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

Riccardo Rainato,Daniele Oss Cazzador,Luca Mao,Lorenzo Picco,A Paquier,N Rivière

doi:10.1051/e3sconf/20184002027

Riccardo Rainato, Daniele Oss Cazzador + Show 4 more

Open Access

https://doi.org/10.1051/e3sconf/20184002027

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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.

Highlights

The bedload transport is challenging to analyze in field and, several assumptions about this topic were made basing on laboratory researches or on short-term field studies
In the Rio Cordon, the bedload monitoring program undertaken using the tracking approach has permitted to investigate, during the period 2012-2015, the sediment mobility and the virtual velocity expressed by 250 clasts
The Passive Integrated Transponders (PIT)-surveys enabled to examine both short periods (< 30 days) affected by flood events as well as longer time intervals influenced by long snowmelt-driven flows

Summary

Introduction

The bedload transport is challenging to analyze in field and, several assumptions about this topic were made basing on laboratory researches or on short-term field studies. These approaches may tend to overestimate the bedload magnitude, when used to assess the low magnitude/high frequency flood events [1, 2]. This boundary contrasts with the importance that bedload transport has in the fluvial systems, and especially in the mountain channels where it can strongly influence the morphological setting, ecological status, channel stability and sediment fluxes [3, 4, 5]. The PITs are detectable by mobile or fixed antennas, which permit to identify the PIT even if buried and, to investigate the bedload dynamics with no disturbance to the streambed organization [13]

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