Reference is also made, where appropriate, to methods for the determination of flow in non-tidal channels, but attention is drawn to their limitations with respect to practicality and/or uncertainty.
ISO 2425:2010 does not describe alternative methods, such as the use of weirs, flumes, dilution gauging, salt velocity and floats, although they might be suitable under certain conditions, especially where the effect of tides only impedes and does not stop or reverse the passage of stream flow. These methods are described in detail in other International Standards.
ISO 2425:2010 specifies two types of technique: techniques for single measurements of tidal flow; techniques for continuous measurement of tidal flow.
Annex A specifies the cubature method of measurement. Annex B specifies methods for the determination of flow under tidal conditions, and Annex C gives an example of the computation for a single vertical. Similar computations are possible for other verticals. Annex D describes the determination of tidal flow using an acoustic Doppler velocity meter.