Search

• 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]

• 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]

[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]

• 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]

• 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]

[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]

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]

• 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]

• Anticlockwise hysteresis type was the dominating hysteresis type. • Complex hysteresis type generated more sediment than either of three other types. • Antecedent rainfall dominated clockwise type, along with time lag for complex type. • Intraday rainfall and sediment separately dominated clockwise and anti-clock types. • Largest patch index and grassland separately dominated complex and other types. This study aims to quantitatively evaluate the effects of hydrological and landscape characteristics on suspended sediment concentration and discharge (SSC-Q) hysteresis. Runoff and sediment data of 405 flood events were collected from 10 basins in Wudinghe River basin on the Loess Plateau of China. Hysteresis analysis is a key tool for the interrogation of transport of sediment, which have been shown to be important within catchments. It can provide insight into catchment function, allowing the development and testing of process-based hypotheses. The principal components and corresponding explanatory power were extracted quantitatively from hydrological and landscape characteristics via principal component analysis (PCA) and redundancy analysis (RDA), respectively. The most common hysteresis type was anticlockwise. The proportions of the total event sediment loads for different hysteresis types were not always generally correlated to the frequency of the corresponding events. Furthermore, the composition and explanatory power of controlling principal components varied among clockwise, anticlockwise, figure-of-eight, and complex hysteresis types. For hydrological principal components, the antecedent precipitation, intraday precipitation, and sediment principal components controlled clockwise, anticlockwise, and figure-of-eight hysteresis types, which had explained 47.03%, 58.82% and 52.05% of the variation of hysteresis index, respectively; the antecedent precipitation and time lag principal component controlled complex hysteresis type and accounted for 28.22% and 34.65% of the variation of hysteresis index, respectively. For landscape principal components, grassland principal component dominated clockwise, anticlockwise, and figure-of-eight hysteresis types, and accounted for 95.00%, 69.70%, and 92.00% of the variation of hysteresis index, respectively. Largest patch index principal component controlled complex hysteresis type and accounted for 100% of the variation of hysteresis index. Therefore, within this catchment, whereas hysteresis patterns varied due to all of the hydrological and landscape variables to some extent, precipitation, suspended sediment, area of grassland, and the largest patch area had stronger impact on hysteresis dynamics. [ABSTRACT FROM AUTHOR]

• Models can account for effects of conservation measures on soil erosion dynamics in tramlines. • Contouring efficiency of tramlines captures variations in slope and sowing directions. • Increased contouring efficiencies of tramlines indicate lower runoff and soil erosion rates. • Reduced tillage indicates significantly lower runoff and soil erosion rates in tramlines. To reduce water erosion, one of the most severe land degradation processes on arable soils, conservation measures such as contour farming or reduced tillage practices can be applied. The general effectiveness of these measures on reducing soil erosion is well understood, however, little is known about the influence on tramline tracks, which have considerable impact on the transport of sediment and runoff. This study assesses the impact of reduced and conventional tillage and slope-related tramline directions on runoff and soil erosion rates at catchment level. For this purpose, a published and freely available dataset was used consisting of soil loss and runoff data modelled for a single soil erosion event considering courses and structural properties of tramlines (cf. Saggau et al., 2022). The orientation of tramlines against the slope direction was defined as contouring efficiency (Cef) and calculated by an approach that relates slope and tramline directions. Finally, results of the statistical analyses are compared with mapped soil erosion data. Results show that i) high-resolution derivation of Cef, based on tramlines, shows reasonable results in capturing variations in slope curvatures within the fields, ii) increased Cefs can significantly reduce runoff and soil erosion in tramlines and, iii) reduced tillage indicates significantly lower runoff and soil erosion rates in tramlines and cultivated areas. The results reveal that tramlines have strong interrelations with surface runoff, water connectivity and soil erosion. The consideration of tramlines in process-based models should be employed in other model approaches as it improves assessments of soil erosion risk and efficiencies of conservation measures, which are necessary in taking appropriate actions in support of soil and water conservation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different delivery pathways have variable impacts on local plant and soil communities. • Bulk density and plant diversity varied significantly downward the pathways. • Slope and contributing area are the main external driver determining gully occurrence. • Erosion resistance determines the development of pathways from partial to full gully. • We established critical thresholds for initiation and development of gully pathways. Road erosion is a global environmental issue. The transport of eroded sediment from road to stream can devastatingly impact water quality. Research efforts to combat this issue have prioritized maintaining roads and preventing erosion. Little research has explored the fate of eroded road materials in their transport from road to stream. Therefore, taking the Xiangchagou watershed in the Dabie Mountains of China as a case, this study investigated how local geography determines the formation and thresholds of different delivery pathways (gullied, partially gullied, and diffuse pathways) for road-eroded sediment through runoff, based on the binary logistic regression analysis, random forest model, and the lowest point data fitting methods. It explored how these different pathways have variable impacts on local plant and soil communities. Our results showed that soil D 50 , bulk density, shrub-grass coverage, and local plant diversity varied significantly (p < 0.05) between different delivery pathways. In particular, soil bulk density and local plant diversity varied significantly (p < 0.05) among different position of these delivery pathways. Specifically, the diffuse pathways are characterized by lower soil bulk density, looser soil structure, and higher species diversity, likely explained by the deposition of sediment-loaded runoff. Gullied pathways, conversely, had significantly more compacted surface soil and lower local plant diversity, likely as a result of scouring by sediment-loaded runoff. Slope gradient of upslope catchment (U s), road segment (R s), and lower hillslope (D s) and effective contributing area (E ca), which determine the intensity and kinetic energy of sediment-loaded runoff, are the main external drivers that determine the occurrence of gullied pathways. By contrast, the soil median particle size, surface roughness, and shrub-grass cover of lower hillslope, which contribute to erosion resistance of hillslope, are the primary intrinsic drivers promoting development of pathways from partial to full gully. Furthermore, we found that the critical topographic thresholds for the initiation of the gully pathways and the continued development of gully from partial to complete gully pathways could be expressed as D s = 0.35E ca −0.13 and D s = 0.41E ca −0.17, respectively. These results are expected to provide basis for understanding the formation and development mechanism of sediment delivery pathways from road to stream. [ABSTRACT FROM AUTHOR]

Debris flow can be very destructive, especially in areas of dense population on mountain foothills. Check dams are constructed across drainage channels and are beneficial for reducing flow velocity and soil erosion, as well as controlling debris flows. On July 26, 1987, a destructive debris flow occurred in a watershed north of Tehran, Iran. A series of check dams were constructed in the watershed to mitigate the hazards of future debris flow due to the importance of the region. This study first proposes a procedure to estimate the volume of the sediments in a debris flow from the calculated volume of an equivalent regular flood. The procedure to estimate the sediments volume is employed in a framework to assess the effects of constructed check dams for a similar debris flow in the region. The framework considers the unfilled storage of the check dams for estimating the volume of the sediments in each catchment. Field measurements were implemented to estimate the available storage of check dams. The volume of sediments in two cases was estimated: 1) the debris flow in 1987 and 2) a probable debris flow at current time considering the available storage of constructed check dams. The comparison shows that the volume of sediments reaching the outlet of the watershed decreased 13% as the effect of check dams in trapping sediments. Applying the proposed framework to this case study shows its ability in assessment of check dams' impact on debris flow. [ABSTRACT FROM AUTHOR]

• Factors contribution to runoff, sediment in different seasons and spatial scales. • Contribution of precipitation and underlying surface to runoff and sediment. • Assess the group relationships between different types of influencing factors. The changes in runoff and sediment are the most active parts of river systems. Identifying the effect of precipitation, vegetation coverage (VC), landscape metrics, land-use and land-cover changes (LUCC) on runoff and sediment variations is essential for understanding hydrological processes and the environmental evolution mechanisms of watersheds. This study selected four watersheds located in the Qinling Mountains in China to quantify the effects of different driving forces on runoff and sediment variations at different scales. The results showed that VC increased significantly in the study watersheds (p < 0.05) by more than 16 % since 1990. Obvious increases in forest area were the main features of land use change after 2000. The annual sediment transport and sediment concentration in the wet season showed downward trends. The change of underlying surface contributed more than 58 % to reductions in runoff and sediment concentration in controlled watersheds in Xiangjiaping and Jingziguan. The factors influencing runoff and sediment variations displayed obvious spatial and temporal differences. The 2000 m buffer scale could better explain the runoff and sediment variations than other spatial scales. Rainfall and VC were the main factors affecting runoff and sediment variations at different spatial scales during the wet season, while the aggregation index at the watershed-scale and VC were the main influencing factors in the dry season. Moreover, the intersections between precipitation and landscape pattern, between precipitation and LUCC & VC, and between landscape pattern and LUCC & VC in the dry season and wet season were −31.9 %, −27.6 %, −29.0 % and −18.7 %, −11.1 % and −2.3 %, respectively. Therefore, multi-scale differences in the impact of driving factors and the group relationships between measures should be considered for effective runoff and sediment regulation. [ABSTRACT FROM AUTHOR]

• Land use experienced reclamation during 1938–1958 and vegetation restoration 1958–2020. • Sediment yields varied consistently with land use changes. • High spatial heterogeneity of landscapes reduce sediment yield and transport. Understanding the response of soil erosion to the changes of land use and landscape pattern is valuable for the optimization of soil and water conservation measures in a watershed. This study selected a typical hilly-gully watershed of the Chinese Loess Plateau, the Zhifanggou watershed, to assess its long-term land use changes from 1938 to 2020 and their impacts on sediment yield by using the spatially distributed soil erosion model WaTEM/SEDEM with an average annual rainfall erosivity of 2000–2010. The results indicated that the main land use types in the Zhifanggou watershed were cropland, forest and grassland, and experienced two changing periods: rapid agricultural reclamation during 1938–1958 and vegetation restoration during 1958–2020. The average annual sediment yields varied consistently with land use changes, showing evident changes from 51.84 t ha−1 y−1 in 1938 to 254.1 t ha−1 y−1 in 1958 and then to 4.27 t ha−1 y−1 in 2020. Correlation analysis suggested that sediment yield was closely related to the landscape indices of interspersion and juxtaposition index and Perimeter-area fractal dimension. The results indicated that increased vegetation cover and high spatial heterogeneity of landscapes could alter sediment transport pathways, reduce sediment connectivity, and induce less sediment discharged into the river. Our findings could provide a good reference for optimizing soil and water conservation measures in the watershed. [ABSTRACT FROM AUTHOR]

• • Thorough analysis of WSRS-induced impacts on the river channel and delta. • • The natural hydrological cycle process has been altered by the artificial floods. • • Reservoirs regulation scheme altered the erosion–deposition regime of the riverbed. • • New light is shed on saving the global sinking deltas. The water and sediment regulation schemes (WSRS) orientated by dams have profoundly adjusted the hydrological process and geomorphological evolution of the lower Yellow River and delta. Two decades since the implementation of WSRS, the observed multidisciplinary datasets allowed us to systematically evaluate the impacts of this unprecedented engineering effort on the river-coastal system. The sediment fluxes transported to the sea showed a notable rebounded and coarsened process due to the erosion of the riverbed during the WSRS periods. The average median grain size of suspended sediment increased from 17.7 μm in the 1990 s to 26 μm in 2002–2009. The natural rhythm of hydrological process is fundamentally altered by WSRS, about 50% and 30% of annual sediments and water delivered to the sea for only 20 days. The water discharge system is more temporally dynamic and complex with higher dimensionality after the operation of WSRS. The erosion pattern has been a dominant feature in all the channel segments downstream the Xiaolangdi Reservoir, with an average total erosion volume of 1.02 × 108 m3/a after the WSRS. However, the erosion efficiency of the lower river showed a decreased trend, due to the riverbed had formed a coarse armored substrate for the continued scouring since 2002. The YRD has changed from the pattern of erosion to progradation for the increase of sediment supply, and the average growth rate of subaerial delta was about 6.89 km2/a during 2003–2014. The lessons learned from the operation of WSRS may provide a valuable reference for the management of global large river systems. [ABSTRACT FROM AUTHOR]

• Quantitative reconstruction of soil erosion, sediment transport and delta deposition. • Soil erosion intensity was weak before the late Holocene, and increased afterwards. • The sediment deposition and soil erosion intensity were synchronous. • Soil erosion was dominated by climate as natural process before the middle Holocene. • Soil erosion was accelerated by human activities in the late Holocene. The Yellow River Basin is ideal for studying fluvial landscape evolution under climate change and human activities. Quantitative reconstruction of soil erosion, sediment transport, and delta deposition in the basin enhances understanding of the dynamic mechanisms of fluvial surface processes. This study reconstructs the spatial and temporal distribution of precipitation and vegetation cover based on geological profile records, paleoclimatic datasets, and historical documentation in the Yellow River basin during the Holocene. A landscape evolution model (Landlab) is introduced to simulate soil erosion and sediment deposition processes. Modeling results show that soil erosion intensity in the middle reaches of the Yellow River was weak during the early and middle Holocene. Since the late Holocene, soil erosion has increased due to vegetation degradation, as the climate became drier, but with more fluctuations. Since 2.0 ka (1 ka = 1,000 calibrated a B.P.), and especially since 1.0 ka, soil erosion in the middle reaches of the Yellow River increased rapidly due to strong human activity, with the intensity-six times higher than the average level before the late Holocene. Average sediment deposition thickness in the lower reach of the Yellow River (North China Plain) was about 2.4 m, and sediment volume was about 3.6 × 1011 m3. The deposition rate and soil erosion intensity showed synchronous changes during the Holocene. Since 2.0 ka, the sediment load and deposition rate have increased rapidly, to 6–10 times higher than in the early and middle Holocene. On this basis, the effects of climate change and human activities on the evolution of the fluvial landscape are discussed. [ABSTRACT FROM AUTHOR]

• Sediment connectivity is influenced by vegetation, slope and watersheds area. • Anticlockwise loop is the most frequent hysteresis type and transport the most sediment. • Indices of connectivity showed a high correlation with sediment parameters and hysteresis index. Sediment connectivity is an important property influencing landscape evolution. Understanding the link between sediment connectivity and hydrologic processes plays an important role in developing strategies for soil and water conservation measures. Based on 10 years of observations for 30 hydrologically monitored watersheds on the Loess Plateau, measurements for 926 hydrologic events were analyzed and the index of connectivity (IC) was calculated. The high-frequency runoff and sediment data were analyzed, and a normalized hysteresis index (HI) was calculated to assess the dominant hysteresis patterns for each watershed. Correlation analysis was conducted to determine the relationship between IC and HI. The results showed that the watersheds with low IC values were located in regions with dense vegetation and flat terrain and were dominated mainly by a clockwise hysteresis pattern, while the watersheds with high IC values were located in regions with sparse vegetation and steep terrain and were dominated by an anticlockwise hysteresis pattern. The anticlockwise hysteresis pattern was the most frequent and the most efficient type in terms of sediment transport among the 30 watersheds. The anticlockwise hysteresis type was more likely to occur as the IC values increased. A significant negative correlation was observed between the IC values and HI values during small and medium hydrologic events. The link is correlated with the notion that the separation into two components in connectivity indexes are similar to the two sediment sources controlling the hysteresis type. The outcomes from this study are helpful for determining the relationship between sediment connectivity and hydrologic behavior and thus for providing insight into the hydrologic processes that are essential to facilitate sustainable watershed management. [ABSTRACT FROM AUTHOR]

Traditionally, braided river research has considered flow, sediment transport processes and, recently, vegetation dynamics in relation to river morphodynamics. However, if considering the development of woody vegetated patches over a time scale of decades, we must consider the extent to which soil forming processes, particularly related to soil organic matter, impact the alluvial geomorphic-vegetation system. Here we quantify the soil organic matter processing (humification) that occurs on young alluvial landforms. We sampled different geomorphic units, ranging from the active river channel to established river terraces in a wandering/braided river system. For each geomorphic unit, soil pits were used to sample sediment/soil layers that were analysed in terms of grain size (< 2 mm) and organic matter quantity and quality (Rock-Eval method). A principal components analysis was used to identify patterns in the dataset. Results suggest that during the succession from bare river gravels to a terrace soil, there is a transition from small amounts of external organic matter supply provided by sedimentation processes (e.g. organic matter transported in suspension and deposited on bars), to large amounts of autogenic in situ organic matter production due to plant colonisation. This appears to change the time scale and pathways of alluvial succession (bio-geomorphic succession). However, this process is complicated by: the ongoing possibility of local sedimentation, which can serve to isolate surface layers via aggradation from the exogenic supply; and erosion which tends to create fresh deposits upon which organic matter processing must re-start. The result is a complex pattern of organic matter states as well as a general lack of any clear chronosequence within the active river corridor. This state reflects the continual battle between deposition events that can isolate organic matter from the surface, erosion events that can destroy accumulating organic matter and the early ecosystem processes necessary to assist the co-evolution of soil and vegetation. A key question emerges over the extent to which the fresh organic matter deposited in the active zone is capable of significantly transforming the local geochemical environment sufficiently to accelerate soil development. [ABSTRACT FROM AUTHOR]

• The Daling River, as a typical small mountainous river, responds strongly to instantaneous extreme flood events. • Restored vegetation is the root cause of the sharp decline of sediment flux, not reservoirs. • Vegetation has altered the characteristics of sediment transport. Understanding the riverine sediment load regime is crucial to sustainably managing fluvial-deltaic ecosystem restoration. However, in studies on global river sediment transport characteristics, small mountainous rivers (SMRs), transporting 45% of the global sediment flux into the sea, have been largely ignored. Furthermore, SMRs have hydrologic characteristics of instantaneous enormous fluxes under extreme climate, but the research on their driving factors affecting sediment transport is insufficient. Partial derivation method and multiple double mass curves were applied to a small mountainous river in North China, the Daling River to study how the three most variable factors—precipitation, vegetation coverage, and reservoirs—have quantitatively controlled sediment flux in the basin and its subregions in the last 50 years. The results of the two methods showed that the 78.55% reduction in sediment flux from 1961–1979 to 1980–2015 was due primarily to restored vegetation coverage (50.42%-61.11%), followed by reservoirs (18.13–44.09%) and precipitation (5.49–22.34%) in the Daling River Basin (DRB) and its subregions. The restored vegetation in the DRB has intercepted a large amount of sediment, reducing the sediment flux transported to the reservoirs. Besides, the Daling River releases enormous amounts of sediment during heavy rainfalls. However, increasing vegetation coverage in recent years has changed the transport characteristics of sediment into temperate changes in runoff and sediment flux under extreme climatic conditions; thus this river provides a useful example of studying the characteristics of sediment transport controlled by nature and human activities against extreme climate conditions. In the DRB, topography, lithology, and vegetation density are the motivators for the differences in sediment flux and its change rates, from upstream to downstream. These findings emphasize the crucial role of vegetation in driving sediment transport from source to sink in temperate SMRs. [ABSTRACT FROM AUTHOR]

• Topography can quantitatively describe the uplift amplitude of plate movement. • Concavity index and stream order can be used to extract sediment-prone areas. • Collapse rate and concavity index can show the evolution of landslides and/or debris flows. This study uses topographical factors to quantitatively describe the uplift amplitude of the plate movement, collects and analyzes the long-term series of rainfall, earthquakes, landslides and debris flows in watersheds from 1993 to 2019, explores the evolution mechanism of landslides, and uses conceptual models to map the areas prone to occurrence of potential debris flows in central Taiwan. Results show that the topographic factors of a watershed can effectively reflect the concavity index (θ) of the crustal uplift, and the spatial distribution of the concavity index in the watershed can be easily estimated. Combining the spatial distribution of concavity index and stream order, a watershed-scale potential debris flow map can be obtained. According to the interpretation rate change of the relationship between the concavity index and the watershed collapse rate, we can understand the occurrence time of landslides and/or debris flows, as well as the sediment transport dynamics of the watershed. The change of the interpretation rate of the concavity index to the collapse rate can be used as a guideline for the establishment of a debris flow warning system. [ABSTRACT FROM AUTHOR]

• Sediment load decreased by about 88% in the middle reaches of the Yellow River Basin. • The causes of sediment loads variations were explored. • Human activity contributes about 93% to sediment reduction in recent two decades. • ENSO is a dominant teleconnection pattern for explaining the sediment variations. The erosion, deposition and transport processes of sediment alter the basin surface environment, and affect the function and structure of ecosystems. The sediment loads showed a significant decreased trend under the impacts of climate changes and human activities in the Yellow River Basin (YRB). Understanding the sediment transport patterns and causes is a prerequisite of sediment management and ecological restoration of the river basins. This study explored the sediment long-term fluctuation characteristics and the influences of various driving factors on the sediment variations based on the sediment loads data from the source region to the delta of the YRB. We found that the sediment fluxes showed a significant decreasing trend in the mainstream and tributaries of the YRB. The average sediment loads of the upper basin decreased to 42.88 ± 26.14 Mt/yr in 2000–2019, which is less than 30% of the average value recorded before 1968. Compared with 1950–1968, the sediment loads in the middle and lower reaches decreased by approximately 88% and 89% from 2000 to 2019, respectively. In addition, the middle reaches of the Yellow River (YR) is in a persistent degradation state prior to 2000, the source-to-sink relationships of sediment downstream the Huayuankou station are changing frequently due to the operation of Sanmenxia and Xiaolangdi reservoirs. According to the sediment rating curves (SRCs), the sediment transport regimes have changed at time scale along the mainstream of the YR in recent three decades. Moreover, the human activities (reservoir constructions, water-soil conservation, etc.) are the dominant factors for explaining the progressively reduction trend of sediment loads, the contributions of human activities to sediment reduction was approximately 93% in recent two decades in the YRB. Precipitation and temperature are the predominant meteorological factors affecting sediment variations, and ENSO is the dominant teleconnection pattern for explaining the multiscale characteristics of sediment loads in the lower reaches of the YRB. The findings of this study could provide effective reference for the ecological restoration and sediment management of the YRB. [ABSTRACT FROM AUTHOR]

• The spatially-distributed OpenLISEM model was applied to a burnt catchment. • Remote sensing and topographic analysis were substitute for field-based estimates. • The model was automatically calibrated for individual storms. • The model was validated using the jack-knife cross-validation procedure. • The model also predicted the spatial patterns of soil erosion. Models are typically applied to estimate the potential adverse effects of fire on land degradation and water resources and the potential benefits of post-wildfire rehabilitation treatments. However, few modeling studies have been conducted for meso -scale catchments, and only a fraction of these studies include transport and deposition of eroded material within the catchment or represent spatial erosion patterns. This study presents an application and evaluation of the OpenLISEM physically-based and spatially-distributed hydrological and soil erosion model for a burned Mediterranean meso -scale catchment (18.5 km2) in a data-scarce environment, using a robust parameterization and calibration procedure: (1) integrating satellite imagery and the topographic wetness index to support model parameterization; (2) event-based automated calibration using the Model-Independent Parameter Estimation and Uncertainty Analysis and parameters ensemble for before and after the fire; (3) a jack-knife cross-validation for model evaluation. The study shows that this procedure used in OpenLISEM provides reasonable results for pre- and post-wildfire catchment discharge and sediment transport (r2 and NSE > 0.5; absolute PBIAS < 25% for discharge and 55% for sediment transport). This may serve the needs of model applications in data-scarce burned areas. The results also provide recommended model parameters for burned areas with high severity such as random roughness (rr) = 2.41 cm, and slope manning's n (n) = 0.038; or post-wildfire to pre-wildfire ratios of model parameters such as saturated hydraulic conductivity (K s) = 0.98×, channel manning's n (chn) = 0.44×, grain size (d50) = 0.61 ×. The simulation results indicate that wildfire did not lead to significantly enhanced hydrological responses and soil erosion at the catchment outlet, partly explained by the spatial patterns of soil erosion. For both pre- and post-wildfire conditions, higher soil erosion was simulated in areas located far from the catchment outlet. The wildfire led to enhanced hillslope erosion, mostly in the upper part of the catchment, providing ample opportunities for transported sediment to deposit before reaching the outlet. [ABSTRACT FROM AUTHOR]

• Nonoccurrence samples acquisition is relevant to resulting susceptibility maps. • ANN models can lose generalization ability if training set is too easy to classify. • Using only easy-to-classify nonoccurrence samples affects maps negatively. Landslide susceptibility assessment using Artificial Neural Networks (ANNs) requires occurrence (landslide) and nonoccurrence (not prone to landslide) samples for ANN training. We present empirical evidence that a priori intervention on the nonoccurrence samples can produce models that are improper for generalization. Thirteen nonoccurrence cases based on GIS data from Rolante River basin (828.26 km2) in Brazil are studied, divided in three groups. The first group was based on six combinations of buffers with different minimum and maximum distances from the mapped scars (BO). The second group (RO) acquired nonoccurrence only from a rectangle in the lowlands, known for not being susceptible to landslides. For BR, six alternatives respectively to BO were presented, with the inclusion of nonoccurrence samples acquired from the same rectangle used for RO. Accuracy (acc) and the Area Under Receiving Operating Characteristic Curve (AUC) were calculated. RO resulted in perfect discrimination between susceptible and not susceptible to landslides (acc = 1 e AUC = 1). This occurred because the model simply provided susceptible classification to points in which attributes are different from those in the rectangle, harming the classification of nonoccurrence sampling points outside the rectangle. RO map shows large areas classified as susceptible which are known to be non-susceptible. In BR, sampling points from the rectangle, which are easy to classify, were added to the verification sample of BR. Average acc for BO 00 m (minimum buffer distance to scars of 0 m): 89.45%, average acc for BR 00 m: 92.33%, average AUC for BO 00 m: 0.9409, average AUC for BR 00 m: 0.9616. Maps of groups BO and BR were alike. This indicates that metrics can be artificially risen if biased samples are added, although the final map is not visibly affected. To avoid this effect, the employment of easily classifiable samples, generated based on expert knowledge, should be made carefully. [ABSTRACT FROM AUTHOR]

• Suspended sediment flux (SF) was estimated at basin scale considering new damming. • The annual mean SF at the outlet of the basin got reduced by 90%. • Dams showed larger impacts on SF than climate variability. • High soil erosion happened in the middle parts of the basin. • Simple rating curves between discharge and SF were proposed. The Red River is an Asian river system strongly affected by global changes. This paper aims to characterize and quantify the suspended sediment flux (SF) over the basin under the influences of short-term climate variability and dam constructions. SF was evaluated at the outlets of main tributaries and along the main course of the Red River from 2000 to 2013 based on daily simulations from a modelling study. A reference scenario (without dams) was carried out to disentangle the impacts of short-term climate variability and damming by comparing to actual conditions. Without dams (reference scenario), the basin would generate 106.9 Mt yr−1 of SF to the downstream delta from 2000 to 2013, with a specific sediment yield (SSY) of 778.8 t km−2 yr−1. However, under the impacts of short-term climate variability and dams, the mean annual SSY decreased to 84.5 t km−2 yr−1. At the outlet of the basin, the annual mean SF of 2008–2013 (after new dam constructions) got reduced by 90% (10% related to short-term climate or atmospheric variability and 80% to dam constructions) compared to the reference scenario (without dams) during 2000–2007. The Thao tributary is the most sensitive to short-term climate variability while the Da tributary is mostly affected by the huge-capacity dams. Mean annual retentions of sediment by dams ranged from 7.1 to 111.0 Mt yr−1. Simple rating curves between monthly mean discharge (Q) and SF were established for estimating SF at the outlet of the tributaries and the Red River. High soil erosion (above 2000 t km−2 yr−1) occurred in the middle Thao and the lower Da tributaries. Precipitation, slope and agriculture practices are the key influence factors for soil erosion in the basin. [ABSTRACT FROM AUTHOR]

• Reversal of sediment load trend between the earlier and later periods was observed. • Divergent trends of sediment transport from the tributaries influenced this reversal. • Dam construction was partly responsible for the recent reduction in sediment load. The Amazon River is the largest river in the world in terms of freshwater discharge and sediment load. Understanding the fluvial sediment transport processes operating in the Amazon basin is critical because the Amazon basin has great research value for the sustainable development of local and global ecosystems. This study investigated changes in the mainstream sediment flux in the Amazon River system during 1996–2018. At the Óbidos gauge station (on the Amazon mainstream), sediment loading significantly increased during 1996–2007 (earlier half of the study period), but the trend then reversed and sediment loading decreased during 2007–2018 (later period). River runoff was relatively stable during 1996–2018. The monthly sediment load and sediment concentration at Óbidos were not synchronized with monthly runoff because of the asynchronism of the peak water discharges of the Solimões, Madeira, and Negro Rivers. We infer that the significant increase in sediment flux from the Solimões River was an important factor affecting the observed sediment increase at Óbidos during 1996–2007. Besides, the increasing wash-load sediment flux at Manacapuru (on the Amazon tributary) should be derived from the Middle and Lower Solimões River, because the sediment transport from the Upper Solimões River was decreasing. We also found that the reversal of the sediment load trend at Óbidos could be partly influenced by the decreasing trend of sediment transport from the Madeira River, and dam construction was one of the important causes. The reduced sediment loading in the Amazon mainstream will have major implications for the downstream ecosystem. Because planned dam constructions are expected to quadruple the number of dams in the Amazon basin, we suggest that the risk of wetland and muddy coast degradation caused by intensive hydropower development is an important pending issue. [ABSTRACT FROM AUTHOR]

• Lithology is an important related factor in the debris flow occurrence in the area. • Fifteen debris flows-related factors were applied to debris flow susceptibility. • All flow tracks and geometrical interval has higher prediction accuracy. • The methodology is easy to reproduce and applied to other mountainous regions. Debris flow and floods represent one of the main natural hazards that impact transport infrastructure, causing serious damage, economic losses and hinder regional economic development. These processes are eventually associated with massive traffic cuts and direct damage to road structures. To enable the prevention of such consequences, this paper employs statistical modeling techniques, various instability factors and geomorphological mapping to generate debris flow susceptibility maps in a portion of an important route on the Dry Andes of San Juan in the Agua Negra River basin, Argentina. A debris flows inventory map was prepared using satellite images and field checks. The debris flows inventory was randomly divided into a model dataset 80% (47 debris flows) and remaining 20% (12 debris flows) data was used for validation purpose. The instability factors chosen that influence debris flows occurrence were: elevation, slope angle, slope aspect, solar radiation, topographic wetness index, stream power index, topographic position index, Melton ruggedness number, terrain ruggedness index, sediment transport capacity index, plan curvature, profile curvature, lithology, distance to road and proximity to stream. Using these factors, six different models of debris flow susceptibility were calculated by Frequency ratio (Fr). Lithology (igneous complex) was found to be important debris flows-related factor in the study area. The precision of the results was evaluated by receiver operating characteristic (ROC) analysis. According to the area under the curve (AUC) the models of all flow track and natural breaks and all flow track and geometrical interval were 0.83 and 0.84, respectively, showing a practically identical predictive capacity. [ABSTRACT FROM AUTHOR]

• The seasonality of annual maximum rainfall, runoff and sediment events is examined. • The extreme rainfall event is the dominant trigger of annual maximum runoff events. • 'Store-release' process plays an important role in sediment transport at some sites. • The shift of dominance from rainfall to storage may related with vegetation impact. Along with big floods, the heavily loaded sediments have caused devastating social and economic impairments in the Yellow River Basin (YRB). However, the regional differences in the dominant mechanisms for these extreme events haven't been fully understood. This study selected 68 hydrological stations in the YRB to examine the seasonality of annual maximum rainfall, runoff and sediment events to explore the dominant factors of the extreme flow and sediment events. Our results show that all the extreme events are concentrated in July and August with limited inter-annual variability. The flood occurrence is usually consistent with extreme rainfall events, especially the weekly precipitation. The extreme sediment events are more closely correlated with precipitation than discharge in the Middle of YRB. While at the main stem of Yellow River and outlets of major tributaries, sediment storage in channel takes over the dominance in extreme sediment events. [ABSTRACT FROM AUTHOR]

• We used suspended sediment data during a period of consecutive explosive cyclogenesis. • Spatial land use plays an important role in the suspended sediment yield. • Sediment concentrations are largely dependent on sediment depletion during the previous events. During the winter of 2013/2014, a sequence of explosive cyclogeneses occurred in NW Spain, causing severe flooding and substantial economic damage. Peak discharges were extremely high in many areas, with return periods in excess of 2–5 years. The heavy flow registered during these episodes provides a unique opportunity to evaluate the sedimentological effects resulting from high-magnitude flow events. Such events are relatively rare and the technical difficulties in sampling with sufficiently high frequency means that few observations on sediment transport can be gathered during the same. In this study, we present detailed hydrological and sedimentological observations across a period of consecutive explosive cyclogeneses from two small-sized catchments (i.e., the Corbeira stream and headwater of the Mero river) located in Galicia (NW Spain), in order to examine the factors controlling suspended sediment (SS) dynamics during high-magnitude flow events. The study sites are representative of the biophysical conditions (e.g. rainfall pattern, land use, vegetation cover and management practice) in NW Spain. The catchments of the Corbeira stream and headwater of the Mero river are similar with respect to climate, land use and management practice. The main differences are the distribution of land use and catchment size (Corbeira: 16 km2 and Mero: 65 km2). Large amounts of sediment were transferred in both catchments in response to flow events. A high variability in SS load during these was also observed in the two catchments, which is attributed to variation in rainfall characteristics, magnitude peak discharge, antecedent conditions controlling sediment availability, and suggests that sediment supply and transport vary widely over time. Higher concentration and variability of SS was observed in the Corbeira catchment. Differences in SS dynamics were also noted between the catchments that may be attributed to differences in the spatial distribution of land use, which influence the location of the erosion source and SS availability, and directly and indirectly affects connectivity between the sediment source area and the stream. In the Corbeira catchment, the SS load was closely linked to the hydrological response and rainfall, whereas in the Mero basin, preceding conditions, i.e. the sediment depletion during the previous events, played an important role. The results demonstrated that peak SS concentrations may coincide with, or lag behind, peak discharge, and factors other than discharge (mainly the location of the sediment source and its connectivity with the drainage network) have a major influence on SS concentrations. [ABSTRACT FROM AUTHOR]

In present study, the sediment yield/loss and Transport Capacity (TC) has been estimated in a highland watershed of Adama Woreda, part of Awash River Basin in Ethiopia. For the study, average hourly 14 years rainfall data obtained from different gauging stations in the study area during 2001–2014 was utilized to calculate rain erosivity (R factor). Subsequently, soil erodibility K, length-slope LS factors of Revised Universal Soil Loss Equation (RUSLE) were adopted for the calculation of WATEM/SEDEM sediment delivery algorithm. The average R factor value for the watershed was evaluated as 2075.27 MJ/ha mm/year. The grid based KTC (Transport Capacity Coefficient) was determined for the WATEM/SEDEM sediment transport estimation through the results of Soil Water Assessment Tool (SWAT) and Revised/Modified USLE. The SWAT simulated suspended solids (SS) versus two years (2013 and 2014) rainfall measured records at single observatory was used for the SWAT calibration and validation. The SWAT sediment yields and Transport Capacity (TC) were used to determine the KTC at each sub-watershed. The mean value of KTC was estimated 8.033 and minimum and maximum values were found 0.080 and 51.49 respectively. Moreover, the Sediment Deliver Ratio (SDR) model equation was calculated and resulted values were found >0.7 in the main streams. For the prioritization, sediment yield and loss estimated values using Sediment Yield Index (SYI) and RUSLE along with SWAT models were employed. The results generated through these models were averaged and accordingly the ranks and severity classes were determined. Unlabelled Image • The study area falls in highlands of Ethiopia which suffers by land degradation. • Multiple modeling is employed to quantify the sediment loss and TC. • Daily runoff was measured during 2013–14 for SWAT model calibration and validation. • Average values of multiple models used for prioritization. [ABSTRACT FROM AUTHOR]