1,721,085 research outputs found
Multi-thread river channels: A perspective on changing European alpine river systems
No full textRivers are natural systems whose planform
pattern in alluvial reaches reflects a balance between
three fundamental ingredients: flow energy, sediment
calibre and supply, and vegetation. Whilst early
research on river channel classification emphasised
flow (stream power) and sediment controls, the
impact of vegetation is now recognised in increasingly
detailed classification schemes. Different planform
patterns are more or less sensitive to changes in these
three fundamental ingredients, which in the absence
of human interventions all respond to changes in
climate, allowing different morphological configurations
to evolve and in some cases shift from one
planform style to another. Multi-thread, braided and
transitional river channel styles are common in European
regions where conditions for the development of
these planform styles, notably high bed material
supply and steep channel gradients, exist. However,
widespread, intense human impacts on European
river systems, particularly over recent centuries, have
caused major changes in river styles. Human activities
impact on all three major controls on channel pattern:
flow regime, sediment regime, vegetation (both riparian
and catchment-wide). Whilst the mix of human
activities may vary greatly between catchments,
research from across Europe on the historical evolution
of river systems has identified consistent trends in
channel pattern change, particularly within rivers
draining the Alps. These trends involve periods of
narrowing and widening, and also switching between
multi-thread and single-thread styles. Although flow
regulation is often the key focus of explanations for
human-induced channel change, our review suggests
that human manipulation of sediment supply is a
major, possibly the dominant, causal factor. We also
suggest that “engineering” by riparian trees can
accelerate transitions in pattern induced by flow and
sediment change and can also shift transition thresholds,
offering a new perspective for interpretation of
channel change in addition to the focus on flow and
sediment regime within existing models. Whilst the
development of planform classifications of increasing
complexity have been crucial in developing terminology
and highlighting the main factors that control
channel styles, additional approaches are needed to
understand, predict and manage European Alpine
river systems. A combination of field, laboratory and
numerical modeling approaches are needed to advance
the process understanding that is necessary to
anticipate river landscape, particularly planform,
changes and thus to make ecologically soundmanagement
choices
Analysis of the large scale dynamics of the Tagliamento River (Italy)
No full textIn the last century human activities have strongly affected the natural river behaviour often constraining complex
patterns into more manageable single-thread channels with the aim to enhance conveyance of water flow and
floods. In much of the developed world, the remarkable degree of spatio-temporal heterogeneity characterising
riverine landscapes has been masked by a long history of river engineering. Floodplain reaches, which exhibit
the highest heterogeneity in their natural state, have been the most severely altered.
The present work is focused on braided rivers whose multiple-thread pattern is related to a highly complex
eco-morphodynamism. The Tagliamento River (Italy), even though it has undergone morphological changes
due to human activities, still displays semi-natural morphodynamic behaviour that would have characterised
the pristine state of the lower valley sections of several alpine rivers. It, therefore, offers the rare opportunity to
investigate the intrinsic dynamics of braided streams.
This study is motivated by the need to recognize and maintain this eco-morphodynamism which prevents
habitat degradation and is therefore crucial to the maintenance of ecological integrity.
An analysis of island and active corridor dynamics is presented for a 16 km island-braided reach of the
gravel-bed Tagliamento River based upon information extracted from three map and 9 aerial photograph
sources, encompassing the period from 1803-present.
The active corridor width showed a general decline over the study period but with some recent widening.
Changes in island extent were achieved by rapid island turnover, which reached a maximum rate of over 50%
per annum. Very few island surfaces were found to persist for more than 24 years.
Despite this enormous dynamism and apparent cyclic behaviour, between 1944/6 and 2005 the ratio of island
area to active corridor area remained relatively constant at around 0.08 and supported a consistently high
bankfull shoreline to downstream length ratio of around 6 km·km-1
ISLAND DYNAMICS IN A BRAIDED RIVER FROM ANALYSIS OF HISTORICAL MAPS AND AIR PHOTOGRAPHS
No full textAn analysis of island and active corridor dynamics is presented for a 16 km island-braided reach of the gravel-bed Tagliamento
River (Italy) based upon information extracted, geocorrected and registered to a common base from three map (1803, 1833,
1927) and nine aerial photograph sources (1944/6, 1954, 1970, 1986, 1991, 1996, 1997, 1999, 2005).
The active corridor width showed a general decline over the study period but with some recent widening. Adjustments in
active corridor width were achieved through processes of floodplain avulsion, island attachment and progressive encroachment
of the edge of the active corridor across gravel areas. These adjustments were accompanied by the preferential creation of
dissection (floodplain avulsion) islands during periods of widening and the construction of mid islands within the corridor during
periods of narrowing. Changes in island extent were achieved by rapid island turnover, which reached a maximum rate of over
50% per annum when corridor narrowing was most rapid between 1970 and 1991. Very few island surfaces were found to persist
for more than 24 years.
Despite this enormous dynamism and apparent cyclic behaviour, between 1944/6 and 2005 the ratio of island area to active
corridor area remained relatively constant at around 0.08 and supported a consistently high bankfull shoreline to downstream
length ratio of around 6 km km1. These intrinsic properties of the dynamics of the study reach and other island-braided
channels need to be recognized and maintained by river managers because they represent a characteristic habitat dynamism that
is crucial to the maintenance of ecological integrity
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
UNDERSTANDING REFERENCE PROCESSES: LINKAGES BETWEEN RIVER FLOWS, SEDIMENT DYNAMICS AND VEGETATED LANDFORMS ALONG THE TAGLIAMENTO RIVER, ITALY
No full textThe Tagliamento River, Northeast Italy, represents an important Alpine to Mediterranean braided system, where interactions
between river flows, sediment dynamics and vegetated landforms can be investigated within a relatively unconfined setting.
We analysed data from contemporary and historical sources, including stage records, photographs and topographic surveys.
From these we identified river stages at which thresholds in surface hydrological connectivity and biogeomorphological
adjustment appeared to occur, contributing to a shifting habitat mosaic.
Significant adjustments in landscape elements within the active tract commence at river stages well below bankfull with return
periods of a few months. Flow pulse events with return periods from a few months to 2 years support a dynamic inundation
pattern, ranging from a patchwork of isolated water bodies within a predominantly terrestrial landscape at low river stages to
isolated vegetated islands within a fully connected aquatic landscape as the river approaches bankfull. Across this range,
interactions between flow, sediment and vegetation lead to gradual and abrupt transitions in persistence, form and connectedness
of different landscape elements. Bankfull flows (return period over 2.5 years) topple and disperse significant numbers of large
trees, seeding the next generation of vegetated patches, and larger floods (return period around 10 years) induce significant
turnover of established islands and floodplain surfaces.
The results reported in this paper illustrate how extensive interdisciplinary research on a single river system can provide useful
insights concerning the time scales and thresholds that characterize water–sediment–vegetation interactions in piedmont reaches
of Alpine to Mediterranean braided systems. Anthropogenic effects on river systems are ubiquitous throughout Europe.
However, systems such as the Tagliamento River that retain significant process dynamism and morphological integrity, provide a
laboratory within which reference processes and process–form interactions can be investigated, understood and then
incorporated into innovative restoration design on more impacted systems
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