How natural are Alpine mountain rivers? Evidence from the Italian Alps

Historical, human-induced channel adjustments in lowland gravel-bed rivers have been documented in several geographical contexts worldwide. In particular, it is now widely accepted that the vast majority of European rivers are far from any natural, reference state prior to anthropic disturbances, and a complete restoration is hardly achievable. However, few investigations have addressed changes that have occurred in mountain rivers of the Alps, and these channels are commonly reckoned quite natural by society. This paper intends to describe how human pressure on Italian Alpine basins has been quite relevant for several centuries in terms of land-use variations, in-channel structures, timber transport (splash damming) and riparian vegetation management such that nowadays reference conditions cannot be found even in small mountain creeks. In addition, recent natural climatic variations (e.g. the Little Ice Age) are superimposed on human disturbances, thus defying the definition of any equilibrium morphological conditions even under human-free states. A summary of published as well as unpublished works on historical channel adjustments in rivers of the Italian Alps is presented in order to document the impacts deriving from human pressure at different basin scales and for different river morphologies, from steep confined streams to large unconfined rivers. General options for river management and restoration actions aiming to combine geomorphological functionality and flood hazard mitigation are discussed, in the light of the current European legislative context. Copyright (C) 2011 John Wiley & Sons, Ltd.