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
From: Jay DeLong
Sent: Wednesday, December 13, 2000 9:16 PM
Subject: Re: NANFA-- tangerines in streams
>Toss it in the water, measure the time it takes to go a pre-measured
>distance and hey, you have the speed of the water at the surface. :)
Correct, Sajjad! Indeed it is Alabama U Dave's self-labeled Auburn U model
current-velocity meter. Why?
1- oranges float
2- they float just below the surface so they aren't affected by wind
3- and they are visible (unless the water is orange, I guess)
Surface velocity isn't the best measurement of current velocity. A better
estimate is made by taking a measurement with an adjustible velocity meter
somewhere near 4/10 the depth from the surface.
>A healthy snack?
Yes, an edible field instrument, and all you have to take back out is the
-- Jay DeLong Olympia, WA
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