904 



THE IRRIGATION AGE. 



Notes on Practical 

 Irrigation 



D. H. Anderson 



The Use of Wells, Streams, Ditches and Reservoirs. r*o 

 Dispose of the Tremendous Supply of Water. 



Statistics show thai: 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 1.728 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 2,435 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 proportionate 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 record 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, ex- 

 cept when an inundation somewhere sweeps away towns 

 and country, showing that she herself is overburdened 

 with the supply. The rain falls and is carried off the 

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

 every thirsty soil is concerned, by means of brooks, rivu- 

 lets, streams, rivers and mighty waterways into the ocean 

 for transl'onnatipn 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 at- 

 mosphere, 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 repeat its 

 beneficial and grateful performance; it penetrates 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 subter- 

 ranean streams and reservoirs. Sometimes, 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 im- 

 penetrable stratum of rock or hard pan, ^and becomes 

 what is known as "surface water." a water table which 

 throws off moisture to be carried to the surface by capil- 

 lary attraction. 



It is a maxim in physics, "nature abhors a vacuum," 

 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 rainless, 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 doing so of its own accord by in- 

 surmountable obstacles in the SOU. 



The' method of reaching these subterranean deposits 

 of water, underground reservoirs and water tables, 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 certain amount of water sup- 

 ply is assured. For domestic purposef, perhaps to irri- 

 gate a small garden patch, where labor is of little consid- 

 eration, 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 irrigation 

 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 neces- 

 sary to have a supply of water running up into the hun- 

 dreds 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 equivalent to 

 27,154 gallons, and for the purpose of irrigation, that is, 

 to give the ground a good wetting, at least two inches 

 of water are necessary, more being required in some 

 localities. 



Professor King has made the following estimate of 

 the quantity of water required during the growing season 

 in various localities: 



Wisconsin ,T4 inches per acre 



California 7'/< to 20 inches per acre 



Colorado 22 inches per acre 



India 48 inches per acre 



F'rance 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 neces- 

 sary to produce the certain plants dry: 



Pounds of Water to Each 

 Pound Dry Product. 



Dent corn 309 



Flint corn 233 



Red clover 452 



Barley 392 



Oats 559 



Field peas 477 



Potatoes 422 



Rye 353 



This enormous quantity of water which must be pro- 

 vide-.l for the needs of plants is not an alarming amount 

 when it is considered that it may be obtained very cheaply 

 by modern machinery where the water supply is adequate 

 and a proper arrangement of ditches and reservoirs is 

 made to economize it, the universal tendency being al- 

 ways toward wxste. 



Where Open Wells Are a Success. 



Ordinary open wells arc _more successful in clay and 

 stone than in sand, there being far less liability of the 

 water running out, the bottom of the well being a re- 

 taining reservoir, which may be greatly enlarged by tun- 

 neling out to any safe distance into the water table or 

 water stratum. Where the water stratum is in sand it 

 is better to use screen points, that is, tubing with per- 

 forated ends, which admit the water but keep out the 

 sand. Several of these screen points may be run down 

 into the water-bearing sand stratum at a sufficient dis- 

 tance to prevent one robbing the other, and all be con- 

 nected with a suction pipe. Experience tells that these 

 screens should be run down to the bottom of the water- 

 carrying sand if possible, and that in any event they 

 should be sized according to the depth of the strata. 



To accomplish this purpose successfully in wells an 

 open well large enough for two men to work in should 

 be sunk down to the sand and curbed to prevent caving. 

 Then by driving ordinary gas piping as a casing for the 

 screens and boring with a common auger, the screens 

 may be lowered to any depth, or if the water-bearing 

 sand is very deep a succession of screens may be put 

 down on top of each other to enlarge the water supply. 



Assuming the water supply to be adequate for the 

 purposes of reasonable irrigation from a well, the next 



