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Introduzione a teoria e recenti applicazioni dell'indice di connettività.

Gathering systematic information on the effects of extreme weather events (e.g., flooded areas, shallow landslide and debris flow activations, windthrows) is a fundamental prerequisite for local authorities to put into practice management strategies and establishing early-intervention priorities. The collection of these data is a resource-demanding task requiring huge personnel effort and financial means. Furthermore, events occurring in remote areas with a low chance of intersecting human infrastructure, are rarely detected and mapped accurately, thus leading to incorrect assumptions in relation to both extreme events spatial distribution and especially to the real occurrence probability. The present work aims at tackling some of the above-mentioned issues by providing a framework for obtaining the automatic identification of severe weather events that may have caused important erosional processes or vegetation damage, combined with a quick and preliminary change detection mapping over the identified areas. The proposed approach leverages the free availability of both high-resolution global scale radar rainfall products and Sentinel-2 multispectral images to identify the areas to be analyzed and to carry out change detection algorithms, respectively. Radar rainfall data are analyzed and areas where high intensity rainfall and/or very important cumulative precipitation has occurred are used as a mask for restricting the subsequent analysis, which, in turn, is based on a multispectral change detection algorithm. The testing phase of the proposed methodology provided encouraging results: applications to selected mountain catchments hit by the VAIA storm in northeastern Italy (October 2018) were capable of identifying flooded areas, debris-flow and shallow landslide activations and windthrows with good accuracy and with the ability to distinguish between erosional processes and windthrows. The described approach can serve as a preliminary step toward detailed post-event surveys, but also as a preliminary "quick and dirty" mapping framework for local authorities especially when resources for ad hoc field surveys are not available. Such a systematic potential change identification, in combination with regular expert-driven validation, can finally pave the way for a process of self-improvement in detection and classification accuracy: if classified changes are validated, machine-learning algorithms can be trained to learn and improve performance not only in change detection accuracy but also in single-scene classification. Future improvements of the described procedure could be finally devised for allowing a continuous operational activity and for maintaining an open-source software implementation.

Il contributo presenta le attività svolte ed i principali risultati ottenuti dal gruppo di lavoro del CNR IRPI e IGG nell'ambito del Progetto Interreg ITA-AUT SedInOut.

Sediment connectivity, defined as the degree to which a system facilitates the transfer of water and sediment through itself by means of coupling relationships between its components, has become a key issue in sediment transfer processes analysis and one of the building blocks of modern geomorphology. The growing availability of high-resolution Digital Elevation Models (DEMs) offers new opportunities for the characterization of sediment connectivity spatial patterns. An index of sediment connectivity, based on DEM derivatives as drainage area, slope, flow length and surface roughness, has been recently developed along with related freeware software tool (SedInConnect). The index aims at depicting spatial connectivity patterns at the catchment scale to support the assessment of the contribution of a given part of the catchment as sediment source and define sediment transfer paths. The increasing interest in the quantitative characterization of the linkages between landscape units and the straightforward applicability of this index led to numerous applications in different contexts. Such works demonstrate that, when carefully applied considering the intrinsic limitations of the geomorphometric approach, the index can rapidly provide a spatial characterization of sediment dynamics, thus improving the understanding geomorphic system behavior and, consequently, hazard and risk assessment. This work presents and discusses the main applications of this sediment connectivity index.

Several heavy precipitation events causing flash floods, debris flows, landslides, and morphological channel changes have occurred in Europe over the last years. In mountain environments, mass movements along the hillslopes are important sources of sediment supply to the rivers and may enhance the geomorphic effects of floods. The Stolla creek (catchment area: 40 km2) is a confined/partly confined channel of the Dolomites (Easter Italian Alps), that was affected by an extreme flood in August 2017, and by a moderate flood in August 2020. The geomorphic effects caused by the two storms were investigated with the aims: to compare the morphological changes induced by the two events in the channel and along the hillslopes; and to assess the impacts of the lateral sediment connectivity to the channel response. A multi-methodical approach was applied, including radar rainfall estimation, rainfall-runoff modeling, field surveys, remote sensing, geomorphological and statistical analysis. Hillslope and channel processes were mapped by comparing multitemporal orthophotos and changes in bed level elevation in the Stolla channel and sediment volume budget along the main channel and along the hillslope were accomplished using the difference of multi-temporal DTMs (DoD technique). Debris-flow connectivity to the main channel was derived by combining field evidence and geomorphometric analysis. The 2017 flood was caused by rainfall with a short duration (6 hrs) and a rain rate exceeding 45 mm h-1. More than 600 debris flows were triggered along the hillslopes. The Stolla channel experienced widening occurred through bank erosion, and overbank depositions and bed level aggradation up to 1.2 m or incision up to -2.2 m. Although 294,000 m3 of sediments eroded in the connected debris flows, limited volumes of sediments (< 1000 m3) were exported to the catchment outlet. The 2020 flood event was characterized by a lower rain rate (max 17 mm h-1) and a long duration (48 hrs) and did not trigger debris flows. The moderate magnitude of the flood peak did not lead to channel widening, but only bed incision (up to -1.4 m) in some reaches. The results show that different rainfall intensities and durations controlled the sediment transport effectiveness during the two floods and that the structural connectivity had an important role on the sediment cascade from the hillslopes to the main channel.

Sediment connectivity, defined as the degree to which a system facilitates the transfer of water and sediment through itself by means of coupling relationships between its components, has become a key issue in sediment transfer processes analysis and one of the building blocks of modern geomorphology. The growing availability of high-resolution Digital Elevation Models (DEMs) offers new opportunities for the characterization of sediment connectivity spatial patterns. An index of sediment connectivity, based on DEM derivatives as drainage area, slope, flow length and surface roughness, has been recently developed along with related freeware software tool (SedInConnect). The index aims at depicting spatial connectivity patterns at the catchment scale to support the assessment of the contribution of a given part of the catchment as sediment source and define sediment transfer paths. The increasing interest in the quantitative characterization of the linkages between landscape units and the straightforward applicability of this index led to numerous applications in different contexts. Such works demonstrate that, when carefully applied considering the intrinsic limitations of the geomorphometric approach, the index can rapidly provide a spatial characterization of sediment dynamics, thus improving the understanding geomorphic system behavior and, consequently, hazard and risk assessment. This work presents and discusses the main applications of this sediment connectivity index.

Debris flows are a widespread natural hazard in mountain catchments causing major damage when they intersect transport vulnerable elements at risk, including transport routes and urban areas. Climate change is expected to lead to an increase in the frequency and magnitude of those phenomena. It is thus fundamental to extend the collection of primary data on debris-flows occurrence and volume in order to evaluate the variations of debris-flow frequency and magnitude with time and, at the same time, provide new tools for the assessment of areas affected by debris flows and their spatial characterization. This work presents the results of the analysis of date of occurrence and volume of a large dataset of debris-flows collected in the eastern Italian Alps. The occurrence, in the last forty years, of some high-magnitude debris flows characterized by the largest unit volumes of the dataset might be associated with current climate changes. In order to deal with the observed increase in this processes in mountain environments, a simple and fast semi-automated procedure is proposed for the regional-scale identification of debris-flow prone channels and alluvial fans. The main aim is to develop a low data-demanding method for a preliminary mapping of potentially debris-flow affected areas to enable priority ranking of channels and alluvial fans at risk by debris flows. This approach has been validated by means of field checks and through its extensive application in the eastern Italian Alps.

Sediment connectivity is an emerging property of geomorphic system. Connectivity within a catchment widely depends on its climatic conditions and morphological heterogeneities, and it is accurately influenced by the anthropogenic (cropland, land use changes, infrastructures) alteration of the landscape (López-Vicente and Álvarez, 2018). Sediment connectivity allows to characterize the structural properties of the landscape (topography, soil roughness, drainage network) and, when considered, at a specific spatio-temporal scale, and in combination with forcing processes (e.g., rainfall-runoff and sediment delivery), can perform as a useful tool for an enhanced landscape management. The assessment of sediment connectivity through usable indices or models is a major concern for the scientific community dealing with catchment/landscape management. In this context, the present study evaluates two connectivity indices at distinct catchment scales: (i) an aggregated and new index of connectivity (AIC) developed by López-Vicente and Ben-Salem (2019) to integrate climatic and soil physical data with topographic and land use information and (ii), an index of connectivity (IC) as expressed in Cavalli et al. (2013). IC was computed using the available 'SedInConnect v2.3' software (Crema and Cavalli, 2018) and two scenarios as weighting factor: the topographic surface roughness and the land cover Manning's n values. The study area is the Vero river catchment (380 km2) that is located in the Southern Pyrenees and within the Ebro river basin (Huesca province, Aragon, NE Spain). The northern part of the catchment is sub-humid, mountainous (deep and sheer gorges are frequent), and covered with forest, whereas the southern part, under semi-arid conditions, has hilly and gentle topography, with alluvial terraces, and it is mainly devoted to agriculture (vineyards, winter cereal, alfalfa, rape, olive and almond groves). Small villages and one village (Barbastro), and many roads and trails appear along the catchment influencing the overland flow pathways. However, there is not any dam that disrupts the permanent river flows. All input (e.g., LiDAR-derived DEMs) and output maps were generated at 5 x 5 m cell size; except for those of a small headwater subcatchment for which 1 x 1 m data were obtained. The analysis in the subcatchment study area aimed at evaluating the effect of different resolutions on indices performance. Results of AIC were compared with those obtained with the two IC scenarios. The major differences of the two approaches were clustered around different cover types and slope values in the different catchment compartments. This can be ascribed to the climatic and soil information integration on the one hand, and to the roughness/slope distribution of upper subcatchments on the other. Further analysis is needed at subcatchment scale.

The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

Debris flows are widespread phenomena in mountain catchments that often cause damage to urbanized areas and transport routes. The spatial characterization of the affected areas is a major issue in the framework of watershed management. We developed a simple and fast semi-automated and low data-demanding procedure for regional-scale identification of debris-flow prone channels and alluvial fans. A GIS-based approach enables a preliminary mapping of potentially debris-flow affected areas and provides information for the priority ranking of channels and alluvial fans exposed to debris flows. The methodology exploits Digital Elevation Models (DEMs) to derive geomorphometric parameters analyzed for the identification of debris-flow triggering areas and their propagation along the channel. Potential initiation sites of debris flows are identified as those exceeding a threshold of local slope versus contributing area, while channel reaches corresponding to debris flows propagation, deceleration and halting conditions are derived from thresholds of local slope. An analysis of longitudinal channel profiles, which considers the traveled distance and the local slope, is used for the computation of the debris-flow runout. The procedure takes into account the presence of hydraulic control works (i.e. check dams) along with information on erosion-resistant bedrock channels and sediment availability. This approach has been validated by means of field checks and through its extensive application in the eastern Italian Alps. The developed methodology has been implemented in a set of freely-available software tools (https://github.com/HydrogeomorphologyTools) in order to facilitate its application and further validation in different environments.

Landslides provoke significant direct and indirect economic losses to infrastructures, in particular along road networks. Thus, it is fundamental identifying the route sectors that could be affected by landslides, in order to reduce the risk level for the population and the economic cost of road damaging. Moreover, several researches conducted in different contexts stressed that the exposure of road networks to slope instabilities could increase because of ongoing climate change and as a consequence of growing economy in several countries. For these reasons, the present work aims to develop and test a data-driven model, based on Genetic Algorithm Method (GAM), for the identification of the sectors road network sectors that are susceptible to be affected by landslides triggered upstream the infrastructure. This work quantifies, also, the impact of sediment connectivity on the susceptibility evaluation in the case studies. The study area corresponds to the north-eastern area of Oltrepò Pavese (northern Italy), a zone very prone to shallow landslides causing severe damages to the road networks. This work shows that the effectiveness of the model in the identification of the most susceptible routes increases including sediment connectivity in the predisposing factors. This parameter, indeed, characterizes runout and the travel distance of a slope instability, improving the ability in identifying the road sectors hit by landslides. The modeled susceptible roads are, then, mapped correctly by the methodology, furnishing an important tool for land use planning and for implementing tools able to reduce the risk for the infrastructures.

Periglacial areas are shaped by very active geomorphic processes resulting in a highly dynamic landscape. In this context, the hillslope-channel coupling plays a fundamental role in controlling catchment sediment dynamics. The sediment produced on hillslopes may reach the channel network and downstream propagation may have important effects on the environment, and create potential hazards. This is the case of the Ala Archa river basin (mean elevation 3160 m a.s.l.), located in the Tian Shan Mountains of Kyrgyzstan. Glaciers cover the upper part of the basin and, along the main valley, numerous fans are formed as a result of glacial lake outburst floods, debris flows, and colluvial processes. The Ala Archa river flows through the Kyrgyz capital city of Bishkek in the lower part, and, in the recent past, floods and debris flows triggered in the upper part of the catchment caused important damage to infrastructures and people. Therefore, the aim of this work is to improve the understanding of the hillslope-channel coupling in the Ala Archa basin, to support hazard and risk assessment, and to shed light into sediment connectivity in high mountain glacial and periglacial regions. A field survey was carried out in summer 2015 to analyse sediment sources and deposition sites (rock slopes, debris flow tracks, fans etc.), in addition, remote sensing and connectivity analyses have also been applied to map and characterize the main morphological characteristics of the basin. Connectivity results permitted to enlighten the role of the fans in coupling/decoupling the hillslpoes to main valley. Furthermore, a focus on periglacial areas allowed for a characterization of connectivity patterns and magnitude in such dynamic environments that will feature the most important changes in sediment dynamics and availability in the near future. This work has been supported by the Swiss National Science Foundation, through the joint SCOPES research project "Debris flow and outburst flood hazard in Tian Shan under impact of changing climate" (DEFENCC; grant no. IZ73Z0_152301).

Debris flows are widespread phenomena in mountain catchments causing major damage when they intersect transport routes or urban areas. The assessment of areas affected by debris flows and their spatial characterization is thus a major issue in the framework of watershed management. This work presents a simple and fast semi-automated procedure developed for a regional-scale identification of debris-flow prone channels and related downstream alluvial fans. The main aim is to develop a low data-demanding method for a preliminary mapping of potentially debris-flow affected areas at the regional scale to enable priority ranking of channels and alluvial fans at risk by debris flows. The methodology is based on a geomorphometric approach that involves the analysis of morphometric parameters derived from Digital Elevation Models (DEMs) for the identification of debris-flow triggering areas and their kinematic along the channel. Potential initiation sites of debris flows are identified as those exceeding a threshold identified on a plot of local slope versus contributing area whereas channel reaches corresponding to debris flows deposition, deceleration and halting conditions are derived from thresholds of local slope. An empirical method, which considers the traveled distance and the local slope along the channel profile, is used for the computation of the debris-flow runout. The presence of hydraulic control works (i.e. check dams) along with information on erosion-resistant bedrock channels and sediment availability are taken into account within the procedure. This approach has been validated by means of field checks and through its extensive application in the eastern Italian Alps. The developed methodology has been implemented in a set of freely-available software tools (https://github.com/HydrogeomorphologyTools) in order to facilitate its application and further validation in different environments. Potential and limitations of the method will be also presented.

In this study, we investigate the surface flow time of rise in response to rainfall and snowmelt events at different spatial scales and the main sources originating channel runoff and spring water in a steep nested headwater catchment (Rio Vauz, Italian Dolomites), characterized by a marked elevation gradient. We monitored precipitation at different elevations and measured water stage/streamflow at the outlet of two rocky subcatchments of the same size, representative of the upper part of the catchment dominated by outcropping bedrock, at the outlet of a soil-mantled and vegetated subcatchment of similar size but different morphology, and at the outlet of the main catchment. Hydrometric data are coupled with stable isotopes and electrical conductivity sampled from different water sources during five years, and used as tracers in end-member mixing analysis, application of two component mixing models and analysis of the slope of the dual-isotope regression line. Results reveal that times of rise are slightly shorter for the two rocky subcatchments, particularly for snowmelt and mixed rainfall/snowmelt events, compared to the soil-mantled catchment and the entire Rio Vauz Catchment. The highly-variable tracer signature of the different water sources reflects the geomorphological and geological complexity of the study area. The principal end-members for channel runoff and spring water are identified in rainfall and snowmelt, which are the dominant water sources in the rocky upper part of the study catchment, and soil water and shallow groundwater, which play a relevant role in originating baseflow and spring water in the soil-mantled and vegetated lower part of the catchment. Particularly, snowmelt contributes up to 64 ± 8% to spring water in the concave upper parts of the catchment and up to 62 ± 11% to channel runoff in the lower part of the catchment. These results offer new experimental evidences on how Dolomitic catchments capture and store rain water and meltwater, releasing it through a complex network of surface and subsurface flow pathways, and allow for the construction of a preliminary conceptual model on water transmission in snowmelt-dominated catchments featuring marked elevation gradients.

Unravelling the spatio-temporal variability of the sediment transfer within a catchment represents a challenge of great importance to quantify erosion, soil redistribution and their impacts on agricultural landscape. Structural and functional connectivity have been identified as useful aspects of connectivity that may clarify how these processes are coupled or decoupled in various types of catchment sediment cascades. In this study, hydrological and sediment connectivity in a Mediterranean agricultural catchment (1.4 km2) modified through traditional drainage systems (i.e. ditches and subsurface tile drainages) was assessed during two contrasted rainfall events occurred in October 2016 (20 mm in 24 h -return period < 1 yr-, I30 6.6 mm h-1 with 32 mm accumulated in 14 days) and in December 2016 (99 mm in 24 h -return period 25 yr-, I30 23 mm h-1 with 39 mm accumulated in 14 days). A morphometric index of connectivity (IC) was calculated to study the spatial patterns of structural connectivity. The identification of the main sediment pathways -in terms of functional connectivity- was conducted by field mapping, whilst the estimation of erosion and deposition rates by the analysis of high resolution digital terrain models (i.e. 5 cm pix-1; RMSE < 0.05 m) obtained from automated digital photogrammetry and unmanned aerial vehicle (UAV). The IC estimations allowed the identification of the most (dis-)connected areas related with the anthropogenic control in the resisting forces of the catchment. On the one hand, in the upper part of the catchment, depositional compartments were created by dry-stone walls that separate agricultural properties laminating flash floods. On the other hand, in the lower part of the catchment these depositional compartments were generated by an orthogonal network of ditches situated topographically above the natural thalwegs. In its turn, the most connected areas are located in the steepest parts of the catchment under rainfed herbaceous crops without dry stone walls and also within the lowland depositional compartments where the pathways are diverted generating parallel concentrated flows because of the greater elevation of these ditches. The observed spatial patterns of functional connectivity showed significant differences between the two events, although well fitted with IC as a clear evidence of anthropogenic controls in the resisting forces. During the October 2016 event -representative of high frequency-low magnitude events in the catchment- traditional drainage systems controlled the water and sediment transfer which was mainly concentrated within the ditches. By contrast, during the event of December 2016 -representative of extreme events- this transfer process was controlled by the natural morphology of the catchment, which activated coupling mechanisms between different compartments, increasing the effective area and triggering erosion processes including the formation of rills and incipient gullies. The spatial location of the sediment mobilization and deposition areas during the extreme event in December 2016 is well fitted with the IC estimations. The application of IC, therefore, may provide useful information to improve the drainage systems design and the implementation of measures to prevent soil losses.

A significant number of mountain catchments have suffered important land use changes due to agricultural abandonment during the second half of the 20th century. These changes do not only induced an increase in the vegetation cover but also a series of natural and anthropic morphological changes (e.g. terraces) that influence the water and sediment flux through catchments. In the present study the effect of these changes (i.e. land cover and topography) on sediment connectivity is analyzed in different scenarios of change in the Upper Cinca Basin (Southern Pyrenees). Potential sediment connectivity can be assessed by a morphometric indicator named Index of Connectivity (IC) developed by Cavalli et al (2013) based upon the original approach by Borselli et al (2008). The input variables of IC are determined by the land use or landscape roughness, and topography. In this work we present a methodological workflow to obtain such variables from historical aerial photos using digital photogrammetry through Structure from Motion and Multi View Stereo algorithms (SfM-MVS). A prerequisite of the analysis is to reconstruct the land use and the landscape properties at the period in which the IC is estimated. The analysis consists of three interrelated steps: (a) extraction of historical ortophotomaps and point clouds from historical photos (aerial photos from 1957 and 1977) using SfM-MVS, (b) derivation of land use maps and topographic models for those periods to parametrize IC, and (c) assessment and comparison of historical sediment connectivity in each period. The workflow was tested in different contrasted sub-catchments representative of three main scenarios: (1) Changes on land cover; (2) Topographic changes on agricultural fields (terracing); (3) Topographic changes associated to infrastructures (road construction). From the methodological point of view, results highlight as the selection of the suitable resolution of the Digital Elevation Models used in each scenario is crucial for the correct analysis of IC changes. Terraces affect connectivity in a major degree than land use changes, following a more spatially concentrated pattern, while the morphological variation due to road construction led to an increase of erosional activities uphill the road. In the light of these results, the developed workflow to assess sediment connectivity at multiple temporal scales has proved to be a promising and useful methodology to plan and asses potential risks associated to morphological and land use changes.

As a consequence of a changing climate the occurrence of unexpected events, like flooding and erosion, that affects urban areas will most likely increase. The infrastructure is especially vulnerable to heavy rainfall events due to high costs and long term investments. Accumulation of water and sediments thus has a large impact on the consequences of such events, and it is therefore essential to identify factors that influence the catchment and the occurrence of flooding. Both spatial and temporal characteristics of the patterns of sediment connectivity is important for estimating the sediment contribution and transfer paths in a catchment. In recent years several approaches have been developed to assess sediment connectivity, as for example the geomorphometric indices of sediment connectivity which mainly picture a static frame of the system. With the development of remote sensing technology and the growing availability of satellite images the opportunity to consider also temporal variability and hydrological parameters as soil moisture within this kind of indices is increasing (e.g., Foerster et al., 2014; Gay et al., 2015). However, there is still a knowledge gap in considering the potential of soil moisture satellite imagery in assessing sediment connectivity at the catchment scale. This study aims to integrate spatial and temporal soil moisture properties in the index of sediment connectivity by Cavalli et al. (2013), which can be used to predict where flood events will have the strongest impact. The results will provide decision makers with a prediction tool to identify road-intersections that are prone to flood risk at the catchment scale. The method developed in this study would increase awareness and be a basis for decision makers and stakeholders to promote action towards enabling sustainable water and land management. References Cavalli, M., Trevisani, S., Comiti, F., Marchi, L. , (2013) Geomorphometric assessment of spatial sediment connectivity in small Alpine catchments. Geomorphology 188: 31-41, doi:10.1016/j.geomorph.2012.05.007. Foerster, S., Wilczok,.C., Brosinsky, A., Segl, K., (2014) Assessment of sediment connectivity from vegetation cover and topography using remotely sensed data in a dryland catchment in the Spanish Pyrenees. J Soils Sediments 14:1982-2000 Gay, A., Cerdan, O., Mardhel, V., Desmet, M. (2015) Application of an index of sediment connectivity in a lowland area. J. Soils Sediments 16(1), 280-293, doi:10.1007/s11368-015-1235-y,.

The Moscardo Torrent (eastern Italian Alps) is a small rugged catchment (drainage area 4.1 km2, range in elevation between 890 and 2043 m) frequently affected by debris flows that deliver large amounts of sediment to the receiving stream, and cause concerns for infrastructures located on the alluvial fan and near the confluence. Over the last decades, hydraulic control works were implemented in the main channel to limit bed erosion and to stabilize channel banks. Although the objectives of training works have been only partly achieved, check dams and hillslope stabilization works have affected the sediment transfer from hillslopes to the channels and along the main channel. The effects of hydraulic control works were investigated by means of multi-temporal Structure from Motion (SfM) surveys based on images taken from the ground and UAV. The ground and air based surveys were carried out over a channel reach in which two check dams have recently been built. SfM surveys were taken before and after three debris-flow events (occurred between June and July 2016), allowing the generation of four high-resolution Digital Elevation Models (DEMs). Geomorphic changes caused by the debris-flow events have been assessed in order to produce the DEM of Differences (DoDs with a 0.2 m spatial resolution) that allowed estimating erosion and deposition volumes in the study area. Furthermore a debris-flow monitoring system has been in operation in the Moscardo Torrent; the analysis of the videos and of the hydrographs recorded by ultrasonic sensors permitted to assess the debris-flow volumes. These estimates were used to characterize the magnitude of events in support of the topographic analysis. By examining the changing pattern of erosion and deposition over time it was possible to understand the check dams' effects on sediment dynamics. The results show that the new check dams effectively stored sediment transported by the three debris flows. However, once the check dams have been completely filled, they lost their functionality, letting sediment flow downstream along paths drawn accidentally by the torrent control works and by the morphology of debris-flow deposits. Moreover, debris-flow lobes deposited upstream of the check dams could act as sediment sources further increasing downstream debris-flow magnitude.

The increasing availability of high-resolution Digital Terrain Models (DTMs) in recent years represents a great opportunity for Geosciences being this input information a fundamental prerequisite for an accurate representation of the surface and of the processes acting on it. Nowadays, a number of techniques in order to produce high-resolution DTMs are available. Depending on the scale of analysis, the most used survey techniques are: i) Radar, ii) LiDAR and iii) Photogrammetry. The raw survey-derived products are often in need of a careful post-processing in order to filter out unwanted features. This, for example, could be the case of vegetation removal for surface processes modeling. After the filtering procedures, usually either the point density under filtered areas drops down or missing data areas are created. Resulting interpolated surfaces, in particular over these areas, could vary significantly, mainly depending on the selected interpolation algorithm, sometimes leading to the creation of artifacts that are not able to mimic the original surface trend and texture. In this work, we devised an experiment in order to compare the results of an image inpainting technique over missing data holes against commonly used interpolators (IDW, Spline, Kriging, Natural Neighbor) quantifying the accuracy of the approaches. The image inpainting technique has demonstrated in all the cases a significantly better performance in reconstructing the original surface. An assessment of the extent up to which such an approach could be regarded as robust has also been carried out. Selected applications of surface propagation models to the reconstructed surfaces have been reported so as to highlight how surface variability and uncertainty in surface reconstruction can influence (positively/negatively) model results. Applications of such an approach could pave the way for accurate surface interpolation and/or surface reconstruction in case of the need to remove selected features to characterize several modeling scenarios or to fill the gaps to reproduce the original surface in a consistent way.

The study of a landslide runout (i.e., the distance traveled by sediment detached by a landslide) is fundamental for a comprehensive understanding of the risk associated with landslide occurrence since sediment mobilized from landslides can often reach downstream areas causing extensive damages. The spatial characterization of sediment dynamics through geomorphic systems (i.e., sediment connectivity) is a key property to define sediment transfer paths. Sediment connectivity is mainly controlled by the morphological complexity of the catchment and the spatial organization of vegetation. In particular, vegetation plays an important role on sediment connectivity, since it influences surface roughness and local sediment retention capacity. Moreover, vegetation changes due to land use and management practice modifications can introduce major changes in sediment delivery dynamics, leading to important effects on earth surface processes, especially in relation to slope instability phenomena. Within this framework, the aim of this work is to evaluate how vegetation characteristics and its modifications over time can affect sediment connectivity in response to shallow landslides occurrence. A GIS-based index of connectivity (IC) was computed for a hilly catchment located in the northern Apennines in Italy. This area was characterized by a high degree of land abandonment, leading to important landscape modifications over the last 60 years. Moreover, the studied catchment was highly affected by shallow landslide phenomena, mainly triggered by an intense rainfall event in 2009. Land use changes characterizing the study area in the last 60 years were integrated into IC computation. The Overland Flow Manning's n Roughness Values was used in order to represent the impedance to water and sediment fluxes related to each land use class. This parameter was integrated into a revised version of IC weighting factor (W). In particular, both a linear e non-linear relationship for the Manning's n based W was computed. This allowed integrating the hydraulic efficiency of overland runoff flow in the analysis framework. Finally, the results of IC implementing the revised W, based on land use change dynamics, was integrated into a data-driven model to evaluate the probability that the sediments produced by instability phenomena could reach downstream areas. In particular, this analysis allowed identifying those areas in which the mobilized sediment could damage the road network blocking traffic, isolating villages and stopping activities.

Sediment connectivity can be regarded as a descriptor of the internal linkages between different landscape components within a catchment. The recent focus of the scientific community on connectivity related topics, both concerning hydrological and sediment connectivity, stresses the importance of understanding the main active pathways for a better estimation of energy and matter transfer at catchment scale. This task can be addressed using topography-based indices that analyse the linkages between landscape units. This approach to characterize connectivity is known as structural connectivity. The main limitation of structural connectivity is that it does not account for the processes driving sediment and energy fluxes (i.e., functional connectivity). In this work the integration between structural and functional approaches is proposed for characterizing sediment connectivity in mountain catchments. The structural approach, based on a topography-based sediment connectivity index, was used for assessing hillslope-to-channel connectivity. Since field data on processes driving sediment transport along the channel network are available, a functional approach has been devised to estimate withinchannel connectivity. An index of unit stream power computed from the hydraulic properties of the channel (i.e., discharge, slope and channel width) has been compared with the critical unit stream power computed from incipient motion thresholds derived from field data to identify the cells of the Digital Terrain Model (DTM) in which sediment can be mobilized under near-bankfull conditions. The index expressing the within-channel connectivity is given by the length of the reaches consisting of contiguous cells that exceed the critical unit stream power. During high-magnitude floods, when unit stream power values exceed the threshold for incipient motion, channels experience an increase in both hydrological and sediment connectivity. The proposed index characterizes those sections of the channel network that are effectively connected under near-bankfull conditions. The model has been developed and tested in a small mountain catchment in the Italian Alps (Strimm catchment, 8.42 km2 ) in which a high-resolution DTM and monitored discharge and sediment transport data are available. The integration between structural and functional indices of sediment connectivity has permitted characterizing the spatial pattern of sediment connectivity on the hillslope and pointing out potential sites for sediment erosion, entrainment and deposition along the main channel network. This combined approach represents a new development of the index of connectivity considering sediment transport process along the channel network, with the only limitation related to field data availability. However, further testing is required to validate the index in order apply it to other catchments.

The degree of linkage between the sediments sources and downstream areas (i.e. sediment connectivity) is one of the most important properties controlling landscape evolution. Many factors have been found to affect sediment connectivity, especially at the catchment scale. In particular, the degree of linkage between different areas within a catchment depends largely on the morphological complexity of the catchment (relief, terrain roughness, stream network density and catchment shape) and the combined effects of vegetation, such as land use changes and land abandonment. Moreover, the analysis of the spatial distribution of sediment connectivity and its temporal evolution can be also useful for the characterization of sediment source areas. Specifically, these areas represent sites of instability and their connectivity influences the probability that a local on-site effect could propagate within a multiple-events feedback system. Within this framework, the aim of this study is to apply a geomorphometric approach to analyze the linkage between landscape complexity and the sediment connectivity at the catchment scale. Moreover, to assess sediment delivery, the index of connectivity (IC) proposed by Cavalli et al. (2013) was used to evaluate the potential connection of sediment source areas with the main channel network. To better understand the relationship between morphological complexity of the catchment's landscape and the sediment spatial distribution and mobilization, two catchments with different size and geomorphological and land use characteristics were analysed: the Rio Frate and Versa catchments (Oltrepo Pavese, Southern Lombardy, Italy). Several shallow landslides, which represents the main sediment source area type in the catchments, were triggered especially in the period from 2009 to 2013. Moreover, relevant modification of land use and drainage system during last decades, especially related to land abandonment, have conditioned the sediment connectivity of these two catchments. To analyse these different aspects, IC was applied by using different stream networks densities. This allowed to investigate the sediment connectivity changes according to different landscape settings. Moreover, a multi-temporal, land-use change analysis was carried out to evaluate its role on the sediment dynamics. Finally, a sediment delivery assessment was performed. Shallow landslides inventories, with the identification of extent, location and typology of landslides phenomena, were used to better characterize the sediment supply to the channel network. This analysis represents an important step toward the realization of a useful tool for the improvement of sediment management strategies.

Identifying areas that are directly delivering sediment to the channel network or to a catchment outlet is of great importance for a sound sediment dynamic characterization and for assessing sediment budget. We present an integration of remote sensing analysis techniques to characterize the effective sediment contributing area that is the sub-portion of the catchment in which sediment is effectively routed towards the catchment outlet. A semi-automatic mapping of active sediment source areas is carried out via image analysis techniques. To this purpose, satellite multispectral images and aerial orthophotos are considered for the analysis. Several algorithms for features extraction are applied and the maps obtained are compared with an expert-based sediment source mapping derived from photointerpretation and field surveys. The image-based analysis is additionally integrated with a topography-driven filtering procedure. Thanks to the availability of High-Resolution, LiDAR-derived Digital Terrain Models, it is possible to work at a fine scale and to compute morphometric parameters (e.g., slope, roughness, curvature) suitable for refining the image analysis. In particular, information on local topography was integrated with the image-based analysis to discriminate between rocky outcrops and sediment sources, thus improving the overall consistency of the procedure. The sediment source areas are then combined with the output of a connectivity assessment. A topography-based index of sediment connectivity is computed for the analyzed areas in order to better estimate the effective sediment contributing area and to obtain a ranking of the source areas in the studied catchments. The study methods have been applied in catchments of the Eastern Italian Alps where a detailed census of sediment source areas is available. The comparison of the results of image analysis with expert-based sediment sources mapping shows a satisfactory agreement between the two approaches. Furthermore, the integration with sediment connectivity maps permitted a first fast assessment of effectively connected sediment source areas. This valuable information could enable land managers to focus on the most active geomorphic paths at catchment\regional scale

Climate changes are predicted to increase precipitation intensities and occurrence of extreme rainfall events in the near future. Scandinavia has been identified as one of the most sensitive regions in Europe to such changes; therefore, an increase in the risk for flooding, landslides and soil erosion is to be expected also in Sweden. An increase in the occurrence of extreme weather events will impose greater strain on the built environment and major transport infrastructures such as roads and railways. This research aimed to identify the risk of flooding at the road-stream intersections, crucial locations where water and debris can accumulate and cause failures of the existing drainage facilities. Two regions in southwest of Sweden affected by an extreme rainfall event in August 2014, were used for calibrating and testing a statistical flood prediction model. A set of Physical Catchment Descriptors (PCDs) including road and catchment characteristics was identified for the modelling. Moreover, a GIS-based topographic Index of Sediment Connectivity (IC) was used as PCD. The novelty of this study relies on the adaptation of IC for describing sediment connectivity in lowland areas taking into account contribution of soil type, land use and different patterns of precipitation during the event. A weighting factor for IC was calculated by estimating runoff calculated with SCS Curve Number method, assuming a constant value of precipitation for a given time period, corresponding to the critical event. The Digital Elevation Model of the study site was reconditioned at the drainage facilities locations to consider the real flow path in the analysis. These modifications led to highlight the role of rainfall patterns and surface runoff for modelling sediment delivery in lowland areas. Moreover, it was observed that integrating IC into the statistic prediction model increased its accuracy and performance. After the calibration procedure in one of the study areas, the model was validated in the other study area, located in the central part of Sweden, since this experienced flooding in relation to the same triggering event.

Alluvial sediment investigations provide fundamental tools to infer the processes that control geomorphological evolution of mountain environments. By analyzing sediment stratigraphy in depth, it is possible to retrieve the source, the geology, the time of deposition, the relative distance travelled by material as well as to distinguish among different type of transport (i.e., gravitational, fluvial or glacial). In this work, we present a combination of log stratigraphy, radiocarbon dating and geophysical surveys carried out on the valley floor of the But River (Carnic Alps, North East Italy). The But River basin drains an area of 326 km2 with a range in elevation from 2769 to 323 m a.s.l.; the bedrock mainly consists of carbonates and quartz arenites with minor inclusions of effusive rocks. After Pleistocene the gravitational deposits from mountain slopes have impounded the But River several times. In particular, we analyzed a sector of the upper portion of the But valley close to the confluence of the Moscardo Torrent, frequently affected by debris flows. A borehole was drilled in the But River floodplain, at the intersection with the Moscardo Torrent alluvial fan, down to a depth of 80 m. The analysis of the core samples allowed discerning three sedimentary levels rich in clay and organic materials, which testify the presence of small dam lakes, originated from the Moscardo debris-flow deposits. Three samples of wood and plant debris were collected from 13, 14 and 23 m of depth, respectively. They were analyzed through radiocarbon dating in order to determine the age of the lakes and, thus, to infer the activity of the debris flows building the Moscardo cone. The calibrated ages of the 3 samples are close to the younger limit of the radiocarbon method indicating a fast aggradation of the valley floor, starting from a period ranging between 1450 - 1632 AD. Historical maps and documents confirm the presence of the lakes until 19th century and they permit to assess their extent and the maximum depths. Two passive seismic campaigns were carried out near the borehole site and along the But valley at different elevations. The aim was to investigate the depth of the buried bedrock and therefore to indirectly characterize the thickness of alluvial deposits. We calibrated the fundamental frequency of each site by constraining average shear velocity of the alluvial sediments close to the borehole site with known stratigraphy. Eight HVSR (Horizontal to Vertical Spectral Ratio, Nakamura, 1989) were carried out, and thus a first sketch of the buried valley floor along a longitudinal profile of about 5 km was depicted. The values of the derived bedrock depth allow to quantify the differences in thickness between the alluvial deposits and the Moscardo Torrent fan deposits. This information helps to address the contribution of the debris-flow processes in damming the upper But River during the last five centuries. The results confirm the role of debris-flow deposits from the Moscardo Torrent in shaping the morphology of the valley floor of But River and show suitability of an integrated approach, encompassing log stratigraphy, geophysical surveys and analysis of historical documents, for gaining insights on the evolution of alpine valleys

In this work the integration between structural, essentially based on the system structure (i.e., topography), and functional (i.e. considering processes driving sediment and energy fluxes) approaches is proposed for characterizing sediment connectivity in a small mountain catchment. The structural approach, based on a topography-based sediment connectivity index, is used for assessing hillslope-to-channel connectivity. Since field data on processes driving sediment transport along the channel network are available, a functional approach has been devised to estimate within-channel connectivity. An index of unit stream power computed from the hydraulic properties of the channel (i.e., discharge, slope and channel width) has been compared with the critical unit stream power computed from incipient motion thresholds derived from field data to identify the cells of the Digital Terrain Model (DTM) in which sediment can be mobilized under near-bankfull conditions. The index expressing the within-channel connectivity is given by the length of the reaches consisting of contiguous cells that exceed the critical unit stream power. During high-magnitude floods, when unit stream power values exceed the threshold for incipient motion, channels experience an increase in both hydrological and sediment connectivity. The proposed index characterizes those sections of the channel network that are effectively connected under near-bankfull conditions. The model has been developed and tested in a small mountain catchment in the Italian Alps (Strimm catchment, 8.42 km2) in which a high-resolution DTM and monitored discharge and sediment transport data are available. The integration between structural and functional indices of sediment connectivity has permitted characterizing the spatial pattern of sediment connectivity on the hillslope and pointing out potential sites for sediment erosion, entrainment and deposition along the main channel network. This combined approach represents a new development of the index of connectivity considering sediment transport process along the channel network, with the only limitation related to field data availability. However, further testing is required to validate the index in order apply it to other catchments.

Geomorphic coupling, i.e. linkages between geomorphic system components, and sediment connectivity, i.e. the degree of linkage that controls sediment fluxes throughout landscape, have important implications for the behavior of geomorphic systems and have become key issues in the study of sediment transfer processes. The detailed characterization of the topographic surface plays a fundamental role for studying sediment dynamics in a catchment. Digital Elevation Models (DEMs) can both improve geomorphological interpretation (e.g. individuation of sediment source areas) and enable the quantitative modeling of sediment fluxes and connectivity. In particular, the availability of LiDAR-derived high-resolution Digital Terrain Models (DTMs), exploited using geomorphometric analysis, extends the applicability and potentialities of topography-based modeling approaches. Indeed, geomorphometry allows to derive detailed characterization of drainage pattern and surface roughness, which are two of the most important parameters in the study of sediment delivery. Since the late 1990s, some GIS-based approaches mainly based on stream-power have been developed for modeling the topographic potential for erosion and deposition and evaluating the impedance to sediment conveyance. But it is in the more recent years that an increasing interest for the quantitative characterization of the linkage between landscape units can be observed in literature. The development of geomorphometric indices, such as the sediment connectivity index (IC) by Borselli et al. (2008) and the version of IC proposed by Cavalli et al. (2013), and related freeware applications, has certainly contributed to this increased interest. In this work, the state of the art on the use of DEMs for sediment connectivity assessment, with a specific focus on the sediment connectivity index and following applications, will be presented. Future perspectives will be also discussed. References Borselli L., Cassi P., Torri D., 2008. Prolegomena to sediment and flow connectivity in the landscape: a GIS and field numerical assessment. Catena, 75(3), 268-277. doi:10.1016/j.catena.2008.07.006 Cavalli M., Trevisani S., Comiti F., Marchi L., 2013. Geomorphometric assessment of spatial sediment connectivity in small Alpine catchments. Geomorphology 188,31-41. doi:10.1016/j.geomorph.2012.05.007

The SedAlp project contributes to an integrated management of sediment transport in Alpine basins. It is directed to an effective reduction of sediment-related risk while promoting the enhancement of riverine ecosystems and reducing the impacts of hydropower plants (balancing the implementation of EU Directives and national law e.g. RES, WFD, NGP etc.). SedAlp includes pilot actions in various representative Alpine river basins of five countries and contributes in particular to monitor sediment and wood transfer in a large set of Alpine catchments. A major goal of the project was to understand spatial and temporal variability of processes and to provide planning, warning and predictive tools but also sediment and wood management recommendations for protecting people. Furthermore the project includes strategy policy development and implementation actions for the improvement of sediment continuity in Alpine river basins. SedAlp regards the geological and climatic variability across the Alps that generate complex patterns of sediment transfer, whereas management conflicts are similar. To reach the ambitious goals of the project, it is essential to understand the key processes of sediment and wood transport. Workpackage 5 with the title "sediment transport monitoring" was focused to enhance the knowledge about these transport processes by conducting the first standardized transnational monitoring of sediment and wood transport in Alpine basins. WP5 concentrated on monitoring and assessing fluxes of sediment and wood at the local scale. Measured fluxes are strongly depending on the supply from the catchment and on the connectivity to source areas, analysed in WP4. The output of WP5 feeds WP6 which studied the interferences between structures and sediment/wood fluxes and forms the basis for WP7 which linked the catchment with channel processes. Finally, the results of WP5 contribute to policy recommendations in WP8. Within WP5, monitoring activities on 28 different pilot sites in Austria, Germany, France, Italy and Slovenia have been conducted between 2012 and 2015. The monitored transport processes covered woody debris, debris flow, bedload and suspended load. The different pilot sites showed a great diversity in catchment size, channel slope and hydraulic parameters and covered the whole bandwidth from small, high alpine catchments (e.g. Strimm: 5 km² catchment size, 2427 m elevation a.s.l) to large catchments in the alpine valleys (e.g. Drau/Dellach: 2131 km² catchment size, 600 m elevation a.s.l). With the results of the monitoring activities, a database using different parameters regarding the transport process has been established and reflects the big diversity of the different pilot sites. The coordinated sediment transport monitoring outlined the links between the various processes responsible for sediment delivery at catchment scale and stresses out the need for a closer integration between the monitoring of various sediment transport processes in Alpine headwaters. Due to the wide range of different measurement methods used within the project, one focus of this work package was to standardize the measurement procedures and harmonize data analysis. This led to the 1st milestone "Protocol on standardized data collection methods in sediment transport monitoring for transboundary exchange". These protocols were intended to describe the used monitoring techniques and data processing methods for debris flows, wood transport and bedload transport. Furthermore, the protocols work also as guidelines to assist in choosing the appropriate monitoring method for supporting prospective monitoring efforts. 4 An important aspect of the project was to understand spatial and temporal variability of the monitored processes. The observed appearance of clockwise and counter clockwise hysteresis effects between sediment and discharge, showed the significant role of the location of the active sediment source in the temporal variability of sediment transport. Analysis of the spatial distribution showed an evolvement of the bedload transport width with increasing discharge which provides vital information for an improved planning of river related measures. To determine these process related variability, the use of appropriate monitoring methods as well as their right application is of great importance. Indirect monitoring methods (e.g. geophone devices) pointed out their potential in the automatic and continuous detection of these transport processes. The presented data reflect a high spatial and temporal variability in the occurrence of bedload, suspended load debris flow and wood transport and reveal significant consequences for the practical usage of monitoring methods, data and application. Many river engineering tasks require detailed information about the extent of sediment transport and wood mobility, which are provided by sediment and wood transport relations and equations. The 3rd milestone "First set of practically applicable bedload/wood transport relations and models" gives an overview about the most common transport relations and formulas. Furthermore it presents the difficulties and challenges in the application of these relations and shows the last developments in improving transport equations. The comparison between measured and calculated specific bedload transport rates showed substantial differences in the derived results. For the practical use of these relations it is strongly recommended to select, calibrate and validate the sediment and wood transport equations using monitored field data. The evaluation of river restoration projects showed the need of an improved process understanding between sediment transport an engineering measures. The functionality and sustainability of river restoration measures are, beside the hydrologic and hydraulic conditions, mainly depending on the superior sediment regime and thus the sediment input into the reach. By increase or decrease of the mean sediment input, the hydraulic and thus morphological conditions of the reach need to rearrange to the given input by e.g. lateral and vertical adjustments of the river bed or by changing the river type.

On November 18, 2013, the North-Eastern part of Sardinia was impacted by extreme flash flooding, which killed 19 people and caused up to 1 billion Euro damage. The flooding was associated with an extratropical cyclone in the western Mediterranean Basin, named Cyclone Cleopatra, which developed slow-moving embedded thunderstorm complexes, as cold air flowing from the north entered the Mediterranean and interacted with warm moist air to the east. The impacted area is up to 1500 km2, and includes a number of basins, including the Posada ( 690 km2) and Cedrino (625 km2) basins. The cyclone brought extremely heavy rain to the area, with up to 450 mm of rain in 12 hours (from 07:00 to 19:00 local time), resulting in severe flooding. A high concentration of fatalities and damages occurred in the area around the northeastern city of Olbia, also due to high vulnerability resulting from inappropriate urbanization. Post-flood documentation, focused on the Cedrino and Posada river systems, included the reconstruction of peak discharge by means of topographic surveys, observations on the geomorphic effects of the event both in the channel network and on hillslopes and assessment of the timing of the flood based on the accounts of eyewitnesses. Technical services of regional authorities and local administrations contributed to the documentation of the flood by providing hydrometeorological data, accounts of volunteers of the civil protection and photos taken during and immediately after the flood. The assessment of unit peak discharges confirmed the severity of the flood, with values up to approximately 10 m3s-1km-2 in catchments up to 500 km2. The strong spatial gradients of the precipitation had a major influence on flood response, with large difference in peak discharge between neighbouring catchments. The availability of high-resolution rainfall estimates from radar observations and a rain gauge network, together with indirect peak discharge estimates from the post-event survey, provided the opportunity to study in detail the hydrometeorological and hydrological mechanisms associated with this extreme storm and the ensuing flood. Observations and model results are combined to examine two main questions, (i) assessment of the distribution of the runoff ratio and how it is controlled by the heterogeneous geological structure; and (ii) analysis of how the spatial and temporal distribution of the extreme rainfall, and more specifically storm motion, controls the flood response.

Sediment connectivity, i.e. the degree of linkage that controls sediment fluxes throughout landscape, and, in particular, between sediment sources and downstream areas, is a key issue in the study of sediment transfer processes in mountainous catchments. The spatial characterization of connectivity patterns in the catchment allows estimation of the contribution of a given part of the catchment as sediment source, and defines sediment transfer paths. A reliable assessment of sediment connectivity is especially useful for giving management priorities. The assessment of sediment connectivity is of particular importance in alpine headwaters, in which both complex and rugged morphology, and heterogeneity in type, extent and location of sediment sources cause large variability in the effectiveness of sediment transport processes. The control of morphology on spatial sediment connectivity acts through sediment transfer on hillslopes and unchanneled valleys, hillslope-channel coupling and decoupling, and sediment transfer along the channel network. In this document, background theory, installation steps and user guidelines of two utilities for the derivation of the Index of Connectivity (IC), as expressed in Cavalli et al. (2013), developed in the frame of the SedAlp project are presented. The utilities are: (i) a Toolbox for ArcGis 10.1 and 10.2 and, (ii) a standalone application not requiring the use of any GIS software. The need for the development of such tools comes from the increasing interest in sediment connectivity issues (Fryirs 2013; Baartman et al. 2013) and its semi-quantitative assessment (Heckmann and Schwanghart 2013; Cavalli et al. 2013; Meßenzehl et al., 2014) to estimate the effectiveness of sediment transport processes at catchment scale. Moreover, the possibility to relate a quantitative estimate of sediment connectivity to sediment sources databases can improve hazard and risk assessment in order to mitigate the effects of dangerous phenomena like debris flows. With an integrated approach, which encompasses sediment sources mapping and connectivity assessment, it is indeed possible not only to evaluate the general availability of sediment but also to estimate the potential for this sediment to reach specific targets.

A very detailed geodatabase of floods, landslides and debris flows is available and kept up to date for the territory of the Autonomous Province of Bolzano, in northeastern Italy (7400 km2). The database is fed by field surveys carried out after the occurrence of instability phenomena and reports locations and attributes of the events for the last 15 years. The on-site analysis grants the gathering of important information and documentation resulting from field measurements and interviews to witnesses of the events. Particular attention is paid to the recognition of location, magnitude and path of landslides and debris flows. Data on shallow landslide locations and debris-flow initiation sites have provided the input to a regional-scale debris flow model aimed at the assessment of debris flow paths and inundation areas. A simple mass propagation model based on topographic attributes (Huggel et al., 2003) has been applied to simulate mass movement phenomena for selected basins using initiation sites listed in the regional database. In the model, debris-flow propagation is given in probability-related values representing the hazard potential for the selected locations. All the simulations have been carried out using a high-resolution (2.5m) LiDAR-derived Digital Terrain Model (DTM). The combination of a georeferenced database of landslides and debris flows and a simple topography-based model constitutes therefore a reliable tool for a fast and preliminary debris-flow hazard estimate, assessment and mapping. References: Huggel C, Kääb A, Haeberli W, Krummenacher B. 2003. Regional-scale GIS-models for assessment of hazards from glacier lake outbursts: Evaluation and application in the Swiss Alps. Natural Hazards and Earth System Sciences 3(6):647-662.

The volumes and dynamics of suspended sediments drained from a watershed are often unknown, especially in small creeks and tributaries where continuous discharge measurements are seldom available. The objective of this study was to assess in a qualitative and quantitative way the sediment dynamics of a small ungauged watershed in the Northern Apennines, Italy. We analysed and correlated the sediment volume concentration and grain-size distribution of the suspended sediments with the precipitation pattern. The study area is a small ungauged watershed (0.15 km2) that is dominated by intensive soil erosion processes and related landforms. The basin is oriented East-West with the south-facing slopes characterized by badland erosion processes. The north-facing slopes are cultivated and dominated by rill-interrill erosion phenomena. An morphometrical characterization of the basin was performed using a high-resolution DTM with a 1 × 1 m resolution. Subsequently, the physical characteristics of the topsoil were investigated based on grain size laboratory analysis. A detailed NDVI analysis of the vegetation was performed using Sentinel-2A images. Finally, we assessed the suspended sediments at the outlet of the basin using a laser diffraction technique. The Suspended Sediment Volume Concentration (SSC) and the Sauter Mean Diameter (SMD) of the eroded sediments, provide insights into the morphogenetic processes and the sediment transport dynamics of the basin. The measurements were conducted in autumn 2018 after an intense precipitation period and in spring 2019 after a dry phase. The results show a direct relationship between precipitation and SSC with a delay of about 2 h after the most intense precipitation events. Moreover, we reveal that the SMD values are inversely related to the precipitation due to turbidity effects. The SSC and SMD measurements allow for a detailed assessment of the dynamics between precipitation and suspended sediment load even though discharge volumes were not measured directly.

The investigation of form and processes in geomorphology and ecology is highly dependent on topographic data: a reliable digital terrain representation is in fact a key issue across environmental and earth sciences. In many cases, the processing of high-resolution topographic data (e.g., light detection and ranging (LiDAR), structure from motion) has to face issues such as void filling, vegetation/feature removal and interpolation accuracy that are usually related to (i) intrinsic limitations of the adopted technology, (ii) local conditions affecting the survey or (iii) specific design scenario. In this paper, we develop a methodology to test the accuracy of an image inpainting algorithm to fill data voids in complex mountain areas. The devised experiment exploits the availability of a high-resolution, LiDAR-derived digital terrain model and the inpainting approach accuracy is checked against some widely used interpolation techniques (natural neighbor, spline, inverse distance weighting, kriging). In order to better mimic the actual surface texture, a methodology to introduce local topographic variability to the interpolated surface is also presented. The results show a better performance of the inpainting algorithm especially in the case of complex and rugged topography. Two examples showing an effective usage and accuracy of the proposed technique are reported, highlighting the drawbacks that a poor surface representation can introduce. The whole procedure is made freely available within a Matlab (R) script with the addition of sample files. (c) 2019 John Wiley & Sons, Ltd. (c) 2020 John Wiley & Sons, Ltd.

The study of fast geomorphic changes in mountain channels and hillslopes, driven by intense geomorphic processes, requires frequent and detailed topographic surveys. In the last two decades, high-resolution topography (HRT) has provided new opportunities in the Earth Sciences. These have benefited from important developments in surveying techniques, methods, sensors, and platforms. Between these, the application of structure-from-motion (SfM) photogrammetry has become a widely used method to acquire HRT and high-resolution orthomosaics at multiple temporal and spatial scales. SfM photogrammetry has revolutionized the possibility to collect multi-temporal HRT in rugged or inaccessible environments like that observed in debris-flow catchments. However, appropriate workflows incorporating survey planning, data acquisition, post-processing, and error and uncertainty assessment are required, especially when multi-temporal surveys are compared to study topographic changes through time. In this paper, we present a workflow to acquire and process HRT. The workflow was applied in a debris-flow channel of the Moscardo Torrent (Eastern Italian Alps). Due to the topographic complexity of the study area, the SfM surveys were carried out integrating photos obtained from an unmanned aerial vehicle and from the ground. This integration guarantees high data density and avoids shadows. Eight photogrammetric surveys were collected between December 2015 and August 2017. In this time interval, five debris flows occurred. The surveying and data processing procedure described in the workflow permitted to summarize and integrate all the analysis steps and helped to identify and minimize potential sources of error in the multi-temporal SfM data (what we consider here 4D). Our case study demonstrates how the developed workflow presented here allows studying the geomorphic effects of debris flows and check dams functionality in mountain environments.