230 



Journal of Agricultural Research 



Vol. V, No. 6 



Table VI. — Discharge and velocity of various types of canals by measurements of two 

 selected verticals 



For vertical-sided flumes 22 gagings were available. The depths 

 varied from 0.7 to 4.4 feet, the widths from 2 to 17.7 feet, and the dis- 

 charges from 2 to 400 second-feet. The velocities and depths at points 

 at a distance of one-fifth and one-sixth of the width from the sides were 

 used to obtain discharges which were then compared with those ob- 

 tained by the complete gaging. In such flumes with vertical sides the 

 depths are practically uniform, and the use of the depth at only two points 

 would cause little error in the resulting area. These results show that 

 the two points whose mean velocities will equal that of the whole cross 

 section lie generally between one-sixth and one-fifth of the width from 

 the sides and that the error in using such index velocities at either pro- 

 portion of the width averages about 2 per cent and does not exceed 5 

 per cent, except in a few cases. 



For concrete-lined canals the canal section is uniform, and the cross- 

 sectional area would be known for any depth. In such canals the dis- 

 charge can be obtained from determinations of velocity and known areas 

 for given depths. The comparisons given in Table VI are based on 



