PCWA-L 467.pdf - PCWA Middle Fork American River Project ...
PCWA-L 467.pdf - PCWA Middle Fork American River Project ...
PCWA-L 467.pdf - PCWA Middle Fork American River Project ...
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5. DlSCHARGE-CURRENT-METER METHOD 91<br />
OPTICAL CURRENT METER<br />
In recent years the U.s. Geological Survey has developed an optical<br />
current meter (fig. 50). The meter and its use have been described by<br />
Chandler and Smitb (1971). The optical current meter is designed to<br />
measure surface velocities in open channels without immersing<br />
equipment in the stream. However, because it measures only surface<br />
velocity, the optical meter is not considered a substitute for conventional<br />
equipment in those situations where good measurements<br />
can be made by standard techniques. It is a device that has extended<br />
the capability ofmaking discharge measurements to a range ofsituations<br />
under which standard current-meter techniques cannot be used.<br />
Those situations include flood velocities that are too high to be measured<br />
by conventional meter-for example, supercritical velocities in<br />
flood ways-or the presence of a debris load during flood periods that<br />
makes it hazardous to immerse a current meter.<br />
Basically, the meter is a stroboscopic device consisting of a lowpower<br />
telescope, a single oscillating mirror driven by a cam, a<br />
variable-speed battery-operated motor, and a tachometer. The water<br />
surface is viewed from above through the meter, while gradually<br />
changing the speed of the motor to bring about synchronization of the<br />
FIGURE SO.-Optical current meter.
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