The velocity of a river is the speed at which water flows along it. River / stream velocity is measured using propeller-type current meters or other methods – increasingly Acoustic Doppler Current Profilers (ADCPs) are being used, the latter offer significant advantages (e.g. speed of flow assessment and greater safety for the operators) over traditional current meters. (Yorke and Oberg 2002)
Yorke, Thomas H, and Kevin A Oberg. 2002. “Measuring River Velocity and Discharge with Acoustic Doppler Profilers.” Flow Measurement and Instrumentation 13 (5–6): 191–95. https://doi.org/10.1016/S0955-5986(02)00051-1.