FIGURE 4
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Rock outcrops cover large areas of alpine headwaters and are entrenched by chutes and couloirs, which are controlled by faults in bedrock. These widespread landforms play an important role in delivering sediment to lower basin slopes. High-resolution topographical data from LiDAR surveys allow investigation of morphometric characteristics and sedim...
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The ongoing recession of Alpine glaciers since the end of the Little Ice Age (LIA) has exposed stores of glacial sediment to the activity of paraglacial processes. Slope wash, fluvial processes and mass movements (including debris flows, slides and falls) within the proglacial area (i.e. the area within the LIA terminal moraines) have received comp...
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... The labels indicate their locations. and sub-vertical rock cliffs are prevalent (Marchi et al., 2008). At the base of steep rock cliffs, scree slopes represent sources of abundant debris. ...
High‐intensity and short‐duration rainfalls can generate sudden and abundant runoff at the base of rocky cliffs that, entraining sediments, may originate debris flows. Two gauge networks have been set up in headwater sites of Dolomites (Northeastern Italian Alps) to monitor rainfall corresponding to the debris‐flow activity occurring there. The rain gauges are positioned both upstream and downstream the initiation areas of debris flows. Other five rain gauges sparse in the area integrate the two networks. In the years 2009–2020, rain gauges recorded rainfalls that triggered 41 debris flows. In most cases, rainfalls show a higher spatial variability along with both distance and altitude. Precipitation data are then compared with rainfalls estimated through a weather radar far about 70 km from there, to verify the possible interchangeability of the two measurement systems for the prediction of debris‐flow occurrence through suitable modeling of triggering discharges. The following results are obtained: (1) raw‐radar images mostly tend to underestimate precipitations recorded by rain gauges; (2) such underestimation entails, on average, a larger one on the simulated discharges and the prediction of debris‐flow occurrences (missed in 65% of the cases). Some methods for the correction on ground truth of raw‐radar images are applied to assess their use for evaluating the triggering discharges. Results show that once corrected using rain gauge data, radar‐derived rainfall estimates produce debris‐flow initiation predictions that more frequently match observations. Therefore, the presence of rain gauges close to the watershed centroids results essential for early warning systems based on triggering discharge modeling.
... In this area, large dolomite ranges dominate the landscape. At high elevations, vertical cliffs with an absence of vegetation are the main features of the environment (Marchi et al. 2002(Marchi et al. , 2008. These particular characteristics promote the accumulation of abundant, unconsolidated debris. ...
Debris flow events, generated by surface runoff, occur with great frequency in the Dolomites (Northeastern Italian Alps) during the summer season. Summer thunderstorms, which are common in the region, can quickly generate runoff at the base of rocky cliffs, which then entrains and propagates downstream the underlying unconsolidated material. In the past, the main atmospheric feature considered in evaluating the initiation of debris flow events was rainfall. Observations led to the development of rainfall intensity–duration thresholds for sediment mobilization, which compared incoming severe rainfalls with the potential for triggering debris flows. This study works toward the examination of another characteristic of the atmosphere, the atmospheric electric field. In particular, the behavior of the electric field prior to convective rainfall is investigated as an indicator of rainfall intensities capable of triggering debris flows, in a basin near Cortina d’Ampezzo (Italy). Results suggest that prior to bursts of intense rainfall, the electric field derivative frequency distribution exhibits a recurrent pattern roughly half the time. When it occurs, the amplitude of derivative frequency distribution intersects the zero axis twice before rainfall reaches maximum intensity. A regression model is designed which considers the amplitude maximum and the difference in time between the crossings of the zero axis. The validation of this model suggests a mild relationship between electric field and rainfall intensity in an alpine environment.
... Scree slopes and cones, however, are sometimes entrenched by debris flows ( Fig. 16.2; Chaps. 10 and 11), usually originating at the interface with overhanging rock gullies ( Marchi et al. 2008). In this case, debris flows establish lateral connec- tivity: when this process occurs, scree slopes become a source of debris, and the debris-flow channels entrenched into the scree provide a link connecting rock slopes to downslope catchment sectors. ...
Sediment connectivity is an emerging property of geomorphic systems and has become a key issue in research on geomorphic processes and sediment cascades. Sediment connectivity represents coupling relationships between system compartments and elementary units, and thus its understanding has important implications for the behaviour of hydro-geomorphic systems. The investigation and characterization of sediment connectivity and its evolution through time are of particular importance in proglacial areas and high-mountain environments since they are subject to intense morphodynamics and frequent changes in their structure and subsequent variations in sediment connectivity. This chapter aims to review the state of the art of sediment connectivity in proglacial and high-mountain environments studies, provides a synopsis of the most widespread landforms in mountain headwater catchments and describes their role with respect to coarse sediment connectivity. In addition, a section of the chapter is dedicated to the description of a recently developed topography-based sediment connectivity index. An example application to two contrasting alpine glacier forefields shows the effectiveness of this index for investigating and interpreting spatial patterns of connectivity in high-mountain catchments. Finally, we sketch avenues for future research regarding sediment connectivity (not only) in proglacial systems.
... Although there is a growing body of research in the subject (Montgomery andDietrich, 1988, 1992;Gomi et al., 2002;Benda et al., 2005;Williams, 2012), much remains unknown, because the development of slopes and channel networks is determined by the local geological structure, climate, and land use (Shreve, 1974;Dietrich and Dunne, 1993;Benda et al., 2005;Marchi et al., 2008) and consequently is different in various mountain areas worldwide. Exploration of headwater systems is therefore necessary in a broad spatial scale (Benda et al., 2005). ...
... The Sp-to-A relationship analyses in various mountain ranges have shown that the trend line illustrating this relationship may have different shapes depending on climate conditions and geological structures (Ijjasz-Vasquez and Bras, 1995;Stock and Dietrich, 2003;Marchi et al., 2008;Šilhán and Pánek, 2010). This method does not always enable the channel head location to be identified, as in some cases the Sp-to-A ratio may be the same for an unchannelled valley and a colluvial channel (Ijjasz-Vasquez and Bras, 1995). ...
The slope-fluvial system comprises two subsystems: (a) the slope subsystem, with the dominance of mass movements, and (b) the fluvial (channel) subsystem, with fluvial processes dominating. The most interesting element of this system, and the most difficult to identify and explore, is the slope-to-channel transition zone between the dominance of slope processes and the dominance of fluvial processes. This article aims at exploring the detailed structure of the slope-fluvial system, with a particular focus on the transition zone between the slope and fluvial subsystems in the alpine and montane environments of the Western Tatra Mountains. This purpose is pursued through: (1) identifying the morphometry of headwaters, and (2) delimiting a theoretical border between the slope subsystem and the fluvial subsystem. To this end, a statistical analysis of morphometric parameters of 50 first- to third-order subcatchments was conducted. Particular attention was paid to analyzing the catchments' gradient-to-area relationship. On the basis of gradient-to-area relationship, seven catchment types were defined, characterized by various sequences of slope-fluvial system sections, as well as a border between the slope subsystem and the fluvial subsystem. Based on the morphometric parameters and the slope-fluvial system structure, the catchments under research may be divided into two groups, representing areas with different natural environmental conditions. Alpine zone comprises mostly catchment systems in their initial development stage, with little-developed drainage networks, classified entirely to the slope subsystem. These catchments have very high gradients, elongated shapes, and low bifurcation ratios. Montane zone is composed mainly of catchments at a similar development stage, with relatively large surface areas (∼1 km²) and well-developed drainage networks, which include fluvial reaches. Such catchments are usually wide-shaped and have low gradients and high bifurcation ratios. The transition from slope process dominance to fluvial process dominance may be either smooth or abrupt.
... outcrops. These relatively high values are likely explained by the degree of fracturing of the Dolomite rock masses[Marchi et al., 2008]and by the aperture of fractures and faults favored by stress relief and dissolution to which seepage flow contributes. We, however, cannot exclude some influence on the calibrated values from the modeling approach. ...
In dolomitic headwater catchments, intense rainstorms of short duration produce runoff discharges that often trigger debris flows on the scree slopes at the base of rock cliffs. In order to measure these discharges, we placed a measuring facility at the outlet (elevation 1770 m a.s.l.) of a small, rocky headwater catchment (area ∼0.032 km², average slope ∼320%) located in the Venetian Dolomites (North Eastern Italian Alps). The facility consists of an approximately rectangular basin, ending with a sharp-crested weir. Six runoff events were recorded in the period 2011-2014, providing a unique opportunity for characterizing the hydrological response of the catchment. The measured hydrographs display impulsive shapes, with an abrupt raise up to the peak, followed by a rapidly decreasing tail, until a nearly constant plateau is eventually reached. This behavior can be simulated by means of a distributed hydrological model if the excess rainfall is determined accurately. We show that using the Soil Conservation Service Curve-Number (SCS-CN) method and assuming a constant routing velocity invariably results in an underestimated peak flow and a delayed peak time. A satisfactory prediction of the impulsive hydrograph shape, including peak value and timing, is obtained only by combining the SCS-CN procedure with a simplified version of the Horton equation, and simulating runoff routing along the channel network through a matched diffusivity kinematic wave model. The robustness of the proposed methodology is tested through a comparison between simulated and observed timings of runoff or debris flow occurrence in two neighboring alpine basins.
... Rock slopes are entrenched by steep couloirs, which correspond to lineaments related to fractures and faults. Accumulations of scree slopes at the foot of rockwalls are caused by various geomorphic processes that include rockfall, snow avalanches, debris flows and channelised runoff from upslope couloirs ( Marchi et al. 2008). The geo-structural settings show remarkable differences between the three study areas. ...
Hypsometric curves and integrals are effective tools for rapid quantitative assessments of topography. High-resolution digital terrain models derived from airborne LiDAR data have been analysed to study the hypsometry of small headwater rock basins (drainage areas up to 0.13 km2) in three study areas in the Dolomites (Eastern Alps) that have similar lithologies and climatic conditions. Hypsometric curves in the studied rocky headwaters display a variety of shapes and present remarkable differences between neighbouring basins. Hypsometric integrals show generally high values in the three study areas (>0.42, mean values between 0.51 and 0.65). The extent of the scree slopes located at the foot of rock basins in the three study areas is larger in the area with lower hypsometric integrals and indicates consistency between the development of basin erosion, which is shown by the hypsometric integral, and debris yield, represented by the extent of scree slope. No clear relations were observed between the hypsometric integrals and basin area and shape. When extending the analysis to larger basins, which encompass rocky headwaters and downslope soil-mantled slopes, a negative correlation is found between the hypsometric integral and catchment area, suggesting that the scale independency of the hypsometric integral occurs essentially in headwater rock basins. Geomorphometric indices (residual relief and surface roughness) have contributed to interpreting the variability of surface morphology, which is related to the geo-structural complexity of the catchments.
... These process domains were initially schematic, based on few data, but have been supported by later work (e.g. Whipple & Tucker 1999;Snyder et al. 2000;Kobor & Roering 2004;Marchi et al. 2008). Brardinoni & Hassan (2006) added an additional domain in which systems, dominated by debris-flow deposition, occupy that part of the alluvial domain of Montgomery & Foufoula-Georgiou (1993) that is located towards higher drainage areas and steeper slopes (Fig. 2a). ...
... Within the diffusive processes domain in slope-area plots, slope increases with drainage area. The most likely reason that most of our data do not show this turnover is that the slopes we studied lack stable vegetation (Dietrich & Perron 2006;Marchi et al. 2008). Another potential contributing factor is that the bedrock and colluvium in our study areas are not naturally cohesive; for example, clay-rich rocks can exhibit convex creep-dominated slopes in unvegetated badlands on Earth. ...
The formation process of recent gullies on Mars is currently under debate. This study aims to discriminate between the proposed formation processes - pure water flow, debris flow and dry mass wasting - through the application of geomorphological indices commonly used in terrestrial geomorphology. High-resolution digital elevation models (DEMs) of Earth and Mars were used to evaluate the drainage characteristics of small slope sections. Data from Earth were used to validate the hillslope, debris-flow and alluvial process domains previously found for large fluvial catchments on Earth, and these domains were applied to gullied and ungullied slopes on Mars. In accordance with other studies, our results indicate that debris flow is one of the main processes forming the Martian gullies that were being examined. The source of the water is predominantly distributed surface melting, not an underground aquifer. Evidence is also presented indicating that other processes may have shaped Martian crater slopes, such as ice-assisted creep and solifluction, in agreement with the proposed recent Martian glacial and periglacial climate. Our results suggest that, within impact craters, different processes are acting on differently oriented slopes, but further work is needed to investigate the potential link between these observations and changes in Martian climate.
... Debris cones, with apexes located at the outlet of couloirs, which cut the superjacent rock slope, are prominent features in the scree belt. Four main processes influence sediment dynamics on the scree slopes and cones, and contribute to their complex morphology, namely, gravitational accumulation of weathered rock fragments, rockfall, snow avalanches, and debris flows ( Marchi et al., 2008). The main morphological features of the studied slope are debris-flow channels and debris-flow deposits (at different stages of evolution and activity), rockfall deposits, planar gravitational scree deposits, and isolated Published by Copernicus Publications on behalf of the European Geosciences Union. ...
Herein, an aerial LiDAR topographic dataset is analysed and interpolated by means of geostatistical techniques in order to examine the morphology of a scree slope area in the Eastern Italian Alps. The LiDAR-derived digital terrain model (DTM) is analysed using variogram maps as spatial continuity indexes. This allowed for evaluation of the reproduction of spatial variability of topography and for the characterization and comparison of different morphological features occurring in the study site. The results indicate that variogram maps efficiently synthesise the spatial variability of topography in a local search window, representing suitable "fingerprints" of surface morphology.
In mountain environments, the coupling of hillslopes processes with the channel network during extreme events is of great importance for rivers dynamics, as debris flows and landslides are among the most important sources of sediments. The Stolla Creek (40 km² drainage area, South Tyrol, Italy) is a confined and partly confined mountain channel that was affected by an extreme flood in August 2017, followed by a smaller event in August 2020. The geomorphic effects of the two floods were investigated both in the main channel and over the entire basin with the aim to assess the impacts of the lateral sediment connectivity to the channel response and to the event-scale sediment export.
An integrated approach was applied, including radar rainfall estimation, hydrologic-hydraulic analysis, analysis of morphological changes and sediment delivery to the stream network. Hillslope and channel processes were mapped and characterized by using geomorphological analysis of multitemporal orthophotos and Digital Terrain Models. Debris-flow connectivity to the main channel was derived by combining field evidence and GIS-based analysis.
The 2017 flood was caused by rainfall with a short duration (6 h) and a rainfall intensity exceeding 45 mm/h. More than 600 debris flows were triggered in the Stolla basin, and the main channel experienced widening (width ratio between 1.3 and 4.9) through bank erosion and overbank deposition. Widening was accompanied by aggradation in the river corridor up to 1.2 m or incision down to −2.2 m. The 2020 flood was characterized by lower rainfall intensity (max 17 mm/h) and a longer duration (48 h), and debris flows were not triggered. The moderate magnitude of the 2020 flood peak did not lead to channel widening, but marked bed incision (up to −1.4 m) occurred in the reaches where aggradation took place during the 2017 event. In both flood events, limited volumes of sediments were exported from the catchment outlet.
Overall, our results highlight how structural connectivity at the basin scale determines the potential sediment cascades linking hillslopes to channels but time-varying functional connectivity – driven by hydrological drivers as rainfall intensities and durations – eventually control the actual sediment transport effectiveness both on hillslopes and along the channel.
High-resolution digital terrain models (HR-DTMs) of regional coverage open interesting scenarios for the analysis of landscape, including derivation and analysis of channel network. In this study, we present the derivation of the channel network from a HR-DTM for the Autonomous Province of Trento. A preliminary automatic extraction of the raw channel network was conducted using a curvature-based algorithm applied to a 4 m resolution DTM derived from an airborne LiDAR survey carried out in 2006. The raw channel network automatically extracted from the HR-DTM underwent a supervised control to check the spatial pattern of the hydrographic network. The supervised control was carried out by means of different informative layers (i.e. geomorphometric indexes, orthophoto imagery and technical cartography) resulting in an accurate and fine-scale channel network.
