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Sediment-Generated Noise and Bed Stress in a Tidal Channel

Study Status: 
Completed
Princple Investigator Contact Information: 

Name: Christopher Bassett

Address: Department of Mechanical Engineering, University of Washington, Stevens Way, Box 352600, Seattle, WA, 98103, US

Email: cbassett@uw.edu

Project Description: 

Tidally driven currents and bed stresses can result in noise generated by moving sediments. At a site in Admiralty Inlet, Puget Sound, Washington State (USA), peak bed stresses exceed 20 Pa. Significant increases in noise levels are attributed to mobilized sediments at frequencies from 4–30 kHz with more modest increases noted from 1–4 kHz. Sediment-generated noise during strong currents masks background noise from other sources, including vessel traffic. Inversions of the acoustic spectra for equivalent grain sizes are consistent with qualitative data of the seabed composition. Bed stress calculations using log layer, Reynolds stress, and inertial dissipation techniques generally agree well and are used to estimate the shear stresses at which noise levels increase for different grain sizes. Regressions of the acoustic intensity versus near-bed hydrodynamic power demonstrate that noise levels are highly predictable above a critical threshold despite the scatter introduced by the localized nature of mobilization events.

Funding Source: 

Funding provided by U.S. Department of Energy award DE‐EE0002654. Student support was provided to Christopher Bassett by National Science Foundation award DGE‐0718124.

Location of Research: 

Admiralty Inlet, Puget Sound, Washington

Project Aims: 
  1. To describe the hydrodynamic conditions that give rise to bed load transport
  2. To describe the spectral content of sediment-generated noise
  3. To describe the relationship of sediment-generated noise given prevailing hydrodynamic conditions
Project Progress: 

Completed

Key Findings: 

Analysis of hydrodynamic and acoustic measurements from a site in Admiralty Inlet, Puget Sound, WA (USA) suggests that sediment‐generated noise is the dominant noise source between 1 and 30 kHz during periods of strong currents. Peak sediment‐generated noise levels from 4 to 20 kHz are associated with mobile gravel and pebbles. Sediment‐generated noise levels in one‐third octave bands exceed noise levels attributed to vessel noise by up to 20 dB. 

Related Publications: 

Bassett, C.; Thomson, J.; Polagye, B. (2013). Sediment-Generated Noise and Bed Stress in a Tidal Channel. Journal of Geophysical Research, 118(4), 2249-2265. https://tethys.pnnl.gov/publications/sediment-generated-noise-and-bed-stress-tidal-channel

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