Quantifying slope and grain size dependent transport thresholds using RFID and accelerometer tracers with on-bed RFID antennas in an upland channel

Abstract:

Integrating accelerometer and radio frequency identification (RFID) embedded tracers with in-stream RFID antennas can provide unique field-based relations for grain size and slope dependent thresholds of motion. We recorded bedload activity at a reach and across individual particles paths during a weeks-spanning snowmelt period in Reynolds Creek, Idaho. Deployed accelerometer tracers logged unique clast mobility, while stationary antennas captured the times when RFID and accelerometer tracers passed through a given reach. We analyze the temporal motion dataset from the stationary antennas along with the reach’s shear stress conditions over the season. The antenna records quantify a grain-size dependent lower envelope for the threshold of motion that is fit with a hiding function. The accelerometer tracers were transported downstream as little as 10 m to more than 2 km, and were deposited in reaches with slopes ranging from 0.5 to 7 percent. The integration of the antenna-based hiding function along with flow modeling, grain size distributions and the accelerometer tracers’ mobility data constrain the dependence of critical shear stress on reach slope. Both the grain-size and slope dependent threshold results gleaned from these novel field methods are then utilized to evaluate how transport capacities fluctuate along the channel during a snowmelt flood. The hiding function results from the stationary antennas also demonstrate promising potential for bedload monitoring programs to include continuous threshold data by deploying multiple antenna stations across watershed scales. This multi-antenna watershed application could provide spatiotemporal comparisons of transport thresholds between reaches of interest. Such an effort could also be used to quantify changes in transport thresholds due to natural perturbations or restoration/management modifications within a watershed.