Estimating Flow Rate using the Float Method

A common but simple method for measuring flow rate through an open channel is the Float method. Although not as accurate as a measuring device such as a flume or a velocity probe, the float method can provide an educated estimate. Briefly put, this method involves measuring the surface velocity of the water with a floating object, and then multiplying this velocity by the width and average depth of the channel.

"The accuracy of float methods are limited by many factors, including a lack of preciseness in the coefficients, too few stream segments being used, appreciable changes in stream depth along the test reach, oblique currents, wind forces, and experimental errors in measuring time and distances. Often, a number of people are required to perform this technique and make observations. The course of the floats is difficult to control, and they can be easily retarded by dragging on submerged debris and on the sides and bottom of the channel." (USBR)

US Bureau of Reclamation document - https://www.usbr.gov/tsc/techreferenc...

See the calculator, instructions, and worksheet on our website at http://inmtn.com/float.
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