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ABSTRACTIn mountain regions, the impact of areas on the sediment conveyance can not only be described by their susceptibility to debris flow release, but also by their structural connectivity to the rivers. This generates the need to combine susceptibility and connectivity for accurate analyses of sediment transport. Our study exploits an approach developed by [Steger, er al. 2022; https://doi.org/10.1002/esp.5421] and upscales it to the South Tyrolean Dolomites region. The approach comprised the modeling of debris flow release susceptibility using an interpretable machine learning algorithm, the training of a logistic regression model, and the combination of the resultant classified maps to create a joint susceptibility-connectivity map. The results show the quantitative thresholds for the susceptibility probability and the Index of Connectivity (IC) that allow to discriminate between susceptible and not susceptible, as well as connected and disconnected areas, which are represented via a variety of maps.

Steep mountain environments are typically characterized by high sediment production. In the case of high hillslope–channel connectivity, high production and intensive transport of sediments are problematic and can cause damage in inhabited areas. At the end of the 19th century, due to flood events, large‐scale torrent control measures were inappropriately applied, disrupting the natural processes, and riparian and water ecosystems in watersheds. Connectivity in watersheds affects the course and magnitude of hazards that threaten human society. This is also why the topic of connectivity should be considered in the management of watercourses. Our study links the issue of sediment connectivity (lateral/longitudinal) and the sediment transport‐related risk in unmeasured forested watersheds Hučivá Desná and Upper Moravice. We applied a methodology for sediment transport‐related risk assessment and the well‐established effective catchment area (ECA) approach and connectivity index (IC) to two headwater streams. The results showed the parts of the streams with the highest degree of hazard related to sediment transport and sediment contribution areas connected to them. Based on the field survey, it was found that the best suitable threshold for ECA delineation for Hučivá Desná catchments is 8° and for Upper Moravice is 10°. Area of sediment contribution areas for Hučivá Desná is four times bigger than for Upper Moravice. The Hučiva Desná, therefore, has a higher potential sediment supply from the slopes, which also increases the possibility of occurrence of hazards associated with the sediment transport regime. All three applied methods confirmed that the parallel roads along channels decrease slope–channel connectivity, especially in the Upper Moravice catchment. The combination of methodologies created a suitable tool to identify the most problematic stretches of streams in terms of sediment connectivity and risk related to sediment transport, which can be useful for water and sediment management in unmeasured forested watersheds. [ABSTRACT FROM AUTHOR]

Sedimentary landforms on Earth and other planetary bodies are built through scour, transport, and deposition of sediment. Sediment connectivity refers to the hypothesis that pathways of sediment transport do not occur in isolation, but rather are mechanistically linked. In dryland river systems, one such example of sediment connectivity is the transport of fluvially deposited sediment by wind. However, predictive tools that can forecast fluvial‐aeolian sediment connectivity at meaningful scales are rare. Here we develop a suite of models for quantifying the availability of river‐sourced sediment for aeolian transport as a function of river flow, wind regime, and land cover across 168 km of the Colorado River in Grand Canyon, USA. We compare and validate these models using topographic changes observed over 10 years in a coupled river sandbar‐aeolian dunefield setting. The models provide a path forward for directly linking fluvial hydrology with the management and understanding of aeolian landscapes. Plain Language Summary: Landscapes on Earth are built from sediment, which is deposited by a variety of processes, especially water and wind. In rivers located in dry regions, sediment is deposited by flowing water during river floods. Once this sediment dries, it is often then moved by wind across the landscape. Although we frequently observe this sediment connectivity between water and wind, we are not currently able to predict when and where windblown transport of river‐deposited sediment may occur. We used maps of sand in Grand Canyon along 168 km of the Colorado River, along with records of river flow, wind speed, and vegetation cover, to develop four models that predict how much sediment is available for wind to move. We compared the results of these models to actual windblown sediment transport at a study site in Grand Canyon, finding that when models predicted more sand was available at the site, we also observed more landscape changes there which were due to wind. Our research makes it possible to understand how changes in river flows affect the amount of sediment moved by wind. Key Points: We developed four methods for modeling the extent of exposed, bare sand available for windblown transport in river valleysOur models employ data on river flow, land cover, wind velocity, and vegetation to predict exposed, bare sand extent at corridor scalesWhere models predict increased areal extent of bare sand, we also observe a greater volume of topographic changes driven by wind [ABSTRACT FROM AUTHOR]

We present a framework for strategic dam planning under uncertainty, which includes GHG emissions mitigation as a novel objective. We focus on the Mekong River Basin, a fast‐developing region heavily relying on river‐derived ecosystem services. We employ a multi‐objective evolutionary algorithm to identify strategic dam portfolios for different hydropower expansion targets, using process‐related and statistical models to derive indicators of sediment supply disruption and GHG emissions. We introduce a robust optimization approach that explores variations in optimal portfolio compositions for more than 5,000 state‐of‐the‐world configurations, regarding sediment origins and trapping and GHG emissions. Thus, we can rank dam projects' attractiveness based on their frequency of inclusion in optimal portfolios and explore how uncertainty affects these rankings. Our results suggest that developing dams in the upper Mekong would be a more robust option for near‐term development than, for example, the lower Mekong and its tributaries, for both environmental and energy objectives. Our work presents a novel approach to better understand the basin‐scale cumulative impacts of dam development in high‐uncertainty, data‐scarce contexts like the Mekong Basin. Plain Language Summary: Hydropower is considered an important energy source to meet many climate mitigation targets. Its negative impacts are however often underestimated, including the emission of greenhouse gases (GHG) from reservoirs. This study introduces a framework for planning dams strategically in the Mekong River Basin, a region heavily dependent on river‐related services. The framework considers uncertainties and incorporates greenhouse gas emissions mitigation and sediment transport disruption as new objectives. Using a multi‐objective evolutionary algorithm, the research identifies optimal dam portfolios for different hydropower expansion goals. To consider uncertainties in the results, the analysis employs a robust optimization approach to assess over 5,000 state‐of‐the‐world configurations. Results indicate that developing dams in the upper Mekong is a more robust option for both environmental and energy goals in the near term. These conclusions showcase the approach's usefulness in understanding dams' cumulative impacts in data‐scarce and uncertain contexts like the Mekong Basin. Key Points: We identify optimal dam portfolios which balance hydropower expansion, sediment supply disruption, and GHG emissions in the MekongWe extracted optimal portfolios under multiple state‐of‐the‐world configurations, to extract robust indicators of project attractivenessResults suggest that near‐term dam development should focus more on the upper Mekong, compared to the lower Mekong and its tributaries [ABSTRACT FROM AUTHOR]

Sediment connectivity at the catchment scale includes the processes linking sediment sources, sinks and the river outlet. Soil erosion models usually estimate yields without considering riverine processes or human infrastructure that may affect sediment connectivity. Quantifying these processes at a large scale is a determinant of understanding sediment transfers from continental lands to marine ecosystems. This study tries to fill this gap by coupling the soil erosion model WaTEM/SEDEM (WS) with the riverine connectivity tool CASCADE to quantify sediment fluxes in the Rhône watershed. The coupling returned a good fit, with deviations of −51.7%. WS alone predicts the exported fluxes better with a deviation of −34.9%. Nevertheless, this paper shows the importance of considering connectivity and transport capacity to develop a more realistic representation of fine sediment dynamics at a large scale. However, connectivity tools depend on the quality of the models (soil erosion and hydrology) and the geomorphological data on which they depend, which is a limiting factor in large‐scale studies. [ABSTRACT FROM AUTHOR]

Proglacial forefields commonly include highly dynamic fluvial systems associated with the fundamental instability between topography, flow hydraulics and sediment transport. However, there is limited knowledge of how these systems respond to changing subglacial hydrology and sediment supply. We investigated this relationship using the first continuous field‐collected data sets for both suspended and bedload sediment export and proglacial river dynamics for an Alpine glacier forefield, the Glacier d'Otemma, Switzerland. The results show a strong sensitivity of fluvial morphodynamics to the balance between sediment transport capacity and supply. When subglacial bedload export rates exceeded fluvial transport capacity, we found bar construction leading to net forefield aggradation and surficial coarsening, especially on bar heads. This intensified braiding buffered the downstream transport of coarse sediment. When subglacial bedload export rates were lower than transport capacity, incision occurred, with reduced braiding intensity, net erosion and important amounts of bedload leaving the proglacial system. We found a net fining of surficial deposits except for very isolated coarsening patterns on bar heads. Thus, proglacial forefield morphodynamics are strongly conditioned by subglacial hydrology and sediment supply, but this conditioning is also influenced by the response of the forefield itself. Proglacial forefields have an important influence on the longitudinal connectivity of sediment flux in regions sensitive to climate change, such as recently deglaciated high mountain areas. The linkages we report between subglacial processes and river morphodynamics are critical for understanding the development of embryonic forefield ecosystems. Plain Language Summary: This study focuses on Alpine proglacial forefields, braided fluvial streams flowing in deglaciated terrains, and their geomorphic response to both sediment and water exported from retreating glaciers. This is achieved using the first continuous field‐collected data sets combining sediment flux quantifications at the glacier terminus and downstream changes of the river over time collected in the Glacier d'Otemma forefield (Switzerland). Results show that the fluvial landscape in recently deglaciated terrains changes rapidly, influenced by the balance between the amount of sediment being transported from under the glacier and the river's capacity to carry it. When the released amount of sediment matches the river's capacity, the deposition of coarser material dominates and the stream becomes more complex with increasing braiding intensity. However, when the river carries more sediment than supplied by the glacier, flow becomes more confined into fewer channels, promoting the erosion of previously deposited material, particularly for the coarser sediment fractions. The study emphasizes how both the river configuration and the landscape near a melting glacier depend on whether the river itself can transport the quantities of sediment delivered by the glacier. This balance can affect the downstream sediment flux from glaciered catchments and the development of ecosystems following climate change‐induced glacier retreat. Key Points: First study combining continuous subglacial sediment export rates and proglacial forefield geomorphic change at the melt season scaleStrong sensitivity of proglacial forefield morphodynamics to subglacial bedload export rates and fluvial transport capacityBar construction processes filter the downstream transport of bedload particles buffering the longitudinal connectivity of sediment flux [ABSTRACT FROM AUTHOR]

Estimating sediment transport in mountain rivers is challenging because of sediment supply limitation, broad grain size distributions, complex flow hydraulics, and large form drag. Consequently, sediment transport equations are lacking for application in rivers where the bed is coarse and largely immobile, but small fractions of finer, transportable sized material contribute disproportionately to bedload transport. We introduce a framework for estimating sediment transport in mountain rivers that addresses two limitations: estimating the shear stress acting on mobile grains, and accounting for the difference between mobility of size fractions, that is, whether or not a specific grain size can move at a given flow, and transportability, which we define as how much of that size present in the bed will be recruited into transport. We use two bedload data sets to develop equations for predicting incipient motion and transport rates of each grain size fraction present in the bed. We tested the new equations against incipient motion and sediment transport data we collected from streams in the Rocky Mountains, USA, and against published regional sediment yield data. Using this method results in transport estimates where the finer fractions, despite being a small fraction of the bed surface, make up a large part of the total yield. Fractions greater than the median bed grain size are mobile only during peak flood flows, consistent with the existing mountain river bedload data sets. The approach is parsimonious, requiring only data that are often readily available or obtainable: a bed grain size distribution, hydraulic geometry measurements, and discharge. Plain Language Summary: In steep mountain rivers, complicated flow hydraulics make predicting sediment transport difficult. Here, we introduce a sediment transport framework that improves the estimates of bedload transport in these types of channels. The new transport model has two primary differences from existing models: it uses a new approach for estimating the fraction of the flow force acting on mobile grains on the bed, and it converts grain size pebble counts into fractions of each grain size by area, which helps to distinguish between mobility and transportability of size fractions. We applied the model to mountain rivers in the Bitterroot River basin in Montana, USA. Results compared well with published regional sediment yields from the area. Key Points: Applying existing sediment transport models to steep, coarse‐bedded streams often requires calibration or specific data collectionWe introduce a new bedload transport framework for coarse‐bedded mountain channels that requires only commonly used geomorphic dataThe predicted bedload yield using this model for streams in Montana was consistent with measured yields within the region [ABSTRACT FROM AUTHOR]

The spatial distribution of vegetation in a basin has a far-reaching influence on the potential for sediment separation and transport capacity. However, many landslides induced by strong earthquakes have greatly changed the existing pattern, which further increases the probability of debris flow in a basin during heavy rainfall and has a significant impact on the stability of the basin. Thus, this study selected the debris flow basin in the Qipan catchment of the Wenchuan earthquake area as the research object. Multisource and high-precision remote sensing images were used to analyze the land use changes in the basin, and the index of connectivity (IC) was introduced to analyze the evolution of sediment transport capacity. An ecosystem stability assessment method suitable for post-earthquake debris flow basins was proposed. Through quantitative assessment of the ecosystem stability of the basin after the Wenchuan earthquake in 2008 and the two debris flow events after the earthquake, the dynamic relationship between the debris-flow-prone area and the ecosystem stability of the basin was revealed. The results showed that the stability of the ecosystem in the Qipan catchment increased annually, indicating a stable and substable state. The spatial distribution characteristics were lower in the north and south and greater in the middle. By comparing the evaluation results with the actual terrain change trend, the accuracy and feasibility of the evaluation method are verified. The results of this study provide a scientific basis for the formulation of regional disaster prevention strategies and help to accelerate the improvement of regional stability in debris-flow-prone areas. [ABSTRACT FROM AUTHOR]

Assessment of the spatial distribution of potential pathways of sediment transport and the degree of linkage between sediment sources and the channel network within a watershed represents a valuable analysis for informing management decisions on sediment yield and transfer. Given the limitations of conventional methods for determining index of sediment connectivity (IC), there is a need to provide a flexible and efficient approach with the ability to apply different factors. In this regard, five decision tree-based machine learning models: M5 prime (M5P), random tree (RT), random forest (RF), alternating model tree (AMT), and reduced error pruning tree (REPT) were tested using geomorphic and climatic factors. Two databases were constructed with 200 and 1600 classes at 50 watersheds in Queensland, Australia. In these models, IC was assessed as an output parameter and six attributes that affect IC were assigned as input parameters (i.e., elevation, slope, area, length of stream channel, normalized difference vegetation index, and rainfall). Statistical validation and comparison of model predictions with calculated IC values based on the approach of Borselli et al. (Catena 75:268–277, 2008) were performed. Based on the statistical criteria, the RF model produced the most robust estimations of IC compared to other models and performed very well for IC modelling, especially in smaller subsections of watersheds. Accordingly, these findings can play an effective role for implementing watershed management and soil and water resources management measures. [ABSTRACT FROM AUTHOR]

Abstract We present a framework for strategic dam planning under uncertainty, which includes GHG emissions mitigation as a novel objective. We focus on the Mekong River Basin, a fast‐developing region heavily relying on river‐derived ecosystem services. We employ a multi‐objective evolutionary algorithm to identify strategic dam portfolios for different hydropower expansion targets, using process‐related and statistical models to derive indicators of sediment supply disruption and GHG emissions. We introduce a robust optimization approach that explores variations in optimal portfolio compositions for more than 5,000 state‐of‐the‐world configurations, regarding sediment origins and trapping and GHG emissions. Thus, we can rank dam projects' attractiveness based on their frequency of inclusion in optimal portfolios and explore how uncertainty affects these rankings. Our results suggest that developing dams in the upper Mekong would be a more robust option for near‐term development than, for example, the lower Mekong and its tributaries, for both environmental and energy objectives. Our work presents a novel approach to better understand the basin‐scale cumulative impacts of dam development in high‐uncertainty, data‐scarce contexts like the Mekong Basin.

Abstract Sedimentary landforms on Earth and other planetary bodies are built through scour, transport, and deposition of sediment. Sediment connectivity refers to the hypothesis that pathways of sediment transport do not occur in isolation, but rather are mechanistically linked. In dryland river systems, one such example of sediment connectivity is the transport of fluvially deposited sediment by wind. However, predictive tools that can forecast fluvial‐aeolian sediment connectivity at meaningful scales are rare. Here we develop a suite of models for quantifying the availability of river‐sourced sediment for aeolian transport as a function of river flow, wind regime, and land cover across 168 km of the Colorado River in Grand Canyon, USA. We compare and validate these models using topographic changes observed over 10 years in a coupled river sandbar‐aeolian dunefield setting. The models provide a path forward for directly linking fluvial hydrology with the management and understanding of aeolian landscapes.

This study applies the WaTEM/SEDEM model, a watershed-scale model based on the Universal Soil Loss Equation (USLE), to enhance sustainable watershed management by identifying high-erosion-risk areas for targeted mitigation at various scales. It focuses on identifying potential errors in using statewide or worldwide land use data layers derived from remote-sensing algorithms and inaccuracies in the spatial distribution of cropland and soil types resulting in misinterpretation of sediment yields. These model limitations emphasize the need for field validation and precise input data, particularly stream data, to improve the reliability of these models. The study examines hydrologic rainfall-runoff processes in Tennessee's 182 km2 Oostanaula catchment using various data sources, including the National Land Cover Database (NLCD), the European Space Agency WorldCover dataset (ESA), and manual field surveys. Three modeling scenarios were evaluated, with and without stream topology corrections, using the WaTEM/SEDEM model. It details the global data used, the methodology of the field survey, the simulation and validation of data, and the critical point identification. Significant discrepancies in long-term sediment transport predictions were found, depending on the land use data source. This study addresses watershed model validity and potential errors and recommendations for the use of globally available data. [ABSTRACT FROM AUTHOR]

The management of basin water and soil resources greatly benefits from investigating the spatial changes and primary determinants of hydrological and sediment connectivity from perspectives of topographic features, vegetation characteristics, structural features of river networks. However, quantifying the effects of influencing factors and their interactions on connectivity is still a challenge in the field of studies of surface processes. To address this challenge, we applied the geographical detector model (GDM) and random forest (RF) to quantify the relative importance and explanatory power of topographic factors, vegetation features, and river network structure on the hydrological connectivity and sediment connectivity and to clarify the interaction mechanism of various factors in the Jinghe River Basin. Results indicate that from 2005 to 2020, the mean value of hydrological connectivity (ICH) witnessed a decreasing trend from −5.47 to −5.58. Similarly, the mean value of sediment connectivity (ICS) declined over the same period from −9.74 to −10.05, with high values registered in valleys and low values in plains. The river density (D) and hydrological weight factor (normalized SCS‐CN) exhibited a greater spatial explanatory power on ICH than other parameters, reaching 0.149 and 0.182, respectively. The vegetation factor (0.299) and sediment weight factor (0.410) manifested considerably more influence over ICS. Spatial integration between relevant elements can enhance our understanding of basin connectivity. Interactions between vegetation, topography, and river network structure provide more explanatory power compared to interactions among same‐type features. Ultimately, this study offers a theoretical template for understanding the management of soil and water resources in the Jinghe River Basin, as well as the spatial variability in soil erosion. [ABSTRACT FROM AUTHOR]

In bedrock-dominated upland terrains, local heterogeneity in the erodibility of rock masses is a critical but under-explored factor constraining sediment erosion, mobilisation and transport. Here we examine how fault-related fracturing controls variations in the erodibility and grain-size of bedrock source material at the hillslope-scale. We then assess how this influences the evolution of slope sediment systems using a case-study from the Southern Uplands, Scotland, UK. Faults are associated with fracture densities that are an order of magnitude greater than background joint- and bedding-related fractures in weakly metamorphosed sedimentary rocks. Thus, fault zones are enhanced source areas yielding more abundant, smaller clasts. They are associated with enhanced erosion, gullying and debris flows, and the development of blanket colluvium on steep open hillsides. The orientation at which faults intersect the hillslope constrains the evolution of the sediment system. Faults with trends closely aligned to the direction of slope are associated with higher erosion via confined-channel debris flow activity in strongly coupled gullies. Faults that are oblique to slope direction disrupt and segment gully systems developed on minor transfer faults. Overall, faults that are oblique to slope direction are associated with lower erosion and give rise to decoupling within debris flow systems. Inclusion of geological weighting parameters in the formulation of a sediment connectivity index to characterise the effect of faulting on the erodibility and mobility of source material improves correspondence of the model with observations and provides a simple approach that could be adapted for other sources of geological heterogeneity. [ABSTRACT FROM AUTHOR]

Introduction: Soil loss is a worldwide environmental problem, and sediment transport is one of its important components. In recent years, a hillslope sediment delivery ratio (SDR) model based on an index of connectivity has been widely used to describe the variation in sediment transport characteristics. However, the hillslope SDR model only considers the structural characteristics of the watershed and ignores the dynamic mechanism of sediment transport, which leads to poor dynamic applicability over short timescales and makes it difficult to reflect changes of sediment yield.Methods: Therefore, we here propose a monthly dynamic SDR model that integrates the hillslope structural connectivity and sediment transport threshold of rainfall event based on the main influencing factors of sediment delivery. We then combine the dynamic SDR model with an empirical erosion model to simulate the hillslope sediment yield in the Mahuyu watershed, and verify the applicability of the coupled model using the Heimutouchuan watershed.Results: The results show that the coupled model can effectively simulate the hillslope sediment yields of the Mahuyu and Heimutouchuan watersheds. The contribution of the rainfall transport threshold factor to sediment delivery and yield is essentially in dynamic stability at the multi-year timescale, but increases the heterogeneity of both inter-month distributions and the spatial distribution of hillslope sediment yield.Discussion: The dynamic SDR model, which considers the rainfall thresholds of transport and re-transport, can effectively improve the simulation accuracy of low and high sediment yield values on hillslopes. Our results can provide a reference for understanding sediment transport processes on hillslopes and optimizing soil and water conservation measures in watersheds.

In mountain regions, the impact of areas on the sediment conveyance can not only be described by their susceptibility to debris flow release, but also by their structural connectivity to the rivers. This generates the need to combine susceptibility and connectivity for accurate analyses of sediment transport. Our study exploits an approach developed by [Steger, er al. 2022; https://doi.org/10.1002/esp.5421] and upscales it to the South Tyrolean Dolomites region. The approach comprised the modeling of debris flow release susceptibility using an interpretable machine learning algorithm, the training of a logistic regression model, and the combination of the resultant classified maps to create a joint susceptibility-connectivity map. The results show the quantitative thresholds for the susceptibility probability and the Index of Connectivity (IC) that allow to discriminate between susceptible and not susceptible, as well as connected and disconnected areas, which are represented via a variety of maps. [ABSTRACT FROM AUTHOR]

The Vakhsh River is tributary to the Amu Dayra, supporting numerous hydropower facilities as well as irrigation and community water supplies. High sediment loads are major concerns for these uses, yet little is known about the spatial distribution of the dominant sediment sources or their connectivity to fluvial systems. Here, we address this gap by combining findings from a series of field expeditions, remotely sensed climate and vegetation assessments, systematic sediment sampling, hydrograph analysis, and a review of local literature. Our preliminary findings show that various mass wasting processes (e.g., landslides, debris flows, rockfall, dry ravel, bank failures) constitute the major connected sources of sediment, particularly in the mid- to downriver reaches, many of which are unaffected by land use. Surface erosion, including the large gullies in loess deposits of the lower basin, are more affected by poor agricultural practices and road runoff, and can supply large loads of fine sediment into the river. Climate trends detected through remote sensing show an increase in rainfall in the lower half of the basin from spring to early summer while solid precipitation has increased in the eastern half in March. These trends may lead to more runoff and increases in sedimentation if they continue. [ABSTRACT FROM AUTHOR]

Sediment connectivity is a valuable metric that characterizes the relationship between sediment transport from the source to the sink, and the ease of sediment erosion. Over the past four decades, changes in land use types and vegetation cover have significantly altered sediment dynamics in the Wei River basin. In this study, we used the index of connectivity (IC) to assess the temporal changes in sediment connectivity at a watershed scale. We employed Landsat images to analyse the relationship between changes in vegetation cover or land use type and sediment connectivity. We used factor detector and interaction detector in Geodetector to analyse the importance and impact of vegetation and slope on IC changes. We assessed the correlation of sediment yield and connectivity to validate our results and it shows that IC has strong or moderate positive correlation with sediment yield from eight out of nine stations in the Wei River Basin. Our findings demonstrate that soil and water conservation measures, as well as the grain for green project, have led to the transformation of cropland and grassland into woodland. This change is reflected in the decrease of the maximum IC value from 6.24 to 5.72 in the Beiluo sub‐basin, indicating a decreasing trend in sediment connectivity. Although the maximum IC value increased from 5.76 to 5.08 in the Jing sub‐basin, driven by human activity, showing an increasing trend. Furthermore, the IC value decreased in the western part of the Wei sub‐basin. Overall, sediment connectivity exhibits a weak decreasing trend in most regions of the Wei River basin, while it shows an increasing trend slightly in the Jing sub‐basin. The correlation coefficients ranged from 0.47 to 0.86, with sediment yield being moderately or strongly correlated with IC. Our study identified vegetation, human activity, and slope as the main influencing factors of IC. The results of factor detector showed that the q value of vegetation was 0.63 and the slope was 0.1, Vegetation played a major role in the change of IC. The results of interaction detector showed that interaction between vegetation and slope was greater than the single factor. The temporal variability of sediment connectivity in the basin provides valuable insights for sediment transport management. Our research highlights the importance of studying sediment connectivity and offers proposals for measures that can be taken to address sediment transport challenges in the Wei River basin. [ABSTRACT FROM AUTHOR]

Context: Wildfires have severe impacts on landscapes' hydrological and sediment processes. They are linked to events such as flash floods and droughts, and high erosion rates which lead to loss of soil organic matter and detachment of seeds and seedlings. Mulching is an effective measure implemented directly after a fire to reduce soil erosion and increase soil water retention. However, its implementation has proved a challenge, mainly due to factors such as cost and public acceptance. Objectives: This research aims to optimize the application of post-fire mulching by using decision-making criteria to select "how" and "where" the technique should be used. The specific objectives were to: (i) investigate the decision-making criteria on "how" to apply mulch by interviewing experts; (ii) define the cost-effectiveness relations of erosion modelling scenarios. Methods: The Monchique 2003 wildfire in Southern Portugal was used as a case study Experts' interviews and literature review were used to construct prioritization scenarios. Post-fire soil erosion was then modelled with the Revised Universal Soil Loss Equation (RUSLE) model and the Sediment Connectivity Index for the three resulting scenarios (the "Soil" scenario, considering the net potential erosion; the "Water" scenario, focusing on th1e protection of water bodies from sedimentation; and the "Road" scenario, focusing on road protection); and at two erosion thresholds (1 and 10 Mg ha−1 year−1). Results: The interviews and the literature review highlighted the importance of socio-economic parameters when it comes to mulch application. Moreover, models showed that small interventions, aimed at areas nearby water bodies and road networks can be more cost-effective than large interventions. Conclusions: Models helped to create a hierarchy of scenarios, enabling land managers to assess decision making tools at the landscape level, linking their priorities with practical issues of emergency stabilization practices. [ABSTRACT FROM AUTHOR]

Sediment connectivity is a conceptualization for the transfer and storage of sediment among different geomorphic compartments across upland landscapes and channel networks. Sediment connectivity and dysconnectivity are linked to the water cycle and hydrologic systems with the associated multiscale interactions with climate, soil, topography, ecology, and landuse/landcover under natural variability and human intervention. We review current sediment connectivity and modeling approaches evaluating and quantifying water and sediment transfer in catchment systems. Many studies highlight the interaction between sediment and water in defining landscape connectivity, but many efforts to quantify and/or simulate sediment connectivity rely on the topographic/structural controls on sediment erosion and delivery. More recent modeling efforts integrate functional and structural connectivity to capture hydrologic properties influencing sediment delivery. Though the recent modeling development is encouraging, a comprehensive sediment connectivity framework, which integrates geomorphic and hydrologic processes across spatiotemporal scales, has not yet been accomplished. Such an effort requires understanding the hydrologic and geomorphic processes that control sediment source, storage, and transport at different spatiotemporal scales and across various geophysical conditions. We propose a path for developing this new understanding through an integrated hydrologic and sediment connectivity conceptual model that broadly categorizes dominant processes and patterns relevant to understanding sediment flux dynamics. The conceptual model describes hydrologic–sediment connectivity regimes through spatial-temporal feedback between hydrologic processes and geomorphic drivers. We propose that in combining hydrologic and sediment connectivity into a single conceptual model, patterns emerge such that catchments will exist in a single characteristic behavior at a particular instance, which would shift with space and time, and with landscape disturbances. Using the conceptual model as a “thinking” tool, we extract case studies from a multidisciplinary literature review—from hydrology, geomorphology, biogeochemistry, and watershed modeling to remote-sensing technology—that correspond to each of the dominant hydrologic–sediment connectivity regimes. Sediment and water interactions in real-world examples through various observational and modeling techniques illustrate the advancements in the spatial and temporal scales of landscape connectivity observations and simulations. The conceptual model and case studies provide a foundation for advancing the understanding and predictive capability of watershed sediment processes at multiple spatiotemporal scales. Plain language summary: Soil erosion and movement across the landscape are closely linked to rain events and flow pathways. Landscape connectivity is a way to consider how soil erosion from different parts of the landscape is connected to the streams. We explore where soil erosion occurs and how eroded soil moves across the landscape through the interaction with rainfall and drainage. The comprehensive understanding of sediment connectivity and its dependence on rainfall characteristics and watershed hydrology may help to inform the effective distribution of conservation funds and management actions to address water pollution from excess sediment.

The integration of geomorphological analysis in archaeological investigations is essential to describe physical geography and land morphology in order to understand the relationship between the environment and human activities. Recently, the sediment flow connectivity index (SfCI) has been demonstrated to be a powerful geomorphic indicator for defining the most sensitive areas to geomorphological modifications in a catchment. This work presents the experimental application of the SfCI for a landscape archaeological analysis in order to assess the contribution of the index to potentially recognize, monitor, and interpret the historical evidence in the evaluation of landscape evolution. The investigation was performed in the basin of Lama Camaggi in the Apulia region (southern Italy), characterized by precious archaeological evidence found on the surface during field surveys in the years 2001–2002 and 2012–2013. The results show (1) the correlation between high-sediment-connectivity areas and areas with high densities of archaeological sites, and (2) the capacity of the SfCI to identify surface processes that may potentially affect the readability of the archaeological records to support data interpretation. These results confirm the advantage of applying an interdisciplinary approach in archaeology and opens innovative research scenarios. [ABSTRACT FROM AUTHOR]

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[Objective] The aims of this study focus on the influence of extreme rainfall events on sediment connectivity of slope-gully system in small watershed, and further provide theoretical basis for comprehensive watershed management. [Methods] The farmland watershed in Caijiachuan watershed in Ji County of the Loess Plateau was taken as the research area. UAV and remote sensing images were used to carry out aerial survey and field survey on slope and gully system before and after the extreme rainfall event in Shanxi in October 2021. The landscape pattern changes before and after extreme rainstorm were analyzed, the sediment connectivity of slope-gully system was quantified, and the spatial distribution and topographic features of landslide points were identified, the responses of typical engineering measures to extreme rainfall were evaluated. [Results] The rainfall event lasted for 84 hours, with a cumulative rainfall of 160.4 mm, a rainfall intensity of 1.9 mm/h and a rainfall frequency of 0.16%. It was an extreme rainstorm that occurred once in a hundred years. After the rainstorm, the number of patches increased, the landscape shape index increased, the Contag index decreased, and the Shannon diversity index decreased. Sediment connectivity unevenly distributed in the watershed before the rainstorm, but it increased after the rainstorm. After the rainstorm, the sediment connectivity of landslide site decreased, and the landslide mainly occurred on the slopes with 0°～10° and 40°～50°, accounting for 29.11% and 17.74%, respectively. [Conclusion] Landslides induced by extreme rainfall events affect sediment connectivity, and the sediment connectivity index can be used to identify landslides sites thus can be used to assess the response of typical soil and water conservation engineering measures to extreme rainfall. The results of this study can provide support for integrated watershed management and ecological restoration after extreme precipitation events. [ABSTRACT FROM AUTHOR]

Soil erosion is an important cause of global land degradation and other ecological and environmental problems. Revealing the influence mechanism of land use/cover change (LUCC) on sediment yield can provide a scientific basis for efficient comprehensive and decision-making management of watersheds. As an important indicator of sediment yield and transport capacity, sediment connectivity has been widely studied in recent years. However, the existing index of sediment connectivity (IC) ignores the influence of upslope land use/cover on confluence and the corresponding changes in downslope sediment transport. Moreover, a formula describing the upslope and downslope components does not establish an effective correlation with existing soil erosion formulas. Therefore, the index is not closely related to the erosion process and does not reflect the physical process of sediment transport and sediment deposition. In addition, there have been few reports concerning the effect of LUCC on sediment connectivity inside (on-site impact) and outside (off-site impact) the changed patches. Consequently, by based on addition of the revised parameters of the effective confluence area (Ar) and the runoff velocity factor (v) of the sediment delivery distributed (SEDD) model, an improved sediment connectivity index (ICZQ) is proposed. The results indicate that ICZQ has a significant linear relationship with annual runoff depth or sediment yield modulus in small watersheds within 100 km2 in the Loess Plateau, except for feature years containing rainstorm events (daily rainfall exceeding 50 mm). Therefore, the runoff and sediment transport capacity of small watersheds can be characterized by ICZQ under the influence of LUCC and rainfall change. In 1982–2020, driven by LUCC with an enhancement in vegetation (forest and grass), the ICZQ decreased in 90% of the area and decreased by a significant or extremely significant level over 48% of the area. To better understand the effects of LUCC on sediment connectivity, we analyzed on-site and off-site impacts with rainfall remaining unchanged to control the variables. The contribution rates of the on-site and off-site impacts caused by LUCC on sediment connectivity in Lvergou were 61% and 39%, 48% and 52%, respectively, over two typical periods (1985–1990 and 2015–2020). Due to the large proportion that off-site impacts occupied in the sediment connectivity change, the impact of LUCC on sediment connectivity cannot be ignored, especially when the associated scale is relatively small. The present study provides a quantitative method for the optimization of land use/cover patterns, such as vegetation restoration in watersheds along with a reference for further revealing the impact mechanism of erosion and sediment yield in watersheds.

Background. The models currently used to predict post-fire soil erosion risks are limited by high data demands and long computation times. An alternative is to map the potential hydrological and sediment connectivity using indices to express the general properties of the burnt landscape. Aims. In this study, we aimed to answer the question: Do these tools identify post-fire sediment mobilisation hotspots? Methods. To achieve this, we assessed the spatial variability distribution of the location of soil erosion hotspots using the Index of Connectivity, Revised Universal Soil Loss Equation and the Sediment Export, and compared it with the simulation results of a more complex Landscape Evolution Model (LAPSUS model). Additionally, we evaluated statistical measures of association between the four tools. Key results. The three tools tested in this study are suitable for identifying sediment mobilisation hotspots, where the erosion rates are above the 95th percentile, and differences between their performance are small. Conclusions. The results indicate that these tools help locate extreme erosion locations in recently burnt areas. Implications. These results can be considered for post-fire and water contamination risk management, especially for fast prioritisation of areas needing emergency post-fire intervention. [ABSTRACT FROM AUTHOR]

Purpose: Although contour trenching is one of the widely used nature-based solutions for soil conservation around the world, its efficiency has not been quantitatively investigated. This study aimed to scrutinize the performance of the contour trenching program, a nature-based solution and common soil erosion prevention measure in hillslopes of a data-scarce region based on the sediment connectivity approach. Materials and methods: Six different hillslopes (A–F) were selected in the Khamsan watershed in Iran, a representative area where contour trenching has been implemented. The sediment connectivity map of each hillslope was generated using the index of connectivity (IC) based on two real scenarios: with (scenario I) and without (scenario II) contour trenching. Two different field-based validation methods were applied on the base of (i) in situ measurements of the sediment depth in contour trenches and Pearson's correlation analysis, and (ii) field index of connectivity (FIC). The validity of the sediment connectivity results was verified using both validation approaches. The sediment connectivity in two scenarios was compared and the impact of the contour trenching was analyzed. The performance of the contour trenching program was quantitatively determined for each hillslope. Results and discussion: The results revealed that contour trenching significantly affected sediment routing and reduced the IC values of all selected hillslopes. The differences in IC value between the two scenarios (∆IC) for hillslopes A, B, C, D, E, and F were found to be 22.6%, 11.27%, 14.69%, 5.83%, 15%, and 7.27%, respectively. Therefore, the spatial pattern of sediment connectivity also differed significantly after implementing contour trenching. Furthermore, Pearson's correlation coefficients revealed that the sediment connectivity and the sediment depth in contours in all hillslopes had a significant negative relationship, resulting in confirming the validity of the sediment connectivity results for all six hillslopes in the current study. Conclusion: Contour trenching significantly reduced the sediment connectivity on all six hillslopes studied. Furthermore, in situ measurements of the sediment depth in contour trenches should be conducted to verify the simulation of sediment connectivity. The proposed methodology can be applied in other data-scarce regions to evaluate the performance of the contour trenching program. [ABSTRACT FROM AUTHOR]

Understanding the spatial distribution characteristics of soil erosion and sediment connectivity is important for formulating integrated watershed management measures. Based on the InVEST sediment delivery ratio model, we used the connectivity index and soil loss model to measure the spatial distribution characteristics of sediment connectivity and soil erosion in Erdaoling watershed of brown soil hilly region of low mountains in western Liaoning. By exploring slope, aspect and land use characteristics under different sediment connectivity levels and soil erosion levels, we analyzed the relationships among topography, land use, sediment connectivity, and soil erosion. The results showed that the average sediment connectivity in the watershed was -3.79, and that the average soil erosion was 614 t ⋅ km² ⋅ a-1. High connectivity was mainly found in sloping farmland, while low connectivity was mainly found in forest and grassland. The soil erosion intensity of 93.3% of the watershed area was below moderate, with only 1.1% of the area being above extremely strong. The higher the sediment connectivity level, the higher the pro-portion of the area <5° slope, while the area proportion of the rest slope was relatively stable. The proportion of cultivated land area increased, while the proportion of forest and grassland land area decreased. The area proportion on negative slope decreased, while that on positive slope increased. With increasing soil erosion intensity, the area proportion of slope <8° increased and the area proportion of the rest slope was relatively stable. The proportion of forest and grassland area decreased, while the proportion of other land use area increased. The proportion of slope area on positive slope increased, while that on negative slope decreased. Land use was a key factor influencing the spatial response relationship between soil erosion and sediment connectivity in this watershed. [ABSTRACT FROM AUTHOR]

Land consolidation can increase the area of arable land and improve the ecology and environment and is widely used worldwide. The Gully Land Consolidation (GLC), as a special type of land consolidation, significantly impacts soil erosion. The purpose of this study was to investigate the effect of the GLC on soil erosion and sediment yield under different rainfall events and hydrological years in the Xingshuyaozi watershed on the Chinese Loess Plateau, where the GLC area accounted for 10.36% of the watershed. A computer model integrated with the Chinese soil loss equation (CSLE) and the continuity equation of sediment was used. Sediment connectivity before and after the GLC was compared to illustrate the effect of the GLC on sediment yield. The results showed that the reduction in soil loss increased with increasing rainfall amount, and the reduction rate of soil erosion was over 50%. The GLC had the greatest effect on soil erosion in wet years. The GLC effectively decreased sediment at the outlet of the watershed, with over 99% of the sediment being trapped. The reduction efficiency of soil erosion and sediment yield decreased in order of wet year, normal year and dry year. The decreased soil erosion and sediment yield resulted from the significantly lowered slope gradients and sediment connectivity after the GLC. These results indicate that the GLC is an effective soil and water conservation measure. These results can provide technical support for the application of the GLC and policymaking. [ABSTRACT FROM AUTHOR]

• A framework is proposed to target ponds for conservation priority. • Accurately assessing MPS function requires consideration of artificial flow paths. • The location of ponds exerts a greater impact on their functionality than size. • Ponds with high pressure and State, and low response scores should be prioritized. Precise targeting of conservation practices to the most effective sites in multi-pond systems (MPSs) is critical for resource optimization and water quality improvement. Previous studies generally prioritized ponds for conservation practices considering nutrient removal efficiency. However, they have frequently overlooked the role of ponds in sediment interception and the impact of human activities and environmental factors around the pond. Herein, the present study developed and applied a novel framework for pond prioritization by integrating the Pressure-State-Response (PSR) model, graph theory, and K-mean clustering. The framework consists of three components. An indicator system is developed to represent the nutrient removal performance of any MPS, impacts on catchment sediment connectivity, external threats, and human-initiated conservation. A flow path network considering natural and artificial elements was constructed to calculate indicator values. A cluster analysis was conducted on the index values of different ponds, and a hierarchical sorting method were used to prioritize ponds. The framework was applied to the Guilinqiao Catchment, a typical fragmented agricultural catchment in the Yangtze River Basin, China. The study has quantified the Pressure, State, and Response indices of different ponds in this catchment, prioritized the ponds, and drawn recommendations for conserving MPSs based on field surveys and remote sensing data. Ponds with higher Pressure index, higher State index, and lower Response index scores should be targeted as conservation priorities. This framework provides an effective method for ensuring management of MPSs to sustainably maximize water cleanup capacity with limited resources. [ABSTRACT FROM AUTHOR]

• Vegetation changes over 8 years and after fires are tracked in Lama Camaggi, Italy. • NDVI detects short-term vegetation changes affecting sediment connectivity. • The introduction of NDVI enhances the flexibility of SfCI on spatial–temporal scale. Land cover plays a fundamental role in surface dynamics that involve sediment connectivity. Land cover types can physically mitigate, prevent or increase sediment production and mobility on the surface. Further, changes in land cover, particularly in vegetation classes, can directly affect these processes, especially if they occur over short time periods or even more rapidly after extreme events such as fires. This study analyses vegetation cover changes in the Lama Camaggi catchment (southern Italy) in relation to its sediment connectivity pattern, described by Sediment flow Connectivity Index (SfCI). The Normalized difference vegetation index (NDVI), derived from satellite data, is utilized to detect vegetation cover changes over 8-year interval and following fire events. The main objective is to evaluate how the NDVI improves the flexibility of SfCI in defining surface dynamics on both spatial and temporal scales. The findings indicate that (1) NDVI changes identify vegetation cover changes in a short period in many areas of the catchment, potentially affecting sediment connectivity, and (2) the implementation of NDVI in the SfCI helps detect post-fire effects on sediment mobility and connectivity. Integrating NDVI enhances the SfCI algorithm providing a more dynamic description of sediment patterns. [ABSTRACT FROM AUTHOR]

• Event magnitude controls new water and sediment timing. • Ensemble approach enhances robustness of Machine Learning-based inference. • Conductivity-based hydrograph separation elucidates sediment hysteresis controls. Hydrologic controls on the timing of sediment transport and sediment hysteresis patterns remain an open area of investigation in hydrology, especially for low-gradient watersheds with substantial instream sediment deposition. Sediment hysteresis, which describes the mismatch between hydrograph peak and sedigraph peak, aids with elucidation of the mechanisms of sediment transport in watersheds. Most frequently, the controls of hysteresis are attributed to the proximity of sediment sources to monitoring locations in a watershed. However, this assumption, while widely applied, is infrequently verified. We investigated the controls of sediment hysteresis in a low gradient system located in the Bluegrass Region of central Kentucky, USA. Turbidity and conductivity sensors installed at the basin outlet provided data to quantify sediment hysteresis and separate hydrologic flow pathways (i.e., by describing the source of water delivered to the watershed's outlet) using a tracer-based approach. Predictive hydrologic parameters, including hydrologic pathways, event magnitude, and antecedent conditions, were estimated and grouped based on hydrologic similitude. Thereafter, we identified parameters required to predict sediment hysteresis using a tailored ensemble feature selection approach coupled with three machine learning algorithms—Random Forest, K-Nearest Neighbors, and Gradient Boosted Trees. Results from the analysis of 68 storm events occurring over a two-year period showed that clockwise events accounted for 85 % of the total sediment yield despite comprising only 53 % of the events. The hysteresis index (HI) can be predicted (r = 0.8, RMSE = 0.12) using three, out of the thirty-nine hydrologic parameters considered. The most important predictors of HI reflect the volume of event rainfall and the relative proportions of new water (i.e., water derived from precipitation during the storm event) and old water (i.e., water previously stored in the watershed) comprising the hydrograph. Further analyses reveal that new water timing—which changes with the rainfall volume—and sediment timing are closely linked, suggesting that variations in the hysteresis patterns are controlled by changes in the response time of fast flowing water pathways. This implies that hydrologic pathways, as opposed to sediment proximity to the watershed outlet, control sediment hysteresis in this watershed. These results have important implications for better understanding the mechanisms controlling sediment transport at the watershed scale. [ABSTRACT FROM AUTHOR]

Global warming significantly impacts sediment dynamics in glaciated catchments, affecting water resource operations, water quality, recreational activities, and ecological systems. The propagation of climate-change-induced geomorphic changes and the catchment's sediment yield are moderated by sediment connectivity, defined as the degree to which a geomorphic system facilitates sediment transfer. Quantifying functional sediment connectivity at the catchment scale remains a challenge. To address this, we propose a novel approach combining graph theory with the morphological method. This approach is exemplified through a detailed case study of a 2022 thunderstorm event in the Grastal valley, Tyrol, Austria. First, a graph of potential sediment cascades is constructed using a geomorphological map, a digital elevation model and a flow routing algorithm. A short-term Digital Elevation Model of Difference (DoD) from consecutive ALS surveys is then used to infer sediment fluxes and calculate the Sediment Delivery Ratio (SDR) for each landform. The primary sediment mobilising processes were debris flows and fluvial erosion, with a significant proportion of debris flow material being deposited on slopes, not reaching the fluvial corridor. Strong fluvial erosion was observed in the proglacial area, but the propagation of these geomorphic changes is halted by an alluvial fan and a lake. Most landforms can be clearly categorised as connecting or disconnecting features based on their SDR. In total, a maximum of 12 % of mobilised sediments exited the catchment. Our findings demonstrate that (i) short-term, catchment-wide DoDs are valuable for assessing functional connectivity at an event temporal scale, (ii) using landforms as fundamental spatial units allows for the identification and in-depth analysis of critical sediment sinks and sources, and (iii) graph analysis facilitates the catchment-wide calculation of sediment delivery ratios between meaningful fundamental units and the delineation of significant sediment cascades. • The morphological method was used to infer sediment fluxes of a 2022 debris flow event • Functional connectivity was assessed at catchment scale using graph theory with landforms as fundamental units • Most landforms could be clearly classified as connecting or disconnecting features • The fluvial system had high sediment delivery ratios, indicating supply limitation • Important disconnecting features were talus slopes, an alluvial fan and a lake at the margin of the proglacial area [ABSTRACT FROM AUTHOR]

• Sediment Continuity Ratio is introduced to evaluate sediment (dis)continuity. • Continuity-connectivity analysis improve torrent control works assessment. • Effect of structures on continuity and connectivity is consistent at 65% • Integrating functionality and maintenance data highlight critical structures. The study investigated the effect of torrent control structures on the sediment cascade in the Vegliato mountain basin (Italy) related to an intense rainfall event of 50 years return interval. The Index of Connectivity (IC) was exploited to analyze the interaction of structures with longitudinal sediment (dis)connectivity. Moreover, the Sediment Continuity Ratio (SCR) was used to assess the effect on sediment (dis)continuity. The SCR is a novel parameter considering for each torrent control structure, the net balance of sediment deposition and erosion, and the cumulative proportion of the sediment cascade arriving from upstream. The SCR emphasises which structure was more prone to continuity or discontinuity during an event and to what extent compared to other structures. Moreover, a multi-perspective framework was carried out to help the interpretation of the SCR results within the context of the study area. The results of the (dis)connectivity assessment showed that the torrent control structures impacted sediment dynamics by influencing the slope and flow confinement, which in turn affected the IC. The (dis)continuity assessment showed structures prone to continuity mainly located in the upstream part of the catchment, where most of the over 60000 m3 of sediment was generated. In contrast, structures prone to discontinuity were located in the downstream part, where deposition processes were favoured during the analyzed period. A total of 65 % of the structures similarly affected both (dis)continuity and (dis)connectivity. Data on individual structure functions and maintenance conditions were also included, emphasizing the importance of these factors in planning mountain basins management interventions. The study proposed a new metric that, despite being based on a single large event and a single basin, still provides a useful approach to investigate the interaction between sediments and individual structures, the entire sediment cascade and the channel control system. [ABSTRACT FROM AUTHOR]

• RUSLE/IC/SDR was explored for simulation of agricultural erosion management. • Erosion management measures (EMM) were simulated at two catchments. • Effectiveness of EMM's varied by catchment and field parcel. • RUSLE/IC/SDR is a promising tool for high-resolution and large scale simulations. Models play a crucial role in guiding agricultural erosion management, though their incorporation of sediment connectivity and management strategies varies. This study evaluated the RUSLE/IC/SDR model's potential for simulating agricultural erosion management at both the field scale and across two catchments. We tested the model's ability to simulate erosion management measures at a high spatial resolution (2 m × 2 m) across diverse topographies, assessed whether incorporating sediment connectivity improves RUSLE-based erosion management planning within catchments, and explored its capacity to tailor measures based on local connectivity characteristics. Our findings showed significant variability in sediment sources and connectivity. The simulation of no-till and buffer strip measures effectively demonstrated their varying effectiveness across fields and catchments. At the catchment scale, erosion management planning that incorporates sediment connectivity through the RUSLE/IC/SDR approach did not contribute to significant additional sediment delivery reduction compared to using RUSLE alone. However, at the field scale, RUSLE/IC/SDR offered improved opportunities for tailoring erosion management measures to local sediment connectivity characteristics. These simulations highlight both the potential and limitations of RUSLE/IC/SDR, advancing our understanding of its application for erosion management. In conclusion, while RUSLE/IC/SDR represents a valuable extension of RUSLE, further research is needed to fully realize its practical applications. Nonetheless, it shows promise for high-resolution simulation of sediment connectivity and erosion management at the field scale, across large catchments and regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spatially, 31% of Tarim basin (China) showed a decreasing trend in index of connectivity (IC). • The explanatory power of geomorphic factors for IC increases gradually over time. • Natural restoration leads to lower IC reductions than anthropogenic restoration. • Sediment connectivity is an effective indicator to detect land degradation. Sediment connectivity influences sediment flux in the Tarim River Basin (TRB), a region facing severe sedimentation and desertification, which directly threaten the region's ecological security. To analyze the potential connectivity of sediment from hillslope to catchment outlets, we calculated the index of connectivity (IC) of TRB from 1990 to 2020 using a sediment connectivity model, referencing catchment outlets, and analyzed the impacts of climatic and geomorphic drivers on sediment connectivity. The results showed that the annual average IC ranged from −10.36 to 2.26 during study period. Approximately 30.56 % of the area exhibited a decreasing trend, and 8.57 % showed an increasing trend. The IC was lower in the downstream area (sediment sinks) than in the upstream area (sediment sources). Additionally, the IC increased with elevation and slope. Furthermore, the pattern and rate of land-use transformation had a substantial influence on sediment connectivity. Land restoration (increase in vegetation cover) resulted in a reduction of IC, particularly in the case of anthropogenic land restoration (Δ I C mean = -0.09). Conversely, land degradation led to an increase in IC (Δ I C mean = 0.04). Attribution analysis indicated that climatic factors had a greater influence on IC than geomorphologic factors, with temperature being the primary driver of IC variation (26.99 %). The explanatory power of geomorphologic drivers (elevation, slope) gradually increased over time. Moreover, a non-linear increase in explanatory power of factor interactions on IC was identified, with clear spatial differentiation characteristics in the interactions. These findings improve our our understanding of the spatial heterogeneity of soil erosion processes in the TRB and provide theoretical support for the implementing soil and water conservation strategies. [ABSTRACT FROM AUTHOR]

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

The Souss Basin is a dryland environment featuring soil, surface and climatic conditions enhancing processes of wind erosion and mineral and organic dust emissions while subject to frequent grazing, tillage and driving. The fine-grained compacted surfaces are covered by physical and biological crusts and stone cover and are sparsely vegetated by open argan woodland and patchily distributed bushes. Wind-tunnel experiments and soil sampling were conducted on the deeply incised alluvial fans originating from High Atlas and Anti-Atlas mountains to investigate the dryland ecosystem, including the open argan woodland, for information on local wind-induced relocation processes and associated dust emission potential. To investigate possible connections between dryland environmental traits and dust emissions, we used two approaches: (a) surface categories (stone cover, crust and cohesionless sand) and (b) Land Cover Classes (wasteland, woodland and wadi). The results indicate omnipresent dynamic aeolian surface processes on a local to regional scale. Wind impact is a powerful trigger for the on-site relocation of available mineral and organic dust and may be crucial to explain the heterogeneous spatial distribution of soil organic carbon and nutrients associated with mineral fines. Aeolian dust flux showed statistically significant relations with surface categories and, to some extent, with Land Cover Classes. While wind erosion processes are key to understanding on-site sediment and nutrient dynamics between fertile dryland islands, the results also indicate a considerable dust emission potential under increasing climate impact and anthropogenic pressure. [ABSTRACT FROM AUTHOR]

This study, using different direct and indirect methodologies, evaluated the sedimentation rate in an artificial reservoir in central Italy. This reservoir is regionally representative and was built in the 1960s for hydroelectric purposes; it has experienced a strong decrease in trap efficiency and a loss of over 70% of the stored water volume. Direct measurements of the lake bottom bathymetry, carried out in 2006 and 2015, and 3D reconstructions performed in a GIS environment, made it possible to calculate the volume of filling material and to verify an increasing trend in the sedimentation rate since 2006. The sample reservoir denudation rate was compared with that obtained using the Revised Universal Soil Loss Equation method to calibrate the fundamental and critical factors of the method itself, and verify the contribution of a hydrological "direct" (through new channels or gullies) or "diffuse" (overland flow) connectivity. Furthermore, the comparison with the results obtained from past studies on ten other artificial regional reservoirs, performed with morphometric analysis, demonstrated a good relationship between soil erosion rate, stream frequency, and contributing area size. The study highlighted how a correct estimate of soil erosion and/or solid transport rates within a hydrographic basin is fundamental for the assessment of the trap efficiency of a reservoir, in a period in which the availability of water resources is becoming more and more vital. [ABSTRACT FROM AUTHOR]

Forest roads often increase runoff and sediment loss, thus greatly impacting hydrological processes in mountainous watersheds. While there has been previous investigation on best management practices (BMPs) to reduce soil erosion from forest roads, few studies have attempted to optimize BMPs based on how much they can decrease sediment connectivity between forest roads and streams. To close this gap in knowledge, we analyzed the spatial relationship between forest roads and streams, presented the spatial distribution of sediment connectivity by integrating the forest roads into the calculation of the index of connectivity (IC), determined how sediment connectivity would respond to additional BMPs through simulating scenarios, and used these data to optimize the BMPs so they would intercept the greatest sediment loads. We found that forest roads and streams in the Xiangchagou watershed in the Dabie Mountain area of China tend to occur within 180 m of each other; however, within the same buffer zones, streams are more often accompanied by forest roads. IC was greatest near road–stream crossings but smaller near streams and forest roads, and it tended to decrease as the buffer distance increased. Furthermore, we found that sediment connectivity was decreased through running a variety of scenarios that used sediment basin and riparian buffers as BMPs between forest roads and streams. Specifically, within this watershed, riparian buffers should be 64 m wide, and there should be 30 sediment basins with a minimum upslope drainage area of 2 ha. At these quantities, the BMPs in this watershed would significantly affect sediment connectivity. By contrast, beyond these thresholds, increasing the width of riparian buffers or the number of sediment basins does not lead to meaningful sediment reductions. In this way, we were able to use the mean change point method to determine the optimal sediment basin quantity (30 with corresponding minimum upslope drainage area of 2 ha) and the optimal riparian buffer width (64 m) for the Xiangchagou watershed. While these results are a first approximation in a novel research area, they can guide forest managers and stakeholders to design and optimize BMPs that control the delivery of eroded sediments associated with forest roads. [ABSTRACT FROM AUTHOR]

Wildfires have become an increasing threat for Mediterranean ecosystems, due to increasing climate change‐induced wildfire activity and changing land management practices. In addition to the initial risk, wildfires can alter the soil in various ways—depending on fire severity—and cause enhanced post‐fire erosion. Usually, post‐fire erosion studies focus on a short time window and lack the attention for sediment dynamics at larger spatial scales. Yet, these large spatial and temporal scales are fundamental for a better understanding of long‐term destructive effects of multiple recurring wildfires on post‐fire erosion processes and catchment sediment dynamics. In this study the landscape evolution model LAPSUS was used to simulate erosion and deposition in the 404 km2 Águeda catchment in north‐central Portugal over a 41‐year (1979–2020) timespan, including eight wildfires each burning >1000 ha. To include variation in fire severity and its impact on the soil, four burn severity classes, represented by the difference normalized burn ratio (dNBR), were parameterized. Although model calibration was difficult due to lack of spatial and temporal measured data, the results show that long‐term post‐fire net erosion rates were significantly higher in the wildfire scenarios (5.95 ton ha−1 yr−1) compared to those of a non‐wildfire scenario (0.58 ton ha−1 yr−1). Furthermore, erosion values increased with burn severity and multiple wildfires increased the overall catchment sediment build‐up. Simulated erosion patterns showed great spatial variability, with large deposition and erosion rates inside streams. This variability made it difficult to identify land uses that were most sensitive for post‐fire erosion, because some land uses were located in more erosion‐sensitive areas (e.g. streams, gullies) or were more affected by high burn severity levels than others. Despite these limitations, LAPSUS performed well on addressing spatial sediment processes and can contribute to pre‐fire management strategies, by identifying locations at risk of post‐fire erosion. [ABSTRACT FROM AUTHOR]

Forest roads significantly affect sediment connectivity in mountainous catchments by contributing to the production of and disturbing the confluence of sediment-loaded runoff. This study considered forest roads as pathways and sinks of sediment-loaded runoff to understand the effects of forest roads on the confluence characteristics and sediment connectivity in mountainous a catchment using a scenario simulation. In order to determine the contribution and spatial relationship between sediment connectivity and influencing factors, this study utilized buffer analysis, an extremely randomized tree model, and multiscale geographically weighted regression. The results show that the presence of forest roads significantly changes the transport process and connectivity of runoff and sediment in the mountainous catchment. Specifically, flow length increases, but flow accumulation, upslope contributing area, and topographic index decrease with increasing distance from roads and streams. Meanwhile, the effects of roads on convergence characteristics and sediment connectivity are mainly manifested within a certain threshold that varies with different confluence characteristics. Moreover, sediment connectivity increases when considering roads as pathways and sinks of sediment-loaded runoff, especially on the upper hillslopes intercepted by roads and at the road–stream crossings. In addition, the closer the distance to the roads, the greater the impact of road on the confluence characteristics and sediment connectivity. Change in flow length is the most important factor affecting the sediment connectivity among all of the other convergence, terrain, and spatial distance characteristics. The longer the flow length, the lower the sediment connectivity. In conclusion, this study demonstrates that the altered confluence processes by roads increases the possibility that sediment-loaded runoff will be transported to the catchment outlet, which is of significance for the proper management of forest roads in mountainous catchments. [ABSTRACT FROM AUTHOR]

Dams, weirs and transverse barriers to rivers interrupt sediment continuity and reduce sediment supply downstream. In this regard, dam removal is an increasingly used river restoration measure to recover longitudinal connectivity of sediment, among many other river processes. In this work we present a 6-year (from 2016 to 2022) monitoring of bedload transport before, during and after the removal of the 7-meters high Olloki dam in the Leitzaran River (Basque Country). The removal process started in 2018 with the upper 3 m and was completed in 2019 with the remaining 4 m of the dam. To monitor bedload transport, we seeded RFID-tagged stones in three reaches: a control reach unaffected by the dam, a reach immediately upstream of the dam, and a reach downstream of the dam. We deployed 300 tagged stones each year (100 by reach), i.e., 1800 in total. We measured important mobilization and displacement of tracer stones (with maximum travel distances of ∼8.8 km of tracers seeded upstream the Olloki dam) during an active hydrological year following the complete removal of the dam, with some tagged particles even travelling across a downstream weir. We also reported changes in the progression of tagged stones in the dam-affected reaches (upstream and downstream) with the removal, with further and faster dispersal of sediments once the dam was removed. In addition, in these reaches we estimated larger volumes of mobilized bedload in the three years following removal than in the previous years, especially in the upstream reach. In this regard, the relationship between bedload and cumulated energy suggests that less energy was expended in the upstream reach for mobilizing bedload once the removal of the dam was completed. Conversely, in the control reach no major changes were observed before and after the removal of the dam; this reach showed only an increase in sediment mobilization during the last hydrological year, which was the most hydrologically active of the whole monitoring period. In summary, our tracer observations document that travel distances and mobilization volumes are considerably increased with dam removal, especially once the dam was completely removed. • Bedload transport is affected by the presence of dams. • Pit-tagged particles are used to monitor bedload transport. • Monitoring is done before, during and after dam removal with a BACI approach. • Travel distances and mobilization volumes increase with dam removal. • Dam affected reaches react especially to dam removal. [ABSTRACT FROM AUTHOR]

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]

• About 70% of eroded sediments remains stored within the catchment. • Initiation of soil erosion from the Neolithic and acceleration over the last 3 millennia. • A long gap is observed between the forest clearance, soil erosion and the acceleration of alluvial filling. • Alluvial sedimentation rate indicate changes in efficiency of the connectivity rather soil erosion intensity. • A sediment budget is needed to evaluate the significance of soil erosion. To contribute to the understanding of Holocene sediment dynamics in Western Europe, a Holocene sediment budget is proposed for the Thue and Mue catchments (52 and 97 km2 respectively) located in NW France. In this budget, soil erosion as well as colluvial sediment storage is estimated from soil profiles analysis for a representative catchment and extrapolated to the entire catchments. Alluvial sediment storage, including a chronology of the alluvial fills, has been quantified by augerings cores distributed on several transects located along the floodplain of the two rivers. The proposed sediment budget highlights significant sediment storage in the catchment: 12.3 Mt (32.5 %) is stored as colluvium and 15.5 Mt as alluvium (40.8 %), i.e. more than 70 % of eroded sediments on the slopes. The remaining eroded sediments (10.2 Mt) are considered to have been exported out of the catchments. The timing of slope erosion and colluvial storages indicates the initiation of soil erosion from the Neolithic period and an acceleration over the last 3 millennia. However, a long gap is observed between forest clearance, soil erosion and the acceleration of alluvial filling underlying a progressive improvement of the connectivity induced by a progressive transformation of the running water circulation within the catchment. The results thus highlight the complexity of Holocene sediment dynamics across spatial and temporal scales and emphasize the necessity to integrate the question of the efficiency of the sediment cascade particularly induced by the landscape structure and drainage density. [ABSTRACT FROM AUTHOR]