Bedload transport in a steep alpine stream: Assessment of sediment mobility and virtual velocity using the bedload tracking

¹ Department of Land, Environment, Agriculture and Forestry, University of Padova, Padova, Italy
² Department of Ecosystems and Environment, Pontificia Universidad Catòlica de Chile, Santiago, Chile

^* Corresponding author: riccardo.rainato@unipd.it

Abstract

The bedload transport is challenging to analyze in field, consequently, several assumptions about it were made basing on laboratory researches or on short-term field studies. During the last decades several monitoring methods were developed to assess the bedload transport in the fluvial systems. The aim of this work is to investigate the transport of the coarse sediment material in a steep alpine stream, using the bedload tracking. The Rio Cordon is a typical alpine channel, located in the northeast of Italy. It is characterized by a rough streambed with a prevalent boulder-cascade and step pool morphology. Since 2011, 250 clasts equipped with Passive Integrated Transponders (PIT) were installed in the main channel, to analyze their mobility along a reach 320 m long. From November 2012 to August 2015, the transport induced by a range of hydraulic forcing between 0.44 m³ s^-1 and 2.10 m³ s^-1 was assessed by 10 PIT-surveys. First, the mobility expressed by the tracers was analyzed, observing marked differences in terms of travel distance. Then, the average recovery rate achieved during the tracer inventories (Rr > 70%) permitted to define the threshold discharge for each grain size class analyzed and, then, to assess the virtual velocity experienced by the tracers.