236 



THE IRRIGATION AGE. 



CANAL AND STREAM MEASUREMENTS.* 



BY A. P. STOVER. 

 Instructor in Irrigation, University of California. 



As one comes in contact with irrigation practice in 

 the West, among the first features to attract attention is 

 the almost universal ignorance of the average irrigator 

 as to the exact amount of water he controls. It is true 

 that he has an idea of how much water is required to 

 satisfy his needs, but to reduce this amount to tangible 

 units is an utter impossibility. His gauge is his eye, aided 

 by his judgment sharpened by constant practice. We 

 may say that all irrigators know when their water supply 

 is short, a comparatively small number know when they 

 have too much, but the percentage who can tell when 

 they are receiving and using the right amount of water 

 is very small. 



Where the value of agricultural land is gauged by 

 the water supply available for use thereon, it would 

 seem that a man's water supply should be measured and 

 divided as accurately as is the land whose producing 

 value it regulates. The average irrigator, if he wishes 

 to know the area of a tract of land, takes a tape line 

 and measures its boundaries and dimensions. He can, 

 with little difficulty, compute the volume of water in 

 his reservoir, but when it comes to determining the 

 discharge of his irrigation stream he too often is con- 

 tented with a mere guess, or relies upon the statement 



box, having a slot in one side through which the water 

 is allowed to escape under a low pressure. With give 

 conditions satisfied relative to the size of the slot, to the 

 head of the opening and to the flow of the water fron> 

 the orifice; the number of square inches of opening is- 

 the number of "inches" being discharged brom the box. 

 A number of States, California among the first, adopted 

 the miner's inch system as the legal method of measure- 

 ment and the statutes prescribed the conditions under 

 which the measurement should be made. 



Colorado law defines the "inch" and prescribes the 

 conditions to be observed in measurement as follows r 



"Every inch shall be considered equal to an inch 

 square orifice under a five-inch pressure, and a five-inch 

 pressure shall be from the top of the orifice * * * 

 to the surface of the water. * * * Slot or aperture- 

 through which the water may be measured shall in ali 

 cases be six inches perpendicular inside measurement 

 except in boxes delivering less than twelve inches which 

 may be square. * * * Box shall have a descending: 

 grade from the water in the ditch of not less than one- 

 eighth of an inch to the foot." 



In most instances the six-inch slot has been pre- 

 scribed, and the head required varies from four inches- 

 above the center in some States to six inches above the 

 top of the orifice in others. Because of this wide varia- 

 tion in the conditions required, not only by statute, but 



Fig. 1. The Foote Modification of the Miner's Inch-box. 



of some one who is probably no more competent to judge 

 than himself. 



To those unfamiliar with the operation, the meas- 

 urement of a stream of flowing water seems quite a 

 complicated and difficult problem. It is but another 

 case, however, where appearances are deceiving, for the 

 operation, when understood, is found to be a compara- 

 tively simple one. The two methods of measuring 

 water to be described viz., by the measuring weir and 

 by the current meter, are those most commonly employed 

 by engineers and others required to control, regulate, or 

 divide flowing water. 



UNITS USED IN EXPRESSING STREAM DISCHARGE. 



The discharge from pumps and from wells is usual- 

 ly expressed in gallons per second, minute or hour. 

 From ditches, canals and streams, however, the gallon 

 is too small a unit and for these the discharge should 

 be expressed in cubic feet per second or in cubic feet 

 per minute, these units being abbreviated often to second 

 feet and minute feet respectively. In addition to these 

 units of flow the "Miner's Inch" is frequently used. 



This method of measuring water by "inches" had 

 its origin in the early days of hydraulic mining. The 

 miner's inch box consists essentially of a rectangular 



"Courtesy California Journal of Technology. 



by custom as well, the use of the inch as a unit of meas- 

 urement is to be deprecated. Its value varies quite wide- 

 ly in various States as shown in the following table. 



Table showing number of inches assumed to be 

 equal to a flow of one cubic foot per second in different 

 Western States: By Custom -By Statute 



Equivalent in California 50 40 



Equivalent in Colorado 38.4 38.4 



Equivalent in Montana 40 40 



Equivalent in Idaho 50 



Equivalent in Arizona 40 



Equivalent in Nevada 50 



Equivalent in Utah 50 



Not only does it vary in different States, but it 

 also has different value in some instances in the same 

 State. For instance, in Nevada the inch in one part 

 of the State may be measured under a four inch pressure, 

 while in another part of the State it is measured under 

 six inch or twelve inch pressure, depending entirely upon 

 local custom. An investigation of the irrigation practice 

 on the Humboldt River,* revealed the fact that not 

 only did the pressure vary between these limits, but ij> 

 some cases water was measured under pressures of two 

 feet, three and one-half feet and four feet. 



* Report of United States Irrigation Investigations, Humboldt 

 River Valley, by J. D. Stannard, 1901. 



