Evaluating velocity measurement techniques in shallow streams

Abstract

Accurate flow field measurements in shallow rivers are necessary for many applications including biological investigations and numerical model development. Unfortunately, river velocity data is difficult to obtain due to the limitations of traditional velocity meters. Acoustic Doppler Current Profilers (ADCP) provide a potential alternative to traditional point-velocity measurements. However, these instruments have not been thoroughly tested against accepted techniques in natural streams. The objectives of this research were to evaluate the adequacy of ADCP instruments for conducting velocity measurements in quasi-wadeable streams and to provide instrument selection guidance for similar flow environments. These objectives were met by conducting ADCP, Acoustic Doppler Velocimeter (ADV), and Price current meter measurements at nine coinciding verticals in two rivers. The performance of each instrument was evaluated with regards to data accuracy, desired parameters, and required sampling time. ADCP measurements compared favorably with ADV and Price meter data for velocity profiles and depth-averaged velocities. The ADCP also showed a significant improvement in estimates of local bed shear stress when compared to global estimates determined from the water surface profile. However, excessive noise reduced the effectiveness of ADCP measurements of velocity standard deviation and velocity components. The results are discussed in the context of instrument selection for parameterization of models

Keywords:

• Acoustic instruments
• velocity profiles
• ecohydraulics
• field methods
• turbulence