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Velocity Observations

The graphs below show continuous velocity measurements made at the North Fork Toutle River in Washington state during 1989. Electromagnetic velocity meters were mounted on the same vertical-support pipe used for sonar. Voltage output from the meters was converted to digital form by sampling simultaneously with the sonar readings at 2 Hertz. Three positions, separated vertically by 0.34 m, were available on the meter frame for velocity measurements.

-- adapted from Dinehart, R.L., 1992, Evolution of coarse-gravel bedforms: Field measurements at flood stage, Water Resources Research, v. 28, n. 10, pp. 2667-2689.

Correlative velocity fluctuations

Correlative velocity fluctuations
Three meters show velocity fluctuations with short-term correlations in the upper half of flow. The fluctuations have a range of durations from a few seconds to over half a minute.




Velocity over a gravel bedform

Velocity over a gravel bedform
Velocity measured near mid-depth shows influence of gravel bedform on mean velocity.




Comparison of velocity over gravel bedforms

Comparison of velocity over gravel bedforms
Standard deviation of velocity near mid-depth decreased as flow receded.

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