United States

A morphodynamic study of a scraped artificial dune built on the sandy beach of Porto Garibaldi (Comacchio, Italy) as a barrier to protect beach facilities from sea storms during the winter season was implemented by analysing Unmanned Aerial Vehicle (UAV)-derived products, such as digital elevation models (DEMs) and orthophotos. The role of elevation data uncertainty and uniform thresholds for change detection (TCDs) on the interpretation of morphodynamic estimations related to non-extreme sea and wind conditions was analysed. The analysed DEMs showed a reasonable agreement with ground truth surveys (Global Navigation Satellite System, GNSS), with RMSE &lt; 0.05 m. The significance of the identified changes was determined by applying a set of TCDs. In this case, a threshold of 0.15 m was able to detect the majority of the morphological variations. However, the set of TCD ≤ 0.15 m was considered to properly discuss the significance of minor changes and the uncertainty of volume change calculations. During the analysed period (21 December 2016–20 January 2017), while water levels and waves affected the front of the artificial dune by eroding the berm area, the aeolian forcing (i.e. winds) remodelled the entire dune, moving the loose sand around the dune and further inland. Notably, sediment volumes mobilised by sea and wind forcing were comparable. In the case of extreme storms, it is expected an important degradation of the dune while preserving the touristic concessions from flooding and beach erosion. It is suggested that UAV-derived coastal morphological variations should be interpreted by integrating a set of uniform thresholds to detect significant changes with the uncertainty generated by the propagation of the original uncertainty of the elevation products. Additionally, the characteristics of the morphodynamic drivers should be evaluated by adopting uncertainty-aware approaches. In this way, the contribution of subtle morphological changes, which magnitudes are comparable with the instrumental accuracy and/or the assessed propagated uncertainty, can be properly accounted for.

SGI 2021

Uncertainty of UAV-derived DEMs and significance of detected morphodynamics: the case study of a scraped dune in the Northern Adriatic

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The National Institute of Oceanography and Experimental Geophysics - OGS and the Department of Mathematics and Geosciences of the University of Trieste are proud to host the 90th Congress of the Italian Geological Society in Trieste on 14-16 September 2021.  The Congress will be held entirely online.

With the motto "Geology Without Borders" this event aims to promote Earth Sciences as a scientific discipline projected into the future, beyond geographical, political and disciplinary boundaries, to better understand the interior of Planet Earth and the structure of the subsurface, defend society from dangerous geological events, better understand climatic variability, plan the use of geo-resources in an ethical way and respecting the environment.


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Earth Sciences should be understood not only as necessary for a better understanding of the interior of the planet Earth, but also as a defense of society from dangerous geological events, for the understanding of climatic variations, for the planning and use of georesources in a ethical and respecting and protecting the environment.

A morphodynamic study of a scraped artificial dune built on the sandy beach of Porto Garibaldi (Comacchio, Italy) as a barrier to protect beach facilities from sea storms during the winter season was implemented by analysing Unmanned Aerial Vehicle (UAV)-derived products, such as digital elevation models (DEMs) and orthophotos. The role of elevation data uncertainty and uniform thresholds for change detection (TCDs) on the interpretation of morphodynamic estimations related to non-extreme sea and wind conditions was analysed. The analysed DEMs showed a reasonable agreement with ground truth surveys (Global Navigation Satellite System, GNSS), with RMSE < 0.05 m. The significance of the identified changes was determined by applying a set of TCDs. In this case, a threshold of 0.15 m was able to detect the majority of the morphological variations. However, the set of TCD ≤ 0.15 m was considered to properly discuss the significance of minor changes and the uncertainty of volume change calculations. During the analysed period (21 December 2016–20 January 2017), while water levels and waves affected the front of the artificial dune by eroding the berm area, the aeolian forcing (i.e. winds) remodelled the entire dune, moving the loose sand around the dune and further inland. Notably, sediment volumes mobilised by sea and wind forcing were comparable. In the case of extreme storms, it is expected an important degradation of the dune while preserving the touristic concessions from flooding and beach erosion. It is suggested that UAV-derived coastal morphological variations should be interpreted by integrating a set of uniform thresholds to detect significant changes with the uncertainty generated by the propagation of the original uncertainty of the elevation products. Additionally, the characteristics of the morphodynamic drivers should be evaluated by adopting uncertainty-aware approaches. In this way, the contribution of subtle morphological changes, which magnitudes are comparable with the instrumental accuracy and/or the assessed propagated uncertainty, can be properly accounted for.

poster

The Siele mine and its smelting plant are part of the world class Monte Amiata mining district (MAMD – Tuscany, Italy). The mine is located close to the Siele creek (c.), which drains the mining area, then flows to the Paglia River (R.), which in turn is an affluent of Tiber River, flowing through the city of Rome to the Mediterranean Sea. After closure in 1981, the mining area was subjected to the first reclamation in the district (and at the worldwide scale), completed in 2001. In this study, we present new data on Hg concentrations in soils, stream sediments, and air in the Siele mining area and along the Siele c., and we review all previously available data, with the aim of quantifying the Hg contribution from the Siele c. into the Paglia R., and of documenting the evolution of the system following mine reclamation. Hg concentrations (up to 5400 mg/kg) in stream sediments are comparable to pre-reclamation values in the first 500 m downstream the mine site. They decrease downstream to the confluence with the Paglia R., but remain anomalous (i.e., above the 1 mg/kg Italian law limit for residential soil). Comparison of pre- and post-remediation data of gaseous elemental mercury (GEM) in air shows that Hg0 emissions in most of the sites within the Siele mining area are lower than pre-reclamation values, but in few outdoor sites, levels are still high (up to 9500 ng/m3), exceeding the existing regulatory limits (“Norma Amiata”: 300 ng/m3 in outdoor sites). On the other hand, Hg mobility, determined by leaching tests, is mostly below the limits defined by pending regulations (1 μg/L), and methyl-Hg concentrations are mostly below 1 ng/kg (with a single value of 6 ng/kg). Results show the Siele c. plays a role by no means negligible in the general picture of the contributions of Hg in the Paglia R. basin, proving to be one of the most critical areas of the entire MAMD. Indeed, concentrations of Hg in sediments and soils in the Siele c. are comparable to those of the Pagliola c., draining the Abbadia S.S. mine (the main site of the MAMD), where reclamation is still under way. Moreover, despite remediation works, Hg emissions from contaminated soil will represent a significant contribution to the atmospheric load of Hg in the future, if no further remediation action is taken. The Siele system has a low resilience and natural recovery will take many years (probably decades), during which the area will remain an important source of Hg for the Paglia and Tiber River systems, and eventually for the Mediterranean Sea. This study provides important background data for local authorities to implement monitoring strategies and find new remediation plans based on the identified critical area. Further, at a global scale, this work contributes additional data to the assessment of the global Hg budget to the atmosphere and the hydrosphere.

Low resilience of a mercury mining area after reclamation: the case of the Siele mine (Mt. Amiata Mining District, Italy)

The Gulf of Gela coincides with the second-order coastal sub-cell n. 4.2 identified by the Regional Plan against Coastal Erosion and falling within the first order coastal sub-cell that extends from Capo Passero Island to Capo San Marco (Regione Siciliana, 2020). The main focus of the study is the shoreline evolution of the Gulf over long- and medium-term periods. The level of fragmentation of the dune systems (Moline et al., 2020) and the impact of coastal works (Aybulatov & Artyukhin, 1993) have been assessed as well and related to the coastal variations. The image analysis has been performed using a heterogeneous cartographic dataset, like IGM aerial photographs (1955, 1966), orthophotos of the National Geoportal (1989, 2000, 2006, 2012), Google Earth images (2016), and UAV (Uncrewed Aerial Vehicle) image acquired in 2018. The Digital Shoreline Analysis System (DSAS), an application of the ESRI ArcGIS© software shorelines, was used to compute the statistical indexes (SCE, NSM, WLR) and assess the shoreline movements. The shoreline change analysis shows that the area close to the Southern Imera river mouth experienced severe landward migration over the medium term with a maximum negative rate of – 3,59 m/year. The medium-term analysis was confirmed by the long-term assessment with a maximum erosion rate of -6,37 m/year recorded eastward the Southern Imera river mouth. The eleven breakwaters set few meters eastward the river mouth partly blocked the shoreline retreat and slight accretion has been here registered. However, the Shoreline Change Envelope (SCE) showed that the main depositional phenomena occurred over the time between 1955 and 1966, whereas progressive and constant landward migration has been observed between 1966 and 1989. Significant depositional phenomena were found up-drift the Scoglitti harbor where the northern dike has been repeatedly implemented and acted as sediment trap of the longshore drift. The area at the southern edge of the Gulf showed mainly a stable trend over the mid-term, but the long-term analysis and the SCE index revealed that accretion mainly occurred over the period between 1955 and 1989 and that the trend has changed between 1989 and 2018 when slight erosion phenomena have been recorded. The study showed that the most intense erosion phenomena have been detected where the level of fragmentation of the dune systems and the coefficient of technogenuos impact is much higher.

Shoreline and environmental changes detection in the gulf of Gela, southern Sicily (Italy)

The present work was focused on the study of the shoreline evolution of the coastal area between Pozzallo (RG) and Santa Maria del Focallo (RG), in Southern Sicily (Italy) and on the image detection of the environmental changes that occurred between 1880 and 2016. The findings were used to identify which events triggered the erosional phenomena and to plan better solutions to mitigate the negative effects. The study combined the grain-size analysis of the beach sediments and the diachronic analysis of shoreline position detected in historical and technical maps, aerial and satellite photographs. The 1928 shoreline was used as baseline and 14 transects were cast orthogonal to the 1928 baseline. The shoreline rates of change were computed thanks to the Digital Shoreline Analysis System (DSAS), an application that works in a GIS environment. Natural (dune systems, coastal quagmires) and coastal infrastructures were identified in each available cartographic dataset and mapped for each year. The diachronic analysis highlighted a shift line speed between 2,6 m/y and -2,6 m/y and a range of shoreline movement between -130,5 m and 107,3 m. It was worthy to note that the Pozzallo port trapped the longshore sediment transport and shoreline has been significantly increasing of several meters over the last decades. However, eastward the Pozzallo port, Santa Maria del Focallo beach has been affected by severe erosion, both due to the Pozzallo port, which acted as sediment trap blocking the longshore drift from the west, and to the loss of the dune system, replaced by holiday houses or greenhouses. Moreover, the coastal ecosystem has been even affected by the loss of the natural coastal quagmires and the implementation of the coastal road (SP 67) few meters nearby the shore. The increasing urbanization and anthropization significantly changed the dynamic balance of the shore. Clear guidelines on the approach to tackle the problem are provided by the European Parliament in the Integrated Coastal Zone Management (GIZC) in Europe (European Council, 2002), which advises the need, on one hand, to promote integrated use of the coast, decreasing unauthorized building, and, on the other hand, to restore natural shore refilling, furthered by renaturalization of the dunes.

Diachronic and environmental analysis in the Ragusa province, southern Sicily (Italy)

According to a recent study based on analysis of long-term satellite imagery datasets (Ninfo et al. 2018), the Po river Delta (Northern Italy) started again a positive sedimentation trend and a constructive process is ongoing at the main river branches. New tidal flats are building up around the tip of the delta, where once agricultural fields were inundated by the strong floods of 1950-60. The evolution of these environments is comparable with recent restoration projects that took place for example in the Venice lagoon, indicating that this case study is a good example for considering future reconstruction of microtidal areas in a deltaic context. A young tidal flat of about 10 ha, located in the Northern part of the Po della Pila branch, was studied by fieldwork activities since October 2018. Morphological surveys, sediment distribution and sedimentary pattern were defined through UAV survey, coring and sediment traps. Moreover, the study was supported by an historical review of orthophotos from the 1950s till the present. The results show that an extended crevasse splay, which covers the central part of the flat, has developed from the early years 21st century, due to human intervention on levees as well as river floods. The tidal flat granulometry is predominately fine sediment (Silty clay and Clayey silt), except for the central area, where the sand percentage increases (Silty sand). Two subfacies were defined: the most surficial one reaches ~10 cm depth below the surface and it is characterized by coarser sediment in the central section of the tidal flat; instead, the sand percentage increases within the sediment column from ~10 to 25 cm next to the inlets. The study area experienced a positive sediment budget and it was characterized by higher rates of accretion after Po river floods. The deposition rates ranged from 0.5 to 3.3 g/m2 per hour during two surveys of September 2019 and March 2021 but increased further from 1.9 to 20 g/m2 per hour during the survey of June-July 2020. All these observations suggest that the tidal flat, as well as the southern part of the lagoon, is fed by sediment from the Po River branch, while the tide redistributes the sediment around the tidal flat. The work finally aims at comparing this case study with other tidal flats and salt marshes worldwide characterized by similar as well different tidal regimes, thus identifying the optimal elevation for vegetation to establish and flourish. This could support the future restoration projects of these environments.

Sedimentary evolution of a young tidal flat in the Northern Part of the Po Delta (Italy): a Strategy for Future Building-with-Nature Management

Video cameras has been widely used in coastal engineering since their first applications in the late Eighties. The main advantages of the video monitoring techniques are a continuous monitoring of the observed region in time, an adequate spatial resolution, and a relatively simple technology to acquire and transfer data. Many studies applied video monitoring techniques to evaluate the shoreline evolution of a littoral (Archetti and Romagnoli, 2011), to reconstruct the intertidal beach or even to extrapolate the whole nearshore (Aarninkhof et al., 2005), thanks to the wave transformation which occurs when waves approach the shore. However, several limits are still present in the current applications. For instance, video cameras are usually quite expensive, produce a huge amount of data and are not always easily managed in near-real time from remote users. Furthermore, current instrumentation and software are mostly commercial. Here, we present a new tool which uses a Raspberry Pi for the development of a smart camera at very low costs. The software scripts, originally realized in MATLAB (Archetti et al. 2020), are also available in Python and OpenCV for open access implementations. At the current state, the low-cost smart camera (LCC) can acquire images, transfer data, perform on-line rectification and off-line post-processing (e.g., shoreline extrapolation and intertidal bathymetry reconstruction) with a minimum human intervention, which is practically limited to a validation of the results. For coastal video monitoring purposes, next future implementations aim to completely automate on-line analyses, and to implement further scripts (e.g., cBathy, see Holman et al., 2013) on Python. Possible evolutions of the video station include the development of machine learning for several environmental applications.

A low-cost camera for coastal video monitoring

The gaseous exchange of mercury (Hg) at the water-air interface represents an important aspect of the biogeochemical cycle of this element in the environment. Particularly at sites impacted by Hg due to anthropogenic activities, evasion can contribute to reduce the amount of this metal in the water column, but also to widen its spreading in the environment due to the long-range atmospheric transport of the element (Driscoll et al., 2013). However, dynamics of gaseous elemental Hg emissions from the water-air interface at Hg contaminated sites are still poorly characterised. In this work, Hg evasion fluxes were monitored by means of a flux chamber coupled with a real-time gaseous Hg analyzer (Lumex RA915M) in 3 freshwater environments characterized by different contamination legacy: the artificial reservoir of Solkan (SK-Slovenia) along the Isonzo River, where Hg contaminated sediments due to cinnabar extraction activities at the Idrija Hg mine have been accumulated since 1984, date of the dam construction; the dock near a chlor-alkali plant at Torviscosa (TR-Italy); the Cavazzo Lake (CV-Italy), chosen as pristine environment with no known Hg sources. At each site, 6 distinct sets of flux measurements were performed at regular time intervals during the diurnal period in 3 different seasons (spring, summer, and autumn). Moreover, the concentrations of dissolved gaseous mercury (DGM) were monitored during the sampling period together with total dissolved Hg, incoming UV radiation and main water physico-chemical parameters. As expected, at all sites the highest Hg fluxes were found in summer, due to higher irradiation, which favours the formation of volatile DGM through photoreduction, and higher water temperatures, which decrease the solubility of Hg. On average, Hg evasion fluxes found in this study were higher than those reported in literature for other background freshwater environments. Surprisingly, Hg fluxes at CV site were comparable to those of the other sites, likely due to re-emission of Hg of atmospheric origin, but further research is needed to confirm this hypothesis. The widest diurnal variability of Hg fluxes was observed at TR site, located inside an industrial complex, and likely related to irregular supplies of Hg through atmospheric depositions and water circulation. Conversely, SK and CV showed a more regular trend, confirming that Hg fluxes are strongly influenced by local conditions and site-specific interaction of different factors. Based on these results, the investigated sites can be considered as secondary sources of Hg for the atmosphere, underlining the importance of direct Hg fluxes monitoring to understand its fate in the environment.

Gaseous mercury evasion from the water-air interface at freshwater environments impacted by different anthropogenic sources

Research studies and numerical models in coastal geomorphology often rely on short to medium-term datasets (months to years), normally depending on available financial resources to enrol employees or adopt up-to-date surveying technologies. Lately, satellite images have largely benefit long-term analyses of coastal change, extending the temporal investigation up to few decades, but limitations related to temporal coverage and spatial resolution remain. An unexploited source of information is represented by historical data, but modern coastal geomorphologists do not take advantage of them due to their poor reliability and accuracy, especially if compared to modern technologies. The keynote will explore a new chance to build long-term datasets of coastal change through the revalue of historical data with modern techniques of Structure-from-Motion (SfM), GIS analyses and reliable estimation of spatial errors. Reliable geographic data were extracted from different sources available from historical archives (i.e., aerial photos, maps, bathymetric charts, topographic data pre-DGNSS era, military reports, newspapers, etc.) for the coastal site of Dundrum Bay in the Irish Sea (Northern Ireland, UK). Historical maps and aerial photographs were analysed to extrapolate 23 shorelines and quantify almost 200 years of shoreline change (1833 to 2020). Vertical aerial photographs were processed thorough SfM techniques to build 3D models and calculate volumetric change of the extensive local coastal dune for the last six decades (1963 to 2020). Geomorphic changes were discussed considering local forcing parameters (wave, wind, water level) from historical or hindcasted datasets available (1901 to 2020). Advantages and limitations of each ‘revaluation’ technique of the historical data were considered. Several potential errors are associated with historical coastal data; however, their advantage is to provide a quantifiable record when other (more accurate) data sources are not available. In the pre-satellite era (pre-1970’s), historical geographic data are the only available source, and they have also the advantage to be coeval with the increase of human pressure on the coast (post Industrial Revolution and post WWII). Long-term datasets are crucial for decision makers, often divided between warnings from the scientific community and the will to give effective and immediate response to concerns from the coastal communities. Adaptation strategies for coastal environments are often conceived without a long-term perspective which is partially caused by the lack of reliable long-term data. In a current situation of rapidly improving machine learning techniques, reliable long-term datasets are crucial to feed algorithms and better refine models of future coastal behaviour, especially in a context of sea level rise and climate change.

Revalue historical data to overcome the persistent lack of long-term datasets in coastal geomorphology: examples from Northern Ireland.

The foreseen global sea level rise threatens the most vulnerable coastal morphotypes, as the barrier islands. Their resilience is linked to processes of sediment deposition, mostly where a high sediment supply occurs, via a source-sink pathway or through cannibalization. Along the barrier islands of the Grado Lagoon (North Adriatic Sea), a system of submerged sand banks (called Mula di Muggia Bank, MMB) extends up to 2 km seawards and their rapid evolution induces conflicts with the touristic uses of the adjacent beaches. In order to quantify the past and present morphological changes and obtain the sediment budget, this work compared the aerial photographs from 1954 to 2019 and topo-bathymetric data (1968, 1985, 2007 and 2019). The temporal morpho-evolutionary analysis shows the preservation of a wide succession of intertidal and subtidal sandy bars, which migrate toward southwest. The migration follows the main littoral drift generated by waves along the sedimentary pathway of the only fluvial source, the Isonzo River. Down-drift, on the western terminus, the bank curves abruptly, inducing bars to shift landward toward the touristic beaches. Therein, sediment tends to accumulate over time, and the area is currently the final sedimentary sink for the entire coastal compartment. The sediment budget from 1968 to 2019 confirms two markedly positive budget sectors: the eastern one, adjacent to the sedimentary source of the Isonzo River, and the westernmost sector, as the trap of the longshore littoral path. Conversely, in the central tract a stable budget would indicate an area of sediment bypass. Here, the deposition prevails on the shallow zone, whereas beyond the -2.5m depth an erosive dynamics occurs with an increase in the steepness of the bank’s outer limit. The causes of these complex dynamics are still unknown, but the role of a bimodal wave regime must be considered: it acts in the opposite way on the seabed at different depths. Moreover, the bimodal wave regime explains the landward shift of the sandy bars in the western area where the influence of the southern swell waves is greater. Despite the cannibalization of the central tract, the very high positive budget resulting in the western sink area of the MMB (about 3 million m3 in 51 years) is difficult to explain in the regional context. In the lack of direct measurements, our hypothesis suggests the effect of climate changes in hydrological and solid regime of the fluvial source could exert a main role in the sedimentary dynamics. Longer summer drought and subsequent greater intensity of late autumn/winter precipitation likely lead to an increase of the Isonzo River solid discharge. Moreover, part of the sediments eroded by the deeper seabed could supply the sedimentary source of the Isonzo river delta, thus increasing the littoral drift.

Evidence of preservation of submerged sand banks: source-to-sink pathway enhanced by climate changes?

Nowadays, given their fundamental importance, the application of coastal sand dunes’ restoration plans is widespread and they are usually aimed at reactivating the natural dynamics of two main components, often compromised: the morphological integrity and the vegetation growth. The aim of this work is to propose a relevant and low-cost methodology for monitoring this kind of restoration projects, which contemplates a simultaneous survey of the geomorphological component as well as the vegetational one. An Unmanned Aerial Vehicle (UAV) was applied to survey these two components’ trend, by means of building high‐resolution Digital Surfaces Models (DSMs) and RGB orthophotos, in an area in the North Adriatic Sea (Punta Marina, Ravenna, Italy): the local coastal environment is particularly suitable because it includes a residual coastal dune system, damaged by decades of erosion and fragmentation by human intervention. The are was recently the subject of a restoration project aimed at limiting its deterioration as well as enhancing dune stability by the construction of walkways and the introduction of vegetation. RGB data from the drone’s photographs were used to identify the spectral signature of vegetation in the visible part of the spectrum as well as that of bare sand. This allowed to monitor changes in the relative cover area extension (vegetated Vs not vegetated) in time. Elevation data from high‐resolution DSMs were used to identify and monitor changes (considering every source of error) of the principal morphological features, such as the Dune Foot Line (DFL), the Dune Crest Line (DCL), the Dune seaward Crest Line (DsCL) and the Stable Vegetation Line (SVL). Both morphological data, as well as orthophotos analysis, confirmed a constant and progressive increase of the vegetated cover area and consolidation of the dune system following the restoration project. The proposed survey protocol resulted to be rapid, low‐cost and easily replicable by coastal managers to quantify the effectiveness of restoration projects.

High resolution and automated monitoring methodology (UAV) for vegetation and morphological dynamics involved in restoration projects in coastal sand dunes environments.

This work aims to assess the role played by a beach berm, reinforced by the accumulation of reed and seagrass wracks, on coastal protection against storm-induced floodings. A huge depositional event, mostly consisting of Arundo donax reeds from nearby river systems and Posidonia oceanica wracks, happened in December 2019 in Poetto beach (southern Sardinia, western Mediterranean). Following the concerns that this event raised among local tourism service providers, the municipal authorities decided to remove the reed wracks. In support of coastal management, a scientific inquiry was commissioned to the Coastal and Marine Geomorphology Group (CMGG), belonging to the Department of Chemical and Geological Sciences of the University of Cagliari (Italy) for the assessment of the berm processes before the removal of the reed wracks. Within the five months between the reed deposition and removal, a video monitoring system collected runup and flooding data during storm wave conditions. These data were integrated by five topographic, three bathymetric and two drone surveys. The presence of the reeds intertwined with seagrass wracks, seems to strengthen the berm, making it more resilient to wave action, eventually offering additional protection against overwash and flooding. These results are supported by a numerical model chain, with the nesting of a phase-resolving model into a phase-averaged model, providing a characterization of wave runup dynamics.

Assessing the role of reed and seagrass wracks in coastal protection. An example with numerical modelling integrated with videomonitoring system data in a southern Sardinia beach

Next from SGI 2021

Low resilience of a mercury mining area after reclamation: the case of the Siele mine (Mt. Amiata Mining District, Italy)

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Short-term effects of storm events on the coastline morphology of a Mediterranean microtidal wave-dominated beach (Piscinnì, SW Sardinia)