Workshop Synopsis

The USGS and CUAHSI convened a three day workshop on Sediment Hydroacoustics Technqiues for Rivers and Streams, March 20-22, 2012. This was the second joint USGS-CUAHSI instrumentation workshop (following last year's successful Joint workshop on In situ Optical Water Quality Sensor Networks), and provided a unique opportunity to convene academic and agency scientists, engineers, manufacturers, and managers interested in hydroacoustic technology applications for measuring/monitoring suspended load, bed load, bed material, and related hydrodynamic characteristics in rivers and streams. The workshop foci included:

• technological advances,
• calibration and uncertainty issues,
• applications, and
• potential opportunities to use the technology to address new research questions.

The gathering provided the opportunity for those working in different environments and disciplines to share information and to evaluate opportunities to advance the technology, application to new ressearch questions and its broad-scale operational use.

CUAHSI and the USGS look forward to continuing collaborations on technical exchange and instrumentation. If you have an idea for a future joint workshop topic, please contact Jennifer Arrigo (jarrigo@cuahsi.org). We invite you to learn more about other CUAHSI collaborations with USGS, including agreements that provide CUAHSI member access to the USGS Hydrologic Instrumentation Facility (HIF) and participation in USGS-run Standard Reference Samples exercises.

Workshop Resources

• Review the workshop presentations here.
• The program committee is in the process of summarizing the key outcomes of the workshop for an EOS meeting report.
• Breakout leaders are currently producing summaries of the discussions. We anticipate continued working groups and discussions to follow from this workshop. We invite all who wish to participate in or learn more about advancing various phases of this effort to contact John Gray (jrgray@usgs.gov).
• A short overview of Hydroacoustic technologies produced by the program committee before the workshop is also provided below.

Synopsis of Hydroacoustic Technologies In Sedimentology

Manually intensive technologies for monitoring sediment transport in rivers that originated in the 1940s are being augmented by technologically advanced means for monitoring that require only periodic manual in-stream calibrations. Hydroacoustics is arguably the most compelling of a number of technologies that can provide a continuous analog time series, including light-based (nephelometry, laser, and digital optics), and pressure-difference technologies. The advantages of hydroacoustic metrics as surrogates for suspended sediment include a large sample volume, environmental robustness, and simultaneous velocity measurement if Doppler-enabled. However, best methods have not been broadly discussed or agreed upon for measuring acoustic attenuation, adjusted backscatter amplitude, and sediment-size class effects.

When deployed in situ in sideways or upward-looking configurations, the continuous active acoustic backscatter sensor (ABS) – as a single frequency, or, more effectively, in multiple-frequency modes – can provide continuous data on suspended-sediment concentrations and in some cases particle-size classes. The ensonified volume of streamflow sampled by the technology typically is orders of magnitude larger than those using an automatic-pumping sampler or sensed by a point-monitoring device. Additionally, it is possible to evaluate profiles of sediment concentration through or across a stream channel. Instrument fouling is of minimal concern given that the acoustic signal is more or less independent of the biological accretions that can impair the signal quality of an optical sensor. The velocity measurement obtained from the same signal data (assuming Doppler-technology enabled) can be used in computing sediment flux, which is often the principal objective, and may also be used in evaluating erosion and transport capacities. Additionally, hydroacoustics are in broad-scale operational use for velocity measurement, and the amount of new sediment data that could be obtained from these metrics is enticing.

Hydroacoustics is also being evaluated for inferring bedload transport in gravel- and sand-bed rivers. Passive hydroacoustics relying on in situ hydrophones or geophones have been shown to provide analog data for bedload transport using empirical relations developed from physical bedload-sampler data. Acoustic Doppler Current Profilers (ADCPs) have been used to infer sand-bedload transport in the ensonified region of the bed.

Finally, hydroacoustics are being used to infer particle-size classes of bed material in lotic and lentic waters.

Although none of the previously described technologies are yet used in large-scale operational sediment- and water-quality monitoring programs, these hydroacoustic technologies show considerable promise toward revolutionizing the way sediment transport is studied and monitored in the Nation's and world's rivers.

Workshop Sponsors
USGS Office of Surface Water	CUAHSI	Advisory Committee on Water Information (ACWI) Subcommittee on Sedimentation