Tagliamento Research Articles

Structural inheritances, fault segmentation and seismogenic potential at the front of the eastern Southern Alps (central Carnic Prealps, NE Italy)

New geological and morphotectonic surface data coupled with the revision of the ENI-Exploration & Production seismic lines, made it possible to review the tectonic structure of the Pliocene-Quaternary front of the eastern Southern Alps in the area between the Cellina River and the Tagliamento River (central Carnic Prealps, NE Italy). The eastern Southern Alps are a SE-verging fold and thrust belt in activity from the middle Miocene to the Present. The presence of Paleogene structural inheritances influenced the current structural arrangement of the thrust-belt and the potential seismogenesis, supporting segmentation of the Neoalpine external front. In particular, the presence of the NW-SE trending Mt.Ciaurlec – Palmanova – Pozzuolo structural high, inherited from the W-ward propagation of the External Dinarides during Paleogene, generated lateral lithological facies change and influenced not only the undulation between the Neogene-Quaternary Maniago-Meduno and Toppo-Forgaria Thrusts, but also the segmentation of the outermost portion of the Neoalpine external front consisting into two segments with different geometric and structural characteristics: 1) the ENE-WSW striking Arba-Sequals segment that runs buried under the upper Pleistocene sequences of the piedmont Friuli plain; 2) the W-E Ragogna segment that shows widespread evidence of surface deformation of the Last Glacial Maximum (LGM) alluvial plain. In particular, the long-lasting activity of the Ragogna segment is testified by the late Miocene-Middle Pleistocene angular unconformities, forced drainage anomalies and tilted and uplifted Quaternary palaeosurfaces. A discussion on the seismogenic potential of the investigated structures is proposed.

Phosphorus enrichment enabled Amorpha fruticosa to invade on the floodplain of the Tagliamento River, Italy

The North American nitrogen-fixing shrub Amorpha fruticosa (false indigo) is an aggressive invader of riverine habitats in Europe, though the reasons for its success are poorly understood. We hypothesized that its spread on the floodplain of the Tagliamento River in Northern Italy was enabled by anthropogenic phosphorus (P) enrichment. To investigate this hypothesis, we surveyed seed production at different locations along the river and performed a growth chamber experiment in which seedlings of three common floodplain shrubs (A. fruticosa, Salix eleagnos and Buddleja davidii) were grown at 10 levels of both nitrogen (N) and P. As a bioassay of N and P availabilities, we analyzed concentrations of these nutrients in Salix eleagnos leaves collected at different positions along the river. P availability was significantly higher in the lower reaches of the river, where A. fruticosa was abundant, than at its upstream limit. Numbers of A. fruticosa seeds per inflorescence increased strongly in a downstream direction and there was a trend for higher seed weight. In the growth experiment, A. fruticosa was more P-demanding than the other species, producing little biomass and no rhizobial nodules at low P. It also exhibited greater plasticity than the other species in both root mass fraction and ratio of longest root length to root mass. We conclude that anthropogenic P enrichment enabled A. fruticosa to invade what was originally a very oligotrophic environment. This N2-fixing shrub exhibits greater phenotypic plasticity than native S. eleagnos, giving it a competitive advantage under conditions of high P availability.

Flow dynamics in rivers with riffle-pool morphology: a dataset from case studies and field experiments

Bars and pools, common for natural riverbeds, form sequential patterns due to interactions between river flow, alluvium and vegetation. While the morphodynamics of bar-pool units are relatively well understood, far less is known about associated riffle-pool hydrodynamics because of a lack of high-resolution data collected in rivers and problems attaining natural scaling in laboratory studies. Here we present a dataset on turbulent flow structure in riffle-pool sequences of a natural river. Two case studies and two field-based experiments were carried out in a side branch of the braided gravel-bed Tagliamento River in Italy. Our case studies deliver detailed information about the three-dimensional structure of mean and turbulent flows in natural riffle-pool/run and pool-riffle/glide transitions. Field-based experiments completed with the in-stream flume models of a riffle-pool transition and a shallow jet model provide a methodological bridge for linking simplified hydrodynamic theories of shallow jets to complex flow structure documented by our case studies. Therefore, this dataset enables examination of scaling effects and can be widely used for validation of numerical models.

Monitoring Braided River-Bed Dynamics at the Sub-Event Time Scale Using Time Series of Sentinel-1 SAR Imagery

Remote sensing plays a central role in the assessment of environmental phenomena and has increasingly become a powerful tool for monitoring shorelines, river morphology, flood-wave delineation and flood assessment. Optical-based monitoring and the characterization of river evolution at long time scales is a key tool in fluvial geomorphology. However, the evolution occurring during extreme events is crucial for the understanding of the river dynamics under severe flow conditions and requires the processing of data from active sensors to overcome cloud obstructions. This work proposes a cloud-based unsupervised algorithm for the intra-event monitoring of river dynamics during extreme flow conditions based on the time series of Sentinel-1 SAR data. The method allows the extraction of multi-temporal series of spatially explicit geometric parameters at high temporal and spatial resolutions, linking them to the hydrometric levels acquired by reference gauge stations. The intra-event reconstruction of inundation dynamics has led to (1) the estimation of the relationship between hydrometric level and wet area extension and (2) the assessment of bank erosion phenomena. In the first case, the behavior exhibits a change when the hydrometric level exceeds 1 m. In the second case, the erosion rate and cumulative lateral erosion were evaluated. The maximum erosion velocity was greater than 1 m/h, while the cumulative lateral erosion reached 130 m. Time series of SAR acquisitions, provided by Sentinel-1 satellites, were analyzed to quantify changes in the wet area of a reach of the Tagliamento river under different flow conditions. The algorithm, developed within the Python-API of GEE, can support many types of analyses of river dynamics, including morphological changes, floods monitoring, and bio-physical habitat dynamics. The results encourage future advancements and applications of the algorithm, specifically exploring SAR data from ICEYE and Capella Space constellations, which offer significantly higher spatial and temporal resolutions compared to Sentinel-1 data.

Detection of the Endangered Stone Crayfish Austropotamobius torrentium (Schrank, 1803) and Its Congeneric A. pallipes in Its Last Italian Biotope by eDNA Analysis

The stone crayfish, Austropotamobius torrentium, is a European freshwater crayfish. Although this species is relatively widespread throughout the continent, it is undergoing significant declines throughout its range. However, as the decline rates have not been quantified in detail, this species is classified as data deficient by the IUCN Red List of Threatened Species. The present study describes the development and validation of two species-specific assays based on hydrolysis probe chemistry for the detection of A. torrentium and A. pallipes environmental DNA (eDNA) in water samples collected in the Julian Alps of Italy (Friuli Venezia Giulia). The eDNA-based method was applied to 14 sites within the Danubian Slizza basin, known to be inhabited by A. torrentium, but with insufficient information on their distribution. In addition, one station in the Tagliamento River basin was sampled to test the performance of the A. pallipes probe. The presence of A. torrentium is confirmed at 6 out of 15 sites. At four of these sites, A. torrentium is detected for the first time. In contrast, the presence of A. torrentium was not detected at two sites already known to harbour the species. Finally, the presence of A. pallipes was confirmed in the station belonging to the Tagliamento basin. The methodology described, which allows the distinction between the two species, paves the way for the parallel detection of the stone crayfish and the white-clawed crayfish (A. pallipes) through eDNA analysis.

What locals want: citizen preferences and priorities for the Tagliamento River

Sustainable river management frameworks are based on the connection between citizens and nature. So far, though, the relationship between rivers and local populations has played a marginal role in river management. Here, we present a blueprint questionnaire to characterize the perception of cultural ecosystem services (CES) by locals, and how preferences change across the river landscape. We investigate how locals value the river and whether their preferences are affected by characteristics such as place of residence, age, frequency of visits and relation to the river. The questionnaire was filled in by more than 4000 respondents, demonstrating huge interest and willingness to contribute to the project. A striking 85% of respondents identify a spiritual value of the river, suggesting a strong emotional connection. River conservation is the main priority for most respondents across the different groups. The map of favorite places shows that most of the river is appreciated by locals, with a high preference for the landscape of the braided middle course. The most valued area of the river, located in the middle course, faces threats due to dam construction projects, which would modify the natural course of the river and likely impact the favorite places of the locals. Our study highlights discrepancies between management choices and citizens´ values and priorities, and shows the need for including river values and CES in river management and their potential role for tackling conflicts. More generally, this work points out that any river intervention should be pondered carefully accounting for its environmental impact also in terms of loss of river values.

A Bidimensional Model of the Tagliamento River

The propagation of a flood wave is a very challenging topic, crucial in managing the flood risk. In the literature, several numerical models have been proposed to deal with this issue; most of them need the roughness coefficients to be assigned by the operator. The bottom roughness calibration of floodplains and channels represents a key point for flood studies, because it can heavily influence the results of any kind of numerical simulation. In this study, a numerical model is applied to the Tagliamento River, in North-East Italy. One of the main characteristics of this river is its natural environment, which changes from a very wide braided channel in the middle course to a narrow meandering river moving towards the sea. This makes the bed roughness extremely variable along the river, with different kind of vegetation, braiding, different grain size, meandering, etc. In this regard, particular care should be devoted to the roughness coefficient attribution and calibration. In the present paper, we present the detailed step of calibration and validation of a bidimensional numerical model on the Tagliamento River. A novel method to assign and calibrate roughness coefficient is introduced. Finally, the model is validated against two main flood events occurred in 1966 and 1996.

Seismic Analysis of a Limestone Rock Slope Through Numerical Modelling: Pseudo-Static vs. Non-Linear Dynamic Approach

In the present work, a seismic analysis was performed in advance on a limestone rock slope (height = 150 m) outcropping along the Tagliamento River valley, in the Friuli Venezia Giulia Region, north-eastern Italy. The analysed slope is characterised by strong rock mass damage, thus resulting in a critical stability condition (unstable volume = 110,000–200,000 m3). The seismic analysis was performed adopting the 2D finite difference method (FDM) and employing both a pseudo-static approach and a non-linear dynamic approach. Model outcomes demonstrate that the seismic motion induces internal, localised ruptures within the rock mass. Some important differences in the mechanical behaviour of the rock slope were highlighted, depending on the specific modelling approach assumed. When adopting a pseudo-static approach, the slope failure occurs for PGA values ranging between 0.056 g and 0.124 g, depending on the different initial static stability condition assumed for the slope (Strength Reduction Factor SRF = 1.00–1.15). According to the non-linear dynamic approach, the slope failure is achieved for PGA values varying between 0.056 g and 0.213 g. Pre-collapse slope displacements calculated with the pseudo-static approach (12–15 cm) are much more greater than those obtained through the non-linear dynamic approach (0.5–3 mm). The modelling results obtained through the non-linear dynamic analysis also testify that the seismic topographic amplification is 1.5 times the target acceleration at the slope face and 2.5 times the target acceleration at the slope toe.

Flood Risk and River Conservation: Mapping Citizen Perception to Support Sustainable River Management

Involving citizens in river and flood risk management is critical for risk reduction and sustainable development within river basins, but local community input is often limited. This is partly due to the difficulty of quantifying the perceived values and risks related to the rivers, because these are based on personal knowledge and opinions. There is a need for more data on locals’ opinions and how they are spatially distributed across the river basin. Studies analyzing how perceived risks match evidence-based data can be a first step to including local knowledge in the decision-making process and pose the basis to enhance preparedness. Here, we present a blueprint questionnaire to characterize the perception of flood risk and its spatial distribution across the river basin. Respondents are asked their perception of the role of the river in terms of flood risk and management, as well as to pinpoint on a map the areas they identify as the most dangerous during floods. The approach is tested on the Tagliamento River in the Italian Alps, characterized by debates regarding flood protection, flood management and ecological conservation. The flood risk perception map shows good agreement between perceived risk and existing flood risk assessment maps in the lower basin, where major floods happened in recent memory (1966). In the upper basin, despite having suffered frequent floods, participants are more uncertain about the risks. There is interest in being involved in the risk management debate, and most respondents believe that risk reduction and river conservation are compatible. Land use planning is identified as a factor that can increase flood risk. The results point to the necessity to tackle together conservation, risk management and land use planning in order to develop risk-oriented river management strategies. Our study demonstrates how online participatory mapping can be used to improve the understanding of citizens’ perceptions and expectations with regards to their river, and support participation in sustainable river management.

Decoding a complex record of anthropogenic and natural impacts in the Lake of Cavazzo sediments, NE Italy

The Lake of Cavazzo is a natural, lacustrine basin in the Friuli-Venezia Giulia region (NE Italy), which occupies a fluvio-glacial suspended valley of the Tagliamento river, at the southern front of the Alpine chain. The lake formed after the melting of major glacial tongues at the end of the Last Glacial Maximum, and has been affected in recent years by natural and anthropogenic events, with economic, cultural and environmental consequences. According to local witnesses, the lake environment has changed dramatically after the 1950s, when the basin was connected to a hydroelectric power plant collecting waters from a wider catchment area, as it served as its final discharge basin.In this work, based on a densely-spaced grid of high-resolution seismic reflection profiles complemented by sediment cores, we analysed the uppermost lake stratigraphy, highlighting major changes occurring at a decadal scale. Our main purpose is to verify whether and how the lake sediments record the transition from pristine/natural to artificial conditions, as well as the effects of multiple natural impacts including the 1976–77 Friuli earthquake sequence. The results of our analysis suggest varying environmental conditions of the lake after the 1950s indicated by changing sediment mineralogy, increased deposition of allochthonous clastic sediments, and recurrent episodes of anoxic conditions at the lake's floor, likely triggered by hyperpycnal flows derived from the hydroelectric power plant discharges. We also observe that the effects of the 1976–77 seismic sequence are recorded in the lake as resedimented levels, likely due to shaking, in situ deformation, landslides, and turbidity currents. Our results stress the importance of lacustrine environments as efficient recorders of anthropogenic and natural events.

Dynamics of shallow wakes on gravel-bed floodplains: dataset from field experiments

Abstract. Natural dynamics of river floodplains are driven by the interaction of flow and patchy riparian vegetation, which has implications for channel morphology and diversity of riparian habitats. Fundamental mechanisms affecting the dynamics of flow in such systems are still not fully understood due to a lack of experimental data collected in natural environments that are free of the unavoidable scaling effects in laboratory studies. Here we present a detailed dataset on the hydrodynamics of shallow wake flows that develop behind solid and porous obstructions. The dataset was collected during a field experimental campaign carried out in a side branch of the gravel-bed Tagliamento River in northeast Italy. The dataset consists of 30 experimental runs in which we varied the diameter of the surface-mounted obstruction, its solid volume fraction, its porosity at the leading edge, the object's submergence and the approach velocity. Each run included: (1) measurements of mean velocity and turbulence in the longitudinal transect through the centreline of the flow with up to 25–30 sampling locations and from 8 to 10 lateral profiles measured at 14 locations, (2) detailed surveys of the free surface topography and (3) flow visualizations and video recordings of the wake patterns using a drone. The field scale of the experimental setup, precise control of the approach velocity, configuration of models and natural gravel-bed context for this experiment makes this dataset unique. Besides enabling the examination of scaling effects, these data also allow the verification of numerical models and provide insight into the effects of driftwood accumulations on the dynamics of wakes. Data are available with open access via the Zenodo portal (Shumilova et al., 2020) with DOI https://doi.org/10.5281/zenodo.3968748.

Investigation of a Gravel-Bed River’s Pattern Changes: Insights from Satellite Images

Changes in river pattern have been documented in the literature. The recognition of islands and vegetated patches, which is indicative of the evolution processes, requires simultaneous information at different points and at different times and field studies are still difficult and scarce. The present work, focusing the attention on a gravel-bed river, explores the possibility to conduct a first-step pattern changes analysis by identifying the evolution of the morphological features and taking information of islands and vegetated patches from satellite images easily available from Google Earth. The study is conducted by combining the information taken from both the satellite images and the field photos and the hydrological data. Here analysis concerns a reach of the Tagliamento River, in Italy, in a decadal timescale characterized by evident stream pattern changes. Results confirm that a combination of different factors determine favorable conditions for the river’s evolution, but the frequency of occurrence of high-magnitude events is the most important factor to consider in a first-step analysis. This is because the frequency of occurrence of high-magnitude events affects, in turn, some of the other influencing factors. In particular, the present study highlights that different morphological features form in time periods characterized by different frequency of occurrence of high-magnitude events. On one hand, this could be related to the fact that high-magnitude events could influence the sediment transport and deposition mechanisms, modifying the ratio coarse-to-fine sediments and the grain-to-grain interactions, with consequences in the sediment flux variation and in the migration of the morphological features. On the other hand, the frequency of occurrence of high-magnitude events could affect the vegetation distribution and growth, contributing to determine a variation of the typology of the vegetation characteristics depending on the tolerances of the vegetation species. A sort of interface between the vegetated-dominated area, where the flow resistance is significant, and the flood-disturbance-dominated area, where the action by flow is significant, is determined with a progressive reduction of the number of active channels and development of the meandering bend.

Linking the 2030 Agenda for Sustainable Development to Research, Newspapers, and Governance: The Case of the Last Free-Flowing Alpine River

Are academic, newspaper and regulatory documents aligned with the United Nations Sustainable Development Goals and the Sendai Framework for Disaster Risk Reduction (SENDAI)? To answer this question, we develop a framework to compare the most commonly occurring keywords across these document types, as well as their use of Sustainable Development Goals and SENDAI keywords. The approach is tested in a case study on the Tagliamento River in the Italian Alps to explore the degree of communication among academia, newspapers and governance. Across the analyzed documents, we found disconnection between academic sources and regulatory documents. Occurrences of SDG-related keywords are positively correlated in regulatory documents and newspapers (r = 0.6), and in academic literature and newspapers (r = 0.38), indicating some degree of agreement. However, no correlation emerges between academic and regulatory documents, indicating a critical gap for communication and understanding between academic research and governance.

A Complete Morphodynamic Study to Face a River Engineering Issue

The last reach of the Tagliamento River, in North East Italy, is progressively changing its planimetric geometry, causing sediment deposition close to a port and preventing the regular navigation in that area. In the present paper, this river engineering issue has been addressed in a complete way, first investigating the cause which brought to the present situation, and then proposing a number of design solution to mitigate the problem. Some of them have been analyzed by means of a morphodynamic numerical model, reproducing the effects on the bottom height of an average year in terms of flow and tides. The results of each simulation are compared to those of the present situation, in order to underline any advantages of the proposed design solution.

Late Quaternary landscape evolution of the buried incised valley of Concordia Sagittaria (Tagliamento River, NE Italy): A reconstruction of incision and transgression

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.

Extending the conceptual model of river island development to incorporate different tree species and environmental conditions

AbstractRiparian vegetation survival and establishment in gravel‐bed rivers depends on the balance between vegetation growth and flood disturbance. We present four examples of vegetation and landform development in gaps (linear open spaces) between established islands and/or floodplain within a reach of the middle Tagliamento River, Italy. Gaps offer shelter to vegetation, supporting higher colonization success and different vegetation‐landform evolution pathways. Time sequences of aerial images track vegetation development over 30 years in the four gaps. In combination with the flood disturbance time series, we interpret vegetation dynamics and identify the fate of sexual and asexual reproduction strategies by observing vegetation expansion from lines of young plants and shrubs and from uprooted deposited trees and pioneer islands, respectively. Analysis of image sequences reveals common features across the four gaps that are generalized to extend a conceptual model of island development. Growing conditions, disturbance energy and time (window of opportunity) between major floods are the main controls on vegetation colonization. These vary among rivers, among reaches along the same river and locally, as in the investigated gaps, allowing different tree species with different life history traits (e.g., Populus nigra, Alnus incana) to engineer local river landforms in different and complementary ways. Although the conceptual model is inspired by observations on the Tagliamento River, consideration of species life history traits and the joint influences of growing conditions, disturbance energy and windows of opportunity provide a framework that may be applied to other temperate rivers where trees drive landform development.

Physical engineering of an island‐braided river by two riparian tree species: Evidence from aerial images and airborne lidar

AbstractFollowing a review of the European distribution, habitat requirements and life history characteristics of two riparian tree species, Alnus incana (L.) Moench (grey alder, a member of the Betulaceae family) and Populus nigra L. (black poplar, a member of the Salicaceae family), we explore their changing spatial distribution and topographic position within a 7 km, island braided reach of the Tagliamento River, Italy, where Populus nigra dominates the woody vegetation cover. Combining field observations and information extracted from aerial images, airborne lidar data and river flow time series for the period 1986–2017, we investigate (a) the changing spatial distribution of all (P. nigra‐dominated) woody vegetation and of A. incana alone; (b) whether river bed topography can be associated with these changing spatial distributions and (c) we consider whether A. incana displays any particular characteristics in its spatial and topographic distribution that may indicate that it is complementing the physical engineering role of P. nigra. We show that A. incana predominantly grows in lines along channel, island and floodplain edges, bordering wooded areas dominated by P. nigra and that areas supporting A. incana are associated with the topographic development of the river bed. We conclude that A. incana appears to be acting as a complementary physical engineer to P. nigra, suggesting that similar complementary physical engineering of river beds may be achieved by species with different life history traits to influence landform development in other river environments.

Turbulence, instream wood and fish: Ecohydraulic interactions under field conditions

AbstractPrevious work suggests that ecohydraulics should consider the broad range of parameters that characterize turbulent flow combining intensity, periodicity, orientation and scale (IPOS; Lacey, Neary, Liao, Enders, & Tritico, 2012), but ecohydraulics research under field conditions in natural river systems remains rare, largely due to practical constraints. A novel combination of turbulence properties, computed from high‐frequency velocity time series, and underwater video of fish habitat use are presented here for two submerged large wood patches on a side channel of the Tagliamento River, Italy, providing insights into ecohydraulic interactions and the first known field application of the IPOS framework. Two adjacent wood patches of similar size reveal distinct differences in turbulence properties and fish habitat use, emphasizing the importance of considering the diverse properties of turbulent flow and reflecting the role of wood structural properties and position in determining the exact nature of hydraulic habitat. Key gradients in turbulence properties derived from multivariate analysis broadly align with IPOS categories, providing statistical validation for the IPOS framework. The application of IPOS to a habitat‐focused study demonstrates its utility in understanding and deriving key trends from large and complex turbulence data sets. The results also provide a preliminary indication that IPOS‐derived gradients may be helpful in explaining fish habitat selection, but these findings need further validation through high spatial resolution studies with different species and bioenergetics models. These insights support previous calls for inclusion of diverse turbulence parameters in ecohydraulics research and, where possible, more explicit consideration of turbulence properties in river assessment, conservation and restoration.

Geomechanical Field Survey to Identify an Unstable Rock Slope: The Passo della Morte Case History (NE Italy)

In this work, a geomechanical study performed on a natural rock slope located in north-eastern Italy (Tagliamento River valley, Friuli Venezia Giulia Region) is presented. The detailed geomechanical survey has provided a large bulk of field data proving that the investigated limestone slope is characterized by strong rock mass damage, thus resulting in a critical stability condition. Field evidence includes: (1) local faults crossing the rock mass and representing internal sliding surfaces; (2) slickensides and fault slips within the rock mass; (3) fracture joints of gravity-induced origin; (4) strong rock mass damage in over-stressed zones of the slope; and (5) slope monitoring data recorded by some installed devices. Three failure scenarios have been identified: a wedge failure involving a limestone block of 110,000 m3 (failure scenario 1: BLOCK1); a larger wedge failure involving an assembled limestone block of 200,000 m3 (failure scenario 2: BLOCK1-2-3); and a retrogressive failure involving a rear dolomitic block possibly triggered by the collapse of the limestone slope, mobilizing a maximum volume of 335,000 m3 (failure scenario 3: DOLOMITIC BLOCK). This paper shows that to comprehensively study stability problems involving natural rock slopes we must consider the interaction between pre-existing discontinuities, internal sub-blocks subdividing the unstable slope, rock mass strength and gravity-induced fractures that form during the delicate phase preceding slope collapse. Gravity-induced joints can be differentiated on the field from those of tectonic origin on the basis of some geometrical features, in particular their lower persistence and higher joint roughness.

Sea defences design in the vicinity of a river mouth: the case study of Lignano Riviera and Pineta

To guarantee the proper functioning of sea defences over a medium-long period, the knowledge of the complex interaction between tidal currents and nearshore wave field is fundamental in order to estimate the longshore sediment transport. In particular, the morphological evolution of coastal environments close to river mouths is deeply affected also by the riverine sediment transport, which can contribute to the overall coastal balance of erosion and deposition processes. Groynes are commonly used to intercept the longshore sediment transport and to stabilize the littorals, as the case of Lignano beach near the Tagliamento river mouth. In particular, the groyne closest to the river has been shortened in the recent years, influencing in this manner the coastline balance. In this study, a numerical model coupling a morphodynamic model and a wave generation spectral model has been used to study the effects of the variation of the groyne length on the beach. Results are presented and discussed, showing that the numerical modelling can be used for the sea defences design to improve the integrated coastal zone planning and management.