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Ricostruzione e previsione dell'evoluzione morfologica di un alveo a fondo ghiaioso (f. Tagliamento): integrazione di modellazione numerica, analisi GIS e rilievi di terreno
Full text linkThe study of channel adjustments and prediction of morphological channel evolution play a primary role in management and conservation river policies. Various techniques taken individually can reach a satisfactory degree of understanding of river morpho-dynamic, but an integrated approach is certainly desirable as it allows to develop a more robust knowledge of river processes and to make judgments with higher confidence levels.
In this research an effort has been undertaken to integrate and combine two approaches very different in terms of methodological and conceptual base: GIS-survey analysis, and numerical morphodynamics modelling. The case study has been a reach of the Tagliamento River (Friuli Venezia Giulia, Italy) of about 49 km in length from the Pinzano gorge to San Mauro. This reach coincides roughly with the so-called Middle Tagliamento.
Through the application of GIS techniques, topographic and geomorphological surveys it was possible to reconstruct the morphological adjustments undergone by Tagliamento River channel over the last 200 years. The quantification of the human activies also helped to highlight the existing link causes-effects with the processes of narrowing and incision started during the first half of the twentieth century, grew in intensity until the 1990s and followed by a recent morphological recovery phase.
Numerical modelling was undertaken in order to support and complete the results of the historical analysis. Space-time scales involved by the historical analysis have led to choose a numerical model that can simulate long time periods on spatial contexts with dimensions similar to those of the study reach. The choice has fallen on a morphodynamic cellular model called CAESAR (Cellular Automaton Evolutionary Slope And River model), which fall into to the so-called Reduced Complexity Models group (RCM). This type of model necessarily required that a thorough sensitivity analysis was carried out before of model calibration and validation. Following validation the model was applied to estimate sediment budgets at reach scale and it was used in a "what-if scenarios" evaluation framework. It was thus possible to bring out the longitudinal variability of the average sediment transport yield, the strong influence of lateral erosion on the sediment transport dynamics and the lack of relevance on the planimetric trend of variation in sediment supply input on the upstream section of the reach.
Integration of numerical evaluations and classic analysis results allowed to isolate the human impact that induced the historical channel adjustments and also to make quantitatively and conceptually based assessments about the likely future morphological evolution of the Tagliamento River.Lo studio delle variazioni morfologiche e la previsione dell'evoluzione futura degli alvei fluviali rivestono un ruolo primario per la loro gestione e conservazione. Diverse tecniche applicate singolarmente conducono a una comprensione soddisfacente dello stato morfodinamico di un alveo fluviale, un approccio integrato è tuttavia auspicabile in quanto permette di sviluppare una conoscenza più robusta dei processi e permette di esprimere giudizi con livelli di confidenza più elevati.
In questo lavoro di ricerca è stato intrapreso lo sforzo di integrare e coniugare due approcci molto diversi dal punto di vista metodologico e concettuale, l'analisi GIS e di campo e la modellazione numerica morfodinamica. Il caso studio oggetto della ricerca è un tratto del fiume Tagliamento (Friuli Venezia Giulia) di circa 49 km impostato tra la stretta morfologica di Pinzano e la località San Mauro, coincidente grossomodo con il cosiddetto Medio Tagliamento.
Attraverso l'applicazione di tecniche GIS, rilievi topografici e rilievi geomorfologici è stato possibile ricostruire con elevato dettaglio le variazioni manifestate negli ultimi 200 anni dall'alveo del fiume Tagliamento. La quantificazione degli impatti antropici ha permesso di evidenziare i legami diretti causa-effetto esistenti con i processi di restringimento ed incisione avviati durante la prima metà del '900, cresciuti per intensità fino agli anni '90 e seguiti da una recente fase di recupero morfologico.
Al fine di supportare e completare le valutazioni emerse da quest'analisi storica, è stata intrapresa una via d'indagine morfologica alternativa modellistico-numerica. Le scale spazio-temporali interessata dall'analisi GIS (Geographic Information System) e di campo hanno vincolato la scelta ad un modello in grado di simulare ampi periodi temporali per contesti con dimensioni assimilabili a quelle del tratto studio. La scelta è ricaduta su un modello morfodinamico a schema cellulare denominato CAESAR (Cellular Automaton Evolutionary Slope And River model), appartenente alla classe di modelli cosiddetti a "complessità ridotta" (Reduced Complexity Models, RCM). La tipologia stessa del modello ha richiesto che fosse affrontata, in via preliminare alla sua calibrazione e validazione, un'approfondita analisi di sensitività . In seguito alla sua validazione il modello è stato applicato per un calcolo a scala di tratto del bilancio di sedimenti e per l'implementazione di una strategia "what-if scenarios". E' stato così possibile far emergere la significativa variabilità longitudinale del trasporto al fondo effettivo medio annuo, l'influenza dell'attività erosiva laterale sulla dinamica complessiva dei sedimenti e la scarsa rilevanza sulle tendenze evolutive planimetriche della variazione di apporto solido in ingresso al tratto studio.
L'integrazione delle valutazioni numeriche e di analisi classica ha permesso di isolare le cause antropiche alla base delle variazioni morfologiche storiche e di esprimere valutazioni quantitativamente e concettualmente più fondate sulla possibile evoluzione morfologica futura del fiume Tagliamento
Reconstructing temporal changes and prediction of channel evolution in a large Alpine river: the Tagliamento river, Italy
No full textThis paper focuses on the temporal elements of
the REFORM hydromorphological framework, illustrating
these elements with an analysis of information from the
lower Tagliamento river, Italy. It presents an analysis of
historical channel adjustments at segment and reach scales
over the last two centuries, reflecting human pressures that
are summarised but not fully developed in this paper, and
an analysis of data from aerial photographs, topographic
surveys, and river flow records. This is followed by an
assessment of likely future changes over the period
2012–2035 based upon both a conceptual model founded
on the historical analysis and numerical modelling. The
Tagliamento river has gone through three main phases of
adjustment. The first two phases, characterized by narrowing
and incision, were driven primarily by human
interventions (i.e. sediment mining and channelization).
The most recent phase represents an attempt of the river to
achieve a new equilibrium condition and is mainly controlled
by flow regime (i.e. frequency and magnitude of
formative discharges) and vegetation establishment. As for
future channel evolution, both models showed that slight
width changes are likely to occur over the period
2012–2035. Channel widening, that could be expected as a
response to an excess of unit stream power, will be hampered
by vegetation establishment. Finally, the ‘‘no intervention’’
strategy seems to be the best option for leading
the river towards a new equilibrium condition and to
achieve different goals (e.g. flood mitigation, conservation
or improvement of ecological status)
Conflitti d'acqua e di uomini nel bacino del Tagliamento: l'utilità di un approccio integrato tra geografia umana e fisica
No full textThis paper comes from a collaboration involving three PhD students of the Department of Geography, University of Padua. The main aims are i) to summarize the results emerged during the 12th European Seminar on Geography of Water (Udine, 28 June - 9 July 2009) within the working group dedicated to Tagliamento river basin; ii) to test a multidisciplinary approach that joins physical and human geography. After a physical and administrative overview of the area, the paper focuses on conflicts between different uses of basin resources (hydropower production, irrigation, industrial use of water, gravel extraction, tourism, recreational activities), and with the risk management related to the Tagliamento. Some general suggestions concerning feasible solutions to the conflicts has been pointed out: i.e. the need to increase local community involvement in public choices, coupled to a reinforcement of a catchment scale vision of the problems. The topics are too vast and complex to be entirely detailed here; but, the analysis has highlighted the potentialities of a successful interdisciplinary collaboration dealing with an issue that requires complementary skills, methods and approaches
Morphological effects of different channel-forming discharges in a gravel-bed river
No full textThe study analyses the morphological response of a gravel-bed river to discharges of different magnitude (from
moderate events that occur several times a year to a 12-year flood) and so defines the range of formative discharges for single
morphological units (channels, bars, islands) and a range of magnitude of morphological activity from the threshold discharges for
gravel transport and minor bar modification up to flows causing major morphological changes.
The study was conducted on the Tagliamento River, a large gravel-bed river in north-eastern Italy, using two different methods,
analysis of aerial photographs and field observation of painted gravel particles. The available photographs (five flights from August
1997 to November 2002) and the two commissioned flights (June 2006 and April 2007) do not define periods with a single flood
event, but the intervals are short enough (11 to 22 months) to have a limited number of flood events in each case. The fieldwork,
which involved cross-section survey, grain-size analysis and observation of painted sediments, complemented the aerial surveys
by allowing analysis of channel response to single flood events.
Substantial morphological changes (e.g. bank erosion of several tens of metres up to more than 100 m) associated with flood
events with a recurrence interval between 1·1 year and 12 years have been documented. Multiple forming discharges were
defined based on the activity of different morphological units. Discharges equal to 20–50% of the bankfull discharge are
formative for the channels, whereas the bankfull discharge (1·1 year flood in this case of the Tagliamento River) is formative for
low bars. Larger floods, but still relatively frequent (with a recurrence interval less than five years), are required for full gravel
transport on high bars and significant morphological changes of islands
Variazioni morfologiche degli alvei dei principali corsi d'acqua veneto-friulani negli ultimi 200 anni
No full textThe streams of the Veneto and Friuli Venezia Giulia Regions, as many other Italian streams, have undergone remarkable channel adjustments
in the last decades, which have been induced by a range of human interventions. The paper, which reports the state of the art
about five streams (Brenta River, Piave River, Cellina Torrent, Tagliamento River and Torre Torrent), aims to compare the evolutionary
trends of such streams and the factors that have driven to channel changes in the medium and short periods (last 200 years). The
selected streams are relatively large (their drainage basins range between 446 km2 and 3899 km2) and have very wide gravel channels,
often with a braided morphology, in the study reaches. Planform changes, in particular channel width variations, have been analysed
using maps and aerial photographs (9 to 12 different maps/photos were available for each stream). Bed-level changes have been investigated
through cross-section comparisons and field surveys.
The river channels have shown very similar evolutionary trends and magnitude of adjustments. Channel changes were not notable over
the 19th century, whereas the channels have been in an unstable condition in the following period. Narrowing and incision have been
the dominant processes during the 20th century, up to the 1980s-1990s. Channel width reduction has been of 50-70 %, referring to the
width in the first half of the 19th century, and bed-level lowering of 2-3 m on average, but locally up to 8-9 m. A different evolutionary
trend, except for the Torre Torrent, has occurred in the last 15-20 years, since channel widening and aggradation have been the most
common processes. The magnitude of changes during the last phase has been generally much smaller in comparison with those of the
previous phases of adjustment.
The gravel mining and channelization works have been the main causes of channel changes, in particular as for the main phase of adjustment
that took place from the 1950s to the 1980s/1990s. The dams (except for the Cellina Torrent), torrent control works, and reforestation
have probably had a smaller effect on channel dynamics than mining and channelization. As pointed out in previous studies, it is
confirmed that human interventions have dramatically altered the sediment regime, whereas a significant change of channel-forming
discharges has been documented in just one case (Cellina)
Channel adjustments and alterations of sediment fluxes in gravel-bed rivers of north-eastern Italy: potentials and limitations for channel recovery
No full textThe aim of this paper is to explore possibilities and limitations of restoring physical processes in five gravel-bed rivers (Brenta,
Piave, Cellina, Tagliamento and Torre Rivers) in north-eastern Italy. The selected rivers were analysed through a range of
techniques, specifically analysis of historical maps and aerial photographs with geographical information systems (GIS),
comparison of topographic surveys and geomorphological surveys. After illustrating channel adjustments and sediment fluxes,
we discuss how the understanding of physical processes can be used for channel restoration.
The studied river channels have undergone notable adjustments in the last 100 years, specifically narrowing by up to 76%,
incision by up to 8.5 m, and changes in channel configuration. Alteration of sediment fluxes, mainly due to in-channel mining,
has been the main factor driving such channel adjustments. Evolutionary trends show that channel recovery is on-going in
several of the selected reaches, since widening and aggradation have occurred over the last 15–20 years. This channel recovery
has been possible because sediment mining has significantly decreased or ceased along the study reaches. However, several
constraints still exist on sediment fluxes (e.g. dams).
Four categories of river channel were defined, taking into account the recent evolution of the studied channels (from ‘A’, high
channel recovery, to ‘D’, no channel recovery). The impact of different sediment management strategies on channel dynamics
over the next 40–50 years was then analysed.Without any intervention, channel recovery would only be possible in those reaches
that have a relatively high degree of connectivity with upstream sediment sources or tributaries, while further incision and
narrowing would be expected in those reaches where connectivity is low. A more substantial channel recovery could be obtained
through interventions at reach (e.g. removal of bank protection) and basin (e.g. sediment transfer downstream of dams) scales.
Notwithstanding such actions, it is likely that channels will not recover in the next few decades to the morphology they exhibited
in the first half of the 20th century, when bed-load yield and connectivity were higher
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
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
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