Seismic Monitoring of Flash Floods at the Arroyo de los Pinos: Investigation of Bedload Flux and Grain Size Distribution

Bedload transport is a key fluvial process. Yet, it is challenging to measure in natural streams, and continuous time series are rare. Seismic methods show promise for continuous monitoring of bedload transport. However, comparisons with direct bedload measurements are required for calibration and validation, and few such data sets exist. We collected high temporal resolution seismic and bedload flux data from 19 flash flood events that occurred during 5 years at the Arroyo de los Pinos experimental watershed in central New Mexico. We use this data set to investigate the variation of seismic signals with bedload flux across events. To compare seismic and bedload data, we first isolated seismic power-spectral density (PSD) in the 30–80 Hz frequency range, largely to exclude local noise sources. Next, we computed the linear regression of recorded PSD with bedload flux measurements to determine the robustness of correlation. We found a good correlation between median PSD in the 30–80 Hz range and bedload flux (Spearman's ρ = 0.77). To further investigate variation in the bedload-PSD relationship, we sieved sediment captured in bedload samplers and determined variations in PSD according to grain size. We found a significant positive correlation between PSD and the median grain size of bedload in motion, but the peak frequencies did not correlate with grain size.