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Application of the modflow groundwater numerical model to hydrogeological volcanic units
No full textThe work of study presented can be retraced in the following main phases:
Comprehensive work of examination and interpretation of several field campaign data and literature
data: well log stratigraphies, geological maps. From a detailed starting approach, in which the
comprehensive volcanic sequence has been analyzed and each deposit’s hydraulic behaviour has
been considered, to a simplified re-organization with the definition of main hydrogeological
complexes.
Conceptual model building: geological and hydrogeological framework has been investigated, a
volumetric reconstruction of the aquifer has been made, were areas with different hydraulic
behaviour were identified and media type defined (porous media and fractured). Then the
identification of the sources and sinks: summarised in the elaborated water budget.
Some issues linked to the conceptual model have to be highlighted:
- The evaluation of the geologic heterogeneity effect on the hydraulic behaviour at the model
scale. Volcanic deposits are characterized by a high heterogeneity which conditions groundwater flow
patterns. So, which value could have an equivalent (effective) hydraulic conductivity, which can
represent the integrated effect of a heterogeneous media? A more detailed analysis of pumping test;
including data coming from other zones of the latium volcanic complex should be useful. Heterogeneity
plays a key part in the uncertainty estimation (Section 4.7.1); it has to be improved for the proper
evaluation of the two key parameters, correlation lenght λ and the σ (standard deviation of lnK).
- There was applied a methodology, suggested by Sonnenborg & Henriksen (2005), to determine the
uncertainty of observational head data in relation to the model. The purpose of quantifying the
uncertainty of observational head data (σ obs) is to achieve a measure of how accurately the model can
reproduce the data. This should in principle be an objective criterion for how data weighted
approximation and more importantly, how data of different types must be relatively weighted (important
when using objective functions).
- It was revealed that the component due to geologic heterogeneity on the whole observational head
uncertainty value, played a major role for such performance assessments and that the lack of
experimental data suggested that this aspect should be further analysed in more depth when doing future
model analysis of volcanic aquifers.
From the conceptual model a numerical groundwater flow model (mathematical model) was set up
using a finite-difference code MODFLOW2000 and in a first step the graphical interface Visual
Modflow 2009-1®. In this first two dimensional, steady state numerical groundwater model, the
aquifer system was represented by a one layer model describing the groundwater flow systems in 2
dimensions. Bracciano Lake area together with the underlying aquifer was represented as a
simplified single aquifer system, with a higher hydraulic conductivity for the lake area compared to
the surrounding areas. Results from calibration and tentative validation of this simplified model did
not satisfy the initial performance criteria and objectives identified, e.g. it was not possible to
evaluate lake-aquifer interactions (see chapter 1) in the required details with this first model. Next
step consisted in setting up a new mathematical model based on a numerical integrated groundwater
flow and lake model by use of Groundwater Vistas®5.41 (ESI), which allowed incorporation of the
implemented lake package in this software, thus it was possible explicitly to include Lake
Bracciano and its interaction with the underlying volcanic aquifer within this package. In order to
keep the model as simple as possible, the whole aquifer was divided in two layers having the same
thickness, except in Lake Bracciano area. In the lake area the upper layer was defined by the lake
depth, whereas the lower layer was comprised by the aquifer.
Calibration and tentative validation tests were carried out on the VMF model. PEST was used for the inverse
calibration, with head targets. The methodology allowed for a comparison of the residual statistics
(difference between simulated and observed head). Hereby, head observational uncertainty when referring to
model scale and other target values could be evaluated for three adopted quantitative accuracy Criteria
(Refsgaard et al., 2010). Criteria value ranges were related to the established model detail that is a function
of the objectives and the ambition level, as reported in Refsgaard et al., 2010. Ambition level can be
considered as: 1) screening/basic (rough calculations), 2) intermediate and 3) high (aquifer
simulation/detailed modelling). In this work of study it was decided, based on the available knowledge and
data, to go for a screening model (as a first step): ”A screening model describes the regional characteristics
of the ground-water-flow system without including the hydrogeologic detail or data density that would be
necessary for answering site-specific questions. A calibrated screening model can be used with confidence to
simulate a regional ground-water-flow system, but with less confidence to simulate local-scale flow. A
screening model is a tool that can be used to improve the overall understanding of the hydrology of a basin
by testing alternative conceptual models of the ground-water-flow system. Additionally, a screening model
can be used to highlight areas where more hydrogeologic or water-quality data are needed”. (Feinstain et al.,
2005)
Calibration carried out using the Groundwater Vistas 5.41® MODFLOW interface was initially focused on a
sensitivity analysis to obtain an acceptable value of the lakebed hydraulic conductivity. A second step was
the “autosensitivity” analysis (Groundwater Vistas tool) that permits to determine in a detailed analysis
which parameters are sensitive to the available targets and which parameters are closely linked. Then PEST
was used to calibrate the model using automatic calibration (inverse routines). At the beginning the head
dataset and four flux values were applied. Subsequently eight flux values were used in combination with the
head data. Head targets were divided in two groups: one representing water table level nearby the lake and
another representing targets all over the study area. Flux (flow in drainage systems) was then the third target
group. When using inverse modelling (PEST) it is important to assign proper weights to the different targets
in order to determine their relative importance in the parameter estimation process and understand by which
weights the model is optimized with respect also to the objectives. Groundwater model results improved
after the calibration process.
One of the objectives of the Bracciano groundwater model was that it should be a useful tool for
testing the current understanding and assumptions established with the conceptual model. The use
of inverse modelling (PEST) here allowed for understanding about whether the constructed model
for the aquifer system and the lake interaction turned out as a credible and reliable model. If that is
the case, then the model can be used in future management of the water resources for the volcanic
basin. Thus two tests are important for evaluating the credibility and reliability: 1) Quantitative
performance e.g. the simulated and observed water balance for aquifer and lake and results of
validation tests (the 3 Criteria), when running the model with data not used for calibration and 2)
Qualitative performance e.g. whether the calibrated parameters are within realistic ranges, whether
the simulated head distribution is credible compared to manual mapped distributions etc.
During calibration process, the water budget values are constantly compared with the
volumes estimation coming out from simulations to evaluate the results.The hydrogeologic system studied is characterized by the presence of four volcanic calderas, two of these
still occupied by lakes (Lake Bracciano and Lake Martignano), there are two big water abstraction sites: one
from lake (Paolo aqueduct) and the other fed by drains on the northwest side of the Lake Bracciano (Traiano
aqueduct). At the same time the area is exposed to a continuous exploitation and dewatering from effect of
the several public and private pumping wells from the groundwater aquifer put in action in the last twenty
years.
The management of this complex system is challenging, and could surely benefit of the predictive capacities
that a calibrated and validated model would enable and provide. It should be an interest and preference of the
public administration to implement a stronger tool as a groundwater model, since a quantitative
understanding of the whole system and its interactions are needed in order to exploit the groundwater aquifer
in a sustainable way. Also for the different water users it is important to manage their own wells based on a
better understanding of the whole system, and how their groundwater abstraction and land use affects the
recharge, water balance of the aquifer, interaction with lake, wetlands near the lake and runoff from the area.
Lections learned with this work of study are:
- The use of the “lake package” to study aquifer-lake interactions appears to be promising
and needed in order to properly address the conceptual model and the objectives defined.
- The MODFLOW model (final Groundwater Vistas model) could be a “basic” model that
could be further improved if running a new model cycle in order to arrive to a starting model useful
for the water resources administrator (with a special focus to Lake Bracciano, which constitute a
site of environmental and economical interest); to reach an intermediate level useful for credible
and reliable predictive simulations of the regional Bracciano aquifer-lake system for practical water
management purposes
- The actual model should be improved by introducing a “zonation” of values of the lakebed
hydraulic conductivity, considering influencing factors as the wave energy, the slope of the bottom
surface, etc. This would probably require additional field investigations of the groundwater – lake
interactions
- Simulation in transient conditions should be considered. This would enable more
possibilities for validating the model, because time series of head and flow including the storage
terms in groundwater and lake could be explicitly included. Lake budget data should be inserted at a
time scale relevant (e.g. monthly): so rain, evaporation, runoff and lake elevation could be
elaborated with this transient model approach. It could be another way to improve Bracciano
groundwater model and to test also the input data (the calculation of monthly net precipitation and
groundwater recharge to the model). A three or more layer model could be considered, with the aim of representing the presence
of the aquitards, perched water tables etc. There are several challenges, and feasibility of different
model codes with respect to describing ‘perched water tables’, unsaturated zone, overland flow,
river and drainage flow etc. needs to be further evaluated before an high ambition model level could
be met
Analisi della vegetazione dunale costiera in relazione alle praterie marine di Posidonia oceanica
No full textCoastal systems are situated at the interface between marine and
terrestrial environments and are particularly sensitive to the changes
in the surroundings. They are strongly linked to marine environments
and an intense exchange of energy and nutrient occurs through the
accumulation of wrack derived from marine seagrasses and
macroalgae. In the Mediterranean, consistent deposits of seagrasses
wrack accumulate along sandy shores. These deposits are mainly
constituted of material from the endemic seagrass Posidonia
oceanica.
Beach-cast wrack plays several roles and influences both the
morphology and the ecological process of coastal environments.
Although coastal vegetation is fundamental for dune formation
processes and for the ecosystem maintenance, few authors have
investigated the effect of beach-cast wrack on plant species. This
decomposing material could be a relevant subsidy in sandy shores,
which are typically nutrient poor. We hypothesize that the
accumulation of P. oceanica beach-cast wrack on coastal dunes has
an important positive effect during the germination and early stages
of plant growth, and consequently, it may contribute to a significant
increment of the total plant diversity.
This project aims at analyzing the effects of P. oceanica beach-cast
wrack on coastal dune vegetation, at species and community levels.
In particular, we focused on the effects of wrack on:
1) seed germination of the most typical coastal plant species
2) seedling development
3) the structure of coastal dune plant communities
The effect of P. oceanica wrack on seed germination was
investigated through germination tests. Germplasm of most typical
dune plant species (Cakile maritima, Elymus farctus and Crucianella
maritima) was collected along the coasts of Lazio, Sardinia and
Balearic Islands. The effect of light, temperatures, NaCl and KNO3
was tested. In this PhD thesis only the results for Crucianella
maritima are shown. The seed germination of this species was
characterized by photo-inhibition, absence of primary dormancy and
a secondary dormancy imposed by salt concentrations, with no
requirement for nutrient-rich soils.
IV
Plant growth experiments were carried out in a greenhouse,
comparing plants growing on substrates with and without P. ocenica
wrack. The presence of wrack enhanced the plant growth, fertilized
the substrate, kept it humid and favoured the nutrient uptake.
The analysis of coastal dune vegetation at community level was
studied through the comparison of phytosociological relevés
(obtained from a literature review) from beaches with high or with
low volumes of beach-cast wrack. High levels of wrack incremented
species cover and influenced species composition.
Our results revealed that P. oceanica beach-cast influences the
vegetation at both species and community level. Moreover, our
findings could provide useful information for coastal management
plans
Investire in energie rinnovabili
No full textObiettivo del lavoro è quello di indagare ed illustrare le principali tecniche di analisi della
convenienza economica dei progetti d’investimento ed in particolare ci riferiremo ad un tipico
esempio di impresa monoprogetto.
Il lavoro è suddiviso in tre parti.
Nella prima parte si offre una panoramica delle tecnologie per l’utilizzo delle fonti rinnovabili
ed in particolare, attraverso delle schede tecniche si offrirà al lettore la possibilità di capire come
realmente funzionano le specifiche tecnologie.
Nella seconda l’attenzione è stata posta su un progetto per la realizzazione e gestione di una
centrale eolica e sui criteri per valutare l’economicità di tale progetto. In particolare si sono
passati in rassegna i diversi metodi per valutare le performance di un progetto, analizzando
prima i metodi contabili come il ROC e ROE e quindi i tipici metodi di capital budgeting basati
sull’attualizzazione dei flussi di cassa come il VAN e il TIR.
Si illustrerà inoltre il processo di determinazione del costo del capitale dell’impresa, illustrando,
prima il modello economico del Capital Asset Pricing Model (CAPM), e quindi il beta
dell’impresa. Si sono quindi evidenziate le differenze tra il beta di impresa e il beta di mercato.
Sono stati inoltre descritti gli strumenti di previsione che ci permettono di analizzare, qualiquantitativamente,
gli scenari alternativi che si presentano lungo la vita del progetto. I flussi di
cassa sono stati considerati, al contrario di quanto fatto nella prima parte non più certi ma
soggetti ad ipotesi e situazioni non prevedibili. In particolare si sono analizzati gli strumenti di
sensibilità, del punto di pareggio, la tecnica dell’albero delle decisioni e in ultimo il metodo
Monte Carlo.
La terza parte, invece, è relativa alla contestualizzazione degli investimenti nell’attuale cornice
regolatoria nazionale ed europea
A pragmatic account of the remote definite article in Somali
No full textThis study is concerned with the role of the remote definite article -kii/-tii in Somali language, the author attempts to characterize more accurately than in previous accounts the range of meanings this determiner conveys.Maqaalkaani wuxuu falanqaynayaa dowrka qodobada af Soomaaliga, gaar ahaan -kii/-tii. Qoraagu wuxuu isku dayayaa in si qoto dheer u falanqeeyo, oo ka duwan siyaabihii hore ee loo baaray, micnaha badan ee xambaarsan qaabka qodobadan.Questo articolo analizza il ruolo del determinante anaforico -kii/-tii in lingua somala: l'autore tenta una caratterizzazione più accurata delle descrizioni precedenti relativamente alla gamma di significati che questo determinante può veicolare.M. Frascarelli (ed
Phonological pitfalls in the business of getting a living: the strange case of Somali stops
No full textIn this paper, the author provides an analysis of the phonological phenomena of Somali known as stop voicing.Qoraagu wuxuu maqaalkaan ku lafagurayaa arrin la xiriita qayb ka mid ah cadaynta af Soomaaliga.In questo articolo, l'autore fornisce un'analisi del fenomeno fonologico in somalo noto come sonorizzazione delle occlusive.M. Frascarelli (ed
Faafinta Rasmiga ah ee Jamhuuriyadda Soomaaliya [Agoosto - Oktoobar 2011]
No full textUrurinta Faafinta Rasmiga ah ee Jamhuuriyadda Soomaaliyeed ee la soo saaray sannadka 201i, bilaha: Ogost, Sebtember iyo Oktoober.Raccolta delle Gazzette Ufficiali della Repubblica Somala relative al 2011, comprendente i mesi di agosto, settembre e ottobre.Collection of the Official Bulletins of Somali Republic published in 2011, including the months of August, September and October.Qareen Cabdullaahi Darmaan ayaa dokumentigan ku deeqay xarunta cilmibaarista (Centro Studi Somali).Documento messo a disposizione del Centro Studi Somali dall'Avv. Abdullahi Darman.Document provided to the Somali Studies Centre by lawyer Abdullahi Darman
Elettronica integrata di front-end e strumentazione di caratterizzazione per sonde ecografiche in tecnologia cMUT ad alta frequenza
No full textLa diagnostica medica nel campo degli ultrasuoni ha fatto sempre uso di sonde con trasduttori
piezoelettrici. Nel corso degli ultimi anni il crescente sviluppo della tecnologia MEMS (Micro-
Electro-Mechanical Systems) ha consentito di utilizzare questa tecnologia per la realizzazione di
trasduttori capacitivi su silicio, dando vita ai trasduttori ultrasonici capacitivi microfabbricati
(cMUT). Molti gruppi di ricerca nel campo degli ultrasuoni ritengono che i cMUT (Capacitive
Micromachined Ultrasonic Transducers), per le loro enormi potenzialità, possano prendere a breve
il posto dei trasduttori piezoelettrici utilizzati attualmente nei sistemi di indagine ecografica.
La tecnologia dei dispositivi MEMS, utilizzata per la realizzazione di trasduttori ultrasonici,
consente in prospettiva di integrare il trasduttore con l’elettronica producendo enormi benefici in
termini di complessità e costi, riducendo le componenti parassite e il numero delle interconnessioni
nonchè di ridurre il rumore aumentando la banda di frequenza del trasduttore, riducendo infine
drasticamente le dimensioni, potenzialità molto apprezzabile soprattutto nelle applicazioni che
necessitano di una sonda piccola e compatta come, ad esempio, nelle indagini intravascolari.
In questo lavoro di Tesi è stato introdotto il trasduttore cMUT e ne è stato descritto il principio di
funzionamento, facendo riferimento ai suoi modelli equivalenti e al processo tecnologico di
fabbricazione. E’ stato descritto il sistema ecografico e i principali componenti che lo compongono.
Sono state inoltre progettate, realizzate e caratterizzate sperimentalmente diverse configurazioni di
elettronica di front-end per le sonde ecografiche in tecnologia cMUT sviluppate presso il
laboratorio Aculab dell’Università Roma Tre. La funzione principale svolta dall’elettronica di frontend
è quella di effettuare un adattamento di impedenza elettrica tra il trasduttore e il cavo che
collega la sonda alla macchina ecografica.
Sono stati successivamente progettati, realizzati e caratterizzati i circuiti di alimentazione della
sonda necessari a fornire la tensione di polarizzazione al cMUT e le tensioni di alimentazione per
l’elettronica di front-end.
E’ stato infine progettato e realizzato un innovativo strumento utilizzato per la caratterizzazione dei
trasduttori cMUT ad alta frequenza. La necessità di realizzare tale strumento in laboratorio è dovuta
al fatto che non esiste in commercio uno strumento concepito appositamente per avere funzioni
adeguate alla caratterizzazione dei cMUT. Lo strumento è un pulsatore/ricevitore utilizzato per
effettuare le tipiche misure di pulse-echo per trasduttori acustici. Tali misure sono molto importanti
per studiare la risposta in frequenza del trasduttore sia in trasmissione che in ricezione. Il
pulsatore/ricevitore è in grado di trasmettere al trasduttore segnali elettrici impulsivi ad alta tensione
al fine di portarlo in vibrazione e di amplificare il segnale elettrico in ricezione prodotto dal
trasduttore in risposta ad un campo acustico incidente sulla sua superficie. Il segnale di ricezione
può essere visualizzato su un oscilloscopio ed essere elaborato attraverso specifici algoritmi per
valutare la risposta in frequenza del trasduttore. Il pulsatore/ricevitore è in grado di lavorare sia in
modalità trasmissione/ricezione che in modalità solo ricezione ed è dotato di tastiera, display e porta
seriale per gestire il controllo dello strumento da locale o attraverso un PC.
Il lavoro portato avanti in questa Tesi ha contribuito all’avanzamento della ricerca sulle sonde
ecografiche in tecnologia cMUT che si ritiene possano a breve competere, non solo dal punto di
vista strettamente tecnico ma anche da quello squisitamente commerciale, con quelle di tipo
piezoelettrico che allo stato attuale detengono il monopolio del mercato mondiale
La rappresentazione di Londra nella letteratura postcoloniale ed europea contemporanea : spazio, memoria, conflitto
No full textLa città è un luogo di incontri, scontri, traiettorie personali e pubbliche che
collidono in un testo continuamente in evoluzione. Si è scelto di analizzare l’immagine
di Londra nella letteratura contemporanea postcoloniale ed europea secondo un
percorso tematico riconoscendo varie tipologie di rappresentazione dello spazio
urbano comuni e costanti in varie opere. Si procede con l’illustrare i diversi significati
che Londra ha assunto nel corpus preso in considerazione, delineando le varie tipologie
di scrittura e gli elementi ricorrenti di ogni declinazione del significante Londra e
dell’utilizzo letterario dello spazio. Questa lettura fornisce gli strumenti per decifrare i
significati più ampi che Londra, intesa sia come spazio fisico ben riconoscibile e
concreto che come spazio dell’immaginario, ha assunto in letteratura come frutto da
una parte di oscillazioni sociali e culturali, legate all’eredità dell’impero, dall’altra di un
potenziale umano e creativo riconducibile alla sua natura di spazio metropolitano in
quanto tale. Si sono quindi riscontrate quattro tipologie di riscrittura dello spazio
urbano: di protesta e ibridismo, per attenuare il conflitto che la poliedricità etnica,
linguistica e culturale dello spazio pone; di alienazione o pazzia, nel caso in cui l'attrito
coloniale che Londra ha in sé crei falle di forte disagio; spazio di iniziazione, dove
l'individuo proietta le ambizioni di crescita intellettuale e compie la propria personale
formazione; e infine spazio di viaggio per confermare come Londra si ponga come uno
sterminato archivio passibile di diverse letture, condizionate di volta in volta dal diverso
background del lettore
