Efficiency of a digital particle image velocimetry (DPIV) method for monitoring the surface velocity of hyper-concentrated flows

Digital particle image velocimetry records high resolution images and allows the identification of the position of points in different time instants. This paper explores the efficiency of the digital image-technique for remote monitoring of surface velocity and discharge measurement in hyper-concentrated flow by the way of laboratory experiment. One of the challenges in the application of the image-technique is the evaluation of the error in estimating surface velocity. The error quantification is complex because it depends on many factors characterizing either the experimental conditions or/and the processing algorithm. In the present work, attention is devoted to the estimation error due …

Velocity field computation in bends of shallow channels

Flow Resistance Law in Channels with Flexible Submerged Vegetation

In this paper, experimental data collected in a straight flume having a bed covered by grasslike vegetation have been used to analyze flow resistance for flexible submerged elements. At first, the measurements are used to test the applicability of Kouwen’s method. Then, a calibration of two coefficients appearing in the semilogarithmic flow resistance equation is carried out. Finally, applying the P-theorem and the incomplete self-similarity condition, a flow resistance equation linking the friction factor with the shear Reynolds number, the depth-vegetation height ratio and the inflection degree is deduced.

Analisi dell’intensità della turbolenza di correnti in moto in alvei in ghiaia

Bank Erosion and Secondary Circulation in a Meandering Laboratory Flume

Abstract This paper reports peculiar results of experimental investigation on the secondary circulation motion of flow along a meander wave. Experiments were conducted in a large amplitude meandering laboratory channel for two values of the width-to-depth ratio. Here attention is focalized on how secondary motion affects the bank shear stress distribution, influencing the stability of the outer bank. The analysis essentially highlights that, especially for small width-to-depth ratio, as the channel curvature increases, besides the classical central-region secondary circulation cell a counter-rotating circulation cell forms in the outer-bank region. Such counter-rotating circulation cell all…

Hyperconcentrated flow and men velocity estimation: a study case

Due to the complexity of the debris-flow process, numerical models to simulate propagation phenomenon are still limited. Different approaches (either monophase or two-phase) have been proposed in literature to solve the set of governing equations. But, the difficulty is due to the fact that these equations require suitable closure relations that should be valid in a very wide range of slope and materials characteristics. The point is that, in order to perform a hazard assessment and/or to design protective measures against debris flows, it is necessary to estimate important parameters such as mean flow velocity, peak discharge and runout distance. Experimental program has been recently cond…

SAFETY COVER HYDRO-PV Dispositivo domotico multifuzione per la manutenzione e la sicurezza dei pannelli fotovoltaici con aumento dell’efficienza e della durabilità del sistema

Con l’aumento dell’uso dell’energia solare, sia in ambito civile che in ambito industriale, diventa sempre più importante il problema della manutenzione e della gestione dei pannelli fotovoltaici.Il dispositivo Safety Cover Hydro - PV, ideato e brevettato dai membri dalla Safety Environmental Engineering (spin-off dell’Università degli Studi di Palermo che opera nell’ambito della Sicurezza Ambientale) consente di superare tali limiti

Cross sectional flow in a meandering laboratory channel with vegetated bed

As it is known, the outer-bank of a meander wave is considerably vulnerable to the erosion processes. Literature indicates that cross-stream circulation strongly affects the redistribution of the downstream velocity and boundary shear stress in curved channels. In steep outside bends, beside a central-region circulation cell, a counter-rotating circulation cell often forms in the upper part of the outer-bank region. Accurate understanding of the role of these circulation cells on velocity redistribution in bends is important to define protective measures of the outer-bank. Literature also shows that vegetation could modify flow velocity and turbulent structure. This work reports preliminary…

Experimental study in a meandering channel: 2.Analysis of “initial” flow pattern

Investigation of a Gravel-Bed River’s Pattern Changes: Insights from Satellite Images

Changes in river pattern have been documented in the literature. The recognition of islands and vegetated patches, which is indicative of the evolution processes, requires simultaneous information at different points and at different times and field studies are still difficult and scarce. The present work, focusing the attention on a gravel-bed river, explores the possibility to conduct a first-step pattern changes analysis by identifying the evolution of the morphological features and taking information of islands and vegetated patches from satellite images easily available from Google Earth. The study is conducted by combining the information taken from both the satellite images and the f…

Riduzione ottimale dell’eterogeneita’ per la calibrazione dei modelli di reti idriche

Analisi delle caratteristiche di turbolenza della corrente nella sezione apice di un canale meandriforme con vegetazione sul fondo

Diverse ricerche (vedi ad esempio Wilson et al, 2003;. Blanckaert e Graf, 2004) hanno dimostrato che il moto di circolazione secondaria, che si sviluppa nei canali con andamento curvilineo, esercita un ruolo fondamentale nei processi di erosione spondale. In particolare, tali studi hanno mostrato che il trasporto della quantità di moto determinato dalla corrente di circolazione trasversale contribuisce a spostare il massimo della velocità longitudinale verso la sponda esterna lungo la curva. Inoltre, tale moto trasversale modifica la distribuzione dell’energia cinetica turbolenta determinando zone di alta/bassa energia turbolenta (Blanckaert e Graf, 2004; Termini e Piraino, 2011). La conosc…

A new approach for a robust solution of the fully dynamic De Saint Venant equations

SIMULATION OF NONUNIFORM SEDIMENT TRANSPORT AT DIFFERENT DISTANCES FROM THE OUTLET

Velocity and turbulence measurements: uncertainty in the application of the Image-based technique

This work focuses on the application of image-based technique to estimate velocity and turbulent flow characteristics. In particular, in the present work digital imaging technique is used for performing surface velocity measurements of hyper-concentrated flows. The analysis is conducted with the aid of data collected in a scale laboratory flume constructed at the Hydraulic laboratory of the Department of Civil, Environmental, Aerospatial and of Materials Engineering (DICAM) – University of Palermo (Italy). In the present paper a brief summary of results obtained in previous works on the flow velocity estimation error and uncertainty related to the acquisition procedure is reported.

1-D numerical simulation of sediment transport in alluvial channel beds: study cases

ABSTRACT Quantitative estimate of sediment transport processes is important especially in river-control engineering and for water management projects. In this paper the sediment routing of a 1-D model is presented and applied to some study cases. The procedure simulates the variations of bed roughness conditions due to natural sorting and to generation and migration of bed forms. The suspended-load and the bed-load are treated separately.

Optimal valves regulation for calibration of pipe networks models

The calibration of a pipe network model is faced by means of a two-steps iterative procedure. The first step of the procedure is the estimation of the parameters in the network simulation model, obtained from a first set of water head measures. The second step of the procedure is the change of the resistances provided by the valves in the network and the acquisition of a new set of measures. The inverse problem is then solved again and the procedure is repeated, until the set of computed parameters converge to stable values. The new resistances are chosen to minimize the sum of the variation coefficients, computed from the Fisher information matrix. The effect of different correlation funct…

Numerical simulation of bed degradation and bed armouring

River bed Evolution downstream a bed sill

Vegetation effects on cross-sectional flow in a large amplitude meandering bend

ABSTRACTCross-stream circulation, which develops in meandering bends, exerts an important role in velocity redistribution. This paper investigates how the presence of vegetation could affect the evolution pattern of cross-stream flow along a high-curvature meandering bend. The analysis is conducted with the aid of data collected in a meandering laboratory flume over non-vegetated and vegetated beds. The experiments reveal that, once the vegetation is introduced, the flow pattern determined by the channel’s curvature is interrupted. In the presence of vegetation, the central-region circulation cell seems to be divided into thin circulation cells developing at the top of the vegetated layer a…

Estimation of chlorine residual in a drinking water distribution system.

Flow-bed interactions analysis and application of automatic close range digital photogrammetric survey in a laboratory flume

This paper reports on a laboratory study in which the automatic digital photogrammetric survey was applied to derive the high-resolution Digital Surface Model (DSM) of the bed topography, used for the flow-bed interactions analysis, in a large amplitude meandering laboratory flume. The analysis has been conducted with the aid of detailed data of three-dimensional flow field previously collected using the acoustic Doppler velocity profiler DOP2000. The applied surveying procedure has allowed the evaluation of the DSM with a resolution of ±0.5 mm. The detailed DSM has been compared with peculiar maps describing the flow velocity pattern (downstream and the crossstream flows) and the shear vel…

Acoustic doppler velocity profiler for velocity and turbulence measurements in a large amplitude meandering flume

Flow over deformed bed of a meandering laboratory channel is experimentally investigated. The velocity components have been obtained using an Ultrasonic Doppler Profiler (DOP2000) that measures the instantaneous flow velocity profile along the probe direction. In this work, some results obtained in peculiar sections along the channel are reported. A refined mesh of the measurement points has been used for each considered cross-section. The analysis of the collected data essentially confirms that when the aspect ratio is small the secondary circulation assumes great importance and, in accordance with previous findings, a second counter-rotating secondary circulation cell appears near the fre…

Momentum transport and bed shear stress distribution in a meandering bend: Experimental analysis in a laboratory flume

The paper concerns the mechanisms underlying the distribution of the bed shear stress in meandering bends. Literature indicates that cross-stream circulation strongly affects the redistribution of the downstream velocity, but the feedback between them is still poorly understood. The aim of this paper is to gain some insight into how the momentum transport by cross-stream circulation contributes to the bed shear stress redistribution. Experimental analysis, based on a detailed dataset collected in a large-amplitude meandering laboratory flume, is presented. From these data an evaluation is made of the terms in the depth-averaged momentum equations and the analysis is especially devoted to te…

Application of Dora-2D model to a distributed catchment dynamics

Studio sperimentale del processo di escavazione a valle del fondo rigido di una struttura di controllo: primi risultati

Dip Phenomenon in High-Curved Turbulent Flows and Application of Entropy Theory

The estimation of velocity profile in turbulent open channels is a difficult task due to the significant effects of the secondary flow. The present paper investigates the mechanism of the velocity-dip phenomenon, whereby the location of the maximum velocity appears to be below the free surface. Previous studies conducted in straight channels relate the mechanism of the velocity-dip phenomenon to secondary flow induced by anisotropy of turbulence. This work focuses on high-curved channels where the secondary motion, which is also induced by the channel’s curvature, evolves along the bend. The width-to-depth ratio, B/h, is one of the most important parameters that are affecting the secondary …

Quasi-geostrophic jet-like flow with obstructions

International audience; Jet-like flows are ubiquitous in the atmosphere and oceans, and thus a thorough investigation of their behaviour in rotating systems is fundamental. Nevertheless, how they are affected by vegetation or, generally speaking, by obstructions is a crucial aspect which has been poorly investigated up to now. The aim of the present paper is to propose an analytical model developed for jet-like flows in the presence of both obstructions and the Coriolis force. In this investigation the jet-like flow is assumed homogeneous, turbulent and quasi-geostrophic, and with the same density as the surrounding fluid. Laws of momentum deficit, length scales, velocity scales and jet cen…

MORPHODYNAMIC PROCESSES DOWNSTREAM OF MAN-MADE STRUCTURAL INTERVENTIONS: experimental investigation of the role of turbulent flow structures in the prediction of scour downstream of a rigid bed

Abstract Experimental program was conducted to analyze scour – caused by a horizontal jet downstream of a rigid bed – and the flow velocity and turbulence characteristics within the scour hole. The experimental program was motivated by the fact that the knowledge of flow field, including turbulent characteristics, is fundamental to correctly simulate the bed-load transport and the temporal evolution of the scour hole and, thus, to define protective measures of scouring. In this paper some results of experiments – carried out to understand the role of flow turbulence in the prediction of scouring process and sediment movement – are reported. The analysis is conducted on the basis of detailed…

Cross-sectional flow and bed shear stress: application of the depth-averaged momentum equation in a meandering laboratory flume

Photogrammetric survey to measure the bed topography of a laboratory large amplitude meandering channel

La degradazione del fondo negli naturali ed il fattore di frizione

Experimental investigation on turbulent structures and sediment transport

Role of vegetation on erosion processes: experimental investigation

Closure to "Analyzing turbulence intensity in gravel bed channel"

Zonazione dei parametri di decadimento del cloro nelle reti idriche: applicazione alla sottorete “Oreto-Stazione” di Palermo.

Finite-Element Modeling of Floodplain Flow

A new methodology for a robust solution of the diffusive shallow water equations is proposed. The methodology splits the unknowns of the momentum and continuity equations into one kinematic and one parabolic component. The kinematic component is solved using the slope of the water level surface computed in the previous time-step and a zero-order approximation of the water head inside the mass-balance area around each node of the mesh. The parabolic component is found by applying a standard finite-element Galerkin procedure, where the source terms can be computed from the solution of the previous kinematic problem. A simple 1D case, with a known analytical solution, is used to test the accur…

Experiments on jets released in rotating vegetated flows

The mixing and spreading of rivers and wastewater flowing into lakes and coastal waters have a great impact in presence of vegetation canopies and mussel coltivation farms.

Experimental Observations of Flow and Bed Processes in Large-Amplitude Meandering Flume

Meanders of large amplitude often exhibit asymmetric planform shape or subsidiary bends. The present work is aimed at improving on understanding of the morphodynamic phenomena affecting the bed evolution of large amplitude meandering channels. Attention is focused on the development of the steady point bar-pool configuration and of the superimposed large-scale migrating bed forms; of particular interest is the role of the changing channel curvature and bed topography variation on flow pattern. A series of experiments was carried out in a sine-generated large-amplitude meandering flume, for two values of width-to-depth ratio. Maps documenting the bed topography and the flow pattern along the…

Cross-sectional flow and velocity redistribution in a meandering laboratory flume

The role played by the cross-stream circulation could be important in the longitudinal flow velocity and bed shear stress redistributions, which determine the bed topography (Blanckaert et al., 2008). Recent experimental results obtained in a strongly curved channel (Blanckaert and Graf, 2001) and in a large amplitude meandering flume (Termini and Piraino, 2011) have highlighted that, besides the main central-region cell, a counter-rotating secondary circulation cell forms near the outer bank along the curved reaches of the channel. In this context, the present work aims at improving the understanding of the flow characteristics along a meandering bend. The analysis is based on detailed vel…

Fluvial eco-hydraulics and morphodynamics: New insights and challenges

The paper concerns the mechanisms underlying the distribution of the bed shear stress in meandering bends. Literature indicates that cross-stream circulation strongly affects the redistribution of the downstream velocity, but the feedback between them is still poorly understood. The aim of this paper is to gain some insight into how the momentum transport by cross-stream circulation contributes to the bed shear stress redistribution. Experimental analysis, based on a detailed dataset collected in a large-amplitude meandering laboratory flume, is presented. From these data an evaluation is made of the terms in the depth-averaged momentum equations and the analysis is especially devoted to te…

RELAZIONE ENTROPICA TRA LA VELOCITA’ MEDIA E LA VELOCITà MASSIMA: verifica sperimentale in un canale meandriforme

Il modello di entropia sviluppato da Chiu (1988) consente di correlare la velocità media, um, e umax mediante una relazione lineare, um,=Φ(M) umax, che dipende dal parametro entropico, M, caratteristico della sezione fluviale. Tale formulazione è stata verificata su diversi corsi d’acqua naturali con differenti caratteristiche idrauliche e geometriche (Ammari et al. 2010, Xia, 1997; Moramarco et al. , 2004). Nel presente lavoro, l’attenzione è rivolta alla verifica della relazione entropica tra la velocità media e la velocità massima al variare delle configurazioni planimetriche del canale (andamento rettilineo e andamento curvilineo) e in presenza di elementi forzanti come la curvatura del…

Applicazione a 5 bacini siciliani di una procedura integrata per lo studio della propagazione delle onde di piena mediante modellazione bidimensionale e uso di cartografia digitale

La maggiore difficoltà per l’applicazione dei modelli numerici alla simulazione delle onde di piena in alvei naturali consiste nella acquisizione dei dati topografici e in una opportuna discretizzazione spaziale del dominio di calcolo. L’uso di modelli monodimensionali comporta la necessità di assegnare un orientamento prefissato alle sezioni di calcolo, di definire la geometria delle sezioni in base alla cartografia digitale, di tornare alla rappresentazione bidimensionale per la restituzione dei risultati. L’uso di mesh triangolari non strutturate e di metodologie numeriche incondizionatamente stabili consente di realizzare una modellazione bidimensionale che, oltre a produrre risultati m…

Flow characteristics in a vegetated flume

Vegetation altering hydrodynamic conditions of an open channel flow controls the exchanges of sediment, nutrients and contaminants. Thus, the knowledge of the hydraulic characteristics of flow over vegetation is very important to support the management of fluvial processes. In this paper the flow over real flexible vegetation is experimentally studied. A 2D-ADV (Acoustic Doppler Velocimeter) is used to measure the local flow velocities for different vegetation concentrations and varying the discharge and the flume slope. The flow velocity measures are used to test the hyperbolic tangent profile of a pure mixing layer and to evaluate the mixing-layer parameters. The formation of turbulence s…

Boundary Shear Stress Distribution and Convective Accelerations: a forecast methodology of planimetric evolution of meandering channels

Evolution of coherent turbulent structures and relation with bed-forms formation in a straight flume

The present paper describes some results of experimental work carried out in a rectilinear flume to investigate the interactions between flow turbulence and sediment motion. The analysis is conducted through the comparison between the periodicity of turbulent structures evolving along the channel and the wavelength of bed forms (alternate bars) forming on the bed. The occurrence of turbulent events (inward interaction, ejection, sweep and burst) has been verified through the conditioned quadrant analysis. The quantitative information about the spatial and temporal scale of the events has been obtained through the space-time correlations of the conditioned data. The analysis essentially high…

Velocity Distribution and Dip Phenomenon in a Large Amplitude Meandering Channel

The prediction of the velocity-dip, whereby the location of the maximum velocity occurs below the water surface, could be important for defining the flow pattern and the momentum transport processes. This study explores the dip-phenomenon in a high-curvature meandering bend. With the aid of data collected in a laboratory flume, the influence of the distance to the outer bank, the channel's curvature and the aspect ratio on the formation and position of the velocity-dip is investigated. Results show that, for the aspect ratios examined, a dip forms in the velocity profiles and its position varies along the bend as a function of the channel's curvature and the aspect ratio. Based on the measu…

Experimental Analysis of Velocity Distribution in a Coarse-Grained Debris Flow: A Modified Bagnold’s Equation

Today, Bagnold&rsquo

Morphodynamic processes around man-made structural interventions

Early Warning Systems and Emergency Plan in Urban Areas: A Study Case

Analisi e previsione dei consumi urbani attraverso l’applicazione di modelli a rete neurale

A Clustering Technique for the Parameter Estimation in Flow Pipe Network Models

The Dora 2D Model: Application to a Natural Carchment in Southern Italy

Determinazione del profilo di velocità e di intensità della turbolenza in canali vegetati

In questa memoria i profili sperimentali della velocità longitudinale misurati in un canale rettilineo di laboratorio con vegetazione sommersa flessibile sul fondo, vengono utilizzati per testare l’applicabilità della legge tangente iperbolica, in genere utilizzata per interpretare il profilo di velocità nello strato di mescolamento (mixing layer). L’adattamento del profilo tangente iperbolica, sia a tutte le distribuzioni sperimentali di velocità presentate in questo lavoro che a quelle misurate da Ghisalberti & Nepf (2002) in differenti condizioni idrodinamiche, ha consentito di localizzare sempre il punto di flesso del profilo ad una distanza prossima all'altezza della vegetazione infles…

Turbulent Flow Structures For Different Roughness Conditions of Channel Walls: Results of experimental investigation in laboratory flumes

Estimating the hydrodynamic and morphodynamic characteristics using Entropy theory at the confluence of Negro and Solimões Rivers

When two mega rivers merge the mixing of two flows results in a highly complex threedimensional flow structure in an area known as the confluence hydrodynamic zone.

Turbulent Flow Structures For Different Roughness Conditions of Channel Walls: Results of experimental

Computation of flow velocity in gravel bed channels

Accurate estimate of flow-velocity profile is of crucial importance both for scientific purposes and for solving numerous engineering problems that include, among others, sediment transport, contaminant transport, flow resistance evaluation. This paper presents a new empirical equation to represent the vertical velocity profile. The proposed equation is essentially a modified form of the well-known logarithm law of the wall and contains three parameters having a clear physical meaning. The applicability of the equation and its accuracy assessment for different hydraulic conditions, including non-uniform conditions, is verified by using experimental data obtained by different sources. The va…

Flow characteristics of a channelized debris-flow and implications in numerical modelling: a study case

As it is known, debris flows are characterized by extreme propagation rapidity and by the ability to move high quantity of fluid mass. Furthermore, debris flows are fluid enough to travel long distances and, thus, to cause damage in vast areas, even far from the trigger ones. Debris-flow runout estimations are important for the delineation of potentially hazardous areas. Especially in recent years, several researches have been conducted in order to define predicitive models. But, existing runout estimation methods need input parameters that can be difficult to estimate. Recent advances in theory and in experimental research have allowed the assessment of the physics of the debris flows. On …

RELAZIONE ENTROPICA TRA LA VELOCITÀ MEDIA E LA VELOCITÀ MASSIMA: verifica sperimentale in canali di laboratorio

Role of secondary circulation on bank erosion in a large amplitude meandering laboratory channel

This paper reports peculiar results of experimental investigation on the evolution of flow secondary circulation motion along a meander wave. The experiments have been conducted in a large amplitude meandering laboratory channel for two values of the width-to-depth ratio. Attention is focalised on how secondary motion affects the bank shear stress distribution, influencing the bank stability. The analysis essentially highlights that, especially for small width-to-depth ratio, as the channel curvature increases besides the classical central-region secondary circulation cell a counter-rotating circulation cell forms in the outer-bank region. Such counterrotating circulation cell allows to obt…

Spatial diversity of chlorine residual in a drinking water distribution system: application of an integrated fuzzy logic technique

A reduction in the concentration of chlorine, which is used as a chemical disinfectant for water in drinking water distribution systems, can be considered to be an index of the progressive deterioration of water quality. In this work, attention is given to the spatial distribution of the residual chlorine in drinking water distribution systems. The criterion for grouping the water-quality parameters normally used is highly subjective and often based on data that are not correctly identified. In this paper, a cluster analysis based on fuzzy logic is applied. The advantage of the proposed procedure is that it allows a user to identify (in an automatic way and without any specific assumption) …

Empirical estimation of maximum scour depth downstream bed sills

Flow velocity profile and turbulence characteristics in a vegetated straight flume

Vegetation affects the hydrodynamic conditions of an open channel flow with direct implications in physical and biophysical processes. In this paper, the vertical flow velocity distribution of a vegetated flow has been analyzed using experimental data collected in a straight flume. The experimental velocity distributions are positively compared with the hyperbolic tangent profile of a pure mixing layer previously verified by Ghisalberti and Nepf (2002). Peculiarly, for different flow and vegetative conditions, fitting of the hyperbolic tangent profile to the experimental velocity distributions has allowed the localization of the inflection point of the velocity profile at a distance from th…

Experimental investigation on Morphodynamic process downstream of a Rigid bed

Analisi sperimentale del moto di circolazione secondaria in un canale meandriforme di elevata ampiezza

Vegetation against erosion downstream of a hydraulic structure

The present work shows the effects of vegetation on sediment transport process. The volume of sediments transported at different time steps is determined by applying a numerical model previously developed [4] and the model parameters are calibrated by using the experimental data.

Effect of Vegetation on Fluvial Erosion Processes: Experimental Analysis in a Laboratory Flume

Abstract The plane evolution of a meander wave is determined by the erosion processes at the banks. Particularly, the outer- bank is considerably vulnerable to the erosion processes. Indirect techniques, which act upon the reduction of the effect of the cross-circulation motion, have been recently proposed to limit the outer-bank erosion. This paper shows preliminary results on the role played by vegetation on cross-circulation motion. The analysis is conducted on the basis of experimental data collected in a large amplitude meandering channel constructed at the hydraulic laboratory of DICAM. Maps describing the cross-stream flow, both over the no-vegetated bed and over the vegetated bed, a…

Un modello Completo per la Simulazione del Campo di Moto di Correnti a Pelo Libero Lentamente Variate: Applicazione Al caso di Alvei Meandriformi

Analisi dell’evoluzione della degradazione del fondo in alvei a fondo non uniforme

River processes and Links between fluvial and coastal systems in a changing climate

It is well known that a changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of extreme weather and climate events. Models indicate substantial warming in temperature extremes by the end of the 21st century (IPCC, 2012). The global warming determines several environmental problems altering the hydrologic cycle, with changes to the amount, timing, and intensity of precipitation (see as an example Rahimpour Golroudbary et al., 2016), and impacting on the soil erosion rate and on the quality of aquatic and marine environments (see as an example Robins et al., 2016). The present Special Issue collects main contributions arising from the aforementio…

Application of a 1-D numerical model to estimate the sediment transported along a river

Natural rivers tend to adjust their plane shape and longitudinal profile in order to assume a configuration compatible with the changing hydraulic and man-made constraints. The causes of these bed variations are related to changes in independent river channel variables (increase in water discharge, decrease in sediment discharge, etc..) or to changes in river slope. River bed degradation and aggradation, often occurring as result of river morphological changes, modify the longitudinal bed profile of the river and the amount of sediment transported along the river until to reach the outlet. As an example, the construction of river dams produces large morphological consequences: when the stre…

Experimental observations of upstream overdeepening

The issue of morphodynamic influence in meandering streams is investigated through a series of laboratory experiments on curved and straight flumes. Both qualitative and quantitative observations confirm the suitability of the recent theoretical developments (Zolezzi & Seminara 2001) that indicate the occurrence of two distinct regimes of morphodynamic influence, depending on the value of the width ratio of the channel β. The threshold value βR separating the upstream from the downstream influence regimes coincides with the resonant value discovered by Blondeaux & Seminara (1985). Indeed it is observed that upstream influence may occur only in relatively wide channels, while narrower stream…

WATER QUALITY ANALYSIS OF A WATER DISTRIBUTION SYSTEM: A CASE STUDY

Modeling Bedload Transport Trajectories along a Sine-generated Channel

This study explores the influences of flow discharge and particle size on bedload transport trajectory by applying a depth-averaged two-dimensional model to a 110° sine-generated laboratory flume with wide-and-shallow sections. Calculated results exhibit two erosion regions in a bend: Zone-1 ‒ foreside of the point bar near the convex bank and Zone-2 ‒ near the apex of the concave bank. Sediments eroded from Zone-1 are mainly transported along the same-side convex bank rather than crossing the channel centerline, indicating the crucial role of longitudinal flow in shaping point bars. Most particles from Zone-2, however, behave more complicated by changing their trajectories with the develop…

Experimental analysis of turbulence characteristics and flow conveyance effects in a vegetated channel

Experimental analysis of flow in a laboratory flume with flexible vegetation

Steady-State Convective Acceleration Computation in Shallow Water Equations

Roots Characteristics of a flexible and mature vegetation: Preliminary results of experimental investigation in a meandering laboratory flume

Vegetation controls sediment dynamics and affects the kinematic characteristics of flow in rivers. The uprooting mechanism is strongly affected by mechanical properties, morphology and branching of the roots system. This work presents preliminary results of experimental work conducted in a laboratory meandering flume. The work aims to investigate how the geometrical and mechanical characteristics of the roots of a real, flexible and mature vegetation could vary along the bend. Results show that both the geometrical and the mechanical characteristics of the roots assume higher/lower values in peculiar sections of the bend suggesting that they could be affected by the kinematic characteristic…

Experimental analysis of transverse flow motion in a large amplitude meandering bend

Analisi dell'escavazione localizzata a valle di una soglia.

Analisi sperimentale delle caratteristiche cinematiche della corrente in un canale meandriforme di elevata ampiezza: primi risultati

Vegetation as biomaterial in Environmental Engineering

It is particularly important to focus attention on environmental technology and related procedures and materials. Bioengineering techniques and materials are needed to reduce the human impact on the environment. As an example, plants and plant materials can be used for erosion control and slope protection to reduce risk events; vegetation used for green roofs and walls is also an important bioengineering measure to protect buildings and adsorbing rainwater, containing air pollution and greenhouse gas emissions, and extending roof life. The use of plants for river bank protection and erosion control has a long tradition in Europe. Literature shows that climate is one of controlling factor of…

Experimental investigation on the “horizontal” turbulence and the bed deformation: preliminary results

Experimental Analysis of Horizontal Turbulence of Flow over Flat and Deformed Beds

Abstract Laboratory experiments in a straight flume were carried out to examine the evolution of large-scale horizontal turbulent structures under flat-bed and deformed-bed conditions. In this paper, the horizontal turbulence of flow under these conditions is analyzed and compared. The conditioned quadrant method is applied to verify the occurrence of turbulent events. The distributions of horizontal Reynolds shear stress and turbulent kinetic energy are also presented and discussed. Results show the occurrence of an “initial” sequence of horizontal vortices whose average spatial length scales with the channel width. Under deformed-bed conditions, this spatial length does not change.

Effect of vegetation on local erosion downstream of a rigid bed: experimental analysis in a laboratory flume

Experimental study in a meandering channel: 1. Analysis of bed topography

Analysing longitudinal turbulence intensity in vegetated channels

Vegetation altering hydrodynamic conditions of an open channel flow controls the exchanges of sediment, nutrients and contaminants. In this paper the turbulence structure of open-channel flow over a flexible grass vegetation is investigated. Velocity measurements were carried out, in a rectangular flume, using a 2D-ADV (Acoustic Doppler Velocimeter) for different values of stem concentration, water discharge, and bed slope. The experimental results showed that: 1) the maximum value of the longitudinal turbulence intensity occurs at a water depth close to the bent vegetation height; 2) the turbulence intensity damps for increasing values of the stem concentration; 3) above the vegetation hei…

Jets interacting with vegetation in the rotating LEGI platform

Rivers and wastewater discharges flowing into lakes and coastal waters strongly affect aquatic ecosystems, based on their transport of turbulence, tracers and sediment particles. Mixing and spreading of outflows have an even greater impact when the receiving site is obstructed by vegetation canopies or mussel cultivation farms. Thus, a thorough knowledge of the interaction between effluents and receiving bodies is required to mitigate impacts and promote best environmental management practices, also following the 2015 EU Marine Strategy Framework Directive.

ANALYSIS OF VELOCITY FIELD AND TURBULENCE CHARACTERISTICS OF FLOW IN A VEGETATED LABORATORY FLUME

Vegetation altering hydrodynamic conditions of an open channel flow controls the exchanges of sediment, nutrients and contaminants. Thus, the knowledge of the hydraulic characteristics of flow over vegetation is very important to support the management of fluvial processes. But, the analysis of the hydrodynamic conditions is complex because vegetation is flexible in varying degrees and it oscillates in the flow changing position. Furthermore, because of temporal changing of roughness due to natural vegetative growth, the response of vegetation to the flow can change in time. Many theoretical and experimental investigations have been performed in order to analyze both the mean flow and turbu…

A water demand model by means of the artificial neural networks method

Analisi sperimentale di laboratorio sulla stima della velocità media del flusso mediante la teoria entropica

Optimal Network Design with the Use of Reliability Constraints and Simulated Annealing Tecnique

Flow characteristics in a large amplitude meandering bend

Effect of flexible vegetation on localized erosion processes

Studio sperimentale dell’evoluzione di strutture turbolente in un canale rettilineo di laboratorio per due condizioni di scabrezza delle pareti

Nella presente memoria sono riportati alcuni risultati sperimentali ottenuti in un canale rettilineo di laboratorio utilizzando misure di velocità locale effettuate al fine di analizzare l’evoluzione di strutture turbolente che nascono in prossimità del fondo. L’analisi è effettuata sia in condizione di pareti lisce che in condizione di pareti scabre. L’evoluzione spazio-temporale delle strutture turbolente è stata analizzata applicando l’analisi dei quadranti ed utilizzando la tecnica della media condizionata.

Flow-induced vegetation uprooting in a meandering bend : experimental investigation

Abstract Vegetation uprooting is a complex process which depends on many interrelated factors. In this paper, attention is focused on the flow-induced uprooting in river bends, where the flow characteristics vary as effected by the channel's curvature and its continuous changing in the downstream direction. Results are presented by an experimental work done in a high-amplitude meandering flume with mature herbaceous vegetation on the bed. In the first part of the paper, the variation along the bend of the geometrical (length, thickness, and radical architecture) and the mechanical (resistance force) characteristics of the roots are analyzed. In the second part of the paper, the transition f…

Experimental analysis of cross-sectional flow motion in a large amplitude meandering bend

Flow in meandering bends is characterized by the formation of a large cross-sectional central-region circulation cell. The width-to-depth ratio is one of the most important parameters affecting the entity of the cross-circulation motion. In steep outside bends, beside the central-region cell, a counter-rotating circulation cell often forms in the upper part of the outer-bank. In spite of its practical importance, the evolving mechanisms of both the circulation cells and their role on boundary shear stress distribution in bends are not yet fully understood. The aim of the present paper is to gain some insight into how cross-sectional flow motion evolves along meandering bends. Experiments ha…

Temporal Evolution of Scour downstream bed sills

Circulation motion in the apex section of a large amplitude meandering flume

Modelli di previsione del consumo idrico istantaneo

Numerical simulation of experiments in a meandering flume

Numerical modelling of the flow in a meandering channel is compared with experiments done by one of the authors. A peculiar 2DH model, where bottom shear stresses are computed taking into account also accelerations, has been developed for the comparison. Good results are obtained in some sections of the channel, but, in others, some experimentally observed flow features are not well reproduced. An explanation is offered for the difficulties encountered in modelling the strong secondary current that appears along the bend.

EXPERIMENTAL ANALYSIS OF RELATION BETWEEN COHERENT TURBULENT STRUCTURES AND BED-FORMS FORMATION

The present paper describes an experimental investigation on the interactions between flow turbulence and sediment motion. During the experiments, detailed measures of flow velocity components have been carried out using an Acoustic Doppler Velocimeter (ADV). The occurrence of turbulent events (inward interaction, ejection, sweep and burst) has been verified through the conditioned quadrant analysis. The quantitative information about the spatial and temporal evolution of turbulent events has been obtained through the space-time correlations of the conditioned data. As the primary objective was to analyse how turbulent structures influence the bed-forms formation, the spatial scale of turbu…

Turbulence structure and implications in exchange processes in high-amplitude vegetated meanders: Experimental investigation

Aquatic plants in rivers interact with flow and exert an important role in maintaining suitable habitat and ecological equilibrium. Understanding turbulence structure in the presence of vegetation is important with respect to environmental processes, such as sediment transport and mixing of transported quantities. Literature indicates that mass and momentum exchanges in the presence of vegetation are strongly influenced by the sequence of coherent structures which form between vegetated and non-vegetated zones. In the present paper we investigate turbulence structure and coherent motion in high-curvature channels with submerged vegetation. The analysis is performed with the aid of detailed …

River-bed erosion due to changing boundary conditions: performance of a protective measure

Abstract. Due to the introduction of man-made sediment barriers along a river, the amount of sediment load entering the downstream river reach is different to that leaving the reach, and erosion processes occur downstream of the barrier itself. Designers are often required to take into account the scouring process and to include adequate protective measures against the local scour. This paper addresses the performance of bio-engineering protective measures against the erosion process. In particular, a green carpet, realized with real flexible vegetation, has been used as the protective measure against erosion processes downstream of a rigid bed. Analyses are based on experimental work carri…

Turbulence structure and coherent motion in a straight laboratory flume

Rilievi del profilo di velocità in un canale con vegetazione sommersa

Flexible vegetation behaviour and effects on flow conveyance: experimental observations

As it is known, vegetation is an important component of aquatic ecosystems. Because of the variety of species and, thus, of the characteristics of the vegetation elements (form, size, stiffness, etc.), it is difficult to develop a widely applicable method to predict mean flow and flow resistance. Despite the intense activity research, much work has to be done in understanding hydrodynamics in vegetated channels. This is important to analyse many physical processes involved in the ecosystem at different spatial and time scales. In this paper, attention is restricted to flexible vegetation. After a brief description of results obtained in previous experimental works conducted in a rectangular…

Entropic approach to estimate the mean flow velocity: experimental investigation in laboratory flumes

The paper deals with the linear entropic relationship between the maximum velocity, u max , and the mean flow velocity, u m , through a dimensionless parameter Φ(M), in open-channel flow. The analysis is conducted with the aid of experimental data collected in straight laboratory flumes under different bed and side-walls roughness conditions. In particular, rough/vegetated beds and smooth/rough side-walls conditions have been investigated. The results show that, in the investigated conditions (with exception of low-submergence vegetated bed—h/k v  < 2), Φ(M) can be assumed equal to a value that is very close to that found in natural channels. This demonstrates that Φ(M) is able to implicitl…

Different scales of erosion processes downstream hydraulic structure

Digital image-based technique for monitoring surface velocity: sensitivity analysis with processing parameters using data of a study case

This paper describes the application of image-based technique for mapping surface velocity of hyper-concentrated flows. The analysis is conducted with the aid of data collected in a scale laboratory flume constructed at the Hydraulic laboratory of the Department of Civil, Environmental, Aerospatial and of Mate-rials Engineering (DICAM) – University of Palermo (Italy). A fully digital images-based technique has been applied to record a large amount of high resolution images identifying simultaneously the position of points in different time instants. The sensitivity analysis of the estimated flow velocity with the acquisition conditions and the number of processed frames is performed

Experimental study on parameters affecting propagation of a channelized debris-flow

Analysis of the role of turbulent structure in bed-forms formation in a rectilinear flume

STIMA DEI PROFILI DI VELOCITA’ DEI FLUSSI IPERCONCENTRATI: analisi di sensitività sui parametri dell’equazione di Bagnold.

Nel presente lavoro l'attenzione è focalizzata sulla dinamica di propagazione delle colate detritiche, fenomeni naturali di elevata pericolosità e forza distruttiva. Com’è noto, una colata detritica si verifica quando il materiale solido (sedimenti e materiale sciolto) di versanti caratterizzati da elevate pendenze viene destabilizzato dal deflusso di ingente volume d’acqua. Durante la propagazione della miscela acqua-sedimento, elementi anche di elevata dimensione (massi, alberi,..) possono essere mobilitati aumentando la forza distruttiva della colata con conseguenti possibili ingenti danni a edifici e infrastrutture, perdita di vite umane e ostruzioni (parziali o totali) dei corsi d’acqu…

La Fotogrammetria Digitale per il Rilievo del fondo Deformato di un Modello Fluviale

Flow in meandering bends

Applicazione di un modello di simulazione delle variazioni longitudinali del fondo di un alveo naturale

A 1D model for sediment transport simulation

Nonuniform sediment transport estimation in non-equlibrium situations: study cases

Analysis of the effect produced by the water flowing of the jutting out elements of historical buildings involucre

Turbulent jet through porous obstructions under Coriolis effect: an experimental investigation

AbstractThe present study has the main purpose to experimentally investigate a turbulent momentum jet issued in a basin affected by rotation and in presence of porous obstructions. The experiments were carried out at the Coriolis Platform at LEGI Grenoble (FR). A large and unique set of velocity data was obtained by means of a Particle Image Velocimetry measurement technique while varying the rotation rate of the tank and the density of the canopy. The main differences in jet behavior in various flow configurations were assessed in terms of mean flow, turbulent kinetic energy and jet spreading. The jet trajectory was also detected. The results prove that obstructions with increasing density…

Application of the DORA 2D Model to some sicilian catchments

Calibrazione dei parametri di qualità nelle reti di approvvigionamento idrico e caratterizzazione della diversità spaziale – applicazione ad un caso di studio

Numerical simulation of bed topography in large meadering channels

Experimental investigation of the kinematic characteristics of flow in a meandering flume with flexible vegetation on the bed: preliminary results

Leaks Analysis in Pipeline Systems by Means of Optimal valve Regulation

Application of entropic approach to estimate the mean flow velocity and Manning roughness coefficient in a high-curvature flume

The entropy-based approach allows the estimation of the mean flow velocity in open channel flow by using the maximum flow velocity. The linear relationship between the mean velocity, umax, and the mean flow velocity, um, through the dimensionless parameter Φ(M), has been verified both in natural rivers and in laboratory channels. Recently, the authors of this study investigated the reliability of the entropy-based formula in a straight channel and under different bed and side-walls' roughness conditions. The present study aims to further validate the entropy-based approach and to explore the effectiveness of entropy-based formula in high curvature channels. Results show that as the effect o…

Bed Topography Reconstruction in a Large Amplitude Meandering Flume: Application of Close Range Photogrammetry

Natural rivers are characterized by continuous variations in bed topography, especially along curved reaches. High resolution topographic data are necessary to analyze the mutual interactions between the downstream flow and the cross-stream flow, which determine the distribution of the bed-shear stress along the channel. Because of the difficulty in acquiring good and accurate data in rivers, the major part of studies have been conducted in laboratory flumes. This paper reports on a laboratory study in which the automatic digital photogrammetric survey was applied to derive the high-resolution Digital Surface Model (DSM) of the bed topography in a large amplitude meandering flume. In order …

Nonuniform sediment transport and flow characteristics downstream of a hydraulic structure

Role of vegetation on flow hydrodynamics and erosion processes

Numerical simulation of river-bed variations: Sensitivity analyses with respect of the initial hydraulic roughness

Two elements affect the efficacy of the numerical models of mobile-bed evolution: the prediction of the hydraulic roughness, related with both sediment distribution on the bed and flow depth, and the prediction of the hydraulic sorting, when the distribution of sediments on the bed is not uniform. In this work the bed profile variation is simulated, by using a numerical model proposed in previous works, in function of the variation of the friction factor, that reflects the coarsening of median sediment diameter, due to armouring process, and the variation of flow conditions. The variation of grains-size distribution of the bed material is predicted by using a probabilistic approach and the …

Experimental observations of Flow and Bed processes in a Large-amplitude Meandering Flume

Meanders of large amplitude often exhibit asymmetric planform shape or subsidiary bends. The present work is aimed at improving on understanding of the morphodynamic phenomena affecting the bed evolution of large amplitude meandering channels. Attention is focused on the development of the steady point bar-pool configuration and of the superimposed large-scale migrating bed forms; of particular interest is the role of the changing channel curvature and bed topography variation on flow pattern. A series of experiments was carried out in a sine-generated large-amplitude meandering flume, for two values of width-to-depth ratio. Maps documenting the bed topography and the flow pattern along the…

Il coefficiente di resistenza in un canale meandriforme di elevata ampiezza

ANALYSIS OF THE RELATION BETWEEN THE FLOW “HORIZONTAL” TURBULENCE AND THE BED DEFORMATION

Ricostruzione automatica della morfologia del fondo di un modello fluviale

Un modello bidimensionale a zero inerzia per il calcolo della propagazione di onde di piena su superfici fortemente irregolari”.

Diversita’ spaziale del cloro residuo nelle reti di approvvigionamento idrico

La qualità dell’acqua nelle reti di distribuzione può essere sensibilmente alterata da una serie di processi che si sviluppano sia lungo il sistema di adduzione che nella stessa rete di distribuzione. La riduzione della concentrazione di cloro, utilizzato per la disinfezione delle acque, può essere considerata un indice del progressivo deterioramento delle caratteristiche igieniche dell'acqua circolante in rete. La concentrazione del cloro, libero o combinato, è infatti strettamente legata alle reazioni che si sviluppano all’interno delle condotte. In questo lavoro particolare attenzione è rivolta alla identificazione della diversità spaziale del cloro residuo in rete. L’analisi viene condo…

Propagation of a channelized debris-flow: experimental investigation and parameters identification for numerical modelling

Experimental investigation on dispersion mechanisms in rigid and flexible vegetated beds

Vegetation in channels strongly affects flow structure and turbulence, with consequences on the hydrological storage of nutrients and chemical tracers, the shelter of stream biota as well as the trapping or transport of sediments. At the same time, all these phenomena are inevitably subjected to alteration of hydrological conditions in fluvial systems due to climate change. The present study intends to provide a thorough investigation into the processes of transport and dispersion induced by flow turbulence within the vegetation structure. Specifically, velocity measurements in vegetated channels were intensively conducted and analyzed in the case of both flexible submerged and rigid emerge…

Bed scouring downstream of hydraulic structures under steady flow conditions: Experimental analysis of space and time scales and implications for mathematical modeling

Abstract Sediment transport and bed deformation in alluvial rivers are space and time dependent. The knowledge of the space and time scales can be helpful for the definition of predictive procedures of an alluvial reach response to changing boundary conditions. In this work, attention is paid to scouring process occurring downstream of the rigid basement of a hydraulic structure. The analysis is focused on transient bed profiles which are determined, under steady flow conditions, by a decrease of the upstream sediment transport rate. In particular, the paper is aimed at improving understanding of the space and time scales required by the alluvial system to reach the equilibrium conditions. …

Experimental observation of the rule of flexible vegetation on erosion processes

Vegetation altering hydrodynamic conditions of an open channel flow controls the exchanges of sediment, nutrients and contaminants. Thus, the knowledge of the hydraulic characteristics of flow over vegetation is very important to support the management of fluvial processes. But, the analysis of the hydrodynamic conditions is complex because vegetation is flexible in varying degrees and it oscillates in the flow changing position. Furthermore, because of temporal changing of roughness due to natural vegetative growth, the response of vegetation to the flow can change in time. Many theoretical and experimental investigations have been performed in order to analyze both the mean flow and turbu…

Friction Factor Variation in a Meandering Channel

Monitoring of surface velocity of hyper-concentrated flow in a laboratory flume by means of fully-digital PIV

This paper investigates the utility and the efficiency of the digital image-technique for remote monitoring of surface velocity in hyper-concentrated flow by the aid of data collected during experiments conducted in the laboratory flume. In particular the present paper attention is focused on the estimation procedure of the velocity vectors and on their sensitivity with parameters (number of images, spatial resolution of interrogation area, ) of the images processing procedure.

Flow Velocity Measurements in Vegetated Channels

Understanding of the hydraulics of flow over vegetation is very important to support the management of fluvial processes. In this paper the flow over flexible bottom vegetation is experimentally studied. A two-dimensional-acoustic doppler velocimeter is used to measure the local flow velocities for different vegetation concentrations, discharges, and flume slopes. The influence of vegetation concentration and the depth/vegetation height ratio on the measured velocity profiles is analyzed. All measured velocity distributions are S-shaped and exhibit a three-zone profile. The relationship between the velocity distribution and the turbulence intensity distribution is also analyzed. The charact…

Influenza morfodinamica nei corsi d’acqua naturali: verifiche sperimentali

Entropic model application to identify cross-sectional flow effect on velocity distribution in a large amplitude meandering channel

Abstract Literature shows the application of the entropy concept in open channels flow. No existing research has been addressed to the application of the entropy concept for evaluating the effect of secondary flow which especially develops in curved channels. The purpose of this paper is to explore the possibility to evaluate the effect of the secondary flow on the stream-wise velocity distribution starting only from the knowledge of the surface velocity and the entropic concept application. The analysis is conducted with the aid of data collected in a large-amplitude meandering laboratory flume for two different values of the width-to-depth ratio. Results show that the location of the maxi…

Experiments on Longitudinal and Transverse Bedload Transport in Sine-Generated Meandering Channels

Bedload grains in consecutive meandering bends either move longitudinally or across the channel centerline. This study traces and quantifies the grains’ movement in two laboratorial sine-generated channels, i.e., one with deflection angle θ0 = 30° and the other 110°. The grains originally paved along the channels are uniform in size with D = 1 mm and are dyed in various colors, according to their initial location. The experiments recorded the changes in the flow patterns, bed deformation, and the gain-loss distribution of the colored grains in the pool-bar complexes. We observed the formation of two types of erosion zones during the process of the bed deformation, i.e., Zone 1 in the foresi…

Experimental analysis of the effect of vegetation on flow and bed shear stress distribution in high-curvature bends

The cross-sectional circulation, which develops in meandering bends, exerts an important role in velocity and the boundary shear stress redistributions. This paper considers the effect of vegetation on cross-sectional flow and bed shear distribution along a high-curvature bend. The analysis is conducted with the aid of data collected in a large-amplitude meandering flume during a reference experiment without vegetation and an experiment with vegetation on the bed. The results show that the presence of vegetation modifies the curvature-induced flow pattern and the directionality of turbulent structures. In fact, in the presence of vegetation, the turbulent structures tend to develop within a…

Flow velocity and turbulence intensity distribution in a vegetated straigth laboratory channel

La Progettazione delle reti idriche con il metodo 'Simulated Annealing

A Numerical Method for the Computation of Bed Degradation Downstream a Dam

Computation of flow velocity in rough channels

Accurate estimate of flow-velocity profile is of crucial importance both for scientific purposes and for solving numerous engineering problems that include, among others, sediment transport, contaminant transport, flow resistance evaluation. This paper presents a new empirical equation to represent the vertical velocity profile. The proposed equation is essentially a modified form of the well-known logarithm law of the wall and contains three parameters having a clear physical meaning. The applicability of the equation and its accuracy assessment for different hydraulic conditions, including non-uniform conditions, is verified by using experimental data obtained by different sources. The va…

Experimental observation of horizontal coherent turbulent structures in a straight flume

The present paper describes results of laboratory experiments carried out to investigate the evolution of horizontal coherent turbulent structures for different roughness conditions of channel walls. The occurrence of turbulent events (inward interaction, ejection, sweep and burst) is identified through the conditioned quadrant analysis. The filtered data set is used to determine the probability density distribution of each turbulent event. Particular attention is focused on sweep and ejection events and peculiar maps showing the distributions of the horizontal Reynolds shear stress, for each examined experimental condition, are also presented and discussed.

Metodo di Previsione della Topografia di Equilibrio del Fondo di un Alveo Meandriforme

1-D numerical simulation of sediment transport in alluvial channel beds

Quantitative estimate of sediment transport processes is important especially in river-control engineering and for water management projects. In this paper the sediment routing of a 1-D model is presented and applied to some study cases. The procedure simulates the variations of bed roughness conditions due to natural sorting and to generation and migration of bed forms. The suspended-load and the bed-load are treated separatel

Use of Vegetation as Biomaterial for Controlling Measures of Human Impact on the Environment

In a context of a climate change, bioengineering techniques and biomaterials are needed to reduce the human impact on the environment. Thus, in recent years, living materials have been used in environmental engineering applications. In the present paper, attention is restricted to the vegetation, and a brief review on its use as biomaterial in engineering control techniques is presented. The core of this review is a comprehensive overview of two important techniques using vegetation as living material for measures limiting the human impact both in extra-urban and in urban sites. In particular, the use of vegetation both as living material for soil erosion protection and river’s bank stabili…

Closure to “Analyzing Turbulence Intensity in Gravel Bed Channels” by F. G. Carollo, V. Ferro, and D. Termini

Non-Contact Measurement of River Surface Velocity and Discharge Estimation with a Low-Cost Doppler Radar Sensor

River discharge is an important variable to measure in order to predict droughts and flood occurrences. Once the cross-sectional geometry of the river is known, discharge can be inferred from water level and surface flow velocity measurements. Since river discharges are of particular interest during extreme weather events, when river sites cannot be safely accessed, noncontact sensing technologies are particularly appealing. To this purpose, this work proposes a prototype of a low-cost continuous wave (CW) Doppler radar sensor, which is able to monitor the surface flow velocity of rivers. The prototype is tested at two gauged sites in central Italy, along the Tiber River. The surface flow v…

Sediment-flow interactions and effects on bed forms mechanism

Recent experimental works conducted in mobile bed rectilinear flume seem to verify the existence of a correspondence between the spatial periodicity of horizontal turbulent structures evolving in streamwise direction and the wavelength of bed forms (alternate bars) observed on the bed. In this study, the effect of the variation of the bed roughness conditions on the evolution of such horizontal turbulent structures is analyzed. Peculiar results obtained by using flow velocity data collected along the flume both with flat bed and with deformed bed are reported.

Reduction of scouring downstream of a rigid bed by means of a vegetated carpet: experimental investigation in a laboratory flume

Vegetation is a critical component of aquatic ecosystems and exerts an important role in river morphodynamics. This paper describes the results of laboratory study carried out to investigate the role of vegetation on flow field and erosion process developing in non-equilibrium situations. Particular attention is paid to scour evolving downstream of a rigid bed and to the effect of a vegetated carpet used as a protective measure against scouring. The reported experimental study shows that the introduction of the vegetated carpet results in a more favourable configuration than in its absence determining reduced values of flow velocity, turbulence intensity and bed shear stress, and modifying …

Analyzing turbulence in gravel bed channels

In this paper, the results of an experimental investigation of the turbulence intensity in gravel bed channels are described. The runs were carried out by measuring, with an acoustic Doppler velocimeter, the turbulence intensity profile along six verticals of a given cross section in a laboratory flume. The analysis of the measured intensity distributions has shown the existence of two different regions, above and below the tops of the roughness elements, in which different intensity profiles occur. Furthermore, the measured profiles have shown a maximum of the turbulence intensity that decreases for increasing values of the roughness height, confirming that the turbulence damping efficienc…

SPATIAL DIVERSITY OF CHLORINE RESIDUAL IN A DRINKING WATER DISTRIBUTION SYSTEM: A STUDY CASE

Experimental investigation on the role of vegetation on sediment transport mechanism: review of recent results

Flow and turbulence characteristics in a vegetated straigth flume

Turbulence in River and Maritime Hydraulics

Understanding of the role of turbulence in controlling transport processes is of paramount importance for the preservation and protection of aquatic ecosystems, the minimisation of deleterious consequences of anthropogenic activity, and the successful sustainable development of river and maritime areas. In this context, the present Special Issue collects 15 papers which provide a representation of the present understanding of turbulent processes and their effects in river and maritime environments. The presented collection of papers is not exhaustive but it allows for highlighting key priority areas and knowledge gaps in this field of research.

Turbulent mixing and dispersion mechanisms over flexible and dense vegetation

The present study investigates flow turbulence and dispersion processes in the presence of flexible and dense vegetation on the bed. The turbulent dispersion coefficients and the terms of the turbulent kinetic energy equation are determined by using data collected in a straight laboratory channel with living vegetation on the bed. Results show that the turbulent integral lengths assume an order of magnitude comparable to the stems’ characteristic dimension independently by the direction and the turbulence assumes an isotropic behavior. The coefficients of dispersion have a trend similar to that of the turbulent lengths and assume low values in the longitudinal, transversal and vertical dire…

Prediction of river discharges at confluences based on Entropy theory and surface-velocity measurements

Hydrodynamic features of the confluence zone of large rivers are complicated because of their three-dimensional flow structure. The confluence between the Rio Negro and the Rio Solimões, characterised by black and white waters, respectively, ranks among the largest river junctions on Earth. An Entropy-based investigation was carried out to assess the discharge and analyse the 2D structure of velocity distribution for large river flows relying on monitoring of near-surface velocity only. The estimated flow data where compared with in-situ ADCP data gathered across some transects of the Negro and Solimões rivers during both low and relatively high flow conditions. Results are illustrated thro…

Optimal Parameter Zonation for Water Distribution Networks

Bioengineering Materials for Environment Protection in a Changing Climate

Climate change is one of the biggest problems of our times and passing the time climate extremes tend to increase both in magnitude and in frequency. Because the severity of the extreme climate events has increased, the interaction of these events with vulnerable human and natural systems has more frequently lead to disasters. Recent climate models projections have also shown a further substantial warming in temperature extremes by the end of the 21st century. The prevision models’ results also indicate that the global warming and the increase in frequency of temperature extremes could be strictly related to the anthropogenic forcing. The present special issue collects contributions represe…

Simulation of Sediment transport and flow characteristics downstream of a hydraulic structure

The presence of a hydraulic structure (such as a dam) in a given river reach determines “constrained” sediment boundary conditions and thus transient transport phenomena. Many predictive mobile-bed one-dimensional models have been developed in or-der to predict sediment transport during transients but, even today, they have not attained a high degree of efficacy. This is because these models are confronted with some difficulties such as the reliable prediction of bed roughness or/and to the presence of flexible vegetation, of hydraulic sorting, of water-bed sediment interchanges in no-equilibrium situations. In the present work, with the aid of a 1-D numerical model previously developed (Te…

Influence of vegetated bed material on erosional patterns of meandering rivers: preliminary experimental results

Hyper-concentrated flow and surface velocity estimation by digital imaging technique: a study case

This paper investigates the utility of digital imaging technique for performing surface velocity measurements of hyper-concentrated flows. The analysis is conducted with the aid of data collected in a scale laboratory flume constructed at the Hydraulic laboratory of the Department of Civil, Environmental, Aerospatial and of Materials Engineering (DICAM) – University of Palermo (Italy). In particular the present paper describes the setup of a laboratory test and the applicability of a fully digital imaging approach.

Computation of the regime configuration of a meandering stream

Regime channel formation is a delicate adaptation to the imposed environmental conditions compatible with flow and sediment transport mechanisms. The present paper concerns the computation of the regime configuration of a meandering stream. It is supposed that the channel develops until it reaches the state of “final thermodynamic equilibrium”, where the ratio of the kinetic energy of the flow to its cross-sectional potential energy is minimum. An optimization procedure that allows the analysis of the regime channel formation is presented and it is checked using a real case.

Analysis of local scour downstream of bed sills: preliminary results of an experimental work

Bed sills are often used to limit bed degradation, to control bed erosion around bridge piers or downstream stilling basins of dams. In this paper, the local scour that takes place downstream of the bed sill, in addition to the general erosion process, is examined. The data collected during experimental work are used to analyse the applicability of the relationship found in the literature and to define the relation between the maximum scour depth and the flow rate.

Experimental investigation of the evolution of secondary motion in a large amplitude meandering flume

The development of secondary motion along open-channel bends strongly affects the bed deformation and the channel plane evolution. Recent experimental results obtained at the apex section of a large amplitude meandering flume have confirmed that besides the main central circulation cell a second counter-rotating cell develops near the free surface of the outer bank. In the light of such results, in this work the attention is devoted to the analysis of the evolution of the observed secondary motion along whole bend. The analysis is conducted on the basis of flow velocity data collected in five transversal sections along half wave-length of the same large amplitude meandering flume.

Resistenze al moto di correnti in canali con vegetazione sul fondo