In a message dated 12/14/00 11:21:54 AM Eastern Standard Time,
HOOVERJ_at_wes.army.mil writes:
<< The citrus-based velocity meter, a favorite with George Moore and his
students, was still in common use by Oklahoma ichthyology students in the
1980's. We did not have ready, or steady, access to velocity meters. It
always bothered me that the oranges drifted off course, got caught in
eddies, and did not allow point measurements across the stream. At the
time, I did not know about "head tubes" but those would have been a
low-tech, big improvement in technology.
Head tubes are home-made devices that apparently work quite well measuring
surface velocity. They are clear plastic tubes (length depending on depth
of streams to be measured) with a clear plastic sleeve marked in
millimeters. You put the tube on the stream bottom, slide the sleeve down
to water's surface, and measure height of the crest formed by the rush of
water at the upstream edge of the tube. This measurement can be converted
to a velocity (in cm/s). You need a velocity meter initially to "calibrate"
your tube and develop the relationship between crest height and known speed,
but once that's done, all you need is the tube. Also, I think that there
are some established relationships you can look up for tubes of specific
diameters. Anyway, this is useful technique for those who do not require
sub-surface velocity or those who like devices that do not require a power
supply. >>
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