Channel adjustments in response to human alteration of sediment fluxes: examples from Italian rivers

In response to various types of human impacts, most Italian rivers have experienced considerable channel adjustments during the last two centuries. Human impact includes reforestation, channelization, construction of dams and sediment mining. The most important effect of human impact has been an alteration of sediment fluxes, and specifically a remarkable decrease in sediment supply to river channels. The five rivers selected in northern Italy (Tagliamento, Piave, Brenta, Trebbia and Vara), which have or used to have a braided morphology, have undergone channel narrowing (between 58 and 85%), decrease of braiding intensity and incision (up to 4–5 m). Narrowing and incision have been the dominant processes during the last two centuries, particularly intense from the 1950s to the 1990s; however, recent data suggest that those processes could now be exhausted since other kinds of adjustments, specifically channel widening and (local) aggradation, have occurred during the last 10–15 years.