THE lEPiIGATION AGE. 



367 



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 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 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, the cubic feet are 

 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: 



Colorado One cubic per second foot equals 38.4 

 statute inches. 



Montana One cubic per second foot equals 40 

 statute inches. 



Idaho One cubic per second foot equals 50 min- 

 er's inches. 



Arizona One cubic per second foot equals 40 

 miner's inches. 



Nevada One cubic per second foot equals 50 

 miner's inches. 



Utah One cubic per second foot equals 50 miner's 

 inches. 



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

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



measure the number of second feet it is only necessary 

 to the number of seconds of time by the cubic 

 feet of the stream to ascertain the iotal 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 

 will give a volume of 100 cubic or second-feet; if it 

 runs two feet per second, then the volume will be 200 

 cubic or second-feet per second of time. 



In measuring the flow of a stream it will be under- 

 stood from the foregoing that the width, depth and 

 speed or velocity are calculated. Streams, however, 

 are very irregular in their measurements and the veloc- 

 ity of the water is not fixed. For instance, the water 

 flows more rapidly in the center or where it is deep ; 

 along the shore where it is shallow the friction against 

 the bank and bottom retard it quite perceptibly. More- 

 over, the water flows more rapidly below the surface 

 than at the surface. In such case it is estimated that 

 the place of the greatest motion is about one-third of 

 the distance beneath the surface, this being the locality 

 where the water is least impeded by friction? 



It is manifestly impossible for one to stand at the 

 delivery point of the water, watch in hand, and calcu- 

 late the number of second-feet that flow, hence a simple 

 way of measuring the whole stream is emite common. 

 A line, say 100 feet, is laid off along the bank and each 

 end of the line is marked by a stake. Then a light float 

 a chip will answer the purpose is cast into the 

 stream above the upper stake and the exact time it 

 passes is noted, and also the exact time it passes the 

 lower stake. If the float requires twenty seconds to 

 travel between the two stakes, then the velocity of the 

 water is assumed to be five feet per second. Other 

 floats are necessary, for the stream runs with unequal 

 velocity, but the average speed together with the aver- 

 age measurement is taken as the basis of a calculation 

 and the number of second-feet determined from that. 

 Thus, if the width averages twenty feet, the depth four 

 feet a cross section is eighty square feet. Then, if 

 the rate of flow is two feet per second, we have a volume 

 of 160 second-feet. 



THE ACRE-FOOT. 



The preceding water measurements are restricted 

 to flowing water for irrigating purposes. There are 

 numerous methods of measuring the volume of water 

 more accurately than in the case of the chip, and it may 

 be said that by means of submerged floats, current 

 meters with electrical attachments, and other con- 

 trivances and calculations based upon scientific princi- 

 ples, very little water will escape the notice of the com- 

 pany who has it for sale, and the farmer may be sure 

 of receiving all he is entitled to for his land. By and 

 by it will be possible for the irrigation farmer to esti- 

 mate exactly the quantity of water required by his 

 plants, and that amount he will be able to give them 

 with accuracy and without any waste or excess. 



It is becoming the practice to store unused water 



