A reference river system for the Alps: the ‘Fiume Tagliamento’

Abstract

A major deterrent to a full understanding of the ecological ramifications of river regulation at the catchment scale is a lack of fundamental knowledge of structural and functional attributes of morphologically intact river systems. For example, both the River Continuum and the Serial Discontinuity Concepts, in their original formulations, had the implicit assumption of a stable, single‐thread channel from headwaters to the sea. The Fiume Tagliamento traverses a course of 172 km from its headwaters in the Italian Alps to the Adriatic Sea. No high dams impede the river's passage as it flows through the characteristic sequence of constrained, braided, and meandering reaches. The Tagliamento, the only large morphologically intact Alpine river remaining in Europe, provides insight into the natural dynamics and complexity that must have characterized Alpine rivers in the pristine state. The Tagliamento has a flashy pluvio‐nival regime (mean Q=109 m3 s−1, with flood flows up to 4000 m3 s−1). Thousands of newly‐uprooted trees were strewn across the active bed and floodplain along the river's course following a major flood in the autumn of 1996. The active floodplain is up to 2 km wide and contains a riparian vegetation mosaic encompassing a range of successional stages. Up to 11 individual channels per cross section occur in the braided middle reaches. Islands are a prominent feature of the riverine landscape and island dynamics are postulated to play a key role in determining pattern and process across scales. Future studies will examine the roles of island dynamics and large woody debris in structuring biodiversity patterns of aquatic biota and successional trajectories of riparian vegetation. The high levels of spatiotemporal heterogeneity exhibited by the Fiume Tagliamento provide a valuable perspective for regulated river ecologists and those engaged in conservation and restoration. Copyright © 1999 John Wiley & Sons, Ltd.

Behavior‐Based Scale Definitions for Determining Individual Space Use: Requirements of Two Amphibians

“…Further detailed information on the Tagliamento catchment and the main study area can be found elsewhere (Ward et al 1999;Arscott et al 2002;Tockner et al 2003).…”

Morphological response to river engineering and management in alluvial channels in Italy

“…Since these disturbances cause substantial changes to the flow and sediment regimes, at present few rivers are in a natural or semi-natural condition. For instance, in the Alps less than 10% of the total length of the rivers is in a semi-natural condition (Ward et al, 1999). Several studies have analysed the response of rivers to human impact, showing that remarkable channel changes generally take place, such as vertical adjustment, changes in channel width and pattern (e.g.…”

“…In addition, during the 20th century and particularly during the last decades, two other types of intervention have been widely carried out, namely the construction of dams, and sediment mining. Within this context, an exception is represented by the Tagliamento River (Eastern Alps) that can be considered the last large river in the Alps essentially retaining pristine morphological and ecological characters (Ward et al, 1999;Gurnell et al, 2001).…”

Relationships between woody vegetation and geomorphological patterns in three gravel-bed rivers with different intensities of anthropogenic disturbance

“…The geomorphological processes creating the pattern of multiple channel belts and the morphology of the individual channel belts in these rivers are controlled, in many different ways, by climate and geology [11,19,68]. However, over periods of major human interference, many rivers have become dominated by incision and narrowing, resulting in relatively simpler channel forms [16,18].…”

“…Bars were identified as higher-relief gravel units exposed at lower flows, either bare or supporting only annual vegetation and a small accumulation of river-transported plants and large wood. Islands were identified as vegetated patches completely surrounded by either channels or exposed gravel [68,42]. In all three rivers, the 20th century incision phase turned the pre-incision floodplains, normally inundated every 1-3 years [24,25], into low terraces that are not reached by the same recurrence interval floods.…”