Operational considerations

The method of velocity sampling across a gauging section depends on the size of the river and its accessibility. Methods include the use of wading rods, bridges, boats, floats and cableways. With wading the current meter is carried on special rods and held in

Moving boat calibration with acoustic Doppler current profiler (ADCP)

Moving boat calibration with acoustic Doppler current profiler (ADCP)

Fig. 7.15 A diagrammatic sketch of an acoustic Doppler current profiler (ADCP). (Reproduced with permission from Herschy, R. W. (2009) Streamflow Measurement, 3rd edn. Taylor & Francis, Abingdon.)

Inoperative paths above surface

Fig. 7.16 A diagrammatic representation of an ultrasonic system. (Reproduced with permission from Herschy, R. W. (2009) Streamflow Measurement, 3rd edn. Taylor & Francis, Abingdon.)

position by the gauger standing on the stream bed a little to the side and downstream of the instrument. This is the ideal method, since the gauger is in full control of the operation, but it is only practicable in shallow streams with low or moderate velocities. Where there is a clear span bridge aligned straight across the river near the gauging station, the current meter can be lowered on a line from a gauging reel carried on a trolley. Care must be taken to sample a section with even flow. For very wide rivers, gaugings may have to be made from a boat either held in position along a fixed wire or under power across the section. Velocity surveys with an ADCP can be undertaken with the ADCP mounted on a float drawn across the channel; though boats and cableways are also used. With a cableway, the gauger remains on the river bank, but winds the current meter across the section on a cableway, lowering it to the desired depth by

Inoperat close to

Inoperative paths above surface

Inoperat close to

Fig. 7.16 A diagrammatic representation of an ultrasonic system. (Reproduced with permission from Herschy, R. W. (2009) Streamflow Measurement, 3rd edn. Taylor & Francis, Abingdon.)

Multiple sound paths

Multiple sound paths

Fig. 7.17 Cableway system. (Reproduced from BS EN ISO 4375: 2004, by permission of BSI.)

remote mechanical control (Fig. 7.17). Normally, the cableway controls are installed in the recorder house alongside the stilling well installed for stage recording.

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