THE IRRIGATION AGE. 



21 



will give a volume of 100 cubic feet per second or sec- 

 ond-feet ; if it runs two feet per second, then the volume 

 will be 200 cubic 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 quite 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 1 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, the cross sectional area 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 

 during the periods when there is an abundant supply 

 that is, to lay aside in reservoirs enough to meet any 

 possible contingency of drought or insufficient supply 

 when most needed. The standard of measurement of 

 water stored in reservoirs, the unit of quantity, is 

 designated as "an acre-foot"; that is, an amount of 

 water which will cover one acre of ground, or 43,560 

 square feet to a depth of one foot. This will give, of 

 course, 43,560 cubic feet, or 325,851 gallons. One 

 cubic foot per second flowing constantly for twenty-four 

 hours equals nearly two acre-feet, and from this it is not 

 difficult to convert cubic feet per second into acre-feet 

 and estimate the quantity of water to be stored in 

 reservoirs for the use and requirements of crops. The 

 reservoirs themselves may also be measured in the same 



manner as a tank, but allowance must be made for 

 evaporation and absorption. 



To further explain the technical units of measure- 

 ments into quantities, the following table is given : 



One second-foot equals 450 gallons per minute. 



One cubic foot equals 7.5 gallons. 



One second-foot equals two acre-feet in twenty-four 

 hours flowing constantly. 



One hundred California inches equal four acre-feet 

 in twenty-four hours. 



One hundred Colorado inches equal five and one- 

 sixth acre-feet in twenty-four hours. 



One Colorado inch equals 17,000 gallons in twenty- 

 four hours. 



One second-foot equals fifty-nine and one-half acre- 

 feet in thirty days. 



Two acre-feet equal one second-foot per day, or 

 .0333 second-feet in thirty days. 



One million gallons equal 3.069 acre-feet. 



Taking water from streams and ditches open to the 

 atmosphere and its changes, rapid evaporation, seepage 

 and absorption, is always attended with an enormous 

 waste, the consequence being that the farmer never 

 knows and no man can tell him whether he is giving 

 his crops the quantity of water they a-bsolutely require. 

 He can not tell how much of the water applied to the 

 soil is utilized by the crops, or is carried off by drain- 

 age, seepage, infiltration to some portion of the land 

 where it is not needed and generally lost for useful 

 purposes. He knows, however, that so much water is 

 measured out to him and that he pays for the amount 

 that runs through the head gate, whether it is of any 

 practical use to him or not. The returns from his crops 

 do not represent as much as he hoped, for the expense 

 takes away a very large slice of his profits. His water 

 tax may represent one-third of his receipts, and though 

 he may be well aware that he never received the water 

 he pays for that is, it never was utilized by his crops 

 there is no way out of his embarrassment, he must pay 

 or quit. His farm belongs to him that is, he has the 

 deed to it but he is paying rent on it all the time. 



CHAPTER XIX. 



PUMPS AND IRRIGATION MACHINERY. 



In Chapter XII is given a calculation of the amount 

 of water precipitated upon the earth's surface and 

 carried into the soil. The amount is enormous, and 

 if not carried off in the variety of ways mentioned 

 would soon reduce the surface of the globe to an un- 

 inhabitable morass. Moreover, if the annual precipita- 

 tions were uniform in all places there would not be 

 any necessity for irrigation or anxiety about drouths 

 and an insufficient water supply. 



We know it to be a fact that all this tremendous 

 annual mass of water poured from the clouds upon the 

 land, or at least a great percentage of it, is carried into 

 the soil, where it filters and seeps down by the force 

 of gravity as far as it can, or until it encounters some 

 obstruction, and if it can not run, seep or drain off' 

 back into surface conveyances it remains stationary, 

 waiting for an exit. 



The water from rivers and streams is a very small 

 quantity compared with the quantity beneath the sur- 

 face. It is, in fact, the "run-off" from rain, snow or 

 saturations of the soil that is utilized in ditch and 



