1,721,120 research outputs found
Channel changes during and after extreme floods in two catchments of the Northern Apennines (Italy)
Full text linkThe Nure and Trebbia catchments were affected by an extreme flood event on 13-14th September 2015. This study investigates the morphological responses to the flood of the Nure and Trebbia rivers and 18 tributaries with the aims to: i) quantify channel changes in width and pattern; (ii) identify the morphological and hydrological factors which might have driven channel response; (iii) quantify channel changes which have occurred after the flood event. Channel changes were characterized by field surveys and geomorphological analysis of multi-temporal orthophotos acquired before (2011), immediately after the flood (2015) and in 2020. In the tributaries, reach-scale channel widths after the flood reached up to 15 times their pre-flood values, whereas in the main channels the post/pre-flood width ratio attained a maximum value of 4. Augmented channel width in the main rivers was mostly associated with banks and islands erosion, whereas in the tributaries it was also due to deposition of coarse sediments onto the former floodplains. Islands were swept away in the main channels while both island erosion and formation occurred in the tributaries. In terms of channel pattern, preflood single-thread reaches displayed mainly multi-thread morphologies after the flood, mostly in response to a sudden input of coarse sediment supply. In the 5 yr following the flood, channels slightly narrowed but still remained wider than in 2011. The narrower reaches before the flood resulted to be the most sensitive to changes even some years after the flood. Statistical analyses between the channel width changes and a series of variables showed significant positive correlations with confinement index, channel slope, and the local storm rainfall depth. This study confirms how channel widening during large floods - usually neglected in flood hazard mapping and river basin management - is a very important process which must be considered in flood hazard assessment in mountain rivers
Fenomeni di erosione localizzata a valle di opere trasversali: integrazioni tra indagini di campo e di laboratorio
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Limitations in the use of Sentinel-1 data for morphological change detection in rivers
Full text linkThe identification of morphological changes occurring along river channels is essential to support river process understanding, assess sediment budgets and evaluate the effectiveness of river management. Among available remote sensing techniques, space-borne synthetic aperture radar (SAR) could potentially provide a powerful complement to optical imagery for this task. However, very few studies have been carried out on the use of SAR datasets to study erosion and deposition processes in river channels. In this work, we investigate the potential of change detection analysis based on Sentinel-1 data, by comparing variations of radar backscattering to river morphology changes identified through high-resolution drone acquisitions. We considered a time series of two years of Sentinel-1 data relative to a period where, despite a moderate fluvial event occurred, morphological changes have been significantly detected in multitemporal drone point clouds. Satellite optical imagery (planet.com) and hydro-meteorological data were used to support the analysis and interpret results. The results show that the spatial and temporal resolution of Sentinel-1 is currently not suitable for accurate discrimination of morphological changes related to river dynamics at local scale. Other spaceborne sensors with sub-metric ground sampling distance and/or daily revisit time would be probably suitable; however, so far, this option would need the use of commercial solutions with a consistent increase of the costs of the investigation
Large wood storage in streams of the Eastearn Italian Alps and the relevance of hillslope processes
Full text linkAn understanding of the dynamics of large wood (LW) in mountain channels provides
the basis for evaluating natural morphological patterns as well as managing potentially
hazardous wood transport during flood events. Few studies have investigated the
distribution of LW in managed streams of the Alps across a wide spatial scale. This paper
presents extensive field measurements of LW storage and channel morphology carried out
in 13 channels of the Eastern Italian Alps with drainage areas ranging from 1.2 to 70 km2,
mean bed slope between 0.03 and 0.38, and channel width between 2 and 20 m. More than
9000 LW elements were measured in the 33 reaches surveyed. A geostatistical, geographic
information system (GIS)-based model for wood recruitment from hillslope instabilities was
also developed and applied to the study basin. LW storage in the study channels results as
being much lower than in seminatural basins of comparable size and climate, and only
basins characterized by extensive mass wasting processes contain high wood loads with
relevant morphological consequences. The statistical analysis of LW storage at the reach
scale indicates that unit stream power is apparently the most significant hydromorphological
factor influencing LW storage, in agreement with studies in other world regions. However,
we argue that the effect of unit stream power on LW storage is not only linked to flow
transport capacity but also derives from its association with LW supply and valley
morphology. Both the GIS model and statistical tests on field data indicate that hillslope
instabilities connected to the channel network dominate the LW recruitment volume and the
distribution of in-channel wood storage
La resistenza al flusso in un torrente montano ad elevata pendenza con morpologia a step-pool
No full textTHE SULDEN/SOLDA GLACIER (EASTERN ITALIAN ALPS): FLUCTUATIONS, DYNAMICS, AND TOPOGRAPHIC CONTROL OVER THE LAST 200 YEARS
No full textThe Sulden/Solda glacier, located in the Ortler/Ortles massif (South Tyrol, Eastern Italian Alps), currently (2017 data) covers an area of ca. 5.2 km2. The glacier ranges in elevation from about 3500 m to 2440 m a.s.l., and it is largely debris-covered below 2900 m. By combining bibliographic resources, topographic maps and aerial images, we reconstructed the evolution of the Sulden Glacier since the beginning of the 19th century. The result is a detailed history of the glacier variations over the last 200 years, which reveals the complex interactions existing between glacier dynamics and valley morphology. The Sulden Glacier is formed by three ice bodies originating in the uppermost part of the Sulden catchment. In the past, the three glaciers merged to a single valley glacier that flowed northward down to the village of Sulden/Solda, at an elevation of ca. 1900 m a.s.l.. The evolution of these three ice bodies has not been uniform through time, and this heterogeneity drove some of the most impressive dynamics which have characterized the glacier history. In particular, the most prominent advances of the 19th century, including the 1818 surge, were driven by the lateral ice bodies of the Sulden Glacier that advanced and pushed the glacier tongue forward. When retreating, the morphology of the valley floor - characterized by several valley steps, played an important role in fragmenting the glacier, creating very large bodies of dead ice. The last prominent advance of the Sulden Glacier occurred in the 1920s (and lasted until 1927) and, excluding the small advance in the 1980s, the glacier hasbeen retreating since the 1930s. From topographic reconstructions we can estimate the volume of ice lost from 1936 to 2019 in ca. 169 million m3 (18.7 m w.e.). Out of these, ca. 144 million m3 (the 85%) have been lost after 1985, highlighting the inexorable impact of recent global warming
Pronounced increase in slope instability linked to global warming: A case study from the eastern European Alps
Full text linkIn recent decades, slope instability in high-mountain regions has often been linked to increase in temperature and the associated permafrost degradation and/or the increase in frequency/intensity of rainstorm events. In this context we analyzed the spatiotemporal evolution and potential controlling mechanisms of small- to medium-sized mass movements in a high-elevation catchment of the Italian Alps (Sulden/Solda basin). We found that slope-failure events (mostly in the form of rockfalls) have increased since the 2000s, whereas the occurrence of debris flows has increased only since 2010. The current climate-warming trend registered in the study area apparently increases the elevation of rockfall-detachment areas by approximately 300 m, mostly controlled by the combined effects of frost-cracking and permafrost thawing. In contrast, the occurrence of debris flows does not exhibit such an altitudinal shift, as it is primarily driven by extreme precipitation events exceeding the 75th percentile of the intensity-duration rainfall distribution. Potential debris-flow events in this environment may additionally be influenced by the accumulation of unconsolidated debris over time, which is then released during extreme rainfall events. Overall, there is evidence that the upper Sulden/Solda basin (above ca. 2500 m above sea level [a.s.l.]), and especially the areas in the proximity of glaciers, have experienced a significant decrease in slope stability since the 2000s, and that an increase in rockfalls and debris flows during spring and summer can be inferred. Our study thus confirms that “forward-looking” hazard mapping should be undertaken in these increasingly frequented, high-elevation areas of the Alps, as environmental change has elevated the overall hazard level in these regions
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