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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]

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]

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]

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]

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• 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]

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]

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]

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]

In this article we apply the CASCADE network-scale sediment connectivity model to the Vjosa River in Albania. The Vjosa is one of the last unimpaired braided rivers in Europe and, at the same time, a data scarce environment, which limits our ability to model how this pristine river might respond to future human disturbance. To initialize the model, we use remotely sensed data and modeled hydrology from a regional model. We perform a reach-by-reach optimization of surface grain size distribution (GSD) and bedload transport capacity to ensure equilibrium conditions throughout the network. In order to account for the various sources of uncertainty in the calculation of transport capacity, we performed a global sensitivity analysis. The modeled GSD distributions generated by the sensitivity analysis generally match the six GSDs measured at different locations within the network. The modeled bedload sediment fluxes increase systematically downstream, and annual fluxes at the outlet of the Vjosa are well within an order of magnitude of fluxes derived from previous estimates of the annual suspended sediment load. We then use the modeled sediment fluxes as input to a set of theoretically derived functions that successfully discriminate between multi-thread and single-thread channel patterns. This finding provides additional validation of the model results by showing a clear connection between modeled sediment concentrations and observed river morphology. Finally, we observe that a reduction in sediment flux of about 50% (e.g., due to dams) would likely cause existing braided reaches to shift toward single thread morphology. The proposed method is widely applicable and opens a new avenue for application of network-scale sediment models that aid in the exploration of river stability to changes in water and sediment fluxes. [ABSTRACT FROM AUTHOR]

The production of coarse sediment in mountain landscapes depends mainly on the type and activity of geomorphic processes and topographic and natural conditions (e.g. vegetation cover) of these catchments. The supply of sediment from these slopes to mountain streams and its subsequent transport lead to sediment connectivity, which describes the integrated coupled state of these systems. Studies from the Northern Calcareous Alps show that the size of the sediment contributing area (SCA), a subset of the drainage area that effectively delivers sediment to the channel network, can be used as a predictor of sediment delivery to mountain streams. The SCA concept is delineated on a digital elevation model (DEM) using a set of rules related to the steepness and length of slopes directly adjacent to the channel network, the gradient of the latter and the vegetation cover. The present study investigates the applicability of this concept to the Western Alps to identify geomorphologically active areas and to estimate mean annual sediment yield (SY) in mainly debris‐flow‐prone catchments. We use a statistical approach that shows a parameter optimisation and a linear regression of SY on SCA extent. We use a dataset of ~25 years of assessed coarse sediment accumulation in 35 sediment retention basins. In the investigated catchments, sediment transport is governed by several factors, mainly by the extent of vegetation‐free areas with a minimum slope of 23° that is coupled to the channel network with a very low gradient of the latter. With our improved framework, we can show that the SCA approach can be applied to catchments that are widely distributed, in a large spatial scale (hectare area) and very heterogeneous in their properties. In general, the investigated catchments show high connectivity, resulting in significant correlations between long‐term average yield and the size of the SCA. [ABSTRACT FROM AUTHOR]

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

The connection between deltaic clinothem growth and the formation of down-dip deep-water systems on continental margins has been extensively discussed as a crucial component of sequence stratigraphic theory. However, in lacustrine settings, the growth of deltaic clinothems and outlying deep-water fans remains comparatively poorly understood. In the southwestern Bozhong Sag, Bohai Bay Basin, China, both lacustrine deltas and outlying sub-lacustrine fans were developed during the Oligocene, providing an opportunity to investigate the connection between lacustrine deltaic clinothem growth and the formation of outlying sub-lacustrine fans in deep-lacustrine systems. We employ 3D seismic data, well data, core data, and sandstone grainsize data to analyze the stacking patterns and internal architectures of these two sedimentary systems in the lower and upper successions of our study interval, SQE d 2 L. In addition, elemental geochemical parameters were utilized to reveal the paleoclimatic signature of the different stratigraphic successions. Our results suggest that there are two main types of deltaic clinothem stacking patterns in the lower and upper successions of SQE d 2 L, respectively: (1) in the lower succession, progradational to aggradational stacking patterns have a flat to steeply rising rollover trajectory, and (2) in the upper succession, aggradational to progradational and degradational stacking patterns have a slightly rising to flat and slightly falling trajectory. Meanwhile, the sub-lacustrine fans with straight channels and thick lobe complexes are coupled with progradational and aggradational (PA) deltaic clinothems in the lower succession. In the upper succession, small-scale sub-lacustrine fans with sinuous channels and thin lobe complexes are coupled with aggradational to progradational and degradational (APD) deltaic clinothems. The sediment connectivity between lacustrine deltas and sub-lacustrine fans stands in stark contrast to their counterparts in marine basins (such as marine APD clinothems coupled with large-scale deep-water fans, while marine PA clinothems rarely produce deep-water fans). In addition, two contrasting paleoclimatic stages have been identified in SQE d 2 L, namely the earlier humid stage in the lower succession and the later semiarid climatic stage in the upper succession. A comprehensive analysis of the differences between lacustrine and marine basins indicates that climatic variations play a pivotal role in deep-lacustrine deposition. Consequently, a climate-cycle-driven, sediment-supply-dominated sedimentary model of delta-to-fan sediment connectivity is proposed that incorporates the efficiency of terrigenous sediment dispersal into deep-lacustrine floors and the architecture of sub-lacustrine fans. The findings of this study further refine the implementation of the sequence stratigraphy paradigm and enhance the understanding of delta-to-fan sediment connectivity in deep-lacustrine depositional systems. • The scale of deep-water fans is coupled with various lacustrine deltaic clinothems. • Sediment connectivity of delta-to-fan in lacustrine basins is opposite to marine. • Climatic variations regulate sediment-supply and deep-lacustrine deposition. • Humid climates led to increased sediment connectivity between deltas and fans. [ABSTRACT FROM AUTHOR]

Climate, edaphic, and physiographic parameters influence wine quality. In this study, we evaluated if climate and sediment connectivity had an effect on the grapevine yield (GY) and wine quality of three ancient (more than 100 years old) vineyards, with 'Garnacha Tinta' variety, managed using the head-pruned system, and during three agronomic years (October 2015 - September 2018). The three rain-fed vineyards are managed using the head-pruned system and named VA (1233 vines), VB (1584 vines) and VS (897 vines). They are located in the Spanish Pyrenees, with oceanic Mediterranean climate, have the same soil type (Haplic Cambisol) and the soil is ploughed to prevent weeds. GY ranged from 380 to 2646 kg·ha-1, and from 0.08 to 0.60 kg·vine-1. The annual production significantly correlated with the total annual rainfall (positive), and with the air temperature during the growing period (negative). A frozen spell and intense rainfall events in spring explained the lower GY observed in 2017 and 2018, respectively. We observed a good correlation between GY (kg·ha-1) in 2018 and wine parameters such as, pH (r = 0.992), titratable acidity (r = -0.862), malic acid (r = 0.979), and potassium (r = 0.998). Annual runoff and sediment connectivity was estimated at each field (and its upslope drainage area) using the aggregated index of connectivity (AIC) at high spatial resolution (1 m of cell size). The lowest connectivity was found in VB, whereas VA and VS presented moderate and high values of connectivity, respectively. AIC correlated very well and negatively with GY (kg·ha-1, r = -0.955; and kg·vine-1, r = -0.972). Higher connectivity - intense overland flow dynamic - favoured lower yield. We concluded that the climate parameters mainly explained the temporal changes of GY, whereas distinct overland flow connectivity clearly influenced the spatial variations of GY under the same climatic conditions. [ABSTRACT FROM AUTHOR]

Abstract The study of sediment connectivity based on the geomorphic characteristics of the watershed has gained interest during the last decades. The calculation of connectivity indexes for a mountainous watershed that is normally susceptible to landslides allows the recognition of the unstable areas that have higher connection to any point such as the watershed outlet. Thus, the knowledge of spatial patterns of connectivity within the watershed is very useful in the sediment-related disaster management because the connectivity provides useful information on sediment pathways. The objective of the present study was to test four different global DTMs to compute the sediment connectivity index (IC) in the Mascarada river watershed (320 km2), southern Brazil. By analyzing the land use for each pixel, the Manning roughness was determined and used for the weighting factor in IC calculation. Field survey and satellite image analysis showed that 420 landslides occurred in this watershed on January 5th, 2017. The calculated IC value maps demonstrated that the hillslopes with landslide occurrences have higher values of IC. Among the tested DTMs, the one with the highest resolution (12.5-m resolution DTM) showed the best representation of the flow paths with high IC values. For all the resolutions, the IC mean values of the landslides scars were larger compared to the remaining area of the hillslopes, where the landslides occurred, which implies higher connectivity of the landslides to the watershed outlet. The results also showed that the 12.5-m resolution DTM generated the lowest mean and the largest amplitude of IC values, differentiating areas with high and low connectivity. It is concluded that the global DTM (12.5-m) is capable to provide important information on sediment connectivity and that together with a landslide inventory it can be an important tool for sediment management in mountainous watersheds. Highlights • We tested four different global DTMs in the sediment connectivity calculation. • The higher values of IC were found on hillslopes with landslide occurrences. • The global DTM (12.5 m) can provide important information about sediment connectivity. [ABSTRACT FROM AUTHOR]

Purpose: Rain storm events mobilise large proportions of fine sediments in catchment systems. Sediments from agricultural catchments are often adsorbed by nutrients, heavy metals and other (in)organic pollutants that may impact downstream environments. To mitigate erosion, sediment transport and associated pollutant transport, it is crucial to know the origin of the sediment that is found in the drainage system, and therefore, it is important to understand catchment sediment dynamics throughout the continuity of runoff events.Materials and methods: To assess the impact of the state of a catchment on the transport of fine suspended sediment to catchment outlets, an algorithm has been developed which classifies rain storm events into simple (clockwise, counter-clockwise) and compound (figure-of-eight; complex) events. This algorithm is the first tool that uses all available discharge and suspended sediment data and analyses these data automatically. A total of 797 runoff events from three experimental watersheds in Navarre (Spain) were analysed with the help of long-term, high-resolution discharge and sediment data that was collected between 2000 and 2014.Results and discussion: Morphological complexity and in-stream vegetation structures acted as disconnecting landscape features which caused storage of sediment along the transport cascade. The occurrence of sediment storage along transport paths was therefore responsible for clockwise hysteresis due to the availability of in-stream sediment which could cause the "first flush" affect. Conversely, the catchment with steeper channel gradients and a lower stream density showed much more counter-clockwise hysteresis due to better downstream and lateral surface hydrological connectivity. In this research, hydrological connectivity is defined as the actual and potential transfer paths in a catchment. The classification of event SSC-Q hysteresis provided a seasonal benchmark value to which catchment managers can compare runoff events in order to understand the origin and locations of suspended sediment in the catchment.Conclusions: A new algorithm uses all available discharge and suspended sediment data to assess catchment sediment dynamics. From these analyses, the catchment connectivity can be assessed which is useful to develop catchment land management. [ABSTRACT FROM AUTHOR]

Abstract Sheet, rill and gully erosion occurring in the snowmelt period (March–April) and rainfall season (May–September) is the main factor of soil degradation and mobilized hillslope sediment redistribution within cultivated lands of the Russian Plain. The evaluation of sediment redistribution for the period since 1986 within catchment sediment cascades was done based on an integrated approach for some representative dry valley catchments located in the western (the Plava River basin, Tula Oblast, Russian Federation) and eastern (the Temeva Rechka Creek catchment, the Myosha River basin, Republic of Tatarstan, Russian Federation) sectors of the forest-steppe landscape zone of the Russian Plain. All the catchments studied are characterized by a high proportion (within the range of 60–80%) of cultivated lands. The modified version of the Universal Soil Loss Equation (USLE), the Russian State Hydrological Institute's erosion model, and the LandSoil erosion model were applied to calculate soil losses within the cultivated lands. The morphological classification of interfluve slopes and hollow slope catchments, in combination with the sediment delivery ratio (SDR) assessment for slopes and hollow slope catchments of different configuration, were used to assess sediment transfer from the cultivated lands. The Chernobyl-derived 137Cs isotope was applied as a chronomarker for sediment dating in different sediment sinks located along pathways from cultivated slopes to river valley bottoms. We found that the morphological features of the dry valley catchments, including a pattern of the dry valleys of different Hortonian orders, dry valley and hollow density, dry valley incision depth, and proportion of slopes and hollow slope catchments of different configurations are the main parameters that determined a proportional input of the different sediment sinks to the sediment interception along the pathways from the cultivated slopes to the river valley bottoms. The land use/cover features are mostly responsible for the pattern of buffer zones within the interfluve parts of the catchments. The quantitative assessment of the sediment budget allowed us to conclude that the mean SDR coefficients for the dry valley catchments of second, third, and fourth Hortonian orders are 0.56, 0.33, and 0.07 respectively. The extrapolation of the study results of sediment redistribution evaluation, obtained from the studied catchments located within the Plava River basin, to the entire basin of the river also allowed us to evaluate the mean value of hillslope-to-river-valley-bottom SDR = 0.27. Highlights • Soil erosion is a driver of denudation within cultivated lands of the Russian Plain. • Dry valley bottoms are the main sediment sink in cultivated catchments in the region. • Only about 1/3 of mobilized hillslope sediments are delivered to regional river bottoms. [ABSTRACT FROM AUTHOR]

Riverine biological communities are highly resilient to extreme flood and/or drying disturbance regimes that would otherwise be destructive because these organisms can recolonise from upstream, floodplain, or hyporheic refugia when suitable conditions return. Healthy rivers require a high degree of connectivity to support complex life cycles of many lotic organisms and associated ecosystem functioning. Similarly, connectivity is required for appropriate geophysical functioning; permitting flux of water and sediment that drives channel-forming and ecological processes. Ecological and geophysical processes have operated in this temporal and spatial patchwork of disturbance and recovery pre-Anthropocene. Human impacts are increasing constraints on river and floodplain connectivity, severing many natural pathways, and degrading river ecosystem functioning. River restoration seeks to re-establish some of those biological and physical connections to enhance some level of system health. However, increasing sediment connectivity may be detrimental to river health in some instances. Strongly connected catchments can transmit excessive quantities of sediment from inappropriate land management, detrimental invasive species can spread more widely, and many ecosystem processes can exceed positive feedback control. Simply restoring connectivity will not necessarily lead to healthy river ecosystems. River management requires a greater understanding of how and when connectivity can and should be restored. Although current thinking is often that greater connectivity is better, we illustrate with examples from New Zealand rivers that this is not always the case. The benefits and costs of maintaining or restoring river connectivity need to be given as much attention as the restoration and maintenance of river systems per se. [ABSTRACT FROM AUTHOR]

Abstract: Connectivity has become an increasingly used concept in hydrological and sediment research. In order to quantify it, various indices have been proposed since the start of the 21st century including the index of connectivity. This index is based on a limited number of factors, the most important one being topography. Sediment connectivity indices values probably depend on the digital elevation model (DEM) resolution. The aim of this study was, first, to compare the effect of DEM pixel size (between 0.25 and 10 m, using an UAV) in the Belgian loess belt, a lowland area. We show that the index values were lower when the pixel size decreased (a difference of about 20% in value between 0.25 and 10 m). In addition, the impact of linear features in the watershed (e.g. grass strip, bank and road) was lower with the largest pixel sizes, and the connectivity pattern was affected with a pixel size of 5 m or more. At lower pixel sizes (1 m or below), some more disconnected regions appeared. These corresponded with zones where there had been water stagnation during and after rainfalls, and was corroborated by field observations. This confirmed the need for a proper resolution according to the objectives of the study. The second aim of this study was to deduce a minimum pixel size for connectivity study, helping local erosion or sedimentation location and consequent land management decisions. In our context, 1 m stands as the optimum DEM resolution. This pixel size permitted location of all ‘key areas’ in terms of erosion. Very high resolutions (<0.5 m) did not generate much more information, and their calculation time was far greater. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Understanding integrated hydrological phenomena in catchments is difficult because of the fragmented nature of soil physical and hydrological data, given these are typically derived from pedons or small plots. Runoff plot and lysimeter or pedon-scale studies do not capture the complexity of surface and subsurface flowpaths in hillslopes. Because pedon/plot scale results are not easily transferable to hillslope and catchment scales, theoretical and empirical approaches to quantify hydrological dynamics based on such ‘point-scale’ data tend to over- or underestimate parameters and fluxes. Unit area sediment flux measured during storms typically (but not always) decreases from small plots to hillslopes owing to sediment deposition and re-infiltration of overland flow in localized areas. At broader scales, re-entrainment of previously stored sediment complicates this generalization, as may the development of rill and gully systems, facilitated by overland flow concentration. Quantifying mass wasting and sediment interactions in channels presents different temporal and spatial challenges, and must be assessed at the catchment scale. Process-based scaling requires an over-arching integration of different hydrogeomorphic concepts and approaches. Nested catchment studies, where processes are monitored at different scales, represent an opportunity to elucidate the diverse spatial and temporal patterns of water and sediment behaviour. The spatial scale dependence inherent in many pedology and catchment hydrology studies can be overcome by incorporating hydrogeomorphic, pedological, and connectivity concepts that demonstrate how soil hydraulic parameters, geomorphic controls, and water/sediment routing change from plot to hillslope to catchment scales. The resulting self-organization generates spatial and temporal dependencies and provides a paradigm to better understand, model, and assess management effects on water and sediment fluxes and pathways in the continuum from plots to catchments. [ABSTRACT FROM AUTHOR]

Climate-driven increase in the frequency of extreme hydrological events is expected to impose greater strain on the built environment and major transport infrastructure, such as roads and railways. This study develops a data-driven spatial-statistical approach to quantifying and mapping the probability of flooding at critical road-stream intersection locations, where water flow and sediment transport may accumulate and cause serious road damage. The approach is based on novel integration of key watershed and road characteristics, including also measures of sediment connectivity. The approach is concretely applied to and quantified for two specific study case examples in southwest Sweden, with documented road flooding effects of recorded extreme rainfall. The novel contributions of this study in combining a sediment connectivity account with that of soil type, land use, spatial precipitation-runoff variability and road drainage in catchments, and in extending the connectivity measure use for different types of catchments, improve the accuracy of model results for road flood probability. [ABSTRACT FROM AUTHOR]

Knowledge of geomorphic characteristics and sediment connectivity is critical in understanding basin-scale surface processes that include steep mountainous and flat lowlands, particularly if the mid-basin and downstream areas are densely populated and disaster-prone. However, the lack of fluvial and sediment connectivity studies in downstream portions of large rivers of South Asia (particularly Bangladesh), where upper basin morphodynamics, hydrology, and sediment flux highly influence the repeated sediment disasters, limits our understanding of the large-scale fluvial geomorphic processes and basin-scale sustainable river management. Therefore, this article attempts to characterize the morphometric and topographic features along with the spatial sediment connectivity pattern of the middle Brahmaputra River basin (Teesta, Torsa, and Manas basins) covering ~75,000 km2 that influences the hydro-geomorphic response of the deltaic landscape of lowland Bangladesh. This work considers a set of morphometric and topographic parameters including the stream network, longitudinal profiles, stream power index (SPI), and topographic wetness index (TWI) for geomorphometric characterization. The linkage between the sediment sources to downstream areas also has been evaluated with the sediment connectivity (IC) index to understand better the sediment dynamics of the middle Brahmaputra River basin, draining towards lowland Bangladesh from the basin's upstream countries of India and Bhutan. The result of this study demonstrates a highly potential hydro-geomorphic response of the downstream areas attributed to steep topography, steep channel longitudinal profiles, high rainfall, and high sediment connectivity in upstream regions. However, the low topography, presence of anthropogenic stressors, almost flat longitudinal channel profiles with limited change in elevation, and lowered sediment connectivity potential in the mid-to-downstream areas depicts sensitivity to the depositional processes therein, impacting the basin-scale geomorphic connectivity from the upstream to the downstream region. These results will be the basic information for exploring the large-scale hydro-geomorphic response and structural sediment dynamics to understand the complex geomorphological processes in the South Asia region, where the fluvial sedimentation process is not fully understood with limited accessibility for field-based investigations. [Display omitted] • Morphodynamics and sediment connectivity patterns are key determinants of fluvial-sediment dynamics in Brahmaputra River basin. • The sediment connectivity varies across the basins and is highly influenced by the upstream's hydro-geomorphic responses. • Partial connectivity or (dis)connectivity in mid-to-downstream is sensitive to deposition, impacting geomorphic linkage. • Understanding large-scale geomorphic processes is required for sustainable river management in disaster-prone South-Asia. [ABSTRACT FROM AUTHOR]

Sediment pulses are triggered through a variety of mechanisms, from landslides to land use change. How do these pulses move through the fluvial system, and how do they evolve? In a system with perfect sediment connectivity, the erosional response to a perturbation and the resulting signal at the river mouth would match, however, this rarely occurs. Many studies have addressed reach-scale dynamics of sediment pulses and how they translate or disperse downstream. At the watershed scale, network structure and storage become more important in modulating the sediment signal. Here, we review the current literature on sediment pulse behavior, and then address the role of network structure on maintaining, dispersing, or transforming sediment pulses in a fluvial system. We use a reduced-complexity network routing model that simulates the movement of bed material through a river basin. This model is run in the Greater Blue Earth River (GBER) basin in Minnesota, USA, first with spatially uniform inputs and then with inputs constrained by a detailed sediment budget. Once the system reaches equilibrium, a sediment pulse is introduced, first at a single location and then throughout the system, and tracked as it evolves downstream. Results indicate that pulses able to translate downstream disperse in place upon arriving at over-capacity reaches as sediment goes into storage. In the GBER basin, these zones occur just upstream of a knickpoint that is propagating upstream through all mainstem channels. As the pulses get caught in these sediment “bottlenecks,” there is a decoupling of the original pulse of sediment and the resulting bed material wave. These results show that the network structure, both in terms of network geometry and the spatial pattern of transport capacity, can play a dominant role in sediment connectivity and should be considered when predicting sediment pulse behavior at the watershed scale. [ABSTRACT FROM AUTHOR]

In the twenty-first century, fluvial geomorphologists are ideally placed to use their science in an applied manner, and provide guidance on environmental issues of concern. Understanding the impact of floods and droughts, land use and climate change, water use, etc. on river forms, processes and evolution requires that we understand interactions between water, sediment and vegetation, and how climate and anthropogenic impacts shape those interactions. More frequently, fluvial geomorphologists are asked to provide answers to a range of river issues, make forecasts about how systems might adjust in the future, and work with managers to implement strategies on-the-ground. To some, the field of fluvial geomorphology is underprepared for this task as several principles of landscape form, process and evolution are yet to be fully explored. Others however, see that geomorphologists have a suite of principles and tools at their disposal, and sufficient understanding to make forecasts about future river adjustments with some level of confidence. One concept that has been lost in recent years, but should lie at the heart of such analyses is that of river sensitivity. In this paper I draw on foundation literature to review the concept of river sensitivity. I provide examples that demonstrate how this concept could be reshaped and used for analyses at landform, reach and catchment scales. At the landform scale, morphological sensitivity is a function of textural and geometric sensitivity. At the reach scale, analyses consider inherent behavioural and change sensitivity. At the catchment scale river response and recovery are a function of locational, transmission and filter sensitivity. I then discuss how some temporal concepts can be used to consider how sensitivity in itself adjusts over time. Finally, I discuss future challenges for analysis of river sensitivity and consider how it could be used to improve geomorphological forecasting for use in river management. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The transfer of sediments through the landscape (sediment connectivity) depends on hydrological conditions. This study aimed at assessing changes in sediment sources engendered under extreme drought. A sediment budget model that considered hillslope sediment connectivity was applied to the Latrobe River catchment (South-east Australia) in a relatively normal period (1990–1996) followed by part of the ‘Millennium Drought’ (1997–2005). Bayesian inference was applied to optimize monthly streamflow and calibrate sediment parameters against mean annual specific sediment yields at ten monitoring stations. In 1990–1996, assessed sediment yield at the outlet was 68 kt/y; 60% of sediments originated from net hillslope erosion and 40% from streambank erosion. In 1997–2005, sediment yield decreased to 13 kt/y, 27% from net hillslope erosion against 65% from streambank erosion. During the drought, both hillslope gross erosion and hillslope sediment connectivity decreased dramatically. Streambank protection is of the utmost importance under all hydrologic conditions and especially during drought periods. [ABSTRACT FROM AUTHOR]

In this study, we quantified spatial patterns of sediment dynamics in a watershed of 311 km 2 over an extreme storm event using watershed modeling and statistical analyses. First, we calibrated a watershed model, Dynamic Watershed Simulation Model (DWSM) by comparing the predicted with calculated hydrograph and sedigraph at the outlet for this event. Then we predicted values of event runoff volume ( V ), peak flow ( Q peak ), and two types of event sediment yields for lumped morphological units that contain 42 overland elements and 21 channel segments within the study watershed. Two overland elements and the connected channel segment form a first-order subwatershed, several of which constitute a larger nested subwatershed. Next we examined (i) the relationships between these variables and area ( A ), precipitation ( P ), mean slope ( S ), soil erodibility factor, and percent of crop and pasture lands for all overland elements (i.e., the small spatial scale, SSS), and (ii) those between sediment yield, Q peak , A , P , and event runoff depth ( h ) for the first-order and nested subwatersheds along two main creeks of the study watershed (i.e., the larger spatial scales, LSS). We found that at the SSS, sediment yield was nonlinearly well related to A and P , but not Q peak and h ; whereas at the LSS, linear relationships between sediment yield and Q peak existed, so did the Q peak – A , and Q peak – P relationships. This linearity suggests the increased connectivity from the SSS to LSS, which was caused by ignorance of channel processes within overland elements. It also implies that sediment was transported at capacity during the extreme event. So controlling sediment supply from the most erodible overland elements may not efficiently reduce the downstream sediment load. [ABSTRACT FROM AUTHOR]

The Dadu River Basin (DRB) is an important economic corridor on the Chuanxi Plateau. The DRB is located in the highly changeable terrain of the eastern Qinghai-Tibet Plateau and is often threatened by debris flows. To mitigate the damage of debris flow disasters to the construction and operation of large infrastructures such as railways, roads and hydropower stations in the DRB, it is necessary to evaluate debris flow susceptibility. The connectivity of potential material sources (CPMS), which proxies the possibility of potential material transfer from the source to the outlet, was calculated using an improved index of connectivity, excess topography and brittle fracture index to identify and quantify debris flow susceptibility. The results show that the IC and the gully scale have a Logartihmic function in the DRB, in which IC decreases as the catchment area increases. In 3967 gullies of the Dadu River and its tributaries, the total connectivity of potential material sources (TCPMS) could be used to distinguish between debris flow gullies and non-debris flow gullies (AUC = 0.748). The TCPMS and average connectivity of potential material sources (ACPMS) were used to classify the scale and activity intensity of the 2398 debris flow gullies into four levels. The moderate- and high-activity intensity and large- and extra large-scale debris flows are mainly distributed in Danba, Luding and Kangding. The results of this study provide reference and evidence for the identification and evaluation of debris flow susceptibility. • A new method for assessing debris flow susceptibility based on potential material sources and sediment connectivity. • The quantitative relationship between the scale of debris flow and conditioning factors. • The contribution of excess topography was considered. [ABSTRACT FROM AUTHOR]

Purpose: Catchments subject to land clearance, soil tillage and grazing suffer legacy effects from altered sediment and hydrological regimes and from changes in sediment connectivity between hillslopes and channels. Sediment dynamics are routinely investigated using the fallout radionuclides (FRNs) caesium-137 (Cs) and excess lead-210 (Pb), which provide information regarding sediment sources and fluvial processes if source types are differentiated with confidence. Downstream transport, mixing and dilution of FRN-labelled fine sediment can obliterate the tracer signal from sources with low initial concentrations, so geomorphic evidence for downstream changes in sediment source types, mixing and fluvial (dis)connectivity should be used with tracers to ascertain the degree of sediment source variation and dominant fluvial processes. Materials and methods: We coupled sediment source tracing with a geomorphic assessment of downstream hydrological, morphological and sedimentological change to quantify key components of fluvial (dis)connectivity in Coolbaggie Creek, a major source of sediment to the Macquarie River, southeastern Australia. Results and discussion: Cs and Pb discriminated between the <63-μm fraction of topsoils from agricultural and forested land (mean ± standard error of Cs is 5.7 ± 1.1 Bq kg and of Pb is 76.2 ± 22.4 Bq kg) and subsoils from channel banks and gullies (Cs = 1.5 ± 0.5 Bq kg; Pb = 3.6 ± 2.4 Bq kg). In-channel sediment was a mix of these two source types (Cs = 0.9 ± 0.3 Bq kg; Pb = 18.8 ± 6.8 Bq kg). FRN concentrations also declined significantly downstream. Mixing model results show topsoils account for 39 % (95 % confidence interval (CI) = 21-88 %) of fine in-channel sediment in the upper reaches, but this declines to 2 % (CI = 0-19 %) after 25 km, and thereafter, subsoils account for an estimated 100 % of fine sediment in the system. This rapid decrease in topsoil contributions coincides with a downstream change in hydrogeomorphic character, including large increases in channel cross-sectional area (∼20 to >200 m) and unit stream power (5.4 to 1,382 W m), and evidence of greater subsoil and reworked sediment contributions from bank and gully erosion. Limited topsoil supply to the trunk stream suggests low catchment erosion rates and reduced connectivity between the catchment and the river. Enlargement and entrenchment of the trunk stream in the lower reaches have resulted in lateral channel-floodplain disconnection, while a sediment slug impedes longitudinal coarse sediment transfer. Conclusions: Hydrogeomorphic change and sediment source variations downstream explain the short-term sediment dynamics in this agricultural catchment, which has broader implications for understanding sediment transport processes and fluvial (dis)connectivity when interpreting sediment source and tracer data. [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]

Quantification and characterization of hydrological and sedimentary transfers are now major challenges to preserving European soils and water resources ( Law on Water, Water Framework Directive). In northwestern France, stream water quality is currently reduced by suspended sediment. However, in these low-energy water systems, sediment origin and dynamics into the catchment remain difficult to analyze from a local to a regional scale because of intermediary traps caused by landscape structure (hedgerow areas) and land use organization on the slopes. To provide a better understanding of sediment dynamics in these systems we proposed to analyze runoff dynamics on slopes and to assess slopes' contribution to the sediment budget of a catchment. This study is based on sediment connectivity analysis, used to accurately determine runoff dynamics between producing areas and the outlet of the catchment. This work is focused on the Lingèvres catchment (15 km2), a typical feature of the low-energy water system located in the western part of France, in between open-field and bocage landscapes. The results demonstrate that in a hedgerow landscape, known for its protective role against runoff connection to the river, sediment delivery from slopes is more important and efficient than in an open-field area where no obstacles are observed. This is explained by diverse drainage densities and spatial organization of roads, and ditch and plot entries which induced differentiated sediment delivery from agricultural plots and the river. However, they also underlined the weakness of sediment delivery from slopes compared with sediment fluxes exported from the catchment. Conversely, they highlight the fundamental role of erosion processes due to agricultural practices and landscape organization in headwater systems, which seem to be the main functional area at the sub-catchment scale. [ABSTRACT FROM AUTHOR]

The efficiency of sediment routing through mountain sediment cascades is controlled by the connectivity of hillslopes to the main river system. A lack of connectivity may cause long-term sediment storage and exclude large fractions of a basin from the sediment routing for several thousand years. Here, we studied sediment dynamics in a small, formerly glaciated valley in the Swiss Alps. To characterise the sediment connectivity to the stream, we calculated a morphometric index using a GIS algorithm. The modelling results were tested against a field based geomorphic mapping of sediment storages, which were evaluated with respect to their state of (de)coupling. In accordance to the field diagnostics, the modelling results indicate very well that the present-day sediment flux is conditioned by the glacial valley morphometry inherited through Pleistocene glaciation. Especially in the upper hanging valleys, the connectivity index is reduced noticeably due to the glacial cirque morphology. Based on the field mapping, 30% of the hillslope sediment cascades are interrupted and 20% of the storage boundaries are currently affected by a lack of material transfer. As a consequence, ~29% of the basin surface is currently disconnected from the main river. Nevertheless, the GIS algorithm overestimates the connectivity within the basin, because it fails to calculate decoupling between neighbouring pixels in digital terrain models (DTMs). Around 35% of the basin surface, which has been mapped in the field as being decoupled, is related to relative high connectivity. Our study highlights the potential of morphometric GIS modelling for studying sediment connectivity, but additionally emphasises the indispensability of geomorphic field mapping for a holistic understanding of mountain cascading systems. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents two new definitions of sediment and water flux connectivity (from source through slopes to channels/sinks) with examples of applications to sediment fluxes. The two indices of connectivity are operatively defined, one (IC) that can be calculated in a GIS environment and represents a connectivity assessment based on landscape''s information, and another that can be evaluated in the field (FIC) through direct assessment. While IC represent a potential connectivity characteristic of the local landscape, since nothing is used to represent the characteristics of causative events, FIC depend on the intensities of the events that have occurred locally and that have left visible signs in the fields, slopes, etc. IC and FIC are based on recognized major components of hydrological connectivity, such as land use and topographic characteristics. The definitions are based on the fact that the material present at a certain location A reaches another location B with a probability that depends on two components: the amount of material present in A and the route from A to B. The distance to B is weighted by the local gradient and the type of land use that the flow encounters on its route to B, while the amount of material present in A depends on the catchment surface, slope gradient and type of land use of said catchment. Although IC and FIC are independent from each other, and are calculated using different equations and different inputs, they complement each other. In fact, their combined use improves IC''s accuracy. Hence, connectivity classes can afterward be rated using IC alone. This procedure has been applied in a medium-size watershed in Tuscany (Italy) with the aim of evaluating connectivity, identifying connected sediment sources and verifying the effects of mitigation measures. The proposed indices can be used for monitoring changes in connectivity in areas with high geomorphological or human induced evolution rates. [Copyright &y& Elsevier]

The Mazeri Valley in the southern Caucasus Mountains, Georgia, is characterized by a highly dynamic landscape with several active mass-wasting processes. The spatial and temporal dynamics of these geomorphic processes have, over time, resulted in the formation of large cones and fans. In this context, the coupling between the hillslope and the channel plays a fundamental role in controlling the catchment sediment dynamics. The sediment produced at higher altitudes on hillslopes may occasionally reach the debris-flow channel network, and downstream propagation may have significant effects on the fluvial environment and create potential hazards for the population and infrastructure. In this regard, we report a tree-ring-based chronology of the debris-flow activity on a large cone to shed light on sediment connectivity and better understand the coupling between the main debris-flow channel and a bedload river in this remote area under global climate change and glacial retreat. The 161 sampled trees demonstrated the appearance of 12 significant events over the last 65 years, with all of the events involving possible sediment input into the stream system of the Dolra River. These successional events, with a return interval of 5.4 years, have partially destabilized the fluvial system and locally induced a switch in the channel style to a braided channel. Surficial sedimentary characteristics, such as morphometric indices, have enabled the discrimination between sediments from the debris-flow activity and river dynamics (alluvium inputs). Finally, most of the reconstructed event-years are characterized by at least one month of above-average rainfall. • The coupling between channelized debris flows and fluvial network was analyzed. • Tree-ring reconstruction of debris flows indicates a return period of 5.4 years. • Sediment inputs in the river induced a switch in channel style to a braided channel. • The roundness index of clasts enables discrimination of sediment sources. [ABSTRACT FROM AUTHOR]

Because connectivity is a key issue for understanding sediment dynamics in catchments, the index of sediment connectivity (IC) can be an important tool for hydrosedimentological studies. The IC depends on factors that promote (upslope area and slope) or reduce connectivity (downslope distance and impedance). Among these factors, the estimation of impedance is the one that offers more obstacles, mainly related to its dependence on characteristics difficult to assess (i.e., the effect of vegetation). The present study aims to propose a new approach to calculate the weighting factor of impedance (W), used in the IC calculation, and to compare its performance with three other approaches by constructing IC maps for a forested catchment. The new approach uses an index called Relative Smoothness (RS), based on the Manning coefficient (n) that preserves the dimensionlessness of the Index. The study area is the Mascarada River catchment (320 km2) in Brazil. About 70% of the total catchment area is covered by forests. Impedance maps with four different procedures and their respective IC maps were generated and compared for the study catchment. The four different procedures for impedance estimation included the use of RS (W RS), the USLE/RUSLE C-factor (W C), 1- n (W n), and the standardized roughness index (W RI). The higher values of IC with W C were observed in the high plain areas that are physically less connected to the catchment outlet. The use of W RS in the IC demonstrates lower IC values in the high plain areas of the upstream catchment and higher IC values in landslide scars. Furthermore, the forested areas presented lower IC values when compared to other methodologies. The use of W RI and W n as the impedance factor could not represent the significant role of forests in the sediment retention. Thus, the results showed that the W RS can represent vegetated regions, especially dense forests. • The performance of the sediment impedance-estimations is assessed in the IC. • A new approach to calculate the weighting factor of the IC is presented. • The new method has potential to be used to represent impedance in forested catchments. [ABSTRACT FROM AUTHOR]

• A connectivity index was coupled with a soil erosion model to estimate sediment yield. • Afforestation led to evident decreases in both the connectivity and the sediment delivery ratio. • The modeled sediment yield showed a 60.7% reduction due to changes in land use and check dams. The hydrological connectivity on the Loess Plateau has been greatly altered by soil and water conservation measures in the past six decades, leading to significant reduction in sediment load. Nevertheless, how these measures affect sediment transport at the catchment scale remains unclear. This study coupled an index of connectivity (IC) with the Revised Universal Soil Loss Equation (RUSLE) model to estimate the sediment yield in the Yanhe catchment (7,725 km2). The model was used to assess the impacts of land use changes and check dam construction on sediment delivery. The land use maps showed increasing grassland (10.3%) and decreasing arable land (12.3%) from 1990 to 2010. The ranges of IC between the two land use scenarios showed significant changes with an average of 0.3 in 1990 and −0.5 in 2010. Land use changes resulted in average sediment delivery ratio decreasing from 0.39 in 1990 to 0.30 in 2010. The model was calibrated by annual sediment load at a gauging station, covering 5,852 km2 of the catchment and by sedimentation rates behind check dams in a representative sub-catchment. Measured and simulated sediment load showed consistent agreement, suggesting acceptable model performance. An approximately 60.7% reduction in sediment yield was attributed to land use changes and increasing check dams′ construction from 1990 to 2010. This study provided a good example of combining the IC with a soil erosion model to identify spatial patterns and temporal variations in sediment yield due to soil conservation measures. [ABSTRACT FROM AUTHOR]

• Morphometric analysis integrated with sediment connectivity and stream power index. • Variable sediment flux in upper Ganga and upper Kosi basins linked to morphometric characteristics. • Variable hillslope-channel and catchment connectivity contributes to sediment flux variations. • Slope variations manifested in stream power index also influence sediment transport. • Morphometric characterization has significant implications for sediment management. The Indo-Gangetic basin exhibits highly diverse hydro-geomorphic settings that influence the hydrology, sediment production, and transport rates of the rivers draining this region, and this, in turn, is manifested in morphometric diversity of river systems. The rivers draining the western Gangetic plains (WGP) show incised channels attributable to high stream power and low sediment yield. In contrast, the rivers draining the Eastern Gangetic Plains (EGP) have formed aggradational landforms such as megafans due to low stream power and high sediment yield. For a better process understanding of the causal factors of such spatial inhomogeneities in a river basin, a morphometric characterization of its hinterland is necessary. In this work, a set of morphometric parameters such as stream network, longitudinal profile, and hypsometric curve have been integrated with data on sediment connectivity and stream power index to establish the form-process relationships in two contrasting basins, the upper Ganga basin (UGB) and the upper Kosi basin (UKB). The results of this study suggest that high sediment flux in the UKB is attributed to high rainfall, steep topography, unstable channel longitudinal profiles, and high sediment connectivity. A large part of these sediments gets deposited within the channel belt in the alluvial reaches and is remobilized during high flow events. However, the UGB produces fewer sediments due to low rainfall, mild topography, stable channel longitudinal profile, and low sediment connectivity. Also, the presence of a major dam at Tehri further reduces the functional sediment connectivity in the Upper Ganga Basin. [ABSTRACT FROM AUTHOR]