Nov. 8, 191S 



Use of Current Meters in Irrigation Canals 



219 



with integration methods are shown, as measurements by this method 

 were not taken in all cases. 



Table I. — Variation in discharge in percentage by the two-point, the single-point, and 

 (he integration method, compared with the multiple- point method 



Table I shows all three methods to give an average discharge greater 

 than the multiple-point gaging. For the two-point and integration 

 methods this is not large, being about three-fourths of i per cent for both 

 of these methods. For the single-point method the average error is 

 + 4.80 per cent. This is large enough to warrant a correction factor, so 

 that all further comparisons with this method are based on a correction 

 of — 5 per cent made to the discharge secured by the single-point method. 



Besides the average error of the series of experiments, the probable 

 or average variation of a single observation is also given. While the 

 mean difference of the two-point and integration from the multiple-point 

 method is the same, the single measurements show a somewhat greater 

 average variation for the integration than for the two-point method. 

 If the results of the single-point observations are reduced by 5 per cent, 

 the corrected results have an average variation but little in excess of the 

 other methods. These results may be expressed by saying that with the 

 two-point method a series of observations will give results three-fourths 

 of I per cent too high. If no correction is made to the results, single 

 observations will have an average error of 1.5 per cent. 



The experiments covered a wide range of discharges and canal types, 

 so that further classifications were made to determine the effect, if any, 

 of differences in the velocity, the depth, or the value of n on the accuracy 

 of the different methods. The results are given in Table II. 



