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Attuali conoscenze sull’evoluzione recente di corsi d’acqua del Bacino Padano ed implicazioni per la gestione e riqualificazione fluviale
No full textViene effettuata una breve rassegna sulle variazioni morfologiche di alvei fluviali dell’Italia settentrionale, con particolare riferimento ai corsi d’acqua nel bacino del Fiume Po, in base alla bibliografia disponibile fino agli ultimi anni. Tale rassegna mette in evidenza come gran parte dei corsi d’acqua in questione abbiano subito due principali tipi di variazioni, un abbassamento del fondo ed un restringimento dell’alveo attivo, accompagnati spesso da una trasformazione della morfologia complessiva da tipologie a canali intrecciati (o pluricursali) verso tipologie a canale singolo (o monocursali). Inoltre si richiamano alcuni concetti che presentano importanti implicazioni ed applicazioni future delle conoscenze sull’evoluzione morfologica degli alvei fluviali alla loro gestione e riqualificazione
Evoluzione morfologica di alvei fluviali mobili nel settore occidentale del Bacino Padano (River channel adjustment in the Western Po System (Northern Italy))
No full textThe research on channel changes in Italian rivers has pointed out processes of incision and narrowing during the last fifty years. The definition of the causes and the practical implications of such variations has stimulated a wish to know more about this phenomenon.
As study cases for analysing the trends in the western sector of the Po system, three Po River tributaries have been selected: the rivers Stura di Lanzo and Orco, both from the Alps, and Trebbia, from the Apennines, flowing into the Po River, respectively at 205 m, 177 m and 43 m a.s.l.. Through GIS procedures (for Orco and Trebbia) and digitizer elaboration (for Stura di Lanzo) and using a topographic map on a 1:10.000 scale as a base layer, the morphological changes of the river channel have been deduced comparing historical maps dating from the end of the 1880s to the 1950s (on a 1:25.000 scale), aerial photographs dating from the 1950s (at scales ranging
between 1:45.000 and 1:5.000) and satellite images (70 cm resolution); topographic observation and field surveys have allowed us to verify the present situation.
The Stura di Lanzo River develops a braided reach 10.5 km long in the upper alluvial plain. The braided pattern was modelled in coarse gravels. The largest narrowing modifications took place until the 1990s, due to sediment gravel mining. This adjustment caused a width reduction of 80% (1881-1989) along the braided reach that was previously 600 m wide and a 4 m deep channel incision that locally downcuts the fine sediments of buried lacustrine deposits. A local single channel modelling has definitively started since the 1980s, due to the fact that the fine sediments in the bed are unable to maintain the former braided pattern.
The studied reach of the Orco River (25 km long, in the middle-lower plain), is incised into a fluvioglacial fan and the Po alluvial plain. Over the 19th century the river channel showed a multi-thread morphology, with a braiding intensity variable in space and time. The progressive simplification of the pattern, already observed since the end of the 19th century, has undergone a diffuse acceleration starting from the 1950s (average reduction of 60% in width over the 1881-1990 period). The analysis of human intervention and floods pointed out two opposing roles: the role of man in starting or accelerating the process of the river pattern simplification; the role of the
floods in attempting to restore the previous pattern in the plain.
The investigated reach of the Trebbia River, 31 km long, is characterized by a braided morphology. A continuous narrowing of the channel has appeared since 1877 (average reduction of 65% in width over the 1877-1990 period). This narrowing reached reductions of 58% between 1954 and 1990 (during the period of most intense gravel mining) and was accompanied by a channel incision of 2-4
meters.
In all studied rivers the channel narrowing, which occurred up to 1990, was characterized by a lengthening of the channel axis. Starting from 1990, the rivers showed a reversal of the previous trend, because channel widening took place, concomitant to a shortening of the channel axis. In the alpine watercourses the opposite trend could be a result of the extreme flood that occurred in 2000; in Trebbia River, the almost total cutback of large-scale gravel mining must be considered
Towards a channel evolution model for alluvial rivers in Italy
No full textRecent studies carried out in twelve rivers have allowed to re-examine existing conceptual models of channel evolution for Italian rivers. The presence of three main phases of channel evolution is confirmed for some river reaches, while in other reaches the third phase (generally occurring over the last 15-20 years) is still unclear since river channels could be already in a quasi-equilibrium condition. Besides, while the first phases of adjustment were caused mainly by alterations of sediment regime, the very recent channel evolution appears to be strongly controlled also by flood magnitude and frequenc
Channel adjustments in northern and central Italy over the last 200 years
No full textThis paper deals with channel evolution over the past 200 yr in 12 selected streams in northern and central Italy and aims at reconstructing the evolutionary trends (e.g., trends of channel width and bed elevation) and understanding the causes of channel
adjustments. The selected streams have been studied using various sources and methods (historical maps, aerial photographs, topographic surveys, and geomorphological
surveys). The selected rivers have undergone almost the same processes in terms of temporal trends; however, the magnitude of adjustments varies according to several factors, such as original channel morphology. Initially, river channels underwent a
long phase of narrowing (up to 80%) and incision (up to 8–10 m), which started at the end of the nineteenth century and was intense from the 1950s to the 1980s. Then, overthe last 15–20 yr, channel widening and sedimentation, or bed-level stabilization, have become the dominant processes in most of the rivers. Different human interventions have been identifi ed as the causes of channel adjustments in Italian rivers (sediment mining, channelization, dams, reforestation, and torrent control works). Such interventions have caused a dramatic alteration of the sediment regime, whereas effects on channel-forming discharges have seldom been observed. Some notable implications for river management and restoration are (1) the state of rivers before major human disturbances and channel adjustments can rarely be taken as a reference, as at present rivers are far from their pristine condition; and (2) sediment management is and will be a key issue in such fl uvial systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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