Interpretation of channel changes is not always straightforward since it requires a detailed reconstruction of the evolutionary trajectory of channel morphology, a quantitative analysis of ...controlling factors and, finally, identification of links between evolutionary trajectories and controlling factors. The aim of this paper is to explain channel adjustments and controlling factors in the Tagliamento River, a large gravel-bed river in northeastern Italy. Traditional methods for studying historical channel changes (i.e., use of aerial photos, topographic data) were employed, but numerical modelling turned out to be very useful for the quantification of bedload transport and for supporting interpretation of past changes and likely future channel evolution.
River channel underwent three main phases of adjustment over the last 200years. The first two phases, from the end of the nineteenth century to the early 1990s, were characterized by narrowing (channel width decreased from 1250 to 540m) and incision (about 1m); and the third phase, from the 1990s to present day, by widening (from 540 to 600m) and slight aggradation (about 0.2m).
Combining evolutionary trajectories of channel morphology and analysis of controlling factors we argue that the long-term channel evolution of the Tagliamento River was driven mainly by human intervention at the reach scale (i.e., sediment mining and channelization). Changes in sediment supply in the catchment area had no, or minor, effects in the study reach. The most recent changes (i.e., widening and slight aggradation) are explained as a response to past disturbances that have produced a remarkable change of channel geometry and an increase of unit stream power in the reach. Magnitude and frequency of formative discharges are a key driving factor of the intensity of recent changes, while this was not the case during the previous phases of adjustment.
► Temporal resolution of data is crucial for interpretation of channel changes. ► Long-term channel evolution was driven by human intervention at reach scale. ► Recent channel adjustments are explained by an excess of unit stream power. ► Coupling historical analysis and numerical modelling.
The trace element and Sr isotope records in two coeval stalagmites characterized by different growth rates and flow regimes at Savi cave (Grotta Savi, NE Italy) reveal different sources and ...incorporation mechanisms for Mg and Sr. Mg is sourced primarily from dissolved cave host rock while particulate Mg derived from soil plays a subordinate role. The presence of particulate-borne Mg is inferred from the co-variation of Mg and particle-associated elements (Th, Al and Mn) which are preferentially concentrated in open columnar calcite layers. Variation in Mg concentrations corrected for particle-influenced components, the Mgc parameter, is controlled by water–rock interaction, with higher and lower Mgc during dry and wet phases, respectively. This is thought to reflect incongruent dissolution of Mg-rich phases. Correction of Sr concentrations for contributions from airborne exogenic Sr, based on 87Sr/86Sr ratios, yields the bedrock-only contribution (Src). Src variation in stalagmite calcite is influenced by speleothem growth rate and by variation of the calcite-water Sr partitioning in wet and dry phases, and only to a minor extent by incongruent dissolution of Mg-rich phases. Concentration profiles for Mgc and Srcg (corrected for growth rate effects) show inverse correlations and are inferred to show hydrological significance which is captured in a hydrological index, HI. We suggest HI provides robust information on water–rock interaction related to hydrological changes and can be utilized in both wet and semi-arid environments, provided the corrections for soil Mg and exogenic Sr can be applied with confidence. Application of the HI index allows correction of Grotta Savi oxygen isotope data, to yield a δ18Oc time series that shows when changes in moisture sources and atmospheric reorganization, or changes in moisture amount, were significant. This is especially evident during the Younger Dryas (YD). The Savi record supports the concept of a two-phase YD, marked by an increase of moisture and stronger impact of Adriatic and Mediterranean Sea influences over the northern Adriatic region from 12.3ka onwards. Then, a large-scale atmospheric reorganization and gradual northward shift of the Polar Front caused a progressive reduction of sea influence over the region from 12.1ka, supporting the concept of a hemispheric change.
This paper investigates the generation of hydrodynamic water waves due to rockslides plunging into a water reservoir. Quasi-3D DEM analyses in plane strain by a coupled DEM-CFD code are adopted to ...simulate the rockslide from its onset to the impact with the still water and the subsequent generation of the wave. The employed numerical tools and upscaling of hydraulic properties allow predicting a physical response in broad agreement with the observations notwithstanding the assumptions and characteristics of the adopted methods. The results obtained by the DEM-CFD coupled approach are compared to those published in the literature and those presented by Crosta et al. (Landslide spreading, impulse waves and modelling of the Vajont rockslide. Rock mechanics,
2014
) in a companion paper obtained through an ALE-FEM method. Analyses performed along two cross sections are representative of the limit conditions of the eastern and western slope sectors. The max rockslide average velocity and the water wave velocity reach ca. 22 and 20 m/s, respectively. The maximum computed run up amounts to ca. 120 and 170 m for the eastern and western lobe cross sections, respectively. These values are reasonably similar to those recorded during the event (i.e. ca. 130 and 190 m, respectively). Therefore, the overall study lays out a possible DEM-CFD framework for the modelling of the generation of the hydrodynamic wave due to the impact of a rapid moving rockslide or rock–debris avalanche.
A multi-parametric study of the space-time evolution of the seismicity from 2015 to the beginning of 2020 is performed within a well-focused area, located between the Alps and the Prealps, in the ...central part of the Friuli Venezia Giulia region (Northeastern Italy). The study area is characterized by a complex tectonic pattern resulting from the interference of differently oriented fault systems and involving mechanically heterogeneous rocks. From 2018 to 2019, the area experienced a significant increase and clustering of radiated seismic energy. The estimated damage pattern emphasizes the tectonic complexity. Notably, the most energetic events are located in correspondence with the sharp transitions from zones of low damage to zones of intermediate damage.
The evolution of seismicity is analyzed through the temporal variation of the Shannon entropy, b-value, fractal dimension, nearest neighbour distance, and changing orientation of the planes inferred from Principal Component Analysis (PCA). The PCA analysis is applied along a geological cross-section to infer the geometry and the time-evolution of the fracturing. It reveals best-fit planes mainly subvertical. Two distinct temporal phases are recognized, characterized by different orientation of planes and propagation of fracturing. The two phases correspond to the changes in the seismic activity, highlighted by the variations of the entropy, b-value, fractal dimension and nearest neighbour distance. The observed spatio-temporal evolution of seismicity is interpreted within the frame of damage evolution in a heterogeneous medium subjected to an applied remote stress.
•A multi-parametric description of seismicity changes is proposed and interpreted as the expression of rocks damage evolution.•North-eastern Italy, for its complex tectonics and rather high seismic hazard, is considered as test area.•Shannon entropy, b-value, fractal dimension, nearest neighbour distance, and Principal Component Analysis are investigated.•Sharp variations of rock mechanical characters control stress concentrations and localization of seismicity.
While recent landscape changes can be usually easily read through accessible morphological features, relatively ancient processes can be difficult to detect as the associated morphologies and ...deposits are often buried below younger sediments. With the aim of understanding the evolution of the distal Venetian-Friulian Plain (NE Italy) after the Last Glacial Maximum (LGM), this work presents the analysis performed on a dataset of ca. 2300 mechanical and hand-made cores, which allowed a detailed reconstruction of the formation and evolution of an incised valley, now almost completely filled and with little to absent morphologic expression. Such valley, up to 1.2 km wide, with a depth of 20 m below the LGM alluvial plain and traced for a length of 25 km, is the result of the complex interplay between minor spring-fed rivers and the Tagliamento River. The detailed characterization of the infilling allowed to identify two main phases in the valley evolution. The first one is related to the activity of the paleo Tagliamento River and led to the deposition of a 10 m thick gravelly unit (ca. 19–9.5 ka cal BP). The second phase, which followed a disconnection of the Tagliamento, is linked to the Holocene marine transgression and led to the formation of a lagoon environment within the valley and to the deposition of a ca. 15 m thick unit of lagoon muds (ca. 8 ka cal BP - historic time). This latter unit lays on top of gyttja deposits, indicating for the first time in this area the presence of widespread lacustrine environments in the Early Holocene. This work presents an in-depth analysis on the evolution of a distal plain incised valley, from its formation to its final filling, providing at the same time the means to describe the development of the entire alluvial plain landscape, spanning from the end of the LGM to the middle Holocene. We present new data on the paleoenvironmental and morphologic evolution of the Venetian-Friulian Plain area as a consequence of the interplay between autogenic forces and sea-level rise. Our study allowed to understand the importance of both Alpine rivers and groundwater-fed streams in the formation of large incised valleys in the coastal sector of the whole Venetian-Friulian Plain. Finally, as during the transgressive phase the upstream sediment input in the valley was almost absent, this study provides insights into facies and architecture of a rare example of downstream-controlled filling of an incised valley.
•A large dataset of cores allowed to reconstruct with unprecedent detail a buried incised valley in the Tagliamento Megafan.•The stratigraphy of the infilling provides a reference for the evolution of the entire northern Adriatic, from the early deglaciation stage to the Holocene marine transgression.•The reconstructed morphology of the buried valley indicates a complex interplay among paraglacial dynamics, autogenic forcing and the stratigraphic architecture of the alluvial plain.
The approval of the national law on collective property (2017) and the almost simultaneous approval of the Friuli Venezia Giulia Regional Landscape Plan(2018) are introducing novelties in the places ...that had mostly seen a resurgence of interest on collective property.. The essay takes as an example one of the areas with the highest density of management claims by fractional communities, one of Carnia's traditional alpine areas, the Canal di Gorto. Its environment was marked both by the demographic crisis and the uncertainty about the stability of the communities in relation to the great economic transformations imposed by globalization and industrial delocalisation. Our aim was to describe the innovations introduced in the last five years in order to understand if any change in the evolution of the management of collective assets is looming. The acknowledgement in the landscape plan of so-called civic uses in Friuli Venezia Giulia has proved to be very partial, despite the cooperation of the Coordination of regional collective properties and the new investigations by the regional planning offices engaged in the formation of the urban planning tool. On the other hand, at least three small villages in 2020 claimed the democratic right to be allowed to manage fractional resources on their own in order to guarantee benefits and services to their inhabitants. The process described is placed within a democratic claim of territorial management capable of producing projects even starting from planning solicitations at a regional level.
The Geoswim programme is an expedition-type project which is aiming to survey, monitor and measure the entire perimeter of rocky coasts of the Mediterranean Sea. The project officially started in ...2012 with the first one-man survey of 193.4 km by snorkeling along the northeastern Adriatic coasts, and is ongoing. So far, 559.5 km of rocky coasts have been surveyed, over 98 days of survey, and several hundred thousand time-lapse images, continuous videos and outline images have been collected, both above and below the waterline. Bathymetric data and physical/chemical parameters, such as temperature and electrical conductivity have also been collected during the snorkel surveys. Instruments are hosted on a specially-built raft, called instrumental-supported raft (ISR). The data are not homogeneous because over the years the approach has changed following the introduction of new technologies and some redesign of the instruments used, and, in part, also the type of data collected. Moreover, observational data for use in coastal studies and for integrating instrumental data are collected. The paper presents and take stock of the geometry of the database and discusses the main results of the Geoswim programme.
Data analysed highlighted that the database is a significant archive that provides 1) images and videos as a baseline for subsequent comparisons, 2) large amount of images to be used to build 3D models of coastal landforms, 3) data for statistics, and 4) a valuable source of possible discoveries of unknown coastal objects, such as sea caves, tidal notches at unexpected sites, ecological observations, etc.
•Presentation and take stock of the database of the Geoswim programme•Discussion of the potentialities of the swim-survey approach through published and new data collected during the expeditions•Analysis of the Geoswim programme and its evolution•Future perspectives of the programme
Decommissioned mines represent a worldwide concern due to the potential long-term effects related to the dispersion of potentially toxic elements (PTEs) in the environment. In this study, 176 water ...samples were collected in the period 2018–2021 at the carbonate-hosted Pb-Zn Raibl mine which is affected by neutral mine drainage (NMD). The post-flotation tailings are the main source of PTEs (Zn, Pb and especially Tl) in the river drainage system. Compared to other dissolved PTEs (Zn, Pb, Cd), Tl was found to be more mobile, reaching concentrations up to 120 μg L−1 in waters flowing in the tailings impoundments. Modelling results suggest that Tl is mainly present in the Tl(I) ionic and mobile form thus suggesting that relevant natural attenuation processes for this element are not expected in the investigated area. In contrast, Zn and Pb attenuation pathways appeared to be governed by pH-dependent speciation and sorption processes, whereas elevated Zn concentrations were likely also limited by hydrozincite precipitation. Metalloids such as As and Sb were almost entirely released into the slightly alkaline waters of the mine drainage system, which are generally characterised by longer residence time or standing waters whereas As and Sb concentrations were negligible in the tailings-seepage waters. However, intense rainy events may increase PTE concentrations of one order of magnitude, especially in the tailings impoundment groundwater as a result of a rise in the water table, and PTE total dissolved loads of three orders of magnitude, in the main stream during high flow events, thus representing the most critical factor in regulating the remobilisation and downward dispersion of PTEs in the river drainage system.
•176 water samples were collected at the Pb-Zn Raibl mine site from 2018 to 2021.•Dispersion of potentially toxic elements persists 30 years after shutdown.•The post-flotation tailings represent the main sources of Thallium in waters.•Intense rainy events may notably increase PTEs and total dissolved loads.•Arsenic was found to be more mobile in gallery seepages.
Future trends in debris flow activity are constructed based on bias-corrected climate change projections using two meteorological proxies: daily precipitation and Convective Available Potential ...Energy (CAPE) combined with specific humidity for two Alpine areas. Along with a comparison between proxies, future number of days with debris flows are analyzed with respect to different regional and global climate models, Representative Concentration Pathways (RCPs), and area for quantile mapping. Two different base periods are also analyzed, as debris flows were observed on only 6 (17) days between 1950 and 1979, yet on 18 (49) days between 1980 and 2009 for Fella River, NE Italy (Barcelonnette, SE French Alps). For both areas, future climate projections vary between no change up to an increase of 6.0 % per decade in days with debris flow occurrences towards the end of 21st century. In Barcelonnette, the base period and proxy have a bigger impact on the future number of debris flow days than the climate model or RCP used. In Fella River, the base period, RCP, and proxy used define the future range. Therefore the selection of proxy, base period and downscaling technique should be carefully considered for future climate change impact studies concerning debris flow activity and associated fast-moving landslides.
•Distance from mainland influences saltmarsh HA properties more than vegetation.•Electron donating capacities of saltmarsh HA increase along the geographical gradient.•HA bound to the mineral phase ...have larger electron donating capacities.
In saltmarsh soils, humic acids (HA) are involved in geochemically important redox processes. The electron donating capacity (EDC) of HA depends on their molecular structure, but also reflects the intensity of biological reduction in tidal environments. We examined twelve soils in three saltmarshes located along a geographical gradient and applied a specific sequential extraction procedure for the isolation of HA fractions bound (BHA) or not (FHA) to the mineral matrix by Ca2+ bridges, and investigated the relationships of their properties, in particular their EDC, with the biogeochemical characteristics of the soils. Spectroscopic assessment was carried out by UV–vis, FTIR and 13C NMR, quantification and characterization of radicals was performed by electron paramagnetic resonance (EPR) spectroscopy. The EDC was determined by using the 2,2′-azinobis-(3-ethylbenzothiazolinesulfonic acid) (ABTS) decolorization assay and experimental data were fitted to a biphasic model to calculate the contributions of the fast and slow reactions to electron transfer. The results confirmed that the two HA fractions possess different structural characteristics and that BHA present higher EDC values compared to FHA. The EDC of both fractions is strongly related to the geochemical characteristics of soils, and represents an easily measured and highly informative parameter to understand mechanisms affecting redox processes in transitional environments.
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