Channel morphology evolution and bedload transport of the Reno river in northern Italy

The Reno R., as many other Italian rivers, has been significantly affected by man activity since Romans time, but in the last decades significant land use changes in the headwater, extensive bed material mining, dams construction, torrent-control works and large fluids extraction from the underground caused important channel morphology and sediment fluxes changes. To better understand such morphological changes and their causes, the hydraulic geometry data of several cross sections and the longitudinal profile data of the Reno river, surveyed at different times, were analysed emphasizing a dramatic streambed incision that took place between 1950s and 1980s, with a volume of sediment lost of about 18 x106 m3. At the same time a field campaign was started in 2003 collecting representative bed material samples and sediment transport measurements with Helley-Smith bedload sampler to assess the present river dynamics and evolution. Bedload transport rate resulted very low also during floods larger than bankfull stage and even those equations renown in the literature to underpredict bedload transport overestimate the sediment transport of the Reno R. Among the equations used those predicting transport rates closer to the actual surveyed values are modified Meyer-Peter & Muller equation The river transport capacity always resulted by far larger than sediment supply and no significant relation was found between flow parameters and the bedload transport rates measured. The occurrence of cyclic peaks and lows of bedload rate and a clear seasonality were as well. Sediment deficit of the Reno river system results from many factors including an increase in forest cover, presence of dams for agricultural and hydroelectric purposes, engineering works on the watershed and on the river channel, large bed material exploitation and likely a decrease in flood frequency.