1,721,138 research outputs found
Influenza della scabrezza sulla valutazione del parametro entropico di velocità nelle correnti a pelo libero
Full text linkSulla base dei risultati derivati dall’analisi di dati di campo e di laboratorio relativi a misurazioni di velocità, è riscontrata una dipendenza del rapporto Φ(M) tra velocità media della corrente e velocità massima dalla scabrezza del fondo espressa in termini di scabrezza relativa. In particolare tale influenza risulta decisamente marcata laddove si presentano condizioni di deflusso in acque basse fino, cioè, a valori del rapporto tra profondità della corrente e dimensione caratteristica degli elementi di scabrezza (D/d) inferiori a 4 , mentre per valori superiori il valore di Φ(M) risulta pressoché indipendente dalla scabrezza relativa. A supporto di tale risultato viene sviluppata una trattazione teorico-analitica che, partendo dalla relazione cardine della legge di distribuzione entropica di velocità e l’impiego delle leggi classiche del moto uniforme e delle resistenze al moto, spiega ampliamente, per l’appunto, la sussistenza di una dipendenza logaritmica del rapporto Φ(M) dalla scabrezza relativa
Erosion processes at the hillslope scale
No full textThe results are presented of an intensive monitoring programme to determine eroded volumes due to observed rainfall
events on a hillslope surface. The surface investigated has been reproduced through a digital elevation model and
analysed in terms of drainage network, contributing area and slope by performing planimetric and altimetric analysis.
Erosion maps were derived from a comparison of consecutive digital elevation models relative to time. These maps
reveal the spatial and temporal evolution of the erosion process at the hillslope scale. The erosion was uniform across
the surface, supporting the assumption of randomness in the erosion process commonly used in surface drainage
development models. The observed value of erosion has been estimated at approximately 0·11 m/m2 per year with
almost 500 mm of total annual rainfall
Entropy velocity distribution in a river
No full textIn the paper the results of the extension of the entropy velocity distribution to a data set collected in field and relative to a natural rivers are presented. The analysis represent the first attempt to use the entropy model to describe the natural flow assessment. Further, the velocity distribution along the vertical has been explained employing the entropy model at the local scale and calibrating the entropy parameter through the average and maximum velocity observed per each vertical. That is, a scaling approach of the entropy profile is proposed and the comparison between the classical formulation and the scaled one is reported in terms of average absolute and global errors observed
Effect of bed roughness on 1-D entropy velocity distribution in open channel flow
Full text linkA theoretic-analytical formulation, based on entropy velocity profile law and classical relationships for uniform flow and friction factor, is proposed enlightening the general logarithmic relationship existing between the parameter Φ(M), defined as mean cross section velocity over maximum velocity, and the ratio water depth/bed roughness (D/d). The relationship Φ(M)-D/d has been applied to a relevant set of experimental velocity measurement data collected both in laboratory and in field, showing different behaviour between small scale and large-intermediate roughness flows. In particular, the roughness influence becomes remarkable whenever shallow water flow conditions occur, that is when the ratio between the flow depth and the roughness height is less than 4, while Φ(M) tends to be constant as the value of D/d increases
Entropy velocity profile: application in natural river
No full textRecent studies, developed in open channel flow and referred to the use of entropy and probability concepts for the characterisation of velocity distribution, have shown a suitable relationship able to describe the flow properties through a simple and single parameter easy to derive. Several analyses have been carried on comparing the entropy profile to those obtained by logarithm and power laws showing the good performance in the water discharge and flow resistance estimation. Almost all of these analyses reported in literature are performed in regular flows and only few are referred to natural rivers scenarios. The present paper is addressed to employ the relation on natural river data extending the application field and showing original results in terms of scaling application of velocity law
Entropy-based approach for rating curve assessment in rough and smooth irrigation ditches
No full textThe aim of the present work is to propose an expeditive methodology derived from the one-dimensional (1D) entropy-based model to evaluate the water discharge in rough and smooth irrigation channels based on the knowledge of relative submergence. Recent studies have demonstrated that, for flow in the presence of high and intermediate roughness, corresponding to low flow depth generally, the entropy parameter seems to be dependent on the relative submergence. Whereas, in the case of very low roughness or smooth channels, the mean-to-maximum velocity ratio can be assumed constant at all water stages. Using detailed laboratory data, collected on smooth and rough flumes with different cross section geometries, the paper discusses the relationship existing between the entropy velocity ratio and the relative submergence to give an operative practical rule for water discharge computation and rating curve assessment in irrigation ditches. The comparison between observed and calculated discharges shows very low errors underlying the reliability of the proposed approach
Distribuzione entropica di velocità in un corso d'acqua naturale
No full textL’interpretazione di misure di velocità mediante leggi derivate nel rispetto del contenuto informazionale ed entropico del sistema fluviale, porge un utile strumento per lo studio dei processi dissipativi attivi all’interno della corrente fluida ed, in particolare, alla caratterizzazione dello sforzo tangenziale al fondo. Il presente lavoro, sviluppato sulla base di dati ottenuti da misurazioni classiche di velocità in sito, prevede l’applicazione del profilo di velocità derivato da Chiu (1987) sia alla scala di sezione trasversale sia per ogni verticale e la determinazione della distribuzione degli sforzi tangenziali al fondo sulla base della stima locale del parametro entropico secondo una discretizzazione della sezione trasversale della corrente
Influence of hydraulic geometry ratios on the entropy parameter in open channel flow
Full text linkThe knowledge of flow velocity distribution is an essential requirement in dealing with stage–discharge relationships, sediments transport processes and prediction of morphological behaviour in alluvial streams, design of stable channels, flood control works and mathematical and physical modelling of flows. Due to the limitations of classical hydraulic methods, Chiu (1987) derived the velocity distribution law basing on the concept of informational entropy introduced by Shannon (1948) and Tsallis (1988). Such velocity profile has been widely employed in many different flow cases and improved by relevant and meaningful both theoretical and applied contributions derived from robust experimental knowledge. Main aspect of such model is related to the need of one parameter M said as entropy parameter. Such parameter is depending on the ratio between the mean cross section velocity over maximum velocity, Φ(M).
The way to evaluate the entropy parameter M through the ratio Φ(M), still represents a relevant issue nourishing a reach discussion among researchers mainly addressed to the reasonable ground about the invariance of Φ(M) for sections along the same river only at high flow while for low stage the ratio Φ(M) can be affected by the influence of roughness, through the relative submergence, the ratio between water depth and roughness height (D/d) as well as by the aspect ratio related to the cross section geometry, the ratio between flow width and flow depth (B/D). Therefore M should be assumed as a peculiar characteristic not only of the monitored site but also of the river reach where sites are located and the observed flow stage. Moving from these bases, using laboratory and field data, the classical hydraulic relationships on entropy velocity profile, the uniform flow and regime theory, a predictor for entropy parameter is proposed for open channel flow. The work proposes a general logarithmic relationship existing between the parameter Φ(M), the relative submergence and the aspect ratio of the flow. The [Φ(M)-(D/d)-(B/D)] relationships have been applied to a set of experimental velocity data collected both in laboratory and in field, showing a good response of the theoretical model but selecting different behaviour depending on the roughness scale. In fact, Φ(M) is strongly depending on the ratio depth/roughness for values of D/d less than 4 when large and intermediate roughness scale occurs, while it might be assumed almost constant to 0.66 for small roughness scale (D/d>4) according to literature for high flow stage. On the other hand, the relationship among Φ(M) and B/D seems to be depending on whether or not the flow is confined, like artificial channel, instead of natural cross section. The comparison between the two set of data, laboratory versus field, enlighten the effect of the aspect ratio which is strongly related to Φ(M) for flume velocity data while it results not depending on Φ(M) for river measurements. Further, even this last issue enforce the difference between the Φ(M) ratio behaviours for high roughness flow and low roughness one, remaking the value of D/d=4 as operative threshold
Vulnerability assessment or preliminary flood risk mapping and management in coastal areas
Full text linkPlanning and management of coastal environment, both terrestrial and marine, is affected by several actions in environment resource conservation and improvement, paying specific attention to risk forecasting and preventing.
In such context the EU flood Directive 2007/60/EC, which requires Member States the assessment and management of flood risk, and the EU water framework Directive (2000/60/EC) are the key factors in the integrated river basin management to assure an efficient and rational use of resources.
Afterwards, coastal risk assessment and mapping is a propaedeutic phase to plan and manage coastal areas. In this work risk analysis refers to the results obtained by the combined application of coastal flooding and erosion risks in the activities carried out to prepare the Regional Coast Management Plan for the Ionian coast of Basilicata Region located in the south of Italy. In order to define the driving forces acting on the shore, high resolution lidar data, bathymetric information and wave climate statistics referred to different acquisition times are used. The systemic vulnerability estimation is achieved by composing both hazard factors combined in the Coastal Criticality Index depending on the assessment of Coastal Flood Index and Coastal Erosion Index based on morphologic and socio-economic variables
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