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 In Marghera in 1975 only 170 l/sec were withdrawn against the 500 l/sec in 1969.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

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

WoodCircus, Underpinning the vital role of the forest-based sector in the Circular Bioeconomy. D2.2 Resource Efficiency, Side Streams and Value Chain Analysis – WP2 Final Report

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From Romeo and Juliet to Rosaline & Benvolio: Refashioning Shakespearean Teenage Lovers

In this essay I analyse a number of narrative retellings of "Romeo and Juliet" for a Young Adult audience. I focus on three novels which, interestingly, replace the star-crossed lovers, with a couple of minor characters, Benvolio and Rosaline: Lisa Fiedler’s "Romeo’s Ex. Rosaline’s Story" (2006), Melinda Traub’s "Still Star Crossed" (2013) and Rachel Caine’s "Prince of Shadows" (2014). In thse versions Rosaline and Benvolio are given centre stage and narrative voices which open up new narrative possibilities; they end up playing a different and a bigger part than in the original play, but firmly refuse that of the victim to the old generation’s decisions and actions. By exploring motivation, establishing new links between the characters, and having narrators pass authoritative moral judgements, all these texts negotiate with well-established critical interpretations of the central characters, often challenging and channeling them into unexpected critical directions. In a way, these retellings “fix” the original “dangerous” characters Romeo and Juliet, by bringing in new characters as mediators, or expand existing secondary characters in order to make them fit into contemporary notions of teenage role models

LAND SUBSIDENCE MONITORING TECHNIQUES A NEW STRATEGY ADOPTED IN THE VENETIAN AREA, ITALY

Among recent research topics dealing with land subsidence in the Venice region, great attention has been given to monitoring techniques. Recently, SAR-based analyses have been used to complement the ground-based methods, and an integrated monitoring system based on levelling, GPS, and InSAR techniques (SIMS), able to optimize the areally distributed information and to provided synoptic maps of ground surface displacements with high accuracy and reliability for both small areas and al regional scale was developed

Present Relative Sea Level Rise in the Northern Adriatic Coastal Area

Relative sea level rise (RSLR), that has been occurred along the entire coastal areas of the Northern Adriatic Sea, includes land subsidence, both natural and maninduced, and eustacy. Their combined effect has produced relative ground settlements ranging from centimetres to meters. RSLR represents one of the geologic hazards threatening the low-lying coast. Recent progresses made in understanding these two processes are presented. Synthetic Aperture Radar (SAR) interferometry has significantly improved the knowledge of actual land subsidence. In particular, comprehensive maps of the vertical displacements occurred over the period 1992-2009 in the region between Venice and Ravenna reveal a significant spatial variability, ranging from a slight 1 to 2 mm/yr uplift, to a serious subsidence of more than 15 mm/yr. The availability of tide gauge data in Trieste, Venice, and Ravenna allows accurate assessment and meaningful observations on sea level change. The period 1896-2006 is characterized by an average rise of 1.2±0.1 mm/yr. The analyses here performed show that a time series at least 50 yr long must be used to obtain statistically significant results and reliable trend, due to the 7-8 year pseudo-cyclicity, recorded at many Mediterranean coastal stations. In Venice and Ravenna the influence of land subsidence on the RSLR amounts to 57% and 85%, respectively. This percentage has been estimated in 95% at the Po Delta