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• T c of soils with varied particle size characteristics was contrasted. • Stream power were preferably recommended to predict T c for four soils. • Median particle size (D 50) and kurtosis (K g) were significantly correlated to T c. • The inclusion of D 50 and K g greatly improved the predictive accuracy of T c equations. The sediment transport capacity (T c) is essential for understanding soil erosion and creating soil erosion prediction models. Although many T c equations exist, they are not universally applicable to sloping farmland on the Loess Plateau. To tailor T c equations for this region, T c for four soils (Shenmu Inceptisol (SM I), Shenmu Entisol (SM E), Ansai Inceptisol (AS), and Yongshou Alfisol (YS)) from sloping farmland on the Loess Plateau was determined through flume tests with slopes ranging from 15.84 % to 38.39 % and flow discharges of 0.05 to 0.11 m2 min−1. Additionally, appropriate particle size characteristics were selected to distinguish the soil types. The results revealed that the T c of SM E exceeded that of YS, followed by SM I and AS in descending order. The T c of the four individual soils increased exponentially with flow discharge (Q) and slope (S). T c for individual soils could be satisfactorily predicted using power functions of mean velocity, shear stress (τ), stream power (ω), or effective stream power (R 2: 0.661–0.950, MAE : 0.020–0.110, RMSE : 0.023–0.151), with ω being identified as an optimal hydraulic parameter for simulating T c. In contrast, the unit stream power was a poor predictor of T c for individual soils (R 2: 0.403–0.700, MAE : 0.035–0.123, RMSE : 0.040–0.161). The median particle size (D 50), sorting coefficient, and kurtosis (K g) exhibited highly significant positive correlations with T c (P < 0.01). Finally, a quadratic power equation for Q , S , D 50 , and K g , along with two ternary power equations for ω (or τ), D 50 , and K g were newly constructed, all with satisfactory accuracies (R 2: 0.808–0.826, MAE : 0.061–0.063, RMSE : 0.086–0.090). The inclusion of σ and K g rectified the inaccuracies in predicting T c for all four soils using Q and S equations or ω (or τ). The results of this study offer valuable insights into the construction of the T c equations. [ABSTRACT FROM AUTHOR]

Based on soil erosion and sediment transport processes, CAMF (Cellular Automata-based heuristic for Minimizing Flow) selects sites for afforestation to minimize sediment influx at a catchment's outlet. CAMF uses a raster representation of the catchment and a steepest ascent hill-climbing optimization heuristic, safeguarding spatial interaction. Its execution time can be prohibitively long for large data-sets. Parallelization results in a speedup of 20 to 24 on 28 cores. We present variants of the optimization method to reduce the number and cost of the iterations. We present a tuning algorithm for the meta-parameters of these variants. The results obtained for two contrasting catchments illustrate that the accelerations reduce the cost by a factor larger than 100, with negligible effect on the afforested cells and magnitude of the sediment reduction. The results indicate that higher levels of spatial interaction have a stronger impact on the accuracy of the results and/or the execution time. • An efficient method to select sites for afforestation to minimize sediment loss. • Modified steepest ascent hill climbing method reduces runtime with minor quality loss. • A parallel implementation achieves nearly optimal speedup on multi-core processors. • Application to two river catchments shows the impact of spatial interaction. [ABSTRACT FROM AUTHOR]

Soil erosion rates after wildfire are strongly controlled by intrinsic properties such as topography, weather, climate, soil, and vegetation. These landscape and hydroclimatic properties are important in determining post-fire erosion rates; however, their influence on post-fire erosion and their interaction with the intensity of a wildfire remains uncertain. A key limitation in resolving this uncertainty is the lack of conceptual models and frameworks for organising data related to the geomorphic sensitivity of landscapes to wildfire. Our aim is to develop a framework for consolidating understanding of post-fire erosion in the context of hydroclimatic conditions which contribute to system states, for example soil and vegetation properties, and wildfire regime. The framework is developed around a simple conceptual model where the change in erosion due to wildfire is a product of change in runoff generation and sediment supply, which is strongly related to landscape net primary productivity (NPP). We hypothesised that geomorphic sensitivity to wildfire should vary as a unimodal humped relationship across a gradient of NPP, peaking at an intermediate level. To develop this framework and to test the hypothesis, we first review intrinsic soil and vegetation properties related to the supply and transport of sediment from burned and unburned hillslopes. Net primary productivity is systematically related to these intrinsic properties because it integrates many processes involved in soil and vegetation development. Empirical data indicate a trend in the change in surface runoff generation with NPP after wildfire, peaking at an NPP of approximately 15 Mg C ha−1 y−1. A simple model of fuel availability and soil heating are correlated with a similar "humped" trend in sediment supply. These results are consistent with our conceptual model, which indicates that sediment supply and runoff contribute towards a distinct peak in wildfire effects on erosion at an intermediate level of NPP. We propose that landscapes of intermediate NPP typically have the highest quantity of fuel available to burn, which cause large changes to the soil surface properties. Landscapes at intermediate NPP also tend to produce intrinsic soil and vegetation properties that promote erosion after wildfire. The interplay between these short and long-term landscape characteristics is strongest at intermediate levels of NPP. Our proposed biogeographic model of geomorphic sensitivity to wildfire was supported by erosion data from burned hillslope and zero-order catchments studies from a range fire-prone landscapes in Australia and North America. Our proposed conceptual model will help identify areas most vulnerable to post-fire erosion changes. [ABSTRACT FROM AUTHOR]

• The runoff, sediment load and runoff erosion power decreased significantly. • Compared with runoff, runoff erosion power-sediment relationship is better. • The power function of runoff erosion power and sediment is better than linear. • Erosion in particular geographic locations responds strongly to runoff erosion power. In recent years, the acceleration of urbanization in the Yangtze River Economic Belt (YREB) has brought about problems such as soil erosion, ecosystem degradation and decline in ecological service functions. Therefore, this paper selects the Fujiang River Basin (FRB) in Upper Yangtze River (UYR), and analyzes the relationship between runoff erosion power (REP) and sediment transport (ST) on the basis of analyzing the variation characteristics of hydrological elements. Based on SWAT model, a variety of scenarios are set up to quantitatively analyze the impact of different land use changes on runoff and ST and REP in the basin. The results indicated that: (1) The annual precipitation in FRB from 1960 to 2018 did not change significantly, while the annual runoff, annual ST and annual REP decreased significantly. Compared with runoff and runoff depth, the relationship between sediment transport modulus (STM) and REP is the best, especially the power function between them is better than the linear function. (2) The results of the evaluation indexes of the simulation results of the SWAT model based on the measured runoff and sediment data from 2008 to 2018 are pass and above, that is, the simulation results are considered reliable. (3) Under the five scenarios of conversion of sloping farmland to forest, conversion of dry land to paddy field and conversion of grassland to bushland and forest land, the runoff and ST in the basin decreased but the overall range was small. The simulation results of SWAT model show that the erosion of specific areas in the basin shows the greatest degree of weakening with the decrease of REP. [ABSTRACT FROM AUTHOR]

• Unprecedented monitoring datasets are available to support land health assessments. • Benchmarks enable objective and actionable data-informed management decisions. • Framework for establishing benchmarks and illustrated examples are presented. • Potential caveats and best practices for benchmarking approaches are described. • Future research needs identified for benchmark research and applications. Soil erosion can have a multitude of negative impacts on agroecosystems and society and there remains an urgent need for tools to support its management. Quantitative benchmarks based on holistic understanding of erosion processes, ecosystem function, and land use objectives can be used with monitoring data and models to inform assessments and make objective and actionable decisions about erosion management. However, managers currently lack a framework for establishing benchmarks. Here, we present a framework and evaluation of different approaches to establishing quantitative benchmarks for soil erosion and ecological monitoring and assessment that can inform land management decisions. We use monitoring data collected across Chihuahuan Desert ecosystems in the United States and an aeolian sediment transport model to illustrate how benchmarks can be established. Approaches include establishing benchmarks from relationships between soil erosion indicators, reference states and land potential, including state-and-transition models, and desired conditions from existing monitoring data. We discuss the benefits and caveats of the different approaches and show how combining different benchmarking approaches can help users ensure that benchmarks appropriately reflect thresholds for soil erosion and achievable management outcomes. We finish by identifying future research needs to support establishment and application of erosion benchmarks across agroecosystems and recognize the opportunity to extend the benchmarking approaches to management of other agroecosystem processes and services. [ABSTRACT FROM AUTHOR]

Literature review reveals that many erosion models have limitations for application to constructed landforms. The new EroCA model aims to address this gap. The model uses established erosion and sediment transport models applied to multiple particle size classes at fine spatial and temporal resolutions, covering both suspended load and bedload. Using data from an experimental plot in Northern Australia, global sensitivity analysis was used to investigate the sources of uncertainty, limitations of the model, and priorities for data collection. Further analysis explored sensitivity to model grid size. The results showed that the Manning roughness, erodibility parameters and particle size are the most important parameters. Results also showed low parameter identifiability and hence the difficulty of calibration, even when using high quality experimental data. EroCA has the capacity to be a powerful landform modelling tool at appropriate scales of application; however ideally its data needs would be considered during monitoring design. • In-depth attempt to develop and assess a high spatial resolution process-based erosion model for a mined landform. • Improved understanding of the effects of various parameters on soil erosion process and modelling. • New insight into the limitations of experimental plot data sets for supporting high resolution erosion models. [ABSTRACT FROM AUTHOR]

• Compared dynamics of discharge and sediment loads in four large basins. • Explored the impact of climate, and human activities on water and sediment. • Sediment transport showed significant decreasing trends with abrupt changes. • Human activities played a predominant role in reducing sediment transport (>80%). • Impacts of land cover change on sediment loads were basin-independent. Human activities and climate are two key factors affecting hydrological and soil erosion processes. Understanding their impacts on water discharge and sediment transport is very important for sustainable development of watersheds, particularly in subtropical regions with high precipitation and high sediment loads. We here compared the long-term dynamics of water discharge and sediment transport in four large contiguous watersheds in subtropical China and explored the importance of the main influencing factors including climate, nature endowment such as geology, and human activities. Significant differences have been observed between watersheds in terms of sediment and water discharge (p < 0.001). Pairwise comparison among the four basins demonstrated significant differences in sediment modulus among 5 of the 6 pairs (p < 0.05). The sediment modulus in the Lishui Basin was significantly higher than those in other basins, mainly due to the substantial presence of steep slopes in the mountainous region, which is prone to soil erosion. Temporally, sediment transport in the four basins was well synchronized showing significant decreasing trends with abrupt change points (p < 0.001). In contrast, no trends and abrupt change points were detected in water discharge, mainly influenced by precipitation. Human activities played a predominant role to the reduction of sediment transport (80% to 102%) compared with those of climate (-2% to 19%) across the four basins. Additionally, our study also showed land cover had various basin-independent impacts on the change of sediment transport. Through cross-basin comparisons of the long-term changes in water discharge and sediment transport, our study revealed the similarities and differences in their driving mechanisms, providing valuable information for land use planning and water resource management in large subtropical basins. [ABSTRACT FROM AUTHOR]

Water erosion on agricultural land and sediment delivery to streams are a major threat to soil productivity and surface water quality. Climate change and different national and international societal drivers now require Denmark to take action to protect soil and water resources. In this study, we adapted the spatially distributed sediment transport model WaTEM using the best data available at national scale. To calibrate and validate the model, sediment yield data from 31 catchments and 189 slope units in Denmark were compared with the model output, which was produced at a fine spatial resolution of 10 × 10 m. Residual analysis and cross-validation were used to identify potential catchment outliers and assess model robustness. We obtained a median Nash & Sutcliffe model efficiency range of 0.06–0.6 for the Danish environment. Based on the equifinality concept, an ensemble of 100, NSE-weighted model realisations for acceptable transport capacity coefficients was used to assess model uncertainty. The comparison between rill survey data and predicted values indicates that although the model captures well the spatial variability in erosion, it may underestimate the long-term average of soil erosion. Based on the modelling, 71% of the agricultural land in Denmark is mapped as stable in terms of the amount of erosion and deposited material. Overall, 6.1% of the farmland is estimated to have unsustainable erosion and 0.9% of the farmland exceeds erosion rates of 7.5 t ha−1 a−1. Sediment export into surface water in Denmark equals 92,000 t a−1, corresponding to an average sediment yield of 2.7 t km−2. The performance of WaTEM is considered satisfactory in this study. Importantly, modelled water erosion exceeds the perceived erosion risk in Denmark. Strengthened by distributed uncertainty assessment at national scale, our study provides an important national knowledge base for engaging land users and regulators in the process of targeted erosion mitigation planning that is required to comply with national and EU regulation. Future investigations concerning the deviation between predicted and observed data and specific catchment parameters for the non-behavioural catchments are required as well as studies that include the establishment of catchment sediment budgets. • High resolution national water erosion modelling for future mitigation planning • Model calibration and validation with 31 nationwide catchments and field surveys • Explicit consideration of model uncertainty [ABSTRACT FROM AUTHOR]

Computer-based coupled soilscape-landform evolution models provide an avenue for estimating the erosion potential of a landform over geological timescales. They also provide tools to understand soil-landform relationships in the context of both field and modelled pedogenesis processes. In this study, we used the State Space Soil Production and Assessment Model (SSSPAM) and CAESAR-Lisflood landform evolution model to simulate the evolution of a natural catchment where soil erosion rates have been closely monitored over the last 20 years. Both models predict comparable erosion rates to that of field measurements and produce similar catchment scale geomorphological patterns. Rock content data measured in the field along two transects were compared with SSSPAM simulations at the same representative points. The results showed that SSSPAM produced similar rock content variation along the respective transects. The findings demonstrate 'SSSPAM's ability to predict catchment scale erosion and surface soil distribution. The insights demonstrated here provide confidence in the SSSPAM model for Soilscape predictions for natural, agricultural and post-mining landform assessment. [Display omitted] • SSSPAM and CAESAR-Lisflood models were used to simulate the evolution of a natural catchment. • Both models produced catchment erosion rates comparable with field observations. • SSSPAM reproduced surface rock content variation on 2 transects observed in the field. • SSSPAM also revealed a possible relationship between area, slope and soil grading. • This study demonstrates SSSPAM's ability to predict erosion and surface soil distribution. [ABSTRACT FROM AUTHOR]

Watershed-scale simulation technology allows quantification of the impact of individual and/or integrated management practices throughout the watershed. In the AnnAGNPS watershed-scale model, the watershed is subdivided into basic modeling units (fields) in which all spatially varying physical parameters are assumed to be homogeneous. Conversely, RUSLE2 model can estimate sediment yield at sub-field scale with enhanced characterization capabilities. In this study, an integrated approach was developed and evaluated that combines both models for enhanced representation of individual fields while accounting for the watershed-wide integrated intra fields effect when routing sediment loads through the watershed. Critical sediment producing areas identified through integrated RUSLE2 erosion and AnnAGNPS sediment transport models can be used to support the development and evaluation of conservation management plans specific to fields but impacting the entire watershed. • Watershed simulation integrating field-scale descriptions of erosional processes. • U.S. Department of Agriculture AnnAGNPS and RUSLE2 integrated technology. • Multi-segmented slope profiles improved modeling capability at finer scale. • Integrated solution allows evaluation of field practices at watershed scales. [ABSTRACT FROM AUTHOR]

Storm surge is a critical component in the evolution of barrier island systems, eroding the shoreface and depositing sediment landward as overwash deposits; this "rollover" process enables barrier islands to migrate landward during periods of rising sea level. However, cyclonic storms may also generate seaward-directed flow and sediment transport, which is not typically accounted for in barrier island modeling. A strong outflow occurred at Port Aransas, Texas during Hurricane Harvey in 2017, as evidenced from field observations, satellite photos, and tide data; modeling indicates that outflow was forced by offshore winds to the left of landfall. To investigate the impact of this event on the barrier system, we collected post-storm multibeam bathymetry data and sediment samples within Aransas Pass and Lydia Ann Channel, important conduits linking the bays to the Gulf of Mexico, and where such data were previously collected in 2009 and 2012. The 2009–2012 comparison provides a baseline against which to ascertain the storm impact contained in the 2012–2017 comparison. Both land- and marine-based evidence indicate that significant erosion accompanied the outflow event, focused at the edges of the Corpus Christi ship channel and Lydia Ann Channel. Large quantities of sand, up to 6.5 m thick, also accumulate in deeps of Aransas Pass and Lydia Ann Channel, presumably as the outflow event waned in strength. We infer that the outflow event transported a large amount of barrier system sands offshore, but do not have sufficient constraints at this time to quantify it. • Hurricane Harvey induced a seaward-directed surge on its left side. • We document loss of inshore sediment, and no overwash deposits in the study region. • Bathymetric data document a major sediment transport event. • Combined evidence suggests net loss of barrier sand to offshore around Port Aransas. [ABSTRACT FROM AUTHOR]

Abstract As rivers approach base level, their water and sediment dynamics are affected by a transitional reach known as the backwater zone. At low flows, backwater zones cause flow deceleration and in-channel sedimentation, but at high flows, they cause flow acceleration and erosion. Over many floods, the dynamics of deposition and erosion in the backwater zone are thought to control the locations of avulsions on some large deltaic channels. However, in various studies, the role of the backwater is often inferred or modeled, and directly observed evidence of how backwater affects channel dynamics at avulsion sites remains scarce. In this study, we show how the backwater zone impacts the evolution and avulsion of the Qingshuigou channel, a recent lobe on the Yellow River Delta, using four decades (1976–2015) of data from systematic surveys of water discharge, sediment load, cross-sectional profiles and water surface elevation. The results show that the channel was commonly eroded during flood seasons and aggraded during nonflood seasons. Erosion rates generally decreased in the downstream direction along the lower channel reach during flood seasons, primarily due to downstream channel widening and the subsequent decrease in sediment transport capacity. The erosion rate reached zero at the cross-sections farthest downstream, which is contrary to expectations under hydrodynamic backwater effects, where drawdown causes erosion to increase downstream during high flows. During nonflood seasons, maximum sedimentation occurred upstream of the backwater zone, possibly due to impacts of local topography of meandering bends or constriction from dikes. Morphodynamic backwater accompanied by the deposition and gradual progradation of a mouth bar resulted in downstream increasing sedimentation, superelevation, and lateral migration rates along the lower channel reach from 1985 to 1996. The predicted avulsion location was near cross-sections Q6 or Q7 with an avulsion length of ~20–30 km upstream of the shoreline, which was consistent with those for historical avulsions. We emphasize the close interplay between backwater effects and channel geometry and argue that morphodynamic backwater may play a more important role than hydrodynamic backwater in setting up and triggering avulsions on the Yellow River Delta. Highlights • Backwater effects are strongly influenced by the downstream changes in channel geometry. • Erosion rate decreased downstream along the widening lower reach during high flows. • Sedimentation under morphodynamic backwater effects rendered the channel unstable. • The channel may be more impacted by morphodynamic than hydrodynamic backwater. [ABSTRACT FROM AUTHOR]

Deforestation in New Zealand has led to increased soil erosion and sediment loads in rivers, adversely affecting aquatic ecosystems. Soil conservation actions over large areas are expensive and need to be targeted to obtain maximum benefit for least cost. Medium-complexity models of soil erosion have been used to target soil conservation, but they involve long-term averages and do not involve time variation. In this paper, an event-based model of soil erosion and sediment transport is developed. It has moderate complexity and is able to be calibrated with a modicum of data. The spatial framework is based on small subcatchments and stream links. For each storm event, the sediment yield for each subcatchment is estimated from peak storm discharge with a power function and routed through the stream network. We run the model on the Manawatū catchment in New Zealand for which all the major tributaries are monitored for water and sediment discharge. Spatial maps of sediment yield are produced for each storm event in a 5-year period from model inputs of maximum storm discharge at the tributaries. To test the model, predicted sediment loads of the storm events in the main channel of the Manawatū, at Teachers College, Palmerston North, are compared with measured sediment loads. The strong agreement between predictions and measurements suggests that the method for converting maximum storm discharge to sediment load at tributaries is robust. Analysis of the sediment concentration and discharge records for storm events revealed that sediment from channel resuspension and bank erosion was much smaller (typically <5%) than total storm sediment loads and could thus be ignored when routing storm sediment loads. The demonstrably small channel resuspension and bank erosion, relative to storm sediment loads, enabled simple routing from subcatchments to construct an event-based model at the catchment scale. [ABSTRACT FROM AUTHOR]

The Sediment Transport and Erosion Prediction (STEP) model is methodically described in this paper. The STEP model was implemented at a 3.47 km × 3.47 km grid resolution in the Kalisapi sub-watershed, Central Java, Indonesia. It was calibrated and validated in the period of 2003–2008 and 2010–2014 respectively. The result shows that the STEP model functions satisfactorily at monthly and annual time window in the calibration and validation periods. In both periods, the STEP model is able to produce fruitful annual sediment transport rates with R2 values of 0.71 and 0.9 in the calibration and validation period respectively. Moreover, the STEP model exhibits more equitable spatial variability than that of the widely known USLE model. Correspondingly, it can be surmised that the STEP model is capable of simulating spatial and temporal variability of sediment transport from a watershed at monthly and annual time scales. • STEP model is developed to simulate soil erosion, deposition and sediment transport processes in time and space. • STEP model has been successfully implemented, calibrated and validated in the Kalisapi sub-watershed, Indonesia. • Calibrating STEP model to fit the observation is straightforward as it only needs to modify two model parameters. • STEP model source code and input data for the study area are freely available in the Bitbucket repository service. [ABSTRACT FROM AUTHOR]

Soil piping is an important land degradation process that occurs in a wide range of environments. Despite an increasing number of studies on this type of subsurface erosion, the impact of vegetation on piping erosion is still unclear. It can be hypothesized that vegetation, and in particular plant roots, may reduce piping susceptibility of soils because roots of vegetation also control concentrated flow erosion rates or shallow mass movements. Therefore, this paper aims to assess the impact of grass roots on piping erosion susceptibility of a sandy soil. The pinhole test was used as it provides quantitative data on pipeflow discharge, sediment concentration and sediment discharge. Tests were conducted at different hydraulic heads (i.e., 50 mm, 180 mm, 380 mm and 1020 mm). Results showed that the hydraulic head was positively correlated with pipeflow discharge, sediment concentration and sediment discharge, while the presence of grass roots (expressed as root density) was negatively correlated with these pipeflow characteristics. Smaller sediment concentrations and sediment discharges were observed in root-permeated samples compared to root-free samples. When root density exceeds 0.5 kg m − 3 , piping erosion rates decreased by 50% compared to root-free soil samples. Moreover, if grass roots are present, the positive correlation between hydraulic head and both sediment discharge and sediment concentration is less pronounced, demonstrating that grass roots become more effective in reducing piping erosion rates at larger hydraulic heads. Overall, this study demonstrates that grass roots are quite efficient in reducing piping erosion rates in sandy soils, even at high hydraulic head (> 1 m). As such, grass roots may therefore be used to efficiently control piping erosion rates in topsoils. [ABSTRACT FROM AUTHOR]

Information on recent changes in sediment yields from small catchments provides a better understanding of temporal trends in soil loss from certain physical and human-influenced landscapes that have been subjected to recent environmental changes, and will help bridge the current knowledge gap that exists between hillslope erosion and sediment transport in rivers. The Yimeng Mountain region, characterized by alternating granite and limestone, is one of the most susceptible regions to soil erosion in northern China, and has been subjected to intensive anthropogenic activity in recent years. Soil loss from areas underlain by granite is particularly obvious, and is the main sediment source for the Yihe River. In this study, we used reservoir deposits to estimate the changes in sediment yields over the past ~ 50 years from a small catchment underlain by granite, namely the Jiangzhuang catchment in the Yimeng Mountain region. Three cores were collected from the Jiangzhuang Reservoir in the catchment. The activities of 137 Cs and 210 Pb ex at different depths, clay (grain size < 5 μm) contents, and sedimentary organic carbon (SOC) contents in the cores were analysed with reference to human activity and environmental change in the catchment. The chronologies of the cores were established by 137 Cs and 210 Pb ex dating. The area-specific sediment yield ( SSY ) for different time periods since dam construction was estimated from each core by referring to the original capacity curve of the reservoir. The results indicate that the depth profiles of 137 Cs, 210 Pb ex , clay, and SOC contents in cores from the Jiangzhuang Reservoir reflect the general history of human disturbances on the catchment over the past ~ 50 years. The estimated SSY value from each core for each period ranged from 7.2 ± 2.7 to 23.7 ± 8.3 t ha − 1 y − 1 , with a mean of 12.5 ± 4.6 t ha − 1 y − 1 . SSY decreased during 1954–1972, and then showed a general tendency to increase. The temporal pattern of the sediment yield largely reflects the history of environmental change influenced by human activity in the catchment. [ABSTRACT FROM AUTHOR]

Construction and operation of cascading dams can pose drastic effects on sediment transport and deposition, thus affecting sedimentary carbon concentrations in the riverine ecosystem. This paper examines the spatial variations of sedimentary organic carbon (OC sed ) and its potential relationship with terrestrial soil loss in two cascade reservoirs (Manwan and Dachaoshan) along the mainstream of Lancang River. During both wet and dry seasons in 2013 and 2014, 25 sampling sections were chosen to evaluate the spatial variations of sedimentary organic carbon. Generally, the contents of OC sed in the upper 5 cm of the bottom sediment in wet seasons were higher than those in dry seasons in both reservoirs. Spatially, lower reservoir (Dachaoshan) preserved higher OC sed content than the upper reservoir (Manwan), at 36.1 kg m −2 and 27.8 kg m −2 , respectively. Additionally, the contents of OC sed in the reservoir heads were higher than those in the reservoir centres and tails, this trend was also observed for terrestrial organic carbon (OC ter ) and liable organic carbon (LOC). Hillslope delivery ratio (HSDR) method are used to estimate the incoming sediment yields from the river basin. The results indicated that Dachaoshan catchment generated higher sediment stream deposits than the Manwan catchment with the high sediment loading (>40 t/ha/year) areas located within 3 km buffers encompassing a higher accumulation of farmlands. The cumulative effects of sediment transport on OC sed along the river channel were further investigated by setting sequential riverine sediment delivery ratios (0–0.55) to explore potential relationships between OC sed and total sediment delivered to stream. The results showed that in the Dachaoshan Reservoir the OC sed contents correlated with the total sediment delivered to streams when the ratios ranged from 0.10 to 0.55, in particular in delivery ratios ranging from 0.50 to 0.55. These findings emphasized the importance of direct and indirect connections between the terrestrial and riverine ecosystems, and also provided a preferable view to understand the cumulative effects of sediment transport on OC sed distributions in the reservoirs generated by cascading dams. [ABSTRACT FROM AUTHOR]

• Modelled erosion losses from arable land were within the error limits of field methods. • Modelling plausibly estimated erosion reduction with cropland reconfiguration. • Simulated net erosion for the entire catchment was underestimated by 3.5–4.5 times. This paper presents very detailed studies of soil erosion within a small arable catchment located in the centre of the East European Plain. Sediment redistribution was estimated based on soil profile truncation, radiocesium methods and erosion modelling. WaTEM/SEDEM and State Hydrological Institute model were used for the evaluation of soil losses during rainfall and snowmelt, respectively. Evaluation of soil erosion and sediment redeposition was carried out taking into account historical changes in the cropland boundaries. Model estimates of soil losses from arable land are in good agreement with evaluations of erosion rates based on the results field method applications, taking into account the uncertainty of the methods. Erosion modelling made it possible to fairly plausibly estimate the decrease in soil erosion losses by approximately by a third as a result of a small (about 5%) reduction in the area of arable land in the studied catchment. The main disadvantage of applied erosion models were associated with the insufficient accuracy of estimates of the sedimentation volume and location deposition zones, mainly outside the arable land. The simulated net erosion for the entire catchment was underestimated by 3.5–4.5 times compared with field methods. This simulation block must be calibrated taking into account the regional coefficients of sediment transport in the bottoms of the dry valley network. [ABSTRACT FROM AUTHOR]

• The aggregated index of sediment connectivity (AIC) was applied for the first time on large regional scale. • Both structural connectivity and functional connectivity were calculated and compared. • The role of AIC factors in the sediment patterns over the months of the year were analysed. • Correlation coefficient between monthly sediment yield data and AIC were calculated as an attempt to validate the AIC result. Hydrological and sediment dynamics have changed considerably on the Chinese Loess Plateau during the last six decades due to large scale land use changes and numerous water regulation actions. Understanding the mechanism of sediment transport change and its effects is of great importance to food and environmental security. Numerical approaches are useful to map and assess spatio-temporal patterns in sediment dynamics. This study evaluates monthly and annual sediment connectivity in the Wei River Basin (134,800 km2) at the basin and sub-basin scales using the aggregated index of sediment connectivity (AIC). For the first time, this index is applied on this relatively large regional scale. The two objectives were to (1) evaluate the performance of the AIC at the regional scale, addressing substantial differences among areas, and (2) analyze how each AIC sub-factor co-determines the monthly sediment and connectivity patterns. Results show that AIC has strong or moderate positive correlation with sediment yield from 15 out of 23 stations in the Wei and Jing sub-basin. The Jing sub-basin has the highest sediment connectivity due to degraded vegetation, while the Beiluo sub-basin has the lowest sediment connectivity on average due to better ecological restoration. Within the year, sediment connectivity is highest in April and lowest in January, due to the rainfall regime and intra-annual land cover variations. Among the AIC factors, the rainfall factor has the highest effect on sediment connectivity, implying that functional connectivity (graded by rainfall and soil cover) determines sediment dynamics more than structural connectivity (mainly determined by topography and soil permeability). This study provides one of the first large-scale estimates of spatial and temporal sediment connectivity from hillslopes to river stream and including large reservoirs, which can be further employed to implement regional ecological construction works and environmental catchment management. [ABSTRACT FROM AUTHOR]

A new modeling platform was developed to simulate spatially distributed sediment production and transport in agricultural landscapes. The sediment production at the grid scale was computed using the stand-alone Water Erosion Prediction Project-Hillslope Erosion code, while an advection-dispersion equation represented sediment transport. The model's performance was tested in the Water Resources and Erosion watersheds at the Oklahoma and Central Plains Agricultural Research Center, El Reno, OK, USA. Results showed that this modeling approach could capture the complex behavior of sediment under different management practices in the watersheds. The modeling framework provides mechanistic processes to simulate the fate and transport of sediment across the watershed at spatio-temporal scales that are useful in assessing the environmental impacts of management schemes. Therefore, this study is expected to help advance the current approaches to estimating soil erosion by bridging scale differences to capture the large-scale effects of small-scale soil erosion processes. • A new modeling framework was developed for estimating soil erosion. • Sediment production is evaluated in fully distributed settings. • Different sizes of sediment are considered in simulations. • The model provides mechanistic processes in simulating sediment transport. • The model is able to capture changes in land and management practices. [ABSTRACT FROM AUTHOR]

The reproduction of seventeen laboratory tests for dune erosion by the surf-beat mode of the two-dimensional horizontal (2DH) model XBeach for storm wave conditions showed that the model overestimates the erosion and thus the deposition volumes. This overestimation becomes particularly significant for very large overtopping rates on coastal barriers, which are commonly induced by extreme storm surges. In this paper, the recent model improvements to overcome this problem are first summarised. Moreover, two physical reasons for these overestimations are identified: (i) the wave nonlinearity effect on sediment transport, which is described in XBeach by a calibration factor for the time-averaged flow depending on the wave skewness and asymmetry and (ii) the considerable excess of the actual shear stress required to initiate the sediment particle motion as compared to that predicted by the common Shields curve. To improve the prediction capability of XBeach in terms of erosion and overwash volumes, two new improvements, related to the two aforementioned reasons for the overestimation, are introduced and implemented in the model. The improved XBeach model is then tested for dune erosion, for barrier breaching as well as for a barrier island erosion and overwash under an extreme storm surge event. The results showed a very good prediction capability of the improved model. Particularly, the second model improvement opens the way toward further model improvements to account for spatially varying soil resistance, which is crucial for reliable prediction of a barrier breaching. [ABSTRACT FROM AUTHOR]

Rapid deterministic modelling of shoreline evolution at regional and coastal-scheme scale enables Monte-Carlo simulations by which long-term shoreline statistics can be estimated. This paper describes UnaLinea, a fast, accurate finite difference solver of the one-line sediment continuity equation. The model is verified for the evolution of an initially straight shoreline of a plane beach subject to regular breaking waves at constant angle of incidence in the presence of either a groyne or a continuous single-point feed of sediment. Grid convergence and stability tests are used to obtain accurate, stable results, with satisfactory computational efficiency. Influences of wave input filtering and event-based sediment loading are considered. The rapid deterministic model is applied to Monte-Carlo simulations of the evolution of the west coast of Calabria, Italy for different scenarios including increased sediment load from a river and selected beach nourishment. The potential role of probabilistic shoreline evolution in regional coastal flood-risk assessment is explored through application to an idealised stretch of the Holderness coastline, U.K., where flood depths and expected damage are estimated for a 1000 year return period event. [ABSTRACT FROM AUTHOR]

This paper treats the numerical modelling of the behaviour of a sand core covered by rocks and exposed to waves. The associated displacement of the rock is also studied. A design that allows for erosion and deposition of the sand core beneath a rock layer in a coastal structure requires an accurate prediction method to assure that the amount of erosion remains within acceptable limits. This work presents a numerical model that is capable of describing the erosion and deposition patterns inside of an open filter of rock on top of sand. The hydraulic loading is that of incident irregular waves and the open filters are surface piercing. Due to the few experimental data sets on sediment transport inside of rock layers, a sediment transport formulation has been proposed based on a matching between the numerical model and experimental data on the profile deformation inside an open filter. The rock layer on top of a sand core introduces a correction term in the Exner equation (the continuity equation for sediment and change in bed level). The correction term originates from the fact that the sand can only be deposited in the pores of the filter material. The numerical model is validated against additional data sets on the erosion and deposition patterns inside of an open filter. A few cases are defined to study the effect of the sinking of the filter into the erosion hole. The numerical model is also applied to several application cases. The response of the core material (sand) to changes in the wave period and wave height is considered. The effect of different layouts of the filter is studied in order to investigate the effect of different filter profiles on the resulting erosion. Finally, it is studied how much the design of a hydraulically closed filter can be relaxed to obtain a reduction in the design requirements of the filter thickness, while the deformation to the sand core remains acceptably small. [ABSTRACT FROM AUTHOR]

Sand nourishments are presently widely applied to maintain or enhance coastal safety and beach width. Over the last decades, global sand nourishment volumes have increased greatly, and the demand for nourishments is anticipated to increase further in coming decades due to sea level rise. With the increase in nourishment size and the request for more complex nourishment shapes, an adequate prediction of the morphodynamic evolution is of major importance. Yet, neither the skill of current state-of-the-art models for such predictions nor the primary drivers that control the evolution are known. This article presents the results of a detailed numerical modelling study undertaken to examine the model skill and the processes governing the initial morphological response of the Sand Engine and the adjacent coastline. The process-based model Delft3D is used to hindcast the first year after completion of the mega-nourishment. The model reproduces measured water levels, velocities and nearshore waves well. The prediction of the morphological evolution is consistent with the measured evolution during the study period, with Brier Skill Scores in the ‘Excellent’ range. The model results clearly indicate that the sand eroded from the main peninsular section of the Sand Engine is deposited along adjacent north and south coastlines, accreting up to 6 km of coastline within just one year. Analysis of model results further show that the erosional behaviour of the Sand Engine is linearly dependent on the cumulative wave energy of individual high energy wave events, with the duration of a storm event being more dominant than the maximum wave height occurring during the storm. The integrated erosion volume due to the 12 events with the highest cumulative wave energy density accounts for about 60% of the total eroded volume of the peninsula, indicating that the less energetic wave events, with a higher probability of occurrence, are also important for the initial response of the Sand Engine. A structured model experiment using the verified Delft3D model indicates that wave forcing dominates the initial morphological response of the Sand Engine, accounting for approximately 75% of the total erosion volume in the first year. The vertical tide is the second most important factor accounting for nearly 17% of the total erosion volume, with surge, wind and horizontal tide playing only a minor role. [ABSTRACT FROM AUTHOR]

XBeach, a process-based numerical model designed to simulate morphologic change during extreme storm events, was calibrated and compared to observations from a large-scale laboratory dune erosion experiment. Wave conditions along the tan, wave runup at the beach, and 3-dimensional position of the dune were measured throughout the experiment. Seiching modes in the tank were simulated and matched the observations once the model was calibrated. Simulated waves were sensitive to γ , the ratio of wave height to water depth, and c f. , the coefficient of friction. Simulated runup explained 50–87% of the observed variance in observations. However, the magnitude of simulated wave runup was underestimated throughout the experiment. Errors in simulated runup were composed of a high bias and gain error in mean water level, low bias in the infragravity swash, and low bias and gain errors in incident swash. Observed probability density functions of swash were statistically consistent between times when swash was confined to the foreshore and times when swash interacted with the dune. However, simulated probability density functions of swash were statistically different during the collision regime. Despite the systematic underestimation of wave runup, modeled dune erosion compared well with observations after the sediment transport parameters were calibrated. Modeled dune erosion was sensitive to the critical slope parameters over the wet and dry regions of the beach, the depth of the interface between the wet and dry regions of the beach, and the threshold depth for sediment transport and return flow. [ABSTRACT FROM AUTHOR]

Sedimentological connectivity is an important issue in soil erosion and sediment transport. Landscape patterns, in combination with the rainfall regime, are known to shape such sedimentological connectivity. The quantification of sedimentological connectivity provides a link between sediment delivery and landscape pattern. There are two categories of connectivity: structural connectivity, which describes the physical coupling of landscape units, and functional connectivity, which delineates the linkage among landscape elements maintained by material transport. To quantify sedimentological connectivity, both the physical coupling of, and material transfer between, the various landscape components need to be assessed. This study quantifies the sedimentological connectivity of a headwater catchment in the Loess Plateau of China using the soil erosion and sediment delivery model (WATEM/SEDEM). Based on the model, two indicators of connectivity were developed: the area of sedimentologically effective catchment area (SEA) that contributes sediment to the sinks, and the minimum sediment output of locations on the flow path that link sources and sinks. This approach effectively represents the annual status of catchment-scale sedimentological connectivity and, furthermore, the simple structure and readily available input data make it highly practicable. However, for larger river systems in which sediment transport between sources and sinks occur over longer time scales and larger spatial scales, we suggest different techniques for quantifying the sediment flux and parameters delineating the physical coupling of landscape units. [ABSTRACT FROM AUTHOR]

The trend and episodes of erosion at Great Kills Park, part of the National Park Service, are products of the origin of the park's location and the impact of a negative sediment budget. Management response to the impacts of erosion is somewhat limited by National Park Service philosophy, but some options remain because the negative sediment budget is a product of barriers to sediment transport updrift of the Park. The erosional situation is exacerbated by an exposure of an antecedent backmarsh feature within the Park that is affecting the inshore pattern of incident waves. Recent monitoring data indicate planform conformity to an updrift log-spiral erosional bluff that extends downdrift to a site with beach and dune features. Despite a general net negative sediment budget in the profile, the dune feature is increasing in volume as it shifts inland, fitting models of foredune development. Seasonal monitoring of the topography records that storms cause a stepwise inland displacement of an updrift portion of the Park and a more linear displacement in the downdrift portion. Among the options consistent with management policy responding to the negative sediment budget issue is an opportunity to work within the scale of the small sediment transport cell and backpass sediment toward the updrift margin of the cell. [ABSTRACT FROM AUTHOR]

Detailed measurements of bed level motions and sheet flow processes in the lower swash are presented. The measurements are obtained during a large-scale wave flume experiment focusing on swash zone sediment transport induced by bichromatic waves. A new instrument (CCM + ) provides detailed phase-averaged measurements of sheet flow concentrations, particle velocities, and bed level evolution during a complete swash cycle. The bed at the lower swash location shows a clear pattern of rapid erosion during the early uprush and progressive accretion during the middle backwash phase. Sheet flow occurs during the early uprush and mid and late backwash phases. Sheet flow sediment fluxes during these instances are highest in the pick-up layer. Sediment entrainment from the pick-up layer occurs not only during instances of high horizontal shear velocities but also in occurrence of wave–backwash interactions. As opposed to oscillatory sheet flow, the pivot point elevation of the sheet flow layer is time-varying during a swash event. Moreover, the upper sheet flow layer concentrations do not mirror the concentrations in the pick-up layer. Both differences suggest that in the lower swash zone the dynamics of the upper sheet flow layer are not only controlled by vertical sediment exchange (such as in oscillatory sheet flows) but are strongly affected by horizontal advection processes induced by the non-uniformity of the flow. [ABSTRACT FROM AUTHOR]

• Landscape wind erosion modeling scheme (LWE) was integrated with the Agricultural Policy/Environmental eXtender (APEX) model. • APEX1905 model simulates wind-driven soil erosion in rangeland reasonably when compared to field measurements. • Surface roughness height strongly influences the horizontal sediment transport. • APEX1905 produced the measured unvegetated gap using plant density and leaf area index parameters. Rangelands provide vital ecosystem services and comprise 36% of U.S. and 25% of world lands. Approximately 20 to 73% of these rangelands are already degraded. Soil erosion driven by winds is a significant cause of this degradation. Minimal work has been done to evaluate the influence of wind erosion on rangeland dominated landscapes or to assess the effect of landscape-scale soil and water conservation and management practices on reducing wind erosion due to its inherent complexity and nonpoint source nature. Our approach is to use an integrated and holistic eco-hydrologic model. The main objective of this study is to integrate process-based landscape wind erosion modeling schemes into the Agricultural Policy/Environmental eXtender (APEX) model (version 1905; APEX1905) for simulating horizontal aeolian sediment transport and vertical particles transport on rangelands. We demonstrate the performance and capability of the model using field data collected at the USDA ARS Jornada Experimental Range in New Mexico, U.S. A benchmark APEX1905 model that runs on high-resolution sub-daily wind speed data and daily average vegetation gap distribution derived from monthly field measurements. The benchmark APEX1905 model captured the variability in observed aeolian sediment transport during 2015–2017 reasonably well with an R2 = 0.58 and a RMSE = 2.60. When the highly variable sub-daily measured wind speed and vegetation gap distribution data were substituted with the daily average wind speed and APEX1905 estimated daily vegetation gap, the APEX1905 reproduced well the benchmark model estimates with the performance statistic of R2 = 0.77 and RMSE=0.54 for the horizontal aeolian sediment transport; and R2 = 0.82 and RMSE = 0.85 for vertical particle transport. Overall, provided limited aeolian watershed data sets, the APEX1905 is demonstrated to be reliable in estimating wind erosion in arid, desert rangeland landscapes using daily average wind speed and simulated vegetation characteristics. Benefiting from the long-established algorithms of simulating plant growth dynamics and topsoil moisture content in APEX, APEX1905 offers a robust and process-based estimation of wind erosion in areas where wind and vegetation data are scarce. [ABSTRACT FROM AUTHOR]

The accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in March 2011 resulted in the deposition of large quantities of radionuclides, such as 134 Cs and 137 Cs, over parts of eastern Japan. Since then high levels of radioactive contamination have been detected in large areas, including forests, agricultural land, and residential areas. Due to the strong adsorption capability of radiocesium to soil particles, radiocesium migrates with eroded sediments, follows the surface flow paths, and is delivered to more populated downstream regions and eventually to the Pacific Ocean. It is therefore important to understand the transport of contaminated sediments in the hydrological system and to predict changes in the spatial distribution of radiocesium concentrations by taking the land-surface processes related to sediment migration into consideration. In this study, we developed a distributed model to simulate the transport of water and contaminated sediment in a watershed hydrological system, and applied this model to a partially forested mountain catchment located in an area highly contaminated by the radioactive fallout. Observed discharge, sediment concentration, and cesium concentration measured from June 2011 until December 2012 were used for calibration of model parameters. The simulated discharge and sediment concentration both agreed well with observed values, while the cesium concentration was underestimated in the initial period following the accident. This result suggests that the leaching of radiocesium from the forest canopy, which was not considered in the model, played a significant role in its transport from the catchment. Based on the simulation results, we quantified the long-term fate of radiocesium over the study area and estimated that the effective half-life of 137 Cs deposited in the study area will be approximately 22 y due to the export of contaminated sediment by land-surface processes, and the amount of 137 Cs remaining in the catchment will be reduced to 39% of the initial total within 30 y after contamination. This study provides a perspective on the transport of suspended sediments and radiocesium in catchments with similar land use and radiocesium contamination. [ABSTRACT FROM AUTHOR]

Abstract: Distributions of woody vegetation on floodplain surfaces affect flood-flow erosion and deposition processes. A large flood along the lower Rio Puerco, New Mexico, in August 2006 caused extensive erosion in a reach that had been sprayed with herbicide in September 2003 for the purpose of saltcedar (Tamarix spp.) control. Large volumes of sediment, including a substantial fraction of sand, were delivered to the reach downstream, which had not been treated with herbicide. We applied physically based, one-dimensional models of flow and suspended-sediment transport to compute volume concentrations of sand in suspension in floodplain flow at a site within the sprayed reach and at a site downstream from the sprayed reach. We computed the effects of drag on woody stems in reducing the skin friction shear stress, velocity of flow, and suspended-sand transport from open paths into patches of dense stems. Total flow and suspended-sand fluxes were computed for each site using well-constrained flood-flow depths, water-surface slopes, and measured shrub characteristics. Results show that flow in open paths carried high concentrations of sand in suspension with nearly uniform vertical distributions. Drag on woody floodplain stems reduced skin friction shear stresses by two orders of magnitude, yet sufficient velocities were maintained to transport sand more than 50m into fields of dense, free-surface-penetrating stems. An increase in shrub canopy extent from 31% in the sprayed reach site to 49% in the downstream site was found to account for 69% of the computed decrease in discharge between the two sites. The results demonstrate the need to compute the spatial distribution of skin friction shear stress in order to effectively compute suspended-sand transport and to predict the fate of sediment and contaminants carried in suspension during large floods. [Copyright &y& Elsevier]

Abstract: Water erosion processes can significantly affect the delivery and distribution patterns of soil organic carbon (SOC) within the landscape. While many studies focus on the erosion processes and runoff transport of SOC, little attention has been paid to the on-site redistribution and vertical transport of SOC. This study characterizes SOC erosion dynamics, including infiltration-associated movement, and discusses the effects of rainfall intensity and slope position on SOC transport within the hilly red soil region of southern China. The results show that SOC loss was likely due to sediment transport rather than runoff. The eroded SOC was not significantly enriched, which may be due to the soil properties and the type of rainfall event. The initial SOC concentration affected the enrichment ratio of eroded SOC in the sediment. On-site horizontal redistribution occurred regardless of rainfall intensity, whereas the SOC transport trends varied with rainfall intensity and slope positions. This demonstrates that soil preservation could reduce SOC loss, and thus influence the global carbon cycle. [Copyright &y& Elsevier]

Abstract: Terrain properties vary at the hillslope and catchment scale and play a significant role in the distribution of water and sediment. Of particular interest in recent years has been the role of hillslope and catchment properties in the spatial and temporal distribution of soil organic carbon (SOC) and the ability to predict SOC from DEM terrain analysis. SOC plays a significant role in soil health and productivity as well as providing a significant store of terrestrial carbon. This study examined SOC concentration along representative pasture transects in a catchment located in southern Western Australia with a Mediterranean climate. Results demonstrate that the majority of SOC (%) is located in the near-surface (300mm) and is concentrated in the top 0.2m. There was no relationship found between SOC (or microbial biomass) and topography or topographic derivatives such as wetness and terrain indices from DEMs. Significant relationships were however found between SOC and environmental tracers (137Cs and 210Pbex) down the soil profile. Weak, yet significant, relationships were found between SOC and the environmental tracers along the hillslope transects, suggesting that organic carbon moves along the same pathways as clay particles in soil. An erosion assessment using 137Cs and also a numerical soil erosion and landscape evolution model found low and comparable erosion rates at the site. The results demonstrate that SOC concentration is relatively uniform across the study site and that a transect scale assessment can provide a measure of hillslope and catchment scale SOC in this environment. [Copyright &y& Elsevier]

Abstract: Geomorphologists have commonly published conclusions about soil erosion and water movement based on experimental data obtained at the catchment scale. The underlying assumptions were that there exists little spatial variation in conditions at the hillslope scale (the fundamental unit) and that the catchments are representative of other catchments in the same region. These assumptions are unlikely to be tenable in practice. Indeed, we suggest that there is substantial spatial variation in geomorphological properties even at small distances when observed at fine spatial resolution and that modern geoinformatics approaches can be used to quantify and characterize this variation. This introduction reviews the ten papers that comprise this Special Issue on Studying Water-Erosion Processes with Geoinformatics, drawn from across the geomorphological sciences. The water erosion processes studied in these papers include sediment transport, fluvial processes, slope denudation, landsliding, bank erosion and bank line migration. The findings suggest that innovative measurement and modeling approaches such as GPS measurements, geostatistics, image processing techniques, and physically-based models deliver new data with which to study water erosion processes. These findings involve domains that are associated with fundamental aspects of geomorphology. Hence, there are strong grounds for claiming that geoinformatics can contribute to greater understanding of water erosion processes through characterization of space–time dynamics. We suggest that geomorphologists need to use more geoinformatics to collect more data relating to the outcomes of water erosion processes, to seek out and apply innovative processing methods and, finally, model the data to provide greater understanding of processes and to forecast and explore future scenarios. [Copyright &y& Elsevier]

Abstract: Sediment transport and storage in mountain stream channels are closely dependent on hillslope activities and bank erosion. This paper analyses bedload measured in 13 mountain streams (989 values with slope higher than 5%) in an attempt to investigate how much the sediment supply condition impacts bedload transport rates. First, the sediment supply condition of each stream was evaluated qualitatively using information available in the original studies. In the second step, the data set was analysed by comparing bedload transport rates considering a Shields stress ratio and by comparing transport rate efficiency with consideration of a dimensionless stream power. The two analyses indicate higher sediment transport rates for the streams identified as “connected” to an active source. The consequences for bedload transport prediction are discussed with a nonthreshold bedload equation. Even though predicting the exact sediment supply condition and the associated transport rate is not yet possible, this study suggests that defining an envelope delimiting minimum and maximum transport for a given river reach should be possible. [Copyright &y& Elsevier]

Abstract: Analysis of typhoon- and earthquake-triggered landsliding and fluvial response in the Tachia River, central Taiwan, documents highly episodic sediment supply over decade to century timescales. Landslide data from the Chi-Chi earthquake (1999) and subsequent typhoons (2001, 2004, and 2005) quantify the sediment supply from these events. Fluvial response was investigated by decadal-scale and century-scale longitudinal river profile data spanning 1904 to 2008 and by sediment delivery recorded in suspended sediment load and reservoir sedimentation data. Our results show that the different time periods of satellite images and aerial photographs used in previous studies make it difficult to unambiguously identify the causes of landslides previously attributed by some studies to the effects of the Chi-Chi earthquake rather than subsequent high intensity precipitation. In response to significant variability in sediment delivery from hillslopes, century-scale profile variation data indicate substantial bed surface elevation change of 2.6±6.7m, and decade-scale bed surface elevation change of 1.1±3.3m. Since 1993, the downstream reaches incised in response to bedload sediment trapping by reservoirs while headwater reaches aggraded in response to increased sediment delivery from uplands. A tremendous increase in reservoir sedimentation after 2000 likely reflects the effects of the highest decade-average daily rainfall since 1900. Suspended sediment load data indicate a post Chi-Chi earthquake increase in sediment concentration in low-flow events but do not exhibit the clear influence on sediment yields at higher flows as (e.g., typhoons) reported by others for fluvial response in the epicentral region. [Copyright &y& Elsevier]

Abstract: The uprooting and toppling of trees during storms transports soil, exhumes bedrock, and thus influences the evolution of hillslopes. Given predicted increased storminess due to future climate change, we adapt a forest-gap model (ForGEM) to explore windthrow-driven sediment transport in a Douglas fir forest under increasingly severe wind regimes in order to better assess potential future impacts on soil erosion. Larger trees are more sensitive to wind loading and are therefore preferentially toppled as storm frequency and intensity increase. Because larger trees have larger root-plate volumes and can move large volumes of sediment, increased wind velocities lead to an increase in sediment flux. With increasingly stormier conditions, however, the proportion of large trees dwindles. The net effect of these two countervailing trends is that sediment transport increases as average annual rates of windthrow approach eight trees per hectare, but begins to decline thereafter. Our results highlight the complex relationship between climate and sediment transport, particularly when it is mediated by the biota. [Copyright &y& Elsevier]

Abstract: The tropics of northern Australia have received relatively little attention with regard to the impact of soil erosion on the many large river systems that are an important part of Australia''s water resource, especially given the high potential for erosion when long dry seasons are followed by intense wet season rain. Here we use 137Cs concentrations to determine the erosion processes supplying sediment to two major northern Australian Rivers; the Daly River (Northern Territory), and the Mitchell River (Queensland). We also present data from five sediment samples collected from a 100km reach of the Cloncurry River, a major tributary of the Flinders River (Queensland). Concentrations of 137Cs in the surface soil and subsurface (channel banks and gully) samples were used to derive ‘best fit’ probability density functions describing their distributions. These modelled distributions are then used to estimate the relative contribution of these two components to the river sediments. Our results are consistent with channel and gully erosion being the dominant source of sediment, with more than 90% of sediment transported along the main stem of these rivers originating from subsoil. We summarize the findings of similar studies on tropical Australian rivers and conclude that the primary source of sediment delivered to these systems is gully and channel bank erosion. Previously, as a result of catchment scale modelling, sheet-wash and rill erosion was considered to be the major sediment source in these rivers. Identifying the relative importance of sediment sources, as shown in this paper, will provide valuable information for land management planning in the region. This study also reinforces the importance of testing model predictions before they are used to target investment in remedial action. [Copyright &y& Elsevier]

Abstract: This paper uses results obtained from the large-scale BARDEX experiments undertaken in the Delta flume to investigate the morphological response of a prototype gravel barrier to wave and tidal forcing during overwash conditions. Gravel barrier behaviour depends upon a number of factors such as sediment properties (porosity, permeability, grainsize), geological setting and wave climate. Since overwash processes are known to control short-term gravel barrier dynamics and long-term barrier migration, the development of a robust quantitative method to define the critical conditions leading to gravel barrier overwashing is important both for scientific and practical management purposes. It is known that when wave runup exceeds the barrier crest elevation, three outcomes are possible: 1) insignificant morphological change, when wave runup just overtops the barrier crest and flow velocities are very weak; 2) overtopping, resulting in accretion on the barrier crest region and barrier stabilisation; and 3) overwashing, resulting in erosion, lowering of the crest region and ultimately to barrier inundation. This study provides an insight into the critical conditions that distinguish these two possible outcomes and to the different mechanisms that provide the required positive and negative feedbacks to the sediment dynamics. In order to define the overwash threshold condition, and to predict the morphological outcome of particular overwash events, use is made here of the Overwash Potential (OP), defined as the difference between the wave runup and the barrier crest elevation. To make effective use of OP it is necessary to identify a reliable runup predictor. Following tests using 12 runup equations the Stockdon et al. [Stockdon, H.F., Holman, R.A., Howd, P.A., Sallenger, A.H., 2006. Empirical parameterization of setup, swash, and runup. Coast. Eng., 53, 573–588] approach has been identified as the best predictor of runup conditions necessary to generate positive values of OP, with overtopping and overwashing predicted to occur for average OP values of 0.2m and 0.5m, respectively. The use of OP values provides a practical means by which to identify potential coastal hazards associated with gravel barrier overwash processes and is considered to have a range of practical coastal management applications. [Copyright &y& Elsevier]

Abstract: Landslides have both immediate and extended-duration effects on sediment discharge. Examining the role of post-failure soil loss/sediment yield of landslides is essential for basin management purposes. The comprehensive measurement of sediment production of existing landslides could provide a better understanding in this aspect. This study investigated the post-failure sediment yield of 13 landslide sites in the Shihmen reservoir watershed, Taiwan, during the rainy seasons of 2006 and 2007 using a total station. Our study showed that soil loss is mainly controlled by rainfall conditions, and the geometric and geographic characteristics of each landslide can significantly influence the efficiency of sediment delivery. We also observed that rainfall is important in determining landslide retrogression/enlargement, although vegetation in the landslide area increases with time. We obtained a large amount of landslide measurement data, which could be useful for future landslide modeling. We suggest two regression models for estimating gross soil loss using cumulative rainfall. The estimated gross soil loss values of 0.78 to 1.06myr−1 are equivalent to 18,096 to 24,592tha−1 yr−1. Using these estimates, we assessed the sources of sediment in the watershed, and found that the ratio of landslide erosion, soil loss after landsliding, and soil erosion from other parts of the watershed was approximately 66:31:3. This study implies that remedying existing landslides is more effective than any other solution in reducing sediment production in the watershed. [Copyright &y& Elsevier]

Abstract: Variations in erosion were quantified across the topographically and morphometrically asymmetrical central Ladakh Range in NW India to elucidate erosion and sediment transfer processes across space and time and to gain insight into how mountains erode and evolve. Morphometric analysis and 10Be cosmogenic nuclide analysis of 14 fluvial sediment samples from active channels in six catchments conducted across the mountain range constrains 100ka timescale erosion rates for catchments on the northern side of the mountain range and are between 56±12 and 74±11m/Ma, while catchments on the southern side of the mountain range to between 20±3 and 39±8m/Ma for the last ~300ka. Maximum elevation from swath analysis across the range shows a strong correlation with the ELAs of 382 contemporary glaciers. The higher erosion rate to the north likely relates to tectonic tilting of the central Ladakh Range and to active rock uplift on the northern side of the range along the Karakoram Fault. Morphometric analysis shows that the maximum and average elevations increase at nearly the same rate on a catchment-scale across the central Ladakh Range, with higher elevation on the northern side. This suggests that greater erosion on the northern side of the range is not keeping pace with rock uplift. Moreover, long-term denudational unloading does not play a significant role in the tectonic tilting of the central Ladakh Range. [Copyright &y& Elsevier]

Abstract: Following construction of the Three Gorges Dam, many farmers resettled in surrounding mountain areas and cultivated marginal lands, which are mostly on steep slopes with soil of poor structure. In general, high soil loss rates occur during intense storms. Therefore, soil erosion is a major environmental problem in the Three Gorges area (TGA) of China. Understanding and quantifying sediment load is important for sustainable agriculture and the environment in this region. This paper analyzes the relationships between rainfall, runoff, and sediment transport in the Wangjiaqiao watershed. Strong seasonal and monthly variability in sediment load was found. Sediment was strongly transported during summer months, a period when frequent flood events of high magnitude and intensity occurred. Analysis of the relationships between precipitation, discharge and sediment transport at an individual event scale showed significant correlations between total precipitation, peak discharge, total water yield, maximum 30min rainfall intensity, and sediment-related variables. Stepwise multiple regression analysis revealed that rainfall amount is the major cause of runoff, while events producing a large discharge in a short time play an important role in inducing severe soil erosion. During 40 flood events, three different types of hysteretic loops were observed: clockwise (28 events, 70%), figure-eight (5 events, 12.5%), and complex (7 events, 17.5%). The results of this study confirm the complex and heterogeneous nature of sediment response in the Wangjiaqiao watershed. [Copyright &y& Elsevier]

Abstract: To better understand the sedimentary history of the erosional crater of Makhtesh Hazera in the hyper-arid Negev Desert of southern Israel we have measured concentrations of in situ 10Be in alluvial sediments from the active drainage system and from abandoned alluvial terraces and dated them using optically stimulated luminescence (OSL). These sedimentary sequences suggest changes in the drainage system behavior over time and show a periodic pattern in which periods of sediment aggradation alternate with periods of degradation through incision and erosion. In alluvial terrace sediments, 10Be concentrations were combined with OSL ages to gain insight of the temporal framework of sediment deposition and shed light on the process of sediment storage. OSL and simple 10Be exposure ages of terrace sediments give deposition ages between ~340ka to ~50ka, at which time the youngest alluvial terrace was incised. Deposition was interrupted twice, at ~300ka and ~160ka, when periods of rapid incision caused the abandonment of the active fluvial surface and the stabilization of a younger and lower fluvial surface. In the active drainage system, 10Be concentrations suggest several possible quartz sources, of which the Lower Cretaceous sandstone bedrock exposed at the base of the cliff enclosing the Makhtesh is the most dominant. The results suggest that sediment eroding form these cliffs are conveyed through the active alluvial channels without significant sediment contribution from alluvial terraces or from eroded bedrock exposed within the Makhtesh. In contrast to our measurements in the active drainage system, 10Be concentrations in alluvial terrace sediments record significant storage within the Makhtesh. We suggest that the geometry of the Makhtesh, mainly the disproportion between the size of the Makhtesh and its narrow outlet, leads to significant accumulation of sediment within the Makhtesh. Episodic breaching of the barrier is followed by rapid and short-lived incision into the stored sediment. The long residence time of sediment within the Makhtesh results in high measured 10Be concentrations. At the end of each of these short incision episodes, when channels are already carved into the alluvial sediment and terraces are formed, the channels only convey sediment directly eroded from the bounding cliff of the Makhtesh; a situation presently observed. [Copyright &y& Elsevier]

Abstract: Climate change and accelerated sea level rise coupled with increased human activities in coastal regions have resulted in severe land loss globally. Mitigating coastal erosion requires better understanding and improved capability of modeling sediment transport. This paper presents the methodology and simulation results of a new mathematical model, Virtual Identity Particles, using a spectral/hp element method for sediment transport driven by shear flows. Assimilated the advantages of Eulerian and Lagrangian methods, this model is capable of modeling each individual grain as well as a bulk of numerous grains where frequent collisions between particles and with walls are characterized by the Speed Proportional Collisions. Besides, this model maintains an excellent balance of accuracy and efficiency through its economical considerations in the formulation, allowing modeling a large number of sediment particles. Simulation results demonstrate that this model holds promising potential for investigating sediment transport and the associated land erosion problems. [Copyright &y& Elsevier]

Abstract: Hydrological and erosion models use water depth to estimate routing velocity and resultant erosion at each spatial element. Yet the shear stress distribution imposed on the soil surface and any resulting flow detachment and rill incision is controlled by the full probability distribution of depths of overland flow. Terrestrial Laser Scanning (TLS) is used in conjunction with simple field-flume experiments to provide high-resolution measures of overland flow depth-distributions for three semi-arid hillslope transects with differing soil properties. A two-parameter gamma distribution is proposed as the optimum model for depths of both interrill and rill flows. The shape and scale parameters are shown to vary consistently with distance downslope reflecting the morphological signature of runoff processes. The scale parameter is related to the general increase of depths with discharge (P <0.0001) as flows gradually concentrate; the shape parameter is more related to the soil surface roughness and potentially provides a control on the rate of depth, but also velocity increase with discharge. Such interactions between surface roughness and overland flows are of crucial importance for flow hydraulics and modeling sediment transport. [ABSTRACT FROM AUTHOR]

Abstract: Large uncertainties still exist on both the rates of soil organic carbon (SOC) mobilization by soil erosion as well as the fate of the eroded C. Using a range of techniques we characterized soil C redistribution by water erosion in two small agricultural catchments in the Belgian Loess Belt. Results from rainfall simulations showed that C enrichment in eroded sediments was much higher than clay enrichment (average enrichment ratios of 2.47 and 1.36 on average respectively). Selectivity was also observed in depositional processes: sediments deposited within the catchments were depleted in C and finer fractions as compared to the source soil. Selectivity was much more pronounced in winter than in summer, which is related to the degree of aggregation of the transported/deposited sediment. The combined selectivity of erosion and depositional processes resulted in a significant C enrichment of the sediment exported from the catchments with the C enrichment ratio (CER) between 1.2 and 3.0. Overall, catchment-scale C enrichment was higher than clay enrichment: enrichment ratios varied both with season and event intensity. The uncertainties on catchment-wide erosion and deposition rates precluded the closure of the sediment-C budgets. However, using a simple model we were able to show that both the magnitude and variation of observed catchment-scale CER was as expected from our understanding of C mobilization and deposition within the catchment. This suggests that most of the mobilized C was not mineralized during the erosion events but either re-deposited within the catchment or exported with the runoff. This was confirmed by the comparison of the elemental and isotopic signatures between exported sediments and source soil. In order to assess the role of erosion in the C cycle, understanding how C is mobilized and re-deposited selectively by erosion appears therefore as important as improving our understanding of the impact of erosion on C mineralization. [ABSTRACT FROM AUTHOR]

Abstract: Catchment scale suspended sediment (SS) transport studies in northwest Spain are of special interest as little research at this scale has been done in this region. However, the role of sediments in the transfer of nutrients and contaminants to coastal areas in this region has been highlighted. Data were collected from the Corbeira catchment during a 3-year period and the variability in SS load at different temporal scales (within-events variability, monthly/seasonal, and annual) was analyzed. The statistical relationship between discharge and suspended sediment concentration (SSC) from samples obtained every 15days as well as during runoff events in October 2004 to September 2007 showed a marked scatter of points. Hence, the rating curve method does not seem appropriate to estimate SSC in this catchment. The results also demonstrated that at the within-events scale, most of the SS peaks preceded the discharge peaks (70% of runoff events), implying that zones nearby or well connected to the stream are the dominant sediment source areas. In some cases, rills and ephemeral gullies developed in cropland were the main source of sediment delivered to the stream. Furthermore, a reduction in SSC was observed in sequences of events, which can be mainly linked to a phenomenon of sediment exhaustion. At the seasonal scale, most of the total annual SS load was transported during the autumn months, the period in which, generally, the largest number of events occurred, while in the summer, total annual SS load was very low (<1%). At the annual scale, specific SS yield (SSY) ranged from 5.4 to 11.2Mg km-2 y-1. The variability in SSY was correlated with the number and magnitude of runoff events recorded yearly, since runoff events dominated SS transport and yield. For instance, in the last hydrological year (2006/07), more than 80% of the SS load was exported in runoff events involving <10% of the time. [ABSTRACT FROM AUTHOR]

Abstract: The Mejillones Peninsula in the coastal Atacama Desert of northern Chile is a region in which ocean–atmosphere–land interactions are particularly strong, resulting in enhanced alongshore winds that erode the surface and transport sand particles to the sea. Because the aeolian particles in the laminated sediments at the bottom of Mejillones Bay record long-term changes in the intensity of prevailing southerly winds, it is fundamental to understand aeolian processes such as wind erosion and sand transport to improve paleoceanographic reconstructions. The aim of the present study is to characterize the wind erosion process over the flat geomorphology of the northern portion of the Mejillones Peninsula, the Mejillones Pampa, including the influence of wind erosion on the initial particle size distribution and the associated fractionation processes of the mineralogical composition of moving particles, through field measurements. In addition, we test the ability of an existing saltation model (MB95) to reproduce the variability of the erosion process during the field experiment. Soil samples from 17 locations on this flat surface contain significant amounts of highly erodible particles with diameters in the 200–300µm and 100–150µm size ranges. Aeolian particles collected in BSNE sand traps located at different heights near the surface, exhibit a bimodal size distribution similar to that of the erodible fraction of the soils; the abundance of the fine class increasing with height. Small stones that have a spatially variable distribution can locally reduce the intensity of wind erosion. The mineralogical composition of moving particles is similar to that of the soils, with quartz, feldspar and calcite as the most important minerals, followed by clay minerals, gypsum and amphibole. A value of u* t is calculated for each soil particle size class. Subsequently, the elementary contribution of each size class to the horizontal flux is calculated using White (1979)''s equation and the total flux is finally obtained by integration. The saltation model successfully reproduces the variability of the wind erosion process during the field experiment, but over-estimates the vertically integrated mass fluxes measured in situ by two orders of magnitude. [Copyright &y& Elsevier]

Abstract: We review the role of landslides in current concepts of the topographic development of mountain ranges. We find that many studies in this field address basin- or orogen-scale competition between rock uplift and fluvial bedrock erosion. Hillslopes in general, and bedrock landslides in particular, are often assumed to respond rapidly to incision and development of the fluvial drainage network. This leads to a one-sided view of the geomorphic coupling between hillslopes and rivers that emphasizes the fluvial control of hillslopes, but ignores the alternative view that landslides can affect the fluvial network. There is growing evidence that landslides are a dominant source of sediment in mountain belts and that they exert a direct geomorphic control on fluvial processes. Landslides can influence the river network in a variety of ways, from determining basin area and drainage divide positions, to setting streamwise variations in sediment load and calibre. The geomorphic legacy of large landslides on hillslope and channel morphologies may persist for up to 104 yr, adding considerable variability to fluvial erosion and sedimentation patterns over these timescales. We identify a number of questions for future research and conclude that a better understanding and quantification of the geomorphic feedbacks between landslides and river channels builds an important link between short-term (<101 yr) process studies and long-term (>105 yr) landscape evolution models. [Copyright &y& Elsevier]

Abstract: In 2003, a wildfire burned nearly two-thirds of the Fishtrap Creek watershed, including the forested floodplain. Annually repeated surveys of the stream channel — combined with bed material tracer studies in 2006 and 2007 — indicate that the channel has become unstable and that the bed material transport dynamics have changed since the fire. Using these data, the morphologic changes have been quantified and event-scale bed material transport rates have been estimated for four post-fire freshets. The immediate response of the channel (during the 2005 and 2006 freshets) was a progressive shift in channel morphology from a relatively featureless plane-bed morphology devoid of significant sediment accumulations to a riffle-pool morphology in which bars cover a significant proportion of the bed. This transformation occurred in association with moderate bed material sediment transport rates and only minor bank erosion within the study reach. Extensive bank erosion occurred during the 2007 and 2008 freshets, producing a dramatic change in channel morphology and increasing the local bed material transport rates by an order of magnitude. Post-fire monitoring of streamflow and suspended sediment concentrations (a surrogate for upstream sediment supply) indicates that post-fire increases are not detectable (presented in Eaton et al., in press), and our analysis demonstrates that major morphologic changes can occur following wildfire even when the common external drivers of stream discharge and sediment supply remain unchanged. [Copyright &y& Elsevier]