–subsurface boundary. • Surface and subsurface exchange due to diffusion and advection was considered. • The coupled H1D-K2 model reproduced the general hydrochemical behaviors in benchmark cases. • Spatial and temporal dynamics of water flow and solute transport at the surface and in the subsurface were obtained. • Computational efficiency was improved by applying sequential coupling, dynamic time steps, and dimensionality reduction. While surface–subsurface interactions strongly impact water quality and quantity in ecosystems, only relatively little attention has been given to solute mass transfers at this boundary. The KINEROS2 (K2) model solves the 1D kinematic wave equation for water flow and the advection–dispersion equation for non-absorbing solute (or sediment) transport at the surface, whereas the HYDRUS-1D (H1D) model solves the Richards equation for flow and the advection–dispersion equation for solute transport in the subsurface. We previously coupled water flow in the surface and subsurface environments using the K2 and H1D models (H1D-K2). Herein, an innovative framework was developed to additionally couple solute transport at the surface–subsurface boundary in the simple, accurate, and computationally efficient H1D-K2 model. To test the H1D-K2 model's accuracy and robustness, simulation results are compared to analytical solutions, experimental data, and results from the two-dimensional HYDRUS-2D (H2D) code. The relative differences in water and solute balance components between the H2D and H1D-K2 models are less than 1% for homogeneous cases and 4% for heterogeneous cases. The simulated hydrograph and chemograph are almost identical for the two models. Furthermore, simulated Bromide (Br) concentration in runoff is in good agreement with observations. The proposed model also accurately reproduces soil erosion under different rainfall patterns and intensities. [ABSTRACT FROM AUTHOR]

• Novel use of temporary, permeable in-channel structures described. • Structures successfully used for 64 years in the Lower Burdekin River. • Temporary structures have advantages for river siltation and fish passage. • Temporary structures are removed by flow events with recurrence intervals of < 0.3 y. A review of in-channel structures finds a wide range of purposes, including enhancement of the storage capacity of rivers to improve water supply reliability and/or flood protection, and various other hydro-ecological, water quality, geomechanical and sediment transport functions. The installation of in-channel structures is typically intended to be permanent, or at least semi-permanent. The purpose of this note is to document the novel use of temporary in-channel structures in the lower reaches of the Burdekin River, within the Australian dry tropics. Their application reduces freshwater discharge to the sea during low-flow periods thereby enhancing the sustainability of irrigated agriculture within the Lower Burdekin Delta. Temporary structures are constructed in the Burdekin River to enhance the reliability of pumping stations by raising the river level locally and preventing sea water from reaching extraction points. The structures are designed to restrict river flow only partially during low-flow periods and to wash away during high-flow events, which provides several benefits, including the passage of riverine fauna and reduced river siltation. The long-term utilisation (1950s to present) of temporary structures in the Burdekin River is testament to their successful implementation, which may offer benefits over permanent structures for other dry-tropical regions. [ABSTRACT FROM AUTHOR]

• 24,918 Landsat images focused on the lower Yellow River were used to monitor SSC during the period 1997–2020. • The proposed HGAR method significantly outperforms other retrieval methods in terms of retrieval accuracy. • HGAR is a reliable method for SSC retrieval and can be used for long-term monitoring of SSCs. Monitoring suspended sediment concentrations (SSCs) of channel waters is essential for evaluating important issues such as erosion, sediment transport and deposition, reservoir siltation, and water pollution throughout watersheds. Remote sensing technology provides a new approach to large-scale SSC monitoring, but the accuracy of existing retrieval methods based on remote sensing technology still needs to be improved for complex environments. This study proposes a new hyperparameter and globally adaptive retrieval (HGAR) method for river SSC retrieval that combines a remote sensing technique and machine learning methods. The HGAR method uses the light gradient-boosting machine method as the basic model for SSC retrieval, and the tree-structured Parzen estimator method, coefficient of determination, and residual prediction deviation are combined to optimize the basic model's hyperparameters. The experiment was conducted in the lower Yellow River, where 24,918 Landsat images from 1997 to 2020 were acquired using Google Earth Engine, and 1,772 monthly cloud-free images were obtained in the end. The sequential backward floating selection method was adopted to determine the optimal modeling features. Two regression and three machine learning methods were compared with the proposed method. The results demonstrate that the proposed HGAR method significantly outperforms other retrieval methods in terms of retrieval accuracy (as evidenced by a correlation coefficient of 0.626 and a Nash-Sutcliffe efficiency coefficient of 0.613), generalizability, and robustness. Finally, the model explanation results show that the HGAR method can successfully capture the key information for SSC retrieval and has higher flexibility than traditional statistical models. In addition, we found that the overall fit and the fit of local extreme values are inconsistent in the lower Yellow River, and the proposed improved accuracy indicator balances the two aspects well. In conclusion, the proposed HGAR method can be used effectively to estimate channel SSC and is expected to provide technical support for long-term and large-scale monitoring of the channel surface SSC. [ABSTRACT FROM AUTHOR]

• A dramatic scour and fill in a streambed is reported. • Reach expansion causes transient scour and fill. • The amount and sign of scour and fill is predictable. Transient scour and fill refers to the general scour and fill in a riverbed due to flood passage. It was given much attention in times of Leopold and Maddock (1953) and Colby (1964) from records of outstanding case studies. Field data from a station in a contracted, long reach of the large sand-bed Pilcomayo River –1192 newly typed in forms– are presented, with sediment concentration in the database up to 60 kg/m3, mostly wash load. Water surface rises and falls during a flood event, whereas streambed evolves in reverse (it renders the analogy to an accordion). Streambed scouring accounts for 36% of the change in flow area during floods and data reveal scouring up to 4 m from the streambed elevation when flood starts. Velocity data display large hysteresis loops inexplicable by unsteady flow only. Once streambed starts to fall, river bed scour is self-sustaining. Water depth gradient appears to be a crucial variable in a novel equation for transient scour and fill derived from Exner equation. It turns out that flow non-uniformity is relevant to explain transient scour and fill in contrast to flow unsteadiness, which is not. Quasi-steady gradually varied flow equation solved along the contracted reach is the base for a model that captures well the recorded bed evolution. The model explains most of the transient scour and fill by the downstream expansion, but the non-uniform flow and the bed material suspended load also play a role. The model fails on the days of highest sediment concentrations. [ABSTRACT FROM AUTHOR]

• Vulnerability assessment for buildings resulted in a plethora of methods. • We present recent advances in quantitative vulnerability functions. • Multiple uncertainties can be detected if vulnerability functions are compared. • The transferability of functions between case studies is challenging. • More research is needed to understand the importance of building design. Irrespective of the magnitude and spatial extend, the consequences of a natural hazard are strongly connected to the vulnerability of elements at risk (e.g. people, buildings and infrastructure). It is, therefore, obvious that an analysis and quantification of vulnerability is required for successful disaster risk reduction. The need for vulnerability assessment is crucial due to the effects of climate change as well as the socio-economic dynamics that may directly impact vulnerabilities and coping capacities of affected communities. Vulnerability is multidimensional (physical, social, economic, etc.), however, the dimension which is mainly related to the direct costs and threat to human lives is the physical one. We focus here on the physical vulnerability of buildings subject to torrential hazards occurring in small and steep mountain catchments. These processes include fluvial sediment transport, debris floods, and debris flows. Furthermore, we included flash flood hazards if these are related to torrential catchments. Physical vulnerability to torrential hazards in mountain areas is a topic that has been under scientific investigation over the last 20 years. Several methods to assess physical vulnerability of buildings towards flash floods, debris flows and hyper-concentrated flows can be found in the literature. The plethora of methods and approaches may be classified under the following three categories: vulnerability matrices, vulnerability curves and vulnerability indices. We provide a short review of these methods which became available over the last decade and which dominate the scientific debate in mountain hazard risk management, giving an emphasis to vulnerability curves. The approaches presented herein are highlighted through case studies from the European Alps and beyond. Furthermore, challenges in vulnerability assessment including data requirements, need for improved event documentation, uncertainties and challenges related to future climate and socio-economic changes are outlined. Finally, a discussion on progress-driving factors such as new technologies (e.g. mobile apps, drones), citizen science and new innovative assessment methods is provided. [ABSTRACT FROM AUTHOR]

• Eight of thirteen typhoons occurred in 2016 impacted the Yangtze Delta wetland. • The impacting typhoons were 450–2000 km away from the delta. • The remote typhoons caused 2–5 times maximum increases in sediment dynamics. Intertidal wetlands are widely considered to be vulnerable to storm impacts. While much attention has been given to the effect of hurricane/typhoon landfall on local erosion/deposition in intertidal wetlands, less is known about how distant hurricanes/typhoons can affect an intertidal wetland or about the comprehensive effects of hurricanes/typhoons on hydrodynamics, sediment transport and seabed stability. Here, we investigate the possible impacts of thirteen typhoons that occurred in the western Pacific during summer–autumn 2016 on an intertidal wetland in the Yangtze Delta. We detected the impacts from eight of the typhoons during half of their duration when these typhoons were 450–2000 km away (nearest distance ever for each typhoon) from the delta. These remote typhoons caused 2–5 times maximum increases in hydrodynamics and suspended sediment concentration. Correspondingly, considerable net mudflat erosion and marsh deposition were observed. We therefore conclude that intertidal wetlands can be strongly affected by typhoons, even those passing by hundreds of kilometres away. These findings contribute to understand how far and in what extent hurricanes/typhoons can affect intertidal wetlands and to increase knowledge needed for coastal management. [ABSTRACT FROM AUTHOR]

• Improve the one-dimensional model with the river regulation works being considered. • Compare the fluvial processes with and without the effect of river regulation works. • Investigate the impacts of river regulation works on channel evolution. In an alluvial river, various kinds of river regulation engineering are usually constructed along the reach for the stability of channel regime and the safety of flood control, which greatly affects the process of channel evolution. Therefore, a one-dimensional (1D) morphodynamic model has been improved to simulate the fluvial processes influenced by large-scale river regulation works. In the refined model, each node of a cross-section was labeled using a specified point code representing the zones of floodplain and main-channel with or without regulation engineering, and sediment transport and bed deformation in different zones were treated separately. In the zones without regulation engineering, both bed deposition and bed erosion were permitted to occur; in the zones with regulation works, bed deposition was allowed, while bed erosion was not permitted to occur owing to the restriction of those engineering, unless there was a deposition layer newly formed over the previous simulation period. Then the improved model was calibrated and verified using field observations through the application to a 347-km-long alluvial channel located in the Middle Yangtze River in China. The results for the year 2016 show that the channel scour volume without the effect of river regulation works was 9% greater than the measured value (34.43 × 106 t), while the outcome considering this effect (35.81 × 106 t) was in closer agreement with the measurements. Moreover, the variation in channel geometry obtained from the improved model agreed better with the observed data. River regulation works would limit the channel incision, and it is likely to scour the other unprotected bed of a cross-section or the downstream cross-sections as the flow cannot carry enough sediment from the protected bed. Simulated results indicate that part of the main-channel zone at the Jing65 section was protected, but the riverbed continued to incise by about 0.68 m in the protected area when the effect of bed-protection works was not considered in the model, which was not in accord with the observed channel geometry. Therefore, this effect of large-scale river regulation works on channel evolution needs to be considered for a higher simulation accuracy. [ABSTRACT FROM AUTHOR]

• The increase in Ks and n could effectively reduce the peak and total flow at different stages of runoff generation. • By increasing Ks , re-vegetation could result in shift of dominant runoff generation mechanism in Loess Plateau. • By increasing n , the vegetation would slow down the flow velocity and trap the water and soil along the flow path. • Smaller erodibility coefficient helped to slow down the fragmentation of landscape in the Loess Plateau. The changes of soil properties caused by ecosystem restoration have played critical roles in controlling water and sediment loss in Loess Plateau. However, it is difficult to isolate and quantify the individual impact of each factor as the impact is hard to monitor separately. The objectives of this study are to explore how the changes in different soil properties influence the hydrologic response and sediment transport at catchment scale. We applied a coupled hydrologic-sediment transport model to a small catchment in the Loess Plateau. Sensitivity analyses were conducted on three influential soil properties: saturated hydraulic conductivity (Ks), Manning's roughness coefficient (n) and the variations of erodibility coefficient (φ). Our results indicated that the increase in near surface saturated hydraulic conductivity could effectively reduce the peak and total flow (i.e. when Ks is smaller than rainfall intensity, 22.5% increase in Ks leads to over 70% reduction in total discharge), and could lead to transition of runoff generation mechanism from Horton Overland Flow to Dunne Overland Flow. The increase in Manning's roughness coefficient would also reduce the discharge and sediment yield substantially by slowing down the flow velocity which leads to more infiltration along the flow path after the runoff is generated. The decrease in erodibility coefficient reduces the sediment rate and total sediment mass delivered (i.e. 20% decrease can reduce total sediment mass by 5%), alleviating the undercutting in upstream gullies and deposition at downstream, eventually slowing down landscape evolution. Our findings could be used to provide valuable guidance in the ecosystem restoration and land use management. [ABSTRACT FROM AUTHOR]

• The larger and faster bed-level changes occurred in extremely shallow waters. • Extremely shallow waters stages have an important influence on the bed-level changes. • Extremely shallow waters stages have an important control on sediment dynamics. Intertidal flats are shallow-water environments that undergo cyclical variations in water depth, leading to a frequent occurrence of extremely shallow water stages (ESWS; water depths <0.2 m). However, relatively little is known about the hydrodynamic conditions and erosion–accretion processes during ESWS, because the water depth is too shallow to measure in situ sediment dynamic processes using traditional methods. To address this gap, based on in situ measurements with four advanced instruments, we quantified the hydrodynamic conditions, erosion and accretion during ESWS in calm weather conditions on a highly turbid intertidal flat in Jiangsu coast, China. Our results revealed that marked erosion and accretion occurred during ESWS at the flood and ebb tidal stages, respectively. The resulting bed-level changes were three times greater during ESWS than relatively deep water stages (RDWS; water depths >0.2 m), and the rate of change was an order of magnitude faster than during RDWS. This larger and faster bed-level change occurred even though the ESWS duration only accounted for 10% of the entire tidal cycle. This result occurred because the bed shear stress due to combined current–wave action during ESWS, was, on average, two times higher than during RDWS at the flood stage causing more extensive erosion. Whereas during the ebb stage, this shear stress during ESWS was only half of that during RDWS resulting in greater accretion. The main implications of these results are that, because ESWS occur frequently (twice every tide) and are associated with large bed shear stress and bed-level changes, these conditions are likely to play an important role in morphological changes of intertidal flats. Our study shows that ESWS have a key influence on intertidal flat hydrodynamics and sediment dynamics. Thus our results are the basis for an improved understanding of the coastal morphodynamic processes on intertidal flats. [ABSTRACT FROM AUTHOR]

• Phosphorus contamination on surface sediment at a confluence is severe. • P variability is primarily affected by floods and temperature. • A model is proposed for P variability on sediment. • The present field observation supplement database on confluence dynamics. River confluences are key features of a river network, and their effects on contaminant transport and transformation need to be understood to control the contamination of a river network. This paper investigates the dynamic characteristics of phosphorus (P) contamination on the surface sediment at a river confluence of the Huai River, China, where water and sediment contamination is severe. The results highlight that P contamination of the surface sediment at a river confluence is more severe than that of the main stream of the river network to which the river confluence belongs. Floods have critical impact on the transport of sediment and its surface texture. In the annual water cycle the initial small flood can convey much more contaminated sediment and pollute the downstream river, whereas the subsequent large flood leads to the coarsening of the surface sediment and decrease of the total P (TP) content on the surface sediment (TPS). Water temperature is one of the most important factors affecting the temporal variability of the TPS at the river confluence. Higher P amounts are adsorbed on the surface sediment during lower water temperatures in winter and spring. Calcium bound P (Ca-P) is a relatively stable fraction of the sedimentary P during the dynamic processes of contamination of the surface sediment, and the nonapatite P gets released from the surface sediment during the summer. Effects of P concentration of the surface water and that of pH on TPS variability are not discernable in the current study. These results will be useful for controlling phosphorus contamination at river confluences and in river networks. [ABSTRACT FROM AUTHOR]

• Groundwater spatial modeling using spring data set. • Presenting new hybrid models of ANFIS-TLBO and ANFIS-BBO for groundwater potential mapping and its zoning. • Predictive capability of spring affecting factors using correlation attribute evaluation method. • Correlation between springs and affecting factors using the PCF algorithm. • ANFIS-TLBO shows the better results in term of AUC value. Groundwater is one of the most beneficial natural resources worldwide. The main aim of the present study is the mapping of groundwater potential of the Zhangjiamao area in China using two novel hybrid data mining techniques that involve the adaptive neuro-fuzzy inference system (ANFIS) ensembled with teaching-learning-based optimization (TLBO) and biogeography-based optimization (BBO). First, 93 spring locations were identified in the study area, which were randomly divided in the ratio of 70:30 to be used for building models and validation, respectively. A total of 16 spring affecting factors viz., slope aspect, altitude, slope angle, plan curvature, profile curvature, curvature, sediment transport index, stream power index, topographic wetness index, distance to roads, distance to rivers, rainfall, lithology, soil, NDVI, and land use/land cover, were used as input variables. The probability certainty factor (PCF) method was applied for the correlation analysis between spring occurrences and the affecting factors. Subsequently, the ANFIS-TLBO and ANFIS-BBO models were generated to produce groundwater spring potential maps (GSPMs). Finally, the GSPMs were evaluated by using the area under the receiver operating characteristic (AUROC). The results showed that the AUROC values for the ANFIS-TLBO model based on the training and validation datasets were 0.866 and 0.905, respectively. In contrast, the AUROC values for the ANFIS-BBO model based on the training and validation datasets were 0.861 and 0.887, respectively. The results of ANFIS-TLBO showed that 25.66% of the study area could be classified into the high and very high groundwater spring potential classes as compared to the ANFIS-BBO model (30.52%). The results of the present study can be useful for groundwater management. [ABSTRACT FROM AUTHOR]

• A detailed model is formulated to optimize the reservoir operation. • The trade-offs among social, economic and ecological benefits are presented. • Operational strategies are compared for achieving the comprehensive benefits. Balancing the multiple purposes of reservoir operation, including the social, economic, and ecological aspects, has become one of the most complicated problems facing the managers and operators worldwide. This paper formulates a detailed mathematical model to optimize the reservoir operation during the flood season, considering the three major operational purposes, i.e. flood control (social purpose), energy production (economic purpose), and management of sediment transport (ecological purpose). The entire formulations conform to a nonlinear programming (NLP) model, which can be solved effectively and efficiently by the Multi-Start Solver from the LINGO software through equivalent transformation. This model is applied to the Three Gorges Project (TGP) in China, which is the world's largest and most complex hydraulic engineering in operation. Three typical flood hydrographs (i.e. dry, normal, and wet scenarios) are selected as model inputs under the three strategies (i.e. design operating rules, increasing the flood control water level (FCWL), and impounding in advance). The trade-offs among these three major operational purposes are quantitatively analyzed. Moreover, phosphorus (P), one of the sediment-associated environmental factors, is introduced for exploring its responses to various scenarios and strategies. Results indicate that a higher fore-bay water level leads to a greater energy production, a smaller flood peak but less sediment and P transports to the downstream. Under the design operating rules, the maximum energy production of the TGP can reach 560, 620, and 699 × 108 KWh, respectively, in dry, normal, and wet scenarios, corresponding to a flood peak of 25000–27500 m3/s, a sediment load of 1517–1999 × 104 t, and a P load of 3152–3740 × 104 kg to the downstream. Whereas, the maximum sediment loads are 2796, 4640, and 5377 × 104 t, and the maximum P loads are 4021, 5345, and 5784 × 104 kg, respectively, in dry, normal, and wet scenarios, corresponding to an energy production of 500–588 × 108 KWh, and a flood peak of 38600–52500 m3/s to the downstream. In terms of achieving the comprehensive benefits of the TGP, impounding in advance is a better choice than both the design operating rules and increasing the FCWL, for it can increase the energy production and the probability of full refill with almost no increase in flood risk to both the dam and the middle and lower reaches of the Yangtze River as well as smaller reduction in the sediment and P transports. The formulated detailed mathematical model is a general one that is applicable to a variety of reservoirs owning multiple operational purposes. Moreover, the achievements gained from this paper will provide important references for the managers and operators. [ABSTRACT FROM AUTHOR]

Highlights • A second-order finite-volume method is presented for solving the total-load non-cohesive sediment transport. • An improved HLLC Riemann solver is derived. • An improved bed slope treatment is derived to account for density variation inside the cell. • A novel implicit source term discretization is presented. • The numerical model shows good agreement with measurement as long as the shallow flow assumptions are valid. Abstract This paper presents novel flux and source term treatments within a Godunov-type finite volume framework for predicting the depth-averaged shallow water flow and sediment transport with enhanced the accuracy and stability. The suspended load ratio is introduced to differentiate between the advection of the suspended load and the advection of water. A modified Harten, Lax and van Leer Riemann solver with the contact wave restored (HLLC) is derived for the flux calculation based on the new wave pattern involving the suspended load ratio. The source term calculation is enhanced by means of a novel splitting-point implicit discretization. The slope effect is introduced by modifying the critical shear stress, with two treatments being discussed. The numerical scheme is tested in five examples that comprise both fixed and movable beds. The model predictions show good agreement with measurement, except for cases where local three-dimensional effects dominate. [ABSTRACT FROM AUTHOR]

Highlights • We employed a high-density electrical resistivity system to detect sediment. • Trenches, boreholes and drillings were used to calibrate the ETR values. • Geometric methods considering three shapes were used to estimate sediment volume. • A four-step approach can estimate sediment yield for ungauged catchments. Abstract Check dams are very important structures for torrent control areas throughout the world. Measuring the sediment deposition behind check dams is thought to be an effective method of estimating the sediment yield of small catchments. In this study, we employed a high-density electrical resistivity system to detect sediment at six check dams distributed in the hilly and gully area of the Loess Plateau. A total of 11 lines were arranged, with 60 electrodes along each line. The resultant resistivity data were inverted into subsurface structures using least-squares inversion techniques. The results indicate that the sediment bottom can been identified using an electrical resistivity contour method. Using trenches, boreholes and drillings to calibrate the calculated values, the accuracy of the high-density electrical resistivity tomography method was found to be quite high (95.7%). The bulk density increases with the sediment deposit depth and can reach a maximum of 1.6 g cm−3. Geometric methods considering three shapes (V-shaped, U-shaped and trapezoidal) were used to estimate the profile area of the check dams; the V-shaped geometric method showed high accuracy. This study provides a four-step approach based on high-density electrical resistivity tomography and a geometric method to estimate sediment yield for check dam-controlled catchments. This methodology enables the measurement of the total sediment yield, including both the suspended and bedload sediment transport, from an ungauged catchment. [ABSTRACT FROM AUTHOR]

Highlights • Two crucial periods for suspended sediment transport were June and November/December. • Analysis of 236 floods highlighted their intermittency and did not show relationships. • Medium-term continuous time series are necessary to assess range of variations of SSF. Abstract In mountainous catchments, soil erosion and sediment transport are highly variable throughout time and their quantification remains a major challenge for the scientific community. Understanding the temporal patterns and the main controls of sediment yields in these environments requires a long term monitoring of rainfall, runoff and sediment flux. This paper analyses this type of data collected during 7 years (2007–2014), at the outlet of the Galabre River, a 20 km2 watershed, in south eastern France, representative of meso-scale Mediterranean mountainous catchments. This study is based on a hybrid approach using continuous turbidity records and automated total suspended solid sampling to quantify the instantaneous suspended sediment concentrations (SSC), sediment fluxes, event loads and yields. The total suspended sediment yield was 4661 Mg km−2 and was observed during flood events. The two crucial periods for suspended sediment transport at the outlet were June and November/December (63% of the total). The analysis of suspended sediment transport dynamics observed during 236 flood events highlighted their intermittency and did not show any clear relationship between rainfall, discharge and SSC. The most efficient floods were characterised by counter-clockwise hysteresis relationships between SSC and discharges. The floods with complex hysteresis were the more productive in the long term, during this measuring period exceeding a decade. Nevertheless, the current research outlines the need to obtain medium-term (five years) continuous time series to assess the range of variations of suspended sediment fluxes and to outline clearly the seasonality of suspended sediment yields. Results suggest the occurrence of a temporal dis-connectivity in meso-scale catchments over short time-scales between the meteorological forcing and the sediment yields estimated at the outlet. These findings have important methodological impacts for modelling and operational implications for watershed management. [ABSTRACT FROM AUTHOR]

Highlights • This study analyzed the intensive fluctuations of runoff and sediment load at the upper Yellow River, which has not yet been studied clearly before. • Temporal variations in runoff and sediment load were discerned in terms of changing trend, abrupt change year, and multi-periods from the full measured datasets of all hydrological stations. • Impact of human activities on the hydrological variations was evaluated based on comparison of the measured and the reconstructed time series. Abstract Operations of amount of large and medium reservoirs have remarkably changed runoff and sediment loads, and consequently affected the fluvial processes intensively on the upper Yellow River. In this study, time series of runoff and sediment transport rates of four major hydrological stations on the upper Yellow River were used to analyze temporal and spatial variations of runoff and sediment loads. Mann-Kendall test and wavelet analysis were applied to analyze the datasets. Temporal variations in runoff and sediment loads were discerned in terms of changing trend, abrupt change year, and multi-periods from the time series. Additionally, a time series of runoffs was reconstructed based on a modeling scenario removing impact of reservoir impoundment and water diversion to indicate the status without human disturbances. Comparison of the measured and reconstructed datasets was conducted to evaluate the impact of reservoir impoundment and water diversion on hydrological variations. The measured runoff and sediment loads showed obvious decreasing trends due to impoundment and water diversion. However, the reconstructed runoffs regarded as only affected by climate change showed no significant changing trend at a 95% confidence level, confirming that, instead of climate change, human activities played the most important roles in variations. The measured datasets indicated that the reservoir construction and operation caused an abrupt change in runoff in 1986, while the reconstructed datasets indicated another abrupt change in 1995. Wavelet transform analysis distinguished the multi-periodical features of the time series. The first, second, and third dominant periodicities of the measured runoffs were 25–27, 16, and 8 years, respectively, whereas the first three dominant periodicities of the reconstructed runoffs were 26–31, 12, and 7 years, respectively. It was indicated that the high-frequency periodicities of runoffs decreased while the low-frequency periodicities increased, owing to reservoir impoundment and water diversion. [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]

[Display omitted] • A text mining algorithm was applied to define common topics in nutrient transport. • Ten topics were determined as frequent topics using quantitative analysis. • The topics were qualitatively analyzed to specify meaningful insights and trends. • Five major research gaps were identified in nutrient transport research. • The study results can guide future research directions and examine research gaps. Nutrient (e.g., nitrogen and phosphorus) loss from point and non-point sources can cause critical environmental problems, deteriorating the quality of surface water and groundwater. Therefore, the protection of surface water and groundwater is imperative for maintaining a healthy environment. Although many review studies have investigated nutrient transport in surface water and groundwater, most of them concentrated on examining nutrient transport in one or two water systems, such as rivers, lakes, and groundwater without considering and including the research gaps in other systems. To date, there are no systematic studies that have determined the main insights and research gaps in the field of nutrient transport in surface and subsurface water using a text mining algorithm and topic identification through a quantitative and qualitative analysis. Therefore, meta-research (research on research) was performed using the Latent Dirichlet Allocation (LDA) algorithm (a text mining algorithm) to identify the most frequent topics in the literature that covered the nutrient transport processes in surface water and groundwater using a quantitative analysis. Based on the results of the quantitative analysis, ten key topics were identified: nitrogen transport in groundwater; nitrogen transport in surface water; phosphorus transport in surface water; sediment transport in watersheds; nutrient loss in subsurface drainage; nutrient transport associated with lakes; nutrient transport in forest-dominated watersheds; modeling of nutrient transport; agricultural watershed management; and effect of soil-litter on nutrient transport. Furthermore, these topics were explained in a qualitative analysis to highlight the most important insights from literature and to identify the main knowledge gaps for further investigation in future studies. According to the most frequent topics in the literature, five research gaps were evident: developing integrated models for nutrient transport processes in the surface water-groundwater interactions; evaluating the effect of climate change and crop management practices on nutrient transport in surface water and groundwater; application of machine learning algorithms in nutrient transport; and describing the in-stream sediment and nutrient transport in fluvial environments such as rivers and creeks. The results of the current meta-research study are a steppingstone towards better identification of the common themes and trends in the previous publications in literature pertaining to nutrient transport in surface water and groundwater by applying an informative text mining algorithm where key knowledge gaps were determined based on the recommendations of these publications. [ABSTRACT FROM AUTHOR]

• A method for 3-D river networks extraction was proposed based on multi remote sensing. • A module for recognizing and retrieving cross section morphology was established. • An improved hydrological model was developed to enhance the simulation performance. Many rivers originating from mountainous areas cannot be adequately measured in the field to obtain sufficient basic data due to the challenging terrain, which poses difficulties for conducting relevant research such as hydrodynamic and sediment transport simulations, fluvial material fluxes. This study utilized a combination of 71 river cross sections extracted from multisource remote sensing data and 34 cross sections measured by hydrological stations between 2010 and 2018 to generate generalized cross sections for all river orders in the middle reaches of the Yellow River. By integrating the generalized cross sections, river surfaces, and traditional DEM river network, a comprehensive 3-D river network has been established to provide a more accurate representation of the morphological changes along the river channel. To tackle the challenge of simulating runoff in data-deficient areas, the Digital Yellow River Integrated Model (DYRIM), a potent distributed hydrological model, was enhanced by incorporating geometric parameters derived from a 3-D river network into almost all input parameters that can be obtained from multi-source remote sensing. This enhancement enabled the model to accurately simulate runoff in representative data-deficient rivers of the Loess Plateau. The Nash Efficiency coefficients for the simulated runoff exhibited improvement of 23% compared to previous studies, surpassing 0.8 for the period between 2010 and 2018. Additionally, the simulated errors for flow velocity and water depth were 7% and 9% respectively. This approach can provide essential data for the simulation of hydrological processes and improving hydrological models, as well as technical methodologies for related research such as sediment transport simulations and river carbon emissions. [ABSTRACT FROM AUTHOR]

• • The concept of hydraulic radius can be reinterpreted as a measure of large-scale turbulent flow structure. • • Hydraulic radius as proxy for large-scale eddies enables new framework for bed shear stress model and unified scaling of scour depth. • • Hydraulic radius formulation provides insight into characterizing large-scale flow structure by geometrical boundary conditions. Hydraulic radius has long been customarily used as a characteristic length to assess the cross-sectional geometry and efficiency of channels and conduits. This review paper revisits the concept of the hydraulic radius in light of its extensive applications in recent studies, with the aim of piecing together a state-of-the-art understanding of its physical underpinnings. The original definition of the hydraulic radius is presented as the ratio of cross-sectional flow area to wetted parameter, which inherently integrates the properties of the flow domain and the contacting surface. The use of hydraulic radius as a versatile characteristic length in classical Manning's formula and the Reynolds number underscores its significance in relation to flow resistance. Through a thorough review of its diverse applications, this paper provides a unified understanding of the physical meaning of hydraulic radius, highlighting its interpretation as a measure of large-scale eddies within a given flow domain. This new insight can be justified beyond uniform flows, as evidenced by its use in addressing sediment transport issues in complex vegetated flows, based on turbulence phenomenological theory. Furthermore, the original formulation of the hydraulic radius provides insights into how large-scale flow structure can be quantified with geometrical boundary characteristics, leading to a promising framework for scour prediction based on large-scale vortex size. This paper highlights the versatility and utility of hydraulic radius across various fields of fluid mechanics and sediment transport research, and proposes its potential for future studies as a proxy for large-scale flow structures. [ABSTRACT FROM AUTHOR]

• Input and output time series from the conduit system of a karst aquifer are analyzed. • A simple water-balance model of epikarst zone is proposed. • Hourly internal runoff and diffuse drainage from epikarst zone are estimated. • Correlation and partial correlation functions are used. • A more precise insight into the sediment transport process in aquifer is obtained. Information about the transport of suspended sediment through a karst aquifer is obtained by the time series analysis of the input and outputs from the conduit system of vadose and phreatic zone. The input is the internal runoff from epikarst zone at the analyzed location. The outputs are the discharge from karst spring, as well as the turbidity and electrical conductivity of spring water. The diffuse drainage from epikarst zone is considered as a control process that changes the quantity of water in the conduit system, and consequently it affects the outputs. The time series of internal runoff and diffuse drainage are obtained by a simple water-balance model of epikarst zone based on the concept of saturation threshold. The proposed model has two parameters: maximal capacity of epikarst storage, and maximal diffuse drainage from epikarst storage, which are estimated by using the cumulative rainfall and turbidity data, as well as the value of runoff coefficient. The time series are analyzed by means of the correlation and partial correlation functions. The presented results show that the overall capability and accuracy of the time series analysis are significantly improved by considering the conduit system separately. It is possible to register and to characterize processes in karst aquifer that are not recognizable by using classical approaches. The results for Jadro Spring show that the memory of hypothetical discharge generated by the internal runoff is practically same as the memory of time series of turbidity. The memory of hypothetical discharge generated by the diffuse drainage is very similar to the memory of time series of discharge. The duration of turbidity response is 22 days, which entirely corresponds to the duration of fresh rainwater withdrawal from the conduit system. During the first 5 days, turbidity is generated mostly by the internal runoff from the central part of catchment. During the last 12 days, turbidity has been generated by the internal runoff from the eastern part of catchment. Two components in turbidity are recognized, which are manifested as two peaks in the turbidity graph. Both peaks are produced dominantly by autochthonous sediment. [ABSTRACT FROM AUTHOR]

• The simulated water level and discharge were more sensitive to roughness coefficients. • Spatio-temporal variability existed in the classification of the most contributing parameter. • Parameter uncertainty analysis indicated the satisfactory accuracy of the model. One-dimensional morphodynamic models are effective tools to conduct flood risk assessment and sediment management of alluvial rivers. In order to gain better understanding of morphodynamic models and improve the simulation efficiency and accuracy, a comprehensive investigation into parameter sensitivity and uncertainty has been conducted for a one-dimensional morphodynamic model. This model was calibrated using the measured flow and sediment data in the Lower Yellow River (LYR). The variance-based Sobol' and GLUE (Generalized Likelihood Uncertainty Estimation) tools were applied to quantify the parameter sensitivity and uncertainty to the simulation of different hydrological indicators in the meandering reach, with various model response surfaces selected. Results show that the importance of input parameters varied with different model outputs. The simulated water level and discharge hydrographs were more sensitive to the roughness coefficient at middle and high flows, with high total- and first-order sensitivity indices to the NSEs and RMSEs, while the simulated sediment concentration was more sensitive to the input parameters related to sediment transport capacity (K and M) and recovery coefficient (b d). Notably, the pairwise interactions between K and different roughness coefficients were significant in the simulated sediment concentration hydrographs. Spatio-temporal variability in the effect of input parameters is also revealed. The most contributing factor was screened as K for the maximum sediment concentration in the uppermost and lowermost reaches of the meandering reach, which turned to be b d in the middle reach. The most sensitive parameter to the simulated sediment concentration was screened as K in the initial period and then turned to be the exponent of recovery coefficient in case of erosion (b e), which was b d in the last period over the simulation period. An analysis of parameter uncertainty indicates that the morphodynamic model can obtain satisfactory accuracy with most observed data concentrating in the 95% confidence interval, and the uncertainty of simulation outputs increased downstream. Improved understanding of parameter sensitivity and uncertainty in morphodynamic modelling can provide the scientific guidance for factor prioritization in the future model calibration. [ABSTRACT FROM AUTHOR]

[Display omitted] • The grain size and major element composition in sedimentary sequences of the Yellow River Basin are presented. • The provenance, transport dynamics and sedimentary characteristics of sediments of the Yellow River is disclosed. • The processes and geomorphological effects of aeolian-fluvial interactions in the Yellow River Basin are identified. • The intensity of aeolian-fluvial interactions is related to sediment erosion and transport. Understanding environmental changes requires the characterization of potential interactions between aeolian and fluvial systems. This study aimed to identify the sedimentary characteristics, provenance, and transport of sediments of the Yellow River Basin, as well as the processes and geomorphological effects of aeolian-fluvial interactions using end-member modelling analysis (EMMA), multidimensional scaling (MDS), and principal component analysis (PCA). Samples (n = 107) collected from sedimentary sequences in the source area, upper, middle, and lower reaches were analyzed for grain size and major element contents. The results showed that sediments in the source area of the Yellow River mainly originated from the Tibetan Plateau, whereas the input of materials from the Chinese Loess Plateau (CLP) gradually increased from the upper to lower reaches. The sediment transport was jointly controlled by simultaneous or alternating aeolian and fluvial processes. Asynchronism in aeolian activity and rainfall and the non-uniformity of runoff and sediment sources resulted in a concentration of aeolian-fluvial interactions in the river reaches traversing through the deserts and CLP. Fluvial sediments in the upper reaches consisted of wash loads deposited in slow-moving water, whereas rapid replenishment of sediment from the CLP in the middle reaches increased sediment transport capacity, thereby enhancing the uniformity of sedimentary characteristics from the upper to lower reaches. Moreover, numerous gullies in the CLP resulted in increased intensities of aeolian-fluvial interactions, thereby accelerating severe sedimentation in the lower reaches. This study can act as a reference for paleoclimatic reconstruction and for soil and water conservation in large-scale watersheds across a range of climatic zones. [ABSTRACT FROM AUTHOR]

Highlights • Worst flash flood in Spain in 1962 caused more than 800 deaths. • Mostly grey literature on the catastrophe is raised to international audience. • Example of highest vulnerability and role of sediment on water levels. Abstract The 1962 Rubí flood was a severe flash flood, the worst to ever take place in Spain, claiming the lives of more than 800 people following 200 mm of rainfall in 2 h. Such a high number of casualties can be explained by the very high vulnerability of people who lived in the floodplains of a wandering, ephemeral stream (a wadi) prone to flash floods. Many publications to commemorate the 50th anniversary of the flood have been used as proxy data for the event, especially in terms of social aspects. The meteorological and pluviometric information is reviewed, while other information is only found in grey literature. Recently, the event has been considered an outlier in the panorama of European flash floods. Because of the above, this paper aims to convey all the information to readers and show that it deserves to be raised to an international level as an example of an extreme flash flood. After addressing some misunderstandings, it can be concluded that the event was not an outlier, nor was it extreme, in terms of total rainfall, return period, discharge, discharge per unit basin area, unit stream power and flow velocity. It may be extraordinary because the flood reached very high levels by transporting large amounts of both fine and coarse sediment particles. The stream is steep, ephemeral, lacking an armour layer, and prone to torrential events, in which the large sediment transport played a role in how high the flood levels rose. The use of flooding marks to compute discharges is also discussed. In addition, the paper presents a torrential calculation based on the momentum principle in a control volume. [ABSTRACT FROM AUTHOR]

Highlights • A novel SDR algorithm was proposed to improve the accuracy of sediment predictions. • The algorithm had good reliability, few parameters, and high computation efficiency. • The annual SDR was less affected by rainfall erosivity but showed a decreasing trend. • The average SDR of 0.38 means the sediment was far less than erosion after governance. Abstract The sediment delivery ratio (SDR) is a bond of slope erosion and channel sediment transport but exhibits poor dynamic applicability, which makes it difficult to accurately identify the spatio-temporal evolutions of sediment yield in an ecological restoration watershed with different governance degrees. i) An innovative piecewise SDR algorithm considering the multi-stage effects of the comprehensive governance degree from 1991 to 2013 was embedded in a dynamic sediment yield model to solve the complex dynamic applicability problem of the SDR in sediment yield predictions. ii) The main advantages of the improved SDR algorithm over the existing models are small data requirements, dynamic mechanism, wide application range, reduced complexity, ease of use and better accuracy. iii) The erosion intensities of sloping farmland and orchards in the Yangou River watershed were both intensive at the early stage of governance in 1997. The trends in erosion and sediment yield were closely related to the watershed management measures. The soil erosion modulus in this watershed decreased from 5657 t/km2 in 1997 to 906.2 t/km2 in 2012, a total decrease rate of 84%. The sediment yield modulus decreased from 4500 t/km2 in 1997 to 51.9 t/km2 in 2012, a total reduction rate of 98.8%. iv) The annual dynamics of the SDR values were not completely affected by the random fluctuations in rainfall erosivity but showed an obvious decreasing trend from 0.932 in 1992 to 0.057 in 2012 due to the soil conservation measures. The annual average SDR in 1991–2013 was approximately 0.38, indicating that the average sediment yield after ecological restoration was significantly less than the average soil erosion in the Yangou River watershed. The results of this study may provide a better understanding of dynamic SDR studies and reveal the profound insights needed to guide watershed soil conservation planning. [ABSTRACT FROM AUTHOR]

Sediment connectivity has been shown in recent years to explain how the watershed configuration controls sediment transport. However, we find no studies develop a watershed erosion modeling framework based on sediment connectivity, and few, if any, studies have quantified sediment connectivity for gently rolling systems. We develop a new predictive sediment connectivity model that relies on the intersecting probabilities for sediment supply, detachment, transport, and buffers to sediment transport, which is integrated in a watershed erosion model framework. The model predicts sediment flux temporally and spatially across a watershed using field reconnaissance results, a high-resolution digital elevation models, a hydrologic model, and shear-based erosion formulae. Model results validate the capability of the model to predict erosion pathways causing sediment connectivity. More notably, disconnectivity dominates the gently rolling watershed across all morphologic levels of the uplands, including, microtopography from low energy undulating surfaces across the landscape, swales and gullies only active in the highest events, karst sinkholes that disconnect drainage areas, and floodplains that de-couple the hillslopes from the stream corridor. Results show that sediment connectivity is predicted for about 2% or more the watershed’s area 37 days of the year, with the remaining days showing very little or no connectivity. Only 12.8 ± 0.7% of the gently rolling watershed shows sediment connectivity on the wettest day of the study year. Results also highlight the importance of urban/suburban sediment pathways in gently rolling watersheds, and dynamic and longitudinal distributions of sediment connectivity might be further investigated in future work. We suggest the method herein provides the modeler with an added tool to account for sediment transport criteria and has the potential to reduce computational costs in watershed erosion modeling. [ABSTRACT FROM AUTHOR]

Accurate estimation of sediment concentration is essential to establish physically-based erosion models. The objectives of this study were to evaluate the effects of flow discharge (Q), slope gradient (S), flow velocity (V), shear stress (τ), stream power (ω) and unit stream power (U) on sediment concentration. Laboratory experiments were conducted using a 10 × 0.1 m rill flume under four flow discharges (2, 4, 8 and 16 L min −1 ), and five slope gradients (5°, 10°, 15°, 20° and 25°). The results showed that the measured sediment concentration varied from 87.08 to 620.80 kg m −3 with a mean value of 343.13 kg m −3 . Sediment concentration increased as a power function with flow discharge and slope gradient, with R 2  = 0.975 and NSE = 0.945. The sediment concentration was more sensitive to slope gradient than to flow discharge. The sediment concentration was well predicted by unit stream power (R 2  = 0.937, NSE = 0.865), whereas less satisfactorily by flow velocity (R 2  = 0.470, NSE = 0.539) and stream power (R 2  = 0.773, NSE = 0.732). In addition, using the equations to simulate the measured sediment concentration of other studies, the result further indicated that slope gradient, flow discharge and unit stream power were good predictors of sediment concentration. In general, slope gradient, flow discharge and unit stream power seem to be the preferred predictors for estimating sediment concentration. [ABSTRACT FROM AUTHOR]

Rainfall or snow-melted water recharge easily saturates loose top soils with a less permeable underlayer, such as cultivated soil slope and partially thawed top soil layer, and thus, may influence the velocity of water flow. This study suggested a methodology and device system to supply water from the bottom soil layer at the different locations of slopes. Water seeps into and saturates the soil, when the water level is controlled at the same height of the soil surface. The structures and functions of the device, the components, and the operational principles are described in detail. A series of laboratory experiments were conducted under slope gradients of 5°, 10°, 15°, and 20° and flow rates of 2, 4, and 8 L min −1 to measure the water flow velocities over eroding and non-eroded loess soil slopes, under saturated conditions by using electrolyte tracing. Results showed that flow velocities on saturated slopes were 17% to 88% greater than those on non-saturated slopes. Flow velocity increased rapidly under high flow rates and slope gradients. Saturation conditions were suitable in maintaining smooth rill geomorphology and causing fast water flow. The saturated soil slope had a lubricant effect on the soil surface to reduce the frictional force, resulting in high flow velocity. The flow velocities of eroding rills under different slope gradients and flow rates were approximately 14% to 33% lower than those of non-eroded rills on saturated loess slopes. Compared with that on a saturated loess slope, the eroding rill on a non-saturated loess slope can produce headcuts to reduce the flow velocity. This study helps understand the hydrodynamics of soil erosion and sediment transportation of saturated soil slopes. [ABSTRACT FROM AUTHOR]

Hydrological processes regulating sediment transport from land to sea have been widely studied. However, anthropogenic factors controlling the river flow-sediment regime and subsequent response of the estuary are still poorly understood. Here we conducted a multi-timescale analysis on flow and sediment discharges during the period 1967–2014 for the two tributaries of the Jiulong River in Southeast China. The long-term flow-sediment relationship remained linear in the North River throughout the period, while the linearity showed a remarkable change after 1995 in the West River, largely due to construction of dams and reservoirs in the upland watershed. Over short timescales, rainstorm events caused the changes of suspended sediment concentration (SSC) in the rivers. Regression analysis using synchronous SSC data in a wet season (2009) revealed a delayed response (average 5 days) of the estuary to river input, and a box-model analysis established a quantitative relationship to further describe the response of the estuary to the river sediment input over multiple timescales. The short-term response is determined by both the vertical SSC-salinity changes and the sediment trapping rate in the estuary. However, over the long term, the reduction of riverine sediment yield increased marine sediments trapped into the estuary. The results of this study indicate that human activities (e.g., dams) have substantially altered sediment delivery patterns and river-estuary interactions at multiple timescales. [ABSTRACT FROM AUTHOR]

Traditional flood risk analysis focuses on the probability of flood events exceeding the design flood of downstream hydraulic structures while neglecting the influence of sedimentation in river channels on regional flood control systems. This work advances traditional flood risk analysis by proposing a univariate and copula-based bivariate hydrological risk framework which incorporates both flood control and sediment transport. In developing the framework, the conditional probabilities of different flood events under various extreme precipitation scenarios are estimated by exploiting the copula-based model. Moreover, a Monte Carlo-based algorithm is designed to quantify the sampling uncertainty associated with univariate and bivariate hydrological risk analyses. Two catchments located on the Loess plateau are selected as study regions: the upper catchments of the Xianyang and Huaxian stations (denoted as UCX and UCH, respectively). The univariate and bivariate return periods, risk and reliability in the context of uncertainty for the purposes of flood control and sediment transport are assessed for the study regions. The results indicate that sedimentation triggers higher risks of damaging the safety of local flood control systems compared with the event that AMF exceeds the design flood of downstream hydraulic structures in the UCX and UCH. Moreover, there is considerable sampling uncertainty affecting the univariate and bivariate hydrologic risk evaluation, which greatly challenges measures of future flood mitigation. In addition, results also confirm that the developed framework can estimate conditional probabilities associated with different flood events under various extreme precipitation scenarios aiming for flood control and sediment transport. The proposed hydrological risk framework offers a promising technical reference for flood risk analysis in sandy regions worldwide. [ABSTRACT FROM AUTHOR]