Accuracy of Current Meter Measurements

Laboratory tests and field experience show that the probable accuracy of a stream flow measurement made by the usual current meter method is approximately 2%. This conclusion is based on a statistical analysis of the component errors of special measurements made on more than one hundred different streams, and on the results of other investigations reported in the literature. The errors considered are due to the rating of the meter, the effect of stream turbulence on the performance of the meter, the time fluctuation of velocity at a point, the assumption that the average of velocities taken at 0.2 and 0.8 depth equals the mean velocity, and the number of stations in the section at which observations are made. The standard deviation of each component error in percent of mean is evaluated from laboratory or field measurements. The individual variances are then combined to give the probable total error.