Global Water
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7
The Flow Probe can be used in three ways to determine average
velocity in a stream.
a. For small streams and pipes, the probe can be moved
slowly and smoothly throughout the flow during average
velocity measurements. Move the probe smoothly and
evenly back and forth from top to bottom of the flow so
that the probe stays at each point in the flow for
approximately the same amount of time. The timer
function in the display can be used to monitor the
measurement time. Keep moving the probe for 20-40
seconds to obtain an accurate average value that
accounts for surging. (Move the probe as if you were
spray painting and attempting to get an even coat of paint
over the entire surface.)
The Flow Probe uses true velocity averaging. Pushing
the RESET button zeros the average/minimum/maximum
velocities and a running average is started. As long as
the probe remains in the flow, the averaging continues.
To stop averaging press the SAVE button, in Save Data
mode the averaging is halted. In this mode the function of
the SAVE button changes to SET. Press SET to store the
data and reset avg/min/max, or press BACK to resume
the previous averaging without storing the data to
memory. One reading is taken per second, and a
continuous average is displayed. For example, after 10
seconds, 10 readings are totaled and then divided by 10
and this average is displayed. Once the average reading
becomes steady, the true average velocity of the stream
is obtained.
b. For larger streams and rivers where the Flow Probe can’t
easily be moved throughout the flow, divide the stream
into subsections 1-3 feet wide, depending on the width of
the stream. We recommend dividing subsections on your
graph paper diagram of the flow profile. Run a measuring
tape across the stream for reference. Obtain a vertical
