Studio dei sedimenti tardo-quaternari del litorale veneziano: contributo alle indagini paleoclimatiche ed ambientali

ABSTRACT The imprints of paleoevolutionary processes that affected the Venice lagoon and its littoral during the Late-Quaternary can be found in the sand and c/ay layers underlying the Venetian basin. Sedimentological characteristics of the Late-Pleistocene and Holocene sand and clay sedimentation during the past 25-30.000 years, before the human impact, in the lagoon of Venice, are reported. The multidisciplinary investigation of clay and sand sediments and the development and application of new analytical techniques and methodologies, allowed the detailed mineralogical, geochemical and textural characterization of the recent sediments. The new data obtained not only may contribute to better understand the paleoevolutionary events that took place in the Venetian basin and the impact of the paleoclimatic variations on the depositional environments, but also they may be used as a sediment natural reference base for a more accurate quantification of the pollution level in the bottom sediments of the lagoon of Venice. RIASSUNTO Gli strati di sabbia e di argilla sottostanti il bacino veneziano conservano le tracce dei processi paleoevolutivi che hanno influenzato la laguna di Venezia ed il suo litorale. Lo studio multidisciplinare dei sedimenti sabbiosi ed argillosi depositatisi durante gli ultimi 25-30.000 anni, prima dell'impatto antropico, e lo sviluppo ed utilizzo di nuove metodologie analitiche, hanno permesso una caratterizzazione mineralogica, geochimica e tessiturale dettagliata dei sedimenti recenti. I nuovi dati ottenuti possono non solo contribuire a meglio comprendere gli eventi paleoevolutivi succedutisi nel bacino veneziano e l'impatto delle variazioni paleoclimatiche sugli ambienti deposizionali, ma possono anche servire come base naturale di riferimento per una più accurata quantificazione dei livelli di inquinamento dei sedimenti di fondo soggetti ad antropizzazione della laguna di Venezia

The Holocene-Pleistocene boundary zone in the Lagoon of Venice (Italy)

The results of a detailed study on the sediments representative of the boundary area from the Late-Pleistocene and the Lower-Holocene sedimentations are reported. Mineralogical, granulometric and geochemical investigations have been carried out to characterize the clay-rich samples taken along the littoral bar and representative of the continental and marine sedimentations. Particular attention was devoted to the study of the overconsolidated clay layer considered to be the last continental deposit before the Holocene (Flandrian) transgression and interpreted as a paleosol

Recent sand sediments grain-size determination by Image Analysis

Presented in this study is the application of the Image Analysis (I.A.) technique as alternative to the traditional mechanical sieving methods for grain size determination (Bonardi & Tosi, 1994a). The application of Image Analysis technique to study the grain size of recent sand sediments has produced analytical data that are comparable to those obtained by conventional methods. Furthermore, the use of the Image Analysis has provided additional morphological parameters such as grain elongation, shape and roundness that can be useful clues to depositional environment reconstruction

Real-time self-adaptive deep stereo

Deep convolutional neural networks trained end-to-end are the state-of-the-art methods to regress dense disparity maps from stereo pairs. These models, however, suffer from a notable decrease in accuracy when exposed to scenarios significantly different from the training set, e.g., real vs synthetic images, etc.). We argue that it is extremely unlikely to gather enough samples to achieve effective training/tuning in any target domain, thus making this setup impractical for many applications. Instead, we propose to perform unsupervised and continuous online adaptation of a deep stereo network, which allows for preserving its accuracy in any environment. However, this strategy is extremely computationally demanding and thus prevents real-time inference. We address this issue introducing a new lightweight, yet effective, deep stereo architecture, Modularly ADaptive Network (MADNet) and developing a Modular ADaptation (MAD) algorithm, which independently trains sub-portions of the network. By deploying MADNet together with MAD we introduce the first real-time self-adaptive deep stereo system enabling competitive performance on heterogeneous datasets.Comment: Accepted at CVPR2019 as oral presentation. Code Available https://github.com/CVLAB-Unibo/Real-time-self-adaptive-deep-stere

Studio sedimentologico di un livello di argilla sovraconsolidata sottostante il litorale veneziano

ABSTRACT The effect of global climatic changes that occurred since the last Würmian glaciation is recognizable in the stratigraphic sequences of the Pleistocene-Holocene boundary zone from several coastal areas in different locations around the world. This study gives the results of mineralogical, chemical, and textural investigations of about fifty samples of the hard clay layers and the clay layers above and below underlying the Venice littoral. This hard clay layer, locally known as caranto, from few centimeters to few meters thick, represents the Holocene/Pleistocene boundary and it carries the marks of climate changes that characterized the last phase of the Pleistocene and the early part of the Holocene. The very dry climate during a period of very limited sedimentation and a long subaerial exposition, desiccated, compacted and oxidized the clay previously deposited, to form the overconsolidated clay level (caranto). RIASSUNTO Gli effetti delle variazioni climatiche succedutesi, su scala globale, a partire dall'ultima glaciazione würmiana sono riconoscibili nelle sequenze stratigrafiche in varie località costiere sparse in tutto il mondo. In questo studio vengono riportati i risultati preliminari di una indagine sulle caratteristiche mineralogiche, geochimiche e tessiturali di circa cinquanta campioni di un livello di argilla sovraconsolidata e degli strati argillosi sopra e sottostanti, lungo il litorale veneziano. Questo strato di argilla sovraconsolidata, noto come "caranto", con spessore variante da pochi centimetri ad alcuni metri, rappresenta il limite Olocene/Pleistocene e conserva gli effetti dei cambiamenti climatici che hanno caratterizzato l'ultima fase del Pleistocene e quella iniziale dell'Olocene. Il clima freddo e molto arido, durante un periodo di sedimentazione molto limitata e la prolungata esposizione subaerea hanno determinato l'essiccamento, la compattazione e l'ossidazione dell'ultima sedimentazione continentale argillosa, sino a formare quel livello sovraconsolidato che e' noto col nome locale di caranto

Situazione altimetrica attuale del comprensorio veneziano e i suoi riflessi sull'ambiente lagunare

Dopo aver inquadrato il processo della subsidenza che dagli inizi degli anni cinquanta ha interessato in modo particolare il territorio e la città di Venezia per le intensive estrazioni di acque sotterranee, viene effettuata un'analisi di dettaglio dell'attuale situazione altimetrica del comprensorio lagunare. Lo studio si basa sostanzialmente sulla interpretazione delle altimetrie 1993 confrontate a quelle del 1973 risultanti dalle due rispettive livellazioni di alta-altissima precisione condotte dal C. N. R., I.S.D.G.M. Questi rilievi, partendo da capisaldi stabili di terraferma (nei pressi della pedemontana) arrivano a Mestre, quotano la superficie della città storica con particolare dettaglio, i capisaldi lungo le linee circumlagunari e l'intero cordone litoraneo, chiudendo l'anello attorno alla laguna. L'analisi relativa all'arco di tempo ventennale ha permesso di confermare la stabilità del territorio accertata definitivamente nel 1975 nella zona industriale e nel centro storico dopo la diversificazione degli approvvigionamenti idrici, di definire con precisione l'andamento della subsidenza naturale, ove l'incidenza antropica è assente, e le aree più fragili del territorio quali quelle litoranee. An overview of the land subsidence occurred in the city of Venice and its hinterland in the past decades is first presented. In particular the responsibility of groundwater withdrawals in the sinking process is briefly de-scribed. Man-induced subsidence averaged about 14 cm in the industrial area of Porto Marghera, the center of groundwater pumping, and 10 cm in the city of Venice, from 1952 to 1969. Starting in 1970 a general piezometric improvement began, because of the regulation and diversification of the water supply in the Venetian area and the shutdown 01 many artesian wells. In Marghera in 1975 only 170 l/sec were withdrawn against the 500 l/sec in 1969. Concurrently with the recovery 01 aquifers, the subsidence slowed down until it stopped and in 1975 a land rebound 01 about 2 cm was recorded in the city 01 Venice. In spite 01 this, one has to keep in mind that the subsidence is mostly irrecoverable and that its effects still remain. Again, since Venice lives on the water, its land elevation must be referred to the mean sea level. The overall loss in elevation with respect to water level can be synthesized as the result 01 three factors: subsidence due to groundwater exploitation, natural subsidence and eustatic rising 01 sea level. Their joint contribution in the «lowering» 01 the surface level 01 Venice with respect to the water level was a total of 22 cm from 1908 to 1975, a determining figure in the recurring phenomenon 01 «acqua alta» (flooding) . After reviewing the past altimetrical situation, an evaluation of the land elevation 01 the territory is then presented lor the last twenty years; a precise regional leveling was infact carried out in 1993 with the same path 01 the 1973 one. These surveys include the lines from Treviso (farther inland, the stable origin 01 the survey) to Mestre (Venice-mainland), from Mestre to the extreme part 01 the city 01 Venice and those all around the lagoon edges including the littoral strips. This 20-year period is quite significant to evaluate the present trend 01 land subsidence alter the cessation 01 the man-induced phenomenon measured first in 1973 and completely verified in 1975. In general the 1993 leveling, compared with that 01 1'973, has pointed out two different behaviors between the zones in the mainland and surroundings 01 Venice and in the city, which are decidedly stable, and the areas along the extreme edges 01 the lagoon and littoral where land sinking is still going on even il the rate 01 subsidence is much lesser than that measured during the previous critical 20- year period. In order to a have view 01 the whole area under examination, the map 01 the 1973-93 contour lines01 equal subsidence has been drawn, using the Kriging technique and comparing the height 01 the 208 bench marks distributed along the leveling lines. Reading these curves il appears even more evident the ground stability 01 the zones in the mainland, Venice and its surroundings, and the negative trend in soil elevation at the northern and southern extremities of the lagoon's edge and along the littoral. It is noted that the variations in elevation along the lines are progressively decreasing either southward or northward going towards the littorals. Concerning the littoral strips, one has to bear in mind that these areas are those 01 more recent deformation with respect to the others and that they are close to the rivers' outflows, so the natural compaction 01 recent deposits is more active here than elsewhere and the rate 01 natural subsidence is greater. An ideal line 01 demarcation between the two above mentioned stable and subsiding lagoon sectors can be outlined. Particular attention has been devoted to the altimetrical situation 01 Venice because 01 its importance in the lagoon environment. The city's area (about 8 km2) is covered by a network 01 123 benchmarks, 65 01 which constitute the base for comparison since 1961. A reliable map 01 subsidence contour lines was drawn by using again the Kriging technique. The pattern 01 these lines, that are positive almost everywhere, stresses the stability 01 the historical city's ground elevation. Some 01 the curves 01 equal subsidence are closed outlining small negative «bowls». Examination 01 data indicates that very localized sinkings occur in the more recently lilied areas (Marittima-Tronchetto and S. Elena-Giardini) where one can suppose that the process 01 consolidation is still going on (even though at a very small rate), and in certain areas bordering the principal canals; the latter could be partly linked to an erosion action induced by the speed 01 water currents along the canals. By analyzing the temporal piezometric surface variations 01 the once exploited aquifers, one can confirms that presently the contribution 01 groundwater withdrawals to land subsidence doesn't exist as a general cause. Only very localized influences can be found

shoreline detection capability of cosmo skymed and high resolution multispectral images

n/

La subsidenza nell’area veneziana: attuali tendenze ed implicazioni

SOMMARIO Il processo della subsidenza, per le estrazioni intensive di acque sotterranee che negli anni cinquanta e sessanta ha interessato il comprensorio lagunare veneziano, producendo un abbassamento irreversibile di 10-14 cm, oggi non e' piu' un problema per la città di Venezia, benché gli effetti del processo irreversibile siano permanenti. Lo studio dell'evoluzione altimetrica del comprensorio veneziano negli ultimi vent'anni ha infatti permesso di confermare la stabilità del territorio, accertata definitivamente nel 1975 nella zona industriale e nel centro storico dopo la diversificazione degli approvvigionamenti idrici, di meglio definire l'andamento della subsidenza naturale, ove l'incidenza antropica è assente, e di individuare le aree oggi più fragili del territorio. In particolare si sono evidenziate due zone a differente comportamento di subsidenza. La prima stabile (subsidenza inferiore a 0.5 mm/anno) include le aree di terraferma e quelle di gronda lagunare ad essa più prossime nonché la stessa città di Venezia; la seconda comprende le zone alle estremità lagunari Sud e Nord e i litorali, cioè quelle di più recente formazione, dove il tasso medio di subsidenza risulta compreso tra 1 e 2 mm/anno. Attualmente gli studi si sono orientati verso queste zone ed in particolare nell’area meridionale, già in precarie condizioni altimetriche e morfologiche, con il territorio spesso a quote inferiori al livello medio del mare. ABSTRACT Land subsidence due to groundwater withdrawal which in the fifties and sixties induced in the Venetian territory an irrecoverable sinking of 10-14 cm, is no longer a problem today for Venice even if the negative effects will never be cancelled. Studies carried out in the last decades have allowed to confirm the ground stability which had been definitely escertained in 1975 for both the city of Venice and the industrial area; to better quantify the natural subsidence in the absence of the induced component, and to point out the frailest areas. Different behaviours in altimetrical evolution have clearly come out. A ground stability belongs to the zones in mainland, Venice and its surroundings, while a certain subsidence still occurs at the northern and southern extremities of the lagoon's edge and along the littoral where the natural compaction of recent deposits is more active than elsewhere and the rate of natural subsidence is greater, ranging between 1 and 2 mm/y. Presently the studies are mainly addressed in these areas and in particular in the southern zone where the saltwater intrusion often due to groundwater exploitation worsen the ground elevation