1,720,996 research outputs found
On the evolution in time of the soil moisture vertical profile in two natural plots
No full textThe evolution in time, t, of the experimental soil moisture vertical profile, observed in natural fields together with associated hydrometeorological quantities, is investigated by a conceptual model to put in evidence and then to simulate the involved processes. The measurements were carried out in two plots located in Perugia, Central Italy. The soil water content, θ, was continuously monitored at different depths, z, using a Time Domain Reflectometry (TDR) system. Four buriable three-rod waveguides were inserted horizontally at the depths 5, 15, 25 and 35 cm, furthermore sensors of air temperature and relative humidity, wind speed, solar radiation, evaporation and rain were operative. A plot characterized by grassland over a sandy soil and an adjacent plot with a bare silty loam soil, both equipped with similar sensors, were simultaneously considered. A conceptual model, developed by Corradini et al. (2000), has been used to simulate the evolution in time of the soil moisture vertical profile during rainfall infiltration and successive redistribution/evapotranspiration periods in each plot. We have found that the commonly used models for continuous simulations of θ(z, t) have to be improved by taking into account the variability in time of the saturated hydraulic conductivity that is due, for bare soils, to the processes of formation and disruption of a sealing layer over the original parent soil and, for grassy soils, to the formation of a two-layered vertical profile with a more permeable upper layer associated to vegetation growth
A laboratory experimental system for infiltration studies
No full textThe investigation of a few hydrological processes under natural conditions can be distorted by their interactions. In this context, a laboratory system that allows a few mechanisms of the infiltration process to be studied univocally is presented. The core component of the system is a physical model consisting of a soil tank with slope angle, γ, adjustable from 1 ° to 15 °. A generator of artificial rainfall can produce rainfall rates up to 50 mm h−1. Surface runoff and deep flow, Qd, are continuously monitored. An overall analysis of three previous investigations performed by the physical system and directed to clarify the infiltration process is also briefly reported. These investigations, that concerned the validation of a local conceptual model for erratic rainfalls, the role of run-on and the effects of sloping soil surfaces, were all carried out by using different configurations of the system. Great slope effects in bare soils were observed. For example, under steady conditions, a ratio Qd(γ = 1 °) / Qd(γ = 10 °) equal to about 4 was observed in a loam soil. Finally, on the basis of the acquired knowledge, further investigations to be realized with the same basic elements are proposed to derive a conceptual model that describes the soil surface gradient effects
EVOLUZIONE CONTINUA DEL PROFILO VERTICALE DI UMIDITÀ DEL SUOLO IN CONDIZIONI NATURALI
No full textViene esaminata la tipologia della modellistica da utilizzare per la simulazione continua del profilo verticale di contenuto d’acqua del suolo che evolve per effetto di infiltrazione della pioggia e redistribuzione/evapotraspirazione dell’umidità del suolo. La modellistica selezionata è di tipo concettuale/semi-analitica ed è stata utilizzata per la simulazione di vari eventi di durata limitata su due parcelle (una con superficie spoglia, l’altra con vegetazione) specificamente realizzate e complete di sensori per la misura del profilo di umidità del suolo (TDR) e di grandezze idrometeorologiche al suolo. In aggiunta sono state usate misure dello stesso tipo acquisite dalla stazione sperimentale di Falkenberg (Berlino) per una parcella con
vegetazione erbosa. I risultati ottenuti indicano che per realizzare una modellistica accurata da applicare con continuità in suolo spoglio è necessario rappresentare
sia la condizione con suolo verticalmente omogeneo sia quella con uno strato di crosta in superficie. La conduttività idraulica di saturazione deve essere parametrizzata attraverso l’intensità della pioggia e la temperatura dell’aria, quest’ultima in quanto legata ai cicli gelo-disgelo. Nel caso invece di suolo con vegetazione è richiesta la formulazione a doppio strato con conduttività idraulica di saturazione dello strato superiore e suo spessore parametrizzati in funzione del
ciclo evolutivo della vegetazione
Hydropower in Central Italy: current status and future prospects
No full textThe largest source of renewable energy comes from a proven technology, hydropower. Hydropower is renewable because it draws its essential energy from the sun which drives the hydrological cycle which, in turn, provides a continuous renewable supply of water. The main goal of this paper is to optimize the use of hydropower resources in Umbria, a region of Central Italy. To this scope, we initially analyse the currently operating hydroelectric plants, taking into account both those of great size and the very small installations. Successively, we discuss the perspectives of this area in terms of exploitable hydraulic potential. It has been found that in Umbria are currently working 38 hydropower installations: 84% of them are run-of-river power plants, 10% are hydropower stations with a reservoir, while 6% works in both ways. Currently, 70 turbines are working: 41 are Francis, while the remaining, excluding a small Pelton and a Banki-Michell, are characterized by high degrees of reaction (Kaplan or helixes). The total installed hydroelectric capacity is over 650 MW, corresponding to an average annual production of approximately 1415 GWh. Most of these hydropower plants, 35 corresponding to 92% of the total, is privately owned: 13 from a big multinational company, 16 from small and medium size companies, 6 from private people. Only 3 installations are owned by municipalities. The described situation characterizes the Umbria region as a geographic area where the ratio between the exploited potential and the economically feasible potential has already reached a value not far from its physiological limit. In this context it is clear that in Umbria no large installations (> 10 MW) can be planned; instead, considering also the low number of existing hydropower stations with respect to the extension of the area (currently equal to 1 plant for each 222 Km2), a significant potential for the realization of small run-of-river power plants exists. At the moment 5 new hydropower plants are under construction, while about 100 small installations (<2 MW) are waiting to finalize their authorization process, during which the following issues are typically addressed and resolved by the local scientific community: 1) the increase of hydraulic risk produced during extreme precipitation events; 2) the management of hydrometric stations located near the new installations; 3) the environmental impact; 4) the definition of selection criteria when in the same location there are two or more requests of hydropower installations
Are heavy rainfalls in central Italy influenced by climate changes?
No full textIn recent years there is a growing concern by the community, scientific and not, about global warming and climate changes. The fact that the global temperature is growing up after the increase of the greenhouse gases emissions is already known, but there is still wondering about its effect on the hydrological cycle and most of all on rainfalls. Many studies supported by the Intergovernmental Panel on Climate Change (IPPC) showed that there is a general increase of heavy rainfalls also in areas where total annual precipitation is not prominently changed. Changings about frequency, intensity, duration in rainfalls and in weather events in general are still object of wonderings and past studies referred to different regions don’t give an unanimous answer about their trends. Mediterranean Area, which includes Italy, is supposed to be one of the most reactive to the climate changes and strong effects of them are expected. This paper deals with the rainfall tendencies in Umbria Region, Central Italy, since almost all the regional territory is included in the Upper Tiber River Basin and many areas are prone to risk of flooding. The climate of Umbria region is variable from areas to areas, in fact the weather is cold and wet in the East areas, near the Apennine Mountains and hotter and drier in the West, close to Tuscany region. Because of this variability a lot of raingauges had been placed in the last 10-15 years and nowadays a very dense raingauge network is present (more than 90 raingauges for a regional area of 8464,33 Km2, about one station each 90 Km2). The aim of this paper is to analyse if the climate changes caused effects on the rainfalls’ intensity in Umbria. Three meteorological stations have been selected: Città di Castello, Todi and Orvieto. They provide the longest series of data and the best quality in their measurements because raingauges have never been relocated. Rainfall measurements began in the thirties and have gone on until nowadays even if there are some interruptions (most of all during the years of the Second World War). For each year there are maxima for 6 durations:1, 2, 3, 6, 12 and 24 hours. The analyses of the data of the three stations, and most of all the one referred to Todi, whose geographical position is barycentric in the regional territory, show that there are not considerable changes in rainfall maxima and intensities in the last seventy years
Relazione idrologico-idraulica
No full textNel lotto della Tomba di Mamia, come del resto in corrispondenza di qualunque area esposta alle naturali intemperie, lo scorrimento incontrollato delle acque piovane e il loro ristagno determinano fenomeni di degrado minacciando l'integrità delle opere presenti. La principale attività del Gruppo di Lavoro di Idrologia è stata indirizzata verso il ripristino di un sistema di drenaggio dell'area di studio (drenaggi secondari) che si integrasse nel più complesso sistema drenante dell'area degli scavi nella sua interezza (drenaggi principali fino ad un recettore finale). Tale attività si è sviluppata in passi successivi che hanno coinvolto l'analisi statistica delle precipitazioni localmente registrate al fine di determinare la pioggia di progetto del sistema drenante, una modellazione idrologica che restituisse la risposta dell'area in termini di deflusso superficiale e la formulazione di una soluzione tecnica caratterizzata da impatto archeologico pressoché nullo per il deflusso di acqua piovana in assenza di erosioni e ristagni
Atmospheric Stability and Meteorological Scenarios as Inputs to Air Pollution Transport Modeling
No full textMeteorological scenarios concerning the data required for engineering applications of pollutant transport modeling in the low layers of troposphere are defined through a simple methodology. This involves only data at soil surface and substantially relies on the determination of atmospheric stability carried out through fictitious vertical profiles of air temperature considered as representative of the actual vertical profiles in a study area. This assumption is supported by comparisons of fictitious vertical profiles, obtained by measurements of air temperature at soil surface but at different heights above sea level, and the temperature vertical profiles observed by the radiosounding station closer to the study area. The fictitious profiles are first used to derive the usual classes of atmospheric stability as unstable atmosphere, neutral atmosphere, stable atmosphere, thermal inversion at the surface and thermal inversion in the upper layers. Then, each scenario is determined through the classes of atmospheric stability observed at 06.00 GMT and 15.00 GMT together with the experimental data of air temperature, relative humidity, wind speed, wind direction, and cloud cover, all averaged in the period of investigation of a few years. An area of Central Italy, where the meteorological measurements for a period of 7 years were available, has been selected for this study
Soil water content vertical profiles under natural conditions: matching of experiments and simulations by a conceptual model
No full textThe prediction of soil moisture content, θ, as a function of depth, z, and time, t, is of fundamental importance for
applications in many hydrological processes. The main objective of this paper is to provide an approach to solve this problem at a local scale in soils with vegetation. The matching of soil moisture vertical profiles observed under natural conditions in grassy plots and their simulations by a conceptual model is presented. Experimental measurements were performed in a plot located in Central Italy, complete with hydrometeorological sensors specifically set up and equipped with a time domain reflectometry system providing the water content, θe(z, t). A conceptual model framework earlier proposed for two-layered soil vertical profiles was modified and adopted for simulations. The changes concern the incorporation of evapotranspiration, the reduction of the original model for applications also to homogeneous soil vertical profiles, and a correction for the differences existing between assumed and observed initial moisture contents. In the model calibration, it was found that the effects of vegetation could be represented adequately by a fictitious soil vertical profile with a more permeable upper layer of saturated hydraulic conductivity, Ks, independent of time. Then, for the validation events, the model simulations in the stages of both infiltration and redistribution/evapotranspiration reproduced appropriately θe(z, t) with typical values of root mean square error in the range 0.0017–0.0657. Similar results were obtained by applying the modified two-layered model for simulations of experimental data observed in three other plots located in Northern Italy and Germany. For all four vegetated sites, the two-layer profile better matched the experimental data than the assumption of a homogeneous profile. Thus, the conceptual approach based on a two-layered scheme for representing θ(z, t) in soils with vegetation appears to be appropriate for many hydrological applications
Infiltration-soil moisture redistribution under natural conditions: experimental evidence as a guideline for realizing simulation models
Full text linkThe evolution in time, <i>t</i>, of the experimental soil moisture vertical profile under natural conditions is investigated in order to address the corresponding simulation modelling. The measurements were conducted in a plot with a bare silty loam soil. The soil water content, θ, was continuously monitored at different depths, <i>z</i>, using a Time Domain Reflectometry (TDR) system. Four buriable three-rod waveguides were inserted horizontally at different depths (5, 15, 25 and 35 cm). In addition, we used sensors of air temperature and relative humidity, wind speed, solar radiation, evaporation and rain as supports for the application of selected simulation models, as well as for the detection of elements leading to their improvement. The results indicate that, under natural conditions, very different trends of the θ(<i>z</i>, <i>t</i>) function can be observed in the given fine-textured soil, where the formation of a sealing layer over the parent soil requires an adjustment of the simulation modelling commonly used for hydrological applications. In particular, because of the considerable variations in the shape of the moisture content vertical profile as a function of time, a generalization of the existing models should incorporate a first approximation of the variability in time of the saturated hydraulic conductivity, <i>K</i><sub>1s</sub>, of the uppermost soil. This conclusion is supported by the fact that the observed shape of θ(<i>z</i>, <i>t</i>) can be appropriately reproduced by adopting the proposed approach with <i>K</i><sub>1s</sub> kept constant during each rainfall event but considered variable from event to event, however the observed rainfall rate and the occurrence of freeze-thaw cycles with high soil moisture contents have to be explicitly incorporated in a functional form for <i>K</i><sub>1s</sub>(<i>t</i>)
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