Hydrophone data from the Methow River, Washington, April 2020 to June 2020

Hydrophones were installed on the Methow River just downstream of the Community Bridge on the Methow Valley Trail and operated during the spring of 2020. Two independent acoustic recording units were installed, one on each bank, with two hydrophone sensors linked to each unit. The right-bank installation was located near the bottom of a steep eroding gravel bank, while the left-bank installation was placed on a low-relief cobble bar. Both units collected 15-minute data from April 24 to June 05, 2020, spanning the spring snowmelt peak flow. No obvious issues were observed in preliminary inspections of the data. McBain and Associates conducted bedload sampling at the monitoring site from May 18 to May 20, 2020. Sampling was performed from a cataraft tethered to a channel-spanning cableway, using a Toutle River II bedload sampler. A total of 19 transects were collected over three sampling days. Those data were archived on the U.S. Geological Survey (USGS) NWIS repository under site number 483414120220801 (Methow River below Trail Bridge near Mazama, WA). Discharge at the site was estimated from USGS streamgage 12447383 (Methow River above Goat Creek near Mazama, WA), located about two kilometers upstream. Discharge records were scaled by the drainage area ratio of the hydrophone monitoring site and the streamgage site, which was 1.12. Each hydrophone unit consisted of custom-built controller and recording system to which one or two distinct hydrophone sensors were attached (Marineau and others, 2016). The controller/recording unit consisted of a Raspberry Pi Zero W using a UUGear Witty Pi 4 real-time clock for time information. These systems used H2a-XLR hydrophones (Aquarian Audio, 2024). Each hydrophone was installed in 0.75-inch 90-degree polyvinyl chloride (PVC) street elbows connected to 0.75-inch non-metallic conduit and affixed to the bed during low-flow conditions using rebar pounded into the gravel substrate and a combination of metal hose clamps and nylon zip ties. The two hydrophones were installed several feet apart with sensors facing towards the center of the channel. Hydrophones were connected to the controller through ART ProAudio Dual Pre Project Series preamplifier with gain set to 10 decibels. When operating, the system would record one-minute 16-bit stereo audio files with a 44.1 kilohertz sampling rate at 15-minute intervals. Audio was recorded in Waveform Audio File (WAV) format and then compressed to Free Lossless Audio Codec (FLAC) format for local storage. Raw audio files were processed in R to obtain average acoustic pressure in micropascals as a function of frequency based on methods discussed in Geay and others (2017). The primary processing tool was the specgram function from the Signal (2023) R package, which applies a Fourier transform to sequential slices of individual audio files to obtain a table of frequency response over time. Processing was done using a Hamming window, dividing the file into 2048 sub-intervals with 50 percent overlap. The output was normalized based on the dynamic range (2.5) and sensitivity (-180 decibels) of the hydrophones and gain of the pre-amplifier (10 decibels) to obtain results in micropascals. The result is a table describing acoustic pressure by frequency at equal 21.5 Hz intervals between 0 and 22 kHz for each of the 2048 time sub-intervals. Final output was then summarized as the median value for each frequency. This process was done for each channel of the stereo audio files separately. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. These data are marked with a Creative Commons Zero v1.0 Universal (CC0-1.0) public domain dedication and do not have any use constraints.

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