Field Methods and Instrument Types: Considerations For Using Seismic Methods To Monitor Bedload In Sand-Rich Gravel Bed Ephemeral Channels

Environmental seismology is a relatively new field of study involving the use of seismic signals to characterize surface processes, including sediment transport and other river processes. Published studies of bedload monitoring have typically used a relatively small number of seismic instruments, often at significant distances from active channels, to characterize signals generated by fluvial processes. We focus here on data collection along a sand-rich (~30% <2mm) gravel ephemeral channel, where even small amounts of water move significant amounts of sediment during monsoon-driven flash flood events. Within the Arroyo de los Pinos watershed in central New Mexico, we have deployed several different types of seismic instrumentation, including very sensitive broadband sensors and easy-to-deploy high-frequency nodal sensors, at various distances from the channel and in different geologic conditions. These instruments are one component of the experimental watershed that also includes Reid-type bedload slot samplers, suspended sediment pump samplers, pressure transducers, and rain gauges to capture the hydrologic, meteorologic, and sedimentologic conditions during flow events. Because flow events frequently include multiple concurrent fluvial processes, and seismic sensors are subject to a wide variety of environmental noise sources, it is essential to understand how the field deployment, site selection, and instrument type affect seismic data and interfere with target signals. Here we describe our seismic field methods, including site location, instrument deployment strategies and characterization of anthropogenic background noise. We also examine seismic data from a mid-size flood that was recorded on multiple instruments to determine how instrument type and deployment conditions affect recorded signals. This comparison will be an informative resource for others who may incorporate seismic monitoring in bedload transport studies.