9532

• UCREFRP Catalog Number: 9532
• Author: Anderson, R. and G. Stewart.
• Title: Riverine Fish Flow Investigations.
• USFW Year: 2000.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

Acoustic Doppler and Marsh McBernie Velocity Meters

For model calibration it is important to have observed measurements of depth and

velocity at known flows. While depth can be gathered using the same technologies that are

used in determining bathymetry, velocity measurements requires another set of instruments.

Two different technologies were used for measuring velocities in this project.

In 1998, a Marsh McBernie Flo-Mate Portable Flowmeter was used in conjunction

with the total station to determine point velocities. The Marsh McBernie has a published

accuracy of l.Scm/s +/- 2% of reading and isbased on the electrical principle known as

Faraday'sLaw, where the flow rate of the fluid can be determined by passing a conductive

fluid through a magnetic field. A wading rod used to hold the meter head which is placed at a

depth chosen to represent average velocity (usually .6 of total depth) Locations were recorded

"';.
by shooting the point with the total station and then recording the average of three 10-second

readings.

In larger rivers with high velocities anddeep areas, it is often not practical to use a

wading rod to measure velocities. In May of2000, a 3MHZ Sontek River Surveyor Acoustic

Doppler Profiler (ADP) was purchased to gather calibration data on the IS-mile reach of the

Colorado River. The ADP measures the velocity of water using a physical principle called the

Doppler shift. This states that if a source of sound is moving relative to the receiver, the

frequency of the sound at the receiver is shifted from the transmit frequency. By determining

the Doppler shift using three beams, it is possible to determine the relative speed and direction

of the flow. Using the Doppler shift from the river bottOllltodet~npine the boat speed and

direction, it is possible to compute absolute velocity and direction. The ADP measures

velocities in 15cm vertical increments down to the river bottom. These velocities are

averaged over a specified time interval.

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