Interazione tra acque marine e acque di falda nella Bassa Pianura Friulana

2010/2011Riassunto: Nell’ambito del dottorato è stata esaminata l’interazione tra le acque marine e le acque di falda in un’area della Bassa Pianura Friulana che si colloca all’interno del Sito di Interesse Nazionale (SIN) della Laguna di Grado e Marano. Il SIN è stato oggetto di diversi studi da parte dell’Agenzia Regionale per la Protezione dell'Ambiente del Friuli Venezia Giulia (ARPA FVG). Per questo motivo è stata instaurata una collaborazione in particolare con il Settore Laboratorio Unico Regionale – Laboratorio di Udine, che negli anni si è occupato di definire e valutare l’influenza e gli effetti dell’interazione tra le acque lagunari e le falde sotterranee. Quanto elaborato conferma ed integra le teorie ed i risultati sviluppati da ARPA FVG e fornisce ulteriori dati e prove della presenza e degli effetti del cuneo salino. La ricerca ha permesso di approfondire le conoscenze relative all’interazione fra acque marine e acque di falda nella Bassa Pianura Friulana. Questo fenomeno si verifica laddove le acque saline del mare e della laguna risalgono i tratti terminali dei corsi d’acqua (ingressione marina) e, infiltrandosi all’interno dei depositi permeabili che ne costituiscono l’alveo, raggiungono le falde sottostanti determinandone la salinizzazione (intrusione salina). Tutti i corsi d‘acqua della Bassa Pianura Friulana sono soggetti ad ingressione marina, la cui intensità dipende dalle portate e dalla morfologia del loro alveo. Per questo si sono effettuati profili di conducibilità elettrica e temperatura all’interno di alcuni dei principali corsi d’acqua e dai dati ottenuti si è elaborata una mappa relativa alla massima ingressione marina. All’interno degli alvei dei Fiumi Aussa, Corno e Stella, inoltre, sono state installate delle stazioni di misura con sonde per il monitoraggio in continuo dei valori di conducibilità elettrica, temperatura ed oscillazione del livello piezometrico. La stazione di monitoraggio sul Fiume Corno (che ricade all’interno del SIN della Laguna di Grado e Marano), data la sua posizione strategica, è stata mantenuta attiva per un periodo di 7 mesi, permettendo di effettuare delle comparazioni dei parametri registrati in continuo con i dati di livello del mareografo di Marano Lagunare (Protezione Civile) e con quelli registrati all’interno di diversi piezometri. L’elaborazione informatica di nuovi dati stratigrafici raccolti per questa parte del SIN della Laguna di Grado e Marano si è concretizzata in un modello idrostratigrafico (dal piano campagna a 35 m di profondità), basato sul grado di permeabilità dei depositi che costituiscono l’area oggetto dello studio delle falde sotterranee. Dal modello sono state estratte diverse sezioni che hanno evidenziato la presenza di tre falde principali. La più superficiale, falda “0”, posta tra 0 e 5 m da p.c., è caratterizzata da una forte discontinuità laterale e da materiali a moderata permeabilità. La falda intermedia, falda “1”, è posta generalmente fra 8 e 20 m da p.c., è continua lateralmente ed è costituita prevalentemente da materiali permeabili. La falda più profonda, falda “2”, è posta fra 25 e 35 m da p.c., costituita da materiali permeabili, risulta discontinua alla scala considerata (questa falda non è stata oggetto di studio dal punto di vista geochimico). Diverse sezioni idrostratigrafiche trasversali al Fiume Corno hanno messo in evidenza che in alcuni tratti l’alveo del fiume poggia direttamente su materiali permeabili, che permettono la comunicazione tra le acque del fiume e le falde “0” e “1”, causandone la salinizzazione. Per determinare le caratteristiche geochimiche delle acque sotterranee nell’area di studio, sono stati monitorati, con diverse metodiche, 41 piezometri. Per ognuno di essi è stato effettuato almeno un profilo di conducibilità elettrica e temperatura per verificare le variazioni di questi due parametri con la profondità. Si sono quindi evidenziati i piezometri al cui interno sono presenti acque saline stratificate, significative della miscelazione delle acque di falda con quelle marine. Per mezzo di sonde multiparametriche sono stati monitorati in continuo 13 piezometri, di cui 2 con tratto filtrante in corrispondenza della falda “0” e i restanti 11 con tratto filtrante in corrispondenza della falda “1”. I valori dei livelli piezometrici hanno evidenziato oscillazioni con frequenze paragonabili a quelle delle maree e ampiezze attenuate in modo differente da piezometro a piezometro. Confrontando i dati ottenuti con quelli relativi alle misure in continuo effettuate all’interno del Fiume Corno, è stata verificata la presenza di una relazione, in 6 piezometri, tra il corso d’acqua superficiale e le due falde sottostanti, confermando quanto mostrato dalle sezioni idrostratigrafiche. Inoltre, i valori di conducibilità elettrica, ottenuti dalle misure in continuo, hanno confermato ancora una volta quanto già evidenziato dai profili verticali e cioè la presenza di acque di origine marina. A supporto delle misure in continuo e dei profili verticali di conducibilità elettrica e temperatura, sono stati effettuati numerosi campionamenti puntuali volti a caratterizzare dal punto di vista geochimico le acque sotterranee. Per quanto concerne la geochimica tradizionale sono stati prelevati campioni d’acqua per la determinazione di: pH, Eh, T, EC, O2, S2- e Fe tot. Questi parametri sono stati utili per definire alcune peculiarità delle falde monitorate. La determinazione delle concentrazioni di ferro totale disciolto, abbinato alle misure di EC effettuate in diverse condizioni di marea, si è dimostrata utile per definire un metodo di campionamento il più possibile idoneo, ripetibile e riproducibile in funzione delle specifiche problematiche presenti nell’area di studio. Il metodo infatti tiene in considerazione variabili di campo quali tempo, volumi e velocità di spurgo, posizione della pompa, diversi pretrattamenti del campione e variabili esterne come la marea, che possono modificare i valori dei principali parametri fisici e le concentrazioni degli ioni presenti nelle acque prelevate, così da ottenere un campione il più possibile rappresentativo della falda monitorata. Per 18 piezometri sono stati resi disponibili dal Laboratorio Unico Regionale - ARPA FVG i dati relativi ai principali componenti chimici, provenienti dalle campagne di monitoraggio degli anni compresi fra il 2006 e il 2011. Questi dati sono stati utili per determinare le facies chimiche a cui appartengono le acque presenti nella falda “0” e “1”. Attraverso l’elaborazione di diagrammi qualitativi si è potuta verificare la presenza di acque a facies bicarbonato calcica ad affinità magnesiaca, a facies cloruro alcalina e acque a composizione intermedia. Si è dunque avuta la conferma, anche dal punto di vista chimico, della presenza di acque dolci (facies bicarbonato calcica ad affinità magnesiaca) mescolate con diverse intensità ad acque di origine marine (facies cloruro alcalina). Risolutiva è infine stata la determinazione, per alcuni piezometri, dei valori di δ18O e δD. I valori dei rapporti isotopici di alcuni piezometri sono risultati maggiori rispetto ai valori isotopici medi delle piogge locali ad ulteriore conferma della presenza di miscelazione fra acque di falda e acque di origine marina. Inoltre, a seguito di campionamenti effettuati ad intervalli regolari durante lo spurgo di alcuni piezometri, si è osservato una decisa variazione dei rapporti isotopici nel tempo, evidentemente dovuta al richiamo di acque a composizione isotopica diversa da quella che caratterizza la falda all’inizio dell’emungimento. Si può quindi affermare con sicurezza che le acque saline del mare, attraverso la laguna, risalgono per ingressione marina il Fiume Corno per diversi chilometri e in corrispondenza dei depositi più permeabili che costituiscono l’alveo si infiltrano, mescolandosi con le acque dolci che caratterizzano la falda “0” e la falda “1” sottostanti. I risultati ottenuti confermano in modo inconfutabile alcune delle tesi già maturate ed affermate da ARPA FVG per il SIN di Grado e Marano (Lutman A. & Pezzetta E., 2007; Pezzetta E. & al., 2008; Pezzetta et al., 2011) La tesi in oggetto costituisce la chiave di volta per spiegare la presenza di squilibri nel chimismo delle acque sotterranee derivanti dalle naturali interazioni con la laguna ed il mare. Di conseguenza supporta e approfondisce le relazioni formulate dall’Agenzia sui valori di fondo nell’area del SIN e risulta di fondamentale importanza per lo sviluppo attuale e futuro dell’area industriale. Inoltre, in generale fornisce indicazioni utili e suggerimenti pratici in merito al corretto, efficace ed efficiente monitoraggio delle acque sotterranee in aree soggette al cuneo salino.XXIV Ciclo198

Classical Karst hydrodynamics: a shared aquifer within Italy and Slovenia

Abstract. The classical Karst transboundary aquifer is a limestone plateau of 750 km2 that extends from Brkini hills in Slovenia to Isonzo River in Italy. For 20 years, and especially in the last two years, the Mathematic and Geosciences Department of Trieste University has run a monitoring project in order to better understand the groundwater hydrodynamics and the relation between the fracture and conduit systems. A total of 14 water points, including caves, springs and piezometers are monitored and temperature, water level and EC data are recorded. Two sectors are highlighted: the southeastern sector mainly influenced by the sinking of the Reka River, and a northwestern sector connected to the influent character of the Isonzo River. Water table fluctuations are significant, with risings of > 100 m. During floods most of the circuits are under pressure, and only a comparative analysis of water levels, temperature and EC permits a precise evaluation of the water transit times in fractured and/or karstified volumes

A multidisciplinary approach in sinkhole analysis: The Quinis village case study (NE-Italy)

During the last recent years, in Quinis, a small village sited in the Alta Val Tagliamento valley (Friuli Venezia Giulia Region, NE Italy), the inhabitants facedwith instability phenomena related to the presence of soluble rocks in the subsurface. The evaporite bedrock is mainly mantled, in fact, by high thickness deposit. This paper explains the methodological approach thatwe used to identify the instabilities in a very complex geo-structural environment where the urbanization limits the applicability of several investigation techniques. Different methods were used to define the bedrock morphology, to characterize the mantling deposits and to identify the processes behind. What emerged from the study is a mandatory multidisciplinary approach to characterize the subsoil, because each technique is not able individually to take to a unique result. The data collected allowed to draft a geo\u2013 hydrogeological conceptual model of the Quinis village. The lessons learned, even ifwith some site-specific dependency, demonstrate the importance of broad-spectrum investigations,which are essential to understand the subsurface characteristics avoiding relevant socio-economic impact and supporting an adequate future territorial planning

Marine notches in the Maltese Islands (central Mediterranean Sea)

We present the first detailed survey of tidal notches in the central Mediterranean area, in particular along the coastline of Gozo and Comino (Malta). The Maltese Islands represent one of the few sites in the Sicily Channel which exhibits coastal carbonate rocks. Marine notches on the islands of Gozo and Comino were surveyed by means of a seven day continuous snorkeling survey around the entire perimeter of the two islands. We surveyed the occurrence, lack and typology of marine notches and we correlated them with late Holocene sea level changes. Sea temperature (T) and electrical conductivity (EC) were collected along the route in order to locate the submarine springs and to relate them to the surveyed notches.A well-carved continuous roof notch was discovered along most of the plunging cliffs. It is well-carved out, in particular along the northern and western coast of Gozo. It develops from about 0.2 m above the mean sea level down and it can be up to 1.5–2 m deep. On the contrary, tidal notches are localised only in 8 sites. In 2 sites, Vermetid trottoirs develop at low tide level. In addition, at about −7 m to −10 m m.s.l., a 2–5 m wide marine terrace develops along extensive tracts of plunging cliffs, always in correspondence with the roof notches. This submerged terrace seem to be the result of the late Holocene slowdown of the sea level rise, which started to smooth the terrace and to carve out the submerged part of the roof notch, thanks to the exposed location of the islands and the favourable lithology.Through the collection of hydrological data, the presence of 21 submarine springs were detected. They occur mainly in the south-western coast of Gozo and on eastern coast of Comino. Anyway, marine notches seem not to be related to the freshwater outflow, such as those in the Adriatic Sea, because the studied islands are very exposed. As a consequence, along the Maltese islands bioerosion seems to be the most effective process in notch development.peer-reviewe

Groundwater sustainability in the Friuli Plain

Groundwater resources in the Friuli Venezia Giulia (FVG) Region (northeast Italy) are an important natural wealth in terms of quantity, quality and ease of supply. This optimal condition, however, has long believed that it allowed an irrational and uncontrolled exploitation that inevitably produced tangible consequences on the water resources availability.The goal of the present research is the evaluation of the sustainable use of the groundwater in the Friuli Venezia Giulia Region aimed at providing guide-lines for its rational use. The study area belongs to the hydrogeological basin of the Friuli Plain and includes part of Veneto Region and Slovenia. The plain area is divided in two parts: the High Plain (HP) characterized by a phreatic aquifer and the Low Plain (LP) where eleven confined aquifer systems were identified. The two physiographic zones are separated by the spring belt. In order to evaluate the groundwater avaliability, a 3D model of the Low Friuli Plain aquifer systems was realized using Rockworks R14 software, starting from 603 lithostratigraphic wells data. Isobath and isopach maps were elaborated using kriging geostatistical method. Precipitation, evapotranspiration, runoff and infiltration were calculated to evaluate the inflow and outflow groundwater budget terms (109 rainfall and 46 thermometric stations, time series 1979-2008). To better define the river influences and the outflows at sea, a series of recent surveys on river discharges and surface withdrawals were considered. To obtain the water-budget in non-natural conditions, as the currents, were taken into account the groundwater withdrawals that were evaluated for each type of use and for each aquifer systems, starting from 2 geodatabases: one for the domestic uses (50101 estimated wells) and one for the industrial, agricultural, fish breeding, hygienic, geothermal and other minor uses (7594 wells). Well withdrawals amount were evaluated on annual base for recent periods and expressed as m3/s. The total current estimated groundwater withdrawals reach 62.4 m3/s, of which 41.1 m3/s from the confined aquifer systems in the LP area. More than 52% of the withdrawals are due to the domestic wells. For the water-budget, the studied territory was considered a “semi-closed box” in which groundwater sharings with the neighboring areas are not relevant and where the recharge is mainly due to the influent character of the river, infiltration, rainfall and irrigation practices. As result, the waterbudget for the confined LP is equal to +2.6 m3/s representing the accuracy, fairly acceptable for the scale of the research. Withdrawal entity, spring belt discharge, phreatic levels and confined aquifer’s pressure are closely interdependent and in dynamic equilibrium. The sustainability comes from the consistency and ratio between recharge and withdrawals. The confined aquifer withdrawals in the LP represent the 23.1% of the groundwater recharge coming from the HP and the 30.6% of the spring belt discharge. Seen that this last one can not further decrease, unless loss of important ecosystems, is likely to think that the present situation can be defined of limit equilibrium

Saltwater intrusion in Friuli Low Plain

In coastal areas, the interaction between seawater and fresh water is in a dynamic equilibrium and occurs both in surface bodies (saltwater ingression) and in groundwater (saltwater intrusion in aquifers). Human actions and climatic changes, especially sea level rising, can alter this equilibrium leading to a contamination of the fresh water and soils by seawater. The shift of salt wedge towards inland can be a consequence of both natural and anthropogenic processes. Natural processes have generally slow effects, except in the case of tsunami, as in Sri Lanka (Villholth and Neupane, 2011). The sea level rising due to climatic changes (Melloul and Collin, 2006) and local subsidence along coastal areas cause a slow salt wedge shifting. Instead, human actions have rapid effects on the coast system. Examples of the human actions are the overexploitation of aquifer, the incorrect and extreme watercourse regimentation, the excavation of floodway canal and dredging for navigation. The salt wedge intrusion can lead to freshwater contamination and consequently to a decrease of water reserve, to coastal area desertification by ground salinization and to a loss of faunistic and floristic species

Rock Fall Characterization in Climbing Spots: The Case Study of the \u201cNapoleonica\u201d Tourist Route (Trieste, NE Italy)

In NE Italy, fast-moving landslides represent a significant threat both to the population and the built environment. In the eastern portion of the Italian Alps, rock falls are common and are often responsible for casualties or severe damage to infrastructure. This type of landslide is characterized by strong relief energy and is triggered by earthquakes or copious rainfall, which often exceeds 2000 mm/yr. To assess rock fall hazard using software analysis, field surveys are crucial to accurately recognize the source areas of falling rock phenomena, to quantify the volumes of unstable blocks and identify the possible block trajectories. The current work takes in detailed geological and geomorphological mapping, through the identification of dislodged blocks, fractures and fallen blocks on a much-frequented limestone cliff in the Trieste Karst used as a climbing spot. Moreover, a popular tourist path (the Napoleonica) lies at the foot of the climbing cliffs. In-depth traditional activities, such as field surveys and aerial photo analysis were undertaken, including morphometric and geomechanical characterization of the whole rock mass, in order to perform a first identification of the more hazardous sections of the Napoleonica. The field data were collected using UAV (Unmanned Aircraft Vehicle) images and videos and this innovative technique allow the reaching and study of difficult sites with excellent resolution and precision. The final output is a GIS-developed map, that will be the starting point for future 2D and 3D simulations, that will lead to the creation of a rock fall susceptibility evaluation of the whole area

Interaction between karst and porous aquifers, the case of Mt. Mia transboundary aquifer.

The Mount Mia massif is located in the eastern side of the Friuli Venezia Giulia Region, across the border between Italy and Slovenia. It is an important karst hydrostructure bounded in the N, E and S by the Natisone River (Figure 1). Several springs are emerging at the toe of the massif mainly in the south-eastern side along the river. The two main springs, Poiana and Tologu, are tapped for the Cividale town water supply. The aim of the present paper is to assess the spring recharge area, its potentialities and vulnerabilities in order to quantify a possible increase withdrawal for the water supply

Evolution of an Alpine fluvioglacial system at the LGM decay: The Cormor megafan (NE Italy).

The dramatic climatic and environmental changes that occurred at the end of the last glaciation led to the formation of landforms (e.g.,moraines, fluvial ridges, and alluvial terraces) that strongly characterize the landscape in the alluvial plains facing the Alps. This also occurred with the Tagliamento glacier, which built a large LGM moraine amphitheatre in the piedmont sector of the southeastern Alps and fed fluvioglacial systems in the Friulian plain (NE Italy). The Cormor stream was one of themain glacial outwashes and formed an alluvial megafan during the peak of the LGM. At the decline of the LGM, the active belt narrowed and was subsequently abandoned. Since the Lateglacial the Cormor system has been an intermittent stream with limited activity. This sequence of events led to the preservation of large LGM surfaces, which enables their investigation, along with correlatable moraine ridges. The study of megafan depositional phases allows us to precisely constrain the chronology of glacial withdrawal at the end of the LGM, which is difficult in large sectors of the southern Alps. The geomorphological and geological study of the Cormor megafan was realized through the use of remote sensing, DEM analysis, field survey, stratigraphic boreholes, and radiocarbon dating. During the peak glaciation of the LGM, the Cormor experienced widespread aggradation with gravel deposition up to 15\u201325 km from the megafan apex, while the distal sector was dominated by fine-grained sediments. At the end of the LGM the Cormor stream incised the apical portion of its megafan, funnelling the sedimentary discharge and experiencing a limited aggradation in the distal sectorwith the formation of a progradational lobe. This deposition buried some swampy areas, sealing peaty and organic-rich clayey horizonswith 2\u20134 mof sediments. The top of these layers is radiocarbon dated at 22.0\u201319.5 ka cal BP and indirectly constrains the chronology of several recessional moraines that formed within the glacial amphitheatre. After this depositional phase, the Cormor megafan was deactivated because of water and sediment discharge concentration of the Tagliamento catchment in the Tagliamento River. This study demonstrates the possibility to reconstruct the timing of the decline of the Tagliamento moraine amphitheatre by studying the distal portion of the related outwash plain. Moreover, new geochronological dating allows chronological comparison of the glacial withdrawal in the eastern sector of the Southern Alps with the global chronology. The results suggest that we can apply this approach also in the distal part of the other alluvial megafans formed by Alpine glacial outwashes in the central part of the Po plain where radiocarbon chronology is almost lacking

GYPSUM\u2019S ROLE IN THE SINKHOLES OF THE TAGLIAMENTO RIVER VALLEY (NE ITALY)

In an area of several kilometers in the Tagliamento Valley, between the villages of Ampezzo and Villa Santina (Friuli, NE Italy), are present frequent points of absorption associated with large and deep sinkholes collapsed in the shallow cemented fluvial-glacial deposits, in the recent alluvial deposits overlying a karstified evaporitic bedrock. In the Quinis village the situation is particularly complex, some houses are affected by failures and in the past, in the fields around the village sudden sinkholes were recorded and some building were demolished also in the centervillage. During the last years a tightening in the phenomena took to the necessity of a deep and multidisciplinary study in order to define the vulnerability of the different areas. For the purpose, were realized 20 piezometer (equipped with devices), 3 seismic lines, 1 electrical tomography, the establishment on the buildings of a topographical monitoring network, 2 assestimeters and a groundwater tracing test campaign. The main vulnerable areas were identified with the presence of holes or caves in the gypsum and soft and unconsolidates alluvial horizons. The big variations in the groundwater levels recorded during the past years and linked to the regime imposed by the dam outflow, underlined an increase in the karstification processes inside the gypsum bedrock and in the above deposits