Bed load measurements with a new passive acoustic sensor
Jim Bogen & Knut Møen
Bok Engelsk 2003
| Medvirkende | Møen, Knut (medforfatter)
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| Utgitt | [Oslo] : NVE , [2003]
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| Omfang | s. 181-192 : ill.
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| Opplysninger | Særtrykk fra: Erosion and Sediment Transport Measurement in Rivers. Technological and Methodological Advances. (Proceedings of the Oslo Workshop, June 2002). IAHS Publ.283, 2003.. - Abstract: Flume experiments and field tests of acoustic bed load sensors have been carried out in three Norwegian rivers. The sensors record the acoustic energy of bed load impacts on a plate fixed to the river bed. Some of the sensors operate in a narrow ultrasonic frequency band, while others record the whole frequency spectrum from 0 to 500 kHz. The systems tested are able to monitor temporal variations in bed load transport and thereby provide additional information about the transport process. The field measurements revealed a markedly irregular pattern of bed load transport rates. The presence of a hysteresis effect indicates some similarity to suspended load transport, with the transport rate being much larger on the rising stage of a flood than on the falling stage. A large difference between maximum and mean acoustic amplitudes over a given time period reflects sporadic transport; the difference is much less when particle transport is continuous. Flume experiment results for a single fraction, 18-27 mm, produced a linear relationship between bed load transport in kg s-1 and acoustic energy integrated over the frequency range. Preliminary analyses indicate that a characteristic relationship exists for each size fraction within the bed load range. The present studies of the transport of different grades also indicate that each fraction may have a characteristic frequency signature. Thus, it is possible that a multivariate calibration model may predict both total load and grain size from acoustic amplitudes and frequency spectra.
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