20 



THE IRRIGATION AGE. 



(We are reproducing in this issue Chapter XVIII of the Primer 

 of Irrigation, which appeared in our issue of October, and in which 

 several mistakes occurred. These errors were overlooked during the 

 absence of the editor, and it was thought better, in view of the fact 

 that a large number of our readers are preserving the copies contain- 

 ing the Primer for reference, to reproduce same in corrected form, 

 so that no mistakes would appear in records saved. Consequently 

 we will ask those who have filed copies of our October issue contain- 

 ing Chapter XVIII of the Primer to destroy those pages on which 

 this matter appears and preserve this issue, which contains both Chap- 

 ters XVIII and XIX.) 



THE PRIMER OF IRRIGATION. 



COPYRIGHTED, 1903, BY D. H. ANDERSON. 



CHAPTER XVIII. 



(Measurement of Water.) 



If we fill a gallon measure with water we know 

 that we have 231 cubic inches of water which weighs 

 eight and one-third pounds. That is the United States 

 standard. We also know, because it is easy to measure 

 it, that a cubic foot of water weighs sixty-two and one- 

 half pounds and measures 1,728 cubic inches, equal to 

 seven and one-half gallons.- 



When it comes to measure water for irrigation 

 purposes it is difficult to ascertain the exact quantity 

 measured, owing to arbitrary standards of what the 

 measure should be. Besides that, the various States 

 and countries are not agreed upon a universal stand- 

 ard of measurement, so that when one reads of fifty 

 inches being required to raise a crop, his measurement 

 may mean a much less number of inches if measured ac- 

 cording to some other standard. Ten thousand gallons 

 of water by accurate measurement may be run into 

 a reservoir, and in twenty-four hours or less that num- 

 ber of gallons will be materially reduced, but the loss 

 can be accurately estimated, and so can the exact quan- 

 .tity run out of it for any purpose be measured almost 

 to a drop. But in the case of taking water from a 

 running or flowing stream or ditch, various difficulties 

 stand in the way of accurate measurement. 



In measuring water from streams, ditches and run- 

 ning or flowing water, generally three standards, or 

 "units of measure" as they are called, have been agreed 

 upon. They, are the inch, the cubic foot per second, 

 and the acre-foot. 



THE INCH. 



The "inch" as a unit of water measurement origi- 

 nated with the placer miners of the W T est and was 

 adopted by irrigators when water came to be used upon 

 the land for the growing of crops. It is the volume of 

 water which will flow through an inch-square open- 

 ing or orifice with a certain other volume of water over 

 and a-bove it to* give it what is known as "pressure." Both 

 the opening as to size and the depth of water above it 

 are regulated by the laws of some of the States, and in 

 many localities it is regulated by custom that is, by 

 agreement. The definition given in the laws of Colo- 

 rado will furnish an idea of what constitutes an inch : 



"Water sold by the inch shall be measured as fol- 

 lows, to-wit: 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 

 of the box put into the banks of the ditch to the sur- 

 face of the water." 



Of course, this opening may* be larger than one 

 inch square; for instance, six inches, or twelve inches, 

 but in that case the inch will become multiplied into 

 as many inches as there are inches in the opening. At 



six inches the volume of water would be thirty-six 

 inches, and at twelve inches there would be delivered 

 144 inches of water. A simple and usual way to meas- 

 ure the inch and retain the pressure is to make the 

 opening one inch wide and any number of inches long 

 a slot, so to speak ; over this slot is arranged a sliding 

 board that can be moved back and forth any number of 

 inches of actual measurement with a carpenter's rule. 

 By this device there will always be the required volume 

 of water, or pressure, above the inch orifice. 



Many irrigators roughly measure the quantity of 

 water delivered from a ditch, or canal, by calculating 

 the number of square inches in a cross section of the 

 ditch and calling the result so many inches of water, 

 but this is not a safe rule to follow, for pressure and 

 the velocity of the stream of water are not taken into 

 consideration, and they make a vast difference some- 

 times in the quantity of water delivered. The orifice 

 measurement under pressure is the most accurate and 

 gives better satisfaction. 



The inch, "however, as a standard of measurement, 

 or unit, is of very little use except for the measure- 

 ment of small quantities of water. It may be adapted 

 to the distribution of water from small main ditches 

 or their laterals. 



CUBIC FOOT PER SECOND OR "SECOND-FOOT." 



Owing to the inconveniences of the "inch" as a 

 unit of measurement, and the limitation on the me- 

 chanical device for measuring it, the cubic foot per sec- 

 ond or "second-foot" has been adopted as better adapted 

 to the measurement of both large and small quantities of 

 water; indeed, it is made the legal unit in most of the 

 arid States and Territories in water contracts and for 

 defining the amounts appropriated from streams. But 

 although made the unit of measurement it is used in 

 connection with the inch that is, a cubic foot per sec- 

 ond is distributed to farmers according to the number 

 of inches it is supposed to contain. This is fixed by law 

 and the following table will show the variations in the 

 number of inches contained in a cubic foot per second : 



In California, Idaho, Nevada and Utah fifty min- 

 ers' inches equal one cubic foot per second, measured 

 under a four-inch pressure from the center of the orifice. 



In Arizona and Montana forty miners' inches equal 

 one cubic foot per second, measured under a six-inch 

 pressure from the top of the orifice. 



In Colorado 38.4 miners' inches equal one cubic 

 foot per second, measured under a five-inch pressure 

 from the top of the orifice. 



A second-foot is a cubic foot which passes a given 

 point in a ditch or canal m one second of time, and to 

 measure the number of second feet it is only necessary 

 to multiply the number of seconds of time by the cubic 

 feet of the stream to ascertain the total quantity of 

 water. To make this clearer, let the reader imagine 

 a small stream filling a square conduit or box one foot 

 wide and one foot deep. This gives a stream the face 

 or sectional area of which is one square foot. Now, 

 if the water runs through this conduit or box at the 

 speed of one foot per second of time, that will measure 

 exactly one cubic foot per second, or one second-foot. 

 If the water moves at a higher speed, as, for example 

 five linear feet per second, the volume will be five cubic 

 feet per second. If the conduit or stream is five feet 

 wide and twenty feet deep, the area of its face is 100 

 square feet, and the water flowing one foot per second' 



