Hydroacoustic Current Meters for the Measurement of Discharge in Shallow Streams and Rivers

Mechanical Current Meters

The USGS traditionally has used mechanical, propeller-type current meters to measure water velocities.  Velocities are computed by the number of revolutions of the propeller per unit of time.

Limitations of mechanical current meters

Mechanical current meters have limitations, including the following:

• Shallow depth limit of 0.3 ft (pygmy meter)
• Low velocity threshold of 0.1 ft/s (foot per second)  (pygmy meter)
• Extensive maintenance required to maintain meter accuracy
• Meter disturbance of  the flow measured

These limitations can hamper the usefulness of mechanical meters, particularly at very low flows when streams can be shallow and slow.  It is during such low-flow periods that accurate discharge data can become critical to government agencies, private firms, and the general public.  While mechanical current meters have served the USGS well, there is new technology that could represent a major improvement in discharge-measurement accuracy. 

Next: Hydroacoustic Technologies for Wading Discharge Measurements

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• The use of  trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the United States Government.
• All information herein is provisional and subject to revision.
• Emphasis on the instruments described in these pages does not imply that these are the only instruments that can be used for this purpose.  The instruments were selected for the following reasons: the instruments are readily adaptable to this purpose, the instruments are on Federal purchase schedules, and the instrument vendors have voluntarily committed resources to this application. Other instruments will be investigated within the limits of project funding and schedules.

U.S. Department of the Interior
U.S. Geological Survey
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Phone: (317)290-3333
Fax: (317)290-3313
URL: http://in.water.usgs.gov/hydroacoustics/acoustic_wading_rod_mechanical.shtml
Last modified:Monday, 13-Aug-2007 16:58:47 EDT
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