Streams of sound

Posted on December 9, 2010

Perhaps surprisingly, the underwater sounds created by the turbulent waters of rivers and streams have received attention only in the last few years.  In a recent Swiss study, a 6 m x 0.4 m flume was used to examine the effects on the underwater soundscape of flow rate, water velocity, flow obstructions and the relative submergence of bottom structures.  Experimental flow rates were 10-50 litres per sec and water velocities were 0.1 – 1.7 m/s.  Sounds were recorded by hydrophones placed in different locations.  Most of the variation in sound intensity was explained by water velocity rather than flow rate, and sound levels in the middle frequency range (125 Hz – 2 kHz) rose as the submergence of objects increased.  Flow obstructions created turbulence and air bubbles, which produced specific sound signatures.  It’s possible that aquatic animals use the underwater soundscape in a range of ways – for example, by employing the contrasting sounds of pools and riffles to locate feeding areas, or by migrating in response to noises created by seasonal runoff.  Engineering and restoration works are likely to have an impact on the soundscape, and thus the ecology, of streams: for example, channelization increases water velocity by straightening the channel, and also flattens the stream bed, which reduces relative submergence. 

Reference:  Tonolla, D., Lorang, M.S., Heutschi, K. & Tockner, K.  2009.  A flume experiment to examine underwater sound generation by flowing water.  Aquatic Sciences 71, 449–462.