Monitoring bed load transport using acoustic and magnetic devices

The work reported was undertaken in the Homerka instrumented catchment in the Polish Flysch Carpathians, where different techniques for monitoring coarse sediment transport have been applied over the past 30 years. The area is characterized by highly active erosion, sediment transport and fluvial sedimentation processes. Bed load transport has been measured using both acoustic and magnetic techniques. The acoustic (hydrophone) method permits continuous measurement and is able to provide a continuous record of coarse particle movement during flood events, which is a direct reflection of the magnitude of bed load movement. In general, bed load transport reaches a peak more rapidly than the water discharge. For a given flood discharge, the intensity of bed load transport varies between the rising and falling stages of a flood event. Coarse material bed load transport has also Iq been measured in the Homerka catchment using magnetic tracers. In this case, magnets are cemented into holes drilled into gravel particles and an electromagnetic sensor is used to track their movement through a designated short reach. In addition, transport distances associated with individual gravel particles tagged with magnets during individual events have been documented by recovering the labelled gravel after the event using a metal detector. These magnetic tracing techniques permit the bed load transport rate associated with individual grain size fractions to be quantified.