1,721,015 research outputs found
Influenza delle variazioni climatiche sul ciclo idrologico nell'Italia Centro-meridionale
No full textThe historical data series for temperature and rainfall avaible for the Italian peninsula indicate that over the last one hundred years there has been a tendency towards an increase in temperature and a decrease in average annual rainfall. The flow data for some hydrogeologic systems confirm these trends, wich are consistent with the scenarios provided by Global Circulation Models (GCM) and with climatic variations in the past. If one assumes that these trends will persist also in the future, their extrapolation to the next 50 years indicates a considerable decrease in the availability of water resources, with extremes of up to 20-30% compared with the average values for the last 50 years
Primi risultati dello studio idrogeologico del bacino del Torrente Nestore (Umbria)
No full textE' stato applicato al T. Nestore, impostato su flysch, un modello matematico non distribuito che simula i deflussi medi mensili. Il modello assimila il bacino a due serbatoi e simula il deflusso medio mensile a partire dai dati di pioggia e temperatura medie mensili di un anno medio
Influence of the geological setting on the response to climatic change and to increasing prolonged drought periods of fractured limestones system.
No full textIt is widely known that, in Southern Europe and the Mediterranean area, in the last hundred years, the temperature has risen by about 1°C, and the average annual precipitation has increased. The analysis at different time scales of historical thermo-pluviometric series recorded in South/Central Italy shows a higher frequency and duration of droughts in the last few decades: the number of three years lasting dry periods recorded since 1990 are as many as those recorded in the interval 1921-1989. The hydrogeological processes regulating both ground and surface water availability are greatly influenced by climate change. If the present trend should continue, a reduction of total yield of 10-20% with respect to present should be expected in the next 50 years. This work shows that the response of a specific hydrogeological system to climate change closely depends on the geological and lithological characteristics of the system. The aquifers hosted in the karst/fractured limestones extensively outcropping in the mountain areas of Central Italy, which supply several mountain springs with high-quality water, are taken as examples. The recharge areas of the springs fed by these aquifers are unaffected by human activity: the analysis of spring discharges is therefore useful to understand the effect of climate change on groundwater regimes. Some of the springs of the Umbria-Marche Apennines, (e.g., Bagnara, Scirca, Pescara di Arquata del Tronto) have long, continuous discharge data sets which show statistically significant negative trends of mean annual and monthly discharges. The Bagnara spring, which is of great importance on the water supplying point of view, is an example of “local system” representing the “overflow” of a deeper regional groundwater circulation, connected with larger “base springs”, the quality of which is often poor due to interactions with evaporitic sediments of Triassic age. Springs of this kind are quite frequent in the Umbria-Marche region. A dynamic groundwater divide, the position of which depends on the amount of recharge, separates the recharge areas of the regional flow from those of local springs as Bagnara: low recharge periods correspond to a low level of the piezometric surface, with the piezometric divide shifted towards the systems located at higher elevations and a consequent reduction of their recharge areas. On the contrary, the other system taken as an example in this work, the Lupa spring, although similar to Bagnara for lithological, topographical and climate characteristics and for mean annual discharge (about 120 l/s), has a geologically defined recharge area the extension of which does not depend on the recharge. The analysis of the recession curves of these two springs showed that the response to prolonged drought periods is more severe for the Bagnara than for the Lupa spring; this result can be extrapolated to all the springs connected to a deep regional groundwater circulation, which are more vulnerable to climate change than those with invariable geologically defined recharge areas
Hydrogeological study of Mt. Cucco (North-East Umbria, Italy)
No full textThis work presents a preliminary quantitative study of carbonate structure of Monte Cucco (North-Eastern Umbria, Italy). The main aquifer of the Monte Cucco structure is delimited by the Marne a Fucoidi formation outcrop, which is the most important aquiclude of the area; the main springs surrounding Monte Cucco rise at the contact between this aquiclude and the highly permeable calcareous formation of Maiolica. The area examined covers approximately 43 km2, at elevations between 500 m and 1560 a.s.l. The structure’s water budget was evaluated by means of some continuous discharge data series and three sets of field measurements which allowed to estimate the annual discharge of all the springs fed by the main aquifers. The natural discharge of the various springs was deduced by adding the flow taken from each for water supply purposes, to the flow released into the streams. Six temperature stations and ten rainfall stations located near the structure were analyzed in order to evaluate the average temperature and rainfall of the area. The analysis of temperature an rainfall data made it possible to evaluate the effective infiltration in the 2004-2005 hydrological year, during which the discharge measurements were made. The effective infiltration values were evaluated separately for high permeability formations (Calcare Massiccio) and for medium–high permeability formations (Corniola, Formazione del Bugarone, Maiolica). The effective infiltration calculated was compared with the water volume released by the spring. This comparison showed that the main aquifers of Monte Cucco can be considered virtually isolated. The study has shown how most of the infiltrated water drains toward the Tyrrhenian slope, with most of it flowing toward the Scirca spring, which releases a mean annual discharge of 180 l/s. This is due to the structural pattern of the Monte Cucco anticline and to the presence of preferential drainage contours of over tectonic discontinuities and along a well developed karst net
Laboratory shear strength parameters of cohesive soils: variability and potential effects on slope stability
No full textThe study quantified laboratory geotechnical variability by analyzing compacted alluvial fine-grained soils commonly used to backfill exhausted quarries in Central Italy. Repeating the test 4 times and combining the relevant results, 256 pairs of friction angle and cohesion values were obtained, with mean values of 27.0°±0.8° and 19.22±4.08 kPa, respectively in the shear stress range 100–250 kPa. The influence of the variability of laboratory drained shear strength parameters on the long-term stability of artificial saturated slopes was examined, taking into account both deterministic and probabilistic approaches. In many cases, when the deterministic approach indicates stability, the probabilistic one indicates a certain probability of instability, even for the lowest slope height (5 m) and a slope angle higher than 15°
Hydrological Uncertainty and Hydro-power: New Methods to Optimize the Performance of the Plant
No full textHydrological uncertainty due to daily flow variability and to the effect of climate change on water resources is a
critical topic in the feasibility evaluations of hydro-power projects, especially for run-of-river power plants.
The effect produced by these factors on the annual energy output of such type of plant was investigated. New
methods for improving the performance of the plant are proposed, which enable the choice of the most suitable
design flow (Qd) according to the hydrological features of the river, the frequency of dry and wet years in the basin
and the target energy production.
The flow data of fifteen catchment basins of the Umbria Region (Italy) were processed in the form of Flow Duration
Curve (FDC) and the slope of each FDC was used as an indicator of the flow regime. The values of the power
developed by hypothetical plants were calculated and relationships between the flow regime of the rivers and the
performance of the plants (i.e. the Hydrological uncertainty - CF) were searched for. Results showed that CF is analytically
linked to the regime flow and it depends to a great extent on it. In particular, CF decreases from a constant run-off
regime to a torrential one and the greater the Qd, the greater the rate of this decrease. A procedure was developed
on the basis of the equations found, which allows for the identification of the optimal Qd only using the slope of
the FDC. Since no other information is required, this approach also enables hydroelectric evaluations in ungauged
basins, through the use of regionalized FDCs. The validation of the procedure indicates that it provides reliable
results whatever the flow regime of the river and the turbine installed at the station.
Additional analysis showed that the effect of extreme weather years on energy production is not the same for all
basins and it depends on design choices. Manipulation of the data obtained by the FDCs of the driest and wettest
year with a 20-year return period showed that the decrease in energy production in dry years, compared to the
annual average, is linearly linked to Qd, as well as its increase in wet years. In particular, if Qd is extrapolated from
the right part of the FDC the negative effect of dry years on CF can be reduced while, if it is extrapolated from the
left part, the increase of flows in wet years can be better exploited to enhance CF. The procedure developed allows
us to derive the characteristic linear function of the river which, together with the knowledge of climate trends in
the area of interest, enables more accurate design of the hydro-power plant
Climatic characterization and response of water resources to climate change in limestone areas: some considerations on the importance of geological setting
No full textThis work analyses the response of springs fed by karst/fractured limestone aquifers, extensively outcropping in Central Italy, to climatic variations which in this area is represented by a general decrease in annual and winter precipitation. It is shown how groundwater regime, the discharge of springs and their response to climate change depend to a great extent on the geologic and structural setting of the system. Some mountain springs of Central Italy are “local systems” representing the “overflow” of a “deeper regional flow” feeding larger “base springs”, often of poor quality. A dynamic groundwater divide separates the recharge areas of base springs from those of local springs: if, due to low recharge, the piezometric surface lowers, the watershed moves towards systems located at higher altitudes, reducing their recharge areas. Therefore, local springs connected to a base flow are more vulnerable to climate change than those which are not. The Bagnara and Lupa springs, taken as examples, have similar mean discharges (about 120 l/s) and recharge areas with comparable lithological, topographical and climate characteristics. Nevertheless, only the discharge of Bagnara, which is connected to a regional flow, fell dramatically during recent prolonged drought periods (e.g., 2001-2003 and 2006-2007)
Fractured carbonate aquifers of Sibillini Mts. (Central Italy)
Full text linkThe aim of the present map is to illustrate a detailed pre-earthquake hydrogeological conceptual model of the Sibillini Mts. This area was struck by a prolonged seismic sequence of up to Mw 6.5 in 2016. Geological, tectonic, and hydrogeological data were collected from the literature before 2016, subsequently standardized and re-interpretated with the aim of presenting a hydrogeological map (1:50,000 scale) of the Sibillini Mts. carbonate system (Central Italy). The map is supported by 11 hydrogeological both cross and longitudinal sections, which show the underground spatial relationship between aquifers, aquicludes, and tectonic elements. This Map provides a model of comparison for the new hydrogeological conditions emerging from the post-seismic research
Importance of geological setup for the impact of climatic changes on groundwater: the case of Mount Cucco and Gualdo Tadino Mountains (Central Apennines, Italy)
No full textMount Cucco and Gualdo Tadino Mountains (Central Apennines), are both east-vergent asymmetric anticlines, delimited by a thrust fault on the east side. They are made of carbonate rocks belonging to the Umbria/Marche Sequence, in which carbonate aquifers alternate with marly aquicludes. The main aquiclude is the Marne a Fucoidi formation, which outcrops almost continuously on the west sides of both structures, and represents a no flow boundary. The thrust line on the east side also represents a no-flow boundary. The Marne a Fucoidi and the thrust line define a “belt” around each structure, enclosing an area of about 43 km2 on Mount Cucco and of about 50.4 km2 on the Gualdo Tadino Mountains. Many springs emerge at the contact between the permeable formations and the impervious “belts”. The karst development is higher on the Calcare Massiccio of Mount Cucco, where there are also important normal and strike-slip faults which connect the aquifer located in the Calcare Massiccio with those hosted in the Maiolica limestone. On the Gualdo Tadino Mountains, there are many springs with average discharge of a few hundreds l/s whereas on the Mount Cucco massif the only Scirca spring has such discharge magnitude (yearly average around 210 l/sec). The springs in the two massifs provide high quality water, for an annual average of about 1500 l/s. The yearly water budget of each structure was studied on the basis of springs discharge measurements and temperature-rainfall data. Since rainfall and temperature data at high elevations were almost completely missing, mean annual temperature and rainfall were estimated by defining elevation/temperature and elevation/rainfall relationships. The climatic data indicate similar rainfall and evapotranspiration for the two structures. According to the estimated water budget, groundwater recharge of Mount Cucco is about 30% higher than the total discharge from the springs, whereas in Gualdo Tadino Mountains the recharge is only about 10% higher than the discharge of the springs, such difference being within the possible range of error. Despite of the high degree of uncertainty, the difference between the results of water budget is too high to be considered as a consequence of the data uncertainty. Although the two recharge areas are similar (about 14% difference) the total discharge of the springs is quite lower in Mount Cucco than in the Gualdo Tadino Mountains (19 Mm3/y vs. 33.7 Mm3/y): this corresponds to a specific groundwater yield of 0.44 m3year-1km-2 for Mount Cucco and of 0.67 m3year-1km-2 for the Gualdo Mountains. On both massifs the structural and geological characteristics suggest that the springs could be fed by an overflow of a deeper regional flow. In such situations the recharge areas of springs and regional flow are separated by groundwater divides, which move as the water table lowers or rises. In Mount Cucco the deep flow development is made easier by the presence of deep karst structures and important tectonic discontinuities, which are not so well developed in the Gualdo Tadino Mountains. This seems to be the reason why the two structures behave in different way. Nevertheless, the uncertainty on the input data suggests to carry out further investigations and to collect new data which would help to define, with more confidence, whether or not a consistent deep flow is also present in the Gualdo Tadino Mountains. This is particularly important because, according to most of the studies on climatic change, a decrease of rainfall has to be expected for the next decades. In the hypothesis of a deep flow hydraulically connected to higher springs, a water table lowering, due to decrease in rainfall, would lead the piezometric divides to move towards the springs, whose recharge area would shrink; a way to minimize the impact of climate change would be to exploit the regional flow, which at present is not explicit ally considered in the water inventories of the area
Hydrological study of some rivers in the Umbria Region and small scale hydropower applications
No full textIl presente studio è stato realizzato su alcuni corsi d’acqua
d’ordine minore della Regione Umbria ed ha permesso di individuarne il regime idrologico e di condurre valutazioni sul potenziale sfruttamento degli stessi a fini idroelettrici, nel campo dell’idroelettrico minore. Dall’analisi delle pendenze delle curve di durata dei deflussi (FDC) e dall’indice del deflusso di base (BFI) è emerso che i corsi d’acqua esaminati sono ascrivibili a due tipologie: bacini a regime idrologico costante e bacini a regime idrologico torrentizio. Le informazioni ottenute dallo studio idrologico condotto
e la verifica in alveo dei salti ottenibili mediante traversa hanno permesso di selezionare, tra le tecnologie idrauliche in uso, quella meglio adattabile: la vite idraulica. Il dimensionamento della macchina impiegata ha messo in evidenza, a livello teorico, l’effetto prodotto dai due diversi regimi sulla producibilità idroelettrica. L’analisi dei rendimenti della macchina e delle portate turbinabili, ha mostrato la capacità dell’impianto di sfruttare la quasi totalità della
portata disponibile per i corsi d’acqua con deflussi regolari, con
rendimenti elevati. Nei corsi d’acqua a carattere torrentizio i
rendimenti e le rese sono invece più variabili, fino a valori nulli in certi periodi dell’anno, con una parte non trascurabile delle portate transitanti che non risulta produttiva ai fini idroelettrici. I bacini ricadenti nella prima tipologia risultano quindi sfruttabili senza particolari accorgimenti e in abbinamento a più soluzioni impiantistiche, mentre i secondi necessitano di valutazioni più accurate in fase di progettazione
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