Field and flume applications of RFID and accelerometer-embedded gravel and cobble tracers to constrain transport during floods

Wednesday, 17 December 2014
Joel P Johnson, Lindsay Olinde and Kealie Goodwin, University of Texas at Austin, Austin, TX, United States
Individually identifiable tracer particles and instrumented clasts provide a wealth of information about coarse bedload transport during floods. The dispersive nature of sediment transport means that tracer methods may constrain effects of spatial variability in the underlying topography of the channel, and effects of temporal variability in discharge (e.g., hydrographs). We highlight results from recent field and flume work that employed both radio frequency identification (RFID) and accelerometer tracers. The overall goal is to demonstrate that a broad range of quantitative constraints on sediment transport can be pulled from these unique datasets. In the field, tracer transport was monitored along ~11 km of Reynolds Creek, Idaho, a snowmelt-dominated gravel-bedded stream with local reach slopes of roughly 0.5% to 7%. Three antennas were installed on the channel bed near a gauging station to measure the exact times that RFID tracers passed the antennas during high flows. The combination of transport data, discharge and flow modeling allows us to calculate a hiding function that quantifies size-dependent thresholds of motion in this particular reach. During transport, RFID and accelerometer tracers became distributed along ~11 and ~2 km of the channel, respectively. The timing of individual particle movements was measured in 10 minute intervals by the accelerometers. These data constrained transport probabilities and bedload hysteresis as a function of changing discharge. Additionally, cumulative travel distances of the accelerometers allow us to put bounds on particle velocities and average individual step lengths. We find that average tracer transport distances are well correlated with cumulative discharge. Using flood magnitude-frequency relations based on the >50 year discharge record of Reynolds creek, the seasonal flow with an ~10 year recurrence interval likely transports coarse gravel the farthest average distance. Finally, in flume experiments on gravel transport by flash flood bores, RFID tracers of different sizes were used to measure size-dependent sorting due to transport and burial in the bed. Accelerometer tracers were sampled at 10 hz to measure actual durations of particle transport and rest.