N. Surian

ABSTRACT Prediction requires use of models (e.g. conceptual, physical, analytical or numerical models). Uncertainty associated with any kind of model and complexity of fluvial systems, specifically of braided rivers, are major issues to be taken into account. This means that we should be aware that prediction of channel morphology has inherent limitations since results of any model are affected by a degree of uncertainty and braided rivers are very complex systems that exhibit self-organized critical behaviour. In this work a long braided reach (33 km in length) of the Tagliamento River (north-eastern Italy) is analysed. This large gravel-bed river (average channel width was 760 m in 2009) underwent notable channel adjustments due to human interventions (i.e. sediment mining and channelization) in the past. Our aim is to explore future channel evolution taking into account different scenarios of flow regime and sediment supply at catchment and reach scale. Two different modelling approaches were combined: (i) a conceptual model based on a historical analysis of channel changes over the last 200 years and controlling factors and (ii) numerical modelling, using a reduced complexity model (CAESAR). According to the conceptual model channel widening will take place in the future, though the evolutionary trajectory will depend on magnitude and frequency of formative discharges. For instance assuming that flow regime in the next years will be similar to that in the period 1993-2009, channel width will increase up to 1020 m in 2080 (in this case an average widening rate of 3.7 m/yr is assumed). From this conceptual model different future trajectories could be derived, for instance more intense channel widening is predicted if an increase in magnitude and frequency of formative discharges is assumed. The numerical modelling, using constant conditions for flow regime and different conditions for sediment supply (i.e. scenarios), showed that channel widening will continue in the next decades, independently from sediment management strategies. As expected, widening turned out to be more intense in the scenario where bank protections were removed (w = 1230 m) compared to the scenario where upstream sediment input was reduced (w = 1130 m). This work should be taken as an attempt to predict channel morphology evolution over long spatial and temporal scales (i.e. tens of km and tens of years) that are rarely considered in river modelling. Such scales are very relevant for river management. Because uncertainty can be very high in modelling long river reaches over several decades, it is worth using different models to reduce uncertainty. The results of the two models used in this study turned to be very coherent, thus increasing reliability of the predictions.

English abstract: This paper deals with the use of landslide records in the analysis of landscape sensitivity, with particular reference to climate change as a forcing process. The dating of past landslide events is useful to reconstruct the evolution of the slope-system at a broad temporal scale and to recognize the different formative events it has experienced. If the environmental context can be defined by means of a multidisciplinary approach which comprises geomorphological, sedimentological, palaeobotanical, dendrochronological ...

Most Italian rivers have experienced widespread channel adjust- ments over the last 100 years, mainly in response to a range of human activities. The aim of this paper is to show how knowledge of channel ad- justment and reconstruction of evolutionary trajectory are or can be used in river management and restoration. The first part of the paper deals with channel adjustments and summarizes the results of recent studies carried out on twelve rivers in northern and central Italy. The second part illustrates three examples of application. The selected rivers have undergone almost the same processes in terms of temporal trends. 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 19th century and was very intense from the 1950s to the 1980s. Then, over the last 15-20 years, channel widening and sedimenta- tion, or bed-level stabilization, have become the dominant processes in most of the rivers, though cha...

ABSTRACT This work addresses the temporal dynamics of riparian vegetation in large braided rivers, exploring the relationship between vegetation erosion and flood magnitude. In particular, it investigates the existence of a threshold discharge, or a range of discharges, above which erosion of vegetated patches within the channel occurs. The research was conducted on a 14 km long reach of the Tagliamento River, a braided river in northeastern Italy. Ten sets of aerial photos were used to investigate vegetation dynamics in the period 1954-2011. By using different GIS procedures, three aspects of geomorphic-vegetation dynamics and interactions were addressed: (i) long-term (1954-2011) channel evolution and vegetation dynamics; (ii) the relationship between vegetation erosion/establishment and flow regime and (iii) vegetation turnover, in the period 1986-2011. Results show that vegetation turnover is remarkably rapid in the study reach with 50 % of in-channel vegetation persisting for less than 5-6 years and only 10 % of vegetation persisting for more than 18-19 years. The analysis shows that significant vegetation erosion is determined by relatively frequent floods, i.e. floods with a recurrence interval of ca. 1-2.5 years, although some differences exist between subreaches with different densities of vegetation cover. These findings suggest that the erosion of riparian vegetation in braided rivers may be not controlled solely by very large floods, as is the case for lower energy gravel-bed rivers. Besides flow regime, other factors seem to play a significant role for in-channel vegetation cover over long time spans. In particular, erosion of marginal vegetation, which supplies large wood elements to the channel, increased notably over the study period and was an important factor for in-channel vegetation trends. This article is protected by copyright. All rights reserved.

.  We adopt a multidisciplinary approach toward the quantitative assessment of juvenile fish habitats in Alpine rivers using analytical modeling. The study focuses on braided and single-thread channel configurations together with their associated hydrodynamic patterns. A distinct difference between flows in these channels is the number and spatial arrangement of recirculation zones. These are due to the separation of flow from

Large floods may produce remarkable channel changes, which determine damages and casualties in inhabited areas. However, our knowledge of such processes remains poor, as is our capability to predict them. This study analyses the geomorphic response of the Nure River (northern Italy) and nine tributaries to a high-magnitude flood that occurred in September 2015. The adopted multi-disciplinary approach encompassed: (i) hydrological and hydraulic analysis; (ii) analysis of sediment delivery to the stream network by means of landslides mapping; (iii) assessment of morphological modifications of the channels, including both channel width and bed elevation changes. The spatial distribution of rainfall showed that the largest rainfall amounts occur in the upper portions of the catchment, with cumulative rainfall reaching 300 mm in 12 h, and recurrence intervals exceeding 100-150 years. The unit peak discharge ranged between 5.2 and 25 m3 s-1 km-2. Channel widening was the most evident effect. In the tributaries, the ratio between post-flood and pre-flood channel width averaged 3.3, with a maximum approaching 20. Widening was associated with channel aggradation up to 1.5 m and removal of riparian vegetation. New islands formed due to the fragmentation of the former floodplain. In the Nure River, the average width ratio was 1.7, and here widening occurred mainly at the expenses of islands. Bed level dynamics in the Nure were varied, including aggradation, incision, and overall stability. The flood geomorphic effectiveness was more pronounced in the middle-higher portions of the basin. Planimetric and elevation changes were well correlated. Regression analysis of the relationship between widening and morphological/ hydraulic controlling factors indicated that unit stream power and confinement index were the most relevant variables. The study provides useful insights for river management, especially with regard to the proportion of the valley floor subject to erosion and/or deposition during large events.

ABSTRACT Vegetation has often a crucial role on braided river dynamics in humid environments. The aim of this work is to investigate island dynamics and, specifically, the controls of such dynamics. We started exploring the relation between islands dynamics and flow regime, testing the hypothesis if islands erosion is associated with floods of specific magnitude. Besides geological (e.g. groundwater depth) and geomorphological (e.g. channel confinement and evolutionary trajectory of channel morphology) controls were taken into account to explain vegetation dynamics. The study was conducted on a 14 km reach of the Tagliamento River (northeastern Italy). Changes in channel morphology and vegetation cover were analyzed over a time period of 25 years, from 1986 to 2011, using 8 sets of aerial photographs (1986, 1993, 1997, 1999, 2003, 2005, 2009, 2011). Ten types of fluvial features were digitized within the fluvial corridor which includes the active channel, floodplain and recent terraces. Vegetation was distinguished in three categories according to its height and tree canopy: herbaceous vegetation and shrubs, shrubs and trees of low-medium height, high trees. The extent of the last two categories, that is extent of vegetated patches where trees are dominant, ranged between 4% (in 2005) and 11% (in 1986) of the whole active channel. Preliminary analyses were focused on the dynamics of such vegetation patches, considering the extent of vegetated areas that were eroded and flow regime for each sub-period (e.g. 1986-1993). Erosion of vegetation occurred during all sub-periods but with different magnitude. Three sub-periods were characterized by less intense erosion (annual rates of erosion varying between 4% and 5%) while during the other four sub-periods annual erosion rates were in the range 11% - 15%. Correlations of those erosion rates with flow regime (i.e. cumulative discharges above a defined threshold) suggest that vegetation erosion is strictly connected to occurrence of flows of medium-high magnitude (e.g. a good statistical correlation was found considering only the floods with a recurrence interval higher than 1.1 yr). On the other hand there is evidence that significant erosion occurred also during a period (1997-1999) with moderate flows. Further analyses of these data will be needed to better define the relations between vegetation dynamics and flow regime in this braided river, in particular aiming to recognition of specific discharge threshold which are more relevant in such dynamics. Besides, the preliminary results of this study suggest that other controls (e.g. geological and geomorphological conditions) should be included for a more comprehensive explanation of vegetation dynamics.

... Nicola SURJAN (*) THE TERRACES OF THE PIAVE RIVER IN THE VALLONE BELLUNESE (EASTERN ALPS, ITALY) Abstract: Sueian N., The ... between terrace and slope deposits, and terrace mapping (Johnson, 1944; Frye & Leonard, 1954; Howard, 1959; Ritter & Miles, 1973 ...

Riassunto Obiettivo di questo studio è quantificare la presenza delle isole con vegetazione arborea in tre alvei ghiaiosi con morfologia braided (fiumi Brenta, Piave e Tagliamento). L'analisi, che ha riguardato gli ultimi 200 anni, è stata svolta utilizzando due cartografie storiche ( ...

Cette étude traite de la production, du transfert et des dépôts de sédiments dans le bassin du fleuve Piave depuis le Dernier Maximum Glaciaire (DMG). Le système sédimentaire est étudié de la haute montagne aux méga-cônes de piedmont et aux deltas. Cette synthèse vise à ...

The Geological Society of America Special Paper 451 2009 Channel adjustments in northern and central Italy over the last 200 years Nicola Surian* Department of Geography, University ofPadova, Via del Santo, 26, Padova 35123, Italy Massimo Rinaldi Department of Civil ...

... 17-25. 24. Nicola Surian. ... Boll. Soc. Geol. It., 58, p. 433-451. Zanferrari A., Bollettinari G., Carobene L., Carton A, Carulli GB, Castaldini D., Cavallin A., Panizza M., Pellegrini GB, Pianetti F. and Sauro U. (1982) - Evoluzione neotettonica dell 'Italia nord-orientale. Mem. Sc. ...

ABSTRACT A methodological framework for hydromorphological assessment, analysis and monitoring (named IDRAIM) has been developed with the specific aim of supporting the management of river processes by integrating the objectives of ecological quality and flood risk mitigation. The framework builds on existing and up-to-date geomorphological concepts and approaches and has been tested on several Italian streams.