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• 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]

[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]

[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]

• 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]

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 • 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]

• CA models for describing runoff are established based on three water distribution rules which significantly impact on confluence. • Dynamic erosion CA models are built by distinguish inter-rill, rill and gully erosions based on critical water depths. • CA models excellently reproduce the runoff and erosion in both the hillslope with rills and the watershed with gullies. • Remain average multi-flow directions algorithm performs the best in runoff and erosion predictions. Rainfall erosion has been calculated and predicted by various soil loss equations, but the progressions of overland flow and sediment transport are less dynamically described. In this study, cellular automata (CA) models based on single flow direction algorithm (SFD), average value multi-flow direction algorithm (AMFD) and remaining average value multi-flow direction algorithm (RAMFD) were constructed. Simultaneously, erosion model was constructed by dividing soil erosion into inter-rill, rill and gully erosions according to critical water depth. The CA models were validated at three scales: a theoretical slope, an in-situ model slope and the natural basin. The results demonstrated the efficient performance of RAMFD in the runoff ascension and recession stages while SFD and AMFD presented unconcentrated runoff distribution, especially in the in-situ slope and basin simulation. Besides, RAMFD model occurred sediment deposition in the basin upstream while SFD and AMFD presented continuous erosion. Furthermore, the runoff Nash-Sutcliffe efficiency (NSE) of three models were 0.85 ∼ 0.95 and 0.65 ∼ 0.94, and the erosion root mean square error (RMSE) were 0.5 ∼ 1.0 kg/min and 0.3 ∼ 0.45 102kg/min in the theoretical slope and natural basin, respectively. Meanwhile, the NSE and RMSE values of RAMFD exhibited the best performance, indicating that this model effectively balanced water distribution while controlling the flow direction to a greater extent. Overall, it is justified to develop an erosion prediction model based on the classification of erosion types, and the rules governing water flow allocation will inevitably result in qualitative and quantitative differences of runoff and erosion. [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]

• Physically based 2D hydrodynamic and sediment transport model, CCHE2D. • High resolution mesh, topography photogrammetry, experimental landform evolution. • Watershed hydrology, raindrop soil detachment, displacement, erosion and transport. • Distributed solution, tilled watershed, cornfield tillage ridge and furrow morphology. • Simulated runoff, sediment transport, landform evolution; channel network analysis. Soil and gully erosion is a critical threat to sustainable agricultural land management and productivity. Soil erosion by rain splash, sheet runoff, and concentrated flow are complex problems conditioned by the combined interactions of soil physical properties, hydrology, human activity, landscape topography, and climate. Effective management of erosion processes driven by rainfall and surface runoff requires a combined effort of field observation, physical experimentation, and numerical simulation. A physically-based hydrodynamic numerical model, CCHE2D with updated raindrop erosion effects, is applied to simulate landscape evolution processes as a result of raindrop impact and overland flow. The numerical model simulates a thin layer of runoff and concentrated flow over complex terrains, and predicts sediment transport due to raindrop splash detachment, transport and soil surface erosions. Soil erosion and landform evolution simulations due to rainfall are presented for an experimental landscape and a tilled large scale agricultural field. Photogrammetric field data were collected using an unmanned aerial system (UAS) following planting and subsequent rainstorms. Numerical simulation results agreed well with the observed experimental soil surface topography, sediment yield, and drainage network developments. The simulated soil and gully erosion in the tilled field also agreed well with observations. This research successfully demonstrates how high resolution spatial and temporal topographic measurements in experimental and field landscapes can be simulated and interrogated by 2D physically-based hydrodynamic and morphodynamic models. The accurate predictions of tillage field and gully erosion process in agriculture watersheds with complex tillage conditions also indicated the usefulness of the model for studying soil and landscape degradation. [ABSTRACT FROM AUTHOR]

• A methodology to interpret a large set of rules in high-dimensional fuzzy models is demonstrated. • Suspended sediment concentrations (SSC) alterations downstream of dams are greater in rivers with higher SSC. • SSC alterations downstream of dams are lesser in basins with higher proportions of vegetation cover. • SSC alterations downstream of dams are greater in basins with higher proportions of silty soils. • Heavy rains can cause sediment release from dams. Small dams for power generation are increasingly being built around the world, and the reported impact caused by these structures on sediment transport varies widely, ranging from substantial to minimal or non-existent alterations among different dams. Such variability is still poorly understood. In this study, we present an original application of fuzzy inference systems (FIS) to extract knowledge concerning the effect of small dams on sediment transport, providing understandings of how different variables related to watershed characteristics, dam characteristics and hydrological variations can affect sedimentological responses of these structures. Numerous small dams have been built, and many more are in development or proposed, in rivers that drain into the Pantanal, a world-renowned tropical wetland, where we apply the methodology. Data on 23 hydropower facilities from the uplands of the Pantanal region were used, with a total of 535 records. The models presented very good results (NS equal to 0.92 for the most detailed FIS model) and provided a better understanding of the phenomenon through their explicit linguistic rules. The upstream suspended sediment concentration (SSC) is the most determinant variable for the alteration caused by dams. Higher SSC entering the reservoir is related to higher sediment retention. Vegetation cover and soil type of the drainage area of dams also influence the alterations on SSC caused by these structures. Dams located in basins with greater vegetation cover tend to affect less sediment transport, and dams located in basins with high percentages of agriculture and pasture tend to alter more. FIS models also confirmed that the size of dams is directly proportional to their capacity to alter sediment transport. The methodologies developed for the interpretation of fuzzy rules proved to be useful for assessing how small dams affect sediment transport along river systems. [ABSTRACT FROM AUTHOR]

• Sediment from upland erosion shows higher carbon oxidation rates than in-stream sediment. • Sediment from upland erosion shows lower nitrogen mineralization-nitrification rates. • Sediment degradation rates are one to two orders magnitude higher than previously assumed. • Dissolved nitrogen of stream water degraded an order of magnitude higher than lake water. • Nitrate concentration increased by an average 35% during experiments. • Nitrogen stable isotopic ratio of nitrate decreased by over 1‰ Knowledge is lacking for sediment organic matter degradation and its influence on water quality for low gradient agriculturally impacted streams despite their importance for freshwater biogeochemical cycles and ecological restoration. We hypothesized degradation rates vary across sediment type and are a function of the connectivity regimes for low gradient systems. We carried out aerobic incubation experiments to assess oxidation and mineralization-nitrification rates and changes in stable isotopic ratios for sediment and dissolved organic matter and nitrate. Sediment originated from erosion across the watershed's surface shows higher carbon oxidation rates (k = 3.9 × 10−3 d−1) and lower nitrogen mineralization-nitrification rates (k = 7.9 × 10−4 d−1) compared to sediment originated from the creek's streambed that integrates algae and other autotrophic matter (k = 1.6 × 10−3 d−1 and k = 3.4 × 10−3 d−1). Differences are attributed to sediment transport of humified and plant matter during storms of high watershed connectivity and sediment transport of autochthonous sediment for low connectivity. Results support our hypothesis and suggest that the sediment connectivity regime of the watershed exhibits control on biogeochemical cycling of the stream network. Cumulatively, sediment degradation rates were one to two orders magnitude higher than previously assumed. Sediment rates reflect aerobic waters and place the organic matter as active and comparable to reported turnover of algae and fine sized leaf litter. Stable isotopic ratios of sediment change marginally for the two sediment types for carbon (ε = 0.4 ‰ and 1.3 ‰) and nitrogen (ε = 3.5 ‰ and 1.5 ‰). Dissolved organic nitrogen of stream water degraded similarly across all experiments (k = 1.8 × 10−2 d−1), and turnover rates were an order of magnitude higher than recent rates reported for lake water. Nitrate concentration in the solute increased by an average 35 % during experiments and the nitrogen stable isotopic ratio of nitrate decreased by over 1 ‰ showing the potential of sediment and dissolved organic matter degradation to influence nitrate flux and its isotopic signal. [ABSTRACT FROM AUTHOR]

Stream sediment loads (both bedload and suspended sediment) are problematic to measure due to the time and equipment needed. There is a dearth of such data sets globally let alone for Australia. However, such data are needed to quantify sediment transport type and rates, landscape evolution, effect of human disturbance as well as patterns and temporal response. Here we present the findings from 8 steepslope forested catchments dominated by headwater streams (size range 15–100 ha) in south-eastern Australia where both bedload and suspended load have been measured over multiple years. The results demonstrate that suspended load is the dominant component and there is no consistent suspended to bedload ratio for the catchments. The suspended sediment to bedload ratio appears to be catchment specific. There was no relationship between total load (or bedload/suspended load) and average catchment slope, stream length, shape or any geomorphic descriptor. However catchment total load was found to be significantly related to catchment area. Of the 8 catchments examined here, 6 had been harvested for timber in previous decades (with large areas of forest removed) while 2 catchments had minimal disturbance (Control catchments). There was no difference in sediment loads from the harvested and Control catchments. The results demonstrate that although land disturbance had previously occurred the management practices employed in each catchment were effective in the long term. This provides confidence that the forest harvesting and subsequent management do not produce detrimental effects in the medium to long term. An assessment of erosion rates and likely soil production rates suggests that the catchments are eroding soil at the rate it is being produced. [ABSTRACT FROM AUTHOR]

Computer based landscape evolution models can provide insight into both erosion rates and processes (i.e. sheetwash, rill, gully erosion). One important data requirement of these models is long term, high quality, high-temporal resolution rainfall data (given that the physical nature of the erosion process is strongly related to rainfall). However, in many cases such data is limited - data is often short, incomplete or not of a sufficient temporal resolution. Therefore, the aim of this study was to test the sensitivity of modelled erosion rates to small changes in rainfall input. To achieve this we firstly assess the existing rainfall data from an established weather station and secondly, stochastically generate rainfall time series based on the longest and most reliable rainfall data. We then test the sensitivity of different rainfall sequences on sediment output using a well-tested landscape evolution and sediment transport model (CAESAR-Lisflood) over a simulated period of 100 y on a proposed rehabilitated mine landform. It was found that each rainfall scenario produces a unique pattern of erosion (i.e. the location and extent of the gullies is variable). Further, each rainfall scenario produces a unique pattern of sediment output that suggests non-linear processes. Importantly, this is the first time stochastically generated rainfall has been employed in landform evolution modeling and provides a statistical approach to quantify sediment transport and landform evolution. The method demonstrates a risk based approach and allows rainfall, runoff and sediment transport studies to be conducted in data poor environments. The findings clearly demonstrate that rainfall variability can greatly affect sediment transport and form of erosion as well as landscape evolution. This information is of particular importance for the design and testing of rehabilitated landscape systems such as post-mining landscapes. [ABSTRACT FROM AUTHOR]

• Streamflow and sediment patterns significantly influence the benefits of cooperative reservoir operation in the YRB. • The three upstream reservoirs Longyangxia, Liujiaxia, and Wanjiazhai contribute most to the grand cooperation. • Shapley value method is recommended to reallocate the incremental benefits of grand cooperation in the YRB. The complicated relationship between water and sediment in the Yellow River Basin (YRB) makes it imperative for reservoir stakeholders to game with each other to balance the short-term and long-term benefits. This paper proposes an integrated model to analyze the cooperation opportunities for major reservoir stakeholders engaged with the Longyangxia, Liujiaxia, Wanjiazhai, Sanmenxia, and Xiaolangdi reservoirs on the YRB mainstream. Multiple benefits are considered, including flood control, water supply, hydropower generation, and sediment trapping. Non-cooperation and cooperation scenarios are compared in this study. The effect of flow and sediment conditions on the incremental benefit of cooperation is examined, which shows that the systematic incremental benefit is larger when the YRB is dryer and sediment concentration is higher. Basin-wide cooperation is especially beneficial when the inflow peak comes earlier and the streamflow process is more fluctuating. Cooperation of reservoir stakeholders in a normal year (2019) can bring more incremental benefit (i.e., $22.57 million) in contrast to the non-cooperation scenario. Longyangxia, Liujiaxia, and Wanjiazhai reservoirs contribute most to the grand cooperation by implementing optimal operation for downstream stakeholders. Three cooperative game theory methods (Shapley value, Gately point, and Nash–Harsanyi solution) are employed to find possible benefit-sharing solutions. Based on cooperative game theory, the results demonstrate the core of basin-wide cooperation in the Yellow River is negligible due to the negative externality effect, implying more measures are needed by the government or non-profit organization to maintain the stability of grand coalition, i.e., water resources utilization control and external compensation. The results also show that Shapley value could be used to reallocate the incremental benefits in the grand cooperation. [ABSTRACT FROM AUTHOR]

• Streamflow and sediment patterns significantly influence the benefits of cooperative reservoir operation in the YRB. • The three upstream reservoirs Longyangxia, Liujiaxia, and Wanjiazhai contribute most to the grand cooperation. • Shapley value method is recommended to reallocate the incremental benefits of grand cooperation in the YRB. The complicated relationship between water and sediment in the Yellow River Basin (YRB) makes it imperative for reservoir stakeholders to game with each other to balance the short-term and long-term benefits. This paper proposes an integrated model to analyze the cooperation opportunities for major reservoir stakeholders engaged with the Longyangxia, Liujiaxia, Wanjiazhai, Sanmenxia, and Xiaolangdi reservoirs on the YRB mainstream. Multiple benefits are considered, including flood control, water supply, hydropower generation, and sediment trapping. Non-cooperation and cooperation scenarios are compared in this study. The effect of flow and sediment conditions on the incremental benefit of cooperation is examined, which shows that the systematic incremental benefit is larger when the YRB is dryer and sediment concentration is higher. Basin-wide cooperation is especially beneficial when the inflow peak comes earlier and the streamflow process is more fluctuating. Cooperation of reservoir stakeholders in a normal year (2019) can bring more incremental benefit (i.e., $22.57 million) in contrast to the non-cooperation scenario. Longyangxia, Liujiaxia, and Wanjiazhai reservoirs contribute most to the grand cooperation by implementing optimal operation for downstream stakeholders. Three cooperative game theory methods (Shapley value, Gately point, and Nash–Harsanyi solution) are employed to find possible benefit-sharing solutions. Based on cooperative game theory, the results demonstrate the core of basin-wide cooperation in the Yellow River is negligible due to the negative externality effect, implying more measures are needed by the government or non-profit organization to maintain the stability of grand coalition, i.e., water resources utilization control and external compensation. The results also show that Shapley value could be used to reallocate the incremental benefits in the grand cooperation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Brazilian semiarid is the most densely populated dry region in the world. • Sediment source apportionment was quantified in a semiarid ephemeral catchment. • The combination of conventional and alternative tracers improved source discrimination. • Our results may gain high visibility given the climate change projections for the semiarid regions. The Brazilian semiarid is the most densely populated dry region in the world. Although climate change projections underline the need for the creation of integrated strategies to protect water resources in the semiarid, sediment source apportionment data remain scant for this environment. Accordingly, we evaluated sediment source contributions in one of the most relevant Brazilian semiarid catchments by combining geochemical and colour tracer properties. In doing so, we explored the applicability of colour tracers as a low-cost alternative to the use of time-consuming and costly properties, such as geochemical tracers. Two source classification schemes were used based on environmentally contrasting regions within the catchment (upper, middle and lower catchment parts) and land use (Caatinga biome - natural vegetation, unpaved roads, and channel banks). Suspended sediments (SS) and bed sediments (BS) were used as target sediment. A total of 660 individual source material samples were collected and composited. Geochemical and colour tracers were measured on the source and target sediment samples and used as potential fingerprints to discriminate and quantify the sediment source contributions. The geochemical tracers provided weak source discrimination based on land use. However, combining geochemical and colour tracers improved the final outputs. Using the MixSIAR model, the lower catchment contributed more sediment than the other regional sources. The Caatinga (SS = 49 %; BS = 47 %) contributed more sediment than channel banks (SS = 35 %; BS = 39 %). Overall, our results suggest that the recovery and conservation of the Caatinga vegetation and the stabilization of channel banks, especially in the lower catchment part, are critical for improving sediment supply control in the semiarid study basin. More studies are needed to evaluate the conservative behaviour of colour tracers in ephemeral rivers. [ABSTRACT FROM AUTHOR]

• We determined the parameters of monthly sediment rating curve (SRC) in karst watersheds. • The SRC parameters of karst watersheds are compared with those of other watersheds in China. • PLS-SEM can decouple the direct and indirect effects of factors on SRC parameters. • Lithology and dam construction complicated the effect of climate and vegetation on SRC parameters. One of the largest contiguous karst areas in the world is southwest China, where special geological conditions, shallow soil layers, the frequency of precipitation extremes, unreasonable land use, and dam construction have rendered the relationship between water discharge and sediment load increasingly complex. Few studies have been devoted to this region to clarify the potential influencing factors of the water–sediment relationship on a monthly basis. Correspondingly, the present study evaluated the temporal variations in sediment rating curves (SRCs: Qs = a Q b , where Q s is the sediment concentration or load, Q is the water discharge, the coefficient a and index b are fitted parameters) and decoupled the effects of climate change and vegetation dynamics on SRC parameters using partial least squares-structural equation modeling (PLS-SEM). To these ends, 2003 to 2017 data on the monthly water discharge, sediment load, climatic and vegetation factors of six karst watersheds were collected and analyzed. No significant trends in interannual variations of SRC parameters occurred. The PLS-SEM showed that the combined effects of climate and vegetation explained 18% to 43% and 8% to 57% of the variations in coefficient a and index b , respectively. In most cases, however, no significant relationship was found among climate, vegetation-related factors, and the SRC parameters. Special hydrogeological conditions and dam construction in the area increasingly complicated the sediment transport process, thus potentially weakening the influence of climate and vegetation on the SRC parameters. This study can serve as guidance for regional ecological management and the sustainable development of soil and water resources. [ABSTRACT FROM AUTHOR]

• We examine eight steep slope forested headwater catchments (15–100 ha). • Bedload organic carbon (OC), soil carbon and dissolved OC was measured. • OC in the bedload was found to be significantly related to catchment area. • Dissolved OC export in stream water declined with catchment area. • There was no difference in OC export from the harvested and non-harvest catchments. Qualitative and quantitative understandings of the origin, transport and fate of organic carbon (OC) in forest systems is needed to advance our understanding of biogeochemical cycling as well as catchment management and forest harvesting. Here we present the findings from eight steep slope forested catchments dominated by headwater streams (size range 15–100 ha) in south eastern Australia where bedload, organic carbon in bedload, hillslope soil carbon together with dissolved organic carbon has been measured over multiple years. OC in the bedload was found to be significantly related to catchment area (p < 0.02). Dissolved organic carbon export in stream water declined with catchment area. Combined bedload organic carbon and dissolved organic carbon export was significantly related to catchment area. There was no significant difference between hillslope soil organic carbon and bedload organic carbon concentration. When corrected for area, OC export by bedload was not significantly different to that of dissolved OC export. Using the environmental tracer 137Cs it was found that there was no significant difference in tracer concentration between bedload and hillslope soil. This suggests a direct link between hillslope and channel and delivery of organic carbon to the channel. Of the eight catchments examined here, six had been harvested for timber in previous decades (with area of forest removed ranging from 25 to 60%) while two catchments had minimal disturbance (Control catchments- no harvest). There was no difference in organic carbon export from the harvested and Control catchments. The results demonstrate that although land disturbance had previously occurred the management practices employed in each catchment were effective in the long term. [ABSTRACT FROM AUTHOR]

• We determined the parameters of monthly sediment rating curve (SRC) in karst watersheds. • The SRC parameters of karst watersheds are compared with those of other watersheds in China. • PLS-SEM can decouple the direct and indirect effects of factors on SRC parameters. • Lithology and dam construction complicated the effect of climate and vegetation on SRC parameters. One of the largest contiguous karst areas in the world is southwest China, where special geological conditions, shallow soil layers, the frequency of precipitation extremes, unreasonable land use, and dam construction have rendered the relationship between water discharge and sediment load increasingly complex. Few studies have been devoted to this region to clarify the potential influencing factors of the water–sediment relationship on a monthly basis. Correspondingly, the present study evaluated the temporal variations in sediment rating curves (SRCs: Qs = a Q b , where Q s is the sediment concentration or load, Q is the water discharge, the coefficient a and index b are fitted parameters) and decoupled the effects of climate change and vegetation dynamics on SRC parameters using partial least squares-structural equation modeling (PLS-SEM). To these ends, 2003 to 2017 data on the monthly water discharge, sediment load, climatic and vegetation factors of six karst watersheds were collected and analyzed. No significant trends in interannual variations of SRC parameters occurred. The PLS-SEM showed that the combined effects of climate and vegetation explained 18% to 43% and 8% to 57% of the variations in coefficient a and index b , respectively. In most cases, however, no significant relationship was found among climate, vegetation-related factors, and the SRC parameters. Special hydrogeological conditions and dam construction in the area increasingly complicated the sediment transport process, thus potentially weakening the influence of climate and vegetation on the SRC parameters. This study can serve as guidance for regional ecological management and the sustainable development of soil and water resources. [ABSTRACT FROM AUTHOR]

• We examine eight steep slope forested headwater catchments (15–100 ha). • Bedload organic carbon (OC), soil carbon and dissolved OC was measured. • OC in the bedload was found to be significantly related to catchment area. • Dissolved OC export in stream water declined with catchment area. • There was no difference in OC export from the harvested and non-harvest catchments. Qualitative and quantitative understandings of the origin, transport and fate of organic carbon (OC) in forest systems is needed to advance our understanding of biogeochemical cycling as well as catchment management and forest harvesting. Here we present the findings from eight steep slope forested catchments dominated by headwater streams (size range 15–100 ha) in south eastern Australia where bedload, organic carbon in bedload, hillslope soil carbon together with dissolved organic carbon has been measured over multiple years. OC in the bedload was found to be significantly related to catchment area (p < 0.02). Dissolved organic carbon export in stream water declined with catchment area. Combined bedload organic carbon and dissolved organic carbon export was significantly related to catchment area. There was no significant difference between hillslope soil organic carbon and bedload organic carbon concentration. When corrected for area, OC export by bedload was not significantly different to that of dissolved OC export. Using the environmental tracer 137Cs it was found that there was no significant difference in tracer concentration between bedload and hillslope soil. This suggests a direct link between hillslope and channel and delivery of organic carbon to the channel. Of the eight catchments examined here, six had been harvested for timber in previous decades (with area of forest removed ranging from 25 to 60%) while two catchments had minimal disturbance (Control catchments- no harvest). There was no difference in organic carbon export from the harvested and Control catchments. The results demonstrate that although land disturbance had previously occurred the management practices employed in each catchment were effective in the long term. [ABSTRACT FROM AUTHOR]

Summary The decision to use either daily-averaged or sub-daily streamflow records has the potential to impact the calculation of sediment transport metrics and stream channel design. Using bedload and suspended load sediment transport measurements collected at 138 sites across the United States, we calculated the effective discharge, sediment yield, and half-load discharge using sediment rating curves over long time periods (median record length = 24 years) with both daily-averaged and sub-daily streamflow records. A comparison of sediment transport metrics calculated with both daily-average and sub-daily stream flow data at each site showed that daily-averaged flow data do not adequately represent the magnitude of high stream flows at hydrologically flashy sites. Daily-average stream flow data cause an underestimation of sediment transport and sediment yield (including the half-load discharge) at flashy sites. The degree of underestimation was correlated with the level of flashiness and the exponent of the sediment rating curve. No consistent relationship between the use of either daily-average or sub-daily streamflow data and the resultant effective discharge was found. When used in channel design, computed sediment transport metrics may have errors due to flow data resolution, which can propagate into design slope calculations which, if implemented, could lead to unwanted aggradation or degradation in the design channel. This analysis illustrates the importance of using sub-daily flow data in the calculation of sediment yield in urbanizing or otherwise flashy watersheds. Furthermore, this analysis provides practical charts for estimating and correcting these types of underestimation errors commonly incurred in sediment yield calculations. [ABSTRACT FROM AUTHOR]

Summary The pluvial erosion process is significantly affected by tempo-spatial patterns of flood flows. However, despite their importance, only a few studies have investigated the sediment flow behavior that is driven by different flood regimes. The study aims to investigate the effect of intra-event-based flood regimes on the dynamics of sediment exports at Tuanshangou catchment, a typical agricultural catchment (unmanaged) in the hilly loess region on the Chinese Loess Plateau. Measurements of 193 flood events and 158 sediment-producing events were collected from Tuanshangou station between 1961 and 1969. The combined methods of hierarchical clustering approach, discriminant analysis and One-Way ANOVA were used to classify the flood events in terms of their event-based flood characteristics, including flood duration, peak discharge, and event flood runoff depth. The 193 flood events were classified into five regimes, and the mean statistical features of each regime significantly differed. Regime A includes flood events with the shortest duration (76 min), minimum flood crest (0.045 m s −1 ), least runoff depth (0.2 mm), and highest frequency. Regime B includes flood events with a medium duration (274 min), medium flood crest (0.206 m s −1 ), and minor runoff depth (0.7 mm). Regime C includes flood events with the longest duration (822 min), medium flood crest (0.236 m s −1 ), and medium runoff depth (1.7 mm). Regime D includes flood events with a medium duration (239 min), large flood crest (4.21 m s −1 ), and large runoff depth (10 mm). Regime E includes flood events with a medium duration (304 min), maximum flood crest (8.62 m s −1 ), and largest runoff depth (25.9 mm). The sediment yield by different flood regimes is ranked as follows: Regime E > Regime D > Regime B > Regime C > Regime A. In terms of event-based average and maximum suspended sediment concentration, these regimes are ordered as follows: Regime E > Regime D > Regime C > Regime B > Regime A. Regimes D and E produce the most runoff volume and the largest amount of sediments, which indicates that these regimes must be at the focus of runoff regulation to control the sediments. Given that the event flood runoff depth remains constant, the sediment yield by different flood regimes is regulated to varying degrees by altering the event-based runoff–sediment relationship. Compared with Regime A, the average decrease rates in the area-specific sediment yield for Regimes B, C, and D are 33%, 78%, and 62%, respectively. The regulative effect of the flood regime conversion on sediment export can be described with several variables that indicate the depth-specific characteristics of individual flood events. Flood regimes indicate the runoff erosivity dynamics and the runoff energy dissipation rates in eroding soil and delivering sediments. Therefore, the flood-regime-dependent sediment flow behavior differs across all regimes. Overall, the predominated controlling factors that influence the final sediment export are regime based. Empirical regime-based runoff–sediment relationships were established via multiple stepwise regressions. The suspended sediment concentration that is driven by different flood regimes can be described by the power function or logarithmic–linear function of runoff-related variables, including instantaneous discharge, runoff erosive power, and event-based flow variability. The regressive equations can explain the major driving forces behind the suspended sediment concentration dynamics. This study highlights the potentials of runoff self-regulation in controlling soil erosion and sediment delivery. The results may provide some evidence for flood regime classification, improve the overall evaluation of the sediment reduction benefits of the runoff regulation system, enrich runoff regulation theory, and improve the runoff control at the catchment scale. [ABSTRACT FROM AUTHOR]

Summary The sediment delivery ratio (SDR) has been a common approach developed to understand change in sediment yield and flux through a catchment. In this study we propose that the underlying concept of the sediment delivery ratio is flawed for a number of reasons: its linear extrapolation is physically meaningless; there is no evidence of the magnitude of storage required by the SDR approach on annual to decadal timescales; and the SDR approach assumes suspended sediment transport is conservative yet it is known to undergo both loss and production in-channel. This study considers the sediment yield from 192 UK catchments from 1974 to 2010 for catchment areas between 4 and 9948 km 2 and shows that linear extrapolation of the SDR approach overpredicts source terms and underpredicts fluxes for large catchments. The SDR approach hides a range of behaviours of suspended sediment flux within catchments with patterns of net deposition, net increase or no change all apparent in UK catchments. The approach proved to be self-correlated which meant that it can result in spurious correlations when compared to catchment area. The change in yield with catchment area can be just as well understood as a change in sediment supply from channels rather than as a change in delivery from hillslope sources. We propose that suspended sediment flux change with catchment area be modelled as a more physically-meaningful Gompertz function (step function) rather than using the traditional SDR approach. [ABSTRACT FROM AUTHOR]

• Geomorphic evolution of the deltaic channel and active river mouth is evaluated. • Morphologic variability of the active delta has a distinct spatial variance. • Offshore fine sediment dispersal processes are simulated and quantified. • The new river regime can improve channel stability and intensify deltaic recession. Intensified human interventions in river basins and deltas lead to more complexities of environmental changes during the Anthropocene. Changes in river regime especially a dramatic reduction in sediment delivery increase challenges of the morphological and ecological sustainability of river deltas. In evaluating deltaic risks and sustainable solutions, researches are often limited to single geomorphic units of the deltaic system, and investigations of sediment source to sink transfer at river deltas under recent river regimes are often missing. The Yellow River Delta (YRD) presents as a typical megadelta under stressors induced by changing environments. This study utilizes a period of 20-yr high-resolution topography data of the deltaic channel and its subaqueous delta to investigate sediment transport and source to sink process by integrated methods of field measurements and numerical simulations. The results indicate that the deltaic channel has transitioned from net accretion to erosion after the implementation of the Water-Sediment Regulation Scheme (WSRS) in 2002. The active river mouth experienced a slow accretion phase since the river channel diverted to Qing 8 channel, with a reduced vertical deposition rate of 0.15 m/yr, whilst its adjacent Gudong littoral zone had a −0.11 m/yr erosion rate. Under the new fluvial regime, the river-borne suspended sediment tends to transport southwards to the Laizhou Bay, followed by the river-derived sediment transport eastward and northward to the offshore delta. It is clear that with the continued human activities in the region, the YRD is at the potential state of deltaic transition both in the deltaic channel and its subaqueous delta. This transition is believed to be beneficial to the deltaic channel stability, but it could significantly impact on the geomorphic and ecologic sustainability of the entire deltaic system. [ABSTRACT FROM AUTHOR]

• High frequency sediment transport data is presented for tributary-river confluences in the ORB. • Sediment rating curves underpredict sediment flux due to variable hysteresis patterns. • Urban and forested landcovers impact temporal variability in sediment fluxes. • Confluence features retain 34% of sediment inputs, buffering downstream sediment delivery. Harmful algal blooms (HABs) have increased in the Ohio River Basin over the past decade. Fine sediment dynamics are now recognized to play an important role in the proliferation and toxicity of HABs. As a result, the fate of sediment at confluences of tributaries and regulated river systems may be important zones for sediment retention and burial. The objective of this study was to improve understanding of watershed sediment loading dynamics and backwater inundation impacts on sedimentation within confluence watersheds. The study site selected for this work was the Fourpole Creek watershed in the Western Allegheny Plateau ecoregion of Appalachia, which is a mixed-use watershed with predominantly forested and urban landcover with a backwater floodplain wetland at the confluence with the Ohio River. Approximately 16 months of high-frequency (15-minute) turbidity data was used as a surrogate for total suspended solids at upstream and downstream nodes of the backwater confluence feature. Continuous sediment yield estimates suggested an annual sediment yield of 82 t/km2 and was found to be higher than sediment yields reported elsewhere in Appalachian watersheds without mining disturbances. A modified sediment rating curve using both seasonal and annual regression approaches were found to underpredict sediment yield by 29% and 80%, respectively. A hysteresis-based source unmixing method and hysteresis index were used to quantify sediment source and flow pathways during events and suggested high variability in sediment source contributions both seasonally and within-seasons, suggesting three likely sediment sources in the watershed including in-channel/gully erosion, resuspension of recently deposited sediment in the fluvial network, and erosion of subsurface macropores from forested uplands. Upstream-downstream monitoring of the confluence floodplain suggested 34% of the annual sediment inputs were retained during the continuously monitored 2019 calendar year. Our results suggest that confluence floodplains play an important role in intercepting and storing sediment inputs. Efforts to limit downstream sediment loads should ensure the function of confluence floodplains is maintained or enhanced when considering watershed management strategies in these landscapes. [ABSTRACT FROM AUTHOR]

• Hydrologic model parameterization produces greatest uncertainty for sediment transport forecasts via GCMs. • Water and sediment forecasts are under-predicted 49% and 35% when only precipitation and temperature are included. • Streamflow and sediment yield forecasts increase by 19% and 14% for the shear-limited landscape and transport-limited stream. Forecasting change in sediment transport using global climate model ensembles is under-developed in the hydrology community due to a lack of knowledge regarding the variance structure of predictions. We investigate the uncertainty of forecast sediment transport from sources, including global climate model realizations, global climate model ensemble design, forecasted hydrologic inputs, and hydrologic modeling parameterizations. We then forecast sediment transport for the gently rolling watershed in Kentucky, USA. Contrary to past research forecasting hydrology with global climate models, hydrologic model parameterization was the most significant source of variance impacting forecasted sediment transport variables. Forecast of sediment transport responses shows the propagation of uncertainty from the hydrologic model parameterization was over two times greater than the uncertainty from the selected global climate model realizations. This result emphasizes researchers focused on forecasting sediment transport with global climate models may need to give as much, or more, consideration to their water–sediment linkages as climate-water–sediment linkages. Hydrologic inputs from climate change, including forecast precipitation, temperature, relative humidity, solar radiation, and wind speed, impacted sediment transport. Considering changes in precipitation and temperature alone under-predicts streamflow and sediment transport by 49% and 35%, respectively, compared to including all meteorological variables inputs. Variance introduced across the three different global climate model ensembles was a relatively small source of variance impacting forecasted streamflow or sediment yield. The results suggest a quantitative effort by the researcher to design the global climate model ensemble by considering representativeness, historical performance, and independency will lead to robust results. Ensemble average forecasts forecast streamflow and sediment yield to increase by 19% and 14%, respectively, for the lowland watershed. The sediment transport forecasts reflect the shear-limited landscape of the watershed and the transport-limited conditions in the stream channel. [ABSTRACT FROM AUTHOR]

[Display omitted] • Intra-storm variations in sediment sources remain under studied in many settings. • Weathering indices and geochemistry used to trace intra-storm sediment sources. • Tributary sub-catchment spatial and individual source types were explored. • Quaternary geology surface soils and channel banks were key sources. There is an increasing need for reliable information on the origin of fine-grained sediment transported by river systems, but critically, at temporal scales that reflect the timing and pattern of sediment mobilization and delivery in response to effective precipitation events. Temporal variability is likely to be more pronounced in steep mountainous catchments. Accordingly, the main objective of this study was to investigate the temporal variability of sediment sources during and between flood events, in a mountainous catchment in Iran, using a geochemical fingerprinting approach and Bayesian un-mixing model. Potential sediment sources were classified as either tributary sub-basin spatial end members or individual source types represented by surface soils and channel banks. A total of 34 geochemical elements, elemental ratios and weathering indices were measured as potential tracers on a total of 155 samples, including 40 target samples collected across the hydrographs of four flood events at the overall catchment outlet. Virtual mixture tests, used to compare the computed source estimates with known source mixtures, revealed better fits in the case of spatial, rather than source type apportionment. The Bayesian un-mixing model results revealed pronounced intra-storm variations in the relative contributions from both the spatial sources and source types, but with Quaternary surface soils and channel banks being dominant at different stages of the hydrographs. For all the suspended sediment samples collected throughout the three small to medium size events, the Babazid, middle upstream sub-catchment, was the major (84%–99%) sediment source while for the largest sampled event, suspended sediment samples predominantly (>98%) originated from the Kalkoshan, the most southern sub-catchment. By investigating both spatial sources and source types, temporal variations in the dominant sources were revealed. Quaternary geology and channel banks were identified as the main sediment sources. By combining instantaneous suspended sediment loads through the sampled flood events (across all floods) and using the corresponding source proportions derived from the MixSIR un-mixing model, channel banks and channel bank and surface soils generated 2911 kg and 34,171 kg of suspended sediment, respectively. Whilst the use of spatial source end members is practical in medium-size drainage basins, integration with estimates of sediment source type contributions is more informative to managers in selecting relevant sediment mitigation methods. The intra-storm results underscore the need to manage sediment loss from both surface soils and channel banks. [ABSTRACT FROM AUTHOR]

• A high-precision 2-D flow and sediment transport model of the Yarlung Zangbo-Brahmaputra River is established. • A comprehensive habitat suitability evaluation system is developed. • Climate change will lead to sediment deposition and wetlands degradation in the study area. • The ecological environment of the wetlands will be deteriorated due to climate change. The Yarlung Zangbo-Brahmaputra River originates from the Tibetan Plateau. Its hydraulic conditions and ecological environment affect the economic, agricultural development and ecological environmental protection of many countries. So far, studies analyzing the impacts of potential climate change on hydrological and water resources conditions in the Yarlung Zangbo-Brahmaputra River Basin are limited. Most of these studies analyzed the overall basin condition at the large and coarse scale. Research on the response of the topography and ecological environment at high spatial resolution scale in river reaches and wetlands to climate change in this area has not been conducted before. In this study, we developed a two-dimensional flow-sediment transport model to simulate the flow and sediment conditions in the middle reaches of the Yarlung Zangbo-Brahmaputra River with the hydrological conditions predicted by a meteorological-hydrological model. We then analyzed the impacts of potential climate change on the riverbed and wetland topography in this region. We further designed a habitat suitability evaluation system to evaluate and compare the ecological environment of the wetland under current climate conditions and with potential climate change. Our research shows that climate change scenario RCP4.5 will result in about 40–90 million cubic meters of sediment deposition in wetlands each year in the next 6 years. The elevation of the main channel will decrease, while the elevation of shoals will increase, which will indirectly lead to wetland degradation. The difficulty of foraging will be increased, and the area available for fish to rest will decrease. Ultimately, the habitat environment of fish will be destroyed and the density of fish populations will be lower. The impact on migratory birds is more complicated. It is expected that the migratory birds' living environment will improve in July (since both selected habitat suitability metrics show a trend of improvement), but it will be worse than the current condition in other months. [ABSTRACT FROM AUTHOR]

• Feedback mechanisms favor the equilibrium state achievement in a short timeframe. • Process of channel infilling undermines the tidal amplification and flood dominance. • Tidal attenuation lowers net sediment import, leading to less sediment trapping. Tidal rivers are a complex fluvial-estuarine nexus where intensively anthropogenic interferences emerge. Understanding the morphodynamic response to river training in tidal river systems is a contemporary challenge. Here we explore the process of channel infilling and the evolution of tidal characteristics after significant dredging activities in the Shenzhen River (SZR) based on field observed data, in order to reveal feedback mechanisms between tidal dynamic and morphology. The results found that the SZR experienced rapid sediment accretion on interannual and seasonal scales since the channel was remarkably deepened before 2008. In a very short timeframe, the excavated part of channel was almost filled in 2012, and after that the SZR performed switch between erosion at wet season and deposition at dry season, indicating a dynamic equilibrium state was obtained. The tidal skewness of three primary combinations of tidal constituents, M 2 /M 4 , M 2 /S 2 /MS 4 and K 1 /O 1 /M 2 , was calculated from the tidal level of 1998, 2007, 2012 and 2016 at SZHK (river mouth) and LH (upstream) stations. During the period of 1998 and 2012, the total tidal skewness significantly rose by 109.25% and 31.26% at SZHK and LH, respectively, while it remained roughly constant from 2012 to 2016, which is concurrent well with the temporal variation of channel deposition. Similarly, tidal range amplification between LH and SZHK (TR LH /TR SZHK) decreased by 9.0% from 1998 and 2012 while much less decline rate was found after 2012, indicating that the tidal attenuation was probably induced by the channel infilling. Furthermore, the impact of tidal characteristics evolution on suspended sediment transport was discussed, eventually unraveling the feedback mechanism between morphology, tidal regime, sediment transport and trapping in the heavily trained SZR. [ABSTRACT FROM AUTHOR]

• We developed a new weighted method to select best GCM for hydrological modelling. • The new method is based on the response of streamflow to precipitation and temperature. • The impacts of precipitation and temperature on streamflow in different seasons are considered in the new method. This study develops a new method for selecting the most representative climate model for use in the Soil and Water Assessment Tool (SWAT) and evaluates this method in the Maumee River Basin. Downscaled temperature and precipitation data from 32 Coupled Model Intercomparison Project Phase 5 (CMIP5) models were used to drive the SWAT. Our model selection approach uses a sensitivity analysis to evaluate the impacts of temperature and precipitation on streamflow and to determine the optimal weights for both variables. This weighting scheme is then used to rank the performance of all climate models and identify which ones are most representative of climate forcing required by the hydrological model. The results of our sensitivity analysis indicate that the response of streamflow to precipitation is consistent throughout the year, while the response to temperature is more complex. During the warm season, higher temperatures cause evapotranspiration to increase and streamflow to decrease; during the cool season, higher temperatures cause more snowmelt and this causes streamflow to increase. Based on our weighting scheme, the GISS-E2-R was identified as the most representative climate model in the Maumee River Basin. We then compared the performance of SWAT-simulated streamflow using all CMIP5 models. The most representative climate model ranked first based on correlation and mean absolute error, and second based on Nash-Sutcliffe efficiency, while the model selected using a simple average method was ranked fifth, fourth and twelfth, respectively. Based on the evaluation of other key variables, such as sediment transport, nitrogen and phosphorus, the optimal climate model also has a higher correlation and a more representative standard deviation than the other CMIP5 models. The selected model also performs better than the 32-model ensemble mean based on correlation and Taylor's skill score. When applying this method at different time scales, the responding time of streamflow to climate factors needs to be considered. The model selection method that was developed in this paper can be applied by hydrological modelers to select the most representative climate models for evaluating the impacts of climate change in other watersheds around the world. [ABSTRACT FROM AUTHOR]

Simulation of flow and transport of sediment in alluvial rivers, particularly during release of water through dams, is a complex problem. Such simulations are generally carried out using various numerical models, subject to availability of requisite morphological and sediment data sets. In addition, various simplifying assumptions, quite often, are part and parcel of most of the available numerical sediment transport models. As such, non-compliance of any of the assumptions or non-availability of all the requite data sets restricts meaningful use of any numerical simulator in estimation of morphological changes in alluvial rives. This study attempts to resolve such issues associated with numerical models by using Artificial Neural Networks (ANN). The primary objective of the study is to explore and identify best performing ANN models in estimating morphological changes in alluvial rivers. In the present study, the one dimensional hydrodynamic modelling system, HEC-RAS (Hydrologic Engineering Centre's River Analysis System), is employed for generating database to train multilayer feedforward networks (MLFN). Performance evaluations of all the developed MLFN models are made by using three statistical parameters, i.e. Mean Square Error (MSE), Mean Absolute Error (MAE) and Coefficient of Determination (R2). The study reveals that there are multiple ANN models, stretching across different training algorithms and transfer functions, which can be reliably used in developing sediment transport models in alluvial rivers. [ABSTRACT FROM AUTHOR]

• River structure was used as a viewpoint to assess the impact of human activities. • Anthropogenic and natural forces were compared to design an indicator system. • his indicator system could track the impact of human activities on river system. • This indicator system is simple and not subject to the reference condition. The impact of human activities on river systems has reached a state in which they can no longer be considered to be controlled only by natural processes of the Earth but also by anthropogenic forces in many regions of world. However, most approaches for assessing the impact still consider human activities to be an external influence in the study of feedback mechanisms between human activities and river systems, and they are usually complicated and specialized. This paper aims to develop an indicator system that includes the artificial water surface ratio (AWSR), artificial water surface density ratio (AWSDR), disruption of longitudinal connectivity ratio (DLCR), artificial river ratio (ARR), sinuosity of artificial cutoff (SAC), channelization ratio (CR), artificial levee ratio (ALR), road along river ratio (RARR), artificial sediment transport ratio (ASTR) and the integrated river structure impact index (IRSII) to quantitatively assess the impact of human activities on river structure by comparing natural and anthropogenic forces in a river system. The Nanliu River basin under the dramatic impact of human activities was selected to validate the indicator system. The case results showed the Nanliu River has become an anthropogenic river according to its high IRSII value (greater than 0.49). The artificial water surface area and artificial sediment discharge were 2.96 (AWSR = 2.96) and 2.51 (ASTR = 2.51) times of the outcome of natural process. The river was dramatically blocked by human-made buildings (DLCR = 68.63) and artificial channel accounts for 54.23% of total length of natural river (ARR = 0.54). Within the river basin, upper and lower sub-basins in areas with a higher economic level were more affected by human activities. Future management of the Nanliu River basin should focus on restoration of river connectivity, sand mining and irrigation issues. Unlike most previous assessment methods, the approach developed in this study is simple and readily comprehensible by the public and decision makers, cost-effective for long-term monitoring and not subject to the reference condition. [ABSTRACT FROM AUTHOR]

• We analyze discharge pulses from sub-daily discharge records in headwater streams. • Differences between temperate and tropical rainforests reflect runoff/precipitation processes. • Pulse metrics demonstrate differences with increasing drainage area between sites. We use sub-daily gage records from montane headwater channels in the Luquillo Experimental Forest of Puerto Rico (tropical rainforest) and the HJ Andrews Experimental Forest of Oregon (temperate rainforest) to characterize differences in discharge pulses (rapid, high-magnitude discharge fluctuations) and determine whether the characteristics of discharge pulses differ with respect to drainage area between these two regions. The study sites have different precipitation regimes and runoff generation mechanisms, and we quantify differences in discharge pulses between sites. The assessment of discharge pulses, which are defined as flows that are higher than one standard deviation above the historical mean flow at each site, represents a novel approach to characterizing flashy discharge events in headwater streams using high temporal resolution datasets. Our analyses indicate a clear difference between regions, with discharge in the Luquillo streams pulsing more frequently, for shorter periods of time, and at higher magnitudes than discharge in the Andrews streams. We also quantify how discharge pulses change with increasing drainage area at each of the sites. Differences in discharge pulse metrics with respect to drainage area include an increase in the number of pulses, an increase in the normalized magnitude of pulses, an increase in the standard deviation in normalized magnitude, and a decrease in kurtosis with increasing drainage area at the Luquillo site. These results indicate that there is no attenuation of discharge pulses with increasing drainage area at Luquillo. In contrast, there is a decrease in the normalized magnitude with increasing drainage area at the Andrews site, indicating some attenuation of discharge pulses with increasing drainage area. The characteristics of these pulsed events have implications for ecological processes by transporting sediment, biota, and organic matter, likely altering stream substrates, biotic communities, and organic matter retention times. [ABSTRACT FROM AUTHOR]

• Cover crops was the WMP with the highest streamflow and sediment reduction. • Crop rotation had the highest NO 3 -N load reduction, but increased the sediment load. • Wetlands and riparian buffer were more area-efficient WMPs for load reduction. • Non-structural WMPs caused the highest overall reductions of both pollutant loads. • Structural WMPs were more area-efficient in nitrate-N and sediment load reduction. Agricultural practices intended to increase productivity can adversely affect our soil and water resources. Expected changes in climate and other social pressure are anticipated to exacerbate these impacts jeopardizing the sustainability of the agro-ecosystems. Watershed Management Practices (WMPs) are meant to achieve a rational use of resources as well as enhance ecosystem resilience to climate change. However, the effectiveness of WMPs depends on the complex interactions between processes occurring across the watershed. The objective of this study was to simulate the impacts of WMPs and projected climate on the sediment and nitrate-nitrogen (NO 3 -N) stream loads in an intensively managed watershed. The modeling framework was developed with the physically-based distributed model Mike SHE for the Upper Sangamon River Basin (USRB), an agricultural watershed in central Illinois. The fate and transport of sediment and NO 3 -N in the watershed and rivers was simulated using a generic advection-dispersion equation (ADE) with NO 3 -N and sediment as the main species. Results showed that non-structural WMPs, such as crop rotation and cover crops, presented the highest reductions of simulated NO 3 -N and sediment load, respectively, while structural WMPs had higher area-efficiency performance. On the other hand, climate conditions had a strong impact on the transport of both pollutants due to water fluxes alterations especially for a future dry climate scenario. Sediment transport was shown to be more sensitive to climate given that rainfall is one of the main drivers of the erosion processes. Outcomes from this research will give a more comprehensive approach toward understanding the impacts of environmental stressors at a watershed scale, and how they may be propagated to ecological systems. [ABSTRACT FROM AUTHOR]

• Bedload to total load ratio varies from 0.1 to 5.4%. • Specific sediment yields are 0.06 Mg ha−1 y−1 as bedload and 22 Mg ha−1 y−1 as suspended load. • Elongated planform delta growth shows predominance of suspended load. • Stream-power based bedload equations performed better. Little is known about the contribution of bedload flux to the total sediment load exported from tropical sand-bed rivers. Yet, predicting bedload transport rates contributes to better river management, more appropriate river engineering works design, accurate knowledge of sediment delivery rates, which greatly benefits sediment-related water resources management. Therefore, bedload, suspended load and runoff discharge were measured at the lower Gilgel Abay River in the Blue Nile catchment of Ethiopia. Catchment area is 3887 km2, average stream discharge in the rainy season 315 (±164) m3 s−1, and the stream surface gradient at the sampling station 0.0007 m m−1. A standard Helley-Smith (U.S. BL-84) cable-suspended sampler was used to take 315 samples to measure bedload fluxes for the 2017 rainy season. The bedload predominantly comprises well to moderately well sorted, medium-sized sand (250–500 µm) with a symmetric and leptokurtic distribution. The mean daily observed bedload discharge varies from 0.7 to 427.5 Mg d−1 with an average rate of 175.1 Mg d−1. Field observations also show that the bedload dynamics become larger near the river banks and decrease towards the middle of the river section due to the presence of a central bridge pier. The average suspended sediment load ranges from 247 to 220,028 Mg d−1 and dominates the total sediment yield (>94.6%). The bedload accounts for only 0.1 to 5.4% of the total sediment load. The area-specific bedload and suspended load are also 0.6 and 22 Mg ha−1 yr−1 respectively. The elongated planform growth of the Gilgel Abay River delta in Lake Tana is also in line with the predominance of very fine, suspended load in the sediment transport of this river, in addition to limited alongshore drifting given the low waves of Tana lake. Among the tested bedload prediction criteria, the stream-power based equations of Martin and modified Bagnold performed better. Yet, the bedload prediction performance of simple power regression equations based on runoff discharge and excess unit stream power parameters provided the best agreement with the observed bedload data (Adj. R2 0.82–0.87). Finally, this study provides plausible estimates of bedload fluxes that are within predicted ranges reported for sand-bed rivers in Africa and other tropical regions. [ABSTRACT FROM AUTHOR]