1,721,213 research outputs found
TIME EVOLUTION OF LOCAL SCOURING DOWNSTREAM OF A RIGID BED:lessons learned from experiments
No full textThis present work concerns the phenomenon of local erosion occurring downstream a rigid bed of a structure constructed along a river. In particular, attention is focused on the time evolution of the maximum scour depth. This chapter reports a brief review of findings obtained by author using both data appositely collected in a laboratory channel and literature data
Mixing processes in vegetated rivers: experimental investigation in a laboratory flume
No full textThe presence of vegetation in rivers exerts an important ecological function and is very important to maintain suitable habitat. Especially in recent years, some researchers (among others Perrucca et al., 2007) have focused their attention on the role of vegetation in channel’s morphodynamics. Alteration of hydrological conditions in fluvial systems inevitably leads to changes in river morphology, riparian or riverbed vegetation and ecosystems. Riparian vegetation distribution could also change in time and in space depending on the combination of factors affecting the settling and growth of vegetated elements. In the present paper attention is focused on the turbulent and mixing processes in presence of flexible submerged vegetation. In particular, the process of transport and dispersion of tracers is investigated. The analysis is performed with the aid of detailed experimental data collected in a laboratory channel for different vegetation patches on the bed and for different growth stages of the vegetated elements
La vegetazione a protezione di processi di escavazione localizzata: risultati di uno studio sperimentale
Full text linkDiversi studi di letteratura mostrano come la vegetazione debba essere considerata un fattore chiave per analizzare i meccanismi di trasporto che si realizzano lungo un corso d’acqua naturale (Jarvela, 2002; Folkard, 2011). In particolare, la presenza di vegetazione sul fondo e/o sulle sponde del corso d’acqua contribuisce sia a stabilizzare i sedimenti che ad aumentare la resistenza al moto della corrente (Tsujimoto 1999; Nepf and Vivoni, 2000; Afzalimehr and Dey, 2009; Nepf, 2012), influenzando i processi di trasporto solido e i conseguenti fenomeni di erosione e di deposito lungo lo stesso corso d’acqua. In questo contesto, nel presente lavoro sono riportati alcuni risultati di uno studio sperimentale condotto nell’ambito di un programma di ricerca rivolto all’analisi dei processi di escavazione che si verificano a valle di una soglia di fondo realizzata lungo il corso d’acqua. In particolare l’obiettivo dello studio oggetto del presente lavoro era quello di analizzare come la presenza di vegetazione erbacea sul fondo potesse modificare il campo di moto e di turbolenza della corrente e, conseguentemente, limitare i processi erosivi a valle della soglia
Experimental investigation of flow turbulent structure in a high-amplitude vegetated meandering laboratory flume
No full textThe present work focuses on high-curved channels which are characterized by a complex flow turbulent structure. The specific aim of work is to analyze the evolution of turbulent coherent motion in the pres-ence of vegetation on the bed
Flow Characteristics around a freshwater mussel in a gravel bed flume
No full textMussels are a defined as “ecosystem engineers” capable of affecting the hydrodynamics, passively and actively
(Navaratnam et al., 2018; Termini et al., 2023; Modesto et al., 2023). The generation of larger-scale turbulence
around the mussels living on the river bed may also affect the quality of the habitat. Thus, it is extremerly
important to know the effects determined to the presence of mussels on flow characteristics. In the present
study reports preliminary results on flow and turbulence characteristics around an isolated mussel over a
gravel-bed. The presence of mussel enhances the effects determined by the rough-bed on the kinematic
characteristics of flow. The analysis is performed on the basis of data collected in a straight laboratory gravelbed flume both in absence and in presence of an isolated and partially buried mussel (Unio elongatulus),
aligned with the incoming flow. In order to take into account spatial heterogeneities, the double-averaged
velocities are considered for the analysis in the absence of mussel on the bed. Results show that, because of
the presence of gravels, in the absence of the mussel, the streamwise velocity profiles show an inflection point
with the formation of a mixing layer whose thickness varies passing from the banks to the channel axis. The
presence of mussel modifies the shape of the velocity profile with the formation of turbulent flow structures
around it. Different effects on the velocity and turbulence fields have been identified in relation with the
mussel’s filtrating capacit
Flow and sediment transport process in vegetated beds: experimental investigation in laboratory flumes
No full textThe uncertainty regarding the interpretation of sediment transport phenomena during the transients determines some limitations in mathematical modeling of scouring process. But, quantitative estimate of sediment transport processes is important, especially in river-control engineering and water management projects. To this aim, literature (among others Hoffmans and Booji, 1993; Chrisochoides et al., 2003) shows it is necessary to well predict the flow velocity field, the eddy-viscosity and the bed shear stress in order to make correct calculations in simulating the bed-load transport and the development of scour hole in time. Particularly, the role of turbulent structures, developing within the scour hole, on process evolution is still unclear.
In such a context, the present work aims to investigate the effect of flexible vegetation planted on the bed on the flow field, turbulence flow structure and sediment transport process. Results are presented and discussed from laboratory experimental campaigns specifically designed to investigate flow characteristics both in presence and in absence of vegetation on the bed
L’acqua e le risorse sostenibili a sostegno delle condizioni di vivibilità locale
No full textIn questo lavoro sono descritte le azioni cche consentono l'uso della risorsa idrica in paesi sottosviluppat
Effects of submerged vegetation on flow and turbulence characteristics at the apex bend of a meandering flume
No full textUnderstanding flow characteristics and turbulent structure in the presence of vegetation is important with
respect to environmental processes as sediment transport and mixing of transported quantities. In the present
paper attention is focused on the kinematic and turbulent processes in presence of flexible submerged
vegetation. In particular, the effect of vegetation on the flux of mass distribution and the process of transport
is investigated. The analysis is performed with the aid of detailed experimental data collected in a laboratory
channel both in the absence and in presence of flexible and submerged vegetation. Results essentially
confirms that mass exchanges in the presence of vegetation are strongly influenced by the presence of
vegetated stems and by turbulent structures which form between vegetated and no-vegetated zones. The
presence of flexible and dense vegetation determines a reduction of the size of turbulent structures and limits
the transport process
Effects of submerged vegetation on flow and turbulence characteristics at the apex section of a meandering flume
No full textUnderstanding flow characteristics and turbulent structure in the presence of vegetation is important with
respect to environmental processes as sediment transport and mixing of transported quantities. In the present
paper attention is focused on the kinematic and turbulent processes in presence of flexible submerged
vegetation. In particular, the effect of vegetation on the flux of mass distribution and the process of transport
is investigated. The analysis is performed with the aid of detailed experimental data collected in a laboratory
channel both in the absence and in presence of flexible and submerged vegetation. Results essentially
confirms that mass exchanges in the presence of vegetation are strongly influenced by the presence of
vegetated stems and by turbulent structures which form between vegetated and no-vegetated zones. The
presence of flexible and dense vegetation determines a reduction of the size of turbulent structures and limits
the transport proces
La presenza dell’acqua
No full textDurante il periodo della dominazione araba, nell’area della Fossa della Garofala fu realizzato un sofisticato ed efficiente sistema idrico di irrigazione che, in parte, è ancora oggi utilizzato.
L’antico sistema di irrigazione comprende un insieme di elementi, quali le gebbie, i risittaculi, i turciuniati e le saie, che sono ancora visibili, e in parte ancora oggi utilizzati, e che identificano un vero e proprio percorso dell’acqua
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