United States

Shoreline variability is a key factor in coastal studies. In the last decades, remote sensing techniques have been widely applied and several algorithms for shoreline detection have been developed to extract the so called Satellite Derived Shorelines (SDS). Multispectral and hyperspectral satellites provide images covering large areas with high spatial and temporal resolution, allowing to perform a near real-time analysis of shorelines worldwide. There are several open source algorithms (e.g. SHOREX (Pardo-Pacual et al., 2012) and CoastSat (Vos et al., 2019)) for shoreline detection at sub-pixel level, using freely available multispectral images (Landsat and Sentinel constellations). However, open source applications for SDSs analysis using hyperspectral data are not yet available. Recently the Agenzia Spaziale Italiana (ASI), has launched the PRISMA mission (PRecursore IperSpettrale della Missione Applicativa), offering medium-spatial (30 m) and high spectral (smaller than 12 nm) resolution. In this study we present the performance of the CoastSat algorithm applied to multispectral images. Additionally, we show the capability of hyperspectral techniques applied to PRISMA images to detect the shoreline given their higher spectral resolution. The performance of the CoastSat algorithm was evaluated in two different microtidal beaches of the Italian Adriatic coast (Emilia-Romagna and Marche Regions): Punta Marina (PM) and Sirolo (SIR). The beach at PM is a typical intermediate fine-sandy beach, while SIR is a mixed coarse sand-gravel reflective beach. SDSs were compared to RTK-DGPS surveyed shorelines, measured following the upper limit of the swash zone, and with shorelines derived from a video monitoring station, after manual mapping on variance images. The shoreline derived from in-situ surveys were coincident with Landsat-5, Landsat-7 and Sentinel-2 satellite overpasses The influence on the identification of SDSs of the run-up extent and beach morphodynamic state was evaluated. The obtained RMSE ranges between ~ 6.5 and 14 m at both sites, indicating that the shoreline is effectively obtained from multispectral images at sub-pixel level. In addition, we analysed the shoreline derived from a PRISMA hyperspectral image of PM. We found that similar results can be obtained using hyperspectral images.

SGI 2021

Performance of remote sensing algorithms for shoreline mapping under different beach morphodynamic conditions

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L'Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS e il Dipartimento di Matematica e Geoscienze dell'Università di Trieste sono orgogliosi di ospitare il 90° Congresso della Società Geologica Italiana a Trieste dal 14 al 16 settembre 2021. La modalità del congresso è interamente online.

Con il motto "Geologia senza frontiere" questo evento mira a promuovere le Scienze della Terra come disciplina scientifica proiettata nel futuro, oltre i confini geografici, politici e disciplinari, per comprendere meglio l'interno del Pianeta Terra e la struttura del sottosuolo, difendere la società da pericolosi eventi geologici, comprendere meglio la variabilità climatica, pianificare l'utilizzo delle georisorse in modo etico e nel rispetto dell'ambiente.


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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.

poster

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

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.

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

Coastal erosion coupled with human-induced pressure has severely affected the coastal areas of the Mediterranean region in the past and continues to do so with increasing intensity today  (Luijendijk et al., 2018). In this context, the Pisa coastal plain shows a long history of erosion, which started at the beginning of the nineteenth century. In this work, shoreline positions derived from historical maps as well as airborne and DGPS (Differential Global Positioning System) surveys were analyzed in a GIS (Geographic Information System) environment to identify the main changes that have occurred in the last 142 years. These analyses were compared with 100 years of discharge data measured at the S. Giovanni alla Vena gauge to identify a possible correlation between the two sets of information. Finally, Sentinel-2 and Landsat images were studied to identify the dispersion of sediments transported by the Arno River. In particular, we found a minimum of fluvial discharge in the years 1954, 1978, and 2012 corresponding to a peak of erosion, while the reduced erosion rate and the fluvial discharge increased in the years 1928–1944, 1954–1975, and after 2012 (Bini et al., 2021). A key topic in the study of the coastal evolution, is the availability of a reliable and quick method of shoreline survey. In this context we would like to identify a new and valid beach topography-based algorithm, able to identify the shoreline. We apply the Structure from Motion (SfM) techniques to reconstruct a high-resolution Digital Elevation Model using a drone for image acquisition. The algorithm is based on the variation of the topographic beach profile caused by the transition from water to sand. The SfM technique is not efficient when applied to reflecting surfaces like sea water resulting in a very irregular and unnatural profile over the sea (Kohv et al., 2017). Taking advantage of this fact, the algorithm searches for the point in the space where a beach profile changes from irregular to regular, causing a transition from water to land. The algorithm is promoted by the release of a QGIS v3.x plugin, which allows the easy application and extraction of other shorelines (Luppichini et al., 2020).

Investigate the coastal environment evolution: climatic and morphological cause and a new method for shoreline identification

The present geomorphology of the Volturno river delta and related strandplains is largely a product of an intricate long-term relationships between geological evolution and human impacts. In order to assess the main drivers of the changed landscape in the last 150 years, a multidisciplinary study was carried out by combining historical and geological data. A 150 year cartographic sources were acquired, georeferenced and managed into a GIS environment. Some 1800 well log stratigraphic data were acquired and interpreted to reconstruct the stratigraphic architecture of the plain. Historical analysis has produced documentary evidence of the geomorphological evolution of the area since the end of the XVII century, when, during the Spanish vice-kingdom, it was subjected to major land reclamation. More than 500 km of canals were built in the coastal area. The development of agriculture and farming on reclaimed land promoted urbanization and increasing landscape fragmentation. The peak was attained between the 1960s and the 1990s, when landscape pattern structure increased in complexity with major alterations of alluvial channels and of the deltaic environment, and retreat of the coastline. Land use maps were reconstructed for the 1957 and 2012. The overgrowth of the urban areas to the sea, coupled with intensification of agricultural and tourism activities, resulted in the loss of high quality ecosystems such as the humid coastal setting, the lacustrine/marshy back-dune area and, in most cases, also the beach-dune system. The negative sedimentary balance resulting from the reclamation works on the river courses, together with the interventions along the Volturno river basin, resulted in an accelerated and severe coastal erosion. Coastline displacement was calculated at 7 time points, showing timing and causes of trends and rates of variation. The anthropic impacts were compared with the subsidence trends previously assessed. The lack of an unequivocal correlation of the latter with agricultural land use and zootechnical farm location indicates that these human activities do not exert a significant impact on regional subsidence rates. On the contrary, a net overlay of the subsiding areas with the geological architecture was recognized and in particular with the areal distribution and thickness of deposits such as clayey silts, clays and peats. From geotechnical point of view, these soils can be classified as fine-grained soil (mostly clayey) with poor mechanical properties (high compressibility and low strength). Moreover, the inclusion of significant amount of peat and organic matter clearly reflects high values for the coefficient of secondary compression. The subsidence rates, coupled with the sea level rise due to climatic changes, increase the vulnerability of the coast to erosion, flooding and storm surge and aquifer salinization.

The changing geomorphology of the Volturno delta and coast (northern Campania, Italy): human influence and geological architecture

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 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

Performance of remote sensing algorithms for shoreline mapping under different beach morphodynamic conditions

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