A flume experiment to examine underwater sound generation by flowing water |
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Authors: | Diego Tonolla Mark S Lorang Kurt Heutschi Klement Tockner |
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Institution: | 1. EAWAG, Swiss Federal Institute of Aquatic Science and Technology, überlandstrasse 133, 8600, Dübendorf, Switzerland 2. IGB, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587, Berlin, Germany 3. Flathead Lake Biological Station, The University of Montana, 32125 Bio Station Lane, Polson, MT, 59860-9659, USA 4. EMPA, Swiss Federal Laboratories for Material Testing and Research, überlandstrasse 129, 8600, Dübendorf, Switzerland 5. Institute of Biology, Free University Berlin, Takustrasse 3, 14195, Berlin, Germany
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Abstract: | The hydrogeomorphology and ecology of rivers and streams has been subject of intensive research for many decades. However,
hydraulically-generated acoustics have been mostly neglected, even though this physical attribute is a robust signal in fluvial
ecosystems. Physical generated underwater sound can be used to quantify hydro-geomorphic processes, to differentiate among
aquatic habitat types, and it has implications on the behavior of organisms. In this study, acoustic signals were quantified
in a flume by varying hydro-geomorphic drivers and the related turbulence and bubble formation. The acoustic signals were
recorded using two hydrophones and analyzed using a signal processing software, over 31 third-octave bands (20 Hz–20 kHz),
and then combined in 10 octave bands. The analytical method allowed for a major improvement of the signal-to-noise ratio,
therefore greatly reducing the uncertainty in our analyses. Water velocity, relative submergence, and flow obstructions were
manipulated in the flume and the resultant acoustic signals recorded. Increasing relative submergence ratio and water velocity
were important for reaching a turbulence threshold above which distinct sound levels were generated. Increases in water velocity
resulted in increased sound levels over a wide range of frequencies. The increases in sound levels due to relative submergence
of obstacles were most pronounced in midrange frequencies (125 Hz–2 kHz). Flow obstructions in running waters created turbulence
and air bubble formation, which again produced specific sound signatures. |
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