Bedload transport in the instrumented catchment of the Rio Cordon, Part I: Analysis of bedload records, conditions and threshold of bedload entrainment

The paper illustrates the results of 10 years of research conducted on the Rio Cordon catchment (5 km2), where an experimental station has been operating for the integral and continuous automatic recording of water discharge and coarse sediment transport. The device operates by separating bedload from water discharge and fine sediment and subsequently measuring the two solid components. The recorded floods are grouped in two distinct categories according to the bedload transport rates: ‘ordinary’ and ‘exceptional’ floods (with return times exceeding 30–50 years). Based on data collected and field studies, the aspects characterising threshold conditions of bedload transport at flood initiation and cessation are illustrated. Then, a description is given of the conditions which are necessary for two distinct mechanisms of incipient motion of bed particles to occur: selective transport and equal mobility of stream bed material.