178 



THE IRRIGATION AGE. 



THE PRIMER OF IRRIGATION. 



COPYRIGHTED, 1903, BY D. H. ANDERSON. 



CHAPTER XII. 



THE USE OF WELLS, STREAMS, DITCHES AND RESERVOIRS 



TO DISPOSE OF THE TREMENDOUS SUPPLY 



OF WATER. 



Statistics show that the mean annual rainfall of 

 the world is thirty-six inches, which is about 50,000,- 

 000 cubic feet per square mile of the earth's surface 

 per annum, a quantity of water which is amazing when 

 reduced to gallons so as to bring it more readily within 

 the average comprehension. 



A gallon of water, United States standard, weighs 

 eight and one-third pounds and contains 231 cubic 

 inches. As there are 17.28 cubic inches in a cubic foot, 

 a simple calculation will show that the annual rainfall 

 on every tract of land equal to 640 acres amounts to 

 374,026,000 gallons, or, reducing it to weight, 1,558,- 

 442 tons of water, being about 2,43o tons per acre. It 

 will, of course, be understood that all this water is not 

 equally distributed, but it all falls upon the earth 

 somewhere and is taken up by the soil in the same pro- 

 portionate amount as by the oceans and seas. The 

 calculation might be made more accurate by assuming 

 that the surface of the earth is about one-third land 

 and two-thirds water, and that, therefore, only one- 

 third of this enormous quantity of water is taken up by 

 the land, but we are dealing with averages and the rec- 

 ord must stand as written. 



This tremendous supply of water must be disposed 

 of by nature in some adequate manner, for if allowed 

 to stand and accumulate the earth would soon be sub- 

 merged. Fortunately, Dame Nature disposes of it, 

 except when an inundation somewhere sweeps away 

 towns and country, showing that she herself is overbur- 

 dened with the supply. The rain falls and is carried 

 off the land so far as the surplus that is not drunk in 

 by the ever-thirsty soil is concerned, by means of 

 brooks, rivulets, streams, rivers and mighty waterways 

 into the ocean for transformation by evaporation into 

 more rain. A large portion of it remaining on the 

 land also evaporates, that is, transformed into vapor, 

 which hangs in the atmosphere, invisible except to 

 touch, when the weather is "damp," as is said, or 

 gathers into clouds which empty their contents back 

 upon the earth. So far, the action of evaporation and 

 rainfall is equal and the equilibrium or eternal balance 

 of nature is maintained. 



SURFACE WATER. 



But an enormous portion of the fallen rain does 

 not return into the atmosphere, whence it came, to re- 

 peat its beneficial and grateful performance ; it pene- 

 trates into the soil, percolates through a myriad of 

 pores, cracks and crannies, until it accumulates beneath 

 the surface of the earth, sometimes at immense depths, 

 and forms subterranean streams and reservoirs. Some- 

 times, when the soil is unyielding, the percolating water 

 does not attain the dignity of a subterranean stream 

 or reservoir, but is held in the grasp of the soil above 

 some impervious or impenetrable stratum of rock or 

 hard pan, and becomes what is known as "surface 

 water," a water table which throws off moisture to be 

 on rried to the surface hv cnpillqry /i 



It is a maxim in physics, "nature abhors a vacu- 

 um," and so whenever there is a vacant place the water 

 fills it, and thus there is a never ending supply of 

 water from rain or melting snow which is practically 

 rain in another form. The fact that there are rain- 

 less, arid regions does not alter the fact, for somewhere 

 beyond them in the mountains is the supply of water 

 the rainless belt should receive, and it sinks beneath 

 the arid lands waiting to be drawn up to the surface 

 by the ingenuity of man, it being prevented from do- 

 ing so of its own accord by insurmountable obstacles 

 in the soil. 



The method of reaching these subterranean de- 

 posits of water, underground reservoirs and water ta- 

 bles, is by what is commonly called "a well." When 

 a well is dug down into the water table or surface 

 water, say from four to six feet in diameter or any 

 other size deemed adequate to insure a good supply 

 of water, and from ten to 100 feet in depth, and curbed 

 with stone or mitred plank, and a windlass and bucket 

 arranged at the top, or a common suction pump, a cer- 

 tain amount of water supply is assured. For domestic 

 purposes, perhaps to irrigate a small garden patch, 

 where labor is of little consideration, a well with the 

 above pumping apparatus will serve, but few farmers 

 will rest content with this ancient system of procuring 

 a water supply, and if anyone aspires to cultivate the 

 soil and irrigate he must largely extend his plant. 



QUANTITY OF WATER NEEDED. 



To estimate the quantity of water that the irriga- 

 tion farmer must provide, it is necessary to go into a 

 few details as to the quantity required to raise a crop. 

 That quantity he must have or go out of business. 



To _ irrigate a few acres successfully it may be 

 necessary to have a supply of water running up" into 

 the hundreds of thousands of gallons. Taking rainfall 

 as the standard of water needed to grow a crop, we find 

 that one inch of rain on an acre of ground is equiva- 

 lent to 27,154 gallons, and for the purposes of irri- 

 gation, that is, to give the ground a good wetting, at 

 least two inches of water are necessary, more being re- 

 quired in some localities. 



Professor King has made the following estimate 

 of the quantity of water required during the growing 

 season in various localities : 



Wisconsin 34 inches per acre 



California 7V 2 to 20 inches per acre 



Colorado 22 inches per acre 



India 48 inches per acre 



France and Italy 50 inches per acre 



To still further go into the details of the quantity 

 of water required to grow a crop to maturity, Professor 

 King gives the following table of amounts of water 

 necessary to produce the certain plants dry: 



Pounds of Water to Each 

 Pound Dry Product. 



Dent corn 309 



Flint corn 233 



Red clover 452 



Bnrley 392 



Oats . 552 



Field peas 477 



' Potatoes 422 



Rye ... .' .' 353 



This enormous quantity bf water which must .be 

 provided for the needs of plants is not *>TI nlirmmo- 

 amount when it is considered that it mav be obtained 



