[Acoustics] Moving Bed Test - Loop Method Protocol

[Huston, Dave]

Hi All,
 
I'd like to know the currently accepted protocol for the "loop method"
of moving bed tests and when one can make a reasonable judgment from a
particular test that the bed was "moving", "fluidized", or whatever
people like to call it [i.e. requiring the use of GGA as the reference
instead of BTM, when processing RDI Workhorse transect files].  All of
this is assuming that the test and flow measurements are being performed
with a DGPS that's working properly and that the ADCP was
compass-calibrated correctly with no ferrous metals in the vicinity of
the ADCP affecting the compass.
 
My present understanding is this:
 
1) Select a good fixed start location, take your edge estimate and start
your loop (hitting F5 in WinRiver and entering in your edge estimate and
the appropriate bank).
2) Crab across to the opposite bank, take your edge estimate, then
loop-back to the starting bank (without hitting F5, which would have
ended the transect).
3) Return to the same start location and take a final edge estimate and
hit F5 to end the "loop"
 
Note A) Taking the edge estimates were simply to allow the data
processor to separate the loop into two separate transects which could
then be used as part of your flow measurements.
Note B) Preferably, the total loop time should have been around 600
seconds (10 minutes).
 
4) Take the DMG (for the BTM ref.) and divide it by the total transect
time in seconds to get "moving bed" velocity  ---  DMG (ft) / transect
time (s) = MB Velocity (ft/s)
5) Go to the Discharge History Tabular (hit F12) and find the value for
Q/Area (ft/s) for the "loop", which is the overall loop water velocity
6) Take your MB Velocity (ft/s) and divide it by the Q/Area (ft/s) for
the "loop" and multiply by 100 to get a percentage of the "moving bed"
velocity to the overall loop water velocity.
 
MB Velocity (ft/s) / Q/Area (ft/s) * 100 = %
 
7) If that percentage is equal to 1% or greater, you could make a
reasonable judgment that the bed is "moving/fluidized" and that the data
processor should use the GGA as the reference.
 
 
What I'm not sure about are two things that could be related (and you
might find more).
 
First, we work at quite a few sites that are channelized with rip-rap on
both levees and not too many trees or objects that are easy to fixate
upon.  So...we can't be entirely sure that our ending point is the same
as our start point.  Is there a simple way to correct for that within
Winriver by using the difference in the GPS coordinate data between the
end ensemble and start ensemble?
 
Second, when calculating the "moving bed" velocity...should I ACTUALLY
be using the difference in the distance made good between the GGA
reference data and the BTM reference data (DMG - DMB) and then divide
that by the total "loop"/transect time?  I'm assuming that if the bed is
moving, I would see a large difference in the distance made good (DMG)
between the two references (GGA and BTM).  This might also help me to
correct out any distance differences between my actual start point and
end point.  Should I be calculating the "moving bed" velocity this way?
 
I'd appreciate any correspondence or help that any of you out there may
offer.  Additionally, this may be good for the collective to discuss and
formalize the protocol in writing.
 
Thanks All,
 
Dave
 
***********************************
Dave Huston, P.E.
Dept. of Water Resources
Central District
3251 S Street, Room E-25
Sacramento, CA. 95816
(916) 227-7583
(916) 227-7600
***********************************
 
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