18
Top-Setting-Wading Rod
Two accepted methods for determining mean velocities of flows are as follows:
1. Measure the velocity at 60% of the depth (from the top) and use this as the mean.
2. Measure the velocity at 20% and 80% of the depth (from the top). Use the average of these
velocities as the mean.
The purpose of the top setting wading rod (Figure 12) is to conveniently set the sensor at 20%, 60%,
or 80% of total depth. The total depth can be measured with the depth gauge rod. Each single mark
represents 0.10 foot, each double mark represents 0.50 foot, and each triple mark represents 1.00 foot.
To set the sensor at 60% of the depth, line up the foot scale on the sliding rod with the tenth scale on
the top of the depth gauge rod. If, for example, the total depth is 2.7 feet, then line up the 2 on the foot
scale with the 7 on the tenth scale.
To set the sensor at 20% of the depth, multiply the total depth by two and repeat the above procedure.
In the above example this would be 5.4 feet. Line up the 5 on the foot scale with 4 on the tenth scale.
To set the sensor at 80% of the depth, divide the total depth by two and repeat the above procedure. In
the above example, this would be 1.35 feet. Line the 1 on the foot scale with 0.35 on the tenth scale.
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