JODIAL OF AGKCllLTllRAL ISEARCH 



DEPARTMENT OF AGRICULTURE 



Vol. V Washington, D. C, November 8, 1915 No. 6 



EXPERIMENTS IN THE USE OF CURRENT METERS IN 

 IRRIGATION CANALS 



By S. T. Harding, 

 Irrigation Engineer, Office of Public Roads and Rural Engineering 



INTRODUCTION 



Comparisons of the relative accuracy of measurements made in irriga- 

 tion canals with current meters using different methods are made in the 

 following discussion. In connection with field experiments made on the 

 flow in various types of canals in order to determine the value of the 

 coefficient n of Kutter's formula,* detail current-meter gagings were 

 necessary. These detail gagings and other observations made at the 

 same time have been used to compare the results obtained by the 

 standard two-point, single-point, and integration methods, as well as 

 by floats and various selected points of measurement. Much experience 

 is now available in regard to the various methods of current-meter 

 observations used in natural channels. The results given here apply to 

 the more regular artificial channels used in irrigation for which there 

 are fewer available data. 



In the experiments referred to, the current-meter readings were care- 

 fully taken at from 12 to 20 points horizontally across the canal section, 

 from four to six readings being made at each point. These detail or 

 multiple-point observations were plotted, and the mean velocity at the 

 diflierent points observed was determined from the vertical velocity 

 curves drawn through the plotted observations. The points across the 

 canal at which observations were made are referred to in the following 

 discussion as the "verticals." The results secured by the multiple-point 

 reading both in each vertical and for the discharge as a whole have been 

 taken as the correct velocities and discharges in the comparisons made. 

 In canals of the size used in most of these experiments determinations of 



' Ganguillet, E., and Kutter, W. R. General Formula for the Uniform Flow of Water in Rivers and 

 Other Channels; translated from the German, with . . . additions ... by Rudolph Hering and J. C. 

 Trautwine. ed. 2, 240 p., pi. New York, 1893. 



Journal of Agricultural Research, Vol. V, No. 6 



Dept. of Agriculture, Washington, D. C. Nov. 8, 1915 



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