Random wave run-up with a physically-based Lagrangian shoreline model

Abstract In the present paper the run-up of random waves was calculated by means of a numerical method. In situ measurements based on a video imaging technique have been used for the validation of the present numerical model. The on-site run-up measurements have been carried out at Lido Signorino beach, near Marsala, Italy,along a transect, normal to the shore. A video camera and a linear array of rods have been used to obtain field data. Numerical simulations with a 1DH Boussinesq-type of model for breaking waves which takes into account the wave run-up by means of a Lagrangian shoreline model have been carried out. In such simulations random waves of given spectrum have been propagated in…

Flow hydraulic characteristics determining the occurrence of either smooth or abrupt sewer pressurization

Laboratory experiments showed that pipe pressurization consequent on a drastic reduction in the downstream discharge can occur either by a gradual rising of the free-surface (“smooth” pressurization) or by propagation of a front filling the whole cross-section (“abrupt” pressurization). This study examines the free-surface flow characteristics that determine smooth or abrupt pressurization pattern through a theoretical approach using dimensionless variables. A critical flow rate value, which separates the pressurization patterns, exists for any given pipe diameter. For flow rates higher than this specific value, only abrupt pressurization occurs. For lower flow rates, either smooth or abrup…

Flow and turbulence characteristics in the presence of a discontinuous ligulate seagrass prairie

Wave energy assessment in Sicily (Italy)

Abstract This research presents an estimation of wave energy potential in Sicily (Italy) carried out using both buoy wave measurements from Rete Ondametrica Nazionale (RON), the Italian Government wave buoy network, and wave parameter data by ERA-INTERIM, a recent meteorological reanalysis project of the European Centre for Medium-Range Weather Forecasts (ECMWF). Starting from these offshore data, we first identified the western part of Sicily as the area with a higher availability of offshore wave energy; subsequently, we selected a study area in the western part of the south coast and assessed the nearshore potential energy by performing propagation using a spectral model (SWAN). The near…

Numerical Comparison of the Hydrological Response of Different Permeable Pavements in Urban Area

Floods are becoming more frequent, especially in urban environments where most of the surface is waterproofed. Permeable pavement (PP) can be applied as low impact development (LID) systems for runoff mitigation in urban areas. Their effectiveness can be assessed, case by case, by numerical simulations. In this study, the effectiveness of mitigating runoff of different permeable pavements has been evaluated. In particular, porous asphalt (PA), pervious concrete (PC), permeable interlocking concrete pavement (PICP) and grid pavement (GP) have been investigated using EPA Storm Water Management Model (SWMM) software. To this aim, a car parking area located in the University Campus of Palermo (…

Modellazione matematica delle oscillazioni di pressione nella pressurizzazione di un condotto fognario

Si esamina il transitorio di pressurizzazione di un condotto fognario, un fenomeno abbastanza frequente nelle reti di drenaggio urbano. Durante tale transitorio si attuano delle intense oscillazioni di pressione, solitamente interpretate addirittura come “fenomeni di colpo d’ariete” e ritenute in grado di danneggia-re la rete. La natura di tali oscillazioni non è ancora chiara, anche se esse sono generalmente imputate, con modalità non definite, alla interferenza fra la corrente liquida e le sacche d’aria di notevoli dimen-sioni imprigionate dalla corrente liquida contro il cielo del condotto. Nella presente memoria, sulla base di precedenti esperienze di laboratorio, si affronta la modella…

Analysis of wave energy conversion process

Since wave energy conversion technologies are developing due to the depletion of fossil fuels and due to their hazardous effects on the environment, an important and unexploited source of energy is wave energy. The paper proposes to compare theoretical data obtained using specialized software and data obtained via laboratory measurements using a scale model, regarding the mechanical torque generated at the axis of the electric motor. The data collected represent the kinetic and potential energy, simulating Black Sea waves using an installation proposed to be patented, an installation that converts off-shore wave energy.

SEWER PRESSURIZATION MODELLING BY A RIGID-COLUMN METHOD

Mathematical modelling of pressurization transient by a rigid-column method is studied based on previous laboratory testing. Of course, such a method is not able to simulate the experimental intense pressure oscillations; however, it is considerably simpler than other feasible methods and more easily implementable within drainage network models. Starting from this operative point of view, the paper aims at recognizing “what” and “how much” of the transient can be simulated by a rigid-column method. Actually, better results were obtained than it was expected. The model proves to be successful in simulation of the filling pipe stage as well as the stabilization stage of flow to the final stea…

Experimental investigation on pressurization transient of a drainage sewer

Applicazione alla verifica delle reti di condotte in una rivisitazione del capitolo del moto uniforme turbolento nelle correnti liquide

Una formula pseudo lineare esprime l’equazione del moto uniforme turbolento di un liquido viscoso, e consente di risolvere fedelmente, senza iterazioni né ricorsi a grafici o a tabelle, entrambi i “problemi di verifica” delle correnti nei tubi e si presta bene al “problema di progetto”. Il risultato è dovuto al ruolo di un nuovo parametro che aggiunto a quello che surroga la scabrezza relativa costituisce una coppia caratterizzante il sistema tubo scabro - liquido viscoso. Entrambi intervengono nella legge di resistenza di Colebrook-White ridotta ad una forma facile a ricordarsi e avente il significato concettuale di misurare il rapporto fra due variabili numeriche: esse sono proporzionali …

Flow resistance of a very dense Posidonia oceanica grassland in shallow water

Ability of software SWMM to simulate sewer smooth pressurization transient

As a consequence of heavy rainfall events or network malfunctioning, filling of sewers (pressurization) and network overflowing may occur. Several models are commonly used to simulate floods in drainage networks and their results are usually thought to be reliable and robust. Actually, mathematical models based on the momentum equation appear to be more suitable in correctly simulating the pressurization moving jump but models based on the energy equation are much more popular because of their greater simplicity in comparison to the former ones. In this paper, on the basis of laboratory pipe tests, the ability of software SWMM (Storm Water Management Model, probably the most popular softwar…

Analisi statistica della marea meteorologica sui tre versanti siciliani

La progettazione di porti, di opere di difesa e di protezione dei litorali e la pianificazione delle attività umane sulla costa richiedono una buona conoscenza delle fluttuazioni del livello del mare. Quest’ultimo è determinato dalla somma di due contributi principali: la marea astronomica, che essendo periodica è di facile predizione, e quella meteorologica, che viene considerata aleatoria. Nel presente lavoro, a partire dalle misure del livello idrico registrate dai mareografi dei porti di Catania, Palermo e Porto Empedocle nel periodo 1999-2010, sono state ricostruite le rispettive maree meteorologiche ed analizzate statisticamente al fine di trovare la migliore distribuzione di probabil…

Analysis of tide measurements in a Sicilian harbour

Designing of ports and coastal protection works as well as planning of coastal human activities require knowledge of tidal oscillations. The latter vary noticeably from site to site and present an “astronomic” component, which is roughly periodic, and a “meteorological” component which is usually considered as random. In this paper, the tidal oscillations observed in a Sicilian harbour in the period 1999-2009 are analysed statistically, in order to recognize a probability distribution which allows one to predict the highest tidal levels. First, the measurements are used to obtain, for each year, the astronomic tide by the harmonic analysis by the software package T_TIDE. The difference betw…

Modellazione matematica del transitorio di pressurizzazione di un condotto fognario

INFLUENCE OF POSIDONIA OCEANICA MEADOW DENSITY ON FLOW RESISTANCE IN SHALLOW WATERS

Aquatic vegetation considerably affects circulation in water bodies with influence increasing as the depth decreases. On the other hand, increasing use of mathematical circulation models for management of coastal sea waters, lagoons and marshes requires determination of such effects and in particular of flow resistance. A typical plant of inshore sandy beds, less than 40 m deep, in the Mediterranean Sea is Posidonia oceanica, which is constituted by a tuft of very thin and flexible ribbon-like leaves about 1 cm wide and up to 1.5 m long. This plant forms meadows with areal density usually ranging between 500 and 1000 plants/m2. Because of its characteristics, Posidonia oceanica constitutes …

Hydraulic jumps at drop and abrupt enlargement in rectangular channel

The different types of hydraulic jumps that occur in a rectangular channel at an abrupt increase in section are experimentally studied. The abrupt section increase is due to both a drop and an increase in the channel width. Experiments were carried out with three different values of the ratio L/l between the channel widths respectively downstream and upstream of the abrupt section increase. For each L/l value five values of Froude number F1, of the supercritical flow upstream of the section increase were considered, and for each of them live values of the depth y1 of the same flow. The experiments showed that, as the depth y2 of the downstream subcritical flow increases, several types of hy…

Particle tracking in a gap of aquatic vegetation meadow

Aquatic vegetation considerably affects the flow field in water bodies, with influence increasing as the depth decreases. As a consequence, vegetation also affects suspended particle transport. In inshore sandy beds less than 40 m deep of the Mediterranean Sea, meadows of Posidonia oceanica are widespread. This plant is constituted by a tuft of very thin and flexible ribbon-like leaves about 1 cm wide and up to 1.5 m long; the meadow areal density can reach 1000-1200 plant/m2. Frequently, such meadows are not continuous but vegetated areas alternate with sand strips (“gaps”). The presence of such discontinuities noticeably affects the flow field and gaps can actually act as particle traps. …

INFLUENZA DELLA DENSITÀ DI UN PRATO DI POSIDONIA OCEANICA SULLA RESISTENZA AL MOTO IN ACQUE BASSE

L’impiego di modelli di circolazione per la gestione di acque costiere, quali lagune, paludi, ecc., richiede la valutazione degli effetti della vegetazione acquatica, i quali crescono al diminuire della profondità idrica. Una pianta tipica dei fondi sabbiosi sotto costa del Mar Mediterraneo è la Posidonia oceanica, la quale per le sue caratteristiche (ciuffi di foglie nastriformi molto flessibili e lunghe fino a 1,5 m) costituisce una particolare scabrezza, poiché al crescere della velocità della corrente le foglie si incurvano sempre più fino ad adagiarsi sul fondo. Nella presente memoria si rielaborano tutti insieme i dati sperimentali di due precedenti indagini degli scriventi, riguardan…

Experimental investigation on a geocontainer submerged reef

Geotextile sand containers (GSC) have been used as permanent construction elements in coastal works for more than 20 years,becoming more and more popular as an alternative to the most typical coastal structures. Aim of this work is to analyze the hydrodynamic, stability and morphodynamic response of a GSC submerged reef by means of an experimental campaign. The first investigated aspect concerned the hydrodynamics. The reflection and transmission coefficients for regular and random waves were determined: the reflection coefficient decreases with increasing of kh; the transmission coefficient decreases with the increase of the incident wave. As regards the stability of the structure, it was …

Trasporto di particelle sospese in una discontinuità di un prato di vegetazione acquatica

La vegetazione acquatica influenza sensibilmente il campo di moto e il trasporto solido nei corpi idrici. Nelle aree sottocosta del Mar Mediterraneo sono molto diffusi i prati di Posidonia oceanica, una pianta costituita da un ciuffo di foglie nastriformi molto lunghe e flessibili. Spesso i prati sono interrotti da frequenti strisce di sabbia, e tali discontinuità, modificando sensibilmente il campo di moto, possono agire come “trappole” per i sedimenti. Nella presente memoria, sulla base di un campo di moto sperimentale, si simula numericamente il trasporto di particelle sospese in una tale discontinuità. A tal fine si adotta un semplice modello lagrangiano che assume assenza di velocità r…

Mathematical modelling of pressure oscillations in sewer pressurization

La pressurizzazione di un condotto fognario: una indagine sperimentale

On the influence of flexible vegetation on flow fields in shallow water: a flume experiment

Ability of Preissmann slot scheme to simulate smooth pressurisation transient in sewers

Urban drainage networks are generally designed to operate in a free-surface flow condition. However, as a consequence of heavy rainfall events or network malfunctioning, filling of sewers (pressurization) and network overflowing may occur. Several softwares are commonly used to simulate floods in drainage networks and their results are usually thought to be reliable and robust. However, no specific studies have been carried out on the behaviour of these softwares during the pressurization transient. Actually, mathematical models based on the momentum equation appear to be more suitable in correctly simulating the pressurization moving jump but models based on the energy equation are much mo…

Flow resistance ofPosidonia oceanicain shallow water

Management of coastal waters and lagoons by mathematical circulation models requires determination of the hydraulic resistance of submerged vegetation. A plant typical of sandy coastal bottoms in the Mediterranean Sea is Posidonia oceanica, which is constituted by very thin and flexible ribbon-like leaves, about 1 cm wide and up to 1.5 m long, and usually covers the bottom with a density of 500-1000 plants/ m2. From the hydraulic viewpoint, P. oceanica constitutes a particular roughness, because, as the velocity increases, the leaves bend more and more until they lie down on the bottom. Although P. oceanica is widespread, in the technical literature it is difficult to find indications about…

Resistenza al moto di un fondo ricoperto da Posidonia Oceanica: confronto fra due densità areali delle piante

Storm sewer pressurization transient – an experimental investigation

Pipe pressurization is examined experimentally by 144 laboratory experiments in a circular tilting pipe between two tanks, in which the transient was triggered by sudden closing of the downstream tank outlet. The experiments cover ranges of values of slope, velocity and filling ratio of the open-channel flow not explored in previous studies. Situations involving considerable air quantity and consequent intense pressure oscillations were also reproduced. Two different pressurization patterns, defined as “smooth” and “abrupt”, were observed, but only the abrupt pattern produced intense pressure oscillations. The comparison among all the abrupt pressurization surges showed how the oscillations…

Evaluation of porous asphalt hydrological performances through rainfall-runoff modelling by EPA SWMM

Over the last few decades, the increase in extreme weather events has caused urban floods to become more and more frequent, with increased risks for road users. Among the different types of pavement structures, permeable pavements (PPs) can effectively increase the hydraulic resilience of the cities since they are specifically designed for reducing runoff by allowing water to infiltrate and be discharged into the soil and/or by drains. This study aims at evaluating the hydrological performance of a Porous Asphalt (PA) using numerical simulations for a case study carried out using EPA SWMM (Storm Water Management Model) software. Several simulations have been carried out, considering differe…

Log velocity profile and bottom displacement for a flow over a very flexible submerged canopy

Management of shallow lagoons and salt marsh environments usually requires use of numerical models in order to understand the hydrodynamic characteristics of these basins. In order for these models to give reliable results one has to have good knowledge of the interaction between the flow and the aquatic vegetation, which strongly alters the hydrodynamic characteristics. Many experimental and theoretical studies are available in the technical literature, but, because of the very different vegetation and flow characteristics, they do not yet allow one to have a clear and general knowledge of the phenomena, in terms of both flow resistance and velocity distribution. The latter is very importa…

Present-day use of an empirical wave prediction method

Knowledge of the offshore wave climate is key to the design of coastal engineering structures and to the study of shoreline evolution. To date, the available wave data have been limited both in time and space; even though there are several options for obtaining wave data calculated using complex numerical models at basin scale, design issues can in some cases be solved by means of simpler models. This paper shows whether, under certain conditions and in an enclosed basin, an old empirical model can provide results that are good enough to determine the design condition necessary for engineering purposes. The empirical model chosen to answer this question is called Sverdrup–Munk–Bretschneide…

CRITICAL ANALYSIS OF SHORELINE LOCALIZATION METHODS BY MEANS OF AERIAL OR SATELLITE IMAGERY ON MEDITERRANEAN SANDY BEACHES

Shoreline localization is fundamental for designing and planning shore protection works as well as for managing and monitoring various anthropic activities along the coast. The sea-land boundary, however, changes continually with time because of waves and tides, which makes the shoreline detection complex and dubious and the boundary line finally assumed can only be conventional. In the last few decades the use of several geomorphologic indicators has been proposed, such as the berm above sea level, the groundwater exit point, historic high tide levels, etc., but the aim has not been achieved yet. Among the methods used, analysis of aerial and satellite imagery is common, in particular when…

Confronto fra valutazioni del run-up fatte con un modello matematico e una formula empirica con misure di campo

La posizione planimetrica della linea di riva, soli tamente, viene determinata attraverso l’uso di immagini aeree ed utilizzata pe r la ricostruzione dell’evoluzione storica dei litorali. Tuttavia, le informazioni est ratte da tali immagini, descrivendo il confine istantaneo acqua-terra, consentono l’indivi duazione della linea di riva esclusivamente come limite asciutto-bagnato proprio nel momento della ripresa. Per una più corretta localizzazione della linea di riva , è quindi necessario quantificare, oltre agli effetti di marea e di trasporto solido, gli effetti prodotti dal moto ondoso su tale posizione e in particolare il cosiddetto ru n-up. Nel presente lavoro si studia il run-up in u…