1,721,007 research outputs found
A Moving Horizon Based Approach for Real Time Flood Forecasting
No full textThe distinction between off-line(nonrecursive) and on-line(recursive) methods is not as rigid as it might seem.
The work of Kalman provided a recursive solution to the minimum variance estimation problem for linear systems with Gaussian variables. The Kalman filter and its equivalence to least-squares is known and the moving horizon approach is formulated as a particular case of both of the methods.
The incorporation of prior knowledge of the unknown variable ranges as inequality constraints is discussed.
A real time flood forecasting application of the approach is shown and the relevance of the horizon-size is discussed
Application of a model for flood forecasting
No full textThe city of Pavia can be inundated by Ticino floods or, more often, by Po backwaters, since Pavia is located not far away from the confluence of the two rivers. A real-time forecasting system has been set up to forecast with a reasonable time advance possible floods. The system is based on data gathered from a monitoring network. A statistical simulation model, whose structure step-by-step linearizes the equations of the hydraulic process, forecasts flood levels in Pavia. The parameters of the model are estimated and updated every hour through a recursive procedure. The model gives the water stages of Ticino in Pavia with a lead time that equals the transfer time of the flood waves
COMPARISON OF TWO SIMPLE REAL-TIME FLOOD FORECAST MODELS: THE CASE STUDY OF THE PO RIVER (ITALY)
No full textThe performance of two simple models for real-time flood forecasting is investigated and compared. The first approach, named as RCM-RT, is based on the Rating Curve Model (RCM) and provides, involving only two parameters, future estimates of both discharge and water level at a river site where only the stage is monitored while the flow is known at an upstream section.
The second model, named MHBA, is described by a linear stochastic formulation of flood wave propagation and is based only on stage data.
Both models require that the forecast lead-time and the parameters are identified a-priori through a calibration phase involving different observed flood events.
The two models are tested on a long reach of the Po River (northern Italy) for several flood events. The obtained results show that both models provide an accurate forecast water level 32 hours in advance
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
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
Spatial-temporal variability of soil moisture: Addressing the monitoring at the catchment scale
Full text linkSoil moisture plays a fundamental role in the mass and energy balance between the land surface and the atmosphere, making its knowledge essential for several hydrological and climatic applications. The aim of this study is to extend the current knowledge of soil moisture spatial-temporal variability at the catchment scale (up to 500 km 2 ). The main implication is to provide guidelines to obtain soil moisture values representative of the mean behaviour at the medium-sized river basin scale, which is useful for remote sensing validation analysis and rainfall-runoff modeling. To this end, 23 measurements campaigns were carried out during a time span of 14 months at 20 sites located within the Upper Chiascio River Basin, a catchment with a drainage area of about 460 km 2 in the Umbria Region (central Italy). The data set allowed the analysis of both soil moisture temporal stability and its dynamics. On the basis of statistical and temporal stability approaches, it was investigated how factors such as climatic regime and geomorphology influence soil moisture behaviour. For the investigated area, the spatial variability of soil moisture was higher in dry periods with respect to wet periods, mainly due to the rainfall pattern characteristics during different periods of the year. Soil moisture values recorded during wet periods showed a better correlation than those recorded during dry periods. The maximum number of required samples, to obtain the mean areal soil moisture with an absolute error of 3% vol/vol, was found equal to 12. The temporal stability analysis showed that during wet periods just one “optimal” measurement point can provide values of soil moisture representative of the catchment-mean behaviour, while during dry periods the number of “optimal” measurement points became equal to two. Therefore, at the adopted spatial scale the use of a single measurement point can lead to significant errors. From the perspective of soil moisture dynamics, the decomposition of the spatial variance showed that the contribution of the time-invariant component (temporal mean of each site) was predominant on respect to the total spatial variance of absolute soil moisture data, for almost the whole observation period. Results provided guidance to optimize soil moisture sampling by performing targeted measurements at a few selected points representative of the catchment-mean behaviour
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
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