from scan to scan at some sites. Because Ultraflow QSD 6537 is very sensitive to variations in velocities, you are able to see the natural velocity changes in the channel.
Although the discharge in a channel may be reasonably constant for a period of time, the velocity distribution is always changing. Different velocity streams wander from side to side and bed to surface as they progress down the channel. Turbulent swirls and eddies are carried downstream for long distances while they slowly decay. Hydrographers will be used to having this action partly removed by the mechanical inertia of a current meter and the period over which a typical measurement is timed. However all will have noticed that the rate of revolutions of the current meter varies during the timing period.
Continual velocity logging at one location with a Ultraflow QSD 6537 will show these cyclic velocity pulsations. The characteristics will be different for different sites and will vary with discharge. Cycles will typically include short period fluctuations (a few seconds) overlaid on longer cyclic fluctuations (up to many minutes). Longer term pulsations may also be seen particularly in larger streams when in flood.
When comparing Ultraflow QSD 6537 velocity and mechanical current meter readings, the display should be observed long enough to estimate the mean of the readings. The Ultraflow
QSD 6537 will do most of this processing internally but if an external logger is being used to record the readings averaging could also be done here this will help attenuate short frequency variations.
Post time: Nov-11-2022