1,720,965 research outputs found
Risposta morfologica della spiaggia compresa tra Lido di Dante e Lido di Classe ad eventi di mareggiata
No full textThe impact of sea storms on low-lying sandy coasts may induce hazardous erosive beach and dune processes and, in the most severe situations, flooding of coastal areas which can cause, on a very limited time scale, significant changes in the littoral. The risk level increases for highly developed areas, where the negative effects on the local economy of the territory are added to the direct consequences of the physical impact of storms. In front of the rapid and continuous population growth in coastal areas, the increased human activities and the threat posed by rising sea level, understanding and forecasting the possible storm induced damage to the coastal environment may represent a useful tool in support decisions in coastal management.
In this context dunes play a role of fundamental importance in granting natural protection to the backbeach during storm events. For the areas behind the shore placed below the mean sea level (which is the case of quite all Emilia-Romagna coastal environment), dunes are at the same time the first line of defense as well as the last barrier against phenomena of marine ingression.
In the present study the response to the storm events befallen in the period between September 2008 and March 2010 is discussed in detail for one of the few remaining dune cordons along the coast of the Emilia-Romagna Region, located between Lido di Dante and Lido di Classe and characterized by an extension of about 6 km.
Storm surge phenomena and wave conditions were analyzed to identify marine storms that may induce significant morphological changes in the beach-dune system. The characteristics of extreme sea levels that occur along the northwestern Adriatic coast were identified through the examination of the longest mareographic series available, highlighting their highly seasonal pattern.
The quantification of the impact of storm surges was carried out comparing the pre and post-storm profiles, spaced a hundred meters apart, and simulating the morphological evolution of beach profiles through SBEACH numerical model. The results show that the combination of storm surge and wave conditions induces the most serious consequences for the considered physical system. The analysis clearly shows that the combination of high sea levels and average wave intensity has a decisive role in erosion and inundation processes that affect the regional coast. The study results indicate that the magnitude of the impacts caused by storm surges is generally controlled by the topographical and morphological beach features (such as slope and amplitude) as well as by dune state (ridge elevation, amount of frontal dune reservoir, distance to sea): these features may prevent extensive erosion in some areas and promote duneface retreat or washover in others.
In spite of the smaller wave heights associated to Scirocco winds, storm surges, which generally are higher during these conditions, may result in particularly dangerous effects for the resilience of the dune system due to the longer wave period depending on the morphology of the Adriatic basin.
An evaluation of the volume lost from the impact of sea storms further indicates that a system like the one located in the northern part of the coastal stretch under consideration, already severely degraded by high human impact and effects of headlong land subsidence, which in this area reaches the highest value of the entire regional coast, becomes increasingly susceptible to storm events and easier involved during less intense storm conditions
Analisi dei livelli marini estremi e delle acque alte lungo il litorale ravennate
No full textIn tutto l’Alto Adriatico i fenomeni di acqua alta espongono i territori costieri ad un elevato livello di rischio
per inondazione marina. Obiettivo del presente studio è la stima dei livelli marini estremi e dei relativi periodi
di ritorno per le aree costiere vulnerabili della Provincia di Ravenna, punto di partenza di grande rilevanza per
la Protezione Civile nella messa a punto di adeguati sistemi di previsione e di allerta.
Le osservazioni disponibili si riferiscono alle registrazioni con cadenza di 10 minuti del mareografo di Porto
Corsini (Ravenna), stazione della Rete Mareografica Nazionale, e coprono un periodo di dieci anni, dal 2000
al 2009. Il controllo di qualità e l’alta correlazione con i valori orari relativi allo stesso periodo archiviati dall’Istituzione
Centro Previsioni e Segnalazioni Maree del Comune di Venezia per la stazione di Punta della Salute
assicurano la validità dei dati utilizzati nell’analisi.
La stima dei valori estremi è stata effettuata considerando la probabilità limite congiunta degli r eventi annuali
più elevati sia della serie temporale dei livelli osservati che di quella dei residui, ottenuta rimuovendo la
marea astronomica tramite analisi armonica effettuata con il programma t_tide. La selezione è stata realizzata
considerando indipendenti valori estremi separati da almeno 78 ore, in modo da includere in un unico evento
le oscillazioni di livello dovute alle sesse che possono accompagnare i fenomeni di surge, e cercando riscontro
nelle serie temporali dei dati meteorologici ed ondametrici registrati dalle stazioni più vicine.
Il probability plot test indica un buon adattamento del modello ai dati esaminati per in corrispondenza del
quale si ottengono livelli di 0.85, 1.05 e 1.28 m e residui di 0.61, 0.79 e 1.02 m per tempi di ritorno rispettivamente
di 2, 10 e 100 anni
Morphological thresholds for the definition of the vulnerability of coastal dunes in northern Italy
No full textCoastal flooding: A copula based approach for estimating the joint probability of water levels and waves
No full textAn accurate joint probability assessment of water levels and waves is of primary importance for effective coastal flooding management even in microtidal environments subjected to severe storm surge events. A copula based approach is presented for modeling the joint distribution derived from almost six years of sea levels and waves at a site suffering from coastal flooding. The evaluation of the upper tail dependence coefficient represents an unavoidable step in the copula selection process since it provides indications on extreme dependence that cannot be neglected to reliably estimate the probability of marine inundation. Based on the results of various statistical tests and estimation of the upper tail dependence coefficient, a one-parameter extreme value copula is selected to model the dependence structure of events representing conditions at peak water levels, including wave height, incoming wave direction and season of occurrence. The joint distribution obtained is subsequently used for reliability analysis. A particular simplified application case is described for the Ravenna coast (Italy) and the probability of failure/inundation is estimated through the direct integration method. Since the failure function employed involves the wave runup depending on wave period, the joint distribution of wave height and wave period is also assessed. The study highlights the importance of taking into account all the variables involved in the flooding phenomenon for a reliable flood probability estimate. The presented methodology can be applied to the assessment of flood probability at coastal sites at risk of inundation due to the combined impact of waves and water levels
Run-up computation behind emerged breakwaters for marine storm risk assessment
No full textFlood vulnerability assessment due to marine storms is very important for integrated coastal zone management. The case study site is a highly developed area (Rimini) along the Emilia Romagna coastline, facing the north Adriatic sea in Italy. This area is composed of low sandy beaches and is completely protected by emerged breakwaters. Rimini was chosen in order to assess the vulnerability of a very important tourist resort that represents one of the most significant revenue for the regional economy. For the vulnerability assessment it was decided to consider the worst scenarios, using a joint probability of occurrence for a 1, 10 and 100 years return period storm, happening at the same time as an atmospheric surge and with the maximum spring tidal level of +0.45 m above MSL (run-up + surge + tide). The beach slope of different profiles was calculated using the a 2004-DTM (Lidar-based). The attenuation effect of the breakwaters was considered inside the run-up formula using the following method: (i) a 1-d model was used to evaluate the wave height at the seaward foot of each structure; (ii) the Van der Meer formula was applied to calculate the wave height behind structures; (iii) the calculated wave height was transported back to deep water conditions using a 1-d model. Different damage categories were created. The results reveal that, even with the one year event, most of the infrastructures are damaged and the areas behind the beach are flooded
Nuovi metodi per la cartografia del rischio da inondazione marina: l’esperienza in Emilia-Romagna
No full textNel presente contesto delle variazioni climatiche e dell’innalzamento del livello marino riveste una particolare importanza la cartografia delle zone costiere per quanto riguarda il rischio da inondazione marina. La Regione Emilia-Romagna ha recentemente completato una cartografia di dettaglio per quanto riguarda la vulnerabilità all’inondazione in condizioni di mareggiata estrema ed acqua alta. Lo studio si è avvalso delle più moderne tecnologie Lidar per la definizione di un modello digitale del terreno con maglia metrica ed ha incluso un calcolo delle massime quote di risalita della lama d’acqua in condizioni di mareggiata. Sono stati considerati eventi con periodo di ritorno di 1, 10 e 100 anni ed è stata elaborata una legenda per l’identificazione del tipo di impatto previsto, discriminando zone protette da difese costiere, zone con insediamenti, fasce dunari, etc. Lo studio ha concluso che anche un evento combinato con un alto periodo di ritorno mette già a rischio buona parte della costa in questione. Si auspica che in futuro tali risultati serviranno per la pianificazione territoriale e per scopi di mitigazione del rischio per la protezione civile. Il protocollo sviluppato verrà in futuro applicato su scala europea nell’ambito del progetto MICORE (Morphological Impact and Coastal Risk from Extreme Storm Events) finanziato dall’Unione Europea nell’ambito del 7° Programma Quadro
Degradation of a dune-ridge at a yearly time-scale:impact of human activities and occurrence of storms
No full textCartografia della vulnerabilità alle mareggiate
No full textNegli ultimi 50 anni la fascia costiera dell'Emilia-Romagna ha conosciuto un massiccio sviluppo urbano in seguito al quale alcuni processi naturali, come l'erosione delle spiagge, che da sempre hanno caratterizzato l'evoluzione del sistema litoraneo, sono divenuti fenomeni dai quali ci si deve difendere. L'erosione delle spiagge è un fenomeno riconducibile alla combinazione di diverse cause tra le quali si annoverano l'eustatismo, la subsidenza, la dinamica litoranea e la diminuzione dell'apporto solido da parte dei fiumi (Bondesan et alii, 1978). L'attenzione verso tale fenomeno in Emilia-Romagna ha prodotti importanti studi che hanno permesso di analizzare in dettaglio le diverse cause e di stabilire l'entità delle perdite della spiaggia negli ultimi 25 anni (Idroser S.p.a., 1996; ARPA Emilia-Romagna, 2002, 2008)
Critical storm thresholds for significant morphological changes and damage along the Emilia-Romagna coastline, Italy
No full textThe definition of storm morphological thresholds along the coast of the Emilia-Romagna Region strictly depends on its configuration and variability. The region is located in northern Italy, facing the Adriatic Sea. The coastline is characterised by very different levels of economic development, ranging from natural zones with dunes to highly developed stretches protected by breakwaters and groynes. The Integrated Coastal Zone Management effort is mainly concentrated on preserving urban areas that generate significant income for the regional economy. Natural areas, while small in comparison to the urbanised zone, are important for environment preservation. Because of such a multiplicity of issues at stake, it was decided to produce two different thresholds: one for the morphological impact on natural sectors and another for inundation and damage to structures along urbanised zones.
The “forcing” component of the threshold definition for natural areas was calculated by summing the effects of surge + tide + waves (run-up elevation) to find the Maximum Water Level (MWL) reached by the sea during one, ten and one-hundred year storm return periods. For urbanised zones, historical storm information was collected starting from the 1960s in order to identify the forcing conditions causing real damages. Each storm was classified in terms of wave height, period, direction and surge level. Morphological information were obtained from Lidar flights performed in 2003 and 2004 and from direct surveys undertaken in September 2008 and February 2009 as part of the monitoring programme for the MICORE Project.
The computed MWL for each return period was then compared to beach elevations along natural areas in order to calculate the Dune Stability Factor (DSF), an index that accounts for the eroded sediment volume above the MWL during a storm. Based on analysis along 41 profile lines at a 500 m spacing, it was found that the 1-in-1 year return period wave height + 1-in-1 year return period surge are able to erode and/or overwash 2/3 of the dunes.
The historical storm hydrodynamic information was used to estimate which wave and surge conditions are able to inundate at least 2/3 of the beach profiles. The MWL was again compared to beach elevations, this time along 63 anthropogenic profiles spaced 500 m apart (or 1/3 of the urbanised coastline). It was found that a wave heights >= 2 m and surge + tide levels >= 0.7 m are able to flood between 18% and 36% of the built-up coast.
The defined thresholds are related to the present coastal characteristics and are not “static”, meaning that they are likely to change according to future evolution of the coastline. They are very important because they can be used as thresholds to issue warnings and alert the Civil Protection. Moreover they are the first thresholds defined for the Emilia-Romagna coastline and will be used as starting values to generate “dynamic” thresholds based on numerical model predictions of morphological change for a given wave and surge level
I nuovi studi su marreggiate e fenomeni erosivi
No full textNegli ultimi anni è cresciuta l'attenzione per il monitoraggio dei fenomeni a forte impatto sul sistema costiero. Il progetto europeo Micore prevede lo sviluppo di un sistema previsionale per la comprensione e previsione dei fenomeni erosivi sulla costa anche in Emilia-Romagna. I risultati per l'inverno 2009-2010 hanno evidenziato il contributo delle acque alte per i fenomeni erosivi e hanno confermato la necessità di un sistema di previsione attivo e di continuare le pratiche di protezione in atto
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