The Tagliamento River: A model ecosystem of European importance

In NE Italy is a remarkable floodplain river that retains the dynamic nature and morphological complexity that must have characterized most Alpine rivers in the pristine stage. This river system, the Fiume Tagliamento, constitutes an invaluable resource not only as a reference site for the Alps, but as a model ecosystem for large European rivers. The Tagliamento has a number of attributes that have not been given due consideration in river ecology: (i) an immense corridor of more than 150 km2 that connects the land and the sea and two biomes, the Alps and the Mediterranean; (ii) unconstrained floodplain segments characterised by a dynamic mosaic of aquatic/terrestrial habitats; and (iii) a large number of vegetated islands (ca. 700). We believe it is critical to understand the functional roles of these endangered attributes in order to effectively engage in river conservation and management programmes. The Tagliamento River in Italy offers the rare opportunity to investigate natural processes at a scale that can be studied almost nowhere else in Europ

The adjustment of river channel capacity downstream from reservoirs in Great Britain

The variety of impacts that reservoir construction may have upon river channels in Britain are identified below fifteen dams located within diverse geomorphic and hydrologic areas. Channel changes are recognised by the comparison of field surveyed channel dimensions between regulated and non-regulated rivers. Regression analyses, relating the non-regulated channel dimensions to drainage area - a surrogate for discharge, provide an estimate of the pre-reservoir channel form. Sedimentological data, flow equations, and dating techniques are employed to corroborate this. approach, and dendrochronology, applied to trees growing on channel sides and on floodplain margins, is demonstrated to be an effective technique for the dating of channel change in Britain.Analyses of discharge records and theoretical flood routing based upon methods advocated by the 'Flood Studies Report', 1975, indicate the variety of discharge changes that may occur consequent upon dam construction, and the significance of flood frequency changes for the channel form are evaluated. The dominant adjustment of river channels to river impoundment is demonstrated to be a reduction of channel capacity, but the observed spatial variation of channel response is complex, The factors influencing this complex response are illuminated and two primary mechanisms for channel adjustment are identified: the impact of reservoirs upon river flows, and the sediment introduced by tributaries are demonstrated to be significant factors. Major floods may be required for channel changes to be initiated, but the adjusted shape of the river channel will reflect the relative importance of sediment transport. Finally, a provisional model is presented to describe the complex adjustment of river channels downstream of reservoirs in Britain.</p