In gravel-bed rivers, measuring the displacement of individual grains by fluid flow is essential in order to understand sediment transport processes and to investigate changes in channel morphology. We present preliminary results of a new technique that traces pebble movements by inserting 23 mm passive integrated transponders (PIT) into individual clasts. Because each PIT has its own signal identification, this technique is ideal for tracking the individual movements of episodically transported particles in gravel-bed rivers. Two hundred and four tagged particles were inserted into a 130-m-long reach of a gravel-bed river with a 2% slope and a bed material with a D50 of 70 mm. The b axis size of the tagged particles ranged from 40 mm to 250 mm. Recovery percentages after two competent floods were 96% and 87%, clearly demonstrating the effectiveness of this new technique. Buried particles can be recovered at a depth of 0.25 m. PIT tags are also suited for long-term studies over several years.

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