[Acoustics] Sontek SW for canal flows

[Tracy Vermeyen]

Hello Grant,

Provided your Sontek SW application is in a stable cross section so the
stage-area relationship does not change you do not need to develop an
index-velocity relationship.  Index-velocity is used when a side-looking
profiler is used to measure the average velocity in a horizontal plane
across the canal (or one point on the vertical velocity profile).  The
SW is a vertical profiler and computes a mean (depth integrated)
velocity that is multiplied by the cross sectional area.  It is good
practice to check the SW-measured flow with another method (ADCP, stream
gaging), but a full blown calibration is typically not required with
this application.

My experience with SWs in canals has been that they work very well in
cross sections that are concrete lined (like the flume and gunited
sections you mentioned).  Performance may be compromised for cross
sections with width-to-depth ratios greater than 12:1, especially for
shallow depth applications.  Sontek recommends using the SW in depths
greater or equal to 2 ft.  I have had good luck using SWs in culverts
for partially full and full flowing conditions.  It you have sediment
transport in your system it is recommended that you closely monitor the
Signal-to-Noise ratios to make sure your transducer is not getting
covered with sediment. 

Lastly, I performed a laboratory evaluation of SWs in a 4-ft-wide flume
and a 18-in plastic culvert and the SW performed within specs for most
of my tests.  If you would like a copy send me a note and I will send
you one.

Hope this information is helpful.



Tracy B. Vermeyen, P.E.                           
Hydraulic Engineer                      
U.S. Bureau of Reclamation                        
Water Resources Research Laboratory    
P.O. Box 25007, D-8560
Denver, Colorado  80225-0007

Phone:  303-445-2154
FAX :     720-544-0551 
Cell:       303-870-9178
e-mail: tvermeyen at do.usbr.gov 
http://www.usbr.gov/pmts/hydraulics_lab/tvermeyen/index.html
>>> "Winslow, Grant" <GJW2 at pge.com> 01/11/05 7:10 PM >>>
Can anyone provide me info as to how best to develop an index velocity
profile for a few canal cross sections where a Sontek SW ADVMs will be
installed?  I have heard that an ADCP can be attached to a cable strung
across the canal, and taking velocity profiles w/ meter facing downward.
The cross section is not necessarily going to have a walkway above it
where I could lower a Price AA on a rod to check various depths.

Please share your experiences using these meters in canals!  In my
situation,  there are canals ranging in depth from 2 - 8 ft, cross
sections from 15 - 25 ft width,  and concrete box flume and gunited
canals, with velocities ranging from 2.5 ft/s - 7.5 ft/s.  

Regards,

Grant