114 IRRIGATION FARMING. 



quires hundreds, aud sub-irrigation tens of gallons for a 

 similar area. 



Measurement of Water. There are also many 

 different standards of measurement of water for irrigat- 

 ing, and so many different conditions under which it is 

 applied, that one is apt to become confused and will decide 

 that there is a good deal of technicality about it that is 

 perplexing and intricate. As before stated the units of 

 measurement are the miner's or statutory inch, cubic 

 and acre feet, or by the gallon. With engineers the cubic 

 foot per second is the standard unit, and the quantity is 

 determined in large volumes by the rate of flow in the 

 sectional area of the channel and in the smaller volumes 

 by the flow over a measuring weir. The theoretical capac- 

 ity of a channel as determined by formulas is almost 

 always in excess of the actual capacity as determined by 

 experiment, by a varying percentage dependent upon the 

 following conditions : First Sinuosity or aggregate de- 

 gree of curvature. Second Sharpness of bends or degree 

 of curvature. Third The uniformity and symmetry of 

 cross section. Fourth The character of the frictional 

 perimeter of the sides and bottom. The simple theory of 

 flowing water in channels is not a difficult matter of 

 understanding, but it is the modification of this theory 

 by the various co-efficients of friction that leads to mis- 

 understanding. 



To properly estimate the flow of water in canals and 

 its distribution through headgates a number of devices 

 have been invented, and these include such things as nilo- 

 meters, current meters, hydrometric sluices, division 

 boxes, modules, weirs and water registers." A measur- 

 ing device is not always necessary, especially where one 

 has his own private water supply, but in taking water 

 from public canals it is always more satisfactory to have 

 an arrangement by which the actual intake of water 

 may be determined. 



