[Acoustics] Sontek SW for canal flows

[Tracy Vermeyen]

Hi Jim,  

You make a very good point.  As with all flowmeters, site selection is
a very important factor in how the meter performs.  Likewise,
calibration is an integral component for developing confidence in the
flowmeter.  My point to Grant was that an Index-Velocity relationship is
not always necessary to achieve good performance with an Argonaut SW
using proper site selection and installation techniques. 

If you have the time and money to develop a index-velocity
relationship, by all means do so, as Sontek mentions in its last bullet
item below.

Sontek has a technical note describing the flow theory it uses in the
Argonaut SW, the following is an excerpt from that note (see attached).

Internal flow calculations are used by the Argonaut-SL and SW for real
time flow data.

* Flow is based on velocity multiplied by cross sectional area.

* Water level is measured using a vertical acoustic beam; cross
sectional area is calculated
based on user-supplied channel dimensions.

* The firmware supports three channel types: irregular (i.e. natural
stream, defined by up to 20
survey points), trapezoidal (i.e. regular concrete lined channel), and
pipe. For flow
calculations, irregular and trapezoidal channels are treated the same
(open channels).

* Velocity is based on the Argonaut measured velocity, which is
modified either by a user-supplied
index calibration or by a theoretical model of how measured velocity
compares with
the mean velocity throughout the channel.

* This document describes the theoretical models used to relate
Argonaut measured velocity to
mean channel velocity.

* An empirically determined index velocity relation will be more
accurate than a theoretical
approach. However, the theoretical approach may provide reasonably
accurate results
without the independent measurements needed to develop the index
velocity relation.

>>> <jbderose at usgs.gov> 01/12/05 12:45PM >>>
Hi Tracy,

I'm not familiar with the SWs, so I'm a little curious.  How do you
know 
for sure that the depth integrated velocity obtained from the SW is the

same as the mean channel velocity?  Our experience has shown (Gartner,

others...) that even in a concreted channel velocity is fastest near 
center and slows down when you get closer to the sides.  Does the SW 
somehow take this into account when it calculates a channel mean
velocity? 
 We treat all our upward ADCPs as an "index" velocity for this very 
reason. 

Thanks,

JB

James B. DeRose
Electronic Technician 
US Geological Survey
Placer Hall 6000 J Street
Sacramento, CA 95189
Ph (916) 278-3056
Cel (916) 826-4518
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