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Sediment budgeting within a landscape is useful in understanding landscape evolution, and hazard prediction and assessment. It has been observed that only a fraction of the total volume of sediment produced within the system gets exported, implying that a part of the total volume of sediment is stored within the system. This sediment mass gets arrested and stored in compartments within the system and is mobilised during extreme stochastic events. These sediment storage compartments are poorly connected with the channel network and hence, do not supply sediment at steady rates. We have evaluated sediment connectivity and conducted field validation within a 93 km2 mountainous river basin (Pranmati catchment) in the NW Himalayas. This assessment relies on the Index of Connectivity (IC), computed through two methods: one employing the original framework and the C-factor from RUSLE, and the other utilizing a multiple flowpath model that incorporates Manning's roughness coefficient. We developed a storage potential index (SPI) by modifying the basic framework of index of connectivity; SPI indicates the potential of a point on the hillslope to arrest sediment flux and store it. Based on the difference of normalised IC and SPI, we have developed a sediment evacuation susceptibility index (ESI S) that indicates the susceptibility of various parts of the hillslope to get evacuated. Using ESI S , a sediment evacuation susceptibility zonation map was prepared that delineates areas on the basis of their stability. Our study indicates that sediment flux gets arrested at the (1) junction of land use and land cover units that have contrasting sediment transporting capacity, (2) grassland/barren land pockets surrounded by forests, (3) croplands, and (4) landslide debris deposits. The parts of the hillslope in the vicinity of the channel network and areas around steep surfaces are highly susceptible to sediment evacuation. Gentle sloped surfaces away from the channel network are relatively stable. Landslide debris are highly stable units of sediment storage. • Sediment connectivity of a catchment was assessed using index of connectivity (IC). • The IC model was modified to identify potential sediment storage zones (SPI). • Sediment evacuation susceptibility index (ESI S) was formulated using IC and SPI. • Sediment evacuation hazard zonation map was prepared using ESI S. [ABSTRACT FROM AUTHOR]

Research into sediment provenance identification in Antarctica is emerging as a relevant field of study, providing a unique insight into understanding geomorphological processes in extreme climatic environments. This study focusses on the mechanisms of sediment redistribution in the catchment of the Korabelny Stream, located at the western end of the Bellingshausen Ice Dome on King George Island (Shetland Islands). The catchment area of the stream covers 2.83 km2, with 1.17 km2 under the glacier. Two main sediment sources have been identified: a) the glacierized part, extending along the glacier edge and represented by a complex of moraine deposits lacking protective vegetation cover, along with part of the catchment under the glacier; b) the periglacial part, occupying territory with permafrost and a thin loose cover unevenly protected by early successional vegetation. We combine a tracer-based fingerprinting technique, sediment delivery estimates based on sediment flow connectivity index and geomorphological mapping to quantify the sources contribution to sediment yield. The proportional contribution of the glacierized part was 60–66 % of the total sediment yield based on two independent methods, suggesting the reliability of the results. It is noteworthy that sediment transport from the glacierized part exceeds that from the periglacial part. However, a significant portion of the sediment is redeposited in temporary reservoirs formed along the glacier edge and Lake Mesyats, located in the central part of the Korabelny Stream catchment. The main factor determining sediment yield in the catchment is the water reserves in snow at the beginning of the ablation season. In years when water reserves in snow significantly exceed long-term average values, such as observed in the austral summer of 2014–2015 when study was conducted, sediment yield was low. This is attributed to the faster melting of ice on the glacier compared to snow, due to differences in albedo. • First time, assessed sediment sources in small Maritime Antarctica catchment. • Two independent methods used to determine proglacial and periglacial contributions. • Proglacial part contributes significantly more to sediment runoff. • The higher snow water reserves at ablation start the lower proglacial sediment runoff. [ABSTRACT FROM AUTHOR]

[Display omitted] • China's large river sediment loadings and runoff have not universally synchronously changed in the past 20 years. • There were 9/13 of large river systems showed downward trends of annual sediment loadings. • Lower reaches of the Yellow River had the maximum annual average sediment loadings. • Runoff volume accounted for over 30% of sediment loading variations among all river systems. • Afforestation plays a crucial role in reducing sediment in arid regions. Understanding the relationship between sediment loading and its environmental implications in river systems is crucial for water resource management and environmental protection. This study explored the spatiotemporal characteristics of sediment loading and their environmental relationships in seven large rivers in China, aiming to quantify the contributions of various factors to changes in sediment transport. Monitoring data spanning twenty-one years (2002 to 2022) on sediments, hydrology, and the environment collected by sixty-five stations were analysed. The multivariate statistical techniques employed included Spearman's correlation analysis, principal component analysis, and multivariate regression modeling. The results show that sediment transport in various river systems exhibited spatial heterogeneity, the maximum annual average sediment loadings (1.59 × 108 t/yr) occur in the lower reaches of the Yellow River, the middle reaches have the highest sediment concentration (41.54 kg/m3), followed by the downstream of the Yellow River (5.85 kg/m3). Sediment loading and runoff changes in the basins did not adhere universally to synchronous patterns. Eleven of the thirteen basins of these river systems showed upward trends in annual runoff volume, whereas nine basins showed downward trends in annual sediment loading. Runoff volume accounted for over 30 % explanatory of sediment loading variations in all seven large river systems, with the Yangtze, Huaihe, Qiantang, and Songhua rivers surpassing 60 % of the explanatory power. The Normalized Difference Vegetation Index of all watersheds showed an increasing trend, whereas the index of nine of the thirteen watersheds was correlated negatively with sediment transport. The influence of human activities on basin sediment transport was higher than that of natural resilience, whereas afforestation significantly reduced sediment in arid regions. This study provides insight into the temporal and spatial characteristics of sediment loadings and the driving effects of environmental factors, which has great significance for watershed environmental management. [ABSTRACT FROM AUTHOR]

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

• A novel model integrating hillslope and in-stream sediment processes is developed. • We quantified the effects of soil-water conservation (SWC) on the Loess Plateau. • SWC contributes to 54.4% and 91.9% of the decline in discharge and sediment load. • Sediment reduction effect of hillslope SWC is more lasting compared to that of check dams. Soil erosion and sediment transport processes, which are intimately connected with hydrological processes, strongly affect land surface morphology and earth system dynamics. Over the past 60 years, intensive Soil-Water Conservation (SWC) measures implemented on the Loess Plateau have significantly reduced sediment load and concurrently exacerbated runoff declines, while the quantitative evaluation of the effects of SWC measures remains challenging. This study develops a sediment module which simulates the hillslope and in-stream sediment processes, and then incorporates the module into a Geomorphology-Based Ecohydrological Model (GBEHM). Besides, the model also couples with an explicit representation of different types of SWC measures, including both Hillslope SWC (HSWC) and River-network SWC (RSWC) measures. The newly developed hydro-sediment model is then applied to the Kuye River basin, a typical river basin on the Loess Plateau, and used for quantifying the effects of SWC measures on river discharge and sediment load during 1982–2019. Compared with Period 1 (1982–2000), the river discharge decreased by 48.7% in Period 2 (2001–2019), while the sediment load experienced a more substantial decrease of 95.3% between the two periods. Based on the numerical experiment results, HSWC and RSWC contributed to 25.4% (58 million m3/yr) and 28.9% (66 million m3/yr) of the annual runoff decline, as well as 58.1% (36 million t/yr) and 33.9% (21 million t/yr) of the annual sediment load reduction between the two periods, respectively. Besides, HSWC plays an increasingly important role in sediment reduction in recent years due to check dam silting. The model developed in this research is useful to evaluate the multi-faceted effects of existing SWC measures and to help with future SWC planning and policymaking. [ABSTRACT FROM AUTHOR]

The Wenchuan earthquake greatly reduced the forest water conservation capacity along the banks of Minjiang River. With the intensified soil erosion and the rapid increasing sediment transport, the sediment erosion of hydraulic turbines running on the river has become more and more serious, especially of high head Francis turbines. In this study, the k-ε multiphase flow turbulence model was used to calculate the sediment-water flow of a high head Francis turbine with long and short blades in Minjiang River. The distribution pattern of sediment concentration (sediment volume fraction) on the blade surface shows that the sediment particles mainly gather on the outlet edge at 10% of the blade height on the suction surface of the long blade, while the sediment concentration on the surface of the short blade is small. The erosion of the 0Cr13Ni5Mo runner blade was tested by the flow around erosion method, and the erosion amount on the blade surface in the severe erosion area was obtained. Based on the test data of erosion and the numerical calculation results of sediment flow, a formula to calculate the sediment erosion rate of flow passage components with 0Cr13Ni5Mo material was given for turbines operating in Minjiang River. By using this formula, the sediment erosion of flow passage components in hydraulic turbines with 0Cr13Ni5Mo or similar materials operating in Minjiang River can be predicted. [ABSTRACT FROM AUTHOR]

• A novel framework for prediction and early-warning of bank erosion is proposed. • The proposed framework captures major bank erosion sites in the MYR. • A model ensemble is better to improve the accuracy of bank erosion prediction. Bank erosion can cause serious damage to flood control infrastructures in alluvial rivers, and thus threaten the safety of riparian residents and industry in heavily populated river systems, such as the Middle Yangtze River (MYR), China. The current study proposes a novel framework for the prediction and early-warning of bank erosion. The prediction of bank erosion is implemented by coupling a dynamic model with a data-driven random forest model. To determine the early-warning level, four indices are proposed corresponding to bank erosion intensity and dangerous degree, respectively. These indices are combined into a final early-warning level of bank erosion. The proposed framework is applied to the MYR, with its performance being evaluated by the corresponding flow, sediment, and topographic measurements. The results show that: (1) the dynamic model reproduces the flow and sediment transport process well in the MYR, with relative errors being less than 6%, 33%, and 4% for the water discharge, sediment discharge, and river stage, respectively. The model is also able to capture the major bank erosion sites well; (2) The performance of the data-driven model is increased when the input data groups are balanced, with a recall rate of 0.67 and an precision of 0.80 being obtained; (3) the calculated distributions of early-warning sites are generally in accordance with the observations in 2020, and the dangerous areas locate close to the outlet of the Jingjiang Reach of MYR. Besides, a model ensemble is probably a better way to improve the prediction of bank erosion, as compared with solely relying on the refinement of a dynamic model. However, some major gaps are also identified in the current framework. [ABSTRACT FROM AUTHOR]

The structure and function of riparian ecosystems generally result from feedbacks between plant dynamics and fluvial processes and landforms, i.e., river morphodynamics. Taxonomic approaches do not allow direct identification and quantification of the mechanisms involved in the interaction between plant communities and the geomorphological environment. Although riparian ecosystems show enormous taxonomic variations, comparable patterns of plant response traits across different taxa may evolve in response to the exposure to similar hydrogeomorphological processes in relation to flow dynamics, sediment transport, and nutrient and water availability. Biogeomorphological functional classifications for plant responses to, and effects on, river morphodynamics at the levels of individual plants, populations, and communities have been proposed in the literature. They serve herein as a basis for identifying and quantifying, within a presented standardized functional trait framework, key plant response and effect traits that can help to explain feedbacks between plants and morphodynamics. In particular, functional guilds and functional diversity metrics can be applied at the population and community levels for exploring feedbacks between vegetation and river morphodynamics worldwide. In this framework, the variability in plant effects across different environments and spatiotemporal scales, related to the biological characteristics of the plants (i.e., morphological reconfiguration of plants into the flow, seasonal phenology, phenotypic plasticity, and vegetation succession), can be explored. New opportunities including remote sensing and numerical modelling approaches, coupled with the inclusion of plant traits through our original framework, will improve our understanding of feedbacks between vegetation and morphodynamics and contribute to an improved prediction of biogeomorphological river trajectories. • Taxonomical approaches do not permit the analysis of plant-geomorphology feedbacks. • Functional traits links hydrological, geomorphological and biological drivers and processes which shape river systems. • Riparian plant traits converge despite taxonomic variation. • The functional trait approach is an opportunity for quantifying riparian vegetation-river interactions worldwide. • The functional trait approach can be supported by remote sensing and numerical modelling of river trajectories of change. [ABSTRACT FROM AUTHOR]

• Fine particles control the exchangeable silica mobilization in the river. • Current sediment in the estuary contain less reactive silica than historical level. • Increased fine particle fraction affect silica sediment with forms variation in estuary. Changes in riverine sediment transport are an important part of land-sea geochemical cycling and further impact geochemical element fluxes in turbid rivers. However, as a vital nutrient element supporting primary productivity, silica mobilization from drainage in turbid rivers is overlooked. The turbid Yellow River has a strong ability to adsorb reactive silica, thereby exerting a substantial impact on the estuarine deposition of silica. Through an integration of monitoring databases, field sampling and historical hydrological data, we concluded that riverine fine particles control the exchangeable silica in the river and its estuary under soil erosion. Indoor simulation further revealed that the adsorbed content of exchangeable silica (ex-Si) in fine sediment constituted 35 % of total sediment matter. In addition, the transport of phosphorus and ex-Si was jointly regulated by fine sediment in global fluvial sediment transport, thereby exerting additional influence on the trophic structure of estuarine ecosystems. Against the backdrop of sediment budget deficit in the estuary, the heightened content of fine particles is depleting the silica storage from estuarine sediments. [Display omitted] [ABSTRACT FROM AUTHOR]

Arid ecohydrology relies on sporadic rainfall and flooding to sustain linear river oases, crucial for supporting flora and fauna during the long dry season and drought years. Growing water demands have led to large reservoir constructions, severely impacting the fragile arid ecosystems. We analyse the hydro-geomorphological impacts of the large Neckartal Dam (completed in 2019) on the Fish River oasis based on existing dams, regional studies, field surveys, hydrological data, and modelling. The Neckartal Dam, along with three smaller dams, impounds 80 % of the desert oasis basin (1235 Mm3, 55,870 km2), exceeding the average annual runoff threefold. A gradient of dam-induced changes was identified, varying with distance from the dam wall. Immediate downstream, hydromorphological impacts include channel narrowing (⁓15 %) and reduce mean annual sediment yield (⁓20 %). Also, water distribution losses create chronic low flows, favour for invasive flora and fauna to spread, significantly disrupting the pristine nature of the desert ecosystem. This phenomenon has been observed over a 70 km stretch below the Hardap Dam. This situation is irreversible, as the invasive flora can withstand even large floods. As the distance increases, the dam suppresses low to moderate annual floods and prolongs droughts from months to years or even decades. Based on our flood routing model, only the largest floods (recurrence interval, RI >25 years) can exceed the dam storage, continue downstream, transport sediment and maintain the pool-bar morphology along 245 km of the oasis. The lack of significant flows between major floods means that sediment from smaller, lower arid basins accumulates in the Fish River valley, filling pools and further reducing water availability during dry periods. The Neckartal Dam's impact assessment demonstrates potential changes in arid river systems globally. [ABSTRACT FROM AUTHOR]

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

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]

Water erosion, a notorious major threat to food security and ecosystem sustainability, is strongly conditioned by spatial and temporal scale effects. This paper systematically reviews the scale issues in runoff and sediment delivery (SIRSD) as a research field by integrating the traditional review approach and bibliometric analysis. This review summarises SIRSD's roots and the scale effect on runoff and sediment delivery. Then, we provide quantitative insights into the SIRSD domain's development history, thematic structure, geographic distribution, international cooperation, and methodologies. Findings show that: i) SIRSD arises from the gap between the non-linearity of runoff and sediment delivery across scales and our ability to measure it. Point-based and short-term measurements cannot capture the non-linearities from the spatio-temporal heterogeneities and cross-scale interactions of factors or processes. ii) Previous literature provides evidence that the spatial scaling of specific runoff (r), soil erosion (SE), sediment yield (SSY), or sediment delivery ratio (SDR) with drainage area (A) or slope length (L) exhibits contrasting patterns due to distinct mechanisms. Infiltration-excess and saturation-excess processes account for inverse and positive r - A relations, respectively. Interrill-erosion and rill-erosion cause inverse and positive SE-L relations. Hillslope-erosion and channel/bank-erosion explain inverse and positive SSY-A relations. Downstream increasing deposition and additional sediment inputs drive inverse and positive SDR-A relations. These scaling relationships can be nonlinear or complex due to spatial heterogeneities in land use, vegetation, topography, climate, lithology, and soil characteristics. Hence, applying an empirical scaling equation developed from the region with distinct environmental contexts is not recommended. Furthermore, the existing scaling patterns or equations may require updating given global climate and land use change. iii) SIRSD is a complex and multidisciplinary issue investigated by scientists from 93 countries since 1928. International research has substantially facilitated the understanding of SIRSD; still, more collaboration should focus on less-developed countries with high soil and water loss risks and urgent conservation needs, such as those in Africa and South America under cropland expansion. iv) Scale mismatch and scale break have discredited large-scale erosion and sediment assessments. Incorporating gully and bank erosion into modelling, extending the scale range of the L factor, and expanding the sediment scaling scope from watershed to slope may make a difference. Therefore, more research with nested design incorporating multiple scales is necessary for cross-scale analysis and scalable modelling. Addressing global climate change requires improving real-time urban flood forecasting and integrating downscaled climate models with hydrology, erosion, and sediment transport models. • A bibliometric review of the global SIRSD research for the first time. • SIRSD is rooted in the gap between natural nonlinearity and our measuring ability. • Scaling of specific runoff, erosion, sediment yield, and SDR has diverse patterns. • Scale mismatch and scale break discredit large-scale modelling and assessments. [ABSTRACT FROM AUTHOR]

[Display omitted] • The new anicut reoperation enhanced upstream impoundment by 16%/year. • The reoperation redoubled flow regime shifts within five years. • It deviated two-third of water level between upstream and downstream. • Multi-fold expansion of upstream channel contracted half of the downstream channel. • Reoperation sequestered 82 % sediment that stopped infilling 0.64 km2 mining pits. In the last century, more than 58,000 large dams were constructed worldwide. Meanwhile, some of these older dams were renovated/reconstructed and started reoperation with enhanced regulation capacity to meet the rising water demand. However, the impact of dam reoperation on rivers is not thoroughly understood. This study aimed to examine the impact of dam reoperation on the Kangsabati River's flow regime, sediment transport and planform adjustments in upstream and downstream of the reconstructed anicut (like a dam/barrage) in the lower Ganga plains. The anicut structure was built by the British in 1866. It was demolished, underwent further reconstruction, and recommenced operation in 2016. While the Kangsabati reservoir (KR), with 1135 million-m3 (MCM) capacity in 80 km anicut's upstream, has been functional since 1974. Together, these regulation structures enable irrigation across 0.4 million hectare cropland in dry regions. Meanwhile, the KR operation reduced 34 % (1974–2010) and 70 % (2010–2015) flow before the new anicut's reoperation. Likewise, within five years, the reoperation reduced 35 % mean annual flow and two-thirds of the non-monsoon flow, despite the anicut's small 6-MCM storage capacity that redoubled the flow regime shift. After the reoperation (16 %/year), the enhanced water impoundment reduced fluvial landform diversity by submerging upstream channel area and abandoning/exposing downstream landforms, as effectively captured with the non-water/water index (NWI). It led to significant channel planform alterations, with 85 % expansion of the upstream channel, 44 % contraction of the downstream channel, and 72 % variation in both upstream and downstream water levels, unlike before the reoperation. Reoperation disrupted sediment infilling of 1.3 MCM downstream sand mining pits. This deprived the downstream communities, relying on mining activities for their livelihoods. Thereby, the reoperation-induced regulations have ignored upstream and downstream ecological connectivity and ecosystem services, resembling the impacts of any large dam. This requires urgent attention and strategies aimed at restoring river ecology and associated benefits. [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]

• The height of sediment traces is used as an alternative indicator to the functional connectivity. • The frequency and magnitude of sediment connectivity are not necessarily synchronized. • The response of sediment connectivity to rainfall is nonlinear in watersheds. • The spatial inhomogeneity and amount of rainfall are important factors influencing sediment connectivity. Sediment connectivity is a fundamental concept for understanding sediment dynamics within watersheds, serving as a crucial component in watershed management and soil and water conservation. However, quantifying sediment connectivity remains a challenging task due to its complexity and the difficulties associated with direct measurements of sediment flux at multiple temporal and spatial scales. Our research aims to address this challenge by monitoring functional sediment connectivity at various scales using two key indicators: sediment yield and sediment marks. Sediment yield is monitored at slope plots, slope-channel cascades, and watershed outlets, while sediment marks provide additional insight into functional sediment connectivity along the sediment transport path, particularly in slope-channel cascades and channels following rainfall events. To record sediment marks, we used wooden sticks wrapped with clean gauze as an alternative to assessing functional connectivity. Our results revealed that the activation of sediment connectivity was influenced by rainfall amount, intensity, and type, with the highest activation observed at the slope plot, followed by the outlet of the slope-channel cascade and the watershed outlet. Notably, strong sediment connectivity at slope plots, slope-channel cascades, and main channels exhibits a weak correlation with sediment connectivity at the watershed outlet. In upper contribution areas with lower vegetation coverage and higher human disturbance, rainfall amount and I 60 values associated with sediment connectivity activation tend to be lower. Furthermore, our research indicates that medium-duration and moderate-intensity rainfall events have a more significant impact on sediment connectivity at slope plots, while rainfall types characterized by longer durations, lower intensity, and larger amounts have a more pronounced effect on sediment transport paths. This suggests that the identification of sediment connectivity switch nodes can be achieved by considering both rainfall characteristics and underlying surface features. Looking ahead, future research can leverage long-term observations and data-driven models to explore rainfall thresholds for sediment connectivity at various scales, ultimately improving sediment transport prediction within watersheds. [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]

• (234U/238U) were analyzed for the Changjiang estuary sediments. • Catchment erosion was revealed by sediment comminution age. • Climate changes play a leading role in catchment erosion. • Human activities changed the natural erosion processes since the late Holocene. Catchment erosion not only plays an important role on landscape evolution, but also determines the exposure of rock debris in the regolith profile, and therefore impacts the chemical weathering and associated CO 2 absorption and ultimately global climate. But climate also modulates erosion and complex interaction loops, especially at large scale can hamper a clear understanding of these processes. Here we mainly use Uranium-series Comminution Age (t com) of core sediments from Changjiang estuary to reconstruct the catchment erosion, and the relationship with climate changes and human activities during the last 14 kyrs. Since 14 ka, the sea level has been rising continuously until current highstand system tract in the East China Sea where the Changjiang estuary is located. The sediments in the Changjiang estuary mainly come from the upper reaches erosion zone during this period, but the sediment supply from the middle and lower reaches has gradually increased since the Late Holocene. The period can be divided into two modes. The first mode happens from the Bølling-Allerød period to the Mid-Holocene when the sea level rose rapidly, and the t com of sediment recorded the residence time in the upper reaches erosion zone, with a periodic pattern of t com in a good agreement with climate changes. During the cold and dry periods, the longer t com (average 460 kyrs) is consistent with less precipitation resulting in shallower erosion with transported material mainly coming from the soil with longer residence time. In contrast, during the warm and wet periods, the t com is shorter (average 290 kyrs), with the more abundant precipitations that contribute to deeper erosion in the upper catchment, and more fresh material transported to the estuary through stronger hydrodynamic forces. The second mode is more chaotic and corresponds to 0 to 4 ka, when climate was warm and humid and stable sea level, but t com fluctuated from 200 kyrs to 650 kyrs. The increasing river flooding caused by abundant precipitation leads to lateral migration of the river channel in the middle and lower reaches, and the sediments deposited in the floodplain were eroded and mobilized again. In addition, the rapid development of human activities since 2 ka has accelerated deforestation and agricultural cultivation, leading to localized erosion of the floodplain. These remobilized sediments were transported to the estuary and deposited, resulting in a larger t com value. This study overall indicates that, in the millennial scale, the t com of fine detrital fraction shows a sensitive and quick response to catchment erosion, and provides new insights into quantifying the time scale of sediment source to sink processes and inferring the paleoenvironment accurately climate changes. [ABSTRACT FROM AUTHOR]

Soil erosion and accompanying sediment issues have a significant impact on environmental sustainability. However, there is not currently a clear understanding of the relationship between soil erosion and sediment sources at the catchment scale, which has led some researchers to regard areas with severe soil erosion as the main sediment source. This view does not apply in all circumstances. • This paper uses 137Cs to study the average annual erosion rate of different land use types. The results show that the erosion rates of woodland, sparse woodland and farmland areas were 400, 1756, and 2771 t·km−2·a−1, respectively, multiplied by the corresponding area. Surface soil erosion levels in the catchments of the three types accounted for 11%, 26% and 25%, respectively, and the total accounted for 62% when the gully bank accounted for 38%. • Fingerprinting technique results show that the relative source contributions of woodland, farmland, sparse woodland and gully bank areas to sediment at the small catchment outlet were 4%, 10%, 48% and 38%, respectively. The results reveal that the detachment process of soil and the transport process of sediment with runoff were internally related and independent of each other. • By comparing on-site erosion rates with downstream source contributions, we have a clearer understanding of soil erosion and subsequent sediment transport process in the agroforestry catchment in mountainous areas. We emphasize the importance of governance and management in areas with severe soil erosion, mainly targeting types such as hillslope framland. In addition, sparse woodland and gully banks should be given more attention, as they account for a large proportion of sediment in the downstream catchment. • Soil erosion using 137Cs based on multiple reference inventories. • Combine on-site erosion by 137Cs with sediment sources by fingerprinting. • Clearer understanding of soil erosion and sediment transport process. [ABSTRACT FROM AUTHOR]

• Lateral sediment flux from hillslopes is directly connected to the curve number. • The curve number summarized the resistance from the soil-group complex. • The lateral sedimentologic connectivity was well represented by the curve number. • The soil-cover complex in a watershed is closely related to watershed erodibility. The flux of suspended sediment and bedload in a watershed is closely linked to the resistance of soil, known as erodibility. However, the relation between the resistance generated by soil to sediment transport from the hillslope to the river flow is still a challenge. Typically, the bedload flux is related to the shear stress of the main channel. However, the link between lateral sediment flux from hillslopes to suspended sediment flux of the main channel and the relation between bedload and suspended sediment flux to soil erodibility need to be developed. For three Brazilian watersheds, suspended sediment and bedload transport, soils, and hydrological data were obtained to determine watershed soil erodibility. The landscape connectivity expressed by hydrological-sediment connectivity was applied to determine the lateral sediment transport to the primary watershed channel. The flow resistance and lateral suspended sediment discharge were represented by the curve number, which summarized the resistance from the soil-group complex leading to soil erodibility. The curve number addressed the lateral flow and suspended sediment transport to represent the lateral connectivity on the landscape. Sediment transport (sand and suspended sediment) from hillslopes was added to the bedload transport along the longitudinal axis of the watershed, and the watershed soil erodibility (K W) was, thus, obtained for each of the three evaluated watersheds. [ABSTRACT FROM AUTHOR]

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

Sediment source-to-sink processes of river systems have significant impacts on depositional environments in coastal and shelf seas and on long-term climate change. Typically, sediments at the outlets of small mountainous rivers (SMRs) are considered to represent the average composition of particles eroded from the entire river basin due to the fast sediment transfer rate and short residence time in the basins. However, this assumption may be challenged by the significant heterogeneity in sediment erosion and transport processes within the SMRs catchments. In this study, we compare the geochemical and provenance heterogeneity of two typical mountainous rivers in subtropical East Asia, the Mulanxi in Mainland China and the Zhuoshuixi in Taiwan. These two SMRs have similar monsoon climate regimes but different tectonic, geomorphic, and hydrological settings, as well as sediment routing processes. Neodymium isotopes (εNd) and stable elemental ratios of Cr/Th and Sc/Th demonstrate the remarkable intra-catchment geochemical heterogeneity of both rivers. The εNd decreases from −7.1 to −10.0 from non-tidal to tidal reaches in the Mulanxi, while it changes from −11.5 in the upper reaches to −14.1 in the lower reaches of Zhuoshuixi. Apart from the general controls of provenance lithology and weathering processes on sediment geochemical heterogeneities between these two SMRs, the intra-catchment heterogeneity of the Zhuoshuixi is mainly induced by uneven sediment mixing in the flat and low connectivity areas (accounting for ∼36.5% of the downstream area). Meanwhile, the strong tidal influence is the primary control for the intra-catchment geochemical heterogeneity of the Mulanxi sediment, and relatively long sediment residence time in the catchment also plays some role. Our study suggests that samples collected at the river mouths cannot be simply treated as representative of the basin average or fluvial end-member to the sea. The compositional heterogeneity of the SMRs and its environmental effects and responses to rapid climate change require more in-depth investigations. • Distinct geochemical heterogeneity observed between SMRs in subtropical East Asia • Tide-induced sediment mixing accounts for heterogeneity of SMRs in SE China coast • Geomorphic features and climate events explain the heterogeneity of Taiwan rivers • Samples in the river mouth cannot represent the fluvial end-member to the sea [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]

• Cross-sectional sample collection were performed for two time steps. • Time marker had a significant impact on predicting sedimentation rates. • There was internal heterogeneity during floodplain sedimentation. • Sampling position had a significant influence on the analysis. • 137Cs measurement may underestimate the sediment deposit rate. Floodplain deposition can provide important historical information about river systems. 137Cs tracer measurement is the most widely used technique for studying floodplain deposition. One-time sampling is normally used to date or estimate erosion and deposition rates, while time-interval sampling has rarely been applied. Northeast China is an important grain production area characterized by intense erosion and a low sediment transport ratio. Most studies of the region have focused on slope sedimentation, while floodplain sedimentation has received little attention. In this study, two-time steps of cross-sectional sediment core sample collection were performed to examine the floodplain sedimentation in the river basin of the Laolai River, a tributary of the Songhua River. The potential for using 137Cs to estimate the sediment deposition rate for a given time-interval was also investigated. A total of 18 cross-sections were acquired, and three repeated cross-sections were selected for double sampling. Significant differences were observed between the results obtained from the samples collected in separate rounds, suggesting the presence of internal heterogeneity during floodplain sedimentation and a significant influence of sampling positions on the analysis results. In the basin examined, sedimentation often occurs midstream, upstream, and at the outlet, and was mainly affected by topography, reservoir construction, and land use. Sedimentation occurs easily at wide, flat outlets or river intersections in braided water systems. It was observed that downstream floodplain sedimentation was increased by sediment interception by upstream reservoirs, but reduced by forests near floodplains. Sedimentation rates were significantly different between the 1954 and 1963 time markers, and we found that using rates from 1954 alone would lead to underestimation. When 137Cs sedimentation and floodplain distribution are used to determine flooding occurrence, variations in 137Cs content and particle size distribution should be considered. River bank erosion in this region should be taken into account, and riparian protection is required to reduce erosion and floodplain deposition. Since 137Cs is absent in fine particles when the sediment is predominantly sand, 137Cs measurement may underestimate the sediment deposition rate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Longitudinal influences of low-water crossing on sedimentological connectivity. • Sedimentologic and morphologic modifications due to different rainfall patterns. • Destruction and deposition of sediments and the channel morphology were analyzed. • Low-water crossings mainly interrupt coarser sediments. • Low-water crossings function similarly to check dams, weirs, and sand dams. This study evaluated the longitudinal influences of low-water crossing on the river system and sedimentological connectivity in a Brazilian semiarid basin. The Lower Piancó River basin was chosen as the study area, and four low-water crossings along the catchment were identified and selected for analysis and diagnosis. The effective catchment areas of each structure were delimited, and their impacts assessed over time. Rainfall data from three gauges were used to analyze precipitation events capable of causing significant sedimentological and morphological modifications. These events were classified into three types according to their magnitudes: high, moderate, and low. Sediment samples were collected at each low-water crossing, and lateral profiles were drawn upstream and downstream of the structures to analyze the destruction and deposition of sediments and channel morphology. The analysis showed that the low-water crossings could act as barriers to sediment flow, especially for coarser sediments, and favor the incision of the downstream channel. However, during exceptional flows, the low-water crossings allowed the transmission of sediments due to the clogging of the upstream channel riverbed. This highlighted a unique interaction between the river system and the low-water crossings over time. The results of the connectivity analyses revealed that low-water crossings have a unique impact on the fluvial system compared to other structures, particularly due to their role in the sedimentological connectivity of coarse sediments. Specifically, sediment transport downstream of the crossing emerged as a significant factor in understanding its influence on the surrounding environment. Compared to other types of small longitudinal fluvial interventions, the stage model and low-water crossings displayed structural and aesthetic similarities with floodways and fords. However, functionally, the low-water crossings had strong similarities with check dams, weirs, and sand dams due to their roles in retaining sediments and altering the morphology of the channels in which they are installed. [ABSTRACT FROM AUTHOR]

• A mathematical model considering the operation of 24 mega reservoirs was proposed. • The sedimentation mainly occurs in the mainstream during the flood season. • The cascade reservoirs operation leads to easier and prolonged sedimentation. The intensive construction of large dams in the upper Yangtze River Basin (UYRB) has formed large-scale cascade reservoirs and obviously altered the flow regime and sediment transport of the basin. However, few studies have quantitatively described the cumulative impact of these reservoirs on sediment interception. In this study, a flow and sediment transport model that fully considers the operation processes of 24 mega reservoirs in the UYRB was established, and the spatial and temporal variations in sedimentation from 2011 to 2080 were elucidated, assuming repeated series of daily input flow discharge and sediment concentration during 2011–2020 and monthly water operation levels of 24 reservoirs during 2018–2021 as boundary conditions. The results showed an annual average sedimentation of more than 300 Mt in the UYRB during 2011–2060, which falls to 270 Mt in the period 2061–2080, and more than 80% of the sedimentation occurs in the flood season. Nearly 80% of the total sedimentation during 2010–2080 was observed in the mainstream reservoirs, especially the four mega reservoirs in the lower Jinsha River and the Three Gorges Reservoir (TGR), which accounted for 31.9% and 22.7% of the total sedimentation, respectively. The proportion of sedimentation in mainstream reservoirs will further increase with increasing operation periods. Most reservoirs in the UYRB will not reach sedimentation equilibrium by 2080, except for reservoirs in the Min River Basin. The ratio of siltation capacity to average annual sediment yield determines the percentage of residual siltation capacity of each reservoir. The operation of the cascade reservoirs in 2013–2020 had no more immediate impact on the middle and lower Yangtze River than that in 2003–2012, when the TGR started impoundment. However, the joint operation of these cascade reservoirs has changed the spatial distribution of sedimentation in the UYRB, and will lead to prolonged impacts on downstream channel erosion. [ABSTRACT FROM AUTHOR]

As home to about 70 million people, the Mekong River Basin (MRB), located in Mainland Southeast Asia, is often influenced by tropical cyclones (TCs) landfalling. The TCs not only cause flood and storm hazards, but also play important roles in providing freshwater resource and welcomed sediment transports. Our study focuses on the climatology of TCs and associated rainfall (TCR) in the MRB for 1983–2016. Results show that: (i) the mean landfall occurrence of TCs is 6.2 yr−1, leading to 36.7 mm yr−1 of annual mean TCR (2.5% of the annual total precipitation), which mainly occur in monsoon-TC season (i.e., June–November); (ii) TCs highly concentrate on the lower eastern MRB, generating the largest TCR contribution of 12.4% to the annual total precipitation; (iii) the annual mean contribution of TCs induced extreme precipitation - R20mm and R50mm (days of heavy precipitation rate ≥20 mm day−1 and ≥50 mm day−1, respectively) - to that from annual total precipitation is large in the lower eastern MRB; (iv) over 60% of the basin area is influenced by TCR on average; and (v) a significant weakening trend of the TC frequency has been observed. The present findings lay a foundation for further in-depth research of the potential influence of the dynamic TCs and the associated rainfall in the MRB. • Annual mean tropical cyclone landfall is 6.2 yr−1 in the Mekong River Basin. • Annual mean tropical cyclone rainfall contributes to 2.5% of annual total precipitation. • Tropical cyclone highly concentrates on the lower eastern basin. • Tropical cyclone contributes largely to extreme precipitation. • A significant weakening trend of tropical cyclone occurrences is observed. [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]

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]

A major challenge in provenance and source-to-sink analysis is deciphering intrabasinal versus extrabasinal sediment sources and processes. This issue is well-illustrated by the Paleogene Pearl River Mouth Basin (PRMB), whose provenance reflects a combination of sediments eroded from the Cathaysia Block (CB), southeastern China, and from intrabasinal structural highs. Here we use new detrital zircon U Pb ages from Paleogene formations in seven boreholes, southern PRMB, to investigate such local versus regional influences on provenance. Detrital zircons from the upper Eocene-lower Oligocene Enping Formation are dominated by Jurassic-Cretaceous ages, with a 125–110 Ma age-cluster, absent in modern river data from the CB and diagnostic of intrabasinal sediment sources. In the northern part of the basin, Mesozoic-dominated zircon age-spectra give way to Paleozoic and Precambrian grains, a pattern also recognized for the late Oligocene Zhuhai Formation, suggesting a major change in provenance likely related to extrabasinal influence from the CB. The age spectra for these samples are most similar to the northeastern Pearl River, narrowing this region as the most likely source. Spatial analysis of the results suggests that during deposition of the Enping Formation, sediment transport was not uniform and that the basin's architecture strongly influenced provenance, with structural highs acting as both sediment sources and barrier to sediment transport from the CB; whereas structural lows, with clear extrabasinal influence, functioned as sediment transport corridors. Such spatial differences are lost in samples from the Zhuhai Formation and their provenance suggests that the paleo-Pearl River and tectono-climatically driven surface processes in the CB dominated deposition thereafter. • Paleogene sediments reflect a combination of intrabasinal and extrabasinal sources and processes. • Sediment delivery from the Cathaysia Block (CB) was not uniform and the basin's architecture strongly influenced provenance. • Erosion and delivery of sediments from the CB was limited to the northeastern Pearl River area until the late Oligocene. [ABSTRACT FROM AUTHOR]

Exceptional megaflood-scale bedforms on Earth are commonly associated with the catastrophic draining of glacial lakes in the late Pleistocene. The widest studied events have been the Missoula and Altai floods with 300–700 m flow depth, 1–20 m bedform height and 10–300 m wavelength. Nowadays, the Saint-Venant equations have succeeded at simulating the catastrophic glacial-lake drainage process numerically, but we still lack a depth-averaged morphodynamic theory able to predict the growth of dunes and antidunes. The disparity of spatial scales in megafloods prevents the use of non-depth-averaged rotational flow equations, motivating the present shallow-water theory for the formation of megaflood-scale bedforms. We adopt a non-equilibrium sediment transport equation rooted in Einstein's pioneering work. Here we prove that the bed instability triggers to form dunes and antidunes simply by lagging the entrainment term for sediment mass conservation, or the bottom shear stress, with respect to the depth-averaged flow velocity. We formalise this result using a linear stability theory that captures the existence regions of dune and antidune in addition to the roll wave instability. Furthermore, in the spirit of Kennedy (Annu. Rev. Fluid Mech. , vol. 1, 1969, pp. 147–168), we derive a closed-form solution of growth rate and wave speed of the bedform. The nondimensional groups controlling the linear instabilities are the Froude number, ℱ r , the Shields parameter, Sh , and the grain roughness relative to flow depth, d. Subsequently, we simulate the drainage of the largest Missoula flood numerically to explain the formation of giant antidunes in the Camas Prairie (Montana, US) during the late stage of the megaflood. Also considered are large fields of gravel dunes in the Kuray-Chuja Lake Basin (Altai Mountains, Siberia). The simulated hydraulic conditions over bedforms in both basins yield values of the nondimensional parameters that lie in the theoretical region of dunes and antidunes according to the proposed theory and in situ measurements in sandy rivers and flume experiments. [ABSTRACT FROM AUTHOR]

Abstract The future trend of water and sediment variation is closely related to the governance of the Yellow River. The increasingly frequent occurrence of extreme rainfall events has rendered the future water and sediment situation of the Yellow River uncertain. Understanding the characteristics of flood and sediment yield of the river basin under extreme rainfall conditions at different times is a prerequisite and foundation for accurate prediction of water and sediment situation in the Yellow River in the future period. We here used the July 26 extraordinary rainstorm event in 2017 in the Wuding River as a starting point for revealing the law of flood and sediment yields changes under extreme rainfall conditions around the year 2000. The results indicated that, during the period from 1960 to 2016, the average proportion of extreme rainfall depth in the middle Yellow River region over the total precipitation depth increased by 5.1%. Areas where extreme rainfall events frequently occur showed a trend of developing from localized regions in the Toudaoguai–Longmen reach to the majority of the middle reaches. There were obvious changes in the rainfall-flood and rainfall-sediment relations under extreme rainfall conditions. Compared with historical extreme rainfall events, the decline in flood and sediment yield in the river basin after 2000 under similar rainfall and intensity conditions was obvious. Among these results, flood decreased by 30.4–78.2%, sediment yield was decreased by 53.0–88.2% and sediment content in flood was decreased by >47.2% on average when compared with the same rainfall conditions in the previous century. Comparative watershed studies showed that, during extreme rainfall events, areas under soil and water loss management programs suffer 57.2% and 75.7% less flood runoff modulus and sediment transport modulus, respectively, than non-managed areas. This indicates that soil and water loss management is the major driving factor for changes in rainfall-flood and rainfall-sediment relations under extreme rainfall conditions. This study highlights the importance of soil and water loss management in the flood control and sediment reduction. We concluded that, with the implementation of soil and water conservation measures, the probability of large flood and sediment events will greatly decrease and the amount of sediment entering the Yellow River under extreme rainfall will further decrease in the next 30 years. Highlights • Frequency of extreme rainstorm events in the Yellow River increased significantly. • Rainstorm-sediment relations exhibited obvious changes after 2000. • Soil and water loess management plays a key role in reducing sediment. • The probability of large flood and sediment events will greatly decrease. [ABSTRACT FROM AUTHOR]

• Tool for optimal selection and implementation (TSI) of the eco-remediation measures. • TSI supports implementation of mitigation measures on the most critical source areas. • TSI reduces the size of required area and cost of implementing measures. Erosion processes in the watershed and sediment transport cause hydro-morphological changes, eutrophication, and the loss of storage capacity in reservoirs. This study examines the tool for the optimal selection and implementation (TSI) of eco-remediation measures (ERM) in the river basin area to improve water quality and to reduce storage loss in the reservoir in question. The main purpose of this tool is to support decisions and measures taken to correct defined problems and to improve water quality and storage capacity in the watershed while minimising sediment transport. This tool enables the effective and necessary implementation of these measures to the most critical source areas (CSAs). In order to verify its operability, we selected the Ledava reservoir with a transboundary area of 105.25 km2 in NE Slovenia and SE Austria. With the use of the Soil and Water Assessment Tool (SWAT), critical source areas were determined and the effects of eight different scenarios on sediment yield and load transport were simulated. The results showed that CSAs occupy 12% of the watershed and that sediment inflow into the Ledavsko jezero reservoir could be reduced by up to 30%. After determining the CSAs and which measures would be most effective, the implementation plan could be defined. Within this framework, the TSI enabled the selection of effective measures and contributed to the long-term improvement of the ecological status of surface waters required by Water Framework Directive (2000/60/EC), improving the quality of water bodies of all types to safeguard water ecosystems from harmful consequences. [ABSTRACT FROM AUTHOR]

Piston core GL-77 was collected in the lower slope of the northern Campos Basin, Brazil, and consists essentially of muds that have been deposited in turbiditic currents over the last 130 ka, at least, which corresponds to the Upper Pleistocene-Holocene interval. The identified ascidian spicules belong to the Didemnidae Family and are represented by species Micrascidites vulgaris , Bonetia brevis , Rigaudia multiradiata and Monniotia fasciculata. These species have irregular abundance and distribution, with Micrascidites vulgaris being the most common. Their occurrence is interpreted as resulting from transport to the depositional site in response to climate fluctuations (glacial and interglacial periods). The transport of ascidian spicules from a shallow-water sea is supported by the presence of terrestrial organic matter, mainly phytoclasts, sporomorphs and microphytoplankton, which were transported to the slope by the river systems. The results found in this study show that the relative frequency distribution pattern of didemnid spicules is a useful tool for monitoring sediment transport in the slope. [ABSTRACT FROM AUTHOR]

Abstract The purpose of this study was to analyse suspended sediment (SS) transport in a small catchment (13 km2) located in the Polish Carpathians affected by various forms of human activity in the period 1970–2017. This period covers two stages of socioeconomic development with contrasting forms of human activity: the centrally planned economy related to the communist system up to 1989 and the period of a free-market economy following. Analysis indicates increases in grassland and forest areas of the analysed catchment of 90% and 10% respectively and a decrease in cultivated land of 82%. Changes in land use and land cover (LULC) have reduced soil erosion by 74% as calculated using the Revised Universal Soil Loss Equation. At the same time, population, number of buildings, and construction works along the stream increased, and number of cart roads decreased. Hydrometeorological data as well as suspended sediment load (SSL) have not shown a statistically significant trend despite changes in forms of human activity in 1970–2017. In the first three decades of the analysed period (1970–1979, 1980–1989, and 1990–1999), SSL gradually decreased. In 2010–2017, suspended sediment load was the highest in the whole investigated period. Principal component analysis (PCA) confirmed that it was a result of the appearance of new sediment sources associated with intensification of landslides and new forms of human activity, such as construction works. The imposition on these factors resulted in an increase in SSL and masked the effects of rainfall LULC change in the catchment. Analysis shows that proper recognition of changes in sediment sources in the catchment is fundamental for correct interpretation of long-term sediment transport in the streams. Highlights • Suspended sediment transport in a small mountain catchment was analysed in 1970–2017. • Precipitation and suspended sediment loads have not shown significant trends. • Besides hydro-meteorological factors, various forms of human activity affected suspended sediment transport. • The relation between land use land cover and suspended sediment load was masked by changes in sediment sources. [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]

Abstract The lower Amazon basin contains vast floodplains that exchange sediment with the main river. The exchange of sediment between the floodplain and the channel follows a seasonal cycle that is anticorrelated with the hydrological cycle. At low water stages, sediment that has been stored in the floodplain for potentially several thousands of years is eroded and transferred from the floodplain to the mainstem. During high water stages, most sediment transported in the main channel stems directly from the eroding source with little intermittent storage. We apply the meteoric cosmogenic 10Be to stable 9Be ratio (10Be/9Be) as a denudation and weathering proxy to investigate this seasonality in sediment transport. Single meteoric 10Be concentrations ([10Be]) have previously been shown to record floodplain storage; whereas fractions of mobilized 9Be, a trace metal released during weathering, provide degrees of weathering. The resulting 10Be/9Be ratio provides denudation rates of the sediment sources. We compare 10Be/9Be measured on suspended sediment from river depth profiles at two sites (Óbidos/Macapa) and during two hydrological seasons (high/low water stage in 2013). We show that careful construction of river depth profiles in combination with Rouse modeling is necessary to exclude the grain size dependence that together with hydrodynamic sorting introduces a bias into single [10Be] and [9Be]. In contrast, the 10Be/9Be is largely uniform across grain sizes and is thus unaffected by sorting. Our 10Be/9Be ratios, the denudation rates derived from them, and mobilized 9Be fractions do not show variations outside their uncertainties across seasons or sites. Thus, 10Be/9Be show that upstream sediment sources were well mixed by multiple cycles of storage and remobilization in the floodplain. Highlights • Meteoric cosmogenic 10Be/9Be record denudation rates of Amazon sediment sources • No seasonal variations in 10Be/9Be resolvable due to sediment mixing • Depth-integrated single 10Be show small seasonal variations due to sediment storage. • River depth integration required for single 10Be to exclude fluvial sorting bias. [ABSTRACT FROM AUTHOR]

Large reservoirs can considerably alter the water-sediment dynamics and morphology of alluvial rivers. Here we review the effects of two mega reservoirs operated with different regulation modes. The Three Gorges Reservoir (TGR) on the Yangtze River has a typical anti-seasonal regulation mode, while the Xiaolangdi Reservoir (XLDR) on the Yellow River undergoes a swift drawdown process shortly before the flood season through the Water and Sediment Regulation Scheme (WSRS). We examine the influence of these regulation schemes on downstream water-sediment dynamics and find that vast sedimentation occurred in both the TGR (128.4 Mt./yr) and XLDR (210.2 Mt./yr). The two rivers have experienced different changes in downstream sediment transport capacity, with coincident flood and sediment peaks in the Yangtze River but with sediment peaks lagging behind flood flow peaks in the Yellow River. On the Yangtze River, highly unsaturated flows from the TGR led to widespread incision downstream, while on the Yellow River, such flows did not induce significant erosion in the first two years following impoundment. The low annual runoff and high sediment yield of the Yellow River mean that riverbed erosion occurred mainly when the water discharge and sediment transport capacity were enhanced by the WSRS. In both rivers, the riverbed eroded and coarsened downstream of the mega dams, lowering the dry season water level. The increase in channel roughness maintained or even raised flood season water levels, potentially increasing flood risk. Sediment budgets reveal that the river segments downstream of the dams switched from sediment sinks to sources due to riverbed incision. Despite new supply from downstream reaches, sediment deficits arising from dam interception and other human activities within the drainage basins have posed significant challenges to the sustainability of the Yangtze and Yellow river deltas, resulting in lower accumulation rates or even transition from progradation to degradation in subaqueous areas. In contrast to the anti-seasonal regulation mode of the TGR, the WSRS of the XLDR has proven very effective at mitigating reservoir sedimentation and has boosted the quantity of sediment reaching the sea, facilitating delta stability and coastal sediment replenishment. [ABSTRACT FROM AUTHOR]

Sediment burial can lead to significant lag times during sediment transport and is an important component of the sediment cycle. The Indo-Gangetic Plain (IGP) is a large sediment conveyer belt and understanding sediment lag times on various time scales is important for short- and long-term sediment transport and denudation-rate estimations. In this study, we have quantified the transport lag time in terms of burial duration with 14 different alluvial drill cores from 4 major Himalayan river basins, including the Ghaggar, Paleo-Yamuna, Ganges, and Kosi rivers. We rely on 56 samples using the paired cosmogenic radionuclides, 26Al and 10Be. The coring locations of paleo-Yamuna and Kosi, along with one of the Ghaggar cores are within ∼100 km from the mountain front, while the Ganges cores are ∼350 km away. The coring locations cover an E-W distance of ∼1200 km on the IGP and the depositional ages range from ∼120 kyr BP to the present day based on previous age estimations. Out of 56 samples, 39 samples show a burial signal ranging from 0.61±0.33 Myr to 3.75±1.9 Myr, with outlier values as large as ∼6 Myr. We show that the Kosi samples due to their proximity to the mountain front show no burial or a lower mean burial duration of ∼1.01 Myr, compared to the samples from the coring locations well within the IGP, such as the Ghaggar (∼2.48 Myr) and the Ganges (∼2.36 Myr). However, despite its proximity to the mountain front, the paleo-Yamuna samples have a mean burial duration of ∼2.20 Myr. Along with the floodplains and megafan surface of the IGP, we identify two potential major sediment-lag sources in the Himalayan catchment: The high and low elevation broad valleys and the Siwaliks. Increased storage spaces in the valleys north of the main Himalayan crest, including drainage-captured catchments are likely to provide long burial durations such as in the case of the Kosi and Ghaggar basins. The upper and middle Siwaliks with burial duration in the range of up to ∼6 Myr constitute a second source. We attribute the no-burial signals of 7 samples of the Kosi basin to rapid sediment generation and transportation, driven by dynamic hillslope erosion and fluvial dynamics. Importantly, our data suggest that even samples close to the mountain front exhibit million years of burial duration. These findings suggest that denudation rates derived from modern river sands or in paleo settings will need to account for burial duration and associated processes. • Million years of lag time observed in multi-millennial scale sediment transport. • 39 out of 56 alluvial drill core samples show burial signal from ∼0.6 Myr to ∼6 Myr. • High and low elevation Himalayan valleys, Siwaliks and megafan act as burial space. • Sediment burial and reworking are facilitated with climatic oscillation. [ABSTRACT FROM AUTHOR]

• Flow frequency distribution and sediment-transport rate were influenced by floodplain lake. • Frequency distribution of medium-high flow agreed well with broken power law. • Sediment-transport rating curve deviated from power law at high flow. • Effective discharges decreased by 10%–20% indicating flood channel shrinkage. In natural quasi-equilibrium rivers or anthropogenically-influenced nonequilibrium rivers, the occurrence frequency and sediment transport capacity of different flow levels are greatly important to understanding the linkage between forms and processes. However, our knowledge of the controlling factors on flow frequency and sediment-transport magnitude in large river systems remains limited. In this paper, the hydrological and sediment-transport characteristics of the middle and lower Yangtze River (MLYR) were systematically examined before and after impoundment of the Three Georges Reservoir (TGR). More than 30 years of daily discharge and suspended sediment concentration data were collected from six hydrological stations. The results showed that in the pre-TGR period, the flow frequency distributions (FFDs) and sediment-transport rating curves had segmentation characteristics. Generally, the FFDs of medium-high flow agreed well with the broken power law, and the sediment-transport rating curves deviated from the power law at high flow. This was because the floodplains, especially the Dongting Lake, had significant effects on flood attenuation and sediment storage. Compared the inflection points of the FFD and the sediment-transport rating curve, as well as the effective discharge and bankfull discharge, these four values were of the same order of magnitude. This suggested that the local river system had a dominant effect on the hydrological and sediment-transport characteristics. In the post-TGR period, the overall characteristics of the FFDs were preserved, but the segmental characteristics of the sediment-transport rating curves at higher discharges disappeared. Through analysis, the effective discharge was largely determined by the inflection value (a 1) of the FFD. The reduced a 1 induced a 10%–20% decrease in effective discharge, which indicated flood channel shrinkage in the long run. These findings not only further the understanding of water-sediment regimes in a large alluvial river with an extensive floodplain system but also offer guidance for improving dam operation schemes for river restoration. [ABSTRACT FROM AUTHOR]

• Rainfall and runoff explained 70–85% of sediment yield variability in two karst watersheds. • Specific rainfall and runoff variables affecting sediment yield the most were identified. • The PLSR model provides a convenient way of solving variable collinearity. As one of the largest and most typical continuous karst distribution belts in the world, Southwest China is vulnerable to soil erosion and rocky desertification because of its unique geological conditions and heterogeneous landscapes. Understanding the rainfall-runoff-sediment transport relationships is critical to effectively controlling soil erosion in karst watersheds. This study aims to evaluate the sediment yield variability at different temporal scales (daily, monthly/seasonal, and annual) from 2014 to 2019 and to further identify the rainfall and runoff variables most associated with sediment yield in the selected Mahuangtian (2.26 km2) and Muzhaihe (0.09 km2) karst watersheds. Since rainfall and runoff variables were highly codependent, the partial least squares regression (PLSR) model was used to quantify the relative importance of rainfall and runoff variables to sediment yield. The variable importance of the projection (VIP) scores>1 was considered to be the most influential predictor of the PLSR model. Results showed that sediment yield was greatly influenced by rainfall and runoff, which can explain 70% and 85% of the variation of sediment yield in the Mahuangtian and Muzhaihe watersheds, respectively. For rainfall variables, three-day antecedent precipitation (VIP = 1.41) and five-day antecedent precipitation (VIP = 1.28) were the main first-order factors controlling sediment yield in the Mahuangtian watershed. In contrast, the rainfall amount (VIP = 1.35) was the dominant factor influencing sediment yield in the Muzhaihe watershed. For runoff variables, runoff amount, runoff coefficient, and maximum discharge were the primary variables controlling the sediment yield in these two karst watersheds. By partially eliminating the co-dependency of the variables, the PLSR approach can conveniently determine the dominant factors controlling sediment yield in heterogeneous karst watersheds. [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]

• 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]

A watershed model was developed using the Soil and Water Assessment Tool (SWAT) that simulates nitrogen, phosphorus, and sediment loadings in the Lower Mississippi River Basin (LMRB). The LMRB SWAT model was calibrated and validated using 21 years of observed flow, sediment, and water-quality data. The baseline model results indicate that agricultural lands within the Lower Mississippi River Basin (LMRB) are the dominant sources of nitrogen and phosphorus discharging into the Gulf of Mexico. The model was further used to evaluate the impact of biomass production, in the presence of riparian buffers in the LMRB, on suspended-sediment and nutrient loading discharge from the Mississippi River into the Gulf of Mexico. The interplay among land use, riparian buffers, crop type, land slope, water quality, and hydrology were anlyzed at various scales. Implementing a riparian buffer in the dominant agricultural region within the LMRB could reduce suspended sediment, nitrogen, and phosphorus loadings at the regional scale by up to 65%, 38%, and 39%, respectively. Implementation of this land management practice can reduce the suspended-sediment content and improve the water quality of the discharge from the LMRB into the Gulf of Mexico and support the potential production of bioenergy and bio-products within the Mississippi River Basin. [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]

Two decades after the construction of the first major dam, the Mekong basin and its six riparian countries have seen rapid economic growth and development of the river system. Hydropower dams, aggregate mines, flood-control dykes, and groundwater-irrigated agriculture have all provided short-term economic benefits throughout the basin. However, it is becoming evident that anthropic changes are significantly affecting the natural functioning of the river and its floodplains. We now ask if these changes are risking major adverse impacts for the 70 million people living in the Mekong Basin. Many livelihoods in the basin depend on ecosystem services that will be strongly impacted by alterations of the sediment transport processes that drive river and delta morpho-dynamics, which underpin a sustainable future for the Mekong basin and Delta. Drawing upon ongoing and recently published research, we provide an overview of key drivers of change (hydropower development, sand mining, dyking and water infrastructures, climate change, and accelerated subsidence from pumping) for the Mekong's sediment budget, and their likely individual and cumulative impacts on the river system. Our results quantify the degree to which the Mekong delta, which receives the impacts from the entire connected river basin, is increasingly vulnerable in the face of declining sediment loads, rising seas and subsiding land. Without concerted action, it is likely that nearly half of the Delta's land surface will be below sea level by 2100, with the remaining areas impacted by salinization and frequent flooding. The threat to the Delta can be understood only in the context of processes in the entire river basin. The Mekong River case can serve to raise awareness of how the connected functions of river systems in general depend on undisturbed sediment transport, thereby informing planning for other large river basins currently embarking on rapid economic development. [ABSTRACT FROM AUTHOR]

The effects of climate change on sediment yield and transport dynamics in cold climate regions are not well understood or reported. In this study, the Soil and Water Assessment Tool (SWAT) has been built-up, calibrated, and validated against streamflow and sediment load at several monitoring stations in a cold climate region watershed - the Athabasca River Basin (ARB) in Alberta, Canada. The model was then fed with bias-corrected spatial disaggregated high-resolution (~ 10 km) future climate data from three climate models for two emission scenarios (RCP 4.5 and 8.5), and two periods (mid- and end-century). Results show that channel erosion and deposition are the dominant processes over hill slope erosion in the basin. On average, a predicted warmer and wetter future climate has both synergetic and offsetting effects on sediment yield. Changes are sub-region specific and land-use type dependent, thus reflecting a marked spatial and temporal heterogeneity within the basin. Increases on sediment yield in future periods in the agricultural areas are up to 0.94 t/ha/yr, and are greater than reported soil formation rates in the region. Similarly, while substantial increases (by more than two fold) in the sediment load transport through the river reaches were obtained, the changes show both temporal and spatial variability, and are closely aligned with the trend of stream flows. We believe that availability of such models and knowledge of the effect of future climatic conditions would help water managers formulate appropriate scenarios to manage such basins in a holistic way. However, significant uncertainties in future sediment yield and transport, as a result of variations in climatic forcing of different climate models, need to be considered in any adaptation measures. [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]

The dramatic changes that occurred to the post-glacial landscape in the headwaters of the Waipaoa River basin are a consequence of perturbations about the equilibrium that exists between the rate of tectonic uplift and fluvial incision. At times when the amount of coarse sediment delivered to channels exceeds the capacity of streams to remove it, the channel bed rises at the rate of tectonic uplift. Once bedload overcapacity is replaced by undercapacity and the alluvial cover is depleted, streams reestablish contact with bedrock and recuperate the time lost to fluvial incision. The first major perturbation occurred during the final phase of the last glaciation (ca. 33–17.5 cal. ka), when aggradation was driven by a climate-forced variation in the relative supplies of sediment and water. We suggest that the subsequent transformation of channels in the headwaters of the Waipaoa River basin, from alluvial to bedrock, occurred as the atmospheric and oceanic circulation converged on their contemporary patterns ca. 12 cal. ka. A second major perturbation that continues to the present began ca. 1910–1912 CE, when a massive increase in sediment load was accompanied by a modest increase in water discharge after the native vegetation cover in the headwaters was replaced by pasture. The processes of terrace creation and incision are inherently unsteady, and in five interim cases incision was arrested by a transient increase in the thickness of the alluvial cover that was a response to climatic forcing. Events that disrupted the native vegetation cover in the headwaters also modulated patterns of sediment dispersal and accumulation in other parts of the fluvial system and caused rapid, storm-driven infilling of the Poverty Bay Flats. Tectonic subsidence dictates the course of the Waipaoa River across Poverty Bay Flats which, because the modern rate of floodplain construction by vertical accretion is rapid relative to the amount of destruction by lateral channel migration, has remained virtually unchanged for the past 100 years. During this time the channel assumed a narrower, deeper form that is in equilibrium with the contemporary supply of sediment and hydraulic regime. [ABSTRACT FROM AUTHOR]