1,721,045 research outputs found
Large scale 3D groundwater flow modeling in fractured rocks: the case of Mt. Amiata volcanic aquifer (southern Tuscany, Italy)
No full textModellazione di un acquifero a porosità fissurale: il complesso vulcanico del M. Amiata (Toscana meridionale)
No full textModellazione di un acquifero a permeabilità fissurale: il complesso vulcanico del M. Amiata (Toscana meridionale)
No full textIl complesso vulcanico del M. Amiata è uno dei più importanti serbatoi idrici naturali della Toscana; tali rocce sono altamente permeabili per fessurazione e contengono un acquifero freatico particolarmente suscettibile ad ingerire e diffondere inquinanti fluidi e idroveicolati, in un territorio dove l’attività umana realmente e potenzialmente inquinante grava sui settori per loro natura più vulnerabili. L’assetto geometrico e la distribuzione spaziale delle fratture determinano le caratteristiche idrauliche dell’acquifero e pongono problemi teorici ed applicativi connessi all’elevata velocità di flusso, all’anisotropia del mezzo, alle limitate possibilità di attenuazione del carico inquinante ed alle difficoltà di quantificazione dei parametri. Il rilievo amiatino è interessato da indagini finalizzate ad approfondire le problematiche connesse alla modellazione dei mezzi anisotropi fratturati, con particolare attenzione alla caratterizzazione del flusso idrico e quindi ai diversi approcci modellistici utili a descrivere, alla grande scala, le condizioni di flusso all’interno di una rete di fratture; vengono presentati i primi risultati ottenuti con l’utilizzo di un programma di simulazione agli elementi finiti e sulla base di una definizione dettagliata dello stato di fratturazione. L’approccio adottato può essere definito “continuo del mezzo poroso equivalente anisotropo”; l’anisotropia generata dai diversi sistemi di fratturazione è stata rappresentata mediante il tensore della conducibilità idraulica sulla base di una campagna di rilevamento finalizzata alla creazione di una banca dati sulle principali caratteristiche delle discontinuità presenti nel complesso vulcanico ed all’identificazione delle famiglie di fratture che presiedono alla circolazione idrica. La modellazione numerica del flusso è stata realizzata con il software FEFLOW, operando in condizioni stazionarie; è stata utilizzata una strategia a complessità crescente partendo dal calcolo del tensore per l’intero dominio, per poi passare ai tensori delle zone a fessurazione simile. La calibrazione del modello numerico è stata basata sulle serie temporali di portata sorgiva a causa dell’assoluta mancanza di misure piezometriche adeguatamente distribuite. I risultati della modellazione effettuata con un unico tensore di conducibilità evidenziano una significativa anisotropia del mezzo lungo l’allineamento NNE-SSO, coincidente con le principali zone di recapito delle acque sotterranee, con una buona convergenza tra flussi misurati e calcolati. La suddivisone del dominio in zone, ognuna con i relativi tensori, ha consentito di individuare una realistica distribuzione del campo di conducibilità idraulica e di ridurre gli scarti tra flussi misurati e calcolati; la maggiore complessità dell’approccio non é comunque sufficiente per tener conto dei fenomeni locali. Il programma di ricerca è finalizzato al conseguimento di simulazioni in transitorio capaci di riprodurre l’andamento delle portate delle sorgenti misurate per significativi periodi di tempo. La corretta rappresentazione del comportamento idrodinamico dell’acquifero costituisce infatti il fondamento necessario per gestire correttamente il suo sfruttamento, per ricavare valide simulazioni del trasporto di eventuali inquinanti ed, in particolare, per delimitare le aree di salvaguardia delle opere di captazione
Simulating the impact of coastal pumping for fish farming purposes on the quality of groundwater: a case study in southern Tuscany, Italy
No full textThe Ansedonia promontory (southern Tuscany, Italy) is characterised by the presence of fish farms that pump 48•106 m3/year of thermal (21-24 °C) saline groundwater in order to guarantee the continuity and quality of production (1.7•103 tons/year); the water is extracted from a carbonate aquifer with high permeability due to fracturing and karstification (cavernous limestone), which is also exploited for irrigation purposes (2•106 m3/year) and domestic use (7•106 m3/year). Such exploitation has led to the degradation of groundwater quality, and remedial actions are required to improve the management of local freshwater resources. Geological, hydrogeological and hydrogeochemical studies reveal the extensive and complex circulation of waters within the aquifer system that allow mixing in variable proportions of fresh and salt waters, both superficial (recent) and deep (old); the flow along the freshwater/saltwater interface may even derive from considerable depths, with the upwelling of waters of different age, salinity and temperature. The conceptual model has allowed the development of a 3D finite element flow and transport numerical model using the FEFLOW code. The freshwater budget was negative (9∙106 m3) in the hydrologic year 2004-2005, indicating that the aquifer was heavily overexploited especially due to the quantity of freshwater extracted by fish farms (26 % of the total). Results suggest that fish farming wells should be extended to deeper portions of the aquifer stably occupied by marine waters in order to limit the environmental impact of facilities; this solution, which is being implemented, will also increase our knowledge of aquifer characteristics and zone mixing, thereby improving the model’s ability to reproduce the behaviour of the aquifer under different stress conditions. The model has also allowed a preliminary forecast of the quantitative and qualitative evolution of resources over time, checking the effects of differing hypotheses of management
Ansedonia: simulazione degli effetti dell'emungimento delle acque sotterranee (seconda parte)
No full textL’aumentata concentrazione di insediamenti umani, associati allo sviluppo delle attività agricole, industriali e turistiche, ha causato lungo le coste un eccessivo sfruttamento delle risorse idriche sotterranee che ha provocato il sollevamento dell’interfaccia acqua dolce/acqua salata (intrusione salina) con conseguente deterioramento della qualità della falda. Questo fenomeno si presenta in crescita in numerose località costiere dei paesi dell’area mediterranea, compreso il nostro (Barrocu, 2003). Anche se esiste nel pubblico la consapevolezza che l’acqua sotterranea sia un bene capace di promuovere o condizionare lo sviluppo economico di una regione, è spesso difficile prevedere nell’ambito gestionale di un territorio gli effetti a medio-lungo termine di un fenomeno come quello dell’intrusione salina che mostra aspetti poco chiari perfino agli esperti del settore. La trattazione di tali problematiche risulta complessa per le numerose componenti e variabili tra loro correlate; essa richiede, inoltre, l'impiego di adeguate metodologie e strumenti avanzati di analisi
A 3D density-dependent model for assessment and optimization of water management policy in a coastal carbonate aquifer exploited for water supply and fish farming
No full textThe Ansedonia promontory (southern Tuscany, Italy) is characterized by the presence of fish farms that pump thermal saline groundwater. The water is extracted from a carbonate aquifer with high permeability due to fracturing and karstification that is also exploited for irrigation purposes and domestic use. Such exploitation has led to the degradation of groundwater quality, producing conflict among the different users. The conceptualization of the aquifer allowed the development of a 3D finite element density-dependent numerical model using the FEFLOW code. The slightly negative freshwater budget in the very humid hydrologic year of 2004-2005 revealed that the aquifer was overexploited, especially due to the extraction of freshwater (along with seawater) from fish farm wells and pumping from public supply wells. The model was also used to forecast the quantitative and qualitative evolution of resources over time, thus testing the effects of different management hypotheses. Results demonstrate that the sustainable management of the aquifer most-ly depends on withdrawals from public supply wells; the quantity extracted by fish farms only significantly affects the freshwater/saltwater interface and, locally, the salinity of groundwater. Actions to counteract seawater intrusion are proposed
Hydrogeological investigations in southern Tuscany (Italy) for coastal aquifer management
No full textOngoing hydrogeological investigations in the Grosseto Province (southern Tuscany, Italy) aim to develop a correct model for the management of coastal aquifers, which are affected by seawater intrusion due to overexploitation for various purposes. This study updates and integrates hydrogeological knowledge of the area; in addition, it proposes a monitoring network and remedial actions. Completed analyses reveal the presence of coexisting flow systems
of different rank which allow the mixing of freshwater and saltwater, both superficial (recent) and deep (old), in various proportions. Hydraulic head measurements reveal the important impact of pumping on the flow of groundwater, with the formation of a negative hydraulic head in areas of intense withdrawal (water supply systems, fish farms). Geochemical data indicate that the chemical composition of groundwater is mainly determined by the mixing of seawater with waters circulating in the cavernous limestone and in neo-autochthonous sediments. The definition of conceptual models for the
aquifers allowed the development of numerical models for hydrodynamic and hydrochemical simulations, which provide useful information on the general evolution of systems under different stress conditions. The study assessed schemes to counteract seawater intrusion, taking into account the characteristics of the multi-aquifer system of the Albegna plain (replacement of the amount pumped for irrigation with treated wastewater and/or surface water stored in reservoirs;
artificial recharge of the aquifer through injection wells or infiltration basins containing treated wastewater and/or infiltration channels which divert the flood water of streams) and of the adjacent carbonate aquifer (requalification of pumping systems in fish farms; redesign of the network of public-supply wells). Lastly, a network of existing wells and additional observation well
Hydrogeological investigations in southern Tuscany (Italy) for coastal aquifer management
No full textOngoing hydrogeological investigations in the Grosseto Province (southern Tuscany, Italy) aim to develop a correct model for the management of coastal aquifers, which are affected by seawater intrusion due to overexploitation for various purposes. This study updates and integrates hydrogeological knowledge of the area; in addition, it proposes a monitoring network and remedial actions. Completed analyses reveal the presence of coexisting flow systems of different rank which allow the mixing of freshwater and saltwater, both superficial (recent) and deep (old), in various proportions. Hydraulic head measurements reveal the important impact of pumping on the flow of groundwater, with the formation of a negative hydraulic head in areas of intense withdrawal (water supply systems, fish farms). Geochemical data indicate that the chemical composition of groundwater is mainly determined by the mixing of seawater with waters circulating in the cavernous limestone and in neo-autochthonous sediments. The definition of conceptual models for the aquifers allowed the development of numerical models for hydrodynamic and hydrochemical simulations, which provide useful information on the general evolution of systems under different stress conditions. The study assessed schemes to counteract seawater intrusion, taking into account the characteristics of the multi-aquifer system of the Albegna plain (replacement of the amount pumped for irrigation with treated wastewater and/or surface water stored in reservoirs; artificial recharge of the aquifer through injection wells or infiltration basins containing treated wastewater and/or infiltration channels which divert the flood water of streams) and of the adjacent carbonate aquifer (re-qualification of pumping systems in fish farms; redesign of the network of public-supply wells). Lastly, a network of existing wells and additional observation wells was identified for quality and quantity monitoring of aquifers
Identification and comparison of perennial yield estimation models using Mt Amiata aquifer (southern Tuscany, Italy) as an example
No full textWith the principal aim of identifying and comparing suitable evaluation and forecasting models of perenni al yield, detailed hydrogeological research was conducted on the cold phreatic aquifer located in the volcanites of Mount Amiata, southem Tuscany's most important water reservoir. The study was based on spring discharge, precipitation, and temperature data. It permitted the identification ofthe following models: (1) ratios between discharge values measured at the springs, (2) depletion curve analysis ofthe springs, (3) multiple regression with clima tic data, and (4) water balance, coefficients of potential infiltration and runoff coefficients derived on a physiographic basis. Analysis of the results obtained using these models shows their excellent ability to forecast in the medium and long term; for short-term (yearly) forecasts, highly satisfactory results have been obtained for most of the methods used. With regard to Mt. Amiata's average perennial yield, it is estimated at 55 x 106 m3/yr (the maximum deviation among the various evaluations performed varies from 4 to 8 percent), and it presents a decreasing trend, which is proportional to the reduction of local precipitation
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