Tracking Large Particle Movement with Passive Radio Transponders in Ephemeral, Alluvial Channels

In the semi-arid southwest, channel runoff associated with intense summer thunderstorms reaches high velocities with sufficient energy to move large gravel and cobbles. Thunderstorm generated runoff hydrographs are characterized by short durations and rapidly rising peaks. Highly variable flow conditions and alluvial channel beds make tracking and relocating individual particles difficult. Previously reported methods for tracking particles include painted rocks, magnetic tracers, and active radio methods. The use of these methods can be limited by difficulty in relocating and identifying individual particles, as well as by expense. This paper presents a description of the use of a commercially available radio frequency identification system for tracking the movement of individual particles. The tracking system consists of transponders, an antenna, a reader, and software. The passive transponder system offers the advantages of low cost, consistent results under harsh environmental conditions, and no need for a power supply in the particle. The radio frequency identification system offers the potential to efficiently collect data for developing sediment transport equations and improving mathematical models for simulating sediment transport under natural runoff conditions.