The IEEE Seventh Working Conference on Current Measurement Technology

Current and Wave Monitoring and Emerging Technologies

March 13-15 | Bahia Hotel | San Diego, CA, USA

  
     

Complete Velocity Distribution in River Cross-sections Measured by Acoustic Instruments

Ralph T. Cheng

Status: Accepted

345 Middlefield Road, MS-496

Menlo Park , California USA
94025

Phone: 650-329-4500
Email: rtcheng@usgs.gov

Co-Authors:
Jeffrey W. Gartner
U. S. Geological Survey
Menlo Park, California 94025

In order to fully understand the hydraulic properties in natural rivers, velocity distribution in the cross-section of rivers must be studied in detail. The measurement task is not as straightforward as it seems because there is not an instrument that can measure the velocity distribution covering the entire cross-section. Particularly, the velocities in regions near the free surface and in the bottom boundary layer are difficult to measure, and yet the velocity properties in the near-surface and near-bottom regions play the most significant role in characterizing the hydraulic properties of a river. To further characterize the river hydraulics, a flow measurement program was carried out with the focus on measuring the velocity distribution in the entire river cross-section. To achieve this objective, three acoustic instruments, namely, an acoustic Doppler velocimeter (ADV), an acoustic Doppler current profiler (ADCP), and a BoogieDopp (BD) were used on measurement platforms that were positioned at fixed stations to measure the detailed velocity profiles. Typically, between 20 and 25 stations were used to represent a given river cross-section. At each station, water velocity profiles were measured independently and concurrently by different instruments whenever possible. The measured velocity properties were compared and used in the computation of river discharge. In a tow-tank evaluation of a BD, it has been confirmed that BD is capable of measuring water velocity at about 11 cm below free-surface. Therefore, the surface velocity distribution across the river was extracted from the BD velocity measurements with which to compute the river discharge. These detailed velocity profiles and the composite velocity distribution were used in assessing the validity of the classic theories of velocity distributions, the conventional river discharge measurement methods, and for evaluations of channel bottom roughness.

Submitted on October 29, 2002