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Evolution and stability of tidal inlets: a comparison between two natural cases along human-affected coastlines
Get PDFIl focus della tesi l'evoluzione di due bocche lagunari non stabilizzate, le bocche di Ancão e S. Andrea, situate in due diversi sistemi multi-inlet influenzati dall'uomo. Vorremmo analizzare le modalità secondo la quali le caratteristiche naturali delle bocche possono essere indirettamente condizionate dalla presenza dell'uomo e dagli eventi naturali. L'obiettivo è quello di riconoscere i conflitti generati dal comportamento libero (senza restrizioni) dei tidal inlet studiati in relazione alle esigenze e agli usi dell'uomo. Attraverso un'analisi di dati morfologici e idrodinamici, vengono proposte alcune linee guida in relazione ai cambiamenti morfologici delle bocche e del sistema di appartenenza.
La bocca di Ancão è un'apertura artificiale, rilocata lungo il suo conosciuto passato percorso migratorio. Una volta aperta, gli è permesso di riprendere naturalmente il suo percorso di migrazione. Si tratta di una piccola bocca, migrante verso est, nel sistema multi-inlet della laguna mesotidale di Ria Formosa (sud del Portogallo). La laguna è stata interessata da alcuni cospicui interventi antropici che hanno modificato l'ex condizione idrodinamica. La bocca di Ancão. Man mano che la migrazione di Ancão procede verso est, la bocca riduce gradualmente la connessione con le altre bocche, diventando più indipendente. L’area di Ancão è costantemente monitorata dal 1997. I dati idro-morfodinamici sono stati raccolti durante diversi rilevamenti topo-batimetrici. I parametri morfologici e i tassi di migrazione sono stati successivamente misurati e correlati con i dati di altezza d'onda e di marea, considerando anche eventuali storm surge, al fine di valutare l'importanza dei diversi meccanismi nelle fasi evolutive della bocca. Il trend di migrazione e le variazioni dei principali dati morfodinamici sembrano essere legati principalmente alle condizioni dominanti del mare da sud-ovest, dimostrando la predominanza del clima d'onda sulle correnti di marea. La natura non vincolata della bocca di Ancão, consente di rispondere alle forze naturali attraverso la migrazione del suo canale principale. Ciò crea problemi nella circolazione dell'acqua nell'area di laguna retrostante oltre a ostacolare la navigazione. Per queste ragioni, la pozione della bocca di Ancão è attualmente controllata e gestita con periodiche rilocazioni updrift, per mantenere la navigabilità, la buona ossigenazione e lo scambio di nutrienti nell’area lagunare.
Il secondo caso studio è la bocca naturale di S. Andrea, situata nella Laguna di Marano e Grado (Mare Adriatico, Italia), un altro sistema multiplo. Questo differisce dalla laguna portoghese per il suo regime microtidale e un poco energico clima d’onda. Nel corso del ventesimo secolo, le bonifiche di terreni, il dragaggio dei canali e, soprattutto, le stabilizzazioni di bocche, hanno causato significativi cambiamenti all'interno del sistema. Questi sono poi stati amplificati da estremi eventi naturali. La bocca di S. Andrea si trova tra le due bocche più efficienti della laguna. Gli interventi, artificiali e naturali, hanno portato ad un aumento dell'efficienza di queste bocche a scapito di quella di S. Andrea. Negli ultimi due decenni i dati di monitoraggio mostrano un progressivo insabbiamento del canale principale e una diminuzione della sua sezione trasversale e del prisma di marea. Al contrario, il volume di delta di riflusso rimane sorprendentemente invariato. La bassa energia d’onda che colpisce questa area è insufficiente a rielaborare il delta. Anche se non cambia la sua posizione, la bocca di S. Andrea potrebbe mostrare gli stessi problemi/conflitti della bocca di Ancão (scarsa circolazione, cattiva ossigenazione, difficile navigazione). Per il momento i problemi causati dall'atrofia dell'entrata non hanno ancora raggiunto un livello di criticità, ma se la riduzione del prisma continuasse, in futuro occorrerebbe adottare alcune misure di gestione.The evolution of two unconstrained tidal inlets (not fixed), Ancão and S. Andrea Inlets, located in different human-affected multi-tidal inlet systems is considered in this thesis. The focus is on how natural features of tidal inlets can be indirectly conditioned by the presence of man and by the natural events in the system. The aim is to understand the conflicts generated by the unconstrained behaviour of the inlets in relation to human needs and uses. Through an analysis of morphological and hydrodynamic data, some guidelines are proposed in relation to the changes in the inlets and in the system.
Ancão Inlet is an artificial inlet, opened (relocated) on the known natural migration path. Once opened, it is allowed to migrate naturally. It is a small eastward-migrating inlet in the mesotidal multi tidal inlets system of Ria Formosa (south of Portugal). The lagoon system has been affected by some strong human interventions that modified the former hydrodynamic condition. The most important changes were due to the opening and stabilization of Faro-Olhão Inlet that caused the narrowing of the nearby Armona inlet. Ancão Inlet, migrating toward the east, the inlet gradually diminishes the connection with the other inlets, becoming more and more independent. The inlet region has been constantly monitored since 1997. Hydro-morphodynamic data were collected during several topo-bathymetric surveys. Morphological parameters and migration rates were subsequently measured and correlated with wave and water level data to evaluate the importance of different mechanisms in the evolutionary phases of the inlet. The migration trend and the variations of the main morphodynamic data seem to be mainly related to the dominant southwest sea conditions, demonstrating the predominance of the wave climate over tidal currents. The unconstrained nature of the inlet allows it to respond to natural forcings by channel migration. This creates some problems in the water circulation in the backbarrier area, as well as hampering navigation. For these reasons, the position of Ancão Inlet is currently controlled by periodic updrift relocation, to maintain navigability and good oxygen and nutrient exchange. Additional management provisions are proposed and discussed.
The second study case is the small natural S. Andrea Inlet, located in Italy, in the Marano and Grado Lagoon (MGL, North Adriatic Sea), another multi tidal inlet system This differs from the Ria Formosa system because of the microtidal regime and low wave-dominance, making this lagoon a relatively tide-dominated environment. During the 20th century, land reclamations, waterway dredging and, especially, inlet stabilizations, caused significant changes within the system. These may have been enhanced by natural extreme events. S. Andrea Inlet is located between the two most efficient inlets in the lagoon i.e. Lignano and Buso Inlets, whose artificial stabilization began in the 1960s in order to improve navigability. These factors led to an increase of efficiency of those inlets at the expense of the S. Andrea Inlet. During the last two decades, morphological monitoring data shows a progressive shallowing of the main ebb channel, as well as a halving of the cross section area and, consequently, tidal prism. In contrast, the ebb tidal delta volume, although compressed in its own area, remained surprisingly unchanged. The low wave energy that affects this region is insufficient to rework the delta. Although it does not changed its position, S. Andrea Inlet could potentially suffer the same conflicts as Ancão Inlet: poor water circulation and thus a bad oxygenation of the backbarrier area, and a difficult navigation of the channel. Considering the limited extent of the S. Andrea basin, the issues caused by the atrophy of the inlet are not yet critical, but if the prism reduction continues, some possible management measures must be adopted
Evolution of a relocated inlet migrating naturally along an open coast
No full textAncão Inlet is a small migrating inlet that was relocated in 1997 and has been monitored since then. In October 2015, it was about to conclude its third eastward migrating cycle since the 1940s. Morphological parameters and migration rates were correlated with oceanographic settings to evaluate the importance of different mechanisms in the evolutionary phases of the inlet. The migration trend is related to the dominant southwest sea conditions, inducing the alongshore sediment transport from west to east. The inherited features of the downdrift side area were also considered as rate of migration constraints. In this paper, we show how storm events, a constant longshore sediment supply from the west, and a lower downdrift barrier island volume control migration rates, noting that inlet efficiency is also strongly influenced by the reshaping of the barrier area
UAV high resolution photogrammetry applied to coastal geomorphology: a dune and a barrier island case
No full textFrom rapid coastal collapse to slow sedimentary recovery: The morphological ups and downs of the modern Po Delta
No full textAs is the case with many deltas in the world, the Po Delta (Italy) and its barrier systems have experienced severe modifications over the last century as a consequence of anthropogenic subsidence and river input decrease. The interruption of subsurface fluid withdrawals in the early 1960s created an opportunity to evaluate the effects of the subsequent subsidence decrease along the 11 km of beaches and 45 km of barrier islands of the Po Delta, and improve the understanding of coastal system response to relative sea level rise. To this aim, shoreline and bathymetric multi-decadal dataset were coupled with the local rate of subsidence and classified with a geomorphic - response approach. From 1954-78, a mean shoreline variation of −224 m (−9.34 m y−1) occurred under high rates of subsidence (14–43 mm y−1) with a diffuse process of landward barrier rollover (up to 1124 m), frequently associated with break-up. This phase is evidenced by the diffuse sinking of the shoreface (up to 4 m), the negative upper-shoreface sediment budget and the parallel drowning of the cross-shore profiles highlighted by the 1968–2008 bathymetric dataset. Despite the loss of altimetry and shoreline retreat being almost irrecoverable, during the period from 1978 to 1996 and 1996 to 2014 barrier islands experienced a stabilisation in response to a decrease in the subsidence rates down to 6 mm y−1. The mean rates of shoreline changes (−0.25 and + 1.51 m y−1 respectively) are the results of different local behaviour with progressively dominant longshore processes and progradation at the most active fluvial branches. The most recent bathymetric data (2008–2014) confirm this reversal trend, both in the altimetry differences and in the upper shoreface sediment budget. This trend is at odds with signals from many of the world's deltas and represents an important issue for the present and future coastal management and adaptation plans
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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