Morphological changes along alpine river reacvhes affected by natural and human impact: examples on river Pellice and Chisone (NW Italy).

The causes of modification along rivers are either natural or human. If the morphological variations in the past were mainly determined by the severe and extreme floods which periodically affected the rivers, since 1940s, as a lot of works and researches demonstrated, the natural impact cannot be separated by the human impact. The presence of dams, the channelization works, the channel modification and river diversion, the bridge crossing, the sediment removal and mining are part of the human causes which have influenced the river adjustments. The present work illustrates a summary of the studies and researches done on channel adjustment and evolutionary trend of two rivers flowing in the North Western sector of Italy. The used methodology is based on the reconstruction of spatial variation in channel morphology and sediment dynamics using historical maps and aerial photos in the medium and short-term period. Contemporary, the principal natural and human interventions on the river have been investigated. All data are inserted in a GIS for the uniformity of the coordinate system. Based on the availability of documentary sources, cartographical, photographical and ortho-photographical data, the method allows a reconstruction of the history of the river. Then, the modification of the channel and the active bankfull were related to the natural and human impacts trying to investigate which is the preponderant cause of variation and how floods and human intervention influence each other. The modification of some index over time, as the width, is a useful tool for interpreting the evolutionary trend of the river and tries also to predict its future evolution. The studied rivers are: River Pellice (35 km - from Luserna San Giovanni to Po confluence), and River Chisone (12 km - from Pinerolo to Pellice confluence).